The role of diffuse matter in galactic coronas

An upper limit to the gas content in the coronas of giant galaxiesM _gas<0.04M _cor has been calculated on the basis of observational data on the emission of clusters of galaxies in different wavelength ranges. An analysis of companion galaxies has revealed a correlation of their morphological types with the distances to central giant galaxies. A gasodynamical interpretation of this regularity is suggested and a possible picture of the evolution of the galactic coronas is presented.     

Concerning the errors arising through the use of Tully-Fisher relation for estimation of the Virgo cluster distance

The distance modulus of the Virgo cluster has been reexamined based on the Tully-Fisher relation between fully corrected B. ₁ ⁰ values and 21 cm velocity width derived from RC3 catalogue for spiral galaxies of Sbc-Sdm types, belonging to the “low-velocity” Virgo subcluster, singled out according to the statistical method proposed by Anosova, and led to the value μ = 31.15 ± 0.57 mag. A strong dependence of the intrinsic scatter in the Tully-Fisher relation on the apparent axes ratio of galaxies has been found, with a value of 0.4 mag for strongly flattened, highly inclined galaxies and galaxies with small inclinations and a value of 0.72 mag for objects with intermediate values of axes ratio. The restriction to samples only with galaxies with photoelectric observations does not lead to a considerable change of amplitude of scatter and decreases the value the of distance modulus. Published in Astrofizika, Vol. 42, No. 1, pp. 37–46, January–March, 1999.     

Active Galactic Nuclei

The term Active Galactic Nuclei includes QSOs (Quasi-Stellar Objects), Seyfert galaxies, BL Lac objects and nuclei showing unusual amounts of star formation. South African work has centred on the photometric properties of these objects, both in the optical(UBVRI) and the infrared(JHKL). Photometry has been used to investigate the nature of the relevant emission mechanisms by studying both the colours of the nuclear components and their variations. In particular, it has been demonstrated convincingly that circumnuclear dust shells are present in several Seyfert 1 galaxies at temperatures of around 1500 K.It has also been shown that the variable component in many Seyfert 1 galaxies retains a constant spectral shape independent of its actual flux at a given time. Further, there is evidence that this shape is largely the same in all Seyfert 1 galaxies. Other studies have concentrated on surveys of morphological, spectroscopic and photometric characteristics of certain classes of galaxies such as those found by the IRAS satellite and those listed in the Arp-Madore catalogue of interacting galaxies.     

Photometry of Chain-Like Groups of Compact Galaxies

The integrated V and R stellar magnitudes of 231 objects, comprising 42 chain-like groups of compact galaxies, have been measured. It has been determined, using a compactness parameter, that 92 of these objects are, with a high probability, stars. Of the 42 groups, 23 consist of galaxies in the vast majority.     

Colour indices of the Markarian galaxies

By use of the ANS ultraviolet fluxes, optical (UBV) and IRAS infrared fluxes, several colour indices for a few Markarian galaxies have been investigated. A comparison of these indices with those for normal NGC galaxies has been carried out. Similarities and differences in the indices for the two groups of galaxies have been discussed and possible causes have been indicated.     

Structures in the large-scale distribution of galaxies with different luminosities

The large-scale structures of volume-limites subsample sorted out from the CfA catalog have been analysed by percolation method. The result shows that the features in the distribution of galaxies with different luminosities are significantly different. Especially, the most luminous galaxies are likely to exhibit hierarchical clustering on a scale about 50h ₅₀ ^–1 Mpc, and the least luminous galaxies in our subsamples show string-like or sheet-like character in their distribution. These results suggest that the large-scale distribution of galaxies consists of clusters or cluster cores of most luminous galaxies and the less luminous galaxies spread out from these cores with a string-like or sheet-like structure. This picture of the large-scale distribution consists with previous results from two-point correlation analysis and fractal analysis. The implication of these results has been discussed.     

HCGs: stable and rotating systems?

