Table 8: Optically type 2 AGN fraction in few representative X-ray surveys.
Sample Energy range Flux range Type 2 fraction Ref./Note
(1) (2) (3) (4) (5)
ROSAT Bright Survey 0.5-2.0 $> \sim 2\times 10^{-12}$ $1 \pm 0.5$% (a)
XMM BSS 0.5-4.5 ${>} 7\times 10^{-14}$ $13 \pm 4$% (b)
XMM HBSS 4.5-7.5 ${>} 7\times 10^{-14}$ $34 \pm 9$% (c)
HELLAS2XMM + Other Surveys 2-10 10-15 - 10-14 $57 \pm 12$% (d)
HELLAS2XMM + Other Surveys 2-10 10-14 - 10-13 $37 \pm 6$% (e)
Columns are as follows: (1) Sample; (2) Energy Selection Band; (3) Investigated flux range; (4) Optically type 2 AGN fraction over the total AGN density in the specific survey; (5) References and Note as follows: (a) From Schwope et al. (2000); (b) From this paper using the BSS sources with Right Ascension below $\rm 5^h$ or above $\rm 17^h$. For this BSS subsample the spectroscopic identification rate is around $88\%$; (c) From this paper using the HBSS sample and taking into account the small number of sources still unidentified as discussed in Sect. 3.6; (d) Fraction of optically obscured AGN from Fiore et al. (2003). The spectroscopic ID rate of the sample in this flux range is ${\sim} 50\%$; (e) Fraction of optically obscured AGN from Fiore et al. (2003). The spectroscopic ID rate of the sample in this flux range is ${\sim} 81\%$.

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