Spectral energy distributions and multiwavelength selection of type 1 quasars

TL;DR: In this article, the spectral energy distributions (SEDs) of 259 quasars with both Sloan Digital Sky Survey (SDS) and Spitzer photometry were analyzed.

Abstract: We present an analysis of the mid-infrared (MIR) and optical properties of type 1 (broad-line) quasars detected by the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z ~ 3, with predictions to z = 7. We demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei (AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259 quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened/obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.

Summary

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).

Figures

Fig. 3.—Color-redshift relation for various combinations of Spitzer colors. Black symbols represent SDSS-DR3 quasars from the XFLS and SWIRE ELAIS-N1/N2 and Lockman Hole areas. Open red squares represent Hectospec-confirmed XFLS quasars (Papovich et al. 2005). Errors are typically 0.14 mag. The dashed green curve indicates the locus of synthetic colors determined from convolving the (redshifted) geometric mean of the optical-IR composite spectrum of Glikman et al. (2006) with the Spitzer IRAC transmission curves. The solid cyan curve shows the expected relation from convolving the Elvis et al. (1994) composite radio-quiet SEDwith the transmission curves. The vertical lines mark the redshifts where 1 m enters the bluest (dotted) and leaves the reddest (dashed) band.

Fig. 9.—Mean quasar SEDs compared to various survey flux limits. The black solid and dashed lines are the z ¼ 0 Elvis et al. (1994) mean radio-quiet and radio-loud SEDs, normalized to i ¼ 16:4 (1 mJy). The colored dashes show the flux density limits for the Spitzer XFLS (red), Spitzer Boötes (brown; Stern et al. 2005), 2MASS (green), SDSS (imaging, blue), SDSS (low-z quasar spectroscopy, orange), andGALEX (cyan) surveys. The lighter gray lines show the radio-quiet SED at z ¼ 0:5, 1.5, and 2.5 normalized to the Boötes field 8 m flux limit [dashed gray line is z ¼ 1:5 SMC-reddened by E(B V ) ¼ 0:25]. The dotted line shows a spectral index of ¼ 0:73 between 8 m and the SDSS r band.

Fig. 12.—Bolometric corrections as a function of frequency for the SEDs in Fig. 11. The color coding is the same as for the previous figure (except that the full SDSS-DR3 mean quasar SED is now shown in gray instead of cyan). The dashed gray curve shows the full-sample mean SED without correction for the host galaxy contribution. The bolometric correction from 5100 8 for the Elvis et al. (1994) radio-quiet SED is 12.17 (thin solid line). As in Fig. 11, the bottom panel shows the 1 error in the bolometric correction derived from the overall mean SED with the most robust parts of the SED shown by thicker line segments. The kinks in the error spectrum attest to the importance of considering the range of quasar SEDs by demonstrating the homogenizing effects of assuming a singlemean SED in our gap repair process. The vertical lines in the bottom panel indicate the frequencies that are compared in Fig. 13.

Fig. 4.—IRAC colors of SDSS + Spitzer objects. Blue contours and dots correspond to objects that have pointlike SDSSmorphologies, while objects classified by the SDSS as extended are shown by red contours and dots. These blue and red contours/dots represent all of the objects detected in all four IRAC bands in the XFLS catalogs that have a match in the SDSS-DR3 photometric database. Note that point sources (blue contours) occupy two distinct regions corresponding to stars in the lower left of each panel and quasars in the upper right of each panel (the latter having just one contour level). Black triangles indicate spectroscopically confirmed type 1 quasars. The few outliers are from the Hectospec sample and may be mis-classified (or host galaxy dominated). The cyan lines represent the z ¼ 0:1 to z ¼ 7 colors predicted from the Elvis et al. (1994) quasar SED; the highest redshift quasars are at the blue (negative) end of the tracks. The green line shows the predicted colors from z ¼ 2 (z ¼ 1 in the top left panel) to z ¼ 7 using the Glikman et al. (2006) composite spectrum. A magenta cross indicates where the lowest redshift from the Glikman et al. (2006) colors falls on the Elvis et al. (1994) curves. Redder colors have more positive values in this representation.

