Polar-ring galaxies: New candidates and statistics

We present the results of our observational study of two candidates for polar-ring galaxies (PRGs). Both objects, A2330-3751 and SDSS J000911.57-003654.7, are giant edge-on galaxies with large-scale structures resembling polar rings observed along their minor axes. The optical diameter of the putative ring reaches 60 kpc in A2330-3751 and 18 kpc in SDSS J000911.57-003654.7. To estimate the space density of PRGs, we have constructed their luminosity function in the range of B-band absolute magnitudes from −17_· ^m 5 to −21_· ^m 5. We have found that ∼10⁻³ of the nearby galaxies exhibit polar structures. Polar rings around early-type (E/S0) galaxies are encountered approximately a factor of 3 more frequently than those around spiral ones. According to our estimates, ∼20–30 PRGs in which large-scale rings are seen almost face-on must be observed among relatively bright galaxies (B ≤ 15 ^m ).     

Blue Compact Galaxies at Redshifts Z=0.2-1.3

We study the nature of faint blue compact galaxies (BCGs) at redshifts z ∼ 0.2 - 1.3 using Keck and HST. Despite being very luminous (L_B ∼ L^*), most distant BCGs have masses M ∼ 10¹⁰M_⊙, i.e., they are dwarf stellar systems. The majority of these galaxies have colors, sizes, surface brightnesses, luminosities, velocity widths, excitations, star formation rates (SFR), and mass-to-light ratios characteristic of the most luminous nearby HII galaxies. The more massive BCGs form a more heterogeneous class of evolved starburst, similar to local disk starburst galaxies. Without additional star formation, HII-like BCGs will most likely fade to resemble today's spheroidal galaxies such as NGC 205. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Studying the first galaxies with ALMA

We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present a summary of current observations of the host galaxies of the most distant QSOs (z∼6). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic objects at these redshifts, meaning hyper-luminous infrared galaxies (L _FIR ∼10¹³ L _⊙). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star forming galaxies (i.e. Ly-α emitters) at z∼6. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust—the fundamental fuel for star formation—in galaxies into cosmic reionization.     

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.     

Quantized redshifts: A status report

The current status of a continuing programme of tests for redshift periodicity or ‘quantization’ of nearby bright galaxies is described. So far the redshifts of over 250 galaxies with high-precision HI profiles have been used in the study. In consistently selected sub-samples of the datasets of sufficient precision examined so far, the redshift distribution has been found to be strongly quantized in the galactocentric frame of reference. The phenomenon is easily seen by eye and apparently cannot be ascribed to statistical artefacts, selection procedures or flawed reduction techniques. Two galactocentric periodicities have so far been detected, ∼ 71 .5km s^-1 in the Virgo cluster, and ∼37. 5km s^-1 for all other spiral galaxies within ∼ 2600km s^-1. The formal confidence levels associated with these results are extremely high.     

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.     

Scaling relations of field spirals at intermediate redshift

In the last few years, galaxies at redshifts up to z ∼ 1 have become accessible for medium-resolved spectroscopy thanks to the new generation of 10 m-class telescopes. With kinematic and photometric information on spiral galaxies in this regime, well-known scaling relations like the Tully-Fisher relation (TFR) can be studied over half a Hubble time. By comparison to local samples, these studies facilitate simultaneous tests of the hierarchical merging scenario and stellar population models. Using the Very Large Telescope, we obtained spatially resolved rotation curves of 78 spiral galaxies in the FORS Deep Field (FDF), covering all Hubble types from Sa to Sm/Irr at redshifts 0.1 < z < 1.0. We find evidence for a B-band luminosity increase of up to 2 mag for low-mass spirals, whereas the most massive galaxies are of the same luminosity as their local counterparts. In effect, the TFR slope decreases significantly. This would explain the discrepant results of previous observational studies. We also present the velocity-size relation and compare it to the predictions of numerical simulations based on the hierarchical merging scenario. This revised version was published online in August 2006 with corrections to the Cover Date.     

