TRACKING DOWN THE SOURCE POPULATION RESPONSIBLE FOR THE UNRESOLVED COSMIC 6-8 keV BACKGROUND

Journal Article · Sat Oct 20 00:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/758/2/129· OSTI ID:22086509

Xue, Y Q; Wang, S X; Brandt, W N; Luo, B; Schneider, D P; Young, M ^[1]; Alexander, D M ^[2]; Bauer, F E ^[3]; Comastri, A; Gilli, R ^[4]; Fabian, A C ^[5]; Lehmer, B D ^[6]; Vignali, C ^[7]

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1. Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
2. Department of Physics, Durham University, Durham DH1 3LE (United Kingdom)
3. Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)
4. INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, Bologna (Italy)
5. Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
6. Department of Physics and Astronomy, The Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States)
7. Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, Bologna (Italy)

Using the 4 Ms Chandra Deep Field-South (CDF-S) survey, we have identified a sample of 6845 X-ray-undetected galaxies that dominates the unresolved Almost-Equal-To 20%-25% of the 6-8 keV cosmic X-ray background (XRB). This sample was constructed by applying mass and color cuts to sources from a parent catalog based on GOODS-South Hubble Space Telescope z-band imaging of the central 6'radius area of the 4 Ms CDF-S. The stacked 6-8 keV detection is significant at the 3.9{sigma} level, but the stacked emission was not detected in the 4-6 keV band, which indicates the existence of an underlying population of highly obscured active galactic nuclei (AGNs). Further examinations of these 6845 galaxies indicate that the galaxies on the top of the blue cloud and with redshifts of 1 {approx}< z {approx}< 3, magnitudes of 25 {approx}< z {sub 850} {approx}< 28, and stellar masses of 2 Multiplication-Sign 10{sup 8} {approx}< M {sub *}/M {sub Sun} {approx}< 2 Multiplication-Sign 10{sup 9} make the majority contributions to the unresolved 6-8 keV XRB. Such a population is seemingly surprising given that the majority of the X-ray-detected AGNs reside in massive ({approx}> 10{sup 10} M {sub Sun }) galaxies. We discuss constraints upon this underlying AGN population, supporting evidence for relatively low mass galaxies hosting highly obscured AGNs, and prospects for further boosting the stacked signal.

• OSTI ID: 22086509
• Journal Information: Astrophysical Journal, Vol. 758, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ASTROPHYSICS
CATALOGS
COLOR
COSMIC PHOTONS
GALAXY NUCLEI
GAMMA ASTRONOMY
KEV RANGE
MASS
PHOTON EMISSION
RED SHIFT
TELESCOPES
X RADIATION
X-RAY GALAXIES