Fig. 8.—Left: Spitzer color-magnitude diagram. The dashed lines show the effects of the 5.8 and 8.0 m flux density limits. Right: SDSS color-magnitude diagram. Faint (ik 18) point sources with g ik 0:8 are either high-redshift quasars or dust-reddened low-redshift quasars. In both panels, the contours/points are coded the same as in Fig. 6.

Fig. 11.—Mean quasar SEDs and the data used to construct them. The points show the data; the lines show themean SEDs. From left to right: black crosses, MIPS70; black points, MIPS24/ ISO15; red points, S8:0; green points, S5:8; cyan points, S4:5; blue points, S3:6; gray points, K; yellow points, H; cyan points, J; black points, z; magenta points, i; red points, r; green points, g; blue points, u; orange points, n; purple points, f ; black crosses, X-ray. The dotted lines show the range of ox with luminosity for the luminosity extremes of our sample (Strateva et al. 2005). From top to bottom (at 1014 Hz) the thick solid lines are color coded as follows: green, optically luminous SDSS quasars; red, optically red SDSS quasars; cyan, all SDSS quasars; blue, optically blue SDSS quasars; black, Elvis et al. (1994) radio-quiet mean SED; gray, Hatziminaoglou et al. (2005) mean SED (normalized to Elvis et al. 1994 at 1 m); orange, optically dim SDSS quasars. The near-IR luminous/dim composites are nearly identical to the optical composites. The thin green, cyan, and orange curves show the host galaxy contribution assuming (LBol/LEdd) ¼ 1 (see eq. [1]) for the elliptical galaxy composite spectrum of Fioc & Rocca-Volmerange (1997). The dashed cyan curve shows the effect of ignoring the host contribution. The inset at the upper right zooms in on theMIR region of the spectrum. The three curves are normalized at 1.3 m, and the y-axis shows relative luminosity ( L ), while the x-axis is in microns. The bottom panel shows the 1 error array (dex) for our overall mean SED. Those frequencies where over 100 quasars contribute to the mean SED are shown as thicker line segments and are relatively unaffected by the gap-repair process.

TABLE 3 Mean Quasar SEDs

Fig. 1.—Location of SDSS-DR3 quasars in the XFLS (left) and SWIRE Lockman Hole (right) fields. Red, yellow, and blue points represent IRAC, IRAC verification, and MIPS70 sources, respectively. Open triangles represent SDSS-DR3 quasars. Green circles represent SDSS-DR3 quasars with IRAC detections in all four bands. Open pentagons indicate GALEX-detected SDSS quasars.

Fig. 2.—Location of SDSS-DR3 quasars in the SWIRE ELAIS N1 (left) and N2 (right) fields. Red points indicate four-band IRAC sources. Blue points indicate MIPS 70 m sources. Open triangles indicate SDSS-DR3 quasars. Green circles indicate SDSS-DR3 quasars with IRAC detections in all four bands.

Fig. 10.—Quasar SED diagnostic plot. Shown in gray are the Elvis et al. (1994) radio-quiet (solid) and radio-loud (dashed) mean SEDs. The colored lines indicate typical spectral indices in the radio, optical, and X-ray using the same sign convention. Also shown is the typical radio-to-optical spectral index for radio-loud quasars and the range of optical–to–X-ray spectral indices. Studies in different bands tend to use different sign conventions for spectral indices and jargon to describe them (e.g., steep/red/soft). The top panel shows f , while the bottom panel shows f . The x-axis is labeled as log ( ) (bottom), and wavelength, energy, and temperature (top).

Fig. 5.— ½3:6 ½5:8 vs. ½5:8 ½24 colors of SDSS + Spitzer objects in the ELAIS areas. Contours and points are as in Fig. 4. Stars (which have very blue ½5:8 ½24 color and generally have pointlike SDSS morphology classification) are muchmore cleanly separated from quasars and galaxies when theMIPS 24 m data is included. However, little is gained in terms of galaxy-quasar separation as they have similarly red ½5:8 ½24 colors.

