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Journal ArticleDOI

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 (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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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
UVsoftX-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 23 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, 166:470497, 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 quasarsas 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
1001 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.

Citations
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Journal ArticleDOI
TL;DR: In this article, a detailed comparison study between the CIV and MgII lines using a sample of active galactic nuclei (AGNs) selected from the Sloan Digital Sky Survey is presented.
Abstract: There are mutually contradictory views in the literature of the kinematics and structure of high-ionization line (e.g. CIV) emitting regions in active galactic nuclei (AGNs). Two kinds of broad emission line region (BELR) models have been proposed, outflow and gravitationally bound BELR, which are supported respectively by blueshift of the CIV line and reverberation mapping observations. To reconcile these two apparently different models, we present a detailed comparison study between the CIV and MgII lines using a sample of AGNs selected from the Sloan Digital Sky Survey. We find that the kinematics of the CIV region is different from that of MgII, which is thought to be controlled by gravity. A strong correlation is found between the blueshift and asymmetry of the CIV profile and the Eddington ratio. This provides strong observational support for the postulation that the outflow is driven by radiation pressure. In particular, we find robust evidence that the CIV line region is largely dominated by outflow at high Eddington ratios, while it is primarily gravitationally bounded at low Eddington ratios. Our results indicate that these two emitting regions coexist in most of AGNs. The emission strength from these two gases varies smoothly with Eddington ratio in opposite ways. This explanation naturally reconciles the apparently contradictory views proposed in previous studies. Finally, candidate models are discussed which can account for both, the enhancement of outflow emission and suppression of normal BEL, in AGN with high Eddington ratios.

89 citations


Cites background from "Spectral energy distributions and m..."

  • ...But it is not important here because the bolometric corrections differ between objects by a factor of 2 (e.g. Richards et al. 2006), much less than the Lbol/LEdd range of our sample....

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Journal ArticleDOI
TL;DR: In this paper, a multidimensional, multiwavelength selection of quasars from mid-infrared (MIR) plus optical data, specifically from Spitzer-Infrared Array Camera (IRAC) and the Sloan Digital Sky Survey (SDSS), was explored.
Abstract: We explore the multidimensional, multiwavelength selection of quasars from mid-infrared (MIR) plus optical data, specifically from Spitzer-Infrared Array Camera (IRAC) and the Sloan Digital Sky Survey (SDSS). Traditionally, quasar selection relies on cuts in two-dimensional color space despite the fact that most modern surveys (optical and IR) are done in more than three bandpasses. In this paper, we apply modern statistical techniques to combined Spitzer MIR and SDSS optical data, allowing up to eight-dimensional (8-D) color selection of quasars. Using a Bayesian selection method, we catalog 5546 quasar candidates to an 8.0 μm depth of 56 μJy over an area of ~24 deg2. Roughly 70% of these candidates are not identified by applying the same Bayesian algorithm to 4-color SDSS optical data alone. The 8-D optical+MIR selection on this data set recovers 97.7% of known type 1 quasars in this area and greatly improves the effectiveness of identifying 3.5 < z < 5 quasars which are challenging to identify (without considerable contamination) using MIR data alone. We demonstrate that, even using only the two shortest wavelength IRAC bandpasses (3.6 and 4.5 μm), it is possible to use our Bayesian techniques to select quasars with 97% completeness and as little as 10% contamination (as compared to ~60% contamination using color cuts alone). We compute photometric redshifts for our sample; comparison with known objects suggests a photometric redshift accuracy of 93.6% (Δz ± 0.3), remaining roughly constant when the two reddest MIR bands are excluded. Despite the fact that our methods are designed to find type 1 (unobscured) quasars, as many as 1200 of the objects are type 2 (obscured) quasar candidates. Coupling deep optical imaging data, with deep MIR data, could enable selection of quasars in significant numbers past the peak of the quasar luminosity function (QLF) to at least z ~ 4. Such a sample would constrain the shape of the QLF both above and below the break luminosity (L* Q ) and enable quasar clustering studies over the largest range of redshift and luminosity to date, yielding significant gains in our understanding of the physics of quasars and their contribution to galaxy evolution.

89 citations


Cites methods or result from "Spectral energy distributions and m..."

  • ...The additional 166 quasars as compared with Richards et al. (2006) come from the COSMOS and Boötes fields....

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  • ...Figure 12 shows the number counts of our sample as compared to the SDSS-DR3 (Richards et al. 2006) and 2QZ results (Croom et al. 2004)....

