Oxygen abundance in giant H II galaxies

A sample of 93 emission-line high luminosity galaxies from the Sloan Digital Sky Survey (SDSS) has been investigated. Line intensities have been measured in 116 SDSS spectra. Oxygen abundance has been determined in the studied galaxies. Since the auroral line of twice ionized oxygen [O III] λ 436.3 nm cannot be detected in the spectra of the sample, the intensity ratio of nebular to auroral lines needed to determine the electron temperature is calculated using the ff-relation. The oxygen abundances obtained in SDSS high luminosity galaxies are 0.2–0.5 dex lower than the maximum attainable value. This is caused by the fact that the sample includes only the gas-rich galaxies in which intense bursts of star formation occur. The equivalent number of O7 V stars which are responsible for excitation of luminescent H II regions in the studied sample is two or three orders of magnitude more than the number of stars which cause the luminescence of the brightest H II regions in nearby galaxies, and it exceeds by one order of magnitude the number of stars which cause gas in SBS 0335-052 E to glow.     

Search for ultrahigh-energy cosmic gamma-ray bursts on the Baksan underground scintillation telescope

Based on data from the Baksan underground scintillation telescope (BUST) for the period 2001–2004, we searched for cosmic gamma-ray bursts (GRBs) at primary photon energies of 0.5 TeV or higher. We obtained constraints on the rate of bursts with durations of 1–10 s for fluences within the range 4.6 × 10⁻³-1.8 × 10⁻² erg cm⁻² in the declination band 30° ≤ δ ≤ 80°. We searched for ultrahigh-energy gamma rays from GRBs detected on spacecraft during and within ±2 h of the burst. No statistically significant excesses above the background of random coincidences were found. The derived constraints on the ultrahigh-energy gamma-ray fluence during GRBs lie within the range 4.6 × 10⁻³-3.7 × 10⁻² erg cm⁻².     

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 ).     

A stringent new limit on bursts from nearby galaxies

If typical gamma-ray bursts [GRBs] have X-ray counterparts similar to those detected byGinga, then sensitive focusing X-ray telescopes will be able to detect GRBs three orders of magnitude fainter than the detection limit of the Burst and Transient Spectroscopy Experiment [BATSE]. If a substantial portion of the burst population detected byBATSE originates in a Galactic halo at distances greater than or equal to 150 kpc, existing X-ray telescopes will be able to detect GRBs in external galaxies out to a distance of at least 4.5 Mpc. As reported in Hamilton, Gotthelf and Helfand (1995) the Imaging Proportional counter [IPC] on board theEINSTEIN Observatory detected 42 transient events with pointlike spatial characteristics and timescales of less than 10 seconds. These events are distributed isotropically on the sky; in particular, they are not concentrated in the directions of nearby external galaxies. For halo models of theBATSE bursts with radii of 150 kpc or greater, we would expect to see several burst events in observations pointed towards nearby galaxies. We see none. We therefore conclude that if theGinga detections are representative of the population of GRBs sampled byBATSE, GRBs cannot originate in a Galactic halo population with limiting radii between 150 kpc and 400 kpc. Inasmuch as halos with limiting radii outside of this range have been excluded by theBATSE isotropy measurements, our result indicates that all halo models are excluded. This result is independent of whether the flashes we do detect have an astronomical origin.     

The correlation between the local density of galaxies and the presence of Gamma‐Ray Bursts

In order to explore the characteristics of the environment surrounding Gamma‐Ray Bursts (GRBs), we have studied the correlation between the local density of galaxies and the presence of bursts. Using the Main Galaxy sample of the Sloan Digital Sky Survey Data Release 3 (SDSS DR3) and the Current BATSE GRB Catalog, we calculate the local surface density of galaxies within a radius of <2° surrounding each burst. It turns out that there is no correlation between the local density of galaxies and the presence of GRBs. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of the properties of galaxy clusters in the Leo supercluster region

