The radio-loud AGN population at z 73 1 in the COSMOS field. I. selection and spectral energy distributions

We select a sample of radio galaxies at high redshifts (z 73 1) in the COSMOS field by cross-matching optical and infrared (IR) images with the FIRST radio data. The aim of this study is to explore the high-z radio-loud (RL) active galactic nuclei (AGN) population at much lower luminosities than the classical samples of distant radio sources, which are similar to those of the local population of radio galaxies. Precisely, we extended a previous analysis focused on low-luminosity radio galaxies. The wide multiwavelength coverage provided by the COSMOS survey allows us to derive their spectral energy distributions (SEDs). We model them with our own developed technique 2SPD that includes old and young stellar populations and dust emission. When added to those previously selected, we obtain a sample of 74 RL AGN. The SED modeling returns several important quantities associated with the AGN and host properties. The resulting photometric redshifts range from z ~ 0.7 to 3. The sample mostly includes compact radio sources but also 21 FR IIs sources; the radio power distribution of the sample covers ~1031.5 - 1034.3 erg s-1 Hz-1, thus straddling the local FR I/FR II break. The inferred range of stellar mass of the hosts is ~1010 - 1011.5M 99. The SEDs are dominated by the contribution from an old stellar population with an age of ~1 - 3 Gyr for most of the sources. However, UV and mid-IR (MIR) excesses are observed for half of the sample. The dust luminosities inferred from the MIR excesses are in the range, Ldust ~ 1043 - 1045.5 erg s-1, which are associated with temperatures approximately of 350-1200 K. Estimates of the UV component yield values of ~1041.5 - 1045.5 erg s-1 at 2000 \uc5. The UV emission is significantly correlated with both IR and radio luminosities; the former being the stronger link. However, the origin of UV and dust emission, whether it is produced by the AGN of by star formation, is still unclear. Our results show that this RL AGN population at high redshifts displays a wide variety of properties. Low-power radio galaxies, which are associated with UV- and IR-faint hosts are generally similar to red massive galaxies of the local FR Is. At the opposite side of the radio luminosity distribution, large MIR and UV excesses are observed in objects consistent with quasar-like AGN, as also proved by their high dust temperatures, which are more similar to local FR IIs

The eMERLIN and EVN view of FR0 radio galaxies

We present the results from high-resolution observations carried out with the eMERLIN UK-array and the European VLBI network (EVN) for a sample of 15 FR0s, i.e. compact core-dominated radio sources associated with nearby early-type galaxies (ETGs) which represent the bulk of the local radio galaxy population. The 5-GHz eMERLIN observations available for 5 objects exhibit sub-mJy core components, and reveal pc-scale twin jets for 4 out of 5 FR0s once the eMERLIN and JVLA archival visibilities data are combined. The 1.66-GHz EVN observations available for 10 FR0s display one- and two-sided jetted morphologies and compact cores. The pc-scale core emission contributes, on average, to about one tenth of the total extended radio emission, although we note a increasing core contribution for flat/inverted-spectrum sources. We found an unprecedented linear correlation between the pc-scale core luminosity ($\sim$10$^{21.3}$-10$^{23.6}$ W Hz$^{-1}$) and [O III] line luminosity, generally considered as proxy of the accretion power, for a large sample of LINER-type radio-loud low-luminosity active nuclei, all hosted in massive ETGs, which include FR0s and FRIs. This result represents further evidence of a common jet-disc coupling in FR0s and FRIs, despite they differ in kpc-scale radio structure. For our objects and for other FR0 samples reported in the literature, we estimate the jet brightness sidedness ratios, which typically range between 1 and 3. This parameter roughly gauges the jet bulk Lorentz factor $\Gamma$, which turns out to range between 1 and 2.5 for most of the sample. This corroborates the scenario that FR0s are characterized by mildly-relativistic jets, possibly as a result of lower spinning black holes (BHs) than the highly-spinning BHs of relativistic-jetted radio galaxies, FRIs

The PG-RQS survey. Building the radio spectral distribution of radio-quiet quasars. I. The 45-GHz data

The origin of the radio emission in radio-quiet quasars (RQQs) remains unclear. Radio emission may be produced by a scaled-down version of the relativistic jets observed in radio-loud (RL) AGN, an AGN-driven wind, the accretion disc corona, AGN photon-ionisation of ambient gas (free-free emission), or star formation (SF). Here, we report a pilot study, part of a radio survey (`PG-RQS') aiming at exploring the spectral distributions of the 71 Palomar-Green (PG) RQQs: high angular resolution observations ($\sim$50 mas) at 45~GHz (7 mm) with the Karl G. Jansky Very Large Array of 15 sources. Sub-mJy radio cores are detected in 13 sources on a typical scale of $\sim$100 pc, which excludes significant contribution from galaxy-scale SF. For 9 sources the 45-GHz luminosity is above the lower frequency ($\sim$1-10 GHz) spectral extrapolation, indicating the emergence of an additional flatter-spectrum compact component at high frequencies. The X-ray luminosity and black hole (BH) mass, correlate more tightly with the 45-GHz luminosity than the 5-GHz. The 45 GHz-based radio-loudness increases with decreasing Eddington ratio and increasing BH mass M$_{\rm BH}$. These results suggest that the 45-GHz emission from PG RQQs nuclei originates from the innermost region of the core, probably from the accretion disc corona. Increasing contributions to 45-GHz emission from a jet at higher M$_{\rm BH}$ and lower Eddington ratios and from a disc wind at large Eddington ratios are still consistent with our results. Future full radio spectral coverage of the sample will help us investigating the different physical mechanisms in place in RQQ cores