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  • ...…set populations, we have not utilized any optical magnitude or color information since optical quasar selection is known to be incomplete in certain redshift ranges (e.g., z ∼ 2.7, Richards et al. 2006), and the inclusion of these MIR-identified sources is our attempt to mitigate this effect....

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Journal ArticleDOI
TL;DR: In this paper, the mean star formation rates (SFRs) in the host galaxies of similar to 3000 optically selected quasi-stellar objects (QSOs) from the Sloan Digital Sky Survey within the Herschel-ATLAS fields, and a radio-luminous subsample covering the redshift range of z = 0.2-2.5.
Abstract: We investigate the mean star formation rates (SFRs) in the host galaxies of similar to 3000 optically selected quasi-stellar objects (QSOs) from the Sloan Digital Sky Survey within the Herschel-ATLAS fields, and a radio-luminous subsample covering the redshift range of z = 0.2-2.5. Using Wide-field Infrared Survey Explorer (WISE) and Herschel photometry (12-500 mu m) we construct composite spectral energy distributions (SEDs) in bins of redshift and active galactic nucleus (AGN) luminosity. We perform SED fitting to measure the mean infrared luminosity due to star formation, removing the contamination from AGN emission. We find that the mean SFRs show a weak positive trend with increasing AGN luminosity. However, we demonstrate that the observed trend could be due to an increase in black hole (BH) mass (and a consequent increase of inferred stellar mass) with increasing AGN luminosity. We compare to a sample of X-ray selected AGN and find that the two populations have consistent mean SFRs when matched in AGN luminosity and redshift. On the basis of the available virial BH masses, and the evolving BH mass to stellar mass relationship, we find that the mean SFRs of our QSO sample are consistent with those of main sequence star-forming galaxies. Similarly the radio-luminous QSOs have mean SFRs that are consistent with both the overall QSO sample and with star-forming galaxies on the main sequence. In conclusion, on average QSOs reside on the main sequence of star-forming galaxies, and the observed positive trend between the mean SFRs and AGN luminosity can be attributed to BH mass and redshift dependencies.

89 citations


Cites background or methods from "Spectral energy distributions and m..."

  • ...To do this we use the 6µm rest-frame luminosity of the fitted AGN components of our bins, and convert to an AGN bolometric luminosity with a bolometric correction factor of 8 (following Richards et al. 2006)....

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  • ...fits and bolometric corrections from the composite SED in Richards et al. (2006) (BC 5100Å = 9.26, BC 3000Å = 5.15 and BC 1350Å = 3.81; see Shen et al. 2011)....

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Journal ArticleDOI
TL;DR: In this article, the J-band luminosity function (LF) of 1838 mid-infrared and X-ray-selected active galactic nuclei (AGNs) in the red-shift range 0 3 was modeled by a double power law and found that it cannot be described by pure luminosity or pure density evolution, but must be a combination of both.
Abstract: We present the J-band luminosity function (LF) of 1838 mid-infrared and X-ray-selected active galactic nuclei (AGNs) in the redshift range 0 3, we observe a decrease in the space density of quasars of all brightnesses. We model the LF by a double power law and find that its evolution cannot be described by either pure luminosity or pure density evolution, but must be a combination of both. We used the bright-end slope determined by Croom et al. (2QZ) as a prior to fit the data in order to minimize the effects of our small survey area. The bright-end power-law index of our best-fit model remains consistent with the prior, while the best-fit faint-end index is consistent with the low-redshift measurements based on the 2QZ and 2SLAQ surveys. Our best-fit model generally agrees with the number of bright quasars predicted by other LFs at all redshifts. If we construct the QSO luminosity function using only the IRAC-selected AGNs, we find that the biases inherent to this selection method significantly modify the behavior of the characteristic density *(z) only for z < 1 and have no significant impact upon the characteristic magnitude M *,J (z).

