Cosmic X-ray surveys of distant active galaxies

Brandt, W. N.; Alexander, D. M.

doi:10.1007/s00159-014-0081-z

Cited by 324 publications

(237 citation statements)

References 547 publications

(561 reference statements)

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“…Deep X-ray observations using ROSAT, Chandra and XMM-Newton (see review by Brandt & Alexander 2015, and references therewithin) have provided us with the ability to resolve a large fraction of the extragalactic X-ray background. From these observations, and extensive follow-up campaigns, we now have a reasonably complete sample of both soft and hard X-ray selected AGN over a wide range of redshifts.…”

Section: Soft X-ray Luminosity Function Of X-ray Tdesmentioning

confidence: 99%

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

Auchettl

Ramírez-Ruiz

Guillochon

2018

ApJ

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One of the main challenges of current tidal disruption events (TDEs) studies is that emission arising from AGN activity may potentially mimic the expected X-ray emission of a TDE. Here we compare the X-ray properties of TDEs and AGN to determine a set of characteristics which would allow us to discriminate between flares arising from these two objects. We find that at peak, TDEs are brighter than AGN found at similar redshifts. However, compared to preflare upperlimits, highly variable AGN can produce flares of a similar order of magnitude as those seen from X-ray TDEs. Nevertheless, TDEs decay significantly more monotonically, and their emission exhibits little variation in spectral hardness as a function of time. We also find that X-ray TDEs are less absorbed, and their emission is much softer than the emission detected from AGN found at similar redshifts. We derive the X-ray luminosity function (LF) for X-ray TDEs using the events from Auchettl et al. (2017). Interestingly, our X-ray LF matches closely the theoretically derived LF by Milosavljević et al. (2006) which assumes a higher TDE rate currently estimated from observations. Using our results and the results of Stone & Metzger (2016), we estimate a TDE rate of (0.7 − 4.7) × 10 −4 yr −1 per galaxy, higher than current observational estimates. We find that TDEs can contribute significantly to the LF of AGN for z 0.4, while there is no evidence that TDEs influence the growth of 10 6−7 M BHs. However, BHs < 10 6 M can grow from TDEs arising from super-Eddington accretion without contributing significantly to the observed AGN LF at z = 0.

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Section: Soft X-ray Luminosity Function Of X-ray Tdesmentioning

confidence: 99%

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

Auchettl

Ramírez-Ruiz

Guillochon

2018

ApJ

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“…Figure 9 shows the distribution of host galaxy inclinations for local CTAGNs (adapted from Gandhi et al 2014), 9 as compared to the expected distribution from random galaxy orientations. If we are missing CTAGNs in the local universe due to AGN host inclination selection efcertain quantities, therefore the inferred value is subjected to errors of a factor of a few (Brandt & Alexander 2015).…”

Section: 12mentioning

confidence: 99%

A New Compton-thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR

Annuar

Alexander

Gandhi

et al. 2017

ApJ

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT NGC 1448 is one of the nearest luminous galaxies (L 8−1000µm > 10 9 L ⊙ ) to ours (z = 0.00390), and yet the active galactic nucleus (AGN) it hosts was only recently discovered, in 2009. In this paper, we present an analysis of the nuclear source across three wavebands: mid-infrared (MIR) continuum, optical, and X-rays. We observed the source with the Nuclear Spectroscopic Telescope Array (NuSTAR), and combined this data with archival Chandra data to perform broadband X-ray spectral fitting (≈0.5-40 keV) of the AGN for the first time. Our X-ray spectral analysis reveals that the AGN is buried under a Compton-thick (CT) column of obscuring gas along our line-of-sight, with a column density of N H (los) 2.5 × 10 24 cm −2 . The best-fitting torus models measured an intrinsic 2-10 keV luminosity of L 2−10,int = (3.5-7.6) × 10 40 erg s −1 , making NGC 1448 one of the lowest luminosity CTAGNs known. In addition to the NuSTAR observation, we also performed optical spectroscopy for the nucleus in this edge-on galaxy using the European Southern Observatory New Technology Telescope. We re-classify the optical nuclear spectrum as a Seyfert on the basis of the Baldwin-Philips-Terlevich diagnostic diagrams, thus identifying the AGN at optical wavelengths for the first time. We also present high spatial resolution MIR observations of NGC 1448 with Gemini/TReCS, in which a compact nucleus is clearly detected. The absorption-corrected 2-10 keV luminosity measured from our X-ray spectral analysis agrees with that predicted from the optical [Oiii]λ5007Å emission line and the MIR 12µm continuum, further supporting the CT nature of the AGN.

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“…A large number of deep and wide X-ray surveys have been carried out, taking advantage of the efficiency and power of X-ray selection (see a recent review by Brandt & Alexander 2015). A number of studies have measured the X-ray luminosity function (XLF) of AGNs out to high redshifts using these samples (e.g.…”

Section: Introductionmentioning

confidence: 99%

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Aird

Coil

Georgakakis

et al. 2015

Monthly Notices of the Royal Astronomical Society

373

559

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We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out to z ∼ 5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately modelling the evolution of the XLFs of unabsorbed (20 < log N H < 22) and absorbed (22 < log N H < 24) AGNs, seeking a model that can reconcile both the hard-and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ∼ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations.

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Cosmic X-ray surveys of distant active galaxies

Cited by 324 publications

References 547 publications

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

A Comparison of the X-Ray Emission from Tidal Disruption Events with those of Active Galactic Nuclei

A New Compton-thick AGN in Our Cosmic Backyard: Unveiling the Buried Nucleus in NGC 1448 with NuSTAR

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

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