The<i>BeppoSAX</i>High‐Energy Large‐Area Survey. V. The Nature of the Hard X‐Ray Source Population and Its Evolution

Franca, F. La; Fiore, F.; Vignali, C.; Antonelli, L. A.; Comastri, A.; Giommi, P.; Matt, Giorgio; Molendi, S.; Perola, G. C.; Pompilio, Fulvio

doi:10.1086/339575

Cited by 57 publications

(69 citation statements)

References 31 publications

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“…Qualitatively, the main reason for this appears to be the fact that our data suggest a change in the LF faint-end slope, which appears to flatten with increasing redshift. This trend, already observed in previous X-ray surveys (La Franca et al 2002;Ueda et al 2003;Fiore et al 2003;La Franca et al 2005) suggests Fig. 6.…”

Section: The Low Redshift Luminosity Functionsupporting

confidence: 84%

“…At the same time, a growing number of observations at different redshifts, in radio, optical and soft and hard X-ray bands, are suggesting that the faint end slope also evolves, becoming flatter at high redshift (Page et al 1997;Miyaji et al 2000Miyaji et al , 2001La Franca et al 2002;Cowie et al 2003;Ueda et al 2003;Fiore et al 2003;Hunt et al 2004;Cirasuolo et al 2005;Hasinger et al 2005). This evolution, now dubbed as "AGN cosmic downsizing" is described either as a direct evolution in the faint-end slope, or as a luminosity-dependent density evolution (LDDE), and it has been the subject of many speculations, since it implies that the space density of low-luminosity AGN peaks at lower redshift than that of bright ones.…”

Section: Introductionmentioning

confidence: 99%

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The VVDS type-1 AGN sample: the faint end of the luminosity function

Bongiorno¹,

Zamorani

Gavignaud

et al. 2007

A&A

128

133

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In a previous paper (Gavignaud et al. 2006, A&A, 457, 79), we presented the type-1 Active Galactic Nuclei (AGN) sample obtained from the first epoch data of the VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN with redshift up to z = 5 and 17.5 < I AB < 24.0, selected on the basis of their spectra. The sample is thus free of the morphological and color selection biases, that lead to significant incompleteness in the optical surveys of faint AGN. In this paper we present the measurement of the Optical Luminosity Function up to z = 3.6 derived from this sample, we compare our results with previous results from brighter samples both at low and at high redshift and finally, through the estimate of the bolometric luminosity function, we compare them also with the results from X-ray and mid-IR selected samples. Our data, more than one magnitude fainter than previous optical surveys, allow us to constrain the faint part of the luminosity function up to high redshift. A comparison of our data with the 2dF sample at low redshift (1 < z < 2.1) shows that the VVDS data can not be well fitted with the PLE models derived by previous samples. Qualitatively, this appears to be due to the fact that our data suggest the presence of an excess of faint objects at low redshift (1.0 < z < 1.5) with respect to these models. By combining our faint VVDS sample with the large sample of bright AGN extracted from the SDSS DR3 (Richards et al. 2006b, AJ, 131, 2766 and testing a number of different evolutionary models, we find that the model which better represents the combined luminosity functions, over a wide range of redshift and luminosity, is a luminosity dependent density evolution (LDDE) model, similar to those derived from the major Xsurveys. Such a parameterization allows the redshift of the AGN space density peak to change as a function of luminosity and explains the excess of faint AGN that we find at 1.0 < z < 1.5. On the basis of this model we find, for the first time from the analysis of optically selected samples, that the peak of the AGN space density shifts significantly towards lower redshift going to lower luminosity objects. The position of this peak moves from z ∼ 2.0 for M B < −26.0 to z ∼ 0.65 for −22 < M B < −20. This result, already found in a number of X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic downsizing", in which the density of more luminous AGN, possibly associated to more massive black holes, peaks earlier in the history of the Universe (i.e. at higher redshift), than that of low luminosity ones, which reaches its maximum later (i.e. at lower redshift).

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Section: The Low Redshift Luminosity Functionsupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

The VVDS type-1 AGN sample: the faint end of the luminosity function

Bongiorno¹,

Zamorani

Gavignaud

et al. 2007

A&A

128

133

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“…The nature of the sources is rather different from the ROSAT sources, with approximately one-third not having prominent broad lines (La Franca et al 2002;Akiyama et al 2003), while in the bright and faint ROSAT samples (Lehmann et al 2000;Appenzeller et al 2000), more than 90% of the AGN identifications have broad lines. The hard X-ray surveys find very few narrow-line Seyfert 1 galaxies compared to the large fraction in the ROSAT surveys.…”

Section: 43mentioning

confidence: 96%

How are AGN Found?

