Among objects that are ever weaker in brilliance, the number of G. is rapidly increasing. So, G. brighter than the 12th magnitude is known approx. 250, 15th - already approx. 50 thousand, and the number of G., which can be photographed with a 6-meter telescope at the limit of its capabilities, is many billions. It indicates means. the remoteness of most
Extragalactic astronomy studies the dimensions of stellar systems, their masses, structure, and optical, infrared, and x-ray properties. and radio emission. The study of the spatial distribution of geometries reveals the large-scale structure of the Universe (it can be said that the part of the Universe accessible to observation is the world of geometries). In the study of the spatial distribution of G. and the ways of their evolution extragalactic. astronomy merges with cosmology - the science of the universe as a whole.
One of the most important extragalactic astronomy remains the problem of determining the distance to G. Due to the fact that the brightest stars of constant brightness (supergiants) were found in the nearest G., it was possible to establish the distances to these G. To even more distant G., in which it is impossible to distinguish even supergiant stars , distances are estimated in other ways (see ).
In 1912, Amer. astronomer V. Slifer discovered a remarkable property of gyros: in the spectra of distant gyros, the whole spectrum. the lines turned out to be shifted to the long-wavelength (red) end in comparison with the same lines in the spectra of sources that are stationary relative to the observer (the so-called lines). In 1929, Amer. astronomer E. Hubble, comparing the distances to G. and their redshifts, found that the latter grow on average in direct proportion to the distances (see). This law has placed in the hands of astronomers an effective method for determining the distances to G. by their redshift. The redshifts of thousands of G. and hundreds have been measured.
Determining the distances to galaxies and their positions in the sky made it possible to establish that there are single and double gyros, groups of gyros, large clusters of them, and even clouds of clusters (superclusters). Wed distances between G. in groups and clusters are several. hundreds of kpc; this is about 10-20 times the size of the largest G. Cf. the distances between groups of galaxies, single gyros, and multiple systems are 1–2 Mpc, and the distances between clusters are tens of Mpc. Thus, stars fill space with a higher relative density than intragalactic stars. space (distances between stars are on average 20 million times greater than their diameters).
According to the radiation power, G. can be divided into several. luminosity classes. The widest range of luminosities is observed in ellipticals. G., in the central regions of certain accumulations of G., so-called. cD-galaxies, which are record-breaking in luminosity (abs. magnitude - 24 m, luminosity ~ 10 45 erg / s) and mass (). And in our Local G. group, ellipticals were found. G. low luminosity (abs. values from -14 to -6 m, i.e. luminosity ~10 41 -10 38 erg / s) and mass (10 8 -10 5 ). At spiral G. an interval abs. stellar magnitudes range from -22 to -14 m , luminosities - from 10 44 to 10 41 erg / s, mass interval 10 12 -10 8 . Incorrect G. in abs. weaker values - 18 m , their luminosity 10 43 erg/s, masses .
The formation of young stars is still going on in the central region of the Galaxy. A gas that has no rotational momentum falls towards the center of the Galaxy. Here, the stars of the 2nd generation of spherical are born. subsystems that make up the core of the Galaxy. But there are no favorable conditions for the formation of supergiant stars in the core, since the gas breaks up into small clumps. In the same rare cases where the gas transmits torque environment and shrinks into a massive body - with a mass of hundreds and thousands of solar masses, this process does not end successfully: gas compression does not lead to the formation of a stable star, it can occur and arise. The collapse is accompanied by the ejection of part of the matter from the galactic region. kernels (see).
The more massive a spiral gyro, the stronger gravity compresses the spiral arms; therefore, massive galaxies have thinner arms, more stars, and less gas (more stars form). For example, in the giant nebula M81, thin spiral arms are visible, while in the nebula M33, which is a medium-sized spiral, the arms are much wider.
Depending on the type, spiral galaxies also have different rates of star formation. The Sc type has the highest speed (about 5 per year), the Sa has the lowest speed (about 1 per year). The high rate of star formation in the former is also apparently associated with the flow of gas from galaxies. coron.
At the elliptical star systems, the evolutionary path should be simpler. The substance in them from the very beginning did not have significant torque and magnetic. field. Therefore, compression in the process of evolution did not lead such systems to a noticeable rotation and strengthening of the magnetic field. fields. All the gas in these systems from the very beginning turned into spherical stars. subsystems. In the course of subsequent evolution, the stars ejected gas, which descended to the center of the system and went to the formation of new generation stars of the same spherical. subsystems. Star formation rate in elliptic. G. should be equal to speed the flow of gas from evolved stars, mainly supernovae, since the outflow of matter from stars in an elliptical. G. slightly. Annual loss of gas by stars in elliptic. G. according to calculations is ~0.1 per galaxy with a mass of 10 11 . It also follows from the calculations that the central parts of the elliptic G. due to the presence of young stars should be bluer than the peripheral regions of G. However, this is not observed. It's about what it means. part of the resulting gas in an elliptical. G. is blown out by the hot wind that occurs during outbursts of supernovae, and in G. clusters it is also blown out by rather dense hot intergalactic matter. gas, discovered recently by its X-ray. radiation.
Comparing the number of stars of different generations in a large number similar G., it is possible to establish possible ways of their evolution. In older galaxies, there is a depletion of interstellar gas reserves and, as a result, a decrease in the rate of formation and in the total number of stars of new generations. But they have a lot - superdense stars of small sizes, representing one of the last stages of the evolution of stars. Herein lies the aging of galaxies. It should be noted that, at the beginning of their evolution, galaxies apparently had a higher luminosity, since they contained more massive young stars. It is possible, in principle, to reveal the evolutionary change in the luminosity of galaxies by comparing the luminosities of nearby and very distant galaxies, from which light comes for many billions of years.
Extragalactic astronomy has not yet given a definitive answer to questions related to the origin of gyratory clusters, in particular, why in spherical clusters are dominated by elliptic. and lenticular systems. Apparently, from relatively small clouds of gas that did not have a rotational moment, spherical ones were formed. clusters with a predominance of elliptic. and lenticular systems, also having a small torque. And from large clouds of gas, which possessed a significant rotational moment, clusters of gyros arose, similar to the Supercluster in Virgo. Here there were more variants of the distribution of the rotational moment among the individual clumps of gas, from which galaxies were formed, and therefore spiral systems are more common in such clusters.
G.'s evolution in clusters and groups has a number of features. Calculations have shown that during collisions of galaxies, their extended gaseous coronas must be “stripped off” and dispersed over the entire volume of the group or cluster. This intergalactic gas was detected by high-temperature X-ray. In addition, the massive members of the clusters, moving among the rest, create "dynamic friction": by their gravity they drag the neighboring hydrometeors, but in turn experience deceleration. Apparently, this is how the Magellanic Stream was formed in the Local Group G. Sometimes massive G. located in the center of the cluster not only "tear off" the gaseous coronas of the G. passing through them, but also capture the "visitor" stars. It is assumed, in particular, that cD galaxies with massive halos formed them in such a "cannibalistic" way.
According to existing calculations, in 3 billion years our Galaxy will also become a "cannibal": it will absorb the Large Magellanic Cloud approaching it.
Uniform distribution of matter on the scales of the Metagalaxy determines the identity of St-in matter and space in all parts of the Metagalaxy (homogeneity) and their identity in all directions (isotropy). These important Holy Islands of the Metagalaxy are characteristic, apparently, for the modern. states of the Metagalaxy, however, in the past, at the very beginning of the expansion, anisotropy and inhomogeneity of matter and space could exist. The search for traces of anisotropy and inhomogeneity of the Metagalaxy in the past is a complex and urgent task of extragalactic astronomy, which astronomers are only just beginning to solve.
