TY - JOUR
T1 - MID-INFRARED COLORS of DWARF GALAXIES
T2 - YOUNG STARBURSTS MIMICKING ACTIVE GALACTIC NUCLEI
AU - Hainline, Kevin N.
AU - Reines, Amy E.
AU - Greene, Jenny E.
AU - Stern, Daniel
N1 - Publisher Copyright:
© 2016. The American Astronomical Society. All rights reserved..
PY - 2016/12/1
Y1 - 2016/12/1
N2 - Searching for active galactic nuclei (AGNs) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ∼18,000 nearby dwarf galaxies (M ∗ < 3 × 109 M ∗, z < 0.055) in the Sloan Digital Sky Survey with significant detections in the first three bands of the AllWISE data release from the Wide-field Infrared Survey Explorer (WISE). First, we demonstrate that the majority of optically selected AGNs in dwarf galaxies are not selected as AGNs using WISE infrared color diagnostics and that the infrared emission is dominated by the host galaxies. We then investigate the infrared properties of optically selected star-forming dwarf galaxies, finding that the galaxies with the reddest infrared colors are the most compact, with blue optical colors, young stellar ages, and large specific star formation rates. These results indicate that great care must be taken when selecting AGNs in dwarf galaxies using infrared colors, as star-forming dwarf galaxies are capable of heating dust in such a way that mimics the infrared colors of more luminous AGNs. In particular, a simple color cut alone should not be used to select AGNs in dwarf galaxies. With these complications in mind, we present a sample of 41 dwarf galaxies that fall in the WISE infrared color space typically occupied by more luminous AGNs and that are worthy of follow-up observations.
AB - Searching for active galactic nuclei (AGNs) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ∼18,000 nearby dwarf galaxies (M ∗ < 3 × 109 M ∗, z < 0.055) in the Sloan Digital Sky Survey with significant detections in the first three bands of the AllWISE data release from the Wide-field Infrared Survey Explorer (WISE). First, we demonstrate that the majority of optically selected AGNs in dwarf galaxies are not selected as AGNs using WISE infrared color diagnostics and that the infrared emission is dominated by the host galaxies. We then investigate the infrared properties of optically selected star-forming dwarf galaxies, finding that the galaxies with the reddest infrared colors are the most compact, with blue optical colors, young stellar ages, and large specific star formation rates. These results indicate that great care must be taken when selecting AGNs in dwarf galaxies using infrared colors, as star-forming dwarf galaxies are capable of heating dust in such a way that mimics the infrared colors of more luminous AGNs. In particular, a simple color cut alone should not be used to select AGNs in dwarf galaxies. With these complications in mind, we present a sample of 41 dwarf galaxies that fall in the WISE infrared color space typically occupied by more luminous AGNs and that are worthy of follow-up observations.
KW - cosmology: observations
KW - galaxies: dwarf
KW - galaxies: evolution
KW - galaxies: nuclei
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U2 - 10.3847/0004-637X/832/2/119
DO - 10.3847/0004-637X/832/2/119
M3 - Article
AN - SCOPUS:85004001462
SN - 0004-637X
VL - 832
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 119
ER -