Fig. 6.—Color-color matrix using an SDSS color (g i), an SDSS + Spitzer color (i ½3:6 ), and a Spitzer color (½3:6 ½4:5 ). See Fig. 4 for an explanation of the plot symbols. Combining Spitzer IRAC photometry with SDSS colors/morphology defines a parameter space where stars, AGNs, and normal galaxies can be efficiently distinguished. The green line in the right panel shows a possible selection criterion for unresolved AGNs; open green squares show the point sources selected by such a cut. Black triangles are confirmed SDSS quasars. The cyan line shows the expected colors of quasars from z ¼ 0:1 to z ¼ 5 (using the Elvis et al. 1994 mean SED); lowredshift quasars having the reddest i ½3:6 colors. The contours and dots are for XFLS sources only, whereas the black and green symbols are drawn from all four areas of sky in our sample.

TABLE 1 SDSS-Spitzer Quasar Photometry I

Fig. 7.—MIR (left) and optical (right) color-color plots showing the location of optical-color/morphology + MIR-color selected populations. See Fig. 4 for an explanation of the plot symbols. Quasar candidates (see Fig. 6) are shown as open green squares. The yellow lines in the left panel show the MIR selection criteria from Lacy et al. (2004), after having multiplied their cuts by 2.5 to convert to a magnitude scale.

TABLE 2 SDSS-Spitzer Quasar Photometry II

Fig. 13.—Histogram of bolometric corrections (from the indicated wavelength/frequency to 100 m–10 keV) for our sample. Likely dust-reddened quasars [those having (g i) > 0:3] have been excluded. The solid histogram shows the bolometric correction from 5100 8 with the vertical line indicating the value from Elvis et al. (1994). The 5100 8 bolometric correction (and thus the accretion rate relative to Eddington) is overestimated by 17% on the average if the Elvis et al. (1994) RQ SED is assumed to apply to all quasars. The dotted and dashed lines show the bolometric corrections at 1014 Hz and 3000 8 respectively (see Fig. 12). Individual objects can have their bolometric corrections misestimated by as much as 50% when assuming a single mean SED.