- Specialty HAC RF01.03.02
- Number of pages 144
1 Methods for determining distances to galaxies.
1.1 Introductory remarks.
12 Photometric methods.
1.2.1 Supernovae and new stars.
1.2.2 Blue and red supergiants.
1.2.3 Cepheids.
1.2.4 Red giants.
1.2.5 KE Lyra.
1.2.6 Using the object luminosity function.
1.2.7 Surface brightness fluctuation method (SVR).
1.3 Spectral methods.
1.3.1 Using the Hubble relation.
1.3.2 Using the Tully-Fisher (TR) relationship.
1.3.3 Using the Faber-Jackson dependency.
1.4 Other methods.
1.5 Comparison of methods for determining distances.
2 The brightest stars in galaxies and their photometry.
2.1 The brightest stars in galaxies.
2.2 Blue and red supergiants.
2.2.1 Method calibration.
2.2.2 Accuracy of the brightest star method.
2.2.3 Budush; her method of the brightest stars.
2.3 Red giants and the TSCR method.
2.3.1 Influence of metallicity and age.
2.3.2 Influence of bright SG and AGB stars and the density of stellar fields on the accuracy of the TRGB method.
2.4 Photometry of stars in galaxies.
2.4.1 Photographic methods.
2.4.2 Aperture photometry with PCVISTA.
2.4.3 Photometry with DAOPHOT.
2.4.4 Features of photometry of HST images.
2.5 Comparison of photometry accuracy of different methods.
2.5.1 Comparison of photographic and CCD photometry.
2.5.2 Comparison of Zeiss-1000 - BTA results.
3 Local complex of galaxies and its spatial structure.
3.1 Introduction.
3.2 Local complex of galaxies.
3.3 Local group of galaxies.
3.3.1 Galaxy ICIO.
3.3.2 Galaxy LGS3.
3.3.3 Galaxy DDO210.
3.3.4 New galaxies of the Local Group.
3.4 Group M81 + NGC2403.
3.5 Group IC342/Maffei.
3.6 Group M101.
3.7 Cloud of galaxies CVn.
3.8 Distribution of galaxies in the Local Complex, velocity anisotropy.
4 The structure of galaxies in the direction of the cluster in
Virgo. Determination of the Hubble constant.
4.1 Introduction.
4.2 The structure of the cluster of galaxies in Virgo.
4.3. Preliminary selection of galaxies by parameters.
4.4 Observations and photometry of stars.
4.5 Accuracy of photometry and distance measurements.
4.6 Spatial distribution galaxies.
4.7 Determination of the Hubble constant.
4.8 Comparison of results.
5 Group NGC1023.
5.1 Introduction.
5.2 The NGC1023 group and its composition.
5.3 Observations of galaxies in the NGC1023 group.
5.4 Photometry of stars in BTA and HST images.
5.5 Determination of distances to the galaxies of the group.
5.5.1 Definition by the brightest supergiants.
5.5.2. Determination of distances based on the TRGB method.
5.6 The problem of the galaxy NGC1023a.
5.7 Distribution of distances of galaxies of the group.
5.8 Determination of the Hubble constant in the direction of NGC1023.
6 Spatial structure of irregular galaxies
6.1 Introductory remarks.
6.2 Spiral and irregular galaxies.
6.2.4 Stellar composition of galaxies.
6.3 Periphery of galaxies.
6.3.1 Galaxies seen "face-on" and "edge-on".
6.3.4 The boundaries of galaxies.
6.4. Red giant disks and the hidden mass of irregular galaxies.
Introduction to the thesis (part of the abstract) on the topic "Spatial distribution and structure of galaxies based on the study of the brightest stars"
Formulation of the problem
Historically, at the beginning of the 20th century, literally an explosion in the study of stars and star clusters, both in our Galaxy and in other star systems, created the basis on which extragalactic astronomy proper appeared. The emergence of a new direction in astronomy took place thanks to the work of Hertzsprung and Ressel, Duncan and Abbe, Leavitt and Bailey, Shapley and Hubble, Lundmark and Curtis, which established an almost modern understanding of the scale of the universe.
In its further development, extragalactic astronomy went to such distances where individual stars were no longer visible, but as before, astronomers involved in extragalactic research published a large number of works that were somehow related to stellar topics: with the elucidation of luminosities stars, building distance scales, studying the evolutionary stages of certain types of stars.
Studies of stars in other galaxies allow astronomers to solve several problems at once. First, clarify the scale of distances. It is clear that without knowing the exact distances, we do not know the main parameters of galaxies - sizes, masses, luminosities. Opening in 1929 Hubble's relationship between the radial velocities of galaxies and their distances makes it possible to quickly determine the distance to any galaxy based on a simple measurement of its radial velocity. However, we cannot use this method if we are studying non-Hubble motions of galaxies, i.e. motions of galaxies associated not with the expansion of the Universe, but with the usual laws of gravity. In this case, we need a distance estimate based not on the measurement of speed, but on the basis of the measurement of other parameters. It is known that galaxies at distances up to 10 Mpc have their own velocities, which are comparable to their speed in the Hubble expansion of the Universe. The summation of two almost identical velocity vectors, one of which has a random direction, leads to strange and completely unrealistic results if we use the Hubble dependence when studying the spatial distribution of galaxies. Those. and in this case we cannot measure distances based on the radial velocities of galaxies.
Secondly, since all galaxies are composed of stars, by studying the distribution and evolution of stars in a galaxy, we somehow answer the question of the morphology and evolution of the galaxy itself. Those. The obtained information on the stellar composition of the galaxy limits the variety of models used for the origin and evolution of the entire stellar system. Thus, if we want to know the origin and evolution of galaxies, we absolutely need to study the stellar population of different types of galaxies to the deepest possible photometric limit.
In the era of photographic astronomy, studies of the stellar population of galaxies were carried out with the largest telescopes in the world. But still, even in this nearby galaxy, like M31, P-type stellar population, i.e. red giants, was at the limit of photometric measurements. Such a technical limitation of possibilities has led to the fact that the stellar population has been studied in detail and in depth only in the galaxies of the Local Group, where, fortunately, galaxies of almost all types are present. In the 1940s, Baade divided the entire population of galaxies into two types: bright young supergiants (type I), located in a thin disk, and old red giants (type II), occupying a more voluminous halo. Later, Baade and Sandage pointed to the presence of Type II Local Populations in all galaxies; old stars that were clearly visible on the periphery of galaxies. In the images of more distant galaxies, only bright supergiants were visible, which Hubble used in its time to determine the distances to galaxies when calculating the expansion parameter of the Universe.
The technical progress of the 1990s in the development of observational facilities led to the fact that rather faint stars became available in galaxies outside the Local Group, and it became possible to actually compare the parameters of the stellar population of many galaxies. At the same time, the transition to a CCD matrix was also marked by a regression in the study of the global parameters of the distribution of the stellar population of galaxies. It has become simply impossible to study a galaxy 30 arc minutes in size with a light receiver 3 arc minutes in size. And only now are CCD matrices appearing, comparable in size to previous photographic plates.
general characteristics work RELEVANCE.
The relevance of the work has several manifestations:
The theory of star formation and evolution of galaxies, the determination of the initial mass function under various physical conditions, as well as the stages of evolution of single massive stars require direct images of galaxies. Only a comparison of observations and theory can give further progress in astrophysics. We have obtained a large amount of observational material, which is already yielding secondary astrophysical results in the form of LBV star candidates, which are then confirmed spectrally. It is known that a program of direct images of galaxies "for the future" is currently being carried out on the HST; these images will be required only after the outbreak of a P-type supernova (supergiant) in such a galaxy. The archive we have is slightly inferior to what is currently being created on HST.
At present, the problem of determining the exact distances to galaxies, both distant and close, has become the main one in the work of large telescopes. If for large distances the goal of such work is to determine the Hubble constant with maximum accuracy, then at small distances the goal is to search for local inhomogeneities in the distribution of galaxies. And for this, exact values of the distances to the galaxies of the Local Complex are needed. In the first approximation, we have already obtained data on the spatial distribution of galaxies. In addition, the calibration of distance methods requires accurate values for those few key galaxies that are basic.
