The X-ray nuclei of intermediate-redshift radio sources

Hardcastle, M. J.; Evans, D. A.; Croston, J. H.

doi:10.1111/j.1365-2966.2006.10615.x

Cited by 189 publications

(287 citation statements)

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“…The second mode of radio activity was first noted by their lack of strong high-excitation narrowline optical excitation expected from the 'quasar' mode (Hine & Longair 1979;Laing et al 1994;Jackson & Rawlings 1997). Moreover, they show no evidence of mid-infrared emission from dusty tori (Whysong & Antonucci 2004;Ogle, Whysong & Antonucci 2006) and no evidence of accretion-related X-ray emission Hardcastle, Evans & Croston 2006). Hardcastle, Evans & Croston (2007) first suggested that this mode, known as the 'lowexcitation', 'radio mode', 'hot mode' or 'jet mode' occurs when hot gas is accreted directly on to the supermassive black hole in a radiatively inefficient manner via advection-dominated accretion flows (e.g.…”

Section: Introductionmentioning

confidence: 99%

Radio-AGN feedback: when the little ones were monsters

Williams

Röttgering

2015

Monthly Notices of the Royal Astronomical Society

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We present a study of the evolution of the fraction of radio-loud active galactic nuclei (AGN) as a function of their host stellar mass. We make use of two samples of radio galaxies: one in the local Universe, 0.01 < z ≤ 0.3, using a combined SDSS-NVSS (Sloan Digital Sky Survey NRAO Very Large Array Sky Survey) sample and the other at higher redshifts, 0.5 < z ≤ 2, constructed from the VLA-COSMOS_DEEP Radio Survey at 1.4 GHz and a K s -selected catalogue of the COSMOS/UltraVISTA field. We observe an increase of more than an order of magnitude in the fraction of lower mass galaxies (M * < 10 10.75 M ) which host radio-loud AGN with radio powers P 1.4 GHz > 10 24 W Hz −1 at z ∼ 1-2 while the radio-loud fraction for higher mass galaxies (M * > 10 11.25 M ) remains the same. We argue that this increase is driven largely by the increase in cold or radiative mode accretion with increasing cold gas supply at earlier epochs. The increasing population of low-mass radio-loud AGN can thus explain the upturn in the radio luminosity function at high redshift which is important for understanding the impact of AGN feedback in galaxy evolution.

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Section: Introductionmentioning

confidence: 99%

Radio-AGN feedback: when the little ones were monsters

Williams

Röttgering

2015

Monthly Notices of the Royal Astronomical Society

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“…Moreover, low-redshift GPS galaxies exhibit column densities not systematically lower than high-redshift ones. Hardcastle et al (2006) remark that heavily absorbed nuclei are rather common in narrow-line radio galaxies, whereas they are comparatively rare in Low-Excitation Radio Galaxies (LERG, Laing et al 1994). There are 7 LERGs in our control sample; 5 of them have no column density measurement; the remaining two have column density of 3 × 10 22 cm −2 (3C 123, Hardcastle et al 2006) and 10 23 cm −2 (3C 427.1, Belsole et al 2006).…”

Section: Obscurationmentioning

confidence: 99%

“…Hardcastle et al (2006) remark that heavily absorbed nuclei are rather common in narrow-line radio galaxies, whereas they are comparatively rare in Low-Excitation Radio Galaxies (LERG, Laing et al 1994). There are 7 LERGs in our control sample; 5 of them have no column density measurement; the remaining two have column density of 3 × 10 22 cm −2 (3C 123, Hardcastle et al 2006) and 10 23 cm −2 (3C 427.1, Belsole et al 2006). Taking into account the low number statistics and the uncertainties on the column density upper limits on formally "unobscured" LERGs, the comparison between X-ray obscuration in LERGs and GPSs is inconclusive.…”

Section: Obscurationmentioning

confidence: 99%

“…The control sample has been built from results recently published in the literature. It is based on observations of z < 1 radio galaxies taken by ASCA (Sambruna et al 1999), BeppoSAX , XMM-Newton and Chandra (FR I: Donato et al 2004;Evans et al 2006;Balmaverde et al 2006, FR II: Belsole et al 2006Evans et al 2006;Hardcastle et al 2006). Only one measurement per source has been retained in the control sample, based on the latest published result.…”

