J/A+A/610/A31 0.8-2.5um spectra of 2 red quasars (Kim+, 2018)
What makes red quasars red? Observational evidence for dust extinction from
line ratio analysis.
Kim D., Im M.
<Astron. Astrophys. 610, A31 (2018)>
=2018A&A...610A..31K 2018A&A...610A..31K (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Spectra, infrared
Keywords: quasars: general - quasars: emission lines -
quasars: supermassive black holes - galaxies: evolution -
galaxies: active
Abstract:
Red quasars are very red in the optical through near-infrared (NIR)
wavelengths, which is possibly due to dust extinction in their host
galaxies as expected in a scenario in which red quasars are an
intermediate population between merger-driven star-forming galaxies
and unobscured type 1 quasars. However, alternative mechanisms also
exist to explain their red colors: (i) an intrinsically red continuum;
(ii) an unusual high covering factor of the hot dust component, that
is, CFHD=LHD/Lbol, where the LHD is the luminosity from the
hot dust component and the Lbol is the bolometric luminosity; and
(iii) a moderate viewing angle. In order to investigate why red
quasars are red, we studied optical and NIR spectra of 20 red quasars
at z∼0.3 and 0.7, where the usage of the NIR spectra allowed us to
look into red quasar properties in ways that are little affected by
dust extinction. The Paschen to Balmer line ratios were derived for 13
red quasars and the values were found to be ∼10 times higher than
unobscured type 1 quasars, suggesting a heavy dust extinction with
AV>2.5mag. Furthermore, the Paschen to Balmer line ratios of red
quasars are difficult to explain with plausible physical conditions
without adopting the concept of the dust extinction. The CFHD of red
quasars are similar to, or marginally higher than, those of unobscured
type 1 quasars. The Eddington ratios, computed for 19 out of 20 red
quasars, are higher than those of unobscured type 1 quasars (by
factors of 3-5), and hence the moderate viewing angle scenario is
disfavored. Consequently, these results strongly suggest the dust
extinction that is connected to an enhanced nuclear activity as the
origin of the red color of red quasars, which is consistent with the
merger-driven quasar evolution scenario.
Description:
We provide 0.8-2.5um spectra of two red quasars (0036-0113 and
1307+2338) taken with NASA IRTF.
Objects:
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RA (2000) DE Designation(s) (redshift)
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00 36 59.85 -01 13 32.30 0036-0113 (z=0.294)
13 07 00.62 +23 38 05.31 1307+2338 = F2MS J1307+2338 (z=0.275)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1a.dat 27 3032 0.8-2.5um spectrum of red quasar 0036-0113
tablea1b.dat 27 3037 0.8-2.5um spectrum of red quasar 1307+2338
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See also:
J/ApJ/812/66 : NIR spectra of 5 red quasars at 0.5<z<0.9 (Kim+, 2015)
Byte-by-byte Description of file: tablea1a.dat tablea1b.dat
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Bytes Format Units Label Explanations
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1- 5 I5 0.1nm Wave Wavelength in Angstroms
7- 16 E10.4 10mW/m2/nm Flambda ?=- Flux in ergs/s/cm2/Angstrom
19- 27 E9.4 10mW/m2/nm e_Flambda ?=- Error in Flambda
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Acknowledgements:
Dohyeong Kim, dh.dr2kim(at)gmail.com
(End) Patricia Vannier [CDS] 05-Mar-2018