Do disk galaxies with abnormally low mass-to-light ratios exist?

We have performed photometric B, V, and R observations of nine disk galaxies that presumably have abnormally low total mass-to-light (M/L) ratios for given color indices. Our data on surface photometry are used to analyze the possible causes of anomalous M/L estimates. In many cases, these can be the result of errors in photometry or rotational velocity determination but can also reflect the real peculiarities of the stellar composition of galaxies. Comparison of the photometric and dynamical disk mass estimates obtained by analyzing the rotational velocities shows that low M/L values for a given color index are probably real for some of the galaxies. This is primarily true of NGC 4826 (Sab), NGC 5347 (Sab), and NGC 6814 (Sb). The small number of such galaxies suggests that the stellar initial mass function is universal. However, a small fraction of galaxies probably may have a non-typical mass function “depleted” in low-mass stars. Such galaxies require a more careful study.     

Radio spectra of some markarian galaxies

Radio spectra of 16 Markarian galaxies are studied between 2.7 and 15.5 GHz. The Seyfert-type galaxies have power-law spectra with an average spectral index of -0.82, except for MRK 348, which is an active galaxy with a complex spectrum. The galaxies with featureless optical spectra have rather flat radio spectra, similar to BL Lac-type objects.     

Barred galaxies. II. Comparative statistics on SB and SA galaxies in visible light

Various characteristics of galaxies with and without a bar are compared in two complete samples compiled by the authors. It is found that the two types of spiral galaxies hardly differ from each other in a number of parameters and properties, such as nuclear activity and degree of concentration in groups. Star formation evidently occurs more efficiently in barred galaxies, however. Bars are encountered more often in intermediate and late subtypes of disk galaxies. Barred galaxies in groups are redder, on the average, than those outside of groups. Luminosity functions are constructed both for galaxies with and without bars. Translated from Astrofizika, Vol. 4L No. 2, pp. 185–196, April-June, 1998     

Properties of OH Megamaser Galaxies in the Radio Continuum. II. Data Analysis

The properties of OH megamaser galaxies in the radio continuum are discussed. Many radio sources in OH megamaser galaxies exhibit relatively flat (α ≥ −0.5) radio spectra between frequencies of 1.49 and 8.44 GHz along with high brightness temperatures (T_b ≥ 10⁴ K). In these galaxies the line and radio continuum fluxes are not correlated. The continuum radio emission of OH megamasers is predominantly nonthermal and is associated either with an active nucleus or with compact star formation. The thermal component of the radio emission from these galaxies can be neglected. The observed flat radio spectra and high brightness temperatures imply the existence of an active galactic nucleus, although some megamasers may be associated with compact star formation.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 281–290 (May 2005).     

Two luminosity classes of quasars

Observations of quasars suggest that compact quasars with flat radio spectra belong to the class of dwarf galaxies and extended quasars with steep spectra to the one of bright galaxies. This can be seen also in the associations of quasars with clusters of galaxies, compact quasars occurring in nearby clusters and extended quasars in distant clusters.     

Segregation of galaxies belonging to different morphological types into groups

Groups of galaxies are studied to identify galaxies of different morphological type in terms of their position relative to the centers of the groups and in terms of their peculiar radial velocities within the groups. The following results are obtained: (1) The mean distances of the galaxies relative to the centers of the groups gradually increase in the transition from the elliptical to the lenticular and spiral galaxies. However, galaxies classified in the subtypes of early or late elliptical are not distinguishable on the basis of this parameter. (b) The peculiar radial velocities of the elliptical, lenticular, and spiral galaxies in the groups are statistically indistinguishable. However, spiral galaxies falling in the early and late subtypes are distinguishable in terms of this parameter. The former subtype exhibit a lesser mean pecular radial velocity than the latter subtype.Translated from Astrofizika, Vol. 37, No. 2, pp. 301–305, March–April, 1994.The present study was supported by grant ESO C & EE No. A-04-069.     

