J/AJ/149/203 Reddening of ∼35000 quasars from SDSS (Krawczyk+, 2015)
Mining for dust in type 1 quasars.
Krawczyk C.M., Richards G.T., Gallagher S.C., Leighly K.M., Hewett P.C.,
Ross N.P., Hall P.B.
<Astron. J., 149, 203 (2015)>
=2015AJ....149..203K 2015AJ....149..203K
ADC_Keywords: QSOs ; Reddening
Keywords: dust, extinction - infrared: galaxies - methods: statistical -
quasars: absorption lines - quasars: emission lines - quasars: general
Abstract:
We explore the extinction/reddening of ∼35000 uniformly selected
quasars with 0<z≤5.3 in order to better understand their intrinsic
optical/ultraviolet (UV) spectral energy distributions. Using
rest-frame optical-UV photometry taken from the Sloan Digital Sky
Survey's (SDSS) 7th data release, cross-matched to WISE in the
mid-infrared, 2MASS and UKIDSS in the near-infrared, and GALEX in the
UV, we isolate outliers in the color distribution and find them well
described by an SMC-like reddening law. A hierarchical Bayesian model
with a Markov Chain Monte Carlo sampling method was used to find
distributions of power law indices and E(B-V) consistent with both the
broad absorption line (BAL) and non-BAL samples. We find that, of the
ugriz color-selected type 1 quasars in SDSS, 2.5% (13%) of the non-BAL
(BAL) sample are consistent with E(B-V)>0.1 and 0.1% (1.3%) with
E(B-V)>0.2. Simulations show both populations of quasars are
intrinsically bluer than the mean composite, with a mean spectral
index (αλ) of -1.79 (-1.83). The emission and
absorption-line properties of both samples reveal that quasars with
intrinsically red continua have narrower Balmer lines and stronger
high-ionization emission lines, the latter indicating a harder
continuum in the extreme-UV and the former pointing to differences in
black hole mass and/or orientation.
Description:
For our data set we use the Mid-InfraRed through UltraViolet
cross-matched catalog provided by Krawczyk et al. 2013 (cat.
J/ApJS/206/4). These data are taken from the SDSS DR7 quasar catalog
(Schneider et al. 2010, cat. VII/260).
We calculated intrinsic power law slopes Δ(αλ)
and Small Magellanic Cloud (SMC) reddening law coefficients E(B-V) for
our ∼35000 selected quasars (see Table 2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 174 35970 Individual fit values
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See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
II/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)
VII/269 : SDSS Quasar Catalog, DR9Q (Paris+, 2012)
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJS/206/4 : SED and bolometric corrections for luminous QSOs
(Krawczyk+, 2013)
J/AJ/125/1711 : Broad Absorption Line Quasars from SDSS (Reichard+, 2003)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name Source identifier (HHMMSS.ss+DDMMSS.s; J2000)
20- 24 F5.2 --- Dal1 [-0.8/0.8] Δαλ, spectral
index difference for SMC reddening law (1)
26- 29 F4.2 --- E_Dal1 [0.05/0.22] Upper uncertainty in Dal1
31- 34 F4.2 --- e_Dal1 [0.04/0.25] Lower uncertainty in Dal1
36- 41 F6.3 mag E(B-V)1 (B-V) color excess with SMC reddening law
43- 47 F5.3 mag E_E(B-V)1 [0.003/0.25] Upper uncertainty in E(B-V)1
49- 53 F5.3 mag e_E(B-V)1 [0.003/0.25] Lower uncertainty in E(B-V)1
55- 61 E7.3 --- cov(aa)1 α,α covariance matrix value
63- 69 E7.3 --- cov(EE)1 E(B-V),E(B-V) covariance matrix value
71- 78 E8.3 --- cov(aE)1 α,E(B-V) covariance matrix value
80- 85 F6.2 --- DIC1 [-60/46] Deviance Information Criterion (2)
87- 91 F5.2 --- Dal2 [-0.5/0.9] Δαλ, Spectral
index difference for L14-QSO reddening law (1)
93- 96 F4.2 --- E_Dal2 Upper limit uncertainty in Dal2
98-101 F4.2 --- e_Dal2 Lower limit uncertainty in Dal2
103-108 F6.3 mag E(B-V)2 (B-V) color excess with L14-QSO reddening law
110-114 F5.3 mag E_E(B-V)2 [0.003/0.23] Upper uncertainty in E(B-V)2
116-120 F5.3 mag e_E(B-V)2 [0.001/0.10] Lower uncertainty in E(B-V)2
122-128 E7.3 --- cov(aa)2 α,α covariance matrix value (3)
130-136 E7.3 --- cov(EE)2 E(B-V),E(B-V) covariance matrix value (3)
138-145 E8.3 --- cov(aE)2 α,E(B-V) covariance matrix value (3)
147-152 F6.2 --- DIC2 [-44/50] Deviance Information Criterion (2)
154 I1 --- BAL [0/1] Broad Absorption Line (0=Non-BAL, 1=BAL)
157-174 I18 --- objID SDSS object identification (3)
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Note (1): L14-QSO reddening law from Leighly et al. (2014ApJ...788..123L 2014ApJ...788..123L).
The difference between the quasar's intrinsic spectral index and
the observed modal quasar spectral index of αλ=-1.72
(αν=-0.28, as determined from the modal colors in Figure 2),
with positive values being bluer, and Rλ is a function dependent
on the properties of the dust.
Note (2): The DIC is a generalization of the Bayesian Information Criterion
(BIC). The DIC is made up of two terms, one that is related to
the likelihood of the model explaining the data (similar to χ2),
and a penalty term based on the complexity of the model (i.e., the
effective degrees of freedom after taking into account the covariances
between the fitted variables). We have calculated the DIC for each
individual quasar and each reddening law to see what model fits better.
Overall we find the SMC reddening law does a better job fitting our data.
Please refer to Section 3.6 in the paper for additional details.
Note (3): the original table2 contained for the cov(*)2 parameters a copy
of the cov(*)1. These columns were corrected at CDS, via private
communications with Coleman Krawczyk; the column "objID" has also
been added; see also the "History" section below.
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History:
* 15-Jun-2015: From electronic version of the journal.
In this original version, the covariance matrix cov(*)2 for the
L14-QSO reddening law was a duplication of the cov(*)1 matrix
corresponding to the SMC reddening law.
* 17-Jul-2015: files with the covariances for the L14-QSO reddening law
parameters (cov(*)2 columns) were given by Coleman Krawczyk to
Francois Ochsenbein; the "objID" column included in the files
supplied by Coleman Krawczyk have been added to the table2.dat file.
(End) Greg Schwarz [AAS]; S. Guehenneux, F. Ochsenbein [CDS] 17-Jul-2015