J/MNRAS/454/3722 AGN in nearby low-mass galaxies (Sartori+, 2015)
The search for active black holes in nearby low-mass galaxies using optical and
mid-IR data.
Sartori L.F., Schawinski K., Treister E., Trakhtenbrot B., Koss M.,
Shirazi M., Oh K.
<Mon. Not. R. Astron. Soc., 454, 3722-3742 (2015)>
=2015MNRAS.454.3722S 2015MNRAS.454.3722S (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Active gal. nuclei
Keywords: galaxies: active - galaxies: dwarf - galaxies: nuclei -
galaxies: Seyfert - infrared: galaxies
Abstract:
We investigated AGN activity in low-mass galaxies, an important regime
that can shed light on to black hole (BH) formation and evolution, and
their interaction with their host galaxies. We identified 336 AGN
candidates from a parent sample of ∼48000 nearby low-mass galaxies
(M*≤109.5M☉, z<0.1) in the Sloan Digital Sky Survey. We
selected the AGN using the classical BPT diagram, a similar optical
emission line diagnostic based on the HeII λ4686 line, and
mid-IR colour cuts. Different criteria select host galaxies with
different physical properties such as stellar mass and optical colour
and only 3 out of 336 sources fulfil all three criteria. This could be
in part due to selection biases. The resulting AGN fraction of ∼0.7
percent is at least one order of magnitude below the one estimated for
more massive galaxies. At optical wavelengths, the HeII-based AGN
selection appears to be more sensitive to AGN hosted in star-forming
galaxies than the classical BPT diagram, at least in the low-mass
regime. The archival X-ray and radio data available for some of the
AGN candidates seem to confirm their AGN nature, but follow-up
observations are needed to confirm the AGN nature of the rest of the
sample, especially in the case of mid-IR selection. Our sample will be
important for future follow-up studies aiming to understand the
relation between BHs and host galaxies in the low-mass regime.
Description:
We assembled a sample of nearby dwarf galaxies in the SDSS DR7
(Abazajian et al., 2009ApJS..182..543A 2009ApJS..182..543A) starting from the OSSY
catalogue (Oh-Sarzi-Schawinski-Yi; Oh et al.,
2011ApJS..195...13O 2011ApJS..195...13O). The OSSY catalogue provides line measurements
for the entire spectral atlas from SDSS DR7 with redshift z<0.2, as
well as fitting quality assessment parameters.2 We selected the
objects in the catalogue with SDSS SpecClass=2 (galaxy) and redshift
lower than z=0.1. We then matched the sample to the MPA-JHU
catalogue (Kauffmann et al., 2003MNRAS.341...33K 2003MNRAS.341...33K; Brinchmann et al.,
2004MNRAS.351.1151B 2004MNRAS.351.1151B) to obtain the stellar mass, and selected the
galaxies with mass lower than M*=109.5M☉. These masses were
derived using fits to photometry and assuming h=0.7. We further
excluded 0.17 per cent of the objects because of unreliable mass
estimation. The final sample of nearby dwarf galaxies consists of
48416 objects.
We searched for AGN in the nearby dwarf galaxy sample by applying
three AGN selection techniques:
1. classical BPT selection (optical emission line diagnostic) based on
the separation lines defined by Kewley et al. (2001ApJ...556..121K 2001ApJ...556..121K),
Kauffmann et al. (2003MNRAS.346.1055K 2003MNRAS.346.1055K) and Schawinski et al.
(2007MNRAS.382.1415S 2007MNRAS.382.1415S);
2. the emission line diagnostic based on HeII λ4686 described
by Shirazi & Brinchmann (2012MNRAS.421.1043S 2012MNRAS.421.1043S) (in the following
Shirazi HeII diagram); and
3. the mid-IR colour criteria described by Stern et al.
(2012ApJ...753...30S 2012ApJ...753...30S) and Jarrett et al. (2011ApJ...735..112J 2011ApJ...735..112J).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 77 48 BPT selected AGN candidates - 1/1
tablea2.dat 74 60 HeII selected AGN candidates - 1/2
tablea3.dat 77 61 HeII selected AGN candidates - 2/2
tablea4.dat 77 59 Mid-IR selected AGN candidates - 1/4
tablea5.dat 77 59 Mid-IR selected AGN candidates - 2/4
tablea6.dat 77 60 Mid-IR selected AGN candidates - 3/4
tablea7.dat 77 11 Mid-IR selected AGN candidates - 4/4
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Byte-by-byte Description of file: tablea?.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID ID number
7- 11 A5 --- n_ID [abc*, ] Notes on ID (1)
13- 14 I2 h RAh Rigth ascension (J2000)
16- 17 I2 min RAm Rigth ascension (J2000)
19- 23 F5.2 s RAs Rigth ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Declination (J2000)
29- 30 I2 arcmin DEm Declination (J2000)
32- 35 F4.1 arcsec DEs Declination (J2000)
37- 50 A14 --- MPF SDSS MJDPlateFibre
53- 58 F6.4 --- z Redshift
60- 63 F4.2 [Msun] logM* ?=- Stellar mass
65- 69 F5.2 [10-7W] L[OIII] ?=- [OIII] luminosity
71 A1 --- BPT [V] Classified as AGN with BPT
selection criterium (2)
73 A1 --- HeII [V] Classified as HeII with HeII
selection criterium (3)
75 A1 --- MidIRS [V] Classified as AGN with Mid-IR Stern et al.
(2012ApJ...753...30S 2012ApJ...753...30S) selection criterium
77 A1 --- MidIRJ [V] Classified as AGN with Mid-IR Jarrett et al.
(2011ApJ...735..112J 2011ApJ...735..112J) selection criterium
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Note (1): Notes as follows:
* = we assumed upper limits for Hβ
a = Classified as AGN also in Moran et al. (2014AJ....148..136M 2014AJ....148..136M)
b = Extended flag in WISE.
c = Classified as AGN also in Reines et al. (2013, Cat. J/ApJ/775/116)
Note (2): classical BPT selection (optical emission line diagnostic) based on
the separation lines defined by Kewley et al. (2001ApJ...556..121K 2001ApJ...556..121K),
Kauffmann et al. (2003MNRAS.346.1055K 2003MNRAS.346.1055K) and Schawinski et al.
(2007MNRAS.382.1415S 2007MNRAS.382.1415S).
Note (3): emission line diagnostic based on HeII λ4686 described
by Shirazi & Brinchmann (2012MNRAS.421.1043S 2012MNRAS.421.1043S) (in the following
Shirazi HeII diagram).
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 21-Jul-2016