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Register a new userThe WISE properties of complete samples of radio-loud AGN
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We present an analysis of four complete samples of radio-loud AGN (3CRR, 2Jy, 6CE and 7CE) using near- and mid-IR data taken by the Wide-Field Infrared Survey Explorer (WISE). The combined sample consists of 79 quasars and 273 radio galaxies, and covers a redshift range 0.003<z<3.395. The dichotomy in the mid-IR properties of low- and high-excitation radio galaxies (LERGs - HERGs) is analysed for the first time using large complete samples. Our results demonstrate that a division in the accretion modes of LERGs and HERGs clearly stands out in the mid-IR-radio plane (L_(22 mu m) = 5x10^(43) erg s^(-1)). This means that WISE data can be effectively used to diagnose accretion modes in radio-loud AGN. The mid-IR properties of all objects were analysed to test the unification between quasars and radio galaxies, consistent with earlier work and we argue that smooth torus models best reproduce the observation. Quasars are found to have higher mid-IR luminosities than radio galaxies. We also studied all the sources in the near-IR to gain insights into evolution of AGN host galaxies. A relation found between the near-IR luminosity and redshift, well-known in the near-IR, is apparent in the two near-IR WISE bands, supporting the idea that radio sources are hosted by massive elliptical galaxies that formed their stars at high redshifts and evolved passively thereafter. Evaluation of the positions of the sample objects in WISE colour-colour diagrams shows that widely used WISE colour cuts are not completely reliable in selecting AGN.
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We explore radio and spectroscopic properties of a sample of 14 miniature radio galaxies, i.e. early-type core galaxies hosting radio-loud AGN of extremely low radio power, 10^(27-29) erg s^(-1) Hz^(-1) at 1.4 GHz. Miniature radio galaxies smoothly extend the relationships found for the more powerful FRI radio galaxies between emission line, optical and radio nuclear luminosities to lower levels. However, they have a deficit of a factor of ~100 in extended radio emission with respect to that of the classical example of 3CR/FRI. This is not due to their low luminosity, since we found radio galaxies of higher radio core power, similar to those of 3CR/FRI, showing the same behavior, i.e. lacking significant extended radio emission. Such sources form the bulk of the population of radio-loud AGN in the Sloan Digital Sky Survey. At a given level of nuclear emission, one can find radio sources with an extremely wide range, a factor of >~100, of radio power. We argue that the prevalence of sources with luminous extended radio structures in flux limited samples is due to a selection bias, since the inclusion of such objects is highly favored. The most studied catalogues of radio galaxies are thus composed by the minority of radio-loud AGN that meet the physical conditions required to form extended radio sources, while the bulk of the population is virtually unexplored.
In a previous paper we showed that the radio sources selected by combining large areas radio and optical surveys, present a strong deficit of radio emission with respect to 3CR radio-galaxies matched in line emission luminosity. We argued that the prevalence of sources with luminous extended radio structures in high flux limited samples is due to a selection bias. Sources with low radio power form the bulk of the radio-loud AGN population but are still virtually unexplored. We here analyze their photometric and spectroscopic properties. From the point of view of their emission lines, the majority of the sample are Low Excitation Galaxies (LEG), similar to the 3CR objects at the same level of line luminosity. The hosts of LEG are red, massive Early-Type Galaxies (ETG) with large black holes masses , statistically indistinguishable from the hosts of low redshift 3CR/LEG sources. No genuine radio-loud LEG could be found associated with black holes with a mass substantially lower than 10^8 M(sun) or with a late type host. The fraction of galaxies with signs of star formation (5%) is similar to what is found in both the quiescent ETG and 3CR/LEG hosts. We conclude that the deficit in radio emission cannot be ascribed to differences in the properties of their hosts. We argue that instead this could be due to a temporal evolution of the radio luminosity. A minority (10%) of the sample show rather different properties, being associated with low black hole masses, with spiral galaxies, or showing a high excitation spectrum. In general these outliers are the result of the contamination from Seyfert and from galaxies where the radio emission is powered by star formation. For the objects with high excitation spectra there is no a clear discontinuity in either the host or nuclear properties as they span from radio-quiet and radio-loud AGN.
We are carrying out a search for all radio loud Active Galactic Nuclei observed with XMM-Newton, including targeted and field sources to perform a multi-wavelength study of these objects. We have cross-correlated the Veron-Cetty & Veron (2010) catalogue with the XMM-Newton Serendipitous Source Catalogue (2XMMi) and found about 4000 matched sources. A literature search provided radio, optical, and X-ray data for 403 sources. Here we summarize the first results of our study.
We present high spatial resolution MIR observations for several nearby radio loud active galactic nuclei (RLAGN), which were obtained using the Gemini North and South telescopes. Of the six observed objects, we detected five in the Si-2 (8.7 microns) and Si-6 (12.3 microns) filters, of which two objects show some evidence of low level extended emission surrounding the unresolved nucleus. In Pictor A, we also obtained an image in Qs (18.3 microns) that has a flux of only half that seen in the Spitzer image, suggesting structure on arcsecond scales. We also used the Si-6 (12.3 microns) flux measurement to investigate correlation between our MIR flux and xray luminosity and compare this to results for AGN in general. This work also forms a basis for future high resolution imaging and spectroscopy of these objects.
We develop a formalism to model the luminosity functions (LFs) of radio-loud Active Galactic Nuclei (AGN) at GHz frequencies by the cosmological evolution of the supermassive black hole (SMBH). The mass function and Eddington ratio distributions of SMBHs have been taken as starting point for this analysis. Our approach is based on physical and phenomenological relations that allow to statistically calculate the radio luminosity of AGN cores, corrected for beaming effects, by linking it with the SMBH at their center, through the Fundamental Plane of black hole activity. Moreover, radio luminosity from extended jets and lobes is also computed through a power-law relationship that reflects the expected correlation between the inner radio core and the extended jets/lobes. Radio-loud AGN are further divided in two classes, characterized by different accretion modes onto the central BH. If the Eddington ratio is <0.01 they are called low-kinetic (LK-mode) AGN; if >0.01, they are called high-kinetic (HK-mode) AGN, being this critical value roughly corresponding to the transition between radiatively inefficient and efficient accretion flows. The few free parameters used in the present model are determined by fitting two different types of observational data sets: local LFs of radio-loud AGN at 1.4 GHz and differential number counts of extragalactic radio sources at 1.4 and 5 GHz. Our present model fits well almost all published data on LFs of LK-mode AGN and of the total AGN population up to redshifts z<=1.5 and, moreover, in the full range of luminosities currently probed by data. On the other hand, it tends to underestimate some recent measures of the LF of HK-mode AGN at low redshifts, but only at low radio luminosities. The present model is also able to provide a very good fit to almost all data on number counts of radio-loud sources at 1.4 and 5 GHz. (abridged)
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