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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.

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55 citations

Journal ArticleDOI
TL;DR: In this article, the authors explore self-similar, dusty disk winds, driven by both magnetocentrifugal forces and radiation pressure, as an explanation for the torus and make predictions of AGN infrared (IR) spectral energy distributions from 2 to 100 µm by varying parameters such as the viewing angle (from i = 0 Degree-Sign to 90 degree-Sign ), the base column density of the wind, the Eddington ratio (from L/L{sub Edd} = 0.01 to 0.1), the black hole mass (from M{sub
Abstract: An integral part of the unified model for active galactic nuclei (AGNs) is an axisymmetric obscuring medium, which is commonly depicted as a torus of gas and dust surrounding the central engine. However, a robust, dynamical model of the torus is required in order to understand the fundamental physics of AGNs and interpret their observational signatures. Here, we explore self-similar, dusty disk winds, driven by both magnetocentrifugal forces and radiation pressure, as an explanation for the torus. Using these models, we make predictions of AGN infrared (IR) spectral energy distributions from 2 to 100 {mu}m by varying parameters such as the viewing angle (from i = 0 Degree-Sign to 90 Degree-Sign ), the base column density of the wind (from N{sub H,0} = 10{sup 23} to 10{sup 25} cm{sup -2}), the Eddington ratio (from L/L{sub Edd} = 0.01 to 0.1), the black hole mass (from M{sub BH} = 10{sup 8} to 10{sup 9} M{sub Sun }), and the amount of power in the input spectrum emitted in the X-ray relative to that emitted in the UV/optical (from {alpha}{sub ox} = 1.1 to 2.1). We find that models with N{sub H,0} = 10{sup 25} cm{sup -2}, L/L{sub Edd} = 0.1, andmore » M{sub BH} {>=} 10{sup 8} M{sub Sun} are able to adequately approximate the general shape and amount of power expected in the IR as observed in a composite of optically luminous Sloan Digital Sky Survey quasars. The effect of varying the relative power coming out in X-rays relative to the UV is a change in the emission below {approx}5 {mu}m from the hottest dust grains; this arises from the differing contributions to heating and acceleration of UV and X-ray photons. We see mass outflows ranging from {approx}1 to 4 M{sub Sun} yr{sup -1}, terminal velocities ranging from {approx}1900 to 8000 km s{sup -1}, and kinetic luminosities ranging from {approx}1 Multiplication-Sign 10{sup 42} to 8 Multiplication-Sign 10{sup 43} erg s{sup -1}. Further development of this model holds promise for using specific features of observed IR spectra in AGNs to infer fundamental physical parameters of the systems.« less

55 citations

Journal ArticleDOI
TL;DR: The most highly accreting quasars (xA) are of special interest in studies of the physics of AGNs and host galaxy evolution, and their observational properties are largely unknown as mentioned in this paper.
Abstract: The most highly accreting quasars (xA) are of special interest in studies of the physics of AGNs and host galaxy evolution. Quasars accreting at high rates (L/LEdd $\sim$ 1) hold promise for use as 'standard candles': distance indicators detectable at very high redshift. However, their observational properties are largely unknown. A large sample of xA can clarify the main properties of quasars radiating near L/LEdd $\sim$ 1 in the Hb spectral range for redshift $\lt$ 0.8. We use selection criteria derived from 4DE1 studies to identify and analyze spectra for a sample of 334 candidate sources identified from the SDSS DR7 database. The source spectra were chosen to show a ratio RFeII between the FeII emission blend at 4570 A and Hb, RFeII $\gt$ 1. Composite spectra were analyzed for systematic trends as a function of FeII strength, line width, and [OIII] strength. We introduced tighter constraints on the signal-to-noise ratio (S/N) and RFeII values that allowed us to isolate sources most likely to be extreme accretors. We provide a database of detailed measurements. Analysis of the data allows us to confirm that Hb shows a Lorentzian function with a FWHM of Hb $\lt$ 4000 km s-1. Systematic [OIII] blue shifts, as well as a blueshifted component in Hb are revealed. We interpret the blueshifts as related to the signature of outflowing gas from the quasar central engine. The FWHM of Hb is still affected by the blueshifted emission, however, the effect is non-negligible if the FWHM Hb is used as a 'virial broadening estimator'. A effect of the viewing angle on Hb broadening, deriving a correction for those sources that shows disagreement between virial and concordance cosmology luminosity values. The scatter between concordance cosmology and virial luminosity estimates can be reduced if a correction for orientation effects is included in the FWHM Hb value.

