Spectroscopy of RC sources

The results of spectroscopic observations of the host galaxies of objects in the RC catalog (the “Big Trio” program) obtained using the new SCORPIO spectrograph of the Special Astrophysical Observatory are presented. The spectroscopic redshifts of the objects are compared with their photometric color redshifts, and the errors in the latter are estimated. Based on BV RI observations obtained on the 6-m telescope of the SAO, the errors for the population of powerful radio galaxies are close to those found previously for radio quiet galaxies (about 10–20%). The detection of Ly α in the B filter in RC 1626+0448 is confirmed. This object is the second spectrally studied FR II radio source from the RC catalog to have a redshift z>2.5. Star formation in its host galaxy began at a redshift z>3.3. This first use of the new SCORPIO spectrograph demonstrates its promise for studies of very distant steep-spectrum radio galaxies brighter than 23^m–24^m in V.     

Identification of sources of ultrahigh energy cosmic rays

The arrival directions of extensive air showers with energies 4×10¹⁹<E≤3×10²⁰ eV detected by the AGASA, Yakutsk, Haverah Park, and Fly’s Eye arrays are analyzed in order to identify possible sources of cosmic rays with these energies. We searched for active galactic nuclei, radio galaxies, and X-ray pulsars within 3-error boxes around the shower-arrival directions and calculated the probabilities of objects being in the 3 error boxes by chance. These probabilities are small in the case of Seyfert galaxies with redshifts z<0.01 and BL Lac objects, corresponding to P>3σ (σ is the parameter of Gaussian distribution). The Seyfert galaxies are characterized by moderate luminosities (L<10⁴⁶ erg/s) and weak radio and X-ray emission. We also analyzed gamma-ray emission at energies E>10¹⁴ eV recorded by the Bolivian and Tian Shan arrays. The source identifications suggest that the gamma rays could have been produced in interactions of cosmic rays with the microwave background radiation and subsequent electromagnetic cascades in intergalactic space. We estimate the strength of intergalactic magnetic fields outside galaxy clusters to be B≤8.7×10^?10 G.     

The active galaxy NGC 3862 in a compact group in the cluster A1367

We study a compact group of 18 galaxies in the cluster A1367 with redshifts z = 0.0208–0.025. The group’s center of activity in the radio is the galaxy NGC 3862, whose radio flux is an order of magnitude stronger than for the other members of the group. We present coordinates derived from the Palomar plate archive together with recessional velocities, and analyze other characteristics of the group’s galaxies. The results of 1400 MHz observations of NGC 3862 with the RATAN-600 radio telescope are presented. These observations indicate that the galaxy’s radio emission is variable.     

Radio-induced activity in galaxy pairs

The close proximity of a radio-loud active galactic nucleus (AGN) can trigger star formation in nearby objects containing gas if they are hit by a radio jet emerging from the active nucleus (as is observed, for example, in the case of Minkowski’s Object). The predicted frequency of such events is modest for close pairs of galaxies—of the order of several percent of all close (with separations of the order of several tens of parsec) pairs containing a radio AGN. A statistical study of this effect is carried out using the SDSS and FIRST surveys, by searching for spatially close pairs (projected separations <150 kpc, relative radial velocities <600 km/s) containing AGNs with radio jets. The frequency of galaxies with bursts of star formation, f _SF, and active nuclei f _AGN, in pairs either containing or not containing an AGN with radio jets are evaluated as functions of the separation of the galaxies in the pair. It is concluded that (1) the predicted effect should be of the order of 5%, falling off with increasing separation between the galaxies in the pair; (2) the observed values of f _SF and f _AGN and their dependences on the galaxy separation are consistent withmodel predictions, but the large uncertainties associated with the limited size of the studied sample hinders firm conclusions about the existence of radio-induced activity in close galaxy pairs; (3) further investigations using a larger volume of observational material are required, for example, using only photometric redshifts.     

