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
33 citations
33 citations
Cites background or methods from "Spectral energy distributions and m..."
...This extends the study of the z-dependence of the mass of active black holes to z ≈ 4, including the redshift region where the quasar activity is maximal (zpeak ∼ 2−3, e.g. Richards et al. 2006a)....
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...To derive the Eddington ratio ( Lbol LEdd ) from spectroscopic data, we adopt the bolometric corrections by Richards et al. (2006b)....
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33 citations
Cites background or methods from "Spectral energy distributions and m..."
...The latter estimated the mass function of active BHs using the quasar sample by Richards et al. (2006a) with a well-understood selection function....
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...…interested to probe the relative growth of optical and radio quasars, and to this purpose we only adopt the optical quasar luminosity function by Richards et al. (2005, 2006a), c© 2008 RAS, MNRAS 000, 1–15 which is not a complete representation of the overall AGN population (e.g., Hopkins et…...
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...The λLλ (4400Å) values are scaled by a bolometric correction factor of 9.20(±0.24), determined from the database of Richards et al. (2006b)....
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...The reader is referred to Richards et al. (2006a) for details on this sample and its selection....
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33 citations
Cites background from "Spectral energy distributions and m..."
...3(a)): a luminosity independent SED (Elvis et al. 1994; Richards et al. 2006) and a luminosity-dependent one (Hopkins et al. 2007)....
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33 citations
Cites background or methods from "Spectral energy distributions and m..."
...From well-studied spectral energy distributions (SEDs) of unobscured Type 1 quasars (Sanders et al. 1988; Elvis et al. 1994; Richards et al. 2006), one can derive bolometric corrections for AGN with less complete SEDs (Elvis et al. 1994; Fabian & Iwasawa 1999; Elvis et al. 2002; Marconi et al.…...
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...The bulk of our sample lies more than an order of magnitude below the average LX of mean quasar SEDs such as those computed from the Sloan Digital Sky Survey (Richards et al. 2006)....
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...For comparison, we also plot in Figure 4 the mean SDSS quasar SED from Richards et al. (2006)....
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...…that the choice of template SEDs is appropriate for our sample.2 In the rare case where the SED exceeds the 2 If we were to instead use the Richards et al. (2006) SDSS quasar template, the template would exceed the MIR flux in 68% of sources. observed MIR luminosity after normalizing to…...
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References
15,988 citations
"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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14,295 citations
10,650 citations
"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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10,039 citations
9,835 citations
"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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