It is shown that the radial velocity dispersion of the elongated HCGs (b/a ≤ 0.2) with smaller two‐dimensional galaxy‐galaxy median projected separation R is, on average, higher than those of the groups with larger R. It shows that galaxies in a group move preferentially along its elongation. Inspection of radial velocities of member galaxies in chain‐like and in roundish HCGs shows that galaxies in HCGs most probably rotate around the gravitational center of the corresponding group. Other two possible mechanisms: flying apart of galaxies from the group in opposite directions, and infall of field galaxies upon the group are excluded. It follows that HCGs are, probably, more stable formations, than it has been assumed. In this case the known inconsistencies between the results of the N‐body simulations and the observational facts are being excluded.     

Search for nearby host galaxies of short gamma-ray bursts detected and well localized by BATSE/IPN

We have collected the observational data accumulated before the Swift experiment to check the possible connection of short gamma-ray bursts (GRBs) with low-redshift galaxies. The BATSE/IPN experimental data on well-localized short GRBs and the SDSS DR5 and PSCz catalogs of galaxies are used. The PSCz sky coverage has allowed us to search for host galaxies for a sample of 34 short GRBs. One or more galaxies have been found in the error boxes of six bursts, but the probability of a chance coincidence for each of them is high. No excess of nearby galaxies in the total sample has been detected. The 90% confidence limit corresponds to the fact that no more than 7%of the short GRBs could originate in nearby galaxies of the PSCz sample. The estimated upper limit of several percent may be considered to be valid in the volume z = 0.015–0.025. Based on the results of our search, we have estimated the lower limits for the isotropic energies E _γiso of 31 short bursts from our sample. Their values lie within the range 1.0 × 10⁴⁷–2.7 × 10⁴⁹ erg. The possible fraction of the flares from magnetars in our sample of short GRBs is discussed. The SDSS sky coverage is currently insufficient to perform a similar analysis.     

Faint Blue Galaxies in the Virgo Cluster Region

Finding charts, coordinates, B magnitudes, and U – B color estimates are given for 110 faint blue galaxies located near the centre of the Virgo cluster of galaxies. The galaxies have been found by blinking on plates taken with the Tautenburg 52 inch SCHMIDT telescope.     

Statistics of interacting galaxies at <Emphasis Type="Italic">z</Emphasis> ∼ 0.7

We present the results of our analysis of the frequencies of galaxies with tidal tails and M51-type galaxies in several deep fields of the Hubble Space Telescope (HDF-N, HDF-S, HUDF, GOODS, GEMS). In total, we have found about seven hundred interacting galaxies at redshifts z ≤ 1.5 in these fields. At z ≤ 0.7, the observed space densities of galaxies with tidal structures and M51-type galaxies have been found to increase as ∝(1 + z) ^m , where m ≈ 2.6. According to our estimates, over the last 6–7 Gyr, i.e., at z ≤ 0.7, about a third of the galaxies with M(B) ≤ −18 ^m must have undergone strong gravitational perturbations and mergers and ∼1/10−1/5 of the galaxies have swallowed relatively low-mass nearby satellites typical of M51-type galaxies. The possible decrease in the time scale on which a distant galaxy appears peculiar with growing z can increase considerably the estimated rate of mergers.     

Redshift distribution in extragalactic objects and evolution of galaxies

In order to see whether the study of redshift distribution in different classes of extragalactic objects, suspected of belonging to different phases in the evolutionary sequence of galaxies, helps in arriving at a possible picture of the evolutionary sequence of galaxies, histograms have been plotted between the number and the redshift for each of the five classes of extragalactic objects, namely, the QSOs, N-galaxies, Seyfert galaxies, radio galaxies and normal galaxies. It is found that: (i) the highest peaks in the five histograms occur at distinctly different redshifts in the order (Z _peak)_QSOs>(Z _peak)_N-galaxies>(Z _peak)_{Seyfert galaxies}>(Z _peak)_{radio galaxies}> (Z _peak)_{normal galaxies} and (ii) sufficient overlap occurs in the redshift ranges of (a) QSOs and N-galaxies, (b) N-galaxies and Seyfert galaxies, (c) Seyfert galaxies and radio galaxies and (d) radio galaxies and normal galaxies. These facts suggest that the extragalactic objects might be evolving in the sequence: QSOsN-galaxiesSeyfert galaxiesradio galaxiesnormal galaxies. Other independent evidences in support of such an evolutionary sequence have been given. Finally, various aspects of the problem associated with the picture of the evolutionary sequence of galaxies have been critically examined.     

