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
46 citations
Cites methods from "Spectral energy distributions and m..."
...…other studies targeting higher redshift type 2 AGN (z ≈ 0.5 Liu et al. 2013a, 2014; Hainline et al. 2014b), where the rest-frame 22 µm flux is not available, we use the rest-frame 15 µm luminosity as our AGN luminosity indicator with a bolometric correction of 9 (Richards et al. 2006), see Tab....
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...30 µm) than dust heated by stars (T ∼ 25 K, λpeak ∼ 100 µm) (Richards et al. 2006; Kirkpatrick et al. 2012; Zakamska et al. 2016; Sun et al. 2014)....
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46 citations
46 citations
Cites background from "Spectral energy distributions and m..."
...The complete mid-IR spectral and SED analysis shows that at least ∼75% of the sample contain dust obscured AGNs, which dominate the mid-IR (3 – 6)µm luminosities but star formation still contribute most of the farIR luminosities (Sajina et al. 2007, 2008)....
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...Finally, the analysis of the HST/NICMOS images, mid-IR spectra and IR SED revealed that most of our sources are mergers, containing dust obscured AGNs dominating the luminosities at (3 – 6)µm....
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...For these 8 sources, the sigma weighted, averaged flux is 1.06± 0.18 mJy (5.9σ), providing constraining power in the SED fitting in Figure 2 (cyan, open stars)....
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...Modeling the IR SED To derive the total and far-IR luminosities (LIR = L3−1000µm,LFIR = L40−120µm), we fit the spectral energy distribution of our sources from near-IR to far-IR (see Table 3)....
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...The LFIR is measured from the full SED fitting described in § 2.3....
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46 citations
Cites methods or result from "Spectral energy distributions and m..."
...Here we adopt αopt = −0.5 because the K-corrections given by Richards et al. (2006b) are obtained by using a canonical slope of −0.5....
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...…luminosity at i-band (7471Å) by assuming a power law spectrum with a canonical slope of αopt = −0.5, and then use the Kcorrection, including the effects of both the continuum and the emission lines, given by Richards et al. (2006b) to calculate the apparent i-band magnitude of each mock QSO....
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...Other estimations of the BCs for QSOs at 5100Å include kbol ∼ 9 (Kaspi et al. 2000), kbol ∼ 10.3 ± 2.1 (Richards et al. 2006b), and kbol ∼ 8.1 ± 0.4 (Runnoe et al. 2012), etc., which are roughly consistent with that shown in Figure 2 and suggest that the systematic uncertainties in the BCs should…...
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46 citations
Cites methods from "Spectral energy distributions and m..."
...Since now we use L3000 on the x axis, we transformed the relation by recomputing L3000 from L5100 using the ratio of the bolometric corrections derived by Richards et al. (2006): L3000 = (10.33/5.62) L5100....
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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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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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