The non-uniform distribution of galaxies from data of the SDSS DR7 survey

We have analyzed the spatial distribution of galaxies from the latest release of the Sloan Digital Sky Survey of galactic redshifts (SDSS DR7), applying the complete correlation function (conditional density), two-point conditional density (cylinder), and radial density methods. Our analysis demonstrates that the conditional density has a power-law form for scales lengths 0.5–30 Mpc/h, with the power-law corresponding to the fractal dimension D = 2.2 ± 0.2; for scale lengths in excess of 30 Mpc/h, it enters an essentially flat regime, as is expected for a uniform distribution of galaxies. However, in the analysis applying the cylinder method, the power-law character with D = 2.0 ± 0.3 persists to scale lengths of 70 Mpc/h. The radial density method reveals inhomogeneities in the spatial distribution of galaxies on scales of 200 Mpc/h with a density contrast of two, confirming that translation invariance is violated in the distribution of galaxies to 300 Mpc/h, with the sampling depth of the SDSS galaxies being 600 Mpc/h.     

Color redshifts and the age of the stellar population of distant RC radio galaxies

BV RI data are presented for the majority of steep-spectrum objects in the RC catalog with m _R <23.5^m. Previously developed programs are applied to these data to estimate the redshifts and ages of the stellar systems of the host galaxies. Applying this program to the color data (BV RI JHK) for distant radio galaxies with spectroscopic redshifts indicates that this approach provides accurate estimates of the redshifts of such radio galaxies, close to those obtained using field galaxies (～20%). The age estimates are much less trustworthy, but a lower limit to the ages of objects that are not very distant (z<1.5) can be determined with certainty. We have identi fied several galaxies whose formal ages exceed the age of the Universe at the corresponding z in simple Cold Dark Matter models for the Universe. The possibility of using such objects to elucidate the role of “dark energy” is discussed. This paradox disappears in models with cosmological constants (Λ terms) equal to 0.6–0.8.     

A RATAN-600 Zenith-Field sky survey. Catalog of radio sources

A catalog of radio sources detected in a deep RATAN-600 survey is presented. The catalog was obtained in the region 0^h ≤ RA_2000.0 ≤ 24^h, Dec_2000.0 = 41°30′42″ ± 2′, at the declination of the bright radio source 3C 84. There were nine sessions of multi-wavelength observations at wavelengths λ = 1–55 cm, and more than 300 daily scans were accumulated at each wavelength. This is the first stage in the reduction of an extensive database accumulated by the Cosmological Gene Project. The RATAN-600 Zenith Field (RZF) catalog was obtained at the central wavelength of 7.6 cm, and contains 437 radio sources, virtually all of which have been identified with NVSS objects. Most of the flux densities for the catalog sources are above the 5σ level. Noise from faint (mainly new) background sources at a level of about 0.8 mJy has been detected. The minimum flux density of the catalog, 2.5 mJy, is comparable to the flux-density linit of the NVSS catalog. The catalog is more than 80% complete for sources with flux densities >3 mJy.     

The KHOLOD experiment: A search for a new population of radio sources

Published data from long-term observations of a strip of sky at declination ?? ?? 5° carried out at 7.6 cm on the RATAN-600 radio telescope are used to estimate some statistical properties of radio sources. Limits on the sensitivity of the survey due to noise imposed by background sources, which dominates the radiometer sensitivity, are refined. The vast majority of noise due to background sources is associated with known radio sources (for example, from the NVSS with a detection threshold of 2.3 mJy) with normal steep spectra (?? = 0.7?C0.8, S ?? ?? ^??? ), which have also been detected in new deep surveys at decimeter wavelengths. When all such objects are removed from the observational data, this leaves another noise component that is observed to be roughly identical in independent groups of observations. We suggest this represents a new population of radio sources that are not present in known catalogs at the 0.6 mJy level at 7.6 cm. The studied redshift dependence of the number of steep-spectrum objects shows that the sensitivity of our survey is sufficient to detect powerful FRII radio sources at any redshift, right to the epoch of formation of the first galaxies. The inferred new population is most likely associated with low-luminosity objects at redshifts z < 1. In spite of the appearance of new means of carrying out direct studies of distant galaxies, searches for objects with very high redshifts among steep and ultra-steep spectrum radio sources remains an effective method for studying the early Universe.     

