On the Spectral Index of Distant Radio Galaxies

The problems of using the spectral index of radio galaxies in various tests, in particular, in selecting distant radio sources are considered. The history of the question of choosing a criterion of searching for distant radio galaxies based on the spectral index is presented. For a new catalog of 2442 radio galaxies constructed from NED, SDSS, and CATS data, an analytical form of the sp ectral index.redshift relation has been determined for the first time. The spectral index.angular size and spectral index.flux density diagrams have also been constructed. Peculiarities of the distribution of sources on these diagrams are discussed.Comment: 7 pages,5 figure

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 degrees 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 ({\alpha} = 0.7-0.8, S \propto {\nu}^{- \alpha}), 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.Comment: 13 pages, 10 figure

Disentangling star formation and AGN activity in powerful infrared luminous radio galaxies at 1 < z < 4

© 2016 ESO. High-redshift radio galaxies present signs of both star formation and AGN activity, making them ideal candidates to investigate the connection and coevolution of AGN and star formation in the progenitors of present-day massive galaxies. We make use of a sample of 11 powerful radio galaxies spanning 1 &lt;z&lt; 4 which have complete coverage of their spectral energy distribution (SED) from UV to FIR wavelengths. Using Herschel data, we disentangle the relative contribution of the AGN and star formation by combining the galaxy evolution code PÉGASE.3 with an AGN torus model. We find that three components are necessary to reproduce the observed SEDs: an evolved and massive stellar component, a submm bright young starburst, and an AGN torus. We find that powerful radio galaxies form at very high-redshift, but experience episodic and important growth at 1 &lt;z&lt; 4 as the mass of the associated starburst varies from 5 to 50% of the total mass of the system. The properties of star formation differ from source to source, indicating no general trend of the star formation properties in the most infrared luminous high-redshift radio galaxies and no correlation with the AGN bolometric luminosity. Moreover, we find that AGN scattered light have a very limited impact on broad-band SED fitting on our sample. Finally, our analysis also suggests a wide range in origins for the observed star formation,which we partially constrain for some sources

Rapidly growing black holes and host galaxies in the distant universe from the Herschel Radio Galaxy Evolution Project

We present results from a comprehensive survey of 70 radio galaxies at redshifts 1 2.5 are higher than the sSFR of typical star forming galaxies over the same redshift range, but are similar or perhaps lower than the galaxy population for radio galaxies at z< 2.5. By comparing the sSFR and the specific ṀBH (sṀBH), we conclude that black holes in radio loud AGN are already, or soon will be, overly massive compared to their host galaxies in terms of expectations from the local MBH–MGal relation. In order to catch up with the black hole, the galaxies require about an order of magnitude more time to grow in mass at the observed SFRs compared to the time the black hole is actively accreting. However, during the current cycle of activity, we argue that this catching up is likely to be difficult because of the short gas depletion times. Finally, we speculate on how the host galaxies might grow sufficiently in stellar mass to ultimately fall onto the local MBH–MGal relation

Properties of IR-selected active galactic nuclei

Context. Active galactic nuclei (AGNs) of galaxies play an important role in the life and evolution of galaxies through the impact they exert on certain properties and on the evolutionary path of galaxies. It is well known that infrared (IR) emission is useful for selecting galaxies with AGNs, although it has been observed that there is contamination by star-forming galaxies. Aims. We investigate the properties of galaxies that host AGNs that are identified at mid- (MIR) and near-IR wavelengths. The sample of AGNs selected at IR wavelengths was confirmed using optical spectroscopy and X-ray photometry. We study the near-UV, optical, near-IR and MIR properties, as well as the [O II

The VLT LBG Redshift Survey- II. Interactions between galaxies and the IGM at z\tilde 3

We have measured redshifts for 243 z&#8776; 3 quasars in nine Very Large Telescope (VLT) Visible Imaging and Multi-Object Spectrograph (VIMOS) Lyman-break galaxy (LBG) redshift survey areas, each of which is centred on a known bright quasar. Using the spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Ly&#0945; forest and 1020 LBGs at z&#8776; 3. We find an increase in neutral hydrogen absorption within &#8776;5 h-1 Mpc of a galaxy in agreement with the results of Adelberger et al. The Ly&#0945;-LBG cross-correlation can be described by a power law on scales larger than 3 h-1 Mpc. When galaxy velocity dispersions are taken into account, our results at smaller scales (<2 h-1 Mpc) are also in good agreement with the results of Adelberger et al. There is little immediate indication of a region with a transmission spike above the mean intergalactic medium value which might indicate the presence of star formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift-space distortion measurements of Bielby et al. We find that the redshift-space transmission spike implied in the results of Adelberger et al. is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Ly&#0945; absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 C iv systems in the quasar spectra and find an LBG-C iv correlation strength on scales of 10 h-1 Mpc consistent with the relation measured at &#8776;Mpc scales