Intrinsic Redshifts and the Tully–Fisher Distance Scale

The Tully–Fisher relationship (TFR) has been shown to have a relatively small observed scatter of ∼±0.35 mag implying an intrinsic scatter < ±0.30 mag. However, when the TFR is calibrated from distances derived from the Hubble relation for field galaxies scatter is consistently found to be ±0.64 to ±0.84 mag. This significantly larger scatter requires that intrinsic TFR scatter is actually much larger than ±0.30 mag, that field galaxies have an intrinsic TFR scatter much larger than cluster spirals, or that field galaxies have a velocity dispersion relative to the Hubble flow in excess of 1000 km s⁻¹. Each of these potential explanations faces difficulties and contradicted by available data and the results of previous studies. An alternative explanation is that the measured redshifts of galaxies are composed of a cosmological redshift component predicted from the value of the Hubble constant and a superimposed intrinsic redshift component previously identified in other studies. This intrinsic redshift component may exceed 5000 km s⁻¹ in individual galaxies. In this alternative scenario a possible value for the Hubble constant is 55–60 km s⁻¹ Mpc⁻¹.     

Inhomogeneous chemical evolution of dwarf spheroidal galaxies

Stellar abundance pattern of n-capture elements such as barium is used as a powerful tool to infer how the star formation proceeded in dwarf spheroidal (dSph) galaxies. It is found that the abundance correlation of barium with iron in stars belonging to dSph galaxies orbiting the Milky Way, i.e., Draco, Sextans, and Ursa Minor have a feature similar to that in Galactic metal-poor stars. The common feature of these two correlations can be realized by our in homogeneous chemical evolution model based on the supernova-driven star formation scenario if dSph stars formed from gas with a velocity dispersion of ∼ 26 km s^-1. This velocity dispersion together with the stellar luminosities strongly suggest that dark matter dominated dSph galaxies. The tidal force of the Milky Way links this velocity dispersion with the currently observed value ≲ 10 km s^-1 by stripping the dark matter in dSph galaxies. As a result, the total mass of each dSph galaxy is found to have been originally ∼ 25 times larger than at present. In this model, supernovae immediately after the end of the star formation can expel the remaining gas over the gravitational potential of the dSph galaxy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinematics of the Local cosmic void

Available data on the distances and radial velocities of galaxies are systematized in order to study the distribution of peculiar velocities in neighborhoods of the Local cosmic void lying in the direction of the Aquila and Hercules constellations. A sample of 1056 galaxies is used, with distances measured in terms of the luminosity of the tip of the red giant branch (TRGB), the luminosity of the cepheids, the luminosity of type 1a supernovae, surface brightness fluctuations (SBF), and the Tully-Fisher relation. The amplitude of the outflow velocity of the galaxies is found to be ∼300 km/s. The average number density of galaxies inside the void is roughly a factor of five lower than the average outside it. The Local void population is characterized by lower luminosities and later morphological types, with medians of M _B = − 15^m.7 and T=8 (Sdm), respectively.     

Structure of clusters with bimodal distribution of galaxy line-of-sight velocities III: A1831

We study the A1831 cluster within the framework of our program of the investigation of galaxy clusters with bimodal velocity distributions (i.e., clusters where the velocities of subsystems differ by more than Δ _cz ∼ 3000 km/s).We identify two subsystems in this cluster: A1831A (cz = 18970 km/s) and A1831B (cz = 22629 km/s) and directly estimate the distances to these subsystems using three methods applied to early-type galaxies: the Kormendy relation, the photometric plane, and the fundamental plane. To this end, we use the results of our observations made with the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the data adopted from the SDSS DR6 catalog. We confirmed at a 99% confidence level that (1) the two subsystems are located at different distances, which are close to their Hubble distances, and (2) the two subsystems are located behind one another along the line of sight and are not gravitationally bound to each other. Both clusters have a complex internal structure, which makes it difficult to determine their dynamical parameters. Our estimates for the velocity dispersions and masses of the two clusters: 480 km/s and 1.9 × 10¹⁴ M _⊙ for A1831A, 952 km/s and 1.4 × 10¹⁵ M _⊙ for A1831B should be views as upper limits. At least three spatially and kinematically distinct groups of galaxies can be identified in the foreground cluster A1831A, and this fact is indicative of its incomplete dynamical relaxation. Neither can we rule out the possibility of a random projection. The estimate of the mass of the main cluster A1831B based on the dispersion of the line-of-sight velocities of galaxies is two-to-three times greater than the independent mass estimates based on the total K-band luminosity, temperature, and luminosity of the X-ray gas of the cluster. This fact, combined with the peculiarities of its kinematical structure, leads us to conclude that the cluster is in a dynamically active state: galaxies and groups of galaxies with large line-of-sight velocities relative to the center of the cluster accrete onto the virialized nucleus of the cluster (possibly, along the filament directed close to the line of sight).     

