Open AccessThe European Large Area ISO Survey – VII. ROSAT observations of ELAIS sources
Author(s) -
Basilakos S.,
Georgantopoulos I.,
PérezFour I.,
Efstathiou A.,
RowanRobinson M.,
CabreraGuerra F.,
GonzálezSolares E.,
Alexander D. M.,
Serjeant S.,
Oliver S.
Publication year - 2002
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2002.05191.x
Subject(s) - physics , qsos , rosat , astrophysics , galaxy , redshift , luminosity , active galactic nucleus , quasar , sky , infrared , flux (metallurgy) , luminous infrared galaxy , astronomy , stars , line (geometry) , doubly ionized oxygen , spectral line , emission spectrum , materials science , geometry , mathematics , metallurgy
We present a cross‐correlation between the European Large Area ISO Survey (ELAIS) 15‐μm ISO survey with the ROSAT (0.1–2 keV) all‐sky survey and the pointed observations WGACAT source catalogue. The resulting sample contains 15 objects. Optical spectroscopic identifications exist for 13 objects: six broad‐line quasi‐stellar objects (QSOs), four narrow‐line galaxies (NLGs) or type 2 active galactic nuclei (AGN) and three stars. We have used both the X‐ray to infrared (IR) luminosity flux ratio f x / f IR and the X‐ray hardness ratios diagnostics to estimate the amount of obscuration in these objects. The X‐ray spectrum of the narrow‐line galaxies does not present strong evidence for obscuration; however, the low f x / f IR ratio combined with the high X‐ray luminosities suggest that at least one of the NLGs is associated with an obscured Seyfert nucleus. Four out of the six QSOs present high f x / f IR ratios and steep X‐ray spectra with Γ>2 . One QSO (ELAISC15−J133442+375736) at a redshift of z =1.89 , has an abnormally low X‐ray/IR flux ratio, with its infrared luminosity approaching that of an hyperluminous galaxy (∼10 12.98 h −2 L ⊙ ). Finally, one radio‐loud QSO is the hardest X‐ray source in our sample, presenting strong evidence for a high absorbing column ( N H ∼10 22 cm ‐2 ) .