The XMM-Newton bright serendipitous survey

Abstract

Aims. We present the optical classification and redshift of 348 X-ray selected sources from the XMM-Newton Bright Serendipitous Survey (XBS), which contains a total of 400 objects (identification level = 87%). About 240 are new identifications. In particular, we discuss in detail the classification criteria adopted for the active galactic nuclei (AGNs) population. Methods. By means of systematic spectroscopic campaigns using various telescopes and through the literature search, we have collected an optical spectrum for the large majority of the sources in the XBS survey and applied a well-defined classification "flow chart". Results. We find that the AGNs represent the most numerous population at the flux limit of the XBS survey (∼10 −13 erg cm −2 s −1 ) constituting 80% of the XBS sources selected in the 0.5-4.5 keV energy band and 95% of the "hard" (4.5-7.5 keV) selected objects. Galactic sources populate the 0.5-4.5 keV sample significantly (17%) and only marginally (3%) the 4.5-7.5 keV sample. The remaining sources in both samples are clusters/groups of galaxies and normal galaxies (i.e. probably not powered by an AGN). Furthermore, the percentage of type 2 AGNs (i.e. optically absorbed AGNs with A V > 2 mag) dramatically increases going from the 0.5-4.5 keV sample ( f = N AGN2 /N AGN = 7%) to the 4.5-7.5 keV sample ( f = 32%). We finally propose two simple diagnostic plots that can be easily used to obtain the spectral classification for relatively low-redshift AGNs even if the quality of the spectrum is not good.

Exploring the active galactic nuclei population with extreme X-ray-to-optical flux ratios (fx/fo > 50)

“…For all the sources reported and discussed here (see Table 1), the offset between the X-ray and the optical position, derived a posteriori, is below 2.1 arcsec, fully consistent with the results obtained by Caccianiga et al (2008) from the analysis of the X-ray to optical offset for the X-ray sources belonging to the XBS. The accumulated magnitudes, combined with the observed 2-10 keV fluxes, have been used to compute the f x / f o ratio and thus to select EXO50 sources.…”

“…Caccianiga et al 2004, Della Ceca et al 2004, Civano et al 2012. For instance, in the XMM-Newton Bright Survey (XBS, Della Ceca et al 2004, Caccianiga et al 2008), a complete sample of bright ( f (0.5−4.5keV) 7 × 10 −14 erg cm −2 s −1 ) X-ray selected sources almost completely identified (spectroscopic identification level ∼ 98%), EXO50 objects represents only ∼ 0.5% of the source population.…”

“…We have looked at and visually inspected all the selected Xray sources for possible optical counterparts, using a search radius of 4 arcsec (see Caccianiga et al 2008), and derived their R magnitude. For all the sources reported and discussed here (see Table 1), the offset between the X-ray and the optical position, derived a posteriori, is below 2.1 arcsec, fully consistent with the results obtained by Caccianiga et al (2008) from the analysis of the X-ray to optical offset for the X-ray sources belonging to the XBS.…”

“…We have assembled an heterogeneous sample of spectroscopically confirmed X-ray selected Type 1 and Type 2 AGN from a few surveys carried out during the last few years using XMM-Newton data: the COSMOS survey (Brusa et al 2010), the XMS survey (Barcons et al 2007) and the XBS survey (Della Ceca et al 2004;Caccianiga et al 2008). This first large comparison sample, composed by 882 Type 1 AGN and 487 Type 2 AGN, will be used below (see Figure 4, left panel) to discuss the position of absorbed and unabsorbed AGN in the f x / f o vs. L X plane.…”

A new sample of X-ray selected narrow emission-line galaxies

“…Caccianiga et al 2008); this threshold rejects all bona fide broadline objects and reduces the contamination by conventional Narrow Line Seyfert 1 (NLS1). Narrow emission-line galaxies correspond at this stage to 1430 sources.…”