J/MNRAS/487/3305 Broad-line velocity shifts in 1.5<z<7.5 quasars (Meyer+, 2019)
New constraints on quasar evolution:
broad-line velocity shifts over 1.5~<z~<7.5.
Meyer R.A., Bosman S.E.I., Ellis R.S.
<Mon. Not. R. Astron. Soc., 487, 3305-3323 (2019)>
=2019MNRAS.487.3305M 2019MNRAS.487.3305M (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs ; Redshifts ; Ultraviolet
Keywords: galaxies: evolution - quasars: emission lines
Abstract:
We present the results of a model-independent investigation of the
rest-frame UV spectra from a comprehensive sample of 394 quasars in
the redshift range 1.5=<z=<7.5. We fit the main broad emission lines
(BELs) in the rest-frame range 1280Å=<λ=<3000Å (OI, CII,
SiIV, CIII, CIV, and MgII) with a lightly supervised spline fitting
technique. Redshifts are derived from the peaks of each fitted BEL and
used to compute relative velocity shifts. We show that our method
gives unbiased velocity shifts and is insensitive to spectral
resolution and instrumental parameters. It is found that the average
blueshift of the CIV line with respect to several low-ionization lines
in luminosity-matched samples does not significantly evolve over
1.5=<z=<6. However, the average blueshift increases significantly by a
factor of ∼2.5 at z≳6. We propose that this redshift evolution can be
explained by CIV winds launched perpendicularly to an accretion disc
with increased torus opacity at high redshift, coupled with a
potential orientation-driven selection bias. Our results open new
exciting avenues of investigation into young quasars in the
reionization epoch.
Description:
In order to study the velocity shifts of quasar UV broad emission
lines (BELs) across cosmic time, we have gathered a large sample of
quasar spectra in infrared and optical light from different surveys
and archival data.
For the SDSS DR7 quasar catalog (DR7Q, Schneider et al.
2010AJ....139.2360S 2010AJ....139.2360S, Cat. VII/260) we make use of the value-added
catalogue of Shen et al. (2011ApJS..194...45S 2011ApJS..194...45S, Cat. J/ApJS/194/45)
that provides redshifts derived from CIV, CIII, and MgII, and the
specific luminosities. In DR7Q, the line-based redshifts (i.e.
redshifts derived from one emission line) are derived by fitting a
multi-Gaussian template to each BEL and taking the template peak to
derive the redshift. In DR12Q however (Paris et al.
2017A&A...597A..79P 2017A&A...597A..79P, Cat. VII/279), all quasars were inspected by eye
and have thus a visual redshift, which is different from the
line-based redshifts.
XQ100 (Lopez et al. 2016A&A...594A..91L 2016A&A...594A..91L) is a legacy European Southern
Observatory (ESO) survey that observed 100 quasars at 3.5=<z=<4.5 at
medium resolution (R∼6000-9000) and a high median signal-to-noise
ratio (SNR) ∼30 with the XShooter instrument (Vernet et al.
2011A&A...536A.105V 2011A&A...536A.105V) at the Very Large Telescope (VLT). The combined
wavelength range of XShooter's UVB, VIS, and NIR arms (3150-24800Å,
or 3150-18000Å, depending on at which point in the survey the
object was observed) is well suited to the aim of this study as all UV
BELs can be retrieved over the entire redshift range.
The Giant Gemini GMOS survey (GGG; Worseck et al. 2014MNRAS.445.1745W 2014MNRAS.445.1745W,
Cat. J/MNRAS/445/1745) obtained spectra of quasars over 4.4=<z=<5.5
with the Gemini Multi Object Spectrometers (GMOS) to study the
Lyman-continuum (LyC) flux at z∼5 and determine the LyC photon mean
free path. The publicly available data release of the GGG survey is
composed of 163 quasars at low resolution (R∼800-900) with a
medium-high SNR∼20, making it also suitable to capture the broad
shapes of the UV BELs.
