The Chandra Cosmos-Legacy Survey: Source X-Ray Spectral Properties

Marchesi, S.; Lanzuisi, G.; Civano, F.; Iwasawa, K.; Suh, Hyewon; Zamorani, G.; Allevato, V.; Griffiths, R. E.; Miyaji, Takeshi; Ranalli, P.; Salvato, M.; Schawinski, Kevin; Silverman, John D.; Treister, Ezequiel; Urry, C. Megan; Vignali, C.

doi:10.3847/0004-637x/830/2/100

Cited by 140 publications

(208 citation statements)

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“…These include unobscured AGN which have a N H < 10 22 cm −2 , obscured AGN which have a N H > 10 22 cm −2 and Compton thick AGN that have N H > 10 24 cm −2 . In the low-redshift (z < 1 − 2) universe, the AGN population is dominated by unobscured and obscured AGN, and the X-ray emission from these objects is best fit with a power-law index Γ ∼ 1.75 (e.g., Tozzi et al 2006;Marchesi et al 2016). …”

Section: Spectral Propertiesmentioning

confidence: 99%

“…The hardness of the X-ray emission arising from an AGN over various redshifts have been studied extensively in a deep extragalactic X-ray survey using Chandra (e.g., Hickox et al 2009;Xue et al 2011;Marchesi et al 2016) and XMMNewton (e.g., Cappelluti et al 2009;Lanzuisi et al 2015). It has been shown that AGN with extended optical counterparts tend to exhibit harder X-ray emission due to the presence of significant gas absorbing softer photons, while AGN without a resolved counterpart tend to be softer (Hickox et al 2009).…”

Section: Spectral Hardness Evolutionmentioning

confidence: 99%

“…The X-ray properties of the AGN population up to a redshift of z ∼ 5 have been extensively studied using multiple deep extragalactic X-ray surveys (e.g., Tozzi et al 2006;Tueller et al 2008;Lanzuisi et al 2015;Marchesi et al 2016;Vito et al 2016, and references therewithin). From these studies, it has been found that there are several populations of AGN which can be distinguished based on their column density (N H ).…”

Section: Spectral Propertiesmentioning

confidence: 99%

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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: Spectral Propertiesmentioning

confidence: 99%

Section: Spectral Hardness Evolutionmentioning

confidence: 99%

Section: Spectral Propertiesmentioning

confidence: 99%

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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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“…The evaluation of possible contributions to our spectra from additional flux from sources located within the spectral extraction radii is performed using the source information provided by the COSMOS-Legacy catalog and the low-energy spectra extracted by Marchesi et al (2016). We did not try joint broadband models with the NuSTAR data (except for the CT source cosmos330) through complicated models, but rather used a flux estimate at low energy with a simple absorbed power-law model to evaluate possible contamination in common energy bands.…”

Section: Appendix Notes On Single Sourcesmentioning

confidence: 99%

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Zappacosta

Comastri

Civano

et al. 2018

ApJ

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We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 14 =´-( -) erg s cm 1 2 --in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z 0 2.1 = -(median z 0.58 á ñ = ). The spectral analysis is performed over the broad 0.5-24keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at 10 keV > to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (N H ), reflection parameter (R), and 10-40keV luminosity (L X ). Heavily obscured ( N log cm 23AGN constitute ∼25% (15-17 sources) and ∼2-3% (1-2 sources) of the sample, respectively. The observed N H distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of N H , accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to N log cm 20 24AGN is poorly constrained, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction ( f abs ) of obscured AGN ( N log cm 22 24as a function of L X in agreement with CXBPSM and previous z 1 < X-ray determinations. Furthermore, f abs at z 0.1 0.5 = -and L log erg s 43.6 44.3agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with L X (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.

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“…In this framework, significant results have been obtained thanks to a number of high-sensitivityX-ray surveys with large and medium sky coverage,such as C-COSMOS Lanzuisi et al 2013), XMM-COSMOS ), COSMOS-Legacy Marchesi et al 2016), CDF-S Luo et al 2008;Xue et al 2011;Luo et al 2017), CDF-N (Brandt et al 2001;Alexander et al 2003;Xue et al 2016), Extended CDF-S (Lehmer et al 2005;Virani et al 2006;Xue et al 2016), AEGIS-X (Laird et al 2009), XMM-LSS (Pierre et al 2007(Pierre et al , 2016, and the XMM survey of CDF-S (Comastri et al 2011;Ranalli et al 2013). Among this set, the CDF-S survey, which recently reached a cumulative exposure time of 7Ms, represents the deepest observation of the X-ray sky obtained as of today and in the foreseeable future (Luo et al 2017).…”

Section: Introductionmentioning

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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The Chandra Cosmos-Legacy Survey: Source X-Ray Spectral Properties

Cited by 140 publications

References 96 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

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

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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