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Register a new userSource Counts Spanning Eight Decades of Flux Density at 1.4 GHz
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Brightness-weighted differential source counts $S^2 n(S)$ spanning the eight decades of flux density between $0.25,mumathrm{Jy}$ and 25 Jy at 1.4 GHz were measured from (1) the confusion brightness distribution in the MeerKAT DEEP2 image below $10,mumathrm{Jy}$, (2) counts of DEEP2 sources between $10,mumathrm{Jy}$ and $2.5,mathrm{mJy}$, and (3) counts of NVSS sources stronger than $2.5,mathrm{mJy}$. We present our DEEP2 catalog of $1.7 times 10^4$ discrete sources complete above $S = 10,mumathrm{Jy}$ over $Omega = 1.04,mathrm{deg}^2$. The brightness-weighted counts converge as $S^2 n(S) propto S^{1/2}$ below $S = 10,mumathrm{Jy}$, so $>99%$ of the $Delta T_mathrm{b} sim 0.06,mathrm{K}$ sky brightness produced by active galactic nuclei and $approx96%$ of the $Delta T_mathrm{b} sim 0.04,mathrm{K}$ added by star-forming galaxies has been resolved into sources with $S geq 0.25,mumathrm{Jy}$. The $Delta T_mathrm{b} approx 0.4,mathrm{K}$ excess brightness measured by ARCADE 2 cannot be produced by faint sources smaller than $approx 50,mathrm{kpc}$ if they cluster like galaxies.
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We present very long baseline interferometry (VLBI) observations of 179 radio sources in the COSMOS field with extremely high sensitivity using the Green Bank Telescope (GBT) together with the Very Long Baseline Array (VLBA) (VLBA+GBT) at 1.4 GHz, to explore the faint radio population in the flux density regime of tens of $mu$Jy. Here, the identification of active galactic nuclei (AGN) is based on the VLBI detection of the source, i.e., it is independent of X-ray or infrared properties. The milli-arcsecond resolution provided by the VLBI technique implies that the detected sources must be compact and have large brightness temperatures, and therefore they are most likely AGN (when the host galaxy is located at z$geq$0.1). On the other hand, this technique allows us to only positively identify when a radio-active AGN is present, i.e., we cannot affirm that there is no AGN when the source is not detected. For this reason, the number of identified AGN using VLBI should be always treated as a lower limit. We present a catalogue containing the 35 radio sources detected with the VLBA+GBT, 10 of which were not previously detected using only the VLBA. We have constructed the radio source counts at 1.4 GHz using the samples of the VLBA and VLBA+GBT detected sources of the COSMOS field to determine a lower limit for the AGN contribution to the faint radio source population. We found an AGN contribution of >40-75% at flux density levels between 150 $mu$Jy and 1 mJy. This flux density range is characterised by the upturn of the Euclidean-normalised radio source counts, which implies a contribution of a new population. This result supports the idea that the sub-mJy radio population is composed of a significant fraction of radio-emitting AGN, rather than solely by star-forming galaxies, in agreement with previous studies.
We present a study of the 1173 sources brighter than $S_{1.4,rm GHz}= 120,mu$Jy detected over an area of $simeq 1.4,hbox{deg}^{2}$ in the Lockman Hole field. Exploiting the multi-band information available in this field for $sim$79% of the sample, sources have been classified into radio loud (RL) active galactic nuclei (AGNs), star forming galaxies (SFGs) and radio quiet (RQ) AGNs, using a variety of diagnostics available in the literature. Exploiting the observed tight anti-correlations between IRAC band 1 or band 2 and the source redshift we could assign a redshift to 177 sources missing a spectroscopic measurement or a reliable photometric estimate. A Monte Carlo approach was used to take into account the spread around the mean relation. The derived differential number counts and luminosity functions at several redshifts of each population show a good consistency with models and with earlier estimates made using data from different surveys and applying different approaches. Our results confirm that below $sim300,mu$Jy SFGs$+$RQ AGNs overtake RL AGNs that dominate at brighter flux densities. We also confirm earlier indications of a similar evolution of RQ AGNs and SFGs. Finally, we discuss the angular correlation function of our sources and highlight its sensitivity to the criteria used for the classification.
We matched the 1.4 GHz local luminosity functions of star-forming galaxies (SFGs) and active galactic nuclei to the 1.4 GHz differential source counts from $0.25 mumathrm{Jy}$ to 25 Jy using combinations of luminosity and density evolution. We present the most robust and complete local far-infrared (FIR)/radio luminosity correlation to date in a volume-limited sample of $approx 4.3 times 10^3$ nearby SFGs, finding that it is very tight but distinctly sub-linear: $L_mathrm{FIR} propto L_mathrm{1.4,GHz}^{0.85}$. If the local FIR/radio correlation does not evolve, the evolving 1.4 GHz luminosity function of SFGs yields the evolving star-formation rate density (SFRD) $psi (M_odot mathrm{year}^{-1} mathrm{Mpc}^{-3}$) as a function of time since the big bang. The SFRD measured at 1.4 GHz grows rapidly at early times, peaks at cosmic noon when $t approx 3 mathrm{Gyr}$ and $z approx 2$, and subsequently decays with an $e$-folding time scale $tau = 3.2 mathrm{Gyr}$. This evolution is similar to, but somewhat stronger than, SFRD evolution estimated from UV and FIR data.
We present results from simulations of the extragalactic polarized sky at 1.4 GHz. As the basis for our polarization models, we use a semi-empirical simulation of the extragalactic total intensity (Stokes I) continuum sky developed at the University of Oxford (http://scubed.physics.ox.ac.uk) under the European SKA Design Study (SKADS) initiative, and polarization distributions derived from analysis of polarization observations. By considering a luminosity dependence for the polarization of AGN, we are able to fit the 1.4 GHz polarized source counts derived from the NVSS and the DRAO ELAIS N1 deep field survey down to approximately 1 mJy. This trend is confirmed by analysis of the polarization of a complete sample of bright AGN. We are unable to fit the additional flattening of the polarized source counts from the deepest observations of the ELAIS N1 survey, which go down to ~0.5 mJy. Below 1 mJy in Stokes I at 1.4 GHz, starforming galaxies become an increasingly important fraction of all radio sources. We use a spiral galaxy integrated polarization model to make realistic predictions of the number of polarized sources at microJy levels in polarized flux density and hence, realistic predictions of what the next generation radio telescopes such as ASKAP, other SKA pathfinders and the SKA itself will see.
Aims. To investigate the flux density modulation from pulsars and the existence of specific behaviour of modulation index versus frequency. Methods. Several pulsars have been observed with the Effelsberg radio telescope at 8.35 GHz. Their flux density time series have been corrected for interstellar scintillation effects. Results. We present the measurement of modulation indices for 8 pulsars. We confirm the presence of a critical frequency at ~1 GHz for these pulsars (including 3 new ones from this study). We derived intrinsic modulation indices for the resulting flux density time series. Our data analysis revealed strong single pulses detected from 5 pulsars.
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