Mushotzky

2004

Supermassive Black Holes in the Distant Universe

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We discuss the very different methods in each wavelength band for selecting and finding Active Galactic Nuclei (AGN). We briefly review the history of the different techniques for finding AGN and compare and contrast the advantages and difficulties of selection in different wavelength bands. We stress the strong selection effects in each wavelength band and the difficulty of defining complete samples. Of all the techniques presently used, we conclude that selection in the hard X-ray band via imaging and spectroscopy is the most complete and allows the best estimate of the number and evolution of active galaxies. However, all of the techniques have difficulties at low luminosities where emission due to stellar processes can have similar sizes and luminosities. IntroductionLooking at the 60 year history of observations of active galaxies, it is clear that the definition of what they are has strongly influenced the methods of finding them. From our present perspective, many of the techniques used over the past 40 years are not truly appropriate and are more in the line of the famous joke of the drunk looking under the lamp post for his lost car keys. In this chapter, I will use the words Active Galactic Nuclei (alias AGN or quasars) to be the equivalent of radiating supermassive black holes, even though this perspective is very recent.The difficulty in finding AGN is defining what makes the observed 1 radiation different from that due to other processes, in particular those 1 While very frequently the inferred emitted radiation is rather different from that intrinsically produced by the region around the black hole, the nature of surveys is such that we must rely on the observed properties of these sources in order to find and identify them.

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“…La Franca et al 2002;Ueda et al 2003;La Franca et al 2005;Ebrero et al 2009;Aird et al 2010), while the exact behaviour of the XLF, particularly at high redshift (z > 2) has been heavily debated. More recent Fig.…”

Section: -10 Kev Luminosity Functionmentioning

confidence: 99%

The XXL Survey

Fotopoulou

Pacaud

Paltani

et al. 2016

A&A

Self Cite

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Context. X-ray extragalactic surveys are ideal laboratories for the study of the evolution and clustering of active galactic nuclei (AGN). Usually, a combination of deep and wide surveys is necessary to create a complete picture of the population. Deep X-ray surveys provide the faint population at high redshift, while wide surveys provide the rare bright sources. Nevertheless, very wide area surveys often lack the ancillary information available for modern deep surveys. The XXL survey spans two fields of a combined 50 deg 2 observed for more than 6Ms with XMM-Newton, occupying the parameter space that lies between deep surveys and very wide area surveys; at the same time it benefits from a wealth of ancillary data. Aims. This paper marks the first release of the XXL point source catalogue including four optical photometry bands and redshift estimates. Our sample is selected in the 2−10 keV energy band with the goal of providing a sizable sample useful for AGN studies. The limiting flux is F 2−10 keV = 4.8 × 10 −14 erg s −1 cm −2 . Methods. We use both public and proprietary data sets to identify the counterparts of the X-ray point-like sources by means of a likelihood ratio test. We improve upon the photometric redshift determination for AGN by applying a Random Forest classification trained to identify for each object the optimal photometric redshift category (passive, star forming, starburst, AGN, quasi-stellar objects (QSO)). Additionally, we assign a probability to each source that indicates whether it might be a star or an outlier. We apply Bayesian analysis to model the X-ray spectra assuming a power-law model with the presence of an absorbing medium. Results. We find that the average unabsorbed photon index is Γ = 1.85 ± 0.40 while the average hydrogen column density is log N H = 21.07 ± 1.2 cm −2 . We find no trend of Γ or N H with redshift and a fraction of 26% absorbed sources (log N H > 22) consistent with the literature on bright sources (log L x > 44). The counterpart identification rate reaches 96.7% for sources in the northern field, 97.7% for the southern field, and 97.2% in total. The photometric redshift accuracy is 0.095 for the full XMM-XXL with 28% catastrophic outliers estimated on a sample of 339 sources. Conclusions. We show that the XXL-1000-AGN sample number counts extended the number counts of the COSMOS survey to higher fluxes and are fully consistent with the Euclidean expectation. We constrain the intrinsic luminosity function of AGN in the 2−10 keV energy band where the unabsorbed X-ray flux is estimated from the X-ray spectral fit up to z = 3. Finally, we demonstrate the presence of a supercluster size structure at redshift 0.14, identified by means of percolation analysis of the XXL-1000-AGN sample. The XXL survey, reaching a medium flux limit and covering a wide area, is a stepping stone between current deep fields and planned wide area surveys.

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TheBeppoSAXHigh‐Energy Large‐Area Survey. V. The Nature of the Hard X‐Ray Source Population and Its Evolution

Cited by 57 publications

References 31 publications

The VVDS type-1 AGN sample: the faint end of the luminosity function

The VVDS type-1 AGN sample: the faint end of the luminosity function

How are AGN Found?

The XXL Survey

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