Only now, after the advent of modern matrices, it has become possible to deeply study the stellar composition of galaxies. This immediately opened the way for reconstructing the history of star formation in galaxies. And the only source material for this is direct images of galaxies resolvable to stars, made in different filters.
The history of the study of weak structures of galaxies has more than a dozen years. This became especially important after obtaining extended rotation curves of spiral and irregular galaxies from radio observations. The results obtained indicated the existence of significant invisible masses, and the search for the optical manifestation of these masses is being intensively pursued in many observatories. Our results show the existence around galaxies of late types of extended disks, consisting of the old stellar population - red giants. Taking into account the mass of these disks can weaken the problem of invisible masses.
PURPOSE OF THE WORK.
The objectives of this dissertation work are:
1. Obtaining the largest homogeneous array of images of galaxies in the northern sky with velocities less than 500 km/s and determining the distances to galaxies based on the photometry of their brightest stars.
Fig. 2. Resolution for stars of galaxies observed in two opposite directions - in the Virgo cluster and in the N001023 group. Determination of distances to named groups and calculation, on the basis of the obtained results, of the Hubble constant in two opposite directions.
3. Study of the stellar composition of the periphery of irregular and spiral galaxies. Determination of the spatial forms of galaxies on long distances from the center.
SCIENTIFIC NOVELTY.
For a large number galaxies on b-m telescope deep images in 2A colors were obtained, which made it possible to resolve galaxies into stars. The photometry of the stars in the images was carried out and color-magnitude diagrams were constructed. Based on these data, distances were determined for 92 galaxies, including those in such distant systems as the Virgo cluster or the N001023 group. For most galaxies, distance measurements have been made for the first time.
The measured distances were used to determine the Hubble constant in two opposite directions, which made it possible to estimate the velocity gradient between the Local Group and the N001023 group, which turned out to be small and does not exceed the measurement errors.
The study of the stellar composition of the periphery of galaxies led to the discovery of extended thick disks in irregular galaxies, consisting of old stars, red giants. The sizes of such disks are 2-3 times larger than the apparent sizes of galaxies at the level of 25 "A/P". Based on the spatial distribution of red giants, galaxies are found to have clearly defined boundaries.
SCIENTIFIC AND PRACTICAL VALUE.
The 6-m telescope obtained multicolor images of about 100 resolvable galaxies. In these galaxies, the colors and brightness of all visible stars. Hypergiants and supergiants with the highest luminosity have been identified.
Based on the works in which the author was directly involved, for the first time a large and homogeneous array of data was obtained on measuring distances for all galaxies in the northern sky with velocities less than 500 km/s. The data obtained make it possible to analyze the non-Hubble motions of the galaxies of the Local Complex, which limits the choice of a model for the formation of the Local "pancake" of galaxies.
The composition and spatial structure of the nearest groups of galaxies in the northern sky have been determined. The results of the work make it possible to carry out statistical comparisons of the parameters of groups of galaxies.
A study was made of the structure of space in the direction of the cluster of galaxies in Virgo. Several relatively close galaxies have been found located between the cluster and the Local Group. Distances were determined and galaxies belonging to the cluster itself and located in different parts of the periphery and center of the cluster were identified.
The distance to the Virgo and Coma Veronica clusters was determined and the Hubble constant was calculated. The brightness of the brightest stars of 10 galaxies of the N001023 group, which lies at a distance of 10 Me, was measured. The distances to galaxies are determined and the Hubble constant in this direction is calculated. The conclusion is made about a small velocity gradient between the Local Group and the N001023 group, which can be explained by the non-dominant mass of the galaxy cluster in Virgo.
FOR DEFENSE ARE SUPPLIED:
Fig. 1. Results of work on the development and implementation of a technique for photometry of stars on automatic microdensitometers AMD1 and AMD2 of the OJSC RAS.
2. Derivation of the calibration dependence of the method for determining distances from blue and red supergiants.
3. Results of photometry of stars in 50 galaxies of the Local Complex and determination of distances to these galaxies.
4. Results of determining the distances of up to 24 galaxies in the direction of the Virgo cluster. Determination of the Hubble constant.
Fig. 5. Results of determining distances to galaxies of the NOC1023 group and determining the Hubble constant in the opposite direction from the cluster in Virgo. Conclusion of a small velocity gradient between the Local group and the NGO1023 group.
6. Results of a study of the spatial distribution of late-type stars in irregular galaxies. Discovery of extended disks of red giants around irregular galaxies.
WORK APPROVAL.
The main results obtained in the dissertation were reported at the seminars of JSC RAS, SAI, AI OPbSU, as well as at conferences:
France, 1993, In ESO/OHP Workshop "Dwarf Galaxies" eds. Meylan G., Prugniel P., Observatoire de Haute-Provence, France, 109.
South Africa, 1998, in lAU Symp. 192, The Stellar Content of Local Group Galaxies, ed. Whitelock P., and Gannon R., 15.
Finland, 2000 "Galaxies in the M81 Group and IC342/Maffei Complex: The Structure and Stellar Populations", ASP Conference Series, 209, 345.
Russia, 2001, All-Russian Astronomical Conference, August 6-12, St. Petersburg. Report: "Spatial distribution of late-type stars in irregular galaxies".
Mexico, 2002, Cozumel, April 8-12, "Stars as a Tracer of the Shape of Irregular Galaxies Haloes".
1. Tikhonov N.A., Results of hypersensitization in hydrogen of astrofilms of the Kaz-NII of the technical project, 1984, Soobshch.SAO, 40, 81-85.
2. N. A. Tikhonov, Photometry of stars and galaxies on direct BTA images. Errors in photometry AMD-1, 1989, Soobshch.SAO, 58, 80-86.
3. Tikhonov N.A., Bilkina B.I., Karachentsev ID., Georgiev Ts.B., Distance of nearby galaxies N00 2366.1С 2574, and NOG 4236 from photographic photometry of their brightest stars, 1991, A&AS, 89, 1-3.
4. Georgiev Ts. V., Tikhonov N.A., Karachentsev ID., Bilkina B.I. The brightest stars and the distance to the dwarf galaxy HoIX, 1991, A&AS, 89, 529-536.
5. Georgiev Ts.B., Tikhonov N.A., Karachentsev I.D., The brightest candidates for globular clusters galaxies M81, 1991, Letters to AJ, 17, 387.
6. Ts. B. Georgiev, N. A. Tikhonov, and I. D. Karachentsev, Estimates of B and V quantities for candidates for globular clusters of the galaxy M 81, 1991, Letters to Azh, 17, nil, 994-998.
7. Tikhonov N.A., Georgiev T.E., Bilkina B.I. Stellar photometry on the 6-m telescope plates, 1991, OAO, 67, 114-118.
8. Karachentsev I.D., Tikhonov N.A., Georgiev Ts.B., Bilkina B.I., Sharina M.E., Distances of nearby galaxies N0 0 1560, NGO 2976 and DDO 165 from their brightest stars, 1991, A&AS, 91, 503-512.
9. Georgiev Ts.B., Tikhonov N.A., Bilkina B.I., The brightest blue and red stars in the galaxy M81, 1992, A&AS, 95, 581-588.
10. Georgiev Ts.B., Tikhonov N.A., Bilkina B.I., The distribution of blue and stars around the M81, A&AS, 96, 569-581.
11. Tikhonov N.A., Karachentsev I.D., Bilkina B.I., Sharina M.E., Distances to three nearby dwarf galaxies from photometry of their brightest stars, 1992, A&A Trans, 1, 269-282.
12. Georgiev Ts.B., Bilkina B.I., Tikhonov N.A., Getov R., Nedialkov P., The precise coordinates of the supergiants and globular cluster candidates of the galaxy M 81, 1993, Bull SAO, 36, 43.
