DISCOVERY OF A POPULATION OF BULGELESS GALAXIES WITH EXTREMELY RED MID-IR COLORS: OBSCURED AGN ACTIVITY IN THE LOW-MASS REGIME?

In contrast to massive, bulge hosting galaxies, very few supermassive black holes (SMBHs) are known in either low-mass or bulgeless galaxies. Such a population could provide clues to the origins of SMBHs and to secular pathways for their growth. Using the all-sky Wide-field Infrared Survey Explorer...

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Bibliographic Details
Published in:The Astrophysical journal 2014-04, Vol.784 (2), p.1-8
Main Authors: Satyapal, S, Secrest, N J, McAlpine, W, Ellison, S L, Fischer, J, Rosenberg, J L
Format: Article
Language:English
Subjects:
Active galactic nuclei
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BLACK HOLES
COLOR
DECOMPOSITION
Disk galaxies
DUSTS
EMISSION
GALAXIES
GALAXY NUCLEI
GROWTH
Infrared
INFRARED SURVEYS
INTERMEDIATE INFRARED RADIATION
MASS
Origins
Sky surveys (astronomy)
SPECTRA
Stellar mass
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Summary:In contrast to massive, bulge hosting galaxies, very few supermassive black holes (SMBHs) are known in either low-mass or bulgeless galaxies. Such a population could provide clues to the origins of SMBHs and to secular pathways for their growth. Using the all-sky Wide-field Infrared Survey Explorer (WISE) survey, and bulge-to-disk decompositions from the Sloan Digital Sky Survey (SDSS) Data Release 7, we report the discovery of a population of local (z < 0.3) bulgeless disk galaxies with extremely red mid-infrared colors which are highly suggestive of a dominant active galactic nucleus (AGN), despite having no optical AGN signatures in their SDSS spectra. Using various mid-infrared selection criteria from the literature, there are between 30 and over 300 bulgeless galaxies with possible AGNs. Other known scenarios that can heat the dust to high temperatures do not appear to explain the observed colors of this sample. If these galaxies are confirmed to host AGNs, this study will provide a breakthrough in characterizing the properties of SMBHs in the low bulge mass regime and in understanding their relation with their host galaxies. Mid-infrared selection identifies AGNs that dominate their host galaxy's emission and therefore reveal a different AGN population than that uncovered by optical studies. We find that the fraction of all galaxies identified as candidate AGNs by WISE is highest at lower stellar masses and drops dramatically in higher mass galaxies, in striking contrast to the findings from optical studies.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/784/2/113