Galaxy gas as obscurer – II. Separating the galaxy-scale and nuclear obscurers of active galactic nuclei

Buchner, Johannes; Bauer, F. E.

doi:10.1093/mnras/stw2955

Cited by 78 publications

(65 citation statements)

References 115 publications

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“…More detailed analysis and complex modelling of high signal-to-noise X-ray spectra where available, in comparison with studies in the literature (e.g. Buchner & Bauer 2017), will aid in separating galacticscale from nuclear-scale absorption contributions. We have also presented the results of a pilot study conducted with the commissioning telescope BETA, as part of preparations for FLASH science with ASKAP.…”

Section: Resultsmentioning

confidence: 99%

Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN

Moss

Allison

Sadler

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Many radio galaxies show the presence of dense and dusty gas near the active nucleus. This can be traced by both 21 cm Hi absorption and soft X-ray absorption, offering new insight into the physical nature of the circumnuclear medium of these distant galaxies. To better understand this relationship, we investigate soft X-ray absorption as an indicator for the detection of associated Hi absorption, as part of preparation for the First Large Absorption Survey in Hi (FLASH) to be undertaken with the Australian Square Kilometre Array Pathfinder (ASKAP). We present the results of our pilot study using the Boolardy Engineering Test Array, a precursor to ASKAP, to search for new absorption detections in radio sources brighter than 1 Jy that also feature soft X-ray absorption. Based on this pilot survey, we detected Hi absorption towards the radio source PKS 1657−298 at a redshift of z = 0.42. This source also features the highest X-ray absorption ratio of our pilot sample by a factor of 3, which is consistent with our general findings that X-ray absorption predicates the presence of dense neutral gas. By comparing the X-ray properties of AGN with and without detection of Hi absorption at radio wavelengths, we find that X-ray hardness ratio and Hi absorption optical depth are correlated at a statistical significance of 4.71σ. We conclude by considering the impact of these findings on future radio and X-ray absorption studies.

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Section: Resultsmentioning

confidence: 99%

Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN

Moss

Allison

Sadler

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Although the difference is only weakly significant, a similar result has also been reported for CT AGNs selected with SwiftBAT (Koss et al 2016a). Other studies, however, find that edge-on galaxy inclinations are not clearly related to CT absorption (e.g., Annuar et al 2017;Buchner & Bauer 2017). .…”

Section: Host Galaxiesmentioning

confidence: 94%

The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV

Lansbury

Alexander

Aird

et al. 2017

ApJ

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We identify sources with extremely hard X-ray spectra (i.e., with photon indices of  G 0.6) in the 13deg 2 NuSTAR serendipitous survey, to search for the most highly obscured active galactic nuclei (AGNs) detected at >10 keV. Eight extreme NuSTAR sources are identified, and we use the NuSTAR data in combination with lower-energy X-ray observations (from Chandra, SwiftXRT, and XMM-Newton) to characterize the broadband (0.5-24 keV) X-ray spectra. We find that all of the extreme sources are highly obscured AGNs, including three robust Compton-thick (CT; >Ń 1.5 10 H 24 cm −2 ) AGNs at low redshift ( < z 0.1) and a likely CT AGN at higher redshift (z = 0.16). Most of the extreme sources would not have been identified as highly obscured based on the low-energy (<10 keV) X-ray coverage alone. The multiwavelength properties (e.g., optical spectra and X-ray-mid-IR luminosity ratios) provide further support for the eight sources being significantly obscured. Correcting for absorption, the intrinsic rest-frame 10-40keV luminosities of the extreme sources cover a broad range, from »5 10 42 to 10 45 erg s −1 . The estimated number counts of CT AGNs in the NuSTAR serendipitous survey are in broad agreement with model expectations based on previous X-ray surveys, except for the lowest redshifts ( < z 0.07), where we measure a high CT fraction of16 . For the small sample of CT AGNs, we find a high fraction of galaxy major mergers (50% ± 33%) compared to control samples of "normal" AGNs.

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“…Generally, the obscuring material is related to the pc-scale dusty torus, which produces the highest N H values, or to the diffuse interstellar medium (ISM) in the host galaxy, which can also create N H as high as 10 22 23.5 -cm −2 (e.g., Simcoe et al 1997;Goulding et al 2012;Buchner & Bauer 2017). It is also found that 100 pc-scale dust filaments, which might be the nuclear fueling channels, could also be responsible for the obscuration (Prieto et al 2014).…”

Section: Introductionmentioning

confidence: 99%

“…Considering the realistic geometry of the torus and the AGN obscuration from torus-scale to galaxy-scale (Buchner & Bauer 2017), it is unlikely that all the reflected X-ray photons could leave the galaxy without any absorption, as expected by the flat-surface reflection model "pexrav." The X-ray reflection, if separated from the transmitted power-law as a stand-alone component, must be self-absorbed by the torus or obscured by material on a larger scale.…”

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confidence: 99%

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

Liu

Tozzi²,

Wang

et al. 2017

ApJS

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We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2–21 months. With this approach, we not only present the power-law slopes, column densities , observed fluxes, and absorption-corrected 2–10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and can be well explained by the continuum suppression with increasing . Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of for the CDF-S AGN population and present reselected subsamples that are complete with respect to . The -complete subsamples enable us to decouple the dependences of on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average and L X of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as .

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Galaxy gas as obscurer – II. Separating the galaxy-scale and nuclear obscurers of active galactic nuclei

Cited by 78 publications

References 115 publications

Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN

Connecting X-ray absorption and 21 cm neutral hydrogen absorption in obscured radio AGN

The NuSTAR Serendipitous Survey: Hunting for the Most Extreme Obscured AGN at >10 keV

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

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