Far infrared emission from galaxies

Until recently far infrared (FIR) observations of galaxies were limited to about a dozen bright and/or active galaxies. New photometric data has become available from Infrared Astronomical Satellite (IRAS) on 33 galaxies (most of them faint) from IRAS Circular Nos. 1, 2, and 3 The FIR spectra of these galaxies are similar. The far infrared fluxF _FIR in the wavelength interval 9–118 m of the brighter galaxies is seen to be correlated with the integrated optical magnitudeB _T ⁰ . The 12 and 25 m fluxes of these galaxies exhibit the same dependence onB _T ⁰ as the 10 and 21 m fluxes from Seyferts and other emission-line galaxies. This suggests that the galaxies detected by IRAS are some type of active galaxies in accord with the high percentage of these galaxies predicted by Lock and Rowan-Robinson (1983).     

Quasi-periodical structures in the galaxy populations: mass and luminosity functions for the cluster galaxies

A search and estimation of the statistical significance of the quasi-periodical structures (QPS) has been carried out: for the luminosity function of the galaxies in a few rich clusters; for the integrated mass function of galaxies in the superclusters identified via = 21 cm observations. Some statistically significant QPS have been revealed. The periods for these structures are in agreement between each other, at this basis the hypothesis has been proposed that an effect of the QPS at the level of galaxies has some universal character. Frequency doubling has been discovered for these QPS.     

Simulation of compact groups of galaxies

Self-consistent simulations of seven groups of galaxies with halos have been performed to find a constraint upon the size of missing halos around spiral galaxies. An initial galaxy, which consists of 100 superstars, has half-mass radius 41 kpc and central velocity dispersion 235 km s^–1. The simulations start from the epoch of maximum expansion. The initial conditions involve a variety of spatial distributions of galaxies, and the velocity dispersion of galaxies as would be permitted for maximum expansion. Dense groups having collapse times shorter than (2/3)H ₀ ^–1 are shown to form multiple mergers in a Hubble timeH ₀ ^–1 . From a comparison of the frequencies of cD galaxies, or multiple mergers, in observed and simulated groups, it is concluded that the effective radius of missing halos is less than 41 kpc.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Photometry of groups of galaxies. II. The NGC 972 group

A nearby group of galaxies, centered at the spiral galaxy NGC 972 and conspicuously rich in faint dwarf spheroidal galaxies, has been investigated photometrically on the B and V plates, obtained with the Tautenburg 2m Schmidt telescope. For ten certain and probable group members the equivalent B and V brightness profiles have been extracted. Integrated magnitudes and mean colours of faint group members have been estimated. Typically, the dwarfs show a “subexponential” (i.e. a convex curvature over the linear radius) surface brightness profile and often a central excess. Their equivalent profiles are reasonably well fitted by modified isothermal (King) models.     

Galaxies with f12 > f25

We have compiled a sample of galaxies whose flux density is higher at 12 microns (f12) than at 25 microns (f25). It is argued thatf12 >f25 effectively selects quiescent galaxies which are less active in infrared, radio, and optical bands than other types of normal galaxies. Moreover galaxies withf12 >f25 do not exhibit the well-known relations that normal galaxies show between far-infrared parameters, for example, the negative correlation betweenf12/f25 andf60/f100. These galaxies also show different far-infrared and radio properties. In our opinion this sample of quiescent galaxies is suitable for use as a control sample when properties of more active galaxies are discussed. It may also be used in modeling galaxies with active star formation or an active nucleus.Translated fromAstrofizika, Vol. 38, No. 3, 1995.     