The search for giant radio galaxies in the PS 102 survey

The possibility of selecting extended radio sources that are potential candidates for giant radio galaxies among objects in the Pushchino catalog at 102 MHz is considered. The method used is based on the analysis of objects in a α ₁–α ₂ diagram, where α ₁ and α ₂ are two-frequency spectral indices (S _ν ～ ν ^?α ), formally calculated using 102–365 and 365–1400 MHz data, based on the identifications of Pushchino radio sources with objects of the Texas (365 MHz) and Green Bank (1400 MHz) catalogs. The calculated spectra are abnormally steep at 102–365 MHz and flat or even inverted at 365–1400 MHz, due to the fact that the 365-MHz flux densities of extended radio sources measured with the Texas radio interferometer are appreciably underestimated. Ten objects among the fifteen Pushchino radio sources selected using this criterion proved to be already known large radio galaxies. The possibility of improving the efficiency of the method by using larger samples and applying some additional criteria selecting candidate giant radio galaxies is considered.     

Radio and optical spectra of objects from three complete samples of radio sources

We present classifications, optical identifications, and radio spectra for 19 radio sources from three complete samples, with declinations 4°–6° (B1950, S _{3.9 GHz} > 200 mJy), 10°–12°30′ (J2000, S _{4.85 GHz} > 200 mJy), and 74°–75° (J2000, S _{4.85 GHz} > 100 mJy). We also present corresponding information for the radio source J0527+0331. The right ascensions are 0–24^h and the Galactic latitudes |b| > 15° for all the samples. Our observations were obtained with the 6 m telescope from the Special Astrophysical Observatory in the range 4000–9000 Å or 4000–7500 Å and the RATAN-600 radio telescope at frequencies in the range 0.97–21.7 GHz. We obtained flux densities for the radio sources and optical spectra for their optical counterparts. Nine objects were classified as quasars with redshifts from z = 1.029 to 3.212; nine objects are emission-line galaxies with redshifts from 0.172 to 0.546, and one is a galaxy with burstlike star formation at z = 0.156, and one is a BL Lac object with z = 0.509. The spectra of five radio sources were decomposed into extended and compact components. The radio source J0527+0331, identified with a BL Lac object, displays significant variations of time scales from several days to several years. Data on flux variations are presented for 11 radio sources, as well as their spectra at several epochs.     

Spectroscopy of “Big Trio” objects using the “Scorpio” spectrograph of the 6-m telescope of the Special Astrophysical Observatory

We present the results of spectroscopy of 71 objects with steep and ultra-steep spectra (α < −0.9, S ∝ ν ^α) from the “Big Trio” (RATAN-600-VLA-BTA) project, performed with the “Scorpio” spectrograph on the 6-m telescope of the Special Astrophysical Observatory (Russian Academy of Sciences). Redshifts were determined for these objects. We also present several other parameters of the sources, such as their R magnitudes, maximum radio sizes in seconds of arc, flux densities at 500, 1425, and 3940 MHz, radio luminosities at 500 and 3940 MHz, and morphology. Of the total number of radio galaxies studied, four have redshifts 1 ≤ z < 2, three have 2 ≤ z < 3, one has 3 ≤ z < 4, and one has z = 4.51. Thirteen sources have redshifts 0.7 < z < 1 and 15 have 0.2 < z < 0.7.Of all the quasars studied, five have redshifts 0.7 < z < 1, seven have 1 ≤ z < 2, four have 2 ≤ z < 3, and one has z = 3.57. We did not detect any spectral lines for 17 objects.     