Section: Comparison With Control Samples Of "Normal" Radio Galaxiesmentioning

confidence: 99%

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The X-ray view of giga-hertz peaked spectrum radio galaxies

Tengstrand

Guainazzi

Siemiginowska

et al. 2009

A&A

100

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Context. This paper presents the X-ray properties of a flux-and volume-limited complete sample of 16 giga-hertz peaked spectrum (GPS) galaxies. Aims. This study addresses three basic questions in our understanding of the nature and evolution of GPS sources: a) What is the physical origin of the X-ray emission in GPS galaxies? b) Which physical system is associated with the X-ray obscuration? c) What is the "endpoint" of the evolution of compact radio sources? Methods. We discuss in this paper the results of the X-ray spectral analysis, and compare the X-ray properties of the sample sources with radio observables. Results. We obtain a 100% (94%) detection fraction in the 0.5-2 keV (0.5-10 keV) energy band. GPS galaxy X-ray spectra are typically highly obscured ( N GPS H = 3 × 10 22 cm −2 ; σ N H 0.5 dex). The X-ray column density is larger than the HI column density measured in the radio by a factor 10 to 100. GPS galaxies lie well on the extrapolation to high radio powers of the correlation between radio and X-ray luminosity known in low-luminosity FR I radio galaxies. On the other hand, GPS galaxies exhibit a comparable X-ray luminosity to FR II radio galaxies, notwithstanding their much larger radio luminosity. Conclusions. The X-ray to radio luminosity ratio distribution in our sample is consistent with the bulk of the high-energy emission being produced by the accretion disk, as well as with dynamical models of GPS evolution where X-rays are produced by Compton upscattering of ambient photons. Further support to the former scenario comes from the location of GPS galaxies in the X-ray to O[iii] luminosity ratio versus N H plane. We propose that GPS galaxies are young radio sources, which would reach their full maturity as classical FR II radio galaxies. However, column densities ∼ > 10 22 cm −2 could lead to a significant underestimate of dynamical age determinations based on the hotspot recession velocity measurements.

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“…However, observational evidence is mounting to suggest that this picture does not give a proper description for low-luminosity radioloud AGN (P 1.4 GHz < ∼ 10 25 W Hz −1 ). These objects produce weaker or no emission lines (Hine & Longair 1979;Jackson & Rawlings 1997), lack the dusty torus infrared emission (Ogle et al 2006), and do not produce the accretion related X-ray emission (Hardcastle et al 2006). It has been suggested that there are indeed two very different modes of AGN activity named the "Quasar mode" and the "Radio mode" (Best et al 2005;Hardcastle et al 2007).…”

Section: Introductionmentioning

confidence: 99%

The dependence of X-ray AGN activity on host galaxy properties and environment

Tasse

Röttgering

Best

2010

A&A

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There is mounting evidence that active galactic nuclei (AGN) selected through optical emission lines or radio luminosities comprise two distinct AGN populations, whose activity is triggered by different processes. In two previous papers, we studied the host galaxies and environment of radio-loud AGN. In this third paper we study the properties of a sample of Type-2 AGN that were selected on the basis of their [2-10] keV X-ray luminosity. We find that the X-ray luminosity function is in good agreement with previous studies and that the fraction of galaxies hosting an X-ray AGN is a strong function of the stellar mass of the host galaxy. The shape of this fraction-mass relation is similar to the fraction of galaxies that are emission-line AGN, while it differs significantly from the relation observed for radio-selected AGN. The AGN in our sample tend to be located in underdense environments where galaxy mergers and interactions are likely to occur. For all host galaxy masses, the Type-2 AGN display a strong infrared excess at short (∼3.5 μm) wavelengths, suggesting the presence of hot dust possibly associated with a hot dusty torus. These results add weight to the belief that the X-ray selection criteria identifies a population of AGN similar to the emission-line selected population but distinct from the radio population at high masses.

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The X-ray nuclei of intermediate-redshift radio sources

Cited by 189 publications

References 67 publications

Radio-AGN feedback: when the little ones were monsters

Radio-AGN feedback: when the little ones were monsters

The X-ray view of giga-hertz peaked spectrum radio galaxies

The dependence of X-ray AGN activity on host galaxy properties and environment

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