88 citations

Journal ArticleDOI
TL;DR: In this article, the authors report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z = 0.4-2.5.
Abstract: We report on the X-ray and multiwavelength properties of 11 radio-quiet quasars with weak or no emission lines identified by the Sloan Digital Sky Survey (SDSS) with redshift z = 0.4-2.5. Our sample was selected from the Plotkin et al. catalog of radio-quiet, weak-featured active galactic nuclei (AGNs). The distribution of relative X-ray brightness for our low-redshift weak-line quasar (WLQ) candidates is significantly different from that of typical radio-quiet quasars, having an excess of X-ray weak sources, but it is consistent with that of high-redshift WLQs. Over half of the low-redshift WLQ candidates are X-ray weak by a factor of gsim 5, compared to a typical SDSS quasar with similar UV/optical luminosity. These X-ray weak sources generally show similar UV emission-line properties to those of the X-ray weak quasar PHL 1811 (weak and blueshifted high-ionization lines, weak semiforbidden lines, and strong UV Fe emission); they may belong to the notable class of PHL 1811 analogs. The average X-ray spectrum of these sources is somewhat harder than that of typical radio-quiet quasars. Several other low-redshift WLQ candidates have normal ratios of X-ray-to-optical/UV flux, and their average X-ray spectral properties are also similar to those of typical radio-quiet quasars. The X-ray weak and X-ray normal WLQ candidates may belong to the same subset of quasars having high-ionization "shielding gas" covering most of the wind-dominated broad emission-line region, but be viewed at different inclinations. The mid-infrared-to-X-ray spectral energy distributions (SEDs) of these sources are generally consistent with those of typical SDSS quasars, showing that they are not likely to be BL Lac objects with relativistically boosted continua and diluted emission lines. The mid-infrared-to-UV SEDs of most radio-quiet weak-featured AGNs without sensitive X-ray coverage (34 objects) are also consistent with those of typical SDSS quasars. However, one source in our X-ray-observed sample is remarkably strong in X-rays, indicating that a small fraction of low-redshift WLQ candidates may actually be BL Lac objects residing in the radio-faint tail of the BL Lac population. We also investigate universal selection criteria for WLQs over a wide range of redshift, finding that it is not possible to select WLQ candidates in a fully consistent way using different prominent emission lines (e.g., Lyα, C IV, Mg II, and Hβ) as a function of redshift.

88 citations


Cites background from "Spectral energy distributions and m..."

  • ...The majority ofthese sources have SEDs consistent with those of typical radio-quiet quasars in Richards et al. (2006), showing theyar more likely to be WLQs in nature rather than BL Lac objects....

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  • ...…SEDs are generally con- WEAK EMISSION-LINE QUASARS AT LOW REDSHIFT 13 14 WU ET AL. sistent with the composite SEDs of typical SDSS quasars in Richards et al. (2006), and they are significantly different from the SEDs of BL Lac objects (see the dotted parabolic line in the top-left panel…...

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References
More filters
Journal ArticleDOI
TL;DR: In this article, a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed, is presented.
Abstract: We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 μm data, we have constructed a map of the dust temperature so that the 100 μm map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected. To generate the full-sky dust maps, we must first remove zodiacal light contamination, as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 μm DIRBE map against the Leiden-Dwingeloo map of H I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 μm flux. This procedure removes virtually all traces of the zodiacal foreground. For the 100 μm map no significant CIB is detected. At longer wavelengths, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 ± 13 nW m-2 sr-1 at 140 μm and of 17 ± 4 nW m-2 sr-1 at 240 μm (95% confidence). This integrated flux ~2 times that extrapolated from optical galaxies in the Hubble Deep Field. The primary use of these maps is likely to be as a new estimator of Galactic extinction. To calibrate our maps, we assume a standard reddening law and use the colors of elliptical galaxies to measure the reddening per unit flux density of 100 μm emission. We find consistent calibration using the B-R color distribution of a sample of the 106 brightest cluster ellipticals, as well as a sample of 384 ellipticals with B-V and Mg line strength measurements. For the latter sample, we use the correlation of intrinsic B-V versus Mg2 index to tighten the power of the test greatly. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles reddening estimates in regions of low and moderate reddening. The maps are expected to be significantly more accurate in regions of high reddening. These dust maps will also be useful for estimating millimeter emission that contaminates cosmic microwave background radiation experiments and for estimating soft X-ray absorption. We describe how to access our maps readily for general use.

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)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors presented a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed.
Abstract: We present a full sky 100 micron map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 micron and 240 micron data, we have constructed a map of the dust temperature, so that the 100 micron map can be converted to a map proportional to dust column density. The result of these manipulations is a map with DIRBE-quality calibration and IRAS resolution. To generate the full sky dust maps, we must first remove zodiacal light contamination as well as a possible cosmic infrared background (CIB). This is done via a regression analysis of the 100 micron DIRBE map against the Leiden- Dwingeloo map of H_I emission, with corrections for the zodiacal light via a suitable expansion of the DIRBE 25 micron flux. For the 100 micron map, no significant CIB is detected. In the 140 micron and 240 micron maps, where the zodiacal contamination is weaker, we detect the CIB at surprisingly high flux levels of 32 \pm 13 nW/m^2/sr at 140 micron, and 17 \pm 4 nW/m^2/sr at 240 micron (95% confidence). This integrated flux is ~2 times that extrapolated from optical galaxies in the Hubble Deep Field. The primary use of these maps is likely to be as a new estimator of Galactic extinction. We demonstrate that the new maps are twice as accurate as the older Burstein-Heiles estimates in regions of low and moderate reddening. These dust maps will also be useful for estimating millimeter emission that contaminates CMBR experiments and for estimating soft X-ray absorption.