Full text

SPECTRAL ENERGY DISTRIBUTIONS AND MULTIWAVELENGTH SELECTION OF TYPE 1 QUASARS
Gordon T. Richards,
1,2
Mark Lacy,
3
Lisa J. Storrie-Lombardi,
3
Patrick B. Hall,
4
S. C. Gallagher,
5
Dean C. Hines,
6
Xiaohui Fan,
7
Casey Papovich,
7
Daniel E. Vanden Berk,
8
George B. Trammell,
8
Donald P. Schneider,
8
Marianne Vestergaard,
7
Donald G. York,
9,10
Sebastian Jester,
11, 12
Scott F. Anderson,
13
Tama
´
sBudava
´
ri,
2
and Alexander S. Szalay
2
Received 2006 January 24; accepted 2006 May 26
ABSTRACT
We present an analysis of the mid-infrared ( MIR) and optical properties of type 1 (broad-line) quasars detected by
the Spitzer Space Telescope. The MIR color-redshift relation is characterized to z  3, with predictions to z ¼ 7. We
demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei
(AGNs) than MIR or optical colors alone. Composite spectral energy distributions (SEDs) are constructed for 259
quasars with both Sloan Digital Sky Survey and Spitzer photometry, supplemented by near-IR, GALEX, VLA, and
ROSAT data, where available. We discuss how the spectral diversity of quasars influences the determination of bolo-
metric luminosities and accretion rates; assuming the mean SED can lead to errors as large as 50% for individual quasars
when inferring a bolometric luminosity from an optical luminosity. Finally, we show that careful consideration of the
shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened / obscured
AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.
Subject h eadinggs: catalogs — galaxies: active — infrared: galaxies — quasars: general — radio continuum: galaxies —
surveys — ultraviolet: galaxies — X-rays: galaxies
Online material: machine-readable tables
1. INTROD UCTION
Access to the mid-infrared ( MIR) region opens up new realms
for quasar science as we are able to study large numbers of ob-
jects with high signal-to-noise ratio data in this bolometrically
important band for the first time. At least four distinct energy gen-
eration mechanisms are at work in active galactic nuclei (AGNs)
from jets in the radio, dust in the IR, accretion disks in the optical–
UV–soft–X-ray, and Compton upscattering in hot coronae in the
hard X-ray. All of these spectral regions need to be sampled with
high precision if we are to understand the physical processes
governing AGN emission. The Spitzer Space Telescope (Werner
et al. 2004) allows the first robust glimpse of the physics of the
putative dusty torus in AGNs out to z  23 and makes it pos-
sible to compare high-quality mid-IR data to the expectations of
the latest models (e.g., Nenkova et al. 2002; Dullemond & van
Bemmel 2005; Fritz et al. 2006).
MIR photometry from Spitzer has provided a better census of
active nuclei in galaxies than has been previously possible (e.g.,
Lacy et al. 2004). Optical surveys are biased against heavily
reddened and obscured objects, and even X-ray surveys may fail
to uncover Compton-thick sources (e.g., Treister et al. 2006).
Thus, the MIR presents an attractive window for determining the
black hole accretion history of the universe. To that end, Spitzer
will be of considerable utility in helping to decipher the nature of
the M
BH
- relation (e.g., Tremaine et al. 2002), in terms of mak-
ing a complete census of AGNs—a necessary condition for a full
understanding of the physical relationship between black holes
and their host galaxies.
High-sensitivity, high-accuracy MIR photometry also fills a
huge gap in our knowledge of the overall spectral energy dis-
tribution (SED) of AGNs, which now lacks only detailed far-IR/
centimeter and extreme-UV meas urements for a large sample of
quasars. Without the mid-IR data, we have been forced to rely on
the mean properties of a few dozen of the brightest quasars (e.g.,
Elvis et al. 1994) to estimate bolometric luminosities (and, in turn,
Eddington masses and accretion rates) for quasars. Since the 1–
100 m part of the spectrum contributes nearly 40% of the bolo-
metric luminosity, this added knowledge represents a significant
gain in our ability to explore the properties of AGNs as a function
of the bolometric luminosity.
This paper builds on and extends the results from recent pa-
pers describing the Spitzer MIR color distribution of AGNs.
Lacy et al. (2004) showed that MIR colors alone can be used to
select AGNs with both high efficiency and completeness, includ-
ing both dust-reddened and optically obscured (type 2) AGNs
that may otherwise be overlooked by optical selection techniques.
We will show that the addition of optical colors and morphology
can be used to improve the MIR-only selection efficiency of type 1
quasars (including those that are moderately reddened).
A
1
Princeton University Observatory, Peyton Hall, Princeton, NJ 08544.
2
Department of Physics and Astronomy, The Johns Hopkins University,
3400 North Charles Street, Baltimore, MD 21218-2686.
3
Spitzer Science Center, California Institute of Technology, Mail Code 220-6,
Pasadena, CA 91125.
4
Department of Physics and Astronomy, York University, 4700 Keele Street,
Toronto, ON M3J 1P3, Canada.
5
Department of Physics and Astronomy, UCLA, Mail Code 154705, 475
Portola Plaza, Los Angeles, CA 90095.
6
Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301.
7
Steward Observatory, University of Arizona, 933 North Cherry Avenue,
Tucson, AZ 85721.
8
Department of Astronomy and Astrophysics, Pennsylvania State Univer-
sity, 525 Davey Laboratory, University Park, PA 16802.
9
Department of Astronomy and Astrophysics, University of Chicago, 5640
South Ellis Avenue, Chicago, IL 60637.
10
Enrico Fermi Institute, University of Chicago, 5640 South Ellis Avenue,
Chicago, IL 60637.
11
Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510.
12
School of Physics and Astronomy, Southampton University, Southampton
SO17 1BJ, UK.
13
Department of Astronomy, University of Washington, Box 351580, Seattle,
WA 9 8 1 9 5.
470
The Astrophysical Journal Supplement Series, 166:470–497, 2006 October
# 2006. The American Astronomical Society. All rights reserved. Printed in U.S.A.

