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2008MNRAS.388..849B - Mon. Not. R. Astron. Soc., 388, 849-862 (2008/August-1)
A multi-coloured survey of NGC253 with XMM-Newton: testing the methods used for creating luminosity functions from low-count data.
BARNARD R., SHAW GREENING L. and KOLB U.
Abstract (from CDS):
X-ray luminosity functions (XLFs) of galaxy populations are often used to characterize their properties. There are several methods for estimating the luminosities of X-ray sources with few photons. We have obtained spectral fits for the brightest 140 sources in the 2003 XMM-Newton observation of NGC253, and compare the best-fitting luminosities of those 69 non-nuclear sources associated with NGC253 with luminosities derived using other methods. We find the luminosities obtained from these various methods to vary systematically by a factor of up to 3 for the same data; this is largely due to differences in absorption. We therefore conclude that assuming Galactic absorption is probably unwise; rather, one should measure the absorption for the population.
A remarkable correlation has been reported between the XLFs of galaxies and their star formation rates. However, the XLFs used in that study were obtained using several different methods. If the sample galaxies were revisited and a single method were applied, then this correlation may become stronger still.
In addition, we find that standard estimations of the background contribution to the X-ray sources in the field are insufficient. We find that the background active galactic nuclei (AGN) may be systematically more luminous than previously expected. However, the excess in our measured AGN XLF with respect to the expected XLF may be due to an as yet unrecognized population associated with NGC253.
Abstract Copyright: © 2008 The Authors. Journal compilation © 2008 RAS
Journal keyword(s): galaxies: individual: NGC253 - X-rays: binaries - X-rays: general
VizieR on-line data: <Available at CDS (J/MNRAS/388/849): tablea1.dat tablea2.dat>
Nomenclature: Table A1: [BGK2008] SNNN (Nos S1-S185).
Status at CDS : All or part of tables of objects could be ingested in SIMBAD with priority 2.
Simbad objects: 8
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