55 citations


Additional excerpts

  • ...The bolometric luminosity is given by L = CλLλ(5100Å), where we assume C ≈ 12.17 as bolometric correction for the luminosity at 5100Å λLλ(5100Å) (Richards et al. 2006)....

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Journal ArticleDOI
TL;DR: In this paper, the authors discuss 76 large amplitude transients (Δm > 15) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN).
Abstract: We discuss 76 large amplitude transients (Δm > 15) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN) They have been discovered as part of the Pan-STARRS1 (PS1) 3π survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT) Based on colours, light-curve shape, and spectra, these transients fall into four groups A few are misclassified stars or objects of unknown type Some are red/fast transients and are known or likely nuclear supernovae A few are either radio sources or erratic variables and so likely blazars However the majority (∼66 per cent) are blue and evolve slowly, on a time-scale of years Spectroscopy shows them to be AGN at z ∼ 03 − 14, which must have brightened since the SDSS photometry by around an order of magnitude It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN By searching the SDSS Stripe 82 quasar database, we find 15 similar objects We discuss several possible explanations for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies A mixture of explanations (iii) and (iv) seems most likely Both hold promise of considerable new insight into the AGN phenomenon

54 citations


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

  • ...For a bolometric correction of 5 (Richards et al. 2006) and an Eddington fraction of f = 0.1, this implies a black hole mass of 4 × 108 M ....

    [...]

  • ...Using standard bolometric corrections from e.g. Elvis et al. (1994) or Richards et al. (2006), our objects have peak luminosities of Lbol ∼ 1039 W....

    [...]

Journal ArticleDOI
TL;DR: In this article, a new approach to the anti-correlation between the optical-X-ray spectral index, alpha_ox, and the monochromatic optical luminosity, l_opt, was developed.
Abstract: We develop a new approach to the well-studied anti-correlation between the optical-to-X-ray spectral index, alpha_ox, and the monochromatic optical luminosity, l_opt. By cross-correlating the SDSS DR5 quasar catalog with the XMM-Newton archive, we create a sample of 327 quasars with X-ray S/N > 6, where both optical and X-ray spectra are available. This allows alpha_ox to be defined at arbitrary frequencies, rather than the standard 2500 Angstroms and 2 keV. We find that while the choice of optical wavelength does not strongly influence the alpha_ox-l_opt relation, the slope of the relation does depend on the choice of X-ray energy. The slope of the relation becomes steeper when alpha_ox is defined at low (~ 1 keV) X-ray energies. This change is significant when compared to the slope predicted by a decrease in the baseline over which alpha_ox is defined. The slopes are also marginally flatter than predicted at high (~ 10 keV) X-ray energies. Partial correlation tests show that while the primary driver of alpha_ox is l_opt, the Eddington ratio correlates strongly with alpha_ox when l_opt is taken into account, so accretion rate may help explain these results. We combine the alpha_ox-l_opt and Gamma -L_bol/L_Edd relations to naturally explain two results: 1) the existence of the Gamma-l_x relation as reported in Young et al. (2009) and 2) the lack of a Gamma-l_opt relation. The consistency of the optical/X-ray correlations establishes a more complete framework for understanding the relation between quasar emission mechanisms. We also discuss two correlations with the hard X-ray bolometric correction, which we show correlates with both alpha_ox and Eddington ratio. This confirms that an increase in accretion rate correlates with a decrease in the fraction of up-scattered disk photons.

54 citations


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

  • ...To calculate the Eddington ratio, we use the Richards et al. (2006) bolometric correction for 3000 Å, κ3000 = 5.62±1.14....

    [...]

  • ...Though bolometric corrections are by nature uncertain, Figure 12 of Richards et al. (2006) shows that 3000, as well as 5100 Å are regions of relatively small dispersion in the composite SEDs....

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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)....

    [...]

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.