A spectrophotometric and morphological study of UV-excess galaxies in whose spectra only absorption lines are observed

We present the results of a spectral and morphological study of 13 UV-excess galaxies in whose spectra only absorption lines are observed. We determine the equivalent widths and FWHM of the lines. We conclude that these objects are in an evolutionary stage between UV-excess galaxies with emission lines and normal galaxies.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

High surface brightness Arakelian galaxies and their environment

The relationship of high surface brightness Arakelian galaxies (ArG) to their environment is studied. This is done using the groups identified by the authors on the basis of the CfA2 red shift survey. Of the 15577 galaxies in the sample, 172 (1.104%) have a high surface brightness. The corresponding percentage for the galaxies with 13.0 < m ≤ 15.0 is 2.05. The following results are obtained: (a) On going from single to poor groups and on to more populated groups, the frequency of occurrence of ArG does not vary. (b) Groups of galaxies containing ArG do not differ on the average from groups which do not contain such galaxies in terms of their dynamic characteristics, such as the dispersion in radial velocity, size, and total luminosity, or their morphological content. (c) ArG do not follow the regular pattern according to which elliptical and lenticular galaxies are more often encountered in groups of galaxies than among single galaxies, i.e., it seems that the frequency of occurrence of elliptical and lenticular ArG in groups is the same as in single galaxies. (d) The surface brightnesses, diameters, and luminosities of ArG in groups of galaxies are greater than those of single ArG. This shows up especially strongly in spiral ArG.     

GHASP: an Hα kinematic survey of spiral and irregular galaxies – V. Dark matter distribution in 36 nearby spiral galaxies

The results obtained from a study of the mass distribution of 36 spiral galaxies are presented. The galaxies were observed using Fabry–Perot interferometry as part of the GHASP survey. The main aim of obtaining high-resolution Hα 2D velocity fields is to define more accurately the rising part of the rotation curves which should allow to better constrain the parameters of the mass distribution. The Hα velocities were combined with low resolution H  i data from the literature, when available. Combining the kinematical data with photometric data, mass models were derived from these rotation curves using two different functional forms for the halo: an isothermal sphere (ISO) and a Navarro–Frenk–White (NFW) profile. For the galaxies already modelled by other authors, the results tend to agree. Our results point at the existence of a constant density core in the centre of the dark matter haloes rather than a cuspy core, whatever the type of the galaxy from Sab to Im. This extends to all types the result already obtained by other authors studying dwarf and low surface brightness galaxies but would necessitate a larger sample of galaxies to conclude more strongly. Whatever model is used (ISO or NFW), small core radius haloes have higher central densities, again for all morphological types. We confirm different halo scaling laws, such as the correlations between the core radius and the central density of the halo with the absolute magnitude of a galaxy: low-luminosity galaxies have small core radius and high central density. We find that the product of the central density with the core radius of the dark matter halo is nearly constant, whatever the model and whatever the absolute magnitude of the galaxy. This suggests that the halo surface density is independent from the galaxy type.     

Observational manifestations and intrinsic properties of the RCR sources in terms of a unified model

We present a summary results of the study of radio sources showing significant variations of integral flux density using the data from the RATAN-600 surveys of 1980–1994 at a frequency of 7.6 cm. The majority of the detected variable sources have flat radio spectra, although there are also all other spectrum types found. Point and compact sources predominate, although all known morphological structures are found in the sample. Variability is detected both in quasars and galaxies. Using the catalog data, we found brightness variations in the optical and/or infrared ranges for a half of host objects of radio sources. We analyzed the properties of nonvariable and variable RCR sources. We compared the ratio of absolute magnitude to radio luminosity for sources with the active nucleus types determined from the optical data. It is found that this parameter is approximately the same for quasars with different radio luminosity. It isminimum for the strongest radio galaxies and grows up to the level characteristic of quasars with the decrease of radio luminosity. Considering that the ratio depends on obscuring properties of a dust torus, such behavior can be explained if we assume that the torus geometry and its optical depth depend on the source long. This parameter is slightly higher among variable sources than among nonvariable ones which counts in favor of the nucleus more open to an observer.     