Stern et al. (2005) also describe a MIR selection technique for
AGNs, making statistical arguments that the obscured AGN frac-
tion may be as high as 76%. We reconsider their argument in light
of the influence that the shape of the mean quasar spectral energy
distribution (SED) has on determining the obscured quasar frac-
tion. Such considerations allow us to demonstrate that the true ob-
scured AGN fraction must be lower than that determined by Stern
et al. (2005).
Finally, Hatziminaoglou et al. (2005) investigated the combined
optical + MIR color distribution of quasars by combining data
from the ELAIS-N1 field in the Spitzer Wide-Area Infrared Extra-
galactic Survey (SWIRE; Lonsdale et al. 2003) with data from the
Sloan Digital Sky Survey (SDSS; York et al. 2000). Using the data
from 35 SDSS quasars they determine the mean optical-MIR SED
of type 1 quasars and investigate their mass and bolometric lumi-
nosity distribution. We expand on these results by determining a
number of different ‘‘mean’’ SEDs as a function of color and lumi-
nosity for 259 SDSS quasars in the Spitzer Extragalactic First Look
Survey
14
(XFLS), SWIRE
15
ELAIS-N1/N2, and SWIRE Lockman
Hole areas. We use these SEDs to demonstrate that the diversity of
quasar SEDs must be considered when determining bolometric
luminosities and accretion rates for individual quasars—as was
emphasized in the seminal SED work of Elvis et al. (1994).
Section 2 reviews the data sets used in our analysis. In x 3we
explore the MIR color-redshift relation and MIR-optical color-
color space occupied by type 1 quasar s. In addition to showing
these relations for the data, we also show the predicted relations
derived from two quasar SEDs convolved with the SDSS and
Spitzer filters curves : one SED derived largely from broadband
photometry ( Elvis et al. 1994), the other from a mean optical +
IR spectral template (Glikman et al. 2006). Section 4 presents a
brief discussion of the determination of the type 1 to type 2 ratio
of quasars. In x 5 we discuss the radio through X-ray SED of qua-
sars and construct new MIR-optical templates from our sample.
We present an overall mean SED along with mean SEDs for sub-
sets of optically luminous/dim, MIR luminous/dim, and optically
blue/red quasars in order to explor e how different optical/MIR
properties are related to the overall SED. Section 6 discusses the
implications of our new SED templates on the determination of
bolometric luminosities and accretion rates. Our conclusions are
presented in x 7.
Throughout this paper we will distinguish between normal
type 1 quasars, dust-reddened/extincted type 1 quasars, and type 2
quasars. By ‘‘type 1 quasars,’’ we mean those quasars having broad
lines and optical colors/ spectral indices that are roughly consistent
with a Gaussian spectral index distribution of 

¼0:5  0:3
( f

/ 

). Red dened type 1 quasars are those quas ars that have
broad lines but have spectral indices that are redder than about


¼1 (e.g., Gregg et al. 2002). Optical surveys can find such
quasars up to E(B  V )  0:5butareincreasinglyincomplete
above E(B  V )  0:1 (Richards et al. 2003). By type 2 quasars,
we mean those that lack rest-frame optical/UV broad emission
lines and have nuclei that are completely obscured in the optical
such that the optical colors are consistent with the host galaxy.
Throughout this paper we use a CDM cosmology with H
0
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).
2. THE DATA
We investigate the mid-IR and optical properties of type 1
quasars that are detected in both the SDSS and in all four bands
of the Spitzer Infrared Array Camera ( IRAC; Fazio et al. 2004).
The Spitzer data are taken from the XFLS and SWIRE ELAIS-N1,
ELAIS-N2, and Lockman Hole areas, which have (R.A., decl.)
centers of (259N5, 59N5), (242N75, 55N0), (249N2, 41N029), and
(161N25, 58N0), respectively.
We begin with SDSS-DR3 type 1 quasars cataloged by
Schneider et al. (2005), the majority of which were selected by
the algorithm given by Richards et al. (2002). This catalog in-
cludes matches to the FIRST (Becker et al. 1995) survey with the
VLA, ROSAT ( Voges et al. 2000), and 2MASS (Skrutskie et al.
1997). For a definition of the SDSS photometric system, see
Fukugita et al. (1996); Adelman-McCarthy et al. (2006) provide
a description of the latest SDSS data release (DR4). All SDSS
magnitudes have been corrected for Galactic extinction accord-
ing to Schlegel et al. (1998).
The 46,420 SDSS quasars of Schneider et al. (2005) are
matched to IRAC detections in the XFLS (main
_
4band.cat;
Lacy et al. 2005b) and the SWIRE ELAIS-N1, -N2, and Lockman
Hole (SWIRE2
_
N1
_
cat
_
IRAC24
_
16jun05.tbl, SWIRE2
_
N2
_
cat
_
IRAC24
_
16jun05.tb l, SWIRE2
_
Lockman
_
cat
_
IRAC24
_
10Nov05.tbl; Surace et al. 2005) areas of sky. The IRAC band-
passes are generally referred to as channels 1 through 4 or as the
3.6, 4.5, 5.8 , and 8.0 m bands, respectively. For a quasar spec-
trum with MIR spectral index of 

