J/MNRAS/464/553 SDSS DR7 QSOs spectral doppelgangers (Rochais+, 2017)
How similar are the properties of quasars with nearly identical
ultraviolet spectra?
Rochais T., Singh V., Chick W., Maithil J., Sutter J., Brotherton M.S.,
Shang Z.
<Mon. Not. R. Astron. Soc., 464, 553-563 (2017)>
=2017MNRAS.464..553R 2017MNRAS.464..553R (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Spectroscopy
Keywords: galaxies: active - quasars: general
Abstract:
The spectrum of a quasar contains important information about its
properties. Thus, it can be expected that two quasars with similar
spectra will have similar properties, but just how similar has not
before been quantified. Here we compare the ultraviolet spectra of a
sample of 5553 quasars from Data Release 7 of the Sloan Digital Sky
Survey, focusing on the 1350Å≤λ≤2900Å rest-frame
region which contains prominent emission lines from SiIV, OIV], CIV,
CIII], and MgII species. We use principal component analysis to
determine the dominant components of spectral variation, as well as to
quantitatively measure spectral similarity. As suggested by both the
Baldwin effect and modified Baldwin effect, quasars with similar
spectra have similar properties: bolometric luminosity, Eddington
fraction, and black hole mass. The latter two quantities are
calculated from the luminosity in conjunction with spectral features,
and the variation between quasars with virtually identical spectra
(which we call doppelgangers) is driven by the variance in the
luminosity plus measurement uncertainties. In the doppelgangers the
luminosity differences show 1σ uncertainties of 57 per cent (or
0.63mag) and ∼70 per cent 1σ uncertainties for mass and
Eddington fraction. Much of the difference in luminosities may be
attributable to time lags between the spectral lines and the
continuum. Furthermore, we find that suggestions that the mostly
highly accreting quasars should be better standard candles than other
quasars are not borne out for doppelgangers. Finally, we discuss the
implications for using quasars as cosmological probes and the nature
of the first two spectral principal components.
Description:
We constructed our sample from the SDSS Data Release 7 (DR7) using
measurements from Shen et al. (2011, Cat. J/ApJS/194/45).
We calculated hyperspace distances for the full pair-wise comparison
of every spectrum in our sample, a total of 15 415 128 pairs. Table 2
provides 1272 pairs with the smallest hyperdistance separations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 100 1272 The best SDSS DR7 spectral doppelgangers
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See also:
J/ApJS/194/45 : QSO properties from SDSS-DR7 (Shen+, 2011)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS1 SDSS name (HHMMSS.ss+DDMMSS.s) for first QSO
20- 23 I4 --- Plate1 SDSS plate number for first source of the pair
25- 27 I3 --- Fiber1 SDSS fiber number for first source of the pair
29- 33 I5 d MJD1 SDSS MJD number for first source of the pair
35- 52 A18 --- SDSS2 SDSS name (HHMMSS.ss+DDMMSS.s) for second QSO
54- 57 I4 --- Plate2 SDSS plate number for second source of the pair
59- 61 I3 --- Fiber2 SDSS fiber number for second source of the pair
63- 67 I5 d MJD2 SDSS MJD number for second source of the pair
69- 79 E11.6 --- d Hyperspace distance between the two spectra (1)
81- 86 F6.2 % DMBH Difference in black hole mass (2)
88- 93 F6.2 % DLcont-CIV Difference in continuum luminosity at CIV (2)
95-100 F6.2 % DL/DLedd Difference in the Eddington fraction (2)
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Note (1): Hyper distance is defined in equation 4 in the paper.
Note (2): The values used to calculate DMBH, DLcont-CIV, DL/LEdd were retrieved
from Shen et al. (2011, Cat. J/ApJS/194/45).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 15-May-2018