Near-infrared template spectra of normal galaxies: k-corrections, galaxy models and stellar populations

We have observed 28 local galaxies in the wavelength range between 1 and 2.4 μm in order to define template spectra of the normal galaxies along the Hubble sequence. Five galaxies per morphological type were observed in most cases, and the resulting rms spread of the normalized spectra of each class, including both intrinsic differences and observational uncertainties, is about 1 per cent in K , 2 per cent in H and 3 per cent in J . Many absorption features can be accurately measured. The target galaxies and the spectroscopic aperture (7×53 arcsec²) were chosen to be similar to those used by Kinney et al. to define template UV and optical spectra. The two data sets are matched in order to build representative spectra between 0.1 and 2.4 μm. The continuum shape of the optical spectra and the relative normalization of the near-IR ones were set to fit the average effective colours of the galaxies of the various Hubble classes. The resulting spectra are used to compute the k -corrections of the normal galaxies in the near-IR bands, and to check the predictions of various spectral synthesis models: while the shape of the continuum is generally well predicted, large discrepancies are found in the absorption lines. Among the other possible applications, here we also show how these spectra can be used to place constraints on the dominant stellar population in local galaxies. Spectra and k -corrections are publicly available and can be downloaded from the web site http://www.arcetri.astro.it/~filippo/spectra .     

A primordial feature at the scale of superclusters of galaxies

We investigate a spatially flat cold dark matter model (with the matter density parameter     with a primordial feature in the initial power spectrum. We assume that there is a bump in the power spectrum of density fluctuations at wavelengths     , which corresponds to the scale of superclusters of galaxies . There are indications for such a feature in the power spectra derived from redshift surveys and also in the power spectra derived from peculiar velocities of galaxies. We study the mass function of clusters of galaxies, the power spectrum of the cosmic microwave background (CMB) temperature fluctuations, the rms bulk velocity and the rms peculiar velocity of clusters of galaxies. The baryon density is assumed to be consistent with the big bang nucleosynthesis value. We show that with an appropriately chosen feature in the power spectrum of density fluctuations at the scale of superclusters, the mass function of clusters, the CMB power spectrum, the rms bulk velocity and the rms peculiar velocity of clusters are in good agreement with the observed data.     

Seyfert Galaxies: Radio Continuum Emission Properties and the Unification Scheme

Seyfert galaxies are classified mainly into type 1 and type 2 depending on the presence and absence of broad permitted emission lines in their optical spectra, respectively. Unification scheme hypothesizes that the observed similarities and differences between the two Seyfert subtypes can be understood as due to the differing orientations of anisotropically distributed obscuring material having a torus-like geometry around the AGN. We investigate the radio continuum emission properties of a sample of Seyfert galaxies in the framework of the unification scheme.     

Radio emission spectra of isolated spiral galaxies and spiral members of pairs of galaxies

It is shown that objects with steep radio emission spectra occur significantly more often among isolated spiral galaxies than among spiral members of double galaxies. This, along with some other facts, indicates that members of pairs of galaxies are at a more active phase of their evolution than isolated galaxies. Translated fromAstrofizika, Vol. 40, No. 1, pp. 39–43, February, 1997.     

Evidence for X-Ray Emission from a Large-Scale Filament of Galaxies?

The large-scale ( approximately 100 kpc) environments of Seyfert galaxies are not significantly different from those of non-Seyfert galaxies. In the context of the interaction model of the formation of active galactic nuclei (AGNs), it has thus been proposed that AGNs form via "minor mergers" of large disk galaxies with smaller companions. We test this hypothesis by comparing the nuclear spectra of 105 bright nearby galaxies with measurements of their R- or r-band morphological asymmetries at three successive radii. We find no significant differences between these asymmetries among the 13 Seyfert galaxies in the sample and galaxies having other nuclear spectral types (absorption, H ii region-like, LINER), nor is there strong qualitative evidence that such mergers have occurred among any of the Seyfert galaxies or LINERs. Thus, either any minor mergers began greater, similar1 Gyr ago and are essentially complete, or they did not occur at all, and AGNs form independently of any type of interaction. Support for the latter interpretation is provided by the growing evidence that supermassive black holes exist in the cores of most elliptical and early-type spiral galaxies, which in turn suggests that nuclear activity represents a normal phase in the evolution of the bulges of massive galaxies. Galaxy mergers may increase the luminosity of Seyfert nuclei to the level of QSOs, which could explain why the latter objects appear to be found in rich environments and in interacting systems.     