Radio continuum and far-infrared emission from the galaxies in the Eridanus group

The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L _20cm > 10²³ W Hz⁻¹) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L _20cm ∼ 10²² W Hz⁻¹) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.     

Dark matter-systematics of its distribution

The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and clusters are shown to lie in a band about the M ∼ ρR³ line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves lie about theM ∼ R ^-3 line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, M_Jmax. corresponding to m_v - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at M_Jmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off asr ^-2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately equals the closure density of the universe.     

The gradient of the brightest star age and density across the spiral arm S4 in the Andromeda galaxy

On a plate obtained with the 2-m RC telescope at the Bulgarian National Observatory about 1400 stars in the spiral arm S4 of the Andromeda galaxy were measured. The limit of completeness is 20 _. ^m 2 (B magnitudes). In the central part of S4 (Figure 3) a pronounced gradient of star luminosity and density is found (Figures 6 and 7a). Here the stars become fainter at about 2 ^m and their surface density decreases tenfold at the distance 1 kpc from the inner edge of the arm. We have interpreted the decline of star maximum brightness from this edge as age gradient and have evaluated from it the velocity of star formation propagation across the arm, which is about 60 km s^–1. If the Andromeda galaxy has trailing spiral arms and the pitch angle of S4 is about 25° in its central part, the pattern velocity p7–14 km s^–1 kpc^–1. This value is close to that obtained earlier with the help of the Cepheids in the same part of S4 (Efremov, 1980). The absence of a pronounced asymmetry in the star distribution across the arm in the OB82 region may be connected with the position of the strongest dust lanes in front of the stellar spiral arm here. We have stressed that in one part of the same spiral arm there may be a pronounced age gradient, and there may be no such gradient in the near-by one. In spite of the known difficulties in understanding the structure of the Andromeda galaxy it is possible to draw some conclusions which are important for the theory of spiral arms. The detailed investigations of the nearest galaxies are, therefore, most useful for understanding the spiral structure nature.     

Tidal dwarf galaxies in the Stephan's Quintet?

We present kinematics and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's Quintet. The central regions of the two most probable parent galaxies, NGC 7319 and NGC 7318B, contain little or no gas whereas the intragroup medium and, in particular, the optical tails that seem to be associated with NGC 7318B are rich in cold and ionized gas. Two tidal dwarf candidates may be located at the edge of a tidal tail, another located within a tail, and for the four others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated with H I clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and high Hα luminosity densities [F(Hα) = (1-60) × 10-14 ergs s^-1 cm^-2]. Their magnitudes (M_B = –16.1 to –12.6), sizes (∼ 3.5 h₇₅ ^-1 kpc), colors (typically B – R = 0.7), and gas velocity gradients (∼ 8 –26 h₇₅ km s^-1 kpc^-1) are typical for tidal dwarf galaxies. In addition, the ratios between their star formation rates determined from Hα and from the B-band luminosity are typical of other tidal dwarf galaxies. The masses of the tidal dwarf galaxies in Stephan's Quintet range from ∼ 2 × 10⁸ to 10¹⁰ M_⊙, and the median value for their inferred mass-to-light ratios is 7 (M/L)_⊙. At least two of the systems may survive possible ‘fallbacks’ or disruption by the parent galaxies and may already be, or turn into, self-gravitating dwarf galaxies, new members of the group. This revised version was published online in September 2006 with corrections to the Cover Date.     

