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
93 citations
Cites background or methods from "Spectral energy distributions and m..."
...The Mg ii broad line FWHM was measured from the best-fitting line profile and the monochromatic continuum luminosity at 3000 Å L3000 is taken from the powerlaw fit....
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...The cosmic evolution of the AGN LF out to z ∼ 2 is by now well established (e.g. Richards et al. 2006a; Bongiorno et al. 2007; Croom et al. 2009)....
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...The resulting average host correction as a function of L3000 is shown in Fig....
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...We used the spectral energy distribution (SED) decomposition of 428 type-1 AGN in the COSMOS field (Bongiorno et al. 2012) to compute the average host correction in several bins of total L3000 and interpolated between the bins....
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...We apply the K-correction from Richards et al. (2006a) to compute the absolute i-band magnitude normalized at z = 2 from the i-band flux and translate this to the continuum luminosity at 2500 Å following Richards et al. (2006a)....
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92 citations
Cites methods from "Spectral energy distributions and m..."
...The bolometric luminosity is estimated from Lbol = 10λLλ(5100 Å) (McLure & Dunlop 2004; Richards et al. 2006), and the Eddington luminosity is LEdd = 1.26 × 1038(MBH/M )....
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92 citations
92 citations
Additional excerpts
...We adopt L12µm,AGN = Lbol,AGN/9 from Richards et al. (2006) and estimate L12µm,AGN = 1.4 × 10 44 erg s−1 for J1506+54....
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92 citations
Additional excerpts
...It is compared with the SED constructed by Richards et al. (2006) scaled to roughly match the flux at the one-micron dip....
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...In this case, the dereddened observed flux in the FUV filter is about 0.23 dex below the Richards et al. (2006) curve, corresponding to ∼ 18% of the intrinsic flux....
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...Interestingly, the dereddened SDSS spectrum matches the (Richards et al. 2006) pho- tometry quite well....
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...We use the scaled (Richards et al. 2006) photometry to obtain the intrinsic flux at 2500Å, measuring that to be 8.95×10−15 erg cm−2 s−1Å−1....
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...We assume that the spectrum would have the same slope as the Richards et al. (2006) SED once the reddening has been removed....
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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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