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
24 citations
Cites methods from "Spectral energy distributions and m..."
...Finally, the bolometric luminosity is calculated using Lbol/L5100 = 9.26 (Richards et al. 2006)....
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...…C IV independently in addition to Mg II; this calculation is performed using a = 0.863 ± 0.009 and b = 7.66 ± 0.41 in Equation 1 (SH11), where the line luminosity is for C IV and the continuum luminosity is for 1350Å, and using a bolometric correction of Lbol/L1350 = 3.81 (Richards et al. 2006)....
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...The bolometric luminosity is estimated by multiplying the continuum luminosity at 3000Å from Equation 1 by the bolometric correction of Lbol/L3000 = 5.15 from Richards et al. (2006)....
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24 citations
Cites background or methods from "Spectral energy distributions and m..."
...The UV spectral energy distribution, however, has a very large dispersion among all AGN (Richards et al. 2006)....
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...When only a single filter was available, we used βdefault = −1.5 based on previous UV studies of quasars (Scott et al. 2004; Richards et al. 2006)....
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24 citations
Cites background from "Spectral energy distributions and m..."
...The bolometric luminosity is ∼1047 erg s−1, assuming a bolometric correction B.C.1350= 3.5 (Richards et al. 2006)....
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24 citations
Cites background from "Spectral energy distributions and m..."
...Standard bolometric correction factors (e.g., Elvis et al. 1994; Kaspi et al. 2000) are not reliable for the intrinsically red quasars with their atypical SEDs....
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...Although we have no mid-IR data for these quasars, IR emission accounts for ∼40% of the bolometric luminosity for a typical quasar SED (Richards et al. 2006)....
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...Figure 12 shows the SED data and model fit for all seven intrinsically red quasars....
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...For the intrinsically red SEDs, we change αx to the value obtained in the X-ray fit, and we change Tcut by the amount expected for the lower accretion rate, calculated according to the Lawrence (2005) scaling relation....
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...This relation was derived for a normal BBB-dominated SED....
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24 citations
Cites background or methods from "Spectral energy distributions and m..."
...2.2 WISE photometry Rest-frame mid-infrared (MIR) emission in the vast majority of SDSS QSOs is dominated by AGN-heated dust (e.g. Richards et al. 2006), which can serve as a useful extinctionfree measure of the intrinsic power of the AGN1....
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...Using L6µm and a 6 µm bolometric correction = 8 (Richards et al. 2006), we constrain the median L6µm of the cQSOs (i.e., typical SDSS QSOs) and read off characteristic values for 〈LIR,SF〉 as a function of redshift directly from Figure 8 of Stanley et al. (2017)....
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...…the kinetic power of a radio source (e.g., Equation 6 from Merloni & Heinz 2007), and take a standard 6 µm bolometric correction for QSOs (≈ 8, Richards et al. 2006), we can convert R to a ratio of kinetic-to-bolometric power in a AGN-powered radio source as follows: log Kinetic Bolometric…...
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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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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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"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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