We analyze the properties of galaxy clusters in the region of the Leo supercluster using observational data from the SDSS and 2MASS catalogs. We have selected 14 galaxy clusters with a total dynamical mass of 1.77 × 10¹⁵ M _⊙ in the supercluster region 130 by 60 Mpc in the plane of the sky (z ≃ 0.037). The composite luminosity function of the supercluster is described by a Schechter function with parameters that, within the error limits, correspond to field galaxies and does not differ from the luminosity function of the richer Ursa Major (UMa) supercluster for the same luminosity range (the bright end). The luminosity functions of early-type and late-type galaxies in Leo at the faint end are characterized by a sharp decrease (α = −0.60±0.08) and a steep increase (α = −1.44± 0.10) in the number of galaxies, respectively. In the virialized cluster regions, the fraction of early-type galaxies selected by the u-r color, bulge contribution, and concentration index among the galaxies brighter than M _K ^* + 1 is, on average, 62%. This fraction is smaller than that in the UMa supercluster at a 2–3σ level. The near-infrared luminosities of galaxy clusters down to a fixed absolute magnitude correlate with their masses almost in the same way as for other samples of galaxy clusters (L _200,K ∝ M ₂₀₀^0.63±0.11)).     

Catalog of nearby isolated galaxies in the volume <Emphasis Type="Italic">z</Emphasis> < 0.01

We present a catalog of 520 most isolated nearby galaxies with angular velocities V _LG < 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG), and discuss their basic optical and HI properties. A half of the LOG catalog is occupied by the Sdm, Im and Ir morphological type galaxies without a bulge. The median ratio M _gas/M _star in the LOG galaxies exceeds 1. The distribution of the catalog galaxies on the sky looks uniform with some signatures of a weak clustering on the scale of about 0.5 Mpc. The LOG galaxies are located in the regions where the mean local density of matter is approximately 50 times lower than the mean global density. We indicate a number of LOG galaxies with distorted structures, which may be the consequence of interaction of isolated galaxies with massive dark objects.     

Study of the dependence of the star formation rate in the nuclear regions of 39 Kazarian galaxies on their integral parameters

A statistical study of the dependence of the star formation rate in the nuclear regions of 39 Kazarian galaxies on the integral parameters of these galaxies is carried out on the basis of spectra from SDSS DR6. The value of SFR/kpc² for our sample lies in the range 0.013÷2.04M _⨀ year⁻¹kpc⁻² (with the maximum value of 2.04 corresponding to the Kaz 98 (merger)). It is found that the surface density of the rate of star formation correlates positively with the bar structure parameter and EW(Hα), and that, for spiral galaxies of early morphological types, SFR/kpc² is greater than for the later types. It is shown that the color B-R for the galaxies and the color (u − g) _nucl for the nuclear region correlate positively with the total absorption A(Hα) in the Ha line for the nuclear region. The average value of A(Hα) for our samples is found to be A(Hα)=1.3±0.09 magnitudes. Translated from Astrofizika, Vol. 52, No. 2, pp. 211–224 (May 2009).     

The environments of short-duration gamma-ray bursts and implications for their progenitors

The study of short-duration gamma-ray bursts (GRBs) experienced a complete revolution in recent years thanks to the discovery of the first afterglows and host galaxies starting in May 2005. These observations demonstrated that short GRBs are cosmological in origin, reside in both star forming and elliptical galaxies, are not associated with supernovae, and span a wide isotropic-equivalent energy range of ～10⁴⁸–10⁵² erg. However, a fundamental question remains unanswered: What are the progenitors of short GRBs? The most popular theoretical model invokes the coalescence of compact object binaries with neutron star and/or black hole constituents. However, additional possibilities exist, including magnetars formed through prompt channels (massive star core-collapse) and delayed channels (binary white dwarf mergers, white dwarf accretion-induced collapse), or accretion-induced collapse of neutron stars. In this review I summarize our current knowledge of the galactic and sub-galactic environments of short GRBs, and use these observations to draw inferences about the progenitor population. The most crucial results are: (i) some short GRBs explode in dead elliptical galaxies; (ii) the majority of short GRBs occur in star forming galaxies; (iii) the star forming hosts of short GRBs are distinct from those of long GRBs, and instead appear to be drawn from the general field galaxy population; (iv) the physical offsets of short GRBs relative to their host galaxy centers are significantly larger than for long GRBs; (v) there is tentative evidence for large offsets from short GRBs with optical afterglows and no coincident hosts; (vi) the observed offset distribution is in good agreement with predictions for NS–NS binary mergers; and (vii) short GRBs trace under-luminous locations within their hosts, but appear to be more closely correlated with the rest-frame optical light (old stars) than the UV light (young massive stars). Taken together, these observations suggest that short GRB progenitors belong to an old stellar population with a wide age distribution, and generally track stellar mass. These results are fully consistent with NS–NS binary mergers and rule out a dominant population of prompt magnetars. However, a partial contribution from delayed magnetar formation or accretion-induced collapse is also consistent with the data.     

