The ROSAT Deep Survey - VI. X-ray sources and Optical identifications of the Ultra Deep Survey

By I. Lehmann, G. Hasinger, M. Schmidt, R. Giacconi, J. Trümper, G. Zamorani, J. Gunn, L. Pozzetti, D. P. Schneider, T. Stanke and 3 more. 2001

134 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/77382201642e69cfd47708c6a50c8ed2ea75c33f

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. D. M. Alexander
2. W. N. Brandt
3. P. Hopkins
4. L. Hernquist
5. G. Hasinger
6. A. Koekemoer
7. P. Capak
8. Mara Salvato

Citations in the corpus

• Deep radio imaging of the SCUBA 8-mJy survey fields: submillimetre source identifications and redshift distribution (2002, background): “This X-ray source was also detected in the Rosat Ultra Deep HRI survey by Lehmann et al. (2001), who propose that the northernmost optical/IR source in Fig.”
• The Chandra Deep Field-South: Optical Spectroscopy. I. (2003, methodology): “This correction is deferred to a later paper concentrating on X-ray spectral analysis of the CDFS sources based on the Chandra and XMM-Newton data.”
• A Classic Type 2 QSO (2001, unknown): “7 in Lehmann et al. 2001).”
• DEEP EXTRAGALACTIC X-RAY SURVEYS (2005, background): “Extensive optical follow-up spectroscopy identified the bulk of these sources as AGN (e.g., McHardy et al. 1998; Schmidt et al. 1998; Zamorani et al. 1999; Lehmann et al. 2001), demonstrating that at least the 0.5–2 keV CXRB is predominantly due to accretion onto SMBH, integrated over cosmic time.”
• The XMM-Newton Wide-Field Survey in the COSMOS Field. III. Optical Identification and Multiwavelength Properties of a Large Sample of X-Ray-Selected Sources (2006, result): “This value is similar to that reported in the ROSAT Deep Survey (Lehmann et al. 2001) and in the ChaMP survey (Green et al. 2004), from the optical identification of large samples (100–300) of soft X–ray selected sources at limiting fluxes similar to that of COSMOS.”
• The Cosmic Evolution of Hard X-Ray-selected Active Galactic Nuclei (2004, methodology): “Steffen et al. (2004) determined median redshifts for the surveys used in the present paper combined with other ROSAT (Lehmann et al. 2001) and XMM-Newton (Mainieri et al. 2002; Fiore et al. 2003) surveys.”
• The faint radio sky: radio astronomy becomes mainstream (2016, background): “Before the launch of theChandraand XMM-Newtonsatellites in 1999 the best one could do with ROSAT was a soft X-ray limit fx ≈ 10−15 erg cm−2 s −1 in onevery small area of the sky (∼ 0.3 deg2: Lehmann et al., 2001).”
• Cosmological Evolution of the Hard X-Ray Active Galactic Nucleus Luminosity Function and the Origin of the Hard X-Ray Background (2003, methodology): “For sources in the Lockman hole we adopt the same classification as in Lehmann et al. (2001).”
• The Chandra Deep Field North Survey. VI. The Nature of the Optically Faint X-Ray Source Population (2001, background): “Luminous AGN (both BLAGN and NLAGN) have typical X-ray-to-optical flux ratios, in both the soft and hard bands, of−1< log( fXfR )< 1 (e.g., Schmidt et al. 1998; Akiyama et al. 2000; Paper II; Lehmann et al. 2001).”
• Luminosity-dependent evolution of soft X-ray selected AGN : New Chandra and XMM-Newton surveys (2005, methodology): “Due to the extreme faintness of the optical counterparts, the lowest identification fractions are achieved in the recent deepest samples: 87% for the XMM–Newton survey in the Lockman Hole and 88% in the CDF–N.”
• The Resolved Fraction of the Cosmic X-Ray Background (2003, background): “The great majority of sources brighter than 5 10 15 ergs s 1 cm 2 were optically identified with unobscured (type I) active galactic nuclei (AGNs; Schmidt et al. 1998; Lehmann et al. 2001).”
• THE CHANDRA COSMOS SURVEY. III. OPTICAL AND INFRARED IDENTIFICATION OF X-RAY POINT SOURCES (2012, methodology): “…a soft X-ray flux was used for this relation (see Introduction), and the majority of luminous spectroscopically identified AGN (both BLAGN and NLAGN) in the Einstein and ASCA surveys were characterized by X/O=0±1 (Schmidt et al. 1998, Stocke et al. 1991, Akiyama et al. 2000, Lehmann et al. 2001).”
• Most Supermassive Black Holes Must Be Rapidly Rotating (2001, methodology): “Using (from E94 andAa (ox)S p 1.35 in agreement with the results from theROSAT deep surveys; Lehmann et al. 2001), we obtain .a(ox) p 1.43eff Reassuringly, we obtain the same result starting from the optically selected sample of PG quasars (Schmidt & Green 1983).”
• THE CHANDRA COSMOS LEGACY SURVEY: OPTICAL/IR IDENTIFICATIONS (2015, methodology): “The relation was first used in the soft X-ray band: in this band, the largest part of bright spectroscopically identified AGN, both BLAGN and non-BLAGN, lie in the region X/O=0±1 (e.g. Schmidt et al. 1998; Stocke et al. 1991; Lehmann et al. 2001), hereafter defined as the “soft locus”.”