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19 April 2024 |
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The Weak Outnumbering the Mighty: Normal Galaxies in Deep Chandra Surveys | | A. E. Hornschemeier
; F. E. Bauer
; D. M. Alexander
; W. N. Brandt
; W. L. W. Sargent
; C. Vignali
; G. P. Garmire
; D. P. Schneider
; | | Date: |
21 Nov 2002 | | Subject: | astro-ph | | Abstract: | Chandra is detecting a significant population of normal and starburst galaxies in extremely deep X-ray exposures. For example, approximately 15% of the sources arising in the 2 Ms Chandra Deep Field-North survey are fairly normal galaxies, where "normal" means "Milky Way-type" X-ray emission rather than simply exhibiting an "optically normal" spectrum. Many of these galaxies are being detected at large look-back times z=0.1-0.5, allowing the study of the evolution of X-ray binary populations over significant cosmological timescales. We are also detecting individual off-nuclear ultraluminous X-ray sources (e.g., X-ray binaries), providing the first direct constraints on the prevalence of lower-mass black holes at significantly earlier times. The X-ray emission from such "normal" galaxies may also be a useful star-formation rate indicator, based on radio/X-ray cross-identifications. We describe the contribution of normal galaxies to the populations which make up the X-ray background and present their directly measured X-ray number counts. We find that normal and starburst galaxies should dominate the 0.5--2 keV number counts at X-ray fluxes fainter than 7e-18 erg cm^{-2} s^{-1} (thus they will outnumber the "mighty" AGN). Finally, we look to the future, suggesting that it is important that the population of X-ray faint normal and starburst galaxies be well constrained in order to design the next generation of X-ray observatories. | | Source: | arXiv, astro-ph/0211487 | | Services: | Forum | Review | PDF | Favorites | |
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