Observations of Faint, Hard-Band X-Ray Sources in the Field of CRSS J0030.5+2618 with the [ITAL]CHANDRA X-RAY OBSERVATORY[/ITAL][ITAL]Chandra X-Ray Observatory[/ITAL] and the Hobby-Eberly Telescope

Brandt, W. N.; Hornschemeier, A. E.; Schneider, Donald P.; Garmire, G. P.; Chartas, G.; Hill, Gary J.; MacQueen, Phillip J.; Townsley, Leisa K.; Burrows, D. N.; Koch, T. S.; Nousek, J. A.; Ramsey, Lawrence W.

doi:10.1086/301367

Cited by 40 publications

(15 citation statements)

References 28 publications

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“…At fainter magnitude one would expect both a larger fraction of dust-reddened objects (in analogy with indications from the X-ray data, Brandt et al 2000;Mushotzky et al 2000) and a more significant contamination from the host galaxy.…”

Section: Colors Of Type-1 Agnmentioning

confidence: 66%

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: Colors Of Type-1 Agnmentioning

confidence: 66%

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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“…Chandra observations have confirmed and extended down to lower fluxes these results (Mushotzky et al 2000;Fiore et al 2000b;Brandt et al 2000;Giacconi et al 2001;Barger et al 2001).…”

Section: Introductionmentioning

confidence: 65%

The BeppoSAX High Energy Large Area Survey

Vignali

Comastri

Fiore

et al. 2001

A&A

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Abstract. We present a comprehensive study of the soft X-ray properties of the BeppoSAX High-Energy Large Area Survey (HELLAS) sources. A large fraction (about 2/3) of the hard X-ray selected sources is detected by ROSAT. The soft X-ray colors for many of these objects, along with the 0.5-2 keV flux upper limits for those undetected in the ROSAT band, do imply the presence of absorption. The comparison with the ROSAT Deep Survey sources indicates that a larger fraction of absorbed objects among the HELLAS sources is present, in agreement with their hard X-ray selection and the predictions of the X-ray background synthesis models. Another striking result is the presence of a soft (additional) X-ray component in a significant fraction of absorbed objects.

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“…Several deep hard X-ray surveys (>2 keV) have been started with Chandra and XMM-Newton to date (e.g., Brandt et al 2000;Mushotzky et al 2000;Hornschemeier et al 2001;Giacconi et al 2001;Hasinger et al 2001), but most of their optical identification is at an early stage or their total number of sources is still relatively small (Barger et al 2001).…”

Section: Introductionmentioning

confidence: 99%

The ROSAT Deep Survey

Lehmann¹,

Hasinger²,

Schmidt³

et al. 2001

A&A

Self Cite

163

232

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Abstract. The ROSAT Deep Surveys in the direction of the Lockman Hole are the most sensitive X-ray surveys performed with the ROSAT satellite. About 70-80% of the X-ray background has been resolved into discrete sources at a flux limit of ∼10 −15 erg cm −2 s −1 in the 0.5-2.0 keV energy band. A nearly complete optical identification of the ROSAT Deep Survey (RDS) has shown that the great majority of sources are AGNs. We describe in this paper the ROSAT Ultra Deep Survey (UDS), an extension of the RDS in the Lockman Hole. The Ultra Deep Survey reaches a flux level of 1.2 10 −15 erg cm −2 s −1 in 0.5-2.0 keV energy band, a level ∼4.6 times fainter than the RDS. We present nearly complete spectroscopic identifications (90%) of the sample of 94 X-ray sources based on low-resolution Keck spectra. The majority of the sources (57) are broad emission line AGNs (type I), whereas a further 13 AGNs show only narrow emission lines or broad Balmer emission lines with a large Balmer decrement (type II AGNs) indicating significant optical absorption. The second most abundant class of objects (10) are groups and clusters of galaxies (∼11%). Further we found five galactic stars and one "normal" emission line galaxy. Eight X-ray sources remain spectroscopically unidentified. We see no evidence for any change in population from the RDS survey to the UDS survey. The photometric redshift determination indicates in three out of the eight sources the presence of an obscured AGN. Their photometric redshifts, assuming that the spectral energy distribution (SED) in the optical/near-infrared is due to stellar processes, are in the range of 1.2 ≤ z ≤ 2.7. These objects could belong to the long-sought population of type 2 QSOs, which are predicted by the AGN synthesis models of the X-ray background. Finally, we discuss the optical and soft X-ray properties of the type I AGN, type II AGN, and groups and clusters of galaxies, and the implication to the X-ray background.

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Observations of Faint, Hard-Band X-Ray Sources in the Field of CRSS J0030.5+2618 with the [ITAL]CHANDRA X-RAY OBSERVATORY[/ITAL][ITAL]Chandra X-Ray Observatory[/ITAL] and the Hobby-Eberly Telescope

Cited by 40 publications

References 28 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

The BeppoSAX High Energy Large Area Survey

The ROSAT Deep Survey

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