13. Karachentsev I.D., Tikhonov N.A., Photometric distances to the nearby galaxies 10 10, 10 342 and UA 86, visible throught the Milky Way, 1993, A&A, 100, 227-235.
14. Tikhonov N.A., Karachentsev I.D., Photometric distances to five dwarf galaxies in the vicinity of M 81, 1993, A&A, 275, 39.
15. Karachentsev I., Tikhonov N., Sazonova L., The brightest stars in three irregular dwarfs around M 81, 1994, A&AS, 106, 555.
16. Karachentsev I., Tikhonov N., Sazonova L., NGC 1569 and UGCA 92 - a nearby pair of galaxies in the Milky Way zone, 1994, Letters to Soviet AJ, 20, 90.
17. Karachentsev L, Tikhonov N., New photometric distances for dwarf galaxies in the Local Volume, 1994, A&A, 286, 718.
18. Tikhonov N., Karachentsev L, Maffei 2, a nearby galaxy shielded by the Milky Way, 1994, Bull. SAO, 38, 3.
19. Georgiev Ts., Vilkina V., Karachentsev I., Tikhonov N. Stellar photometry and distances to close galaxies: Two differences in estimates for the parameter "ra per X" bl. 1994, Obornik with the report of VAN, Sofia, p.49.
20. Tikhonov N., Irregular galaxy Casl - a new member of the Local Group, Astron.Nachr., 1996, 317, 175-178.
21. Tikhonov N., Sazonova L., A color - magnitude diagram for Pisces dwarf galaxy, AN, 1996, 317, 179-186.
22. M. E. Sharina, I. D. Karachentsev, and N. A. Tikhonov, Photometric distance to the galaxy N0 0 6946 and its satellite, 1996, Letters to Azh, 23, 430-434.
23. Sharina M.E., Karachentsev I.D., Tikhonov N.A., Photometric distances to NGC 628 and its four companions, 1996, A&AS, 119, n3. 499-507.
24. Georgiev Ts. V., Tikhonov N.A., Karachentsev I.D., Ivanov V.D. Globular cluster candidates in the galaxies NGC 2366.1C 2574 and NGC 4236, 1996, A&A Trans, 11, 39-46.
25. Tikhonov N.A., Georgiev Ts. V., Karachentsev I.D., Brightest star cluster candidates in eight late-type galaxies of the local complex, 1996, A&A Trans, 11, 47-58.
26. Ts. B. Georgiev, I. D. Karachentsev, and N. A. Tikhonov, Distance modules up to 13 nearby isolated dwarf galaxies, Letters to A.Zh., 1997, 23, 586-594.
27. Tikhonov N. A., The deep stellar photometry of the ICIO, 1998, in lAU Symposium 192, ed. P. Whitelock and R. Cannon, 15.
28. Tikhonov N.A., Karachentsev I.D., CCD photometry and distances of six resolved irregular galaxies in Canes Venatici, 1998, A&AS, 128, 325-330.
29. Sharina M. E., Karachentsev I. D., Tikhonov N. A., Distances to Eight Nearby Isolated Low-Luminosity Galaxies, 1999, AstL, 25, 322S.
30. Tikhonov N.A., Karachentsev I.D., Distances to the Two New Companions of M 31, 1999, AstL, 25, 332.
31. Drozdovskii 1.0., Tikhonov N.A., The stellar content and distance to the nearby blue compact dwarf galaxy NGC 6789, 2000, A&AS, 142, 347D.
32. Aparicio A., Tikhonov N.A., Karachentsev I.D., DDO 187: do dwarf galaxies have extended, old halos? 2000, AJ, 119, 177A.
33. Aparicio A., Tikhonov N.A., The spatial and age distribution of stellar population in DDO 190, 2000, AJ, 119, 2183A.
34. Lee M., Aparicio A., Tikhonov N, Byin Y.-I, Kim E., Stellar populations and the Local Group membership of the dwarf galaxy DDO 210, 1999, AJ, 118, 853-861.
35. Tikhonov N.A., Galazutdinova O.A., Drozdovskii I.O., Distances to 24 Galaxies in the Direction of the Virgo Cluster and a Determination of the Hubble Constant, 2000, Afz, 43, 367.
STRUCTURE OF THE THEsis
The dissertation consists of an Introduction, six chapters, a Conclusion, a list of cited literature and an Appendix.
Dissertation conclusion on the topic "Astrophysics, radio astronomy", Tikhonov, Nikolai Alexandrovich
The main conclusions of this chapter concern irregular and, to a lesser extent, spiral galaxies. Therefore, these types of galaxies should be considered in more detail, focusing on the differences and similarities between them. We touch, to a minimum extent, those parameters of galaxies that do not manifest themselves in any way in our studies.
6.2.1 Issues of classification of galaxies.
Historically, the entire classification of galaxies has been created on the basis of images obtained in the blue rays of the spectrum. Naturally, in these images, those objects that have a blue color stand out especially brightly, i.e. star forming regions with bright young stars. In spiral galaxies such regions form spectacularly prominent branches, and in irregular galaxies they form bright areas scattered almost randomly over the body of galaxies.
The apparent difference in the distribution of star-forming regions became the initial boundary that separated spiral and irregular galaxies, regardless of whether the classification is carried out according to Hubble, Vaucouleur, or van den Bergh 192,193,194]. In some classification systems, the authors tried to take into account other parameters of galaxies, in addition to their appearance, but the simplest classification of Hubble remained the most common.
Naturally, there are physical reasons for the difference in the distribution of star-forming regions in spiral and irregular galaxies. First of all, this is the difference in masses and rotation speeds; however, the initial classification proceeded only from the type of galaxies. At the same time, the boundary between these two types of galaxies is very relative, since many bright irregular galaxies have signs of spiral arms or a bar-like structure in the center of the galaxy. The Large Magellanic Cloud, which serves as an example of a typical irregular galaxy, has a bar and faint signs spiral structure, which is characteristic of Sc-type galaxies. Signs of the spiral structure of irregular galaxies are especially noticeable in the radio range when studying the distribution of neutral hydrogen. As a rule, an extended gas cloud exists around an irregular galaxy, in which signs of spiral arms are often visible (for example, in ICIO 196], Holl, IC2574).
The consequence of such a smooth transition of their general properties from spiral galaxies to irregular galaxies is subjectivity in the morphological definitions of the types of galaxies by different authors. Moreover, if the first photographic plates were sensitive to infrared rays, and not to blue, then the classification of galaxies would be different, since star-forming regions would not be distinguished in galaxies in the most noticeable way. In such infrared images, those regions of galaxies that contain the old stellar population - red giants - are best seen.
Any galaxy in the IR range has a smoothed appearance, without contrasting spiral branches or star formation regions, and the disk and bulge of the galaxy are most pronounced. In the images in the IR range of Irr, the galaxies are visible as disk dwarf galaxies, oriented towards us at different angles. This is clearly seen in the IR atlas of galaxies. Thus, if the classification of galaxies were initially carried out on the basis of images in the infrared range, then both spiral and irregular galaxies would fall into the same group of disk galaxies.
6.2.2 Comparison of general parameters of spiral and irregular galaxies.
The continuity of the transition from spiral galaxies to irregular ones is visible when considering the global parameters of a sequence of galaxies, i.e. from spiral ones: Sa Sb Sc to irregular ones: Sd Sm Im . All parameters: masses, sizes, hydrogen content indicate a single class of galaxies. The photometric parameters of galaxies have a similar continuity: luminosity and color. ticks, we did not try to meticulously find out the exact type of galaxy. As further experience showed, the distribution parameters of the stellar population in dwarf spiral and irregular galaxies are approximately the same. This once again emphasizes that both types of galaxies should be united under one name - disk.
