The most important scientific achievements for 2011–2017

1) Studying distributions of stars of different ages in irregular and spiral galaxies we found for each galaxy a clear correlation between the age of stars and the spatial size of the subsystems of stars of this age. We believe that the dependency found by us can be explained by the hypothesis of galaxy expansion over time.

Tikhonov N., Galazutdinova O., AA Transac., V. 27, Iss.2, 227, 2012.
Tikhonov N., Galazutdinova O., Astronomy Letters, V. 38, Iss.3, p. 147, 2012.
Tikhonov N., Astronomy Letters, V. 38, Iss.8, p. 497, 2012.
Tikhonov N., Astronomy Letters, V. 39, Iss.5, p. 298, 2013.


Fig. 1. HST image of the PGC9962 galaxy (on top). Hertzsprung-Russell diagram for this galaxy is shown with isochrones of different ages (in the bottom left corner) and number density distribution diagrams for stars of different ages perpendicular to disk plane (in the bottom right corner). The numbers on the diagrams denote the age of stars in millions of years.

2) The NGC 1313 galaxy, being, perhaps, the most mysterious galaxy of the sky, has been studied based on the Hubble Space Telescope images. In normal images, it looks like a normal spiral galaxy but deep images show that the galaxy is highly distorted by gravitational interaction. However, the images do not show any neighboring galaxy, which would create the deformation of a stellar structure. We made a stellar photometry of eight NGC 1313 fields and of its dwarf companion AM 0319-662 and studied the visible distribution of stars of different ages and of metallicity in the galaxy. It has been found that the spatial distribution of low metallicity stars is substantially different from the distribution of high metallicity stars. This distinction has allowed us to identify the fragments of a dwarf galaxy destroyed by now, being almost merged with NGC 1313. This disappeared galaxy was the cause of the gravitational deformation of NGC 1313.

Tikhonov N., Galazutdinova O., Astronomy Letters, V. 42, Iss.7, p. 428, 201, 2016.
Tikhonov N., Galazutdinova O., Galaxy NGC 1313 mystery (poster), VAK-2017, Yalta, 17 September, 2017.


Fig. 2. Galaxy NGC 1313 (image made with 8 meter  telescope (VLT)).

3) We have developed the new method for determining the size of groups and clusters of galaxies from cumulative distribution of number of galaxies in dependence on squared clustercentric distance. For 29 systems of galaxies we have determined dynamical masses within the effective radius Re which are about 1.65 times less then masses enclosed within R200 radius. A comparison of the inferred dynamical masses and the hydrostatic masses determined from the radiation of hot gas in galaxy groups and clusters (based on published data) led us to conclude that the inferred masses for the main sample of 21 groups and clusters, which does not include merging clusters with irregular structure, the dynamical masses exceed the X-ray masses an average by 12%, with an rms scatter of 35%.

         Kopylov A.I., Kopylova F.G., Astrophysical Bulletin, 70, Iss.3,  p. 243, 2015.


Fig. 3. A comparison of the X-ray masses (MX,200) obtained by gas radiation in X-ray band with the dynamical masses (M200) measured from the radial velocities of galaxies. The objects of the main sample are shown by filled circles.

4) We have developed a new method for determining the size of galaxy clusters, the region with a radius of Rh (or Rsp) (>R200), from the cumulative distribution of the number of galaxies depending on the squared clustercentric distance, where Rh (or Rsp) radius of apocenter of orbits of galaxies. This allowed to determine for the systems of galaxies the total K-luminosity and the number of galaxies corrected for the background. K-luminosity, effective radius containing either half of the luminosity, or half the number of galaxies and dispersion of radial velocities of galaxy systems form a Fundamental plane (FP) LK = Re0.70(N/2)×σ1.34. In Schaefer et al. (MNRAS, L21, 263, 1993) (for comparison) for 16 clusters of galaxies in the filter V by another method is obtained the FP: LV = Re0.89×σ1.28.

Kopylova F.G., Kopylov A.I.,  Astrophysical Bulletin, 71, Iss.3, p. 257, 2016.

