J/A+A/542/A16 X-ray detection of radio-selected SF galaxies (Ranalli+, 2012)
X-ray properties of radio-selected star forming galaxies in the
Chandra-COSMOS survey.
Ranalli P., Comastri A., Zamorani G., Cappelluti N., Civano F.,
Georgantopoulos I., Gilli R., Schinnerer E., Smolcic V., Vignali C.
<Astron. Astrophys. 542, A16 (2012)>
=2012A&A...542A..16R 2012A&A...542A..16R
ADC_Keywords: Galaxies, radio ; Active gal. nuclei ; X-ray sources ; Redshifts
Keywords: X-rays: galaxies - radio continuum: galaxies -
galaxies: fundamental parameters - galaxies: active -
galaxies: high redshift
Abstract:
X-ray surveys contain sizable numbers of star forming galaxies, beyond
the AGN which usually make the majority of detections. Many methods to
separate the two populations are used in the literature, based on
X-ray and multiwavelength properties. We aim at a detailed test of the
classification schemes and to study the X-ray properties of the
resulting samples. We build on a sample of galaxies selected at 1.4GHz
in the VLA-COSMOS survey, classified by Smolcic et al.
(2008ApJS..177...14S 2008ApJS..177...14S) according to their optical colours and observed
with Chandra. A similarly selected control sample of AGN is also used
for comparison. We review some X-ray based classification criteria and
check how they affect the sample composition. The efficiency of the
classification scheme devised by Smolcic et al. (2008ApJS..177...14S 2008ApJS..177...14S)
is such that ∼30% of composite/misclassified objects are expected
because of the higher X-ray brightness of AGN with respect to
galaxies. The latter fraction is actually 50% in the X-ray detected
sources, while it is expected to be much lower among X-ray undetected
sources. Indeed, the analysis of the stacked spectrum of undetected
sources shows, consistently, strongly different properties between the
AGN and galaxy samples. X-ray based selection criteria are then used
to refine both samples. The radio/X-ray luminosity correlation for
star forming (SF) galaxies is found to hold with the same X-ray/radio
ratio valid for nearby galaxies. Some evolution of the ratio may be
possible for sources at high redshift or high luminosity, tough it is
likely explained by a bias arising from the radio selection. Finally,
we discuss the X-ray number counts of star forming galaxies from the
VLA- and C-COSMOS surveys according to different selection criteria,
and compare them to the similar determination from the Chandra Deep
Fields. The classification scheme proposed here may find application
in future works and surveys.
Description:
The tables contains the catalogues of radio-selected SF- and
AGN-candidate sources with an X-ray detection in C-COSMOS. The columns
report: VLA and Chandra names, Chandra ID from Elvis et al. (2009,
Cat. J/ApJS/184/158), redshifts, X-ray fluxes (in erg/s/cm^2) and
luminosities (rest-frame; in erg/s) for the soft (0.5-2.0keV) and hard
(2.0-10keV) bands; rest-frame hardness ratios; X-ray/optical flux
ratios; X-ray/radio flux ratio q; classification from optical
spectroscopy (A: absorption line galaxy; E: emission line galaxy; L:
spectrum with low signal/noise ratio; T1: type-I AGN; T2: type-II
AGN); final classification (see Sect.4.5 in the paper).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 129 33 Catalogue of radio-selected SF-candidate sources
with an X-ray detection in C-COSMOS
table3.dat 129 82 Catalogue of radio-selected AGN-candidate sources
with an X-ray detection in C-COSMOS
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See also:
J/ApJS/184/158 : Chandra COSMOS survey I. (Elvis+, 2009)
J/ApJS/172/46 : VLA-COSMOS survey. II. (Schinnerer+, 2007)
J/ApJS/188/384 : The VLA-COSMOS survey. IV. (Schinnerer+, 2010
Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- --- [COSMOSVLA-]
11- 29 A19 --- COSMOSVLA VLA name (JHHMMSS.ss+DDMMSS.s)
31- 35 A5 --- --- [CXOC-]
36- 51 A16 --- CXOC Chandra name (JHHMMSS.s+DDMMSS)
53- 57 I5 --- Seq Chandra ID from Elvis et al.
(2009, Cat. J/ApJS/184/158)
59- 63 F5.3 --- z Spectroscopic redshift
64 A1 --- n_z [a] a for photometric redshift
66 A1 --- l_FS Limit flag on FS
67- 74 E8.3 mW/m2 FS X-ray flux in soft band (0.5-2keV, erg/cm2/s)
76 A1 --- l_FH Limit flag on FH
77- 84 E8.3 mW/m2 FH X-ray flux in hard band (2-10keV, erg/cm2/s)
86 A1 --- l_LS Limit flag on LS
87- 94 E8.3 10-7W LS X-ray luminosity in soft band (0.5-2keV, erg/s)
96 A1 --- l_LH Limit flag on LH
97-104 E8.3 10-7W LH X-ray luminosity in hard band (2-10keV, erg/s)
106-110 F5.2 --- HR Hardness ratio (H-S)/(H+S)
112 A1 --- l_X/O Limit flag on X/O
113-117 F5.2 [---] X/O X-ray/optical flux ratio (1)
119 A1 --- l_q Limit flag on q
120-124 F5.2 --- q X-ray/radio flux ratio, q=Log(FS/S1.4GHz)
126-127 A2 --- Ocl [T12 EAL] Optical classification (2)
129 I1 --- Xcl [1/3] Classification according to this paper (3)
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Note (1): X-ray/optical flux ratio: X/O=log(FX)+0.4R+5.71,
where FX is the 0.5-2keV flux, and
R is the optical apparent magnitude in the R filter.
Note (2): Optical classification as follows:
T1 = type-I QSO
T2 = type-II QSO
E = emission line galaxy
A = absorption line galaxies
L = low signal/noise
Note (3): This paper classification as follows:
1 = source fulfils all the conditions
2 = source fulfils all conditions but one
3 = source for which there are at least two conditions not satisfied
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Acknowledgements:
Piero Ranalli, piero.ranalli(at)oabo.inaf.it
(End) Patricia Vannier [CDS] 10-May-2012