¼1(f

/ 

), the effec-
tive wavelengths of the IRAC bandpasses are actually closer to
3.52, 4.46, 5.67, and 7.70 m. The SWIRE catalogs also include
24 m photometry from the Multiband Imaging Photometer for
Spitzer (MIPS; Rieke et al. 2004). In the XFLS field, 24 m
sources are cataloged by Fadda et al. (2006) and we include
matches from that catalog as well. As the limits of the mid-IR
catalogs are much deeper than the SDSS spectroscopic survey,
we consider only objects detected in all four IRAC bands. Within
a matching radius of 1B0 there are 44 SDSS-DR3 quasar matches
in the XFLS area, 29 in the ELAIS-N1 area, 44 in the ELAIS-N2
area, and 142 in the Lockman Hole area. All but one of the op-
tically selected SDSS quasars has four-band IRAC coverage in
the regions of overlap between the SDSS and Spitzer data; see
Figures 1 and 2. The ex ception is SDSS J104413.47 +580858. 9
(z ¼ 3:7), which has only a limit in IRAC channel 3.
To construct the most detailed quasar spectral energy distribu-
tions (SEDs) possible, we include data available at other wave-
lengths. We include matches to MIPS 70 m sources in the XFLS
(FLS70
_
sn7
_
jul05.txt; Frayer et al. 2006) and in the SWIRE
(SWIRE2
_
EN1
_
70um_23nov05.tbl, SWIRE2
_
EN2
_
70um
_
23nov05.tbl, SWIRE3
_
Lockman
_
70um
_
23nov05.tbl; Surace
et al. 2005) areas. No MIPS 160 m data are included as the
flux density limits of these data in the XFLS and SWIRE areas
are much brighter than expected flux densities of even the bright-
est SDSS-DR3 quasars in these fields. For the SDSS quasars in
the ELAIS fields we have extracted 15 mphotometryfromthe
Rowan-Robinson et al. (2004) catalog. We also extract J /H/K and
radio information from this catalog if that information was not
otherwise available.
Some of these areas of sky have been observed by GALEX
(Martin et al. 2005), and the data were released as part of GALEX
GR1. Quasars are readily detected by GALEX (see Bianchi et al.
2005 and Seibert et al. 2005); thus, we also include GALE X pho-
tometry where available. Matc hing of the GALEX catalogs and
the SDSS DR3 quasar sample is described by Trammell et al.
(2005). The effective wavelengths of the GALEX NUV and
FUV bandpasses (hereafter referred to as n and f magnitudes)
are 2267 and 1516 8. GALEX photometry has been corrected
for Galactic extinction assuming A
n
/E(B  V ) ¼ 8:741 and
A
f
/E(B  V ) ¼ 8:376 (Wyder et al. 2005). A total of 55 and 88
14
See http://ssc.spitzer.ca ltech.edu/fls/.
15
See http://swire.ipac.caltech.edu/swire/.
SEDs OF TYPE 1 QUASARS 471

