J/MNRAS/466/2879 Active galactic nuclei from HeII (Bar+, 2017)
Active galactic nuclei from He II: a more complete census of AGN in SDSS
galaxies yields a new population of low-luminosity AGN in highly star-forming
galaxies.
Bar R.E., Weigel A.K., Sartori L.F., Oh K., Koss M., Schawinski K.
<Mon. Not. R. Astron. Soc., 466, 2879-2887 (2017)>
=2017MNRAS.466.2879B 2017MNRAS.466.2879B (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Redshifts
Keywords: galaxies: active - galaxies: evolution - galaxies: nuclei -
galaxies: Seyfert - galaxies: star formation
Abstract:
In order to perform a more complete census of active galactic nuclei
(AGN) in the local Universe, we investigate the use of the HeII
λ4685 emission line diagnostic diagram by Shirazi & Brinchmann
(2012, Cat. J/MNRAS/421/1043) in addition to the standard methods
based on other optical emission lines. The HeII-based diagnostics is
more sensitive to AGN ionization in the presence of strong star
formation than conventional line diagnostics. We survey a
magnitude-limited sample of 63915 galaxies from the Sloan Digital Sky
Survey Data Release 7 at 0.02<z<0.05 and use both the conventional BPT
emission line diagnostic diagrams, as well as the HeII diagram to
identify AGN. In this sample, 1075 galaxies are selected as AGN using
the BPT diagram, while additional 234 galaxies are identified as AGN
using the HeII diagnostic diagram, representing a 22 per cent increase
of AGN in the parent galaxy sample. We explore the host galaxy
properties of these new HeII-selected AGN candidates and find that
they are most common in star-forming galaxies on the blue cloud and on
the main sequence where ionization from star formation is most likely
to mask AGN emission in the BPT lines. We note in particular a high He
II AGN fraction in galaxies above the high-mass end of the main
sequence where quenching is expected to occur. We use archival Chandra
observations to confirm the AGN nature of candidates selected through
He II-based diagnostic. Finally, we discuss how this technique can
help inform galaxy/black hole coevolution scenarios.
Description:
We base our sample on the seventh data release (DR7) of the Sloan
Digital Sky Survey (SDSS; York et al. 2000AJ....120.1579Y 2000AJ....120.1579Y; Abazajian
et al. 2009ApJS..182..543A 2009ApJS..182..543A). We cross-match the New York Value-Added
Galaxy Catalog (Blanton et al. 2005AJ....129.2562B 2005AJ....129.2562B; Padmanabhan et al.
2008ApJ...674.1217P 2008ApJ...674.1217P) with the Max Planck Institute for Astrophysics
John Hopkins University (Kauffmann et al. 2003MNRAS.346.1055K 2003MNRAS.346.1055K;
Brinchmann et al. 2004MNRAS.351.1151B 2004MNRAS.351.1151B) catalogue to obtain properties
such as stellar masses and star formation rates. We used nebular
emission line strengths provided by the OSSY catalogue (Oh et al.
2011ApJS..195...13O 2011ApJS..195...13O). This yields a total of 605019 objects. In order
to obtain a magnitude limited sample, we limit the redshift interval
to 0.02<z<0.05 and only consider the galaxies with absolute
Petrosian r-band magnitude ←19.0. The remaining sample consists of
63915 galaxies. For the BPT diagram, we further restrict our sample
to the presence of the [OIII], [NII], Hα and Hβ lines with
signal to noise (S/N)>3 resulting in a sample of 37425 galaxies; for
the HeII emission line diagnostic diagram, the restricted sample based
on the presence of the HeII, [NII], Hα and Hβ lines with
S/N>3 is 872 galaxies.
We provide of all the BPT-selected AGN candidates and the additional
AGN candidates selected by the HeII method in table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 81 1316 All the BPT-selected AGN candidates and additional
AGN candidates selected by the HeII method
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS SDSS ObjId
20- 28 F9.5 deg RAdeg Right ascension (J2000)
30- 39 F10.6 deg DEdeg Declination (J2000)
41- 52 E12.6 --- z Redshift
54- 62 F9.5 Msun Mass Mass
64- 71 F8.6 mag u-r ?=- SDSS u-r colour index
73 I1 --- BPT-AGN [0/1] BPT-selected AGN candidates ?
75 I1 --- HeII-AGN [0/1] HeII-selected AGN candidates ?
77 I1 --- HeII-BPT-AGN [0/1] AGN candidates selected by both
methods ?
79 I1 --- HeII-only [0/1] HeII-only AGN candidates ?
81 I1 --- BAD [0/1] 1 when HeII spectra considered as
unreliable
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 17-Oct-2019