ABSTRACT
The mJy variable extragalactic radio sky is known to be broadly non-changing with approximately $3{{\ \rm per\ cent}}$ of persistent radio sources exhibiting variability that is largely ...active galactic nucleus-related (AGN). In the faint (<mJy) flux density regime, it is widely accepted that the radio source population begins to change from AGN dominated to star formation dominated, together with an emergent radio-quiet AGN component. Very little is known about the variable source component in this sub-mJy regime. In this paper, we provide the first insight into the μJy variable sky by performing a careful analysis using the deep VLA data in the well-studied GOODS-N field. Using five epochs spread across 22 yr, we investigate approximately 480 radio sources finding 10 that show signs of variability. We attribute this variability to the presence of an AGN in these systems. We confirm and extend the results of previous surveys, finding that variability in the faint radio sky is rather modest with only ≤2 per cent of sources exhibiting significant variability between any two epochs. We find that 70 per cent of variable sources show variability on time-scales of a few days while on longer decadal time-scales, the fraction of variable sources decreases to $\lt 1{{\ \rm per\ cent}}$. This suggests that the radio variability peaks on shorter time-scales as suggested by other studies. We find that 80 per cent of variable sources have VLBI counterparts, and we use multiwavelength data to infer that these may well be core-dominated FR-I sources as postulated by the wide-field VLBI surveys and semi-empirical simulations.
AGN WITH AKARI AND HERSCHEL Barthel, Peter
Ceonmunhag noncong/Cheonmunhak nonchong,
03/2017, Volume:
32, Issue:
1
Journal Article
Open access
AKARI and the subsequent Herschel Space Observatory have yielded tremendous advancement in our knowledge of the infrared-submillimeter properties of active galaxies and active galactic nuclei, AGN. ...This short review describes some highlights. Active galaxies are found to do what they are supposed to do: build up their stellar bodies while building up their central black holes.
Abstract
While supermassive black holes are ubiquitous features of galactic nuclei, only a small minority are observed during episodes of luminous accretion. The physical mechanism(s) driving the ...onset of fueling and ignition in these active galactic nuclei (AGN) are still largely unknown for many galaxies and AGN-selection criteria. Attention has focused on AGN triggering by means of major galaxy mergers gravitationally funneling gas toward the galactic center, with evidence both for and against this scenario. However, several recent studies have found that radio-loud AGN overwhelmingly reside in ongoing or recent major galaxy mergers. In this study, we test the hypothesis that major galaxy mergers are important triggers for radio-loud AGN activity in powerful quasars during cosmic noon (1 ≲
z
≲ 2). To this end, we compare Hubble Space Telescope WFC3/IR observations of the
z
> 1 3CR radio-loud broad-lined quasars to three matched radio-quiet quasar control samples. We find strong evidence for major-merger activity in nearly all radio-loud AGN, in contrast to the much lower merger fraction in the radio-quiet AGN. These results suggest major galaxy mergers are key ingredients in launching powerful radio jets. Given many of our radio-loud quasars are blue, our results present a possible challenge to the “blowout” paradigm of galaxy evolution models in which blue quasars are the quiescent end result following a period of red quasar feedback initiated by a galaxy merger. Finally, we find a tight correlation between black hole mass and host galaxy luminosity for these different high-redshift AGN samples that is inconsistent with those observed for local elliptical galaxies.