of the DR3 quasars have GALEX detections in the f and n bands,
respectively.
In the radio, we have matched to the deeper VLA data taken in
the XFLS area by Condon et al. (2003), which catalogs 5  de-
tections with fluxes higher than 115 Jy (about an order of mag-
nitude deeper than FIRST). Deep VLA data also exists for the
ELAIS and Lockman Hole areas, but only over a small area of
sky (e.g., Ciliegi et al. 1999, 2003).
Most of our objects are fainter than the 2MASS (Skrutskie
et al. 1997) limits, but we have supplemental near-IR data for a
few. Near-IR (JHK
s
) magnitudes for SDSS J1716+5902 were ob-
tained on 2003 September 9 UT using the GRIM II instrument on
the Apache Point Observatory 3.5 m telescope. Dithered images
were obtained and reduced in the standard fashion, using running
flat-fielding and sky-subtraction (e.g., Hall et al. 1998) with all
available good images in a given filter for each object. Four
other sources (SDSS J171732.94+59474 7.5, SDSS J171736.90+
593011.4, SDSS J171748.43+594820.6, and SDSS J171831.73+
595309.4) were observed at Palomar Observatory.
Finally, to better characterize the optical + MIR color distri-
bution of type 1 quasars, we include 87 broadline quasars that are
fainter than the SDSS spectroscopic magnitude limit, but that
Fig. 2.—Location of SDSS-DR3 quasars in the SWIRE ELAIS N1 (left)andN2(right) fields. Red points indicate four-band IRAC sources. Blue points indicate
MIPS 70 m sources. Open triangles indicate SDSS-DR3 quasars. Green circles indicate SDSS-DR3 quasars with IRAC detections in all four bands.
Fig. 1.—Location of SDSS-DR3 quasars in the XFLS (left) and SWIRE Lockman Hole (right) fields. Red, yellow, and blue points represent IRAC, IRAC
verification, and MIPS70 sources, respectively. Open triangles represen t SDSS-DR3 quasars. Green circles represent SDSS-DR3 quasars with IRAC detections in all
four bands. Open pentagons indicate GALEX-detected SDSS quasars.
RICHARDS ET AL.472 Vol. 166

TABLE 1
SDSS-Spitzer Quasar Photometry I
Name (SDSS J) z
em
L
bol
a
log (ergs s
1
)
L
opt
b
log (ergs s
1
)
L
ir
c
log (ergs s
1
)BC
a
X-Ray
log (counts s
1
)
f
(AB mag)
n
(AB mag)
u
(AB mag)
g
(AB mag)
r
(AB mag)
i
(AB mag)
z
(AB mag)
105705.39+580437.4 .......... 0.140 45.06 44.49 44.78 10.60 0.708 18.31  0.08 18.15  0.04 17.92  0.03 17.61  0.05 17.25  0.02 16.83  0.02 16.56  0.04
171902.28+593715.9 .......... 0.178 45.21 44.74 44.93 9.41 1.221 18.10  0.01 17.99  0.01 17.49  0.02 17.50  0.02 17.36  0.02 17.06  0.02 17.20  0.02
160655.34+534016.8 .......... 0.214 45.13 44.45 44.91 11.87 ... ... ... 18.85  0.03 18.71  0.02 18.22  0.02 17.86  0.02 17.91  0.03
163111.28+404805.2........... 0.258 45.68 45.27 45.19 9.84 0.551 ... ... 16.98  0.01 17.05  0.02 17.08  0.01 17.10  0.01 16.86  0.01
171207.44+584754.4 .......... 0.269 45.49 45.06 45.12 12.29 1.235 17.97  0.01 18.08  0.01 17.83  0.02 17.93  0.02 17.88  0.02 17.94  0.02 17.51  0.02
171033.21+584456.8 .......... 0.281 45.15 44.46 44.95 10.44 ... 20.59  0.04 20.06  0.02 19.58  0.03 19.25  0.03 18.70  0.02 18.52  0.02 18.10  0.03
105644.52+572233.4 .......... 0.286 45.08 44.53 44.78 10.12 ... ... ... 19.36  0.03 19.26  0.02 18.88  0.02 18.69  0.02 18.32  0.02
104739.49+563507.2 .......... 0.303 45.19 44.66 44.88 9.82 ... ... ... 19.16  0.04 19.02  0.04 18.72  0.04 18.57  0.03 18.20  0.03
155936.13+544203.8 .......... 0.308 45.42 44.87 45.15 11.75 ... ... ... 18.55  0.03 18.42  0.04 18.27  0.02 18.38  0.03 17.87  0.03
105626.96+580843.1 .......... 0.342 45.29 44.66 45.03 8.40 ... ... 21.50  0.20 19.45  0.03 18.95  0.02 18.57  0.03 18.46  0.02 17.88  0.02
Note.—Table 1 is available in its entirety in the electronic edition of the Astrophysical Journal Supplement. A portion is shown her e for guidance regarding its form and content.
a
Bolometric (100 m to 10 keV) luminosity and bolometric correction (from 5100 8).
b
1–0.1 m integrated luminosity.
c
100–1 m integrated luminosity.