Our first high-redshift sample (hereafter 'z6') consists of a subset
of quasars from the extensive list of z∼6 objects from Bosman et al.
(2018MNRAS.479.1055B 2018MNRAS.479.1055B), of which some were re-reduced later by Meyer et
al. (2019MNRAS.483...19M 2019MNRAS.483...19M). We keep only those with near-infrared
coverage and high SNR, limiting the sample to 11 objects.
Our second high-redshift sample is composed of the Mazzucchelli et al.
(2017ApJ...849...91M 2017ApJ...849...91M) quasars that are observed far enough in the
infrared to detect at least CIV, to which we add the present
record-holding z=7.54 quasar (Banados et al. 2018Natur.553..473B 2018Natur.553..473B),
kindly provided by private communication of the authors. This sample
thus comprises 12 quasars observed with various instruments with
=6.73, median SNR∼6 (although individual spectra range from ∼2 to
∼100), and resolution R∼6000.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sdssz.dat 45 108 BEL-based redshifts for SDSS Quasars
xq100z.dat 54 100 BEL-based redshifts for XQ100 Quasars
gggz.dat 34 123 BEL-based redshifts for GGG Quasars
z6z.dat 40 11 BEL-based redshifts for z6 Quasars
z7z.dat 40 12 BEL-based redshifts for z7 Quasars
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See also:
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)
VII/279 : SDSS quasar catalog: twelfth data release (Paris+, 2017)
J/MNRAS/445/1745 : Giant Gemini GMOS survey. I. (Worseck+, 2014)
Byte-by-byte Description of file: sdssz.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- ID SDSS spectroscopic Plate-MJD-Fiber identifier
17- 20 F4.2 --- zOI ? OI-based redshift
22- 25 F4.2 --- zCII ? CII-based redshift
27- 30 F4.2 --- zSiIV ? SiIV-based redshift
32- 35 F4.2 --- zCIV ? CIV-based redshift
37- 40 F4.2 --- zCIII ? CIII-based redshift
42- 45 F4.2 --- zMgII ? MgII-based redshift
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Byte-by-byte Description of file: xq100z.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Name Quasar name
26- 29 F4.2 --- zOI ? OI-based redshift
31- 34 F4.2 --- zCII ? CII-based redshift
36- 39 F4.2 --- zSiIV ? SiIV-based redshift
41- 44 F4.2 --- zCIV ? CIV-based redshift
46- 49 F4.2 --- zCIII ? CIII-based redshift
51- 54 F4.2 --- zMgII ? MgII-based redshift
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Byte-by-byte Description of file: gggz.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- Name Quasar name (SDSSJHHMM+DDMM)
16- 19 F4.2 --- zOI ? OI-based redshift
21- 24 F4.2 --- zCII ? CII-based redshift
26- 29 F4.2 --- zSiIV ? SiIV-based redshift
31- 34 F4.2 --- zCIV ? CIV-based redshift
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Byte-by-byte Description of file: z6z.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Quasar name, JHHMM+DDMM
(QSO JHHMM+DDMM in Simbad)
12- 15 F4.2 --- zOI ? OI-based redshift
17- 20 F4.2 --- zCII ? CII-based redshift
22- 25 F4.2 --- zSiIV ? SiIV-based redshift
27- 30 F4.2 --- zCIV ? CIV-based redshift
32- 35 F4.2 --- zCIII CIII-based redshift
37- 40 F4.2 --- zMgII ? MgII-based redshift
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Byte-by-byte Description of file: z7z.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Quasar name
12- 15 F4.2 --- zOI ? OI-based redshift
17- 20 F4.2 --- zCII ? CII-based redshift
22- 25 F4.2 --- zSiIV SiIV-based redshift
27- 30 F4.2 --- zCIV CIV-based redshift
32- 35 F4.2 --- zCIII ? CIII-based redshift
37- 40 F4.2 --- zMgII ? MgII-based redshift
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 16-Nov-2022