14,295 citations

Journal ArticleDOI
TL;DR: In this article, the authors find that the emerging standard model of cosmology, a flat -dominated universe seeded by a nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data.
Abstract: WMAP precision data enable accurate testing of cosmological models. We find that the emerging standard model of cosmology, a flat � -dominated universe seeded by a nearly scale-invariant adiabatic Gaussian fluctuations, fits the WMAP data. For the WMAP data only, the best-fit parameters are h ¼ 0:72 � 0:05, � bh 2 ¼ 0:024 � 0:001, � mh 2 ¼ 0:14 � 0:02, � ¼ 0:166 þ0:076 � 0:071 , ns ¼ 0:99 � 0:04, and � 8 ¼ 0:9 � 0:1. With parameters fixed only by WMAP data, we can fit finer scale cosmic microwave background (CMB) measure- ments and measurements of large-scale structure (galaxy surveys and the Lyforest). This simple model is also consistent with a host of other astronomical measurements: its inferred age of the universe is consistent with stellar ages, the baryon/photon ratio is consistent with measurements of the (D/H) ratio, and the inferred Hubble constant is consistent with local observations of the expansion rate. We then fit the model parameters to a combination of WMAP data with other finer scale CMB experiments (ACBAR and CBI), 2dFGRS measurements, and Lyforest data to find the model's best-fit cosmological parameters: h ¼ 0:71 þ0:04 � 0:03 , � bh 2 ¼ 0:0224 � 0:0009, � mh 2 ¼ 0:135 þ0:008 � 0:009 , � ¼ 0:17 � 0:06, ns(0.05 Mpc � 1 )=0 :93 � 0:03, and � 8 ¼ 0:84 � 0:04. WMAP's best determination of � ¼ 0:17 � 0:04 arises directly from the temperature- polarization (TE) data and not from this model fit, but they are consistent. These parameters imply that the age of the universe is 13:7 � 0:2 Gyr. With the Lyforest data, the model favors but does not require a slowly varying spectral index. The significance of this running index is sensitive to the uncertainties in the Ly� forest. By combining WMAP data with other astronomical data, we constrain the geometry of the universe, � tot ¼ 1:02 � 0:02, and the equation of state of the dark energy, w < � 0:78 (95% confidence limit assuming w �� 1). The combination of WMAP and 2dFGRS data constrains the energy density in stable neutrinos: � � h 2 < 0:0072 (95% confidence limit). For three degenerate neutrino species, this limit implies that their mass is less than 0.23 eV (95% confidence limit). The WMAP detection of early reionization rules out warm dark matter. Subject headings: cosmic microwave background — cosmological parameters — cosmology: observations — early universe On-line material: color figure

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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Journal ArticleDOI
TL;DR: The Sloan Digital Sky Survey (SDSS) as mentioned in this paper provides the data to support detailed investigations of the distribution of luminous and non-luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of pi steradians above about Galactic latitude 30 degrees in five broad optical bands.
Abstract: The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and non- luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of pi steradians above about Galactic latitude 30 degrees in five broad optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey of the approximately one million brightest galaxies and 10^5 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS, and serves as an introduction to extensive technical on-line documentation.

10,039 citations

Journal ArticleDOI
Donald G. York1, Jennifer Adelman2, John E. Anderson2, Scott F. Anderson3  +148 moreInstitutions (29)
TL;DR: The Sloan Digital Sky Survey (SDSS) as discussed by the authors provides the data to support detailed investigations of the distribution of luminous and non-luminous matter in the universe: a photometrically and astrometrically calibrated digital imaging survey of π sr above about Galactic latitude 30° in five broad optical bands to a depth of g' ~ 23 mag.
Abstract: The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and nonluminous matter in the universe: a photometrically and astrometrically calibrated digital imaging survey of π sr above about Galactic latitude 30° in five broad optical bands to a depth of g' ~ 23 mag, and a spectroscopic survey of the approximately 106 brightest galaxies and 105 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS and serves as an introduction to extensive technical on-line documentation.

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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Related Papers (5)
Frequently Asked Questions (1)
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.