The ROSAT Bright Survey: I. Identification of an AGN sample with hard ROSAT X-ray spectra

The ROSAT Bright Survey (RBS) aims to completely optically identify the more than 2000 brightest sources detected in the ROSAT all-sky survey at galactic latitudes |b| > 30° (excluding LMC, SMC, Virgo cluster). This paper presents a subsample of 66 bright point-like ROSAT survey sources with almost hard PSPC spectra, the hardness ratio HR1 is > 0.5 for most of the sources. Teh subsample could be nearly completely identified by low-resolution optical spectroscopy with the following breakdown into object classes: 31 Seyfert galaxies, 22 BL Lac candidates, 5 clusters of galaxies, 1 cataclysmic variable, and 5 bright stars. Only one object remained unidentified and one X-ray source was a spurious detection. The redshift distrbution peaks around 0.06 for the Seyferts and around 0.13 for the BL Lac candidates. Observations with medium spectral resolution were obtained for most of the new Seyfert galaxies. A large fraction (20 objects) are type 1 Seyfert galaxies, the other fraction includes Seyfert galaxies of type 1.5 – 1.8 (5 objects), two LINERs, and 4 possible narrow-line Seyfert 1 galaxies (NLS1). About one third of the new Seyfert's have nearby companion galaxies displaying either emission or absorption lines at the same redshift. Among them are a couple of systems showing direct morphological evidence for interaction. The large fraction of interacting galaxies among our sample suggests a scenario where interaction is the main trigger of AGN activity.     

Spectro-morphology of galaxies

We present a quantitative method of classification of the multi-wavelength morphology of galaxies, elaborated from the nearby galaxies and usable to high redshift objects. We use the morphological parameters of concentration of light at the galaxy center and 180^°-rotationnal asymmetry, computed in several wavelengths, from ultraviolet (UV) to R band. The variation of these indices with λ reflects the proportion of young and old stellar populations in galaxies, that is characteristic of every morphological type: elliptical/lenticular, spiral and irregular. We need to elaborate some templates of these variation spectra from the study of nearby objects, for an application to distant galaxies. This revised version was published online in August 2006 with corrections to the Cover Date.     

Population synthesis of H ii galaxies

We study the stellar population of galaxies with active star formation, determining ages of the stellar components by means of spectral population synthesis of their absorption spectra. The data consist of optical spectra of 185 nearby ( z 0.075) emission-line galaxies . They are mostly H  ii galaxies, but we also include some starbursts and Seyfert 2s, for comparison purposes. They were grouped into 19 high signal-to-noise ratio template spectra, according to their continuum distribution, absorption- and emission-line characteristics. The templates were then synthesized with a star cluster spectral base.
The synthesis results indicate that H  ii galaxies are typically age-composite stellar systems, presenting important contributions from generations up to as old as 500 Myr. We detect a significant contribution of populations with ages older than 1 Gyr in two groups of H  ii galaxies. The age distributions of stellar populations among starbursts can vary considerably despite similarities in the emission-line spectra. In the case of Seyfert 2 groups we obtain important contributions from the old population, consistent with a bulge.
From the diversity of star formation histories, we conclude that typical H  ii galaxies in the local Universe are not systems presently forming their first stellar generation.     

Strongly flattened galaxies in the abastumani merged catalogue of galaxies

1200 strongly flattened galaxies with axis ratio b/a ≤ 0.15 were selected from the UGC catalogue, contained in the Abadumani Merged Catalogue of Galaxies, and their properties were studied. The possibility of using strongly flattened galaxies and several other samples of galaxies according to their morphological type as a distance indicator has been examined by the Tully-Fisher relation. The investigation has shown that angular diameters of strongly flattened as well as flat, seen edge-on galaxies designated as F and L in the MCG catalogue can be used for the estimation of distance moduli with accuracy O.^m7. The distribution of absolute magnitudes of strongly flattened galaxies was approximated by analytic Schechter expression with main parameters M* = -21.^m2 and α = -1.0. The statistical method of the nearest companion applied to the apparent distribution of strongly flattened galaxies has shown that these galaxies are considerably more frequently found in mixed pairs and multiple systems than spirals. Published in Astrofizika, Vol. 41, No. 1, pp. 23–34, January-March, 1998.