6.2.3 Spatial forms of galaxies.
Let us turn to the spatial structure of galaxies. The flattened shapes of spiral galaxies need no explanation. When describing this type of galaxies, the bulge and disk of the galaxy are usually distinguished on the basis of photometry. Since the extended and flat curves of the radial velocities of spiral galaxies require their explanation in the form of the presence of significant masses of invisible matter, an extended halo is often added to the morphology of galaxies. Attempts to find a visible manifestation of such a halo have been made repeatedly. Moreover, in many cases, the absence of a central cluster or bulge in irregular galaxies leads to the fact that only the exponential disk component of the galaxy is visible on photometric sections without signs of other components.
To elucidate the shapes of irregular galaxies along the Z axis, observations of edge-on galaxies are required. A search for such galaxies in the LEDA catalog, with selection by rotation speed, axis ratio, and size, led us to compile a list of several dozen galaxies, most of which are located at large distances. With deep surface photometry, it is possible to reveal the existence of low surface brightness subsystems and measure their photometric characteristics. The low brightness of the subsystem does not at all mean its small influence on the life of the galaxy, since the mass of such a subsystem can be quite large due to the large value of M/L.
UGCB760, VTA. 1800s
20 40 60 in RADIUS (arcsec)
Position (PRCSEC)
Rice. 29: Color distribution (Y - Z) along the major axis of the N008760 galaxy and its isophote up to HE - 27A5
On fig. Figure 29 shows the results of surface photometry of the irregular galaxy 11008760 obtained by us at the VTA. The isophotes of this galaxy show that, at deep photometric limits, the shape of the outer parts of the galaxy is close to an oval. Second, the galaxy's faint isophotes extend along the major axis much farther than the main body of the galaxy, where bright stars and star-forming regions are visible.
One can see the continuation of the disk component beyond the limits of the main body of the galaxy. Nearby is the color change from the center of the galaxy to the faintest isophotes.
Photometric measurements have shown that the main body of the galaxy has a color of (Y-th) = 0.25, which is quite typical for irregular galaxies. Measurements of the color of regions far from the main body of the galaxy give the value (V - K) = 1.2. This result means that the faint = 27.5""/P") and extended (3 times larger than the size of the main body) outer parts of this galaxy should consist of red stars. It was not possible to find out the type of these stars, since the galaxy is located further photometric limits of VTA.
After such a result, it became clear that studies of nearby irregular galaxies were needed in order to be able to say more definitely about the stellar composition and spatial forms of the faint outer parts of galaxies.
Rice. 30: Comparison of the metallicity of red supergiant giant (M81) and dwarf galaxies (Holl). The position of the supergiant branch is very sensitive to the metallicity of the galaxy
6.2-4 Stellar composition of galaxies.
The stellar composition of spiral and irregular galaxies is exactly the same. Based on the G-R diagram alone, it is almost impossible to determine the type of galaxy. Some influence is introduced by the statistical effect, brighter blue and red supergiants are born in giant galaxies. However, the mass of the galaxy still manifests itself in the parameters of the born stars. in massive galaxies heavy elements, formed during the evolution of stars, remain within the galaxy, enriching the interstellar medium with metals. As a result, all subsequent generations of stars in massive galaxies have an increased metallicity. On fig. 30 shows a comparison of the G - R diagrams of a massive (M81) and dwarf (Holl) galaxies. The different positions of the branches of the red supergiants are clearly visible, which is an indicator of their metal personality. For the old stellar population - red giants - in massive galaxies, the existence of stars in a large range of metallicity 210] is observed, which affects the width of the giant branch. In dwarf galaxies, narrow giant branches (Fig. 3$) and low metallicity values are observed. The surface density of giants varies exponentially, which corresponds to the disk component (Fig. 32). A similar behavior of red giants was also found by us in the IC1613 galaxy.
Rice. 32: Variation in the surface density of red giants in the F5 field of the ICIO galaxy. A jump in the density of giants is visible at the disk boundary, which does not drop to zero beyond the disk boundary. A similar effect is observed in spiral galaxy MZZ. Graph scale in minutes of arc from the center.
Considering these results and everything said earlier about irregular galaxies, it could be assumed that it is the old red giant stars that form the extended periphery of galaxies, especially since the existence of red giants on the outskirts of the Local Group galaxies has been known since the time of W. Vaade. A few years ago, Minity and his colleagues announced that they had found red giant halos around two galaxies: WLM and NGC3109, but the publications did not investigate the issue of changes in the density of giants with distance from the center and the size of such halos.
To determine the law of change in the surface density of stars different type, including giants, deep observations of nearby galaxies were needed, located
Rice. 33: Change in the density of stars in the galaxies BB0 187 and BB0190 from the center to the edge. It is noticeable that the red giants have not reached their boundary and continue beyond our image. Graph scale in arcseconds. laid flat, as seen in ICIO.
Our observations with the 2.5-m Nordic telescope of the galaxies DD0187 and DDO 190 confirmed that these irregular galaxies seen face-on also exhibit an exponential drop in the surface density of red giants from the center to the edge of the galaxy. Moreover, the extent of the structure of red giants far exceeds the size of the main body of each galaxy (Fig. 33). The edge of this halo/disk is outside of the applied CCD array. An exponential change in the density of giants has also been found in other irregular galaxies. Since all the studied galaxies behave in the same way, we can speak, as an established fact, about the exponential law of change in the density of the old stellar population - red giants, which corresponds to the disk component. However, this still does not prove the existence of discs.
The reality of disks can only be confirmed from edge-on observations of galaxies. Observations of such galaxies to search for a visible manifestation of a massive halo have been carried out repeatedly using various equipment and in different areas spectrum. The discovery of such a halo has been repeatedly announced. illustrative example The complexity of this task can be traced in publications. Several independent researchers have announced the discovery of such a halo around N005007. Subsequent observations with a fast telescope with a total exposure of 24 hours (!) closed the question of the existence of a visible halo of this galaxy.
Among nearby irregular galaxies seen edge-on, attention is drawn to the dwarf in Pegasus, which has been repeatedly studied. BTA observations of several fields allowed us to fully trace the change in the density of stars of different types in it, both along the major and minor axes. The results are presented in fig. 34, 35. They prove that, firstly, the structure of red giants is three times larger than the main body of the galaxy. Second, the shape of the distribution along the b axis is close to an oval or ellipse. Thirdly, no halo consisting of red giants is noticeable.
Rice. 34: The boundaries of the Pegasus Dwarf galaxy based on the study of red giants. Locations of BTA images are marked.
AGB blue stars Q O O
PegDw W « «(W Joko* 0 0 oooooooooo
200 400 600 majoraxis
Rice. 35: Surface density distribution of different types of stars along the major axis of the Pegasus Dwarf galaxy. The border of the disk is visible, where sharp drop density of red giants. about 1
Our further results are based on the photometry of NCT images obtained by us from the archive of free access. The search for NCT galaxies, resolvable as red giants and visible face-on and edge-on, gave us about two dozen candidates for study. Unfortunately, the field of view of the NCT, insufficient for us, sometimes hindered the goals of our work - to trace the parameters of the distribution of stars.
After standard photometric processing, G-R diagrams were constructed for these galaxies and stars of various types were identified. Their research showed:
1) For face-on galaxies, the decrease in the surface density of red giants follows an exponential law (Fig. 36).
-|-1-1-1-E-1-1-1-1-1-1-1-1--<тГ
PGC39032 / w "".
15 red giants Z sh
Rice. Fig. 36: Exponential change in the density of red giants in the dwarf galaxy RCC39032 from center to edge based on NCT observations
2) Not a single edge-on galaxy has an extended, along axis 2, halo of red giants (Fig. 37).
3) The shape of the distribution of red giants along the b-axis has the form of an oval or ellipse (Fig. 38).
