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
366 citations
Cites background or methods from "Spectral energy distributions and m..."
...…a lack of evolution in the spectral energy distribution (SED) compared to lower redshift counterparts (e.g., Elvis et al. 1994; Glikman et al. 2006; Richards et al. 2006), which demonstrates the existence of ‘‘mature’’ quasars at early times and comparable metal enrichment in quasars at all cosmic…...
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...This finding is supported by observations of J1148+5251 in NIR (e.g., Charmandaris et al. 2004; Hines et al. 2006; Dwek et al. 2007), which show a remarkably flat SED and suggest an AGN origin for the flux excess....
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...In Li et al. (2007b) we calculate the SEDs of the quasar system and its galaxy progenitors....
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...We find that the SEDs of the system at z > 8 are characterized by those of starburst galaxies (Sanders & Mirabel 1996), while at the peak quasar phase, the SEDs resemble those observed in z 6 quasars (Jiang et al. 2006)....
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...Adopting the mean observed intrinsic quasar continuum SED (Richards et al. 2006) gives a B-band luminosity that is well approximated by the following equation given by Marconi et al. (2004): log (Lbol/LB) ¼ 0:80 0:067Lþ 0:017L2 0:0023L3, where L ¼ log (Lbol/L ) 12 and kB ¼ 4400 8....
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362 citations
Cites background or methods or result from "Spectral energy distributions and m..."
...…BLAGN hosts does not depend strongly on the set of galaxy SED templates used to fit the composite AGN+galaxy spectral energy distribution, provided that the same AGN SED is used (we adopt here the Richards et al. (2006) mean QSO SED, allowing for additional dust extinction of the nuclear light)....
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...Indeed, the mean SED of the “pointlike” type–1 COSMOS AGN with Lbol > 10 45.5 shows a less pronounced dip in the 1µm region than either the Elvis et al. (1994) or the Richards et al. (2006) templates....
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...In most of the objects of the sample the nuclear AGN emission dominates the emission in all optical bands, and the constraints on the host galaxy emission are derived mostly in the wavelength range where the AGN SED has a minimum, around 1.2 µm, (Elvis et al. 1994; Richards et al. 2006)....
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...For the AGN component we adopt the Richards et al. (2006) mean QSO SED (but see § 6.3 for a discussion of possible alternative choices), as derived from the study of 259 IR selected quasars with both Sloan Digital Sky Survey and Spitzer photometry....
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...An obvious possible objection to our results is that, if the AGN SED were markedly different from the Richards et al. (2006) template at the typical luminosities of the zCOMSOS bright sample, we would be introducing a severe bias in our measures of the host galaxy parameters....
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360 citations
Cites methods from "Spectral energy distributions and m..."
...We estimate the bolometric AGN luminosity (Lbol) to be 8.8×10 44 erg s−1, using λL5100 (see Richards et al. 2006, for a discussion of the reliability of various bolometric luminosities) and a conversion factor of 8.1 to convert from monochromatic to bolometric luminosity (Runnoe et al. 2012)....
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344 citations
Cites background or methods from "Spectral energy distributions and m..."
...These values are shown in Figure 11a together with spectral energy distributions of unobscured quasars (Richards et al. 2006)....
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...…the spectral energy distribution of our sources to 30µm using the observed slopes, hope that the emission at that wavelength is not significantly affected by absorption, and again use the bolometric correction derived from unobscured quasars (factor of 13 at this wavelength, Richards et al. 2006)....
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...The simplest approach is to apply the standard photometric corrections derived from unobscured quasars (e.g., a factor of 9 at 12µm, Richards et al. 2006)....
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...(7) Bolometric luminosity (logarithmic scale, in erg s−1), derived from 12µm WISE luminosity with a bolometric correction of 9 from Richards et al. (2006)....
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...(8) Bolometric luminosity (logarithmic scale, in erg s−1), derived from 30µm WISE luminosity (extrapolated from the measurements) with a bolometric correction of 13 from Richards et al. (2006)....
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342 citations
References
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"Spectral energy distributions and m..." refers methods in this paper
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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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10,039 citations
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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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