Global properties of star formation in spiral galaxies

Samples of spiral galaxies from two catalogues of 21 cm line observations and a catalogue of near-infrared observations of nearby galaxies have been used in conjunction with Infrared Astronomical Satellite data to study correlations involving M_G, the dynamic mass of the galaxies, the luminosities in theH band (1.6Μm), the blue band and the far infrared bands and the mass of atomic hydrogen, it is found that both the blue and the far-IR luminosities which are indicators of star formation averaged over ∼3 × l0⁹ and ∼10⁷ years respectively, have a linear dependence onM _G On the other hand, theH luminosity which is a measure of star formation averaged over the lifetime of galaxies, has a steeper power law dependence onM _G. The correlations observed do not have significant dependence on the morophological type of the galaxies There is a poor correlation between the far-infrared luminosity and the mass of atomic hydrogen. The mass of atomic hydrogen has a dependence of the formM _G. Because of the decrease in the mean mass for later morphological types and due to differences in power law dependences of luminosities in different bands onM _G, the mean value of luminosity-to-mass ratio is a constant for blue and far-IR bands, decreases for theH band and the gas-to-mass ratio increases as morphological type increases.     

The peaks and gaps in the redshift distributions of active galactic nuclei and quasars

The distributionsf(z) of the redshifts for active galaxies (Seyfert galaxies, radio galaxies, and quasars) have been studied. Some statistically-significant maxima and minima are observed in the distributionsf(z) for these objects. The significance of peaks and gaps increases for the brighter objects, for which the samples are more complete. The clustering of the Seyfert galaxies is significantly different from that of the nearby normal galaxies. The distributionf(z) for the radio galaxies is similar to the analogous distribution for the galaxy clusters. Three of the five peaks in the distributionf(z) for the radio quasars may be caused by the selection effects. Two peaks within the intervalsz (0.5, 0.7) and (1.0, 1.1) are probably real. The corresponding scales of the QSO clustering along the line-of-sight are about 100h ^–1 Mpc (h is the Hubble constant in the units of 75 km s^–1 Mpc^–1). The possibility of some global quasi-periodical cycles for the processes of activity is discussed. The period of a cycle for the Seyfert and radio galaxies is about 1×10⁸ years that corresponds to the distances of about 30h ^–1 Mpc between the shells.     

Comparisons of u ‐, g ‐, r ‐, i ‐, and z ‐band luminosity distributions between galaxy members of compact groups and isolated galaxies

To investigate the environmental dependence of u ‐, g ‐, r ‐, i ‐, and z ‐band luminosities, we perform comparative studies of luminosity distributions between galaxy members of compact groups (CGs) and isolated galaxies. It is found that for the r, i, and z bands isolated galaxies have a higher proportion of faint galaxies and a lower proportion of luminous galaxies than galaxy members of CGs, but for the u band an opposite trend is observed. The correlation between the g ‐band luminosity and the environment has different trends in different luminosity regions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Faint companions of isolated 2MIG galaxies

We present the results of a search for companions around the isolated galaxies from the 2MIG catalog. Among 3227 2MIG galaxies we detected 125 objects with a total of 214 neighbors having radial velocity differences of ΔV < 500 km/s and projected separations of R _p < 500 kpc relative to the 2MIG galaxies. The median luminosity of the companions is 1/25 of the luminosity of catalog galaxies, which has little effect on the dynamic isolation of the latter. The median ratio of the orbital mass to the K-luminosity determined from 60 companions of E and S0 2MIG galaxies, 63M _⊙/L _⊙, is significantly greater than that found from the spiral galaxy companions (17M _⊙/L _⊙). We note that a fraction of 2MIG galaxies with companions may be a part of low-contrast diffuse structures: clouds and filaments.