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
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64 citations
Cites background or methods from "Spectral energy distributions and m..."
...Luminous AGNs display a red MIR power-law spectral energy distribution (SED), which is dominated by thermal emission from hot dust (Neugebauer et al. 1979; Elvis et al. 1994; Rieke & Lebofsky 1981)....
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...Host Galaxies With the exception of broad-line sources, the optical SEDs of the IR-AGN and X-ray AGN samples are dominated by light from the host galaxy, which allows us to determine galaxy properties for these sources....
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...The Polletta et al. (2008) IR template set consists of four quiescent galaxy templates, eight star-forming galaxy templates, and six AGN templates, based on the observed SED of a representative sample of local galaxies and AGNs....
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...We convolve the redshifted SED with each IRAC filter to predict the observed IRAC colors....
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...Comparison with IR SED Templates In this section, we investigate the trends in the previous section using empirical galaxy and AGN SED templates....
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64 citations
Cites background or methods from "Spectral energy distributions and m..."
...For quasars, the lower redshift limit comes from the R I color requirement, determined from the Richards et al. (2006) model discussed above; indeed, the z ¼ 5:39 quasar identified by Cool et al. (2006) is too blue in R I to meet our selection criteria (Fig....
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...The thick solid line shows the expected colors of 3 z 7 quasars, calculated using the Richards et al. (2006) SDSS quasar template subject to the Madau (1995) formulation for the opacity of the intergalactic medium as a function of redshift....
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...Figure 6 plots the observed SEDs of these two sources, with a model brown dwarf spectrum from Burrows et al. (2006) and a model high-redshift quasar from Richards et al. (2006)....
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64 citations
Cites result from "Spectral energy distributions and m..."
...This is in agreement with previous works: the typical value of the spectral slope at optical/UV wavelengths is αλ ∼ −1.5 (e.g. Richards et al. 2006; Vanden Berk et al. 2001; Shankar et al. 2016), however our analysis allows for the first time to estimate the slopes on a very large sample, using a…...
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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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