**Table 3:** OFS with a spectroscopic redshift in the CDF-S.
XID^a	CXO CDFS^b	R^c	R-K^d	z^e	Q^f	Opt^g	X-ray^h	FSⁱ	FH^j	HR^k
45	J033225.8-274306	25.3	5.1	2.291	1	LEX	QSO abs	$1.02\pm0.08$	$4.67\pm0.46$	$-0.12\pm0.06$
54	J033214.7-275422	25.7	<5.4	2.561	3	HEX	QSO abs	$0.61\pm0.07$	$3.37\pm0.46$	$-0.01\pm0.09$
117	J033203.1-274450	25.5	4.9	2.573	3	HEX	AGN abs	$0.61\pm0.07$	$1.19\pm0.34$	$-0.52\pm0.11$
263	J033218.9-275136	25.3	5.1	3.660	3	HEX	QSO abs	$0.10\pm0.04$	$1.23\pm0.31$	$+0.35\pm0.20$
265	J033233.4-274236	>26	>5.2	1.215^m	1	LEX	AGN abs	$0.19\pm0.05$	$3.33\pm0.45$	$+0.50\pm0.11$
606	J033225.0-275009	25.3	4.3	1.037	1	LEX	AGN abs	<0.06	$1.25\pm0.30$	$+0.68\pm0.19$

^a XID from Giacconi et al. (2002).
^b IAU registered name, based on original X-ray coordinates.
^c Vega R magnitude for the optical counterpart.
^d Vega R-K colour for the optical counterpart.
^e Optical spectroscopic redshift for the optical counterpart (Szokoly et al. 2004).
^f Quality flag of the optical spectrum (see Szokoly et al. 2004).
^g Optical classification (see Szokoly et al. 2004).
^h X-ray classification.
ⁱ Flux in soft (0.5-2 keV) band, in units of 10^-15 erg cm^-2 s^-1.
^j Flux in hard (2-10 keV) band, in units of 10^-15 erg cm^-2 s^-1.
^k Hardness ratio, defined as (H-S)/(H+S) where H and S are the net counts in the hard and soft bands, respectively.

Source LaTeX | All tables | In the text

	1 Introduction
	2 The sample
	3 Comparison of the optically bright and optically faint X-ray source samples
	4 Photometric redshift technique applied to an X-ray selected sample
	5 The properties of OFS with spectroscopic redshifts
	6 X-ray-to-optical flux ratios
	7 X-ray spectroscopy
	8 X-ray absorbed QSOs
	9 Ultra deep field
	10 Conclusions
	References