Abstract
XMM-Newton spectra of five red, 2MASS AGN, selected from a sample observed by Chandra to be relatively X-ray bright and to cover a range of hardness ratios, confirm the presence of substantial absorbing material in three sources with optical classifications ranging from Type 1 to Type 2. A flat (hard), power law continuum is observed in the other two. The combination of X-ray absorption and broad optical emission lines suggests either a small (nuclear) absorber or a favored viewing angle so as to cover the X-ray source but not the broad emission line region (BELR). A soft excess is detected in all three Type 1 sources. We speculate that this may arise in an extended region of ionised gas, perhaps linked with the polarised (scattered) optical light present in these sources. The spectral complexity revealed by XMM-Newton emphasizes the limitations of the low S/N \chandra data. The new results strengthen our earlier conclusions that the observed X-ray continua of red AGN are unusually hard at energies >2 keV. Their observed spectra are consistent with contributing significantly to the missing hard/absorbed population of the Cosmic X-ray Background (CXRB) although their intrinsic power law slopes are typical of broad-line (Type 1) AGN (Gamma ~1.7-1.9). This suggests that the missing X-ray-absorbed CXRB population may include Type 1 AGN/QSOs in addition to the Type 2 AGN generally assumed.
Highlights
The Two Micron All Sky Survey (2MASS) has revealed a large number of highly reddened active galaxies (AGNs) not previously found in optical/UV color-selected surveys (Cutri et al 2002; Francis et al 2004)
XMM-Newton spectra of five red 2MASS active galactic nuclei (AGNs), selected from a sample observed by Chandra to be relatively X-ray bright and to cover a range of hardness ratios, confirm the presence of substantial absorbing material in three sources with optical classifications ranging from type 1 to type 2
As X-ray–absorbed AGNs, these sources may contribute to the X-ray–absorbed population predicted by modeling of the cosmic X-ray background (CXRB; Gilli et al 2001; Comastri et al 1995)
Summary
The Two Micron All Sky Survey (2MASS) has revealed a large number of highly reddened active galaxies (AGNs) not previously found in optical/UV color-selected surveys (Cutri et al 2002; Francis et al 2004). A better estimate of the fraction of extinguished AGNs comes from Glikman et al (2004), who examined a sample of Faint Images of the Radio Sky at Twenty cm (FIRST) radio sources with 2MASS near-infrared detections but without optical counterparts They concluded that this population accounts for approximately 20% of all QSOs. The Rontgensatellit (ROSAT ) found that, while known AGNs dominate the soft (0.1–2.0 keV) CXRB (Lehmann et al 2000), an additional population of heavily absorbed AGNs would be required to account for the harder high-energy spectrum (Comastri et al 1995). The hard X-ray sources correspond to both optically faint objects and bright, nearby elliptical galaxies, as well as more traditional broad-line or narrow-line AGNs (Silverman et al 2005) They frequently have red continua (1:5 < J À Ks < 2:5) that, combined with their optical colors, are consistent with the moderate amounts of gas and dust absorption required to match the CXRB at energies
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