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CHAPTER 2: AGN SURVEYS WITH XMM-Newton
Table 2.4 Spectroscopic facilities used to identify XMS sources. The first column lists the
ground-based facility; the second, the instrument used, and the last four columns the
spectral range, slit width, spectral resolution and type of the instrument, respectively.
Telescope Instrument Spectral Slit width Spectral Comments
range (Å) (arcsec) resolution a (Å)
WHT/ORM WYFFOS 3900-7100 2.7 b 7 Fibre
WHT/ORM WYFFOS 3900-7100 1.6 b 6 Fibre
WHT/ORM ISIS 3500-8500 1.2-2.0 3.0-3.3 Long slit
TNG/ORM DOLORES 3500-8000 1.0-1.5 14-15 Long slit
NOT/ORM ALFOSC 4000-9000 1.0-1.5 4 Long slit
3.5m/CAHA MOSCA 3300-10000 1.0-1.7 24 Long slit
UT1/ESO FORS2 4400-10000 1.0 6-12 Long slit
a Measured from unsaturated arc lines; b Width of individual fibres
X-ray surveys such as the SXDS ([227]) or the HBS ([50]), which means that
the vast majority of the XMS sources required optical spectroscopy in order to
identify them.
Optical spectroscopy was conducted in a number of ground-based optical facilities
(see Table 2.4). Due to the low surface density of the XMS sources
(∼100 deg −2 ), the use of multiobject slit-mask spectrographs was not very efficient.
In some cases, a fibre spectrometer (WYFFOS) was used to carry out
the identifications, but only for sources brighter than r ′ ∼20.5 mag due to the
problems to substract the sky light that enters the fiber along with the light
coming from the target and, therefore, the strategy that best fitted the optical
magnitude distribution of the sample was long-slit spectroscopy. A number of
these instruments were used in a variety of ground-based telescopes with apertures
ranging from 2.5 m to 8.2 m (see Table 2.4). The spectra thus obtained are
reliable only for identification purposes based on broad/narrow emission lines
and absorption bands, but not for calculating line fluxes or line ratios. The identification
completenesses achieved in each band are listed in Table 2.5. It can be
seen that the high completitudes, in particular in the soft and XID bands, make
the XMS sample specially suitable for cosmic evolution works (see Chapter 5).
The identification breakdown of the XMS sample in several bands is summarised
in Table 2.6, and the different source types are based on those of [13]. Extra-
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