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.     

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.     

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.     

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.     

Radio Sources in the Central Section of the RZF Catalog. Search for Objects with Ultra-Steep Spectra

Results of reducing and selecting data from the Ratan Zenith Field (RZF) are presented. A deep survey in the region 0^h ≤ R.A. ≤ 24^h, 40.5° ≤ DEC ≤ 42.5° carried out on the RATAN-600 radio telescope was used. Within +2′ of the center of the survey region, 448 objects were detected, 69 of them with ultra-steep spectra (USS). The SDSS digital optical survey (DR12), NVSS radio maps, and the FIRST catalogs have been used to cross-identify 208 radio sources from the RZF catalog, obtained as part of the “Genetic Code of the Universe” project. The characteristics of these objects are studied, and the distribution of the SDSS galaxies in a two-color diagram is obtained. Photometric redshifts and radio luminosities at 3940 and 1400 MHz are determined for 27 objects with spectral indices α < −1.1 (S ∝ ν^α) for which magnitudes in various filters are presented in the SDSS. In the sample of USS objects, 12 galaxies have redshifts z < 0.5, are detected at wavelength λ = 7.6 cm, and have relatively high radio luminosities (type FR II or intermediate type FR I–FR II). Only one radio galaxy proved to be a rare nearby galaxy with relatively low radio luminosity L_{1400 MHz} = 1.51 × 10²⁴ W/Hz (type FR I). Two objects are candidate GHz-Peaked Spectrum objects.

     

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.     

Objects from a cross-identification of the IRAS and low-frequency Texas radio catalogs

A cross-identification of objects in the low-frequency (365 MHz) Texas radio catalog and in IRAS catalogs at four infrared wavelengths has yielded a list of 715 objects for further studies. Objects with steep spectra for which the difference in the centers of gravity of the radio and infrared sources was less than 3″ were selected from this list. Seventeen of the objects have been observed at six wavelengths using the RATAN-600 radio telescope. Spectra of nine objects from the initial list for which there were candidate optical counterparts were obtained using the 2.1-m telescope of the INAOE. The results of these observations are discussed. The presence of steep spectral indices for the radio sources is confirmed. The possible optical counterparts include interacting galaxies, an infrared galaxy, two emission-line galaxies, and a candidate BL Lac object. Optical images of the optical counterparts are presented together with radio and optical spectra.     

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.     

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.     

Sources of the RCR catalog with normal and flat spectra according to data from the Planck microwave survey

Fields of the Planck cosmic-microwave background maps in the regions of radio sources of the RCR catalog have been studied. Using measurements from the Planck catalog, calibration curves have been plotted in order to determine the objects’ luminosities. The flux densities at millimeter and submillimeter wavelengths of 83 objects with normal radio spectra have been estimated for the first time; their spectra have also been constructed, they have been optically identified, and information available in various databases has been collected. A statistical comparison with a sample of sources with steep radio spectra has been carried out. Faint, difficult to characterize microwave sources make an additional contribution to the secondary anisotropy on angular scales < 7′. An algorithm for selecting candidate objects with the Sunyaev–Zel’dovich effect has been proposed, based on the use of data on the radio spectral indices and the signal in cosmic-microwave background maps.     

Search for and study of weak radio galaxies with large angular sizes using the NVSS data

A new method for distinguishing candidate giant radio galaxies is proposed and applied. The method is based on comparing the axes of the extended components of NVSS radio sources with separations exceeding 4′, described in a catalog of presumably independent objects. Objects detected using the proposed algorithm include 16 new weak giant-radio-galaxy candidates, for which optical and radio identifications have been obtained using the CATS, NED, SDSS, and SkyView databases.     