Tidal dwarf galaxies at intermediate redshifts

We present the first attempt at measuring the production rate of tidal dwarf galaxies (TDGs) and estimating their contribution to the overall dwarf population. Using HST/ACS deep imaging data from GOODS and GEMS surveys in conjunction with photometric redshifts from COMBO-17 survey, we performed a morphological analysis for a sample of merging/interacting galaxies in the Extended Chandra Deep Field South and identified tidal dwarf candidates in the rest-frame optical bands. We estimated a production rate about 1.4×10⁻⁵ per Gyr per comoving volume for long-lived TDGs with stellar mass 3×10⁸⁻⁹ M_⊙ at 0.5<z<1.1. Together with galaxy merger rates and TDG survival rate from the literature, our results suggest that only a marginal fraction (less than 10%) of dwarf galaxies in the local universe could be tidally-originated. TDGs in our sample are on average bluer than their host galaxies in the optical. Stellar population modelling of optical to near-infrared spectral energy distributions (SEDs) for two TDGs favors a burst component with age 400/200 Myr and stellar mass 40%/26% of the total, indicating that a young stellar population newly formed in TDGs. This is consistent with the episodic star formation histories found for nearby TDGs.     

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.     

Catalog of isolated galaxies selected from the 2MASS survey

We search for isolated galaxies based on the automatic identification of isolated sources from the Two Micron All-Sky Survey (2MASS) followed by a visual inspection of their surroundings. We use the modified Karachentseva criterion to compile a catalog of 3227 isolated galaxies (2MIG), which contains 6% of 2MASS Extended Sources Catalog (or 2MASX) sources brighter than K _s = 12 ^m with angular diameters a _K ≥ 30″. The catalog covers the entire sky and has an effective depth of z ∼ 0.02. The 2493 very isolated objects of the catalog, which we include into the 2MVIG catalog, can be used as a reference sample to investigate the effects of the environment on the structure and evolution of galaxies located in regions with extremely low density of matter.     

Isolated Shakhbazian compact groups

It is more appropriate to study the dynamics and evolution of compact groups using a sample of isolated compact groups in the nearby vicinity of which there are no accordant redshift galaxies. To look for isolated compact groups we inspected the environment of 78 Shakhbazian compact groups, with known redshifts. We found that 26 of nearby groups with V < 40000 km s⁻¹ are isolated compact groups in the vicinity of which up to a projected distance of 1 Mpc there are no accordant redshift galaxies. For four of them, the redshift of only two members are known, so their being groups is not certain. In the vicinities of eleven distant groups (V > 40000 km s⁻¹) no accordant redshift galaxies are detected as well. The reason for this may be the faintness of galaxies there. These groups may possibly be isolated.     

Gamma-ray burst investigation via polarimetry and spectroscopy (GRIPS)

The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using γ-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of γ-ray energies (200 keV–50 MeV) and of polarimetry (200–1000 keV). The γ-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 10²⁸cm^− 2. Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through γ-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies. See for the authors’ affiliations.     

The Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) is going to carry out a uniform survey of π steradians of the sky in the Northern Galactic cap and ∼ 225 deg² in the Southern Hemisphere. The survey consists of a photometric and a spectroscopic survey. The SDSS will generate accurate photometry in five bands of approximately tens of millions of galaxies, tens of millions of stars and roughly a million quasars. It will also take spectra and measure redshifts of approximately a million galaxies and ten thousand quasars. The main characteristics and components of the survey are a dedicated 2.5m telescope, wide field correctors for photometry and spectroscopy that will provide a field of view of ∼ 3 degrees, a photometric camera with 30 photometric and 22 astrometric CCDs, and two fibre-fed spectrographs of 320 fibres each. The survey will produce a publicly available science database of Terabytes dimensions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Study of Extended Radio Galaxies at 151.6 MHz using the Mauritius Radio Telescope

