Spectral energy distributions and multiwavelength selection of type 1 quasars
Summary (2 min read)
3. MIR/OPTICAL COLORS OF TYPE 1 QUASARS
- For the Spitzer color, the authors chose the two highest S/N bands (S3:6 and S4:5); this choice happens to produce the greatest separation of classes and has the added attraction that it does not rely on the longer wavelength bands that will be lost when Spitzer’s coolant runs out.
- Judicious rotation of the axes in Figure 6 may allow for relatively clean AGN selection without having to rely on morphology information.
- Quasars with z > 2:2 have redder optical colors even if they are not dust-reddened, and a large fraction of this population will still be identified by the SDSS quasar-selection algorithm.
- A multidimensional MIR + optical Bayesian color-selection approach (Richards et al. 2004) that avoids any morphology bias may yield optimal completeness and efficiency for all AGN subclasses and will be the subject of future work.
4. THE OBSCURED QUASAR FRACTION
- SinceMIR emission fromAGNs comes from larger scales and is thought to bemore isotropic than optical/UVemission, theMIR is an ideal part of the spectrum to constrain the fraction of quasars that are obscured (within the context of the so-called unifiedmodel; Antonucci 1993).
- E.g., Polletta et al. 2000; Kuraszkiewicz et al. 2003; Risaliti & Elvis 2004), complete SEDs have been compiled for only a small number (P100) of quasars and the mean SED from Elvis et al. (1994) is arguably still the best description of the SED of quasars and is certainly the most commonly used.
- To assess the importance of the host galaxy correction where it matters most, the authors determine the ratio of host galaxy to total luminosity at 1.6 m in the rest frame, where the elliptical template spectrum has its peak.
- The standard deviation of the overall mean and the luminosity- and color-subdivided mean SEDs give the reader an idea of the range of SED shapes.
- There are significant differences between the most and least optically luminous quasars in their sample.
6. BOLOMETRIC LUMINOSITIES AND ACCRETION RATES
- The determinations of quasar physical parameters such as bolometric luminosity, black hole mass, and accretion rate have been revolutionized by two bodies of work from the past decade or so.
- As discussed above, the biases inherent to the sample of objects used by Elvis et al. (1994) in addition to these authors’ warnings of the diversity of individual SEDs, coupled with the use of their mean SED as a single universal template, is what motivates this investigation.
- It seems likely that the minimum in this region results from this region being a relative minimum in the combination of host galaxy contamination in the near-IR and dust extinction in the UV.
- Figures 12 and 13 demonstrate that the smallest bolometric corrections and errors are found at optical wavelengths.
- Clearly, if the authors are ever to understand the accretion rate distribution of quasars, they must either measure the bolometric luminosity directly or determine bolometric corrections to an accuracy better than that which is afforded by assuming the mean SED.
7. CONCLUSIONS
- The authors have compiled a sample of 259 SDSS type 1 quasars with four-band Spitzer IRAC detections.
- Figure 14 presents the individual SEDs of each of the 259 quasars in their sample.
- The SDSS spectra are shown as solid black lines (smoothed by a 19 pixel boxcar).
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Citations
211 citations
Cites methods from "Spectral energy distributions and m..."
...In galaxies dominated by an AGN, the W2 luminosity is well-correlated with the AGN bolometric luminosity (Richards et al. 2006)....
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204 citations
Cites methods from "Spectral energy distributions and m..."
...We then multiply this by a factor of 8 to convert the 6 μm luminosity density to LAGN (following Richards et al. 2006)....
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199 citations
Cites methods from "Spectral energy distributions and m..."
...For ease of comparison, we convert all observations to bolometric luminosities given the appropriate bolometric corrections from Hopkins et al. (2007e) (see also Elvis et al. 1994; Richards et al. 2006)....
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...For convenience to the comparison here, we convert all the observed AGN luminosities to bolometric luminosities using the bolometric corrections in Hopkins et al. (2007e) (using instead those in Elvis et al. 1994; Marconi et al. 2004; Richards et al. 2006, makes no dif- ference)....
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197 citations
Cites background or methods from "Spectral energy distributions and m..."
...…to the Chandra-COSMOS high-z sample of Civano et al. (2011), the XMM-COSMOS sample of Brusa et al. (2009a), the GOODS sample of Fontanot et al. (2007), the faint optical AGN sample of Glikman et al. (2011), and the luminous optical AGN samples of Richards et al. (2006) and Jiang et al. (2009)....
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...Large area optical surveys such as the SDSS, the CFHQS, and the NOAO DWFS/DLS have already been able to discover large samples of z > 4.5 QSOs (e.g. Richards et al. 2006; Glikman et al. 2011) and about 50 QSOs at z > 5.8 (e.g. Jiang et al. 2009; Willott et al. 2010a)....
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196 citations
Cites background from "Spectral energy distributions and m..."
...H07 adopted a distribution of luminosity dependent bolometric corrections for each selection wave band, as well as a large baseline of intrinsic (i.e. corrected for obscuration) AGN SED shapes (from Richards et al. 2006; Steffen et al. 2006)....
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...…connection through the “downsizing” scenario, according to which most massive BHs accrete earlier, faster and with more extreme accretion rates than their lower mass counterparts (Ueda et al. 2003; Le Floc’h et al. 2005; Pérez-González et al. 2005; Hasinger et al. 2005; Richards et al. 2006)....
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...…“bolometric” AGN luminosity adopted throughout the paper are assumed to have the same physical meaning. c© 2014 RAS, MNRAS 000, 1–20 Hopkins et al. (2007) derived their kbol values by assuming different amounts of obscuration applied to an average, unobscured, type-1 AGN SED (Richards et al. 2006)....
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...However, the intrinsic SEDs of Richards et al. (2006) also include an additional IR (λ > 1 µm) contribution arising from the torus reprocessed radiation....
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References
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"Spectral energy distributions and m..." refers methods in this paper
...All SDSS magnitudes have been corrected for Galactic extinction according to Schlegel et al. (1998)....
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"Spectral energy distributions and m..." refers methods in this paper
...Throughout this paper we use a CDM cosmology with H0 ¼ 70 km s 1 Mpc 1, ¼ 0:7, and m ¼ 0:3, consistent with the WMAP cosmology (Spergel et al. 2003, 2006)....
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"Spectral energy distributions and m..." refers methods in this paper
...…Hatziminaoglou et al. (2005) investigated the combined optical + MIR color distribution of quasars by combining data from the ELAIS-N1 field in the SpitzerWide-Area Infrared Extragalactic Survey (SWIRE; Lonsdale et al. 2003) with data from the Sloan Digital Sky Survey (SDSS; York et al. 2000)....
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