2018A&A...610A..31K


Query : 2018A&A...610A..31K

2018A&A...610A..31K - Astronomy and Astrophysics, volume 610A, 31-31 (2018/2-1)

What makes red quasars red? Observational evidence for dust extinction from line ratio analysis.

KIM D. and IM M.

Abstract (from CDS):

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.

Abstract Copyright: © ESO 2018

Journal keyword(s): quasars: general - quasars: emission lines - quasars: supermassive black holes - galaxies: evolution - galaxies: active

VizieR on-line data: <Available at CDS (J/A+A/610/A31): tablea1a.dat tablea1b.dat>

Simbad objects: 16

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Number of rows : 16
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 FIRST J003659.8-011332 QSO 00 36 59.8312535184 -01 13 32.518899516   21.63 20.76 20.023 18.630 ~ 10 0
2 Mrk 1502 Sy1 00 53 34.9331107632 +12 41 35.929269132   14.41 14.03     ~ 1115 1
3 2MASS J08173959+4354199 Sy1 08 17 39.5809057368 +43 54 20.230011648   21.29 20.29 18.66   ~ 9 0
4 QSO J0825+4716 QSO 08 25 02.059 +47 16 51.99   21.19 20.77 20.45   ~ 14 0
5 2MASS J09150172+2418121 Sy1 09 15 01.7199333984 +24 18 12.092683104   20.69 20.38 20.80   ~ 28 0
6 2MASS J11135466+1244390 Sy1 11 13 54.6593262552 +12 44 39.060865860   21.59 20.74 19.00   ~ 33 0
7 2MASS J12092107-0107168 QSO 12 09 21.0894344160 -01 07 17.001623100   20.07 19.22 17.86   ~ 7 0
8 [VV2006] J122703.2+505356 QSO 12 27 03.1962516984 +50 53 56.208944256   20.02 19.27 18.77   ~ 26 0
9 2MASS J13070066+2338050 QSO 13 07 00.6300561336 +23 38 05.144506728   20.81 19.92 19.37   ~ 25 0
10 2MASS J13091697+6042086 QSO 13 09 16.971 +60 42 08.63   22.95 22.09 20.80   ~ 8 0
11 2MASS J14340456+0935287 QSO 14 34 04.5805237368 +09 35 28.509398556   23.48 22.05 19.88   ~ 6 0
12 2XMM J153233.2+241526 QSO 15 32 33.177 +24 15 25.79   20.6   20.1   ~ 9 0
13 QSO J1656+3821 QSO 16 56 47.128 +38 21 36.70   23.70 22.68 20.80   ~ 13 0
14 2MASS J17202762+6156577 QSO 17 20 27.5737304952 +61 56 57.370261920   23.64 22.43 20.38   ~ 6 0
15 2MASS J23254988-1052441 QSO 23 25 49.8862601208 -10 52 43.891375872   20.98 20.13 19.70   ~ 7 0
16 2MASS J23390381-0912211 Sy1 23 39 03.8253377688 -09 12 21.261644928   21.50 20.31 18.6   ~ 28 0

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2022.12.07-04:47:55

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