FRIICAT: A FIRST catalog of FR II radio galaxies

Aims. We built a catalog of 122 FR II radio galaxies, called FRIICAT, selected from a published sample obtained by combining observations from the NVSS, FIRST, and SDSS surveys. The catalog includes sources with redshift ≤ 0.15, an edge-brightened radio morphology, and those with at least one of the emission peaks located at radius r larger than 30 kpc from the center of the host.Methods. The radio luminosity at 1.4 GHz of the FRIICAT sources covers the range L1.4 ~ 1039.5−1042.5erg s-1. The FRIICAT catalog has 90% of low and 10% of high excitation galaxies (LEGs and HEGs), respectively. The properties of these two classes are significantly different. The FRIICAT LEGs are mostly luminous (−20 ≳ Mr ≳ −24), red early-type galaxies with black hole masses in the range 108 ≲ MBH ≲ 109M⊙; they are essentially indistinguishable from the FR Is belonging to the FRICAT. The HEG FR IIs are associated with optically bluer and mid-IR redder hosts than the LEG FR IIs and to galaxies and black holes that are smaller, on average, by a factor ~2.Results. FR IIs have a factor ~3 higher average radio luminosity than FR Is. Nonetheless, most (~ 90%) of the selected FR IIs have a radio power that is lower, by as much as a factor of ~100, than the transition value between FR Is and FR IIs found in the 3C sample. The correspondence between the morphological classification of FR I and FR II and the separation in radio power disappears when including sources selected at low radio flux thresholds, which is in line with previous results. In conclusion, a radio source produced by a low power jet can be edge brightened or edge darkened, and the outcome is not related to differences in the optical properties of the host galaxy

The high energy view of FR0 radio galaxies

A new class of low-power compact radio sources with limited jet structures, named FR 0, is emerging from recent radio-optical surveys. This abundant population of radio galaxies, five times more numerous than FR Is in the local Universe (z &lt; 0.05), represent a potentially interesting target at high and very-high energies (greater than 100 GeV), as demonstrated by a single case of Fermi detection. Furthermore, these radio galaxies have been recently claimed to contribute non-negligibly to the extra-galactic γ-ray background and to be possible cosmic neutrino emitters. Here, we review the radio through X-ray properties of FR 0s to predict their high-energy emission (from MeV to TeV), in light of the near-future facilities operating in this band.</p

Radio-loud Narrow Line Seyfert 1 under a different perspective: a revised black hole mass estimate from optical spectropolarimetry

Several studies indicate that radio-loud (RL) active galactic nuclei (AGNs) are produced only by the most massive black holes (BH), MBH ∼ 108–1010 M⊙. This idea has been challenged by the discovery of RL Narrow Line Seyfert 1 (RL NLSy1), having estimated masses of MBH ∼ 106–107 M⊙. However, these low MBH estimates might be due to projection effects. Spectropolarimetry allows us to test this possibility by looking at RL NLSy1s under a different perspective, i.e. from the viewing angle of the scattering material. We here report the results of a pilot study of Very Large Telescope spectropolarimetric observations of the RL NLSy1 PKS 2004−447. Its polarization properties are remarkably well reproduced by models in which the scattering occurs in an equatorial structure surrounding its broad-line region, seen close to face-on. In particular, we detect a polarized Hα line with a width of ∼9000 km s−1, ∼6 times broader than the width seen in direct light. This corresponds to a revised estimate of MBH ∼ 6 × 108 M⊙, well within the typical range of RL AGN. The double-peaked polarized broad Hα profile of the target suggests that the rare combination of the orientation effects and a broad line region dominated by the rotation might account for this class of objects, casting doubts on the virial estimates of BH mass for type-I AGN

The origin of radio emission from radio-quiet active galactic nuclei

The central nuclei of galaxies, where supermassive black holes (SMBHs) are thought to reside, can experience phases of activity when they become active galactic nuclei (AGNs). An AGN can eject winds and jets and produce radiation across the entire electromagnetic spectrum. The fraction of the bolometric emission in the radio spans a factor of approximately 10 5 across the different classes of AGNs. The weakest radio sources, radio-quiet (RQ) AGNs, are typically 1,000 times fainter than the radio-loud (RL) AGNs, and represent the majority of the AGN population. In RQ AGNs, the absence of luminous jets allows us to probe radio emission from a wide range of possible mechanisms: star formation, AGN-driven wind, free-free emission from photoionized gas, low-power jets and the innermost accretion disk coronal activity. All these mechanisms can now be probed with unprecedented precision and spatial resolution, owing to the current and forthcoming generation of highly sensitive radio arrays. </p