Abstract
We constrain the emission mechanisms responsible for the prodigious electromagnetic output generated by active galactic nuclei (AGNs) and their host galaxies with a novel state-of-the-art ...AGN radio-to-X-ray spectral energy distribution model fitting code (ARXSED). ARXSED combines multiple components to fit the spectral energy distributions (SEDs) of AGNs and their host galaxies. Emission components include radio structures such as lobes and jets, infrared emission from the AGN torus, visible-to-X-ray emission from the accretion disk, and radio-to-ultraviolet emission from the host galaxy. Applying ARXSED to the radio SEDs of 20 3CRR quasars at 1 <
z
< 2 verifies the need for more than a simple power law when compact radio structures are present. The nonthermal emission contributes 91%–57% of the observed-frame 1.25 mm to 850
μ
m flux, and this component must be accounted for when using these wavelengths to estimate star formation properties. We predict the presence of strong radio-linked X-ray emission in more than half the sample sources. ARXSED estimates median (and the associated first and third quartile ranges) BH mass of
2.9
1.7
6.0
×
10
9
M
☉
, logarithm of Eddington ratio of
−
1.0
−
1.2
−
0.6
, and spin of
0.98
0.94
0.99
for our sample. The inferred AGN torus and accretion disk parameters agree with those estimated from spectroscopic analyses of similar samples in the literature. We present the median intrinsic SED of the luminous radio-loud quasars at 1 <
z
≲ 2; this SED represents a significant improvement in the way each component is modeled.
Using the Herschel Space Observatory we have observed a representative sample of 87 powerful 3CR sources at redshift z< 1. The far-infrared (FIR, 70-500 mum) photometry is combined with mid-infrared ...(MIR) photometry from the Wide-Field Infrared Survey Explorer and cataloged data to analyze the complete spectral energy distributions (SEDs) of each object from optical to radio wavelength. To disentangle the contributions of different components, the SEDs are fitted with a set of templates to derive the luminosities of host galaxy starlight, dust torus emission powered by active galactic nuclei (AGNs), and cool dust heated by stars. The level of emission from relativistic jets is also estimated to isolate the thermal host galaxy contribution. The new data are in line with the orientation-based unification of high-excitation radio-loud AGN, in that the dust torus becomes optically thin longwards of 30 mum. The low-excitation radio galaxies and the MIR-weak sources represent an MIR- and FIR-faint AGN population that is different from the high-excitation MIR-bright objects; it remains an open question whether they are at a later evolutionary state or an intrinsically different population. The derived luminosities for host starlight and dust heated by star formation are converted to stellar masses and star-formation rates (SFR). The host-normalized SFR of the bulk of the 3CR sources is low when compared to other galaxy populations at the same epoch. Estimates of the dust mass yield a 1-100 times lower dust/stellar mass ratio than for the Milky Way, which indicates that these 3CR hosts have very low levels of interstellar matter and explains the low level of star formation. Less than 10% of the 3CR sources show levels of star formation above those of the main sequence of star-forming galaxies.
AKARI and the subsequent Herschel Space Observatory have yielded tremendous advancement in our knowledge of the infrared-submillimeter properties of active galaxies and active galactic nuclei, AGN. ...This short review describes some highlights. Active galaxies are found to do what they are supposed to do: build up their stellar bodies while building up their central black holes.
Starbursts and dusty tori in distant 3CR radio galaxies Podigachoski, Pece; Rocca-Volmerange, Brigitte; Barthel, Peter ...
Monthly Notices of the Royal Astronomical Society,
11/2016, Volume:
462, Issue:
4
Journal Article
Peer reviewed
Open access
We present a study of the complete ultraviolet to submillimetre spectral energy distributions (SEDs) of 12 3CR radio galaxy hosts in the redshift range 1.0 < z < 2.5, which were all detected in the ...far-infrared by the Herschel Space Observatory. The study employs the new spectro-chemical evolutionary code pégase.3, in combination with recently published clumpy active galactic nuclei (AGN) torus models. We uncover the properties of the massive host galaxy stellar populations, the AGN torus luminosities, and the properties of the recent starbursts, which had earlier been inferred in these objects from their infrared SEDs. The pégase.3 fitting yields very luminous (up to 1013 L⊙) young stellar populations with ages of several hundred million years in hosts with masses exceeding 1011 M⊙. Dust masses are seen to increase with redshift, and a surprising correlation – or better upper envelope behaviour – is found between the AGN torus luminosity and the starburst luminosity, as revealed by their associated dust components. The latter consistently exceeds the former by a constant factor, over a range of one order of magnitude in both quantities.
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