Statistical Tests of the Unification Scheme for High Luminosity Double Radio Sources

We have carried out some statistical tests of relativistic beaming and radio source orientation scenarios using the core dominance parameter Rand linear size D of a recent sample of double-lobed quasars and radio galaxies as orientation indicators. Our results show that the maximum Doppler boosting occurs within a cone angle of ∼ 13^°corresponding to an optimum Lorentz factor of ∼ 5. On the average, quasar cores appear to be boosted by a factor of ∼ 10 relative to those of radio galaxies. In general, we found that quasars lie at closer angles to the line of sight than radio galaxies with median values of 28^° and 51^°respectively, implying a relative foreshortening factor of ∼ 2. These results are consistent with the simple relativistic beaming and orientation-based unification hypotheses in which quasars are the beamed counterparts of powerful radio galaxies which form the isotropic parent population. The results show a strong evidence that orientation of source axis with respect to the line of sight is a crucial parameter in the classification schemes for radio sources. This revised version was published online in July 2006 with corrections to the Cover Date.     

The BIMA Survey of Nearby Galaxies (BIMA SONG)

BIMA SONG is a systematic imaging study of the 3 mm CO J = 1 → 0molecular emission within the centres and discs of 44 nearby spiral galaxies on size scales of a few hundred parsecs (6-9"). The overall goal of the survey is to study the role of molecular gas in the evolution of spiral galaxies. To this end, BIMA SONG addresses 1) the distribution and physical conditions of the molecular gas in galactic discs and its relation to star formation, 2) the effects of a stellar bar on the kinematics of molecular gas, including the possible inflow of gas along a bar, and 3) the distribution and role of molecular gas in the central few hundred parsecs of active and quiescent galaxies. The source list includes all (except M33and M31) 44 galaxies of Hubble types Sa–Sd, with declinations δ >−20^°, visual magnitudes B < 11.0, velocities v _hel <2000 km s^-1, and inclinations i < 70^°. Beyond the specific scientific questions we will address, this survey will provide a unique database for astronomers who study galaxies at all wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

Clustering evolution between z=1 and today

We present results of an investigation of clustering evolution of field galaxies between a redshift of z ∼ 1 and the present epoch. The current analysis relies on a sample of ∼ 14000 galaxies in two fields of the COMBO 17 survey. The redshift distribution extends to z ∼ 1. The amplitude of the three-dimensional correlation function can be estimated by means of the projected correlation function w(r _p ). The validity of the deprojection was tested on the Las Campanas Redshift Survey (LCRS). In a flat cosmology with non-zero cosmological constant for bright galaxies (M _B ≤-18) the clustering growth is proportional to (1+z) ^-2. However, the measured clustering evolution clearly depends on Hubble type. While locally the clustering strength of early type galaxies is equal to that of the bright galaxies, at high redshifts they are much stronger clustered, and thus the clustering has to evolve much more slowly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Peculiar velocities of 3000 spiral galaxies from the 2MFGC catalog

The 2MFGC catalog we have used contains 18020 galaxies selected from the extended objects in the 2MASS infrared sky survey as having apparent ratios of the axes b/a<0.3. Most of them are spiral galaxies of later morphological types whose disks are seen almost edge-on. The individual distances to the 2724 2MFGC galaxies with known rotation velocities and radial velocities are determined using a multiparameter infrared Tully-Fisher relation. A list of the distances and peculiar velocities of these galaxies is presented. The collective motion of the 2MFGC galaxies relative to the cosmic microwave background is characterized by a velocity V = 199 ± 37 km/s in the direction l = 304° ±11°, b = −8°±8°. Our list is currently the most representative and uniform sample for analyzing non-Hubble motions of galaxies on a scale of ∼100 Mpc. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 527–540 (November 2006).