Fig. 4. The Fundamental plane of galaxy groups and clusters in NIR range. The regression relation have the form of: LK = Re0.70(N/2)×σ1.34. The red circles show galaxy groups with σ < 420 km/s.

5) Stellar photometry for three fields in the Virgo cluster of galaxies has been performed on the basis of archival Hubble Space Telescope ACS/WFC images. The densely populated red giant branches belonging to cluster galaxies are seen on the constructed Hertzsprung-Russell diagrams. The distances to eight galaxies in the Virgo cluster have been determined by the TRGB method  (from 14 to 18 Mpc). The sizes of the stellar subsystems and the gradients in the number density of red giants along the galactic radius have been determined for the investigated galaxies. The stellar periphery of the galaxies has been found to extend to great distances and to cover the entire area of the images used. Therefore, the stars that have previously been thought to be intracluster stars actually belong to the periphery of neighboring galaxies.

Tikhonov N.,  Astronomy Letters, V. 43, Iss.1, p. 21, 2017.

Fig. 5. Image of the galaxies LBS 31, NGC 4407 and VCC 871 in the DSS review. The square F2 of the Hubble Space Telescope with the ACC/WFC chamber is noted. The ellipses around NGC 4407 and VCC 871 mark the visible boundaries of the star subsystems of these galaxies. It can be seen that the subsystems overlap the HST image of the telescope and make it impossible to search for intergalactic stars in this field. The size of the picture is 10'×10', the north is at the top.

6) According to the archives of the SDSS DR10 catalogue for clusters of galaxies A1656 (Coma), A1139, A1314 (Leo supercluster), A2040, A2052, A2107 (Hercules supercluster) the specific star formation rate is determined. We have obtained that the fraction of galaxies with quenched star formation decreases continuously with a radius of 0.87±0.02 in the center to 0.43±0.03 in the outskirts, beyond the Rsp. Thus remains more, than in the field on average on 26%. We also found that galaxies actively forming stars are, as a rule, on the outskirts of clusters of galaxies and have dispersion of radial velocities more than galaxies with quenched star formation.

Kopylova, F.G., Kopylov, A.I., Astrophysical Bulletin, 73,  Iss.1,  p. ?, 2018.

Fig. 6. Variations of spatial distribution and kinematics of galaxies in clusters depending on their specific star formation rate (log sSFR), divided into 4 bins. The size of the symbols correspond to these bins: large symbols
log sSFR = [1.75,1.35], [1.35,1.05] Gyr1, small symbols [1.75,4.00], [4.00, all the rest] Gyr1. Thus, large symbols mark the star formong galaxies, small galaxies with quenched star formation.

7) On the basis of the Hubble Space Telescope images stellar photometry of nine fields around the giant elliptical galaxy M87 from the Virgo cluster was performed  to determine the boundary of the influence of giant galaxies of groups and clusters on neighboring dwarf galaxies. The populated branches of red giants and AGB stars are visible on the Hertzsprung-Russell diagrams. Distances to M87 for each field are determined based on the TRGB method. An increase in the distance modulus is found when approaching the center of the galaxy, indicating either the influence of high-metallic red giants, or the existence of a weak gas-dust cloud around M87 with a diameter of approximately 20' and maximum absorption in filter I to 0.18m near the center of the galaxy. The average value of the distance modulus was determened  as (m–M) = 30.93 by the outlying from the center of the M87 fields, which corresponds to a distance D = 15.4 Mpc. This value puts M87 not in the center of the cluster, but on its near edge. The star subsystem of the galaxy is defined up to a distance of 190 kpc and has an even greater continuation. It is shown that the stars at this distance belong to the galaxy M87 and are not intergalactic stars, as previously thought. For the first time distances to three dwarf galaxies were measured: P4_anon, NGC4486A and VCCA039.These galaxies  turned out to be M87 satellites.

Tikhonov N.A., Galazutdinova O., Karataeva G.M.,
Astrophysical Bulletin, 73, Iss.2,  p.?,  2018.

dss M87

Fig. 7. DSS-image of the Virgo cluster with galaxy M87.