Taking into account the randomness of the sampling and the uniformity of the results obtained in terms of the shape of the distribution of giants in all the studied galaxies, it can be argued that most of the galaxies have such a red giant distribution law. Deviations from the general rule are possible, for example, in interacting galaxies.
It should be noted that among the studied galaxies there were both irregular and non-giant spiral galaxies. We have not found significant differences between them in the laws of distribution of red giants along axis 2, with the exception of the gradient of the fall in the density of giants.
6.3.2 Spatial distribution of stars.
By selecting stars of different types on the G - R diagram, we can see their distribution in the galaxy image or calculate the parameters of their spatial distribution over the body of the galaxy.
It is well known that the young stellar population of irregular galaxies is concentrated in star-forming regions that are randomly scattered throughout the body of the galaxy. However, the apparent randomness immediately disappears if we trace the change in the surface density of young stars along the radius of the galaxy. On the graphs of Fig. 33 shows that the general, close to exponential, distribution is superimposed by local fluctuations associated with individual star formation regions.
For the older population - stars of the extended asymptotic giant branch, the distribution has a smaller density drop gradient. And the smallest gradient has the ancient population - the red giants. It would be interesting to check this dependence for obviously the most ancient population - horizontal branch stars, however, in those galaxies where these stars are reachable, we see their insufficient number for statistical studies. The clearly visible dependence of the age of stars and parameters of spatial density can have a completely logical explanation: although star formation occurs most intensively near the center of the galaxy, the orbits of stars become larger and larger with time, and over a period of several billion years, stars can move to the periphery of galaxies . Difficult to
Rice. Fig. 37: Decline in the density of red giants along axis 2 in several edge-on galaxies
Rice. 38: An image of a nearly edge-on dwarf galaxy shows the positions of the red giants found. The general form of the distribution is to set an oval or an ellipse, how such an effect can be verified in observations. Probably, only modeling the evolution of the galaxy disk can help with the regeneration of such hypotheses.
6.3.3 Structure of irregular galaxies.
Summarizing what has been said in other sections, one can imagine the structure of an irregular galaxy as follows: the most extended star system in all coordinates is formed by red giants. The shape of their distribution is a thick disk with an exponential drop in the surface density of giants from the center to the edge. The thickness of the disk is almost the same throughout its entire length. Younger star systems have their subsystems nested in this disk. The younger the stellar population, the thinner the disk it forms. And although the youngest stellar population, blue supergiants, is distributed over individual chaotic star-forming regions, in general, it also obeys a general pattern. All nested subsystems do not avoid each other, i.e. Star-forming regions may contain old red giants. For the most dwarf galaxies, where one star-forming region occupies the entire galaxy, this scheme is very arbitrary, but the relative sizes of the disks of the young population and the old population are also valid for such galaxies.
If, however, to complete the survey of the structure of irregular galaxies, radio data are also involved, then it turns out that the entire stellar system is immersed in a disk or cloud of neutral hydrogen. The size of the disk from HI, as it follows from the statistics of 171 galaxies, is approximately 5-6 times larger than the visible body of the galaxy at the level of Hv = 25" *. For a direct comparison of the sizes of hydrogen disks and disks from red giants, we have too little data.
In the ICIO galaxy, the sizes of both disks are approximately equal. For a galaxy in Pegasus, the hydrogen disk is almost half the size of a disk of red giants. And the galaxy NGC4449, which has one of the most extended hydrogen disks, is unlikely to have an equally extended disk of red giants. kah is confirmed not only by our observations. We have already mentioned reports by Minity and his colleagues about the discovery of a halo. Having obtained an image of only a part of the galaxy, they took the size of the thick disk along the b axis as a manifestation of a halo, which they reported without attempting to investigate the distribution of stars in these galaxies along the major axis.
In our studies, we did not touch on giant galaxies, but if we consider the structure of our Galaxy, then for it there already exists the concept of a "thick disk" for a low-metal old population. As for the term "halo", it seems to us that it is applicable to spherical, but not to flattened systems, although this is only a matter of terminology.
6.3.4 The boundaries of galaxies.
The question of the boundaries of galaxies has probably not been fully explored yet. Nevertheless, our results can make a certain contribution to its solution. It is usually believed that the stellar density at the edges of galaxies gradually decreases to zero, and the boundaries of galaxies, as such, simply do not exist. We measured the behavior of the most extended subsystem, consisting of red giants, along the Z axis. In those edge-on galaxies, data on which we obtained from photometry of images, the behavior of the density of red giants was uniform: there was an exponential decrease in density to zero (Fig. 37) . Those. the galaxy along the Z axis has a sharply defined edge, and its stellar population has a well-defined boundary, and does not gradually disappear.
It is more difficult to study the behavior of stellar density along the radius of the galaxy at the point where the stars disappear. For edge-on galaxies, the disk size is more convenient to determine. A galaxy in Pegasus along the major axis shows a sharp drop in the number of red giants to zero (Fig. 36). Those. the galaxy has a quite sharp disk boundary, beyond which there are practically no red giants. Galaxy J10, in the first approximation, behaves in a similar way. The density of stars decreases, and at some distance from the center of the galaxy, a sharp decrease in their number is observed (Fig. 33). However, in this case, the decrease does not occur to zero. It is noticeable that red giants also exist outside the radius of their density jump, but beyond this limit they have a different spatial distribution than that which they had closer to the center. It is interesting to note that red giants are distributed similarly in the MZZ spiral galaxy. Those. exponential density drop, jump and continuation beyond the radius of this jump. There was an assumption that this behavior is related to the mass of the galaxy (ICIO is the most massive irregular galaxy, after the Magellanic clouds, in the Local Group), but a small galaxy was found with the same behavior of red giants (Fig. 37). The parameters of red giants beyond the jump radius are unknown, do they differ in age and metallicity? What is the type of spatial distribution for these distant stars? Unfortunately, today we cannot answer these questions. Research is needed on large telescopes with a wide field.
How large is the statistics of our research to speak of the existence of thick disks in late-type galaxies as a widespread or general phenomenon? In all galaxies that had sufficiently deep images, we revealed extended structures of giant giants
Having studied the NCT archive, we found images of 16 galaxies seen edge-on or face-on, and resolvable as red giants. These galaxies are located at distances of 2-5 Me. Their list: N002976, VB053, 000165, K52, K73, 000190, 000187, iOSA438, P00481 1 1, P0C39032, ROS9962, N002366, i0C8320, iOCA442, N00625, N001560.
The exponential drop in density for face-on galaxies and the appearance of the distribution of red giants around edge-on galaxies proves that in all these cases we see manifestations of thick disks.
6.4 Disks of red giants and the hidden mass of irregular galaxies.
Radio observations in H1 of spiral and dwarf galaxies showed little difference in the behavior of the rotation curves of galaxies. For both types of galaxies, for an explanation
To change the shape of the rotation curves, the presence of significant masses of invisible matter is required. Could the extended disks we have found in all irregular galaxies be the invisible matter we are looking for? The masses of the red giants themselves, which we observe in the disks, are of course completely insufficient. Using our observations of the 1C1613 galaxy, we determined the parameters of the fall in the density of giants towards the edge and calculated their total number and mass in the entire galaxy. It turned out that Mred/Lgal = 0.16. Those. taking into account the mass of giant branch stars slightly increases the mass of the entire galaxy. However, it should be remembered that the stage of a red giant is a relatively short stage in the life of a star. Therefore, significant corrections should be made to the mass of the disk, taking into account the number of less massive stars and those stars that have already passed the red giant stage. It would be interesting, based on very deep observations of nearby galaxies, to check the population of subgiant branches and to calculate their contribution to the total mass of the galaxy, but this is a matter for the future.
Conclusion
Summing up the results of the work, let us dwell once again on the main results.
The 6-m telescope obtained deep multicolor images of about 100 stellar-resolvable galaxies. Data archive created. These galaxies can be referred to when studying the stellar population, primarily high-luminosity variable stars of the LBV type. In the studied galaxies, the colors and brightness of all visible stars were measured. Hypergiants and supergiants of the highest luminosity are distinguished.