Spectral studies with the Special Astrophysical Observatory 6 m and RATAN-600 telescopes

We present optical identifications, classifications, and radio spectra for 19 radio sources from a complete sample in flux density with declinations 10°–12°30′ (J2000) obtained with the 6-m optical telescope (4000–9000 Å) and RATAN-600 radio telescope (0.97–21.7 GHz) of the Special Astrophysical Observatory. Twelve objects with redshifts from 0.573 to 2.694 have been classiffied as quasars, and two objects with featureless spectra as BL Lac objects. Four objects are emission-line radio galaxies with redshifts from 0.204 to 0.311 (one also displaying absorption lines), and one object is an absorption-line galaxy with a redshift of 0.214. Radio flux densities have been obtained at six frequencies for all the sources except for two extended objects. The radio spectra of five of the sources can be separated into extended and compact components. Three objects display substantial rapid (on time scales from several days to several weeks) and long-term variability of their flux densities.     

Giant radio galaxies: Old long-lived quasars?

The properties of giant radio sources (GRS’s) are considered with the aim of identifying conditions contributing to their formation, using data from the literature, the Sloan Digital Sky Survey (SDSS), and the APM catalog. The optical and radio properties of normal-size radio sources, (≤1 Mpc), are compared. The following conclusions are reached. (1) The fraction of objects with broad emission lines among GRS’s with high-excitation spectra is the same as for isotropic samples of radio sources; in the framework of the “unified scheme,” this testifies to an isotropic distribution of angles between the radio jets of GRS’s and the line of sight, i.e., GRS’s do not represent a population of objects whose radio jets are in the plane of the sky. (2) Giant radio sources do not differ from normal radio sources in the distributions of various asymmetry parameters for their extended radio components; in the unified scheme, the similarity of the asymmetry distributions for giant radio galaxies and giant radio quasars suggests that the origin of the asymmetry of their extended radio components is inhomogeneity of the external conditions. (3) The observed powers of the radio jets of giant and normal radio sources do not differ, making it unlikely that the large sizes of the GRS’s are due to this factor. (4) The richness and character of the environments of giant and normal radio sources do not differ: giant host galaxies are found in both isolated fields and in clusters of up to Abell class 1 in richness. This argues against the idea that a low density of the environment is the only origin of GRS’s. (5) The relatively large fraction of radio sources with two pairs of extended radio components (so-called double-double radio sources) among GRS’s testifies that the lifetimes of GRS’s are approximately an order of magnitude longer than those of normal radio sources.Given the equal spatial densities of nearby (z < 0.1) GRS’s and FR II radio sources with powers P _{1.4 MHz} > 10²⁵ W/Hz, this indicates that ∼10% of FR II radio sources have lifetimes an order of magnitude longer, and evolve into GRS’s. (6) The small (∼0.1) ratio of the number of known GRS’s to the number of normal FR II radio sources, together with the observed spatial density of GRS’s at z ∼ 0.6, which is an order of magnitude lower than the predicted value, suggests that a considerable number of GRS’s were missed by surveys at z > 0.1, possibly due to observational selection effects because of their relatively low radio powers and radio surface brightnesses. (7) The absence of “double-double” giant quasars suggests that these objects have a shorter activity time scale than GRS’s. In an evolutionary scenario that is an alternative to the unified scheme uniting “radio loud” quasars and radio galaxies, radio quasars evolve with time into radio galaxies, and the observed relative number of radio quasars among the GRS’s (∼10%) can be interpreted as reflecting the existence of a long-lived population of “radio loud” quasars comprising ∼10% of all radio quasars, with such a population of long-lived radio quasars being the parent population for giant radio galaxies.     

Morphology of Seyfert Galaxies

We probed the relation between properties of Seyfert nuclei and morphology of their host galaxies. We selected Seyfert galaxies from the Sloan Digital Sky Survey with redshifts less than 0.2 identified by the Vé ron Catalog (13th). We used the FracDev parameter from SDSS galaxy fitting models to represent the bulge fractions of the Seyfert host galaxies. We found that the host galaxies of Seyfert 1 and Seyfert 2 are dominated by large bulge fractions, and Seyfert 2 galaxies are more likely to be located in disk galaxies whereas most of the Seyfert 1 galaxies are located in bulge-dominant galaxies. These results indicate that the types of AGNs are related to their host galaxies and cannot be explained by the traditional unification model of Seyfert galaxies.     