The MRT survey will be by far one of the most extensive survey at low frequencies. This survey will provide a moderately deep radio catalog reaching a source density of about 2 × 10⁴ sr^-1over the southern sky with an angular resolution of 4' × 4' and a limiting flux density of 70 mJy (1 σ) at 151 MHz. The availability of zero spacing and short baselines in the MRT array will make it sensitive to the background temperature and to large scale features in the sky. In addition to this feature, the low frequency operation makes a study of continuum emission from large radio sources by MRT to have several interesting and important implications in the study of radio galaxies. This paper discusses the parameter space of radio galaxies which can be explored using the MRT. Images of a few extended radio galaxies are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pitch angles of distant spiral galaxies

We have studied the pitch angles of spiral arms for 31 distant galaxies at z ∼ 0.7 from three Hubble Deep Fields (HDF-N, HDF-S, HUDF). Using the pitch angle-rotation velocity relation calibrated from nearby galaxies, we have estimated the rotation velocities of galaxies from the deep fields. These estimates have a low accuracy (∼50 km s⁻¹), but they allow low-mass and giant galaxies to be distinguished. The Tully-Fisher relation constructed using our velocity estimates shows satisfactory agreement with the actually observed relations for distant galaxies and provides evidence for the luminosity evolution of spiral galaxies.     

Perspectives of observing the color indices of optical afterglows of gamma-ray bursts with ESA <Emphasis Type="Italic">Gaia</Emphasis>

We propose a strategy for detecting and analyzing optical afterglows (OAs) of long gamma-ray bursts (GRBs) without the need to obtain their light curves. This approach is useful for the Gaia satellite, which provides sampled optical ultra-low-dispersion spectroscopic observations of the sky. For this purpose, we show that most OAs of long GRBs display specific values of some of their color indices, representing synchrotron emission of the jet. They are stable in time during the event. These indices, which can be determined from the spectra, are very similar for the ensemble of OAs with redshift z < 3.5 and display a strong clustering in some color-color diagrams. These indices also enable to constrain the properties of the local interstellar medium of GRBs. The long-lasting mapping of the sky with the Gaia instruments also gives us a hope to search for the so-called orphan afterglows, which, according to some authors, can be considerably more numerous than OAs of the observed GRBs. We also show how to resolve OAs from other transients in the Gaia data. The color indices and the properties of the quiescent sources (host galaxies of OAs detectable later by the large ground-based telescopes at the co-ordinates of the OA determined by Gaia) would tell us which one, among transients detected by Gaia, is a GRB OA.     

GRB host galaxies studies with X‐shooter

Gamma‐ray bursts (GRBs) are the most powerful explosions since the formation of the Universe, associated with the death of massive stars or mergers of compact stellar objects. Several recent striking results strongly support the idea that host galaxies of GRBs are opening a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ∼ 8. They form a unique sample of galaxies which cover a wide range of redshift, they are typically weak with low mass and unlike other methods they are not selected on luminosity. In recent years, thanks to the support of new generation instruments, multi‐band photometry and spectroscopy allow us to better investigate the properties of these host galaxies (e.g., stellar mass, age, SFR, metallicity), to study their possible evolution and to compare them with field galaxies and other classes of galaxies. GRB host spectroscopy is one of the main science drivers behind the X‐shooter spectrograph. In this paper, we present the first results of the program devoted to Italian‐French GTO multiband spectroscopy of GRB host galaxies with X‐shooter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probing the feeding and feedback of activity near and far

High-resolution CO maps are an essential tool to search for observational evidence of AGN fueling in galaxy nuclei. While their capabilities will be surpassed by ALMA, current mm-interferometers can already provide relevant information on scales which are critical for the process of angular momentum transfer in fueling the AGN. In this context we present the latest results issued from the NUclei of GAlaxies (NUGA) project, a high-resolution (0.5^′′–1^′′) CO survey of low luminosity AGNs conducted with the IRAM Plateau de Bure interferometer (PdBI). The use of more specific molecular tracers of dense gas can probe the feedback influence of activity on the chemistry and energy balance in the interstellar medium of nearby galaxies, a prerequisite to understanding how feedback operate at higher redshift galaxies. We discuss the results obtained in an ongoing study devoted to probe the feedback of activity from nearby Seyferts to high-redshift QSO.