A large and homogeneous array of distance measurement data was obtained for all galaxies in the northern sky with velocities less than 500 km/s. The results obtained personally by the dissertator are very significant among the total amount of data. The obtained distance measurements make it possible to analyze the non-Hubble motions of the galaxies of the Local Complex, which limits the choice of a model for the formation of the Local "pancake" of galaxies.
Based on distance measurements, the composition and spatial structure of the nearest groups of galaxies in the northern sky is determined. The results of the work make it possible to carry out statistical comparisons of the parameters of groups of galaxies.
A study was made of the distribution of galaxies in the direction of the cluster of galaxies in Virgo. Several relatively close galaxies have been found located between the cluster and the Local Group. Distances were determined and galaxies belonging to the cluster itself and located in different parts of the periphery and center of the cluster were identified.
The distance to the clusters in Virgo was determined, which turned out to be 17.0 Mpc and Coma Veronica, equal to 90 Mpc. On this basis, the Hubble constant was calculated equal to R0 = 77 ± 7 km/s/Mpc.
Based on the photometry of the BTA and HST images, the brightness of the brightest stars in 10 galaxies of the N001023 group, located at a distance of 10 Mpc, was measured. The distances to galaxies are determined and the Hubble constant in this direction is calculated. It is concluded that there is a small velocity gradient between the Local Group and the NGC1023 group, which can be
121 to be explained by the relatively small mass of the cluster of galaxies in Virgo in comparison with all the surrounding galaxies.
Based on studies of the spatial distributions of red giants in late-type galaxies, thick and extended disks of old stars have been discovered. The size of such disks is 2-3 times larger than the size of the visible body of the galaxy. It is found that the boundaries of these disks have rather sharp edges, beyond which there are very few stars.
Despite the large-scale studies of the distances to the galaxies of the northern sky, there are no fewer questions for the future than there were before the start of work. But these questions are of a different quality, since now, especially in connection with the work of space telescopes, it has become possible to make accurate measurements that can change our understanding of near space. This concerns the composition, structure, and kinematics of nearby groups of galaxies, the distances to which are intensively determined by the TCM method.
The periphery of galaxies is attracting more and more attention, especially because of the search for dark matter and the history of the formation and evolution of galactic disks. It is remarkable that in autumn 2002 the first meeting on the periphery of galaxies will be held at the Lovell Observatory.
Thanks
Over the long years that the work on the topic of the dissertation presented by me was carried out, many people, in one way or another, assisted me in my work. I am grateful to them for this support.
But it is especially pleasant for me to express my gratitude to those whose help I felt constantly. Without the highest qualifications of Galina Korotkova, the work on the dissertation would have dragged on for an incredibly long time. Olga Galazutdinova's passion and tenacity in doing the work allowed me to get results on a large number of objects in Virgo and N001023 in a fairly short period of time. Igor Drozdovsky, with his small service programs, gave us great help in the photometry of tens of thousands of stars.
I am grateful to the Russian Foundation for Basic Research, whose grants I received (95-02-05781, 97-02-17163,00-02-16584), for financial support for eight years, which allowed me to conduct research more effectively.
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How are galaxies distributed in space?
It turned out that this distribution is extremely uneven. Most of them are part of the clusters. Clusters of galaxies are as diverse in their properties as the galaxies themselves. In order to put at least some order in their description, astronomers came up with several of their classifications. As always in such cases, no classification can be considered complete. For our purposes, it suffices to say that clusters can be divided into two types - regular and irregular.
Regular clusters are often huge in mass. They are spherical and contain tens of thousands of galaxies. As a rule, all these galaxies are elliptical or lenticular. In the center are one or two giant elliptical galaxies. The closest regular cluster to us lies in the direction of the constellation Coma Berenices at a distance of about three hundred million light-years and has a diameter of more than ten million light-years. The galaxies in this cluster are moving relative to each other at speeds of about a thousand kilometers per second.
Irregular clusters are much more modest in mass. The number of galaxies in them is ten times less than in regular clusters, and these are galaxies of all types. Their shape is irregular, there are separate concentrations of galaxies inside the cluster.
Irregular clusters can be quite small, up to small groups consisting of several galaxies.
Recently, studies by Estonian astrophysicists J. Einasto, A. Saar, M. Jõeveer and others, American specialists P. Peebles, O. Gregory, L. Thompson have shown that the largest-scale irregularities in the distribution of galaxies are of a “cellular” nature. There are many galaxies and their clusters in the “walls of the cells”, and inside there is emptiness. Cell sizes are about 300 million light years, wall thickness is 10 million light years. Large clusters of galaxies are located at the nodes of this cellular structure. Separate fragments of the honeycomb
structures i are called superclusters. Superclusters often have a highly elongated shape like threads or noodles. And even further?
Here we are faced with a new circumstance. So far, we have seen increasingly complex systems: small systems formed a large system, these large systems, in turn, combined into an even larger one, and so on. That is, the Universe resembled a Russian nesting doll. A small nesting doll is inside a large one, and that one is inside an even larger one. It turned out that there is the largest matryoshka doll in the Universe! The large-scale structure in the form of “noodles” and “cells” is no longer assembled into larger systems, but evenly, on average, fills the space of the Universe. The Universe on the largest scales (more than three hundred million light years) turns out to be the same in its properties - homogeneous. This is a very important property and one of the mysteries of the Universe. For some reason, on a relatively small scale, there are huge clumps of matter - celestial bodies, their systems, more and more complex, up to superclusters of galaxies, but on a very large scale, structure disappears. Like sand on a beach. Looking close, we see individual grains of sand, looking from a distance and covering a large area with our eyes, we see a homogeneous mass of sand.
What The universe is homogeneous, it was possible to trace up to the distances ten billion light years!
We will return to the solution of the riddle of homogeneity, but for now let's turn to a question that probably arose in the reader. How is it possible to measure such huge distances to galaxies and their systems, to speak confidently about their masses, about the speeds of motion of galaxies?
Novikov I.D.
Usually galaxies are found in small groups containing ten members, often combined into vast clusters of hundreds and thousands of galaxies. Our Galaxy is part of the so-called Local Group, which includes three giant spiral galaxies (our Galaxy, the Andromeda nebula and the nebula in the constellation Triangulum), as well as more than 15 dwarf elliptical and irregular galaxies, the largest of which are the Magellanic Clouds. The average size of galaxy clusters is about 3 Mpc. In some cases, their diameter can exceed 10–20 Mps. They are divided into scattered (irregular) and spherical (regular) clusters. Open clusters do not have a regular shape and have blurred outlines. The galaxies in them are very weakly concentrated towards the center. An example of a giant open cluster is the nearest cluster of galaxies in the constellation Virgo. In the sky, it occupies about 120 square meters. degrees and contains several thousand predominantly spiral galaxies. The distance to the center of this cluster is about 11 Mpc. Spherical clusters of galaxies are more compact than open ones and have spherical symmetry. Their members are noticeably concentrated towards the center. An example of a spherical cluster is the cluster of galaxies in the constellation Coma Berenices, which contains a lot of elliptical and lenticular galaxies (Fig. 242). Its diameter is almost 12 degrees. It contains about 30,000 galaxies brighter than 19 photographic magnitude. The distance to the center of the cluster is about 70 Mpc. Many rich clusters of galaxies are associated with powerful extended X-ray sources, the nature of which is most likely associated with the presence of hot intergalactic gas, similar to the coronas of individual galaxies.