TABLE 2
SDSS-Spitzer Quasar Photometry II
Name (SDSS J) J (Vega) H (Vega) K (Vega)
S
3:6
(Jy)
S
4:5
(Jy)
S
5:8
(Jy)
S
8:0
(Jy)
S
15
(mJy)
S
24
(mJy)
S
70
(mJy)
Radio
(mJy)
L
rad
log (ergs s
1
Hz
1
)
105705.39+580437.4 ........... 14.99  0.08 14.21  0.09 13.48  0.07 2351.5  5.6 2366.9  7.3 2838.0  15.1 6273.4  16.1 ... 16.61  0.02 98.0  0.6 ... <29.69
171902.28+593715.9 ........... 15.89  0.09 15.02  0.09 14.15  0.06 2925.1  293.1 4095.1  409.8 5365.6  541.1 7193.8  720.4 ... 26.91  0.04 22.9  4.0 0.23 29.28
160655.34+534016.8 ........... 16.37  0.10 15.33  0.11 14.32  0.07 1396.7  4.6 1657.2  5.7 2047.6  14.1 2973.1  10.9 7.72 14.80  0.02 37.7  1.6 ... <30.09
163111.28+404805.2............ 16.24  0.10 15.45  0.12 14.48  0.09 2729.7  5.0 3632.2  6.6 4686.4  15.1 6218.9  11.9 ... 16.90  0.03 ... ... <30.26
171207.44+584754.4 ........... 16.26  0.10 15.36  0.09 14.61  0.10 2024.6  203.1 2411.9  242.2 3162.9  321.5 4353.7  437.9 ... 13.34  0.07 ... 0.14 29.45
171033.21+584456.8 ........... 16.90  0.18 15.68  0.11 14.96  0.10 589.2  59.9 708.4  71.8 709.8  78.1 1571.6  159.5 ... 6.06  0.07 44.0  8.0 ... <30.34
105644.52+572233.4 ........... 16.71  0.10 16.33  0.27 15.10  0.12 1161.4  4.4 1280.1  5.2 1417.1  13.2 1742.5  9.7 ... 3.18  0.02 ... ... <30.36
104739.49+563507.2 ........... 16.63  0.16 16.24  0.24 15.51  0.18 572.2  2.6 671.2  2.6 886.3  10.7 1566.3  6.5 ... 8.61  0.02 ... ... <30.41
155936.13+544203.8 ........... 16.61  0.20 16.77  0.10 14.92  0.16 1093.4  2.6 1437.4  3.8 1997.8  8.6 3268.1  8.7 ... 14.59  0.02 ... 3.40 30.96
105626.96+580843.1 ........... 16.74  0.17 16.25  0.27 15.42  0.16 1362.5  5.2 1660.5  4.9 1975.0  15.5 2303.3  9.0 ... 4.23  0.02 ... ... <30.53
Note.—Table 2 is available in its entirety in the electronic edition of the Astrophysical Journal Supplement. A portion is shown her e for guidance regarding its form and content.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Spectral energy distributions and multiwavelength selection of type 1 quasars" ?

The authors present an analysis of the mid-infrared ( MIR ) and optical properties of type 1 ( broad-line ) quasars detected by the Spitzer Space Telescope. The authors demonstrate how combining MIR and optical colors can yield even more efficient selection of active galactic nuclei ( AGNs ) than MIR or optical colors alone. The authors discuss how the spectral diversity of quasars influences the determination of bolometric luminosities and accretion rates ; assuming themeanSED can lead to errors as large as 50 % for individual quasars when inferring a bolometric luminosity from an optical luminosity. Finally, the authors show that careful consideration of the shape of the mean quasar SED and its redshift dependence leads to a lower estimate of the fraction of reddened /obscured AGNs missed by optical surveys as compared to estimates derived from a single mean MIR to optical flux ratio.