Astron.Astrophys.329:482-494,1998 The ROSAT Deep Survey in the Lockman Hole is the most sensitive X-ray survey
performed to date, encompassing an exposure time of 207 ksec with the PSPC and
a total ...of 1.32 Msec with the HRI aboard ROSAT. Here we present the complete
catalogue of 50 X-ray sources with PSPC fluxes (0.5--2 keV) above $ 5.5 \times
10^{-15} erg cm^{-2} s^{-1}$. The optical identifications are discussed in an
accompanying paper (Schmidt et al., 1997). We also derive a new log(N)--log(S)
function reaching a source density of $970 \pm 150 deg^{-2}$ at a limiting flux
of $10^{-15} erg cm^{-2} s^{-1}$. At this level 70-80% of the 0.5--2 keV X-ray
background is resolved into discrete sources. Utilizing extensive simulations
of artificial PSPC and HRI fields we discuss in detail the effects of source
confusion and incompleteness both on source counts and on optical
identifications. Based on these simulations we set conservative limits on flux
and on off-axis angles, which guarantee a high reliability of the catalogue. We
also present simulations of shallower fields and show that surveys, which are
based on PSPC exposures longer than 50 ksec, become severely confusion limited
typically a factor of 2 above their $4\sigma$ detection threshold. This has
consequences for recent claims of a possible new source population emerging at
the faintest X-ray fluxes.
Keywords: surveys -- cosmology: diffuse radiations -- X-rays: galaxies
Radio surveys with the Australia Telescope Compact Array have been carried
out at 1.4 and 2.4 GHz with a limiting flux of 0.2 mJy at each frequency in the
Marano Field, in which deep optical and ...X-ray (ROSAT) data are also available.
In this paper we present the two radio samples, complete at the 5 sigma local
level, consisting of 63 and 48 sources respectively at 1.4 and 2.4 GHz. The 1.4
GHz normalized differential source counts show a flattening below about one
mJy, in agreement with the results from previous surveys. The 2.4 GHz counts,
which are the deepest at this or similar frequencies (e.g. 2.7 GHz), agree well
with the 2.7 GHz counts at higher fluxes and with the extrapolations down to 2
mJy based on fluctuation analyses. The 2.4-1.4 GHz spectral index distributions
are presented for both the complete samples in two flux density intervals. The
median spectral index for the 1.4 GHz sample remains constant at about 0.8,
down to the lowest fluxes (S(1.4)=0.2 mJy), while for the higher frequency
sample the spectral index distribution flattens in the lower flux density
interval (S(2.4) < 0.8 mJy). A significant number of sources with inverted
spectrum (< 0) does appear in both samples, at low flux level (< 2 mJy). These
sources, which are about 25% of the complete sample at 2.4 GHz, are probably
the ``bright'' counterpart of the inverted spectrum sources which appear to be
almost 50% of the sources in the even deeper radio surveys (at about 20-40
microJy).
Astron.Astrophys. 329 (1998) 495-503 The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with
fluxes in the $0.5 - 2$ keV band larger than 5.5 $10^{-15}$ erg cm$^{-2}$
s$^{-1}$ in ...the Lockman field (Hasinger et al., Paper I). We have obtained deep
broad-band CCD images of the field and spectra of many optical objects near the
positions of the X-ray sources. We define systematically the process leading to
the optical identifications of the X-ray sources. For this purpose, we
introduce five identification (ID) classes that characterize the process in
each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of
galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified
so far; two of these objects may have an unusually large ratio of X-ray to
optical flux.
Keywords: surveys -- galaxies: active -- quasars: emission lines -- galaxies:
Seyfert -- X-rays: galaxies
The ROSAT Deep Survey in the Lockman Hole is the most sensitive X-ray survey performed to date, encompassing an exposure time of 207 ksec with the PSPC and a total of 1.32 Msec with the HRI aboard ...ROSAT. Here we present the complete catalogue of 50 X-ray sources with PSPC fluxes (0.5--2 keV) above \( 5.5 \times 10^{-15} erg cm^{-2} s^{-1}\). The optical identifications are discussed in an accompanying paper (Schmidt et al., 1997). We also derive a new log(N)--log(S) function reaching a source density of \(970 \pm 150 deg^{-2}\) at a limiting flux of \(10^{-15} erg cm^{-2} s^{-1}\). At this level 70-80% of the 0.5--2 keV X-ray background is resolved into discrete sources. Utilizing extensive simulations of artificial PSPC and HRI fields we discuss in detail the effects of source confusion and incompleteness both on source counts and on optical identifications. Based on these simulations we set conservative limits on flux and on off-axis angles, which guarantee a high reliability of the catalogue. We also present simulations of shallower fields and show that surveys, which are based on PSPC exposures longer than 50 ksec, become severely confusion limited typically a factor of 2 above their \(4\sigma\) detection threshold. This has consequences for recent claims of a possible new source population emerging at the faintest X-ray fluxes. Keywords: surveys -- cosmology: diffuse radiations -- X-rays: galaxies
Radio surveys with the Australia Telescope Compact Array have been carried out at 1.4 and 2.4 GHz with a limiting flux of 0.2 mJy at each frequency in the Marano Field, in which deep optical and ...X-ray (ROSAT) data are also available. In this paper we present the two radio samples, complete at the 5 sigma local level, consisting of 63 and 48 sources respectively at 1.4 and 2.4 GHz. The 1.4 GHz normalized differential source counts show a flattening below about one mJy, in agreement with the results from previous surveys. The 2.4 GHz counts, which are the deepest at this or similar frequencies (e.g. 2.7 GHz), agree well with the 2.7 GHz counts at higher fluxes and with the extrapolations down to 2 mJy based on fluctuation analyses. The 2.4-1.4 GHz spectral index distributions are presented for both the complete samples in two flux density intervals. The median spectral index for the 1.4 GHz sample remains constant at about 0.8, down to the lowest fluxes (S(1.4)=0.2 mJy), while for the higher frequency sample the spectral index distribution flattens in the lower flux density interval (S(2.4) < 0.8 mJy). A significant number of sources with inverted spectrum (< 0) does appear in both samples, at low flux level (< 2 mJy). These sources, which are about 25% of the complete sample at 2.4 GHz, are probably the ``bright'' counterpart of the inverted spectrum sources which appear to be almost 50% of the sources in the even deeper radio surveys (at about 20-40 microJy).
The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the \(0.5 - 2\) keV band larger than 5.5 \(10^{-15}\) erg cm\(^{-2}\) s\(^{-1}\) in the Lockman field (Hasinger et ...al., Paper I). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux. Keywords: surveys -- galaxies: active -- quasars: emission lines -- galaxies: Seyfert -- X-rays: galaxies