Classification of optical identifications of radio sources from complete samples

Classifications of the optical counterparts and radio spectra of nine radio sources are presented. The observations were carried out using the 2.1-m optical telescope in Cananea (Mexico) at 4200–9000 Å and the RATAN-600 radio telescope at 0.97–21.7 GHz. Five objects have been classified as quasars (three have redshifts z>2), two as BL Lac objects, one as an elliptical galaxy, and one as an absorption-line galaxy.     

Phenomenological model for the evolution of radio galaxies such as Cygnus A

A phenomenological model for the evolution of classical radio galaxies such as Cygnus A is presented. An activity cycle of the host galaxy in the radio begins with the birth of radio jets, which correspond to shocks on scales ～1 pc (the radio galaxy B0108+388). In the following stage of the evolution, the radio emission comes predominantly from formations on scales of 10–100 pc, whose physical parameters are close to those of the hot spots of Cygnus A (this corresponds to GHz-peaked spectrum radio sources). Further, the hot spots create radio lobes on scales of 10³–10⁴ pc (compact steep-spectrum radio sources). The fully formed radio galaxies have radio jets, hot spots, and giant radio lobes; the direction of the jets can vary in a discrete steps with time, creating new hot spots and inflating the radio lobes (as in Cygnus A). In the final stage of the evolutionary cycle, first the radio jets disappear, then the hot spots, and finally the radio lobes (similar to the giant radio galaxies DA 240 and 3C 236). A large fraction of radio galaxies with repeating activity cycles is observed. The close connection between Cygnus A-type radio galaxies and optical quasars is noted, as well as similarity in the cosmological evolution of powerful radio galaxies and optical quasars.     

Studies of bright steep-spectrum radio sources

Results of studies of bright radio sources in the constellation Cetus are presented. More than 50% of the sources have radio spectral indices steeper than 0.9. Optical identifications have been determined for 35 sources. A large fraction of the radio sources are identified with weak blue galaxies. Given their spectral indices, it is likely that these objects have redshifts z=0.4–1.0. More than 20% of the steep-spectrum sources do not have optical identifications and appear to be weak galaxies with z>2.     

The magnetic fields and density of relativistic electrons in the nucleus of NGC 1052

We analyze observations of the compact GHZ-peaked-spectrum radio source in the nucleus of the weakly active galaxy NGC 1052, assuming that the low-frequency turnover in its spectrum is due to synchrotron self-absorption. The analysis is based on a model for an inhomogeneous source of synchrotron radiation. It is shown that the magnetic field is not uniform, but the change in the field strength from the center to the edge of the compact radio source does not exceed an order of magnitude. The maximum magnetic-field strength in the nucleus of NGC 1052 is 20 G < H _⊥ < 200 G, and the density of relativistic electrons is 0.018 cm⁻³ < n _e < 0.18 cm⁻³ on scales of 0.1 pc; everywhere in the radio source, the energy density of the magnetic field exceeds the energy density of the relativistic electrons. The physical conditions are similar to those in the nuclei of the nearby radio galaxies 3C 111 and 3C 465, and differ strongly from those in the nucleus of the radio galaxy 0108+388, which is a compact GHz-peaked-spectrum source (these three galaxies were studied by the authors earlier using the same method).     

Compilation of a complete sample of giant radio sources from a survey at 102.5 MHz

A search for giant radio sources has been carried out using the PC102 catalog, which was compiled from a survey of the northern sky at 102.5 MHz. 117 extended sources were detected in an area with right ascensions 0^h?4^h and declinations from ?17? to +82?. Half of these sources have linear sizes in the plane of the sky of more than 500 kpc. A catalog of giant radio sources that is complete for radio sources with redshifts less than 0.2 has been compiled.     

Gas dynamics of a central collision of two galaxies: Merger, disruption, passage, and the formation of a new galaxy

Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small, their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies (M _g = 10⁹ M _⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision. If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision, a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (M _g ≤ 10⁹ M _⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar population in some elliptical galaxies.