2018MNRAS.478.2576M -
Mon. Not. R. Astron. Soc., 478, 2576-2591 (2018/August-1)
Intermediate-mass black holes in dwarf galaxies out to redshift ∼2.4 in the Chandra COSMOS-Legacy Survey.
MEZCUA M., CIVANO F., MARCHESI S., SUH H., FABBIANO G. and VOLONTERI M.
Abstract (from CDS):
We present a sample of 40 active galactic nucleus (AGN) in dwarf galaxies at redshifts z <= 2.4. The galaxies are drawn from the Chandra COSMOS-Legacy survey as having stellar masses 107 <= M* <= 3 x 109 M☉. Most of the dwarf galaxies are star forming. After removing the contribution from star formation to the X-ray emission, the AGN luminosities of the 40 dwarf galaxies are in the range L_0.5-10 keV_ ∼ 1039-1044 erg s–1. With 12 sources at z > 0.5, our sample constitutes the highest-redshift discovery of AGN in dwarf galaxies. The record-holder is cid_1192, at z = 2.39 and with L_0.5-10 keV_ ∼ 1044 erg s–1. One of the dwarf galaxies has M* = 6.6 x 107 M☉ and is the least massive galaxy found so far to host an AGN. All the AGN are of type 2 and consistent with hosting intermediate-mass black holes (BHs) with masses ∼104-105 M☉ and typical Eddington ratios >1 per cent. We also study the evolution, corrected for completeness, of AGN fraction with stellar mass, X-ray luminosity, and redshift in dwarf galaxies out to z = 0.7. We find that the AGN fraction for 109 < M* <= 3 x 109 M☉ and LX ∼ 1041-1042 erg s–1 is ∼0.4 per cent for z <= 0.3 and that it decreases with X-ray luminosity and decreasing stellar mass. Unlike massive galaxies, the AGN fraction seems to decrease with redshift, suggesting that AGN in dwarf galaxies evolve differently than those in high-mass galaxies. Mindful of potential caveats, the results seem to favour a direct collapse formation mechanism for the seed BHs in the early Universe.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
galaxies: active - galaxies: dwarf - galaxies: starburst - X-rays: galaxies
Simbad objects:
49
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