Abstract
We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red AGN selected from the 2MASS survey on the basis of their red J-K$_S$ color (>2 mag) and later observed by Chandra. In comparison with optically-, radio-, and X-ray selected AGN, their median SEDs are red in the optical and near-IR with little/no blue bump. It thus seems that near-IR color selection isolates the reddest subset of AGN that can be classified optically. The shape of the SEDs is generally consistent with modest absorption by gas (in the X-ray) and dust (in the optical-IR). The levels of obscuration, estimated from X-rays, far-IR and our detailed optical/near-IR color modeling are all consistent implying N_H < few*10^{22} cm^{-2}. We present SED models that show how the AGN optical/near-IR colors change due to differing amounts of reddening, AGN to host galaxy ratio, redshift and scattered light emission and apply them to the sources in the sample. We find that the 2MASS AGN optical color, B-R, and to a lesser extent the near-IR color, J-K$_S$, are strongly affected by reddening, host galaxy emission, redshift, and in few, highly polarized objects, also by scattered AGN light. The obscuration/inclination of the AGN allows us to see weaker emission components which are generally swamped by the AGN.
Highlights
The orientation dependence of the appearance of an active galactic nucleus (AGN) has been well known for many years
Using the ugri color–color, low-z QSO selection criteria from Richards et al (2002) we find that six of these sources would have been excluded : three (13%) blue sources (NLS1/BALQSOs with optical colors dominated by AGN emission) due to (u − g) < 0.5 criterion and three (13%) red sources whose optical colors fall too close to the stellar locus
We have analyzed a sample of 44 AGNs selected from the 2MASS survey based on their red J − KS > 2 color and later observed by Chandra
Summary
The orientation dependence of the appearance of an active galactic nucleus (AGN) has been well known for many years. Radio observations clearly demonstrate extended, often very large structures that appear different as a function of their orientation (Barthel 1989) to our line of sight. Optical polarization reveals the presence of AGNs in scattered light that are not visible directly due to high obscuration (Antonucci & Miller 1985). These results led to the development of unification models which relate observationally different AGNs and radio galaxies to one another via viewing angle (Antonucci 1993). Evidence for a large, obscured subset of the AGN population which is mostly “missing” was demonstrated by modeling of the cosmic X-ray background (CXRB; Comastri et al 1995; Gilli et al 1999).
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