There is reason to believe that clusters of galaxies, in turn, are also unevenly distributed. According to some studies, the clusters and groups of galaxies surrounding us form a grandiose system - the Supergalaxy. In this case, individual galaxies apparently concentrate towards a certain plane, which can be called the equatorial plane of the Supergalaxy. The cluster of galaxies just discussed in the constellation Virgo is at the center of such a gigantic system. The mass of our Supergalaxy should be about 1015 solar masses, and its diameter should be about 50 Mpc. However, the reality of the existence of such clusters of second-order galaxies currently remains controversial. If they exist, then only as a weakly expressed inhomogeneity in the distribution of galaxies in the Universe, since the distances between them can slightly exceed their sizes. On the evolution of galaxies The ratio of the total amount of stellar and interstellar matter in the Galaxy changes with time, since stars form from interstellar diffuse matter, and at the end of their evolutionary path they return only part of the matter to interstellar space; some of it remains in white dwarfs. Thus, the amount of interstellar matter in our Galaxy should decrease with time. The same should happen in other galaxies. Being processed in the stellar depths, the matter of the Galaxy gradually changes its chemical composition, being enriched with helium and heavy elements. It is assumed that the Galaxy was formed from a gas cloud, which consisted mainly of hydrogen. It is even possible that, apart from hydrogen, it did not contain any other elements. Helium and heavy elements were formed in this case as a result of thermonuclear reactions inside stars. The formation of heavy elements begins with the triple helium reaction 3He4 ® C 12, then C 12 combines with a-particles, protons and neutrons, the products of these reactions undergo further transformations, and thus more and more complex nuclei appear. However, the formation of the heaviest nuclei, such as uranium and thorium, cannot be explained by gradual growth. In this case, one would inevitably have to go through the stage of unstable radioactive isotopes, which would decay faster than they could capture the next nucleon. Therefore, it is assumed that the heaviest elements at the end of the periodic table are formed during supernova explosions. A supernova explosion is the result of the rapid contraction of a star. At the same time, the temperature rises catastrophically, chain thermonuclear reactions take place in the contracting atmosphere, and powerful neutron fluxes arise. The intensity of neutron fluxes can be so high that intermediate unstable nuclei do not have time to collapse. Before that happens, they capture new neutrons and become stable. As already mentioned, the abundance of heavy elements in the stars of the spherical component is much less than in the stars of the flat subsystem. This is apparently due to the fact that the stars of the spherical component were formed in the very initial stage of the evolution of the Galaxy, when the interstellar gas was still poor in heavy elements. At that time, the interstellar gas was an almost spherical cloud, the concentration of which increased towards the center. The stars of the spherical component that formed in this epoch also retained the same distribution. As a result of collisions of clouds of interstellar gas, their speed gradually decreased, kinetic energy turned into thermal energy, and the general shape and size of the gas cloud changed. Calculations show that in the case of rapid rotation, such a cloud should have taken the form of an oblate disk, which is what we observe in our Galaxy. Stars formed at a later time therefore form a flat subsystem. By the time the interstellar gas formed into a flat disk, it had been processed in the stellar interior, the abundance of heavy elements had increased significantly and the stars of the flat component were therefore also rich in heavy elements. Often the stars of the flat component are called second generation stars, and the stars of the spherical component are called first generation stars, to emphasize the fact that the stars of the flat component were formed from matter that had already been in the stellar interior. The evolution of other spiral galaxies probably proceeds in a similar way. The shape of the spiral arms in which the interstellar gas is concentrated is apparently determined by the direction of the lines of force of the general galactic magnetic field. The elasticity of the magnetic field, to which the interstellar gas is "glued", limits the flattening of the gaseous disk. If only gravity acted on the interstellar gas, its compression would continue indefinitely. In this case, due to its high density, it would quickly condense into stars and practically disappear. There is reason to believe that the rate of star formation is approximately proportional to the square of the density of the interstellar gas.
If the galaxy rotates slowly, then the interstellar gas is collected by gravity in the center. Apparently, in such galaxies the magnetic field is weaker and hinders the compression of the interstellar gas less than in rapidly rotating ones. The high density of interstellar gas in the central region leads to the fact that it is quickly consumed, turning into stars. As a result, slowly rotating galaxies should have an approximately spherical shape with a sharp increase in stellar density in the center. We know that elliptical galaxies have just such characteristics. Apparently, the reason for their difference from the spiral ones lies in the slower rotation. From what has been said above, it is also clear why there are few stars of early classes and little interstellar gas in elliptical galaxies.
Thus, the evolution of galaxies can be traced from the stage of a gaseous cloud of approximately spherical shape. The cloud consists of hydrogen, it is not uniform. Separate clumps of gas, moving, collide with each other - the loss of kinetic energy leads to cloud compression. If it rotates quickly, a spiral galaxy is obtained, if it rotates slowly, an elliptical one. It is natural to ask why the matter in the Universe broke up into separate gas clouds, which later became galaxies, why we observe the expansion of these galaxies, in what form was the matter in the Universe before the formation of galaxies.
where H¾ Hubble constant. In relation (6.12) V expressed in km/s, but r¾ in Mps.
This law is called Hubble law . Hubble constant is currently taken to be H = 72 km/(s∙Mpc).
Hubble's law allows us to say that The universe is expanding. However, this does not mean at all that our Galaxy is the center from which the expansion proceeds. At any point in the Universe, the observer will see the same picture: all galaxies have a redshift proportional to their distance. Therefore, it is sometimes said that space itself is expanding. This, of course, should be understood conditionally: galaxies, stars, planets, and we are not expanding.
Knowing the value of the redshift, for example, for some galaxy, we can determine the distance to it with great accuracy using the ratio for the Doppler effect (6.3) and the Hubble law. But for z ³ 0.1, the usual Doppler formula is no longer applicable. In such cases, use the formula from the special theory of relativity:
| . | (6.13) |
Galaxies are very rarely single. Usually galaxies are found in small groups containing ten members, often combined into vast clusters of hundreds and thousands of galaxies. Our galaxy is part of the so-called local group, which includes three giant spiral galaxies (our Galaxy, the Andromeda nebula and the galaxy in the constellation Triangulum), as well as several dozen dwarf elliptical and irregular galaxies, the largest of which are several megaparsecs long. . They are divided into irregular And regular clusters. Irregular clusters do not have a regular shape and have blurred outlines. The galaxies are the Magellanic Clouds.
On average, the sizes of halo clusters in them are very weakly concentrated towards the center. An example of a giant open cluster is the nearest cluster of galaxies in the constellation Virgo. In the sky, it occupies about 120 square meters. degrees and contains several thousand predominantly spiral galaxies. The distance to the center of this cluster is about 15 Mps.
Regular clusters of galaxies are more compact and symmetrical. Their members are noticeably concentrated towards the center. An example of a spherical cluster is the cluster of galaxies in the constellation Coma Berenices, which contains a very large number of elliptical and lenticular galaxies. It contains about 30,000 galaxies brighter than 19 photographic magnitude. The distance to the center of the cluster is about 100 Mps.
Many clusters containing a large number of galaxies are associated with powerful extended X-ray sources.
There is reason to believe that clusters of galaxies, in turn, are also unevenly distributed. According to some studies, the clusters and groups of galaxies surrounding us form a grandiose system - supergalaxy or Local supercluster. In this case, individual galaxies apparently concentrate towards a certain plane, which can be called the equatorial plane of the Supergalaxy. The cluster of galaxies just discussed in the constellation Virgo is at the center of such a gigantic system. The cluster in Veronica's Hair is the center of another, nearby supercluster.
The observable part of the universe is usually called Metagalaxy . A metagalaxy is made up of various observable structural elements: galaxies, stars, supernovae, quasars, etc. The dimensions of the Metagalaxy are limited by our observational possibilities and are currently taken equal to 10 26 m. It is clear that the concept of the dimensions of the Universe is very arbitrary: the real Universe is unlimited and does not end anywhere.
Long-term studies of the Metagalaxy revealed two main properties that make up basic cosmological postulate:
1. The metagalaxy is homogeneous and isotropic in large volumes.
2. The metagalaxy is not stationary.