Long-term variability of a complete sample of flat-spectrum radio sources at declinations 10°–12°30′ (J2000)

The paper reports the results of ten-year centimeter-wavelength observations with the RATAN-600 radio telescope of a complete sample of 83 flat-spectrum sources from the GB6 catalog of the MGB Survey, with S _4.85 > 200 mJy at declinations 10°?C12°30??. Starting in 2000, the observations were conducted simultaneously at six frequencies in the range 0.97?C21.7 GHz. Seventy-six sources (including 54 quasars) have been identified with optical objects, which have redshifts in the range z = 0.331?C3.601. Analysis of light curves and spectra at different activity phases has shown that, in most cases, the dynamics of the development of flares is consistent with a model in which the variability results from the evolution of a shock in a radio jet. A relationship between the time scales for the rise and fall of the flares has been found. There is no redshift dependence of the true linear dimensions of the radiating regions and the variability indices obtained over ten years. These facts can be interpreted as an absence of cosmological evolution of quasars at least up to z ?? 3.     

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.     

A catalog of star-forming regions in the galaxy

This Catalog of Star-Forming Regions in the Galaxy contains coordinates and fluxes of young objects in the radio and infrared, as well as data on the radial velocities of recombination and molecular lines, for more than three thousand star-forming regions. In addition to photometric and kinematic data, we present information on diffuse and reflecting nebulae, dark and molecular clouds, and other objects related to young stars. The catalog consists of two parts. The main catalog lists star-forming regions in order of Galactic longitude and is supplemented by analogous information for star-forming regions in complexes of dark clouds with large angular sizes that are closest to the Sun. The main catalog is located at http://www.strasbg.-u.fr/pub/cats. In our preliminary study of the catalog data using a formal classification of the star-forming regions, we subdivided these objects into several classes and characterized them as being populated primarily by massive or low-mass stars at early or late stages of the star-formation process. We also distinguish between relatively nearby and distant complexes.     

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.     

Spectral characteristics of faint radio sources of the KHOLOD survey

Radio sources detected at 3.94 GHz in RATAN-600 observations made in 1980–1981 (the KHOLOD Survey) have been identified with objects from the NVSS catalog down to 5 mJy at 1.4 GHz, and their spectral indices have been estimated. Of the 1311 NVSS objects in the KHOLOD survey region, 836 are present in both catalogs. The average flux density of the common objects is 40 mJy, and the median flux density is 14 mJy. The average spectral indices of these objects for four flux-density intervals were calculated. The average spectral index grows with flux density. The fraction of objects with inverted spectra is 2–4%, and the average flux density of these sources is about 10 mJy. Optical identifications of the NVS S objects in the KHOLOD survey region have been carried out to R=20.5^m using the Palomar plates. About 20% of the radio sources are identified with optical objects in all the radio flux-density intervals.     

Construction of a celestial coordinate reference frame from VLBI data

A large number (～2 million) of VLBI observations have been reduced in order to refine the measured coordinates of the observed radio sources. The data reduction was carried out in the OCCAM package using the least squares colocation method. Corrections to the coordinates of 642 objects were derived. The accuracy of the catalog is no worse than 0.2 milliseconds of arc for stable sources.     

Long-term variability of a complete sample of flat-spectrum radio sources at declinations of 4°–6° (B1950)

We present the results of twenty-year observations of a complete sample of 68 flat-spectrum radio sources with flux densities S _{3.9 GHz} > 200 mJy carried out at centimeter wavelengths with the RATAN-600 radio telescope. Since 1995, we have observed simultaneously at six frequencies between 0.97 and 21.7 GHz. Of the 56 sources identified with optical objects, 41 are quasars with redshifts between 0.293 and 3.263. Based on our analysis of the spectral shapes, we divide the sources into four classes. Changes of spectral class for individual sources are fairly rare. Based on the light curves and spectra, in most cases, a flare’s evolution is in accordance with a model in which the variations result from the evolution of a shock in the radio jet. The main result of our study is that there is no redshift dependence for the true linear sizes of the radiating regions, the variability indices derived for all 20 years of data or for individual flares, or the peak frequencies of the spectra of the compact radio emission. We suggest that this testifies to an absence of cosmological evolution of the sample quasars, at least to z ≈ 3.     

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.