The PG-RQS survey. Building the radio spectral distribution of radio-quiet quasars. I. The 45-GHz data

The origin of the radio emission in radio-quiet quasars (RQQs) remains unclear. Radio emission may be produced by a scaled-down version of the relativistic jets observed in radio-loud (RL) AGN, an AGN-driven wind, the accretion disc corona, AGN photon-ionization of ambient gas (free–free emission), or star formation (SF). Here, we report a pilot study, part of a radio survey (‘PG-RQS’) aiming at exploring the spectral distributions of the 71 Palomar–Green (PG) RQQs: high angular resolution observations (∼50 mas) at 45 GHz (7 mm) with the Karl G. Jansky Very Large Array of 15 sources. Sub-mJy radio cores are detected in 13 sources on a typical scale of ∼100 pc, which excludes significant contribution from galaxy-scale SF. For 9 sources the 45-GHz luminosity is above the lower frequency (∼1–10 GHz) spectral extrapolation, indicating the emergence of an additional flatter-spectrum compact component at high frequencies. The X-ray luminosity and black hole (BH) mass, correlate more tightly with the 45-GHz luminosity than the 5-GHz. The 45 GHz-based radio-loudness increases with decreasing Eddington ratio and increasing BH mass MBH. These results suggest that the 45-GHz emission from PG RQQs nuclei originates from the innermost region of the core, probably from the accretion disc corona. Increasing contributions to 45-GHz emission from a jet at higher MBH and lower Eddington ratios and from a disc wind at large Eddington ratios are still consistent with our results. Future full radio spectral coverage of the sample will help us investigating the different physical mechanisms in place in RQQ cores

Simultaneous millimetre-wave and X-ray monitoring of the Seyfert galaxy NGC7469

We report on daily monitoring of the Seyfert galaxy NGC 7469, around 95 GHz and 143 GHz, with the IRAM 30 m radio telescope, and with the Swift X-Ray and UV/Optical telescopes, over an overlapping period of 45 days. The source was observed on 36 days with IRAM, and the flux density in both mm bands was on average ~10 mJy, but varied by ±50%, and by up to a factor of 2 between days. The present IRAM variability parameters are consistent with earlier CARMA monitoring, which had only 18 data points. The X-ray light curve of NGC 7469 over the same period spans a factor of 5 in flux with small uncertainties. Similar variability in the mm-band and in the X-rays lends support to the notion of both sources originating in the same physical component of the AGN, likely the accretion disk corona. Simultaneous monitoring ineight UV/optical bands shows much less variability than the mm and X-rays, implying this light originates from a different AGN component, likely the accretion disk itself. We use a tentative 14 day lag of the X-ray light curve with respect to the 95 GHz lightcurve to speculate on coronal implications. More precise mm-band measurements of a sample of X-ray-variable AGN are needed, preferably also on time scales of less than a day where X-rays vary dramatically, in order to properly test the physical connection between the two bands

COMP2CAT: hunting compact double radio sources in the local Universe

We present a catalog of compact double radio galaxies (hereafter COMP2CAT) listing 43 edge-brightened radio sources whose projected linear size does not exceed 60 kpc, the typical size of their host galaxies. This is the fifth in a series of radio source catalogs recently created, namely: FRICAT, FRIICAT, FR0CAT, and WATCAT, each of which focuses on a different class of radio galaxies. The main aim of our analysis is to attain a better understanding of sources with intermediate morphologies between FR IIs and FR 0s. COMP2CAT sources were selected from an existing catalog of radio sources based on NVSS, FIRST and SDSS observations because they have (i) edge-brightened morphologies typical of FR IIs, (ii) redshifts z &lt;  0.15, and (iii) projected linear sizes smaller than 60 kpc. With radio luminosities at 1.4 GHz 1038 ≲ L1.4 ≲ 1041 erg s−1, COMP2CAT sources appear as the low radio luminosity tail of FR IIs. However, their host galaxies are indistinguishable from those of large-scale radio sources: they are luminous (−21 ≳ Mr ≳ −24), red, early-type galaxies with black hole masses in the range 107.5 ≲ MBH ≲ 109.5 M⊙. Moreover, all but one of the COMP2CAT sources are optically classifiable as low-excitation radio galaxies, in agreement with being the low radio luminosity tail of FR Is and FR IIs. This catalog of compact double sources, which is ∼47% complete at z &lt;  0.15, can potentially be used to clarify the role of compact double sources in the general evolutionary scheme of radio galaxies