Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey

Chen (陳建廷), C.-T.J.; Brandt, W.N.; Reines, A.E.; Lansbury, G.; Stern, D.; Alexander, D.M.; Bauer, F.; Moro, A. Del; Gandhi, P.; Harrison, F.A.; Hickox, R.C.; Koss, M.J.; Lanz, L.; Luo, B.; Mullaney, J.R.; Ricci, C.; Trump, J.R.

doi:10.3847/1538-4357/aa5d5b

Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey

Chen (陳建廷), C.-T.J.; Brandt, W.N.; Reines, A.E.; Lansbury, G.; Stern, D.; Alexander, D.M.; Bauer, F.; Moro, A. Del; Gandhi, P.; Harrison, F.A.; Hickox, R.C.; Koss, M.J.; Lanz, L.; Luo, B.; Mullaney, J.R.; Ricci, C.; Trump, J.R.

Authors

C.-T.J. Chen (陳建廷)

W.N. Brandt

A.E. Reines

G. Lansbury

D. Stern

Professor David Alexander d.m.alexander@durham.ac.uk
Professor

F. Bauer

A. Del Moro

P. Gandhi

F.A. Harrison

R.C. Hickox

M.J. Koss

L. Lanz

B. Luo

J.R. Mullaney

C. Ricci

J.R. Trump

Abstract

We present a sample of 10 low-mass active galactic nuclei (AGNs) selected from the 40-month NuSTAR serendipitous survey. The sample is selected to have robust NuSTAR detections at 3−24~keV, to be at z<0.3, and to have optical r-band magnitudes at least 0.5~mag fainter than an L⋆ galaxy at its redshift. The median values of absolute magnitude, stellar mass and 2--10 X-ray luminosity of our sample are ⟨Mr⟩=−20.03, ⟨M⋆⟩=4.6×109M⊙, and ⟨L2−10keV⟩=3.1×1042 erg s−1, respectively. Five objects have detectable broad Hα emission in their optical spectra, indicating black-hole masses of (1.1−10.4)×106M⊙. We find that 30+17−10% of the galaxies in our sample do not show AGN-like optical narrow emission lines, and one of the ten galaxies in our sample, J115851+4243.2, shows evidence for heavy X-ray absorption. This result implies that a non-negligible fraction of low-mass galaxies might harbor accreting massive black holes that are missed by optical spectroscopic surveys and <10 keV X-ray surveys. The mid-IR colors of our sample also indicate these optically normal low-mass AGNs cannot be efficiently identified with typical AGN selection criteria based on WISE colors. While the hard (>10 keV) X-ray selected low-mass AGN sample size is still limited, our results show that sensitive NuSTAR observations are capable of probing faint hard X-ray emission originating from the nuclei of low-mass galaxies out to moderate redshift (z<0.3), thus providing a critical step in understanding AGN demographics in low-mass galaxies.

Citation

Chen (陳建廷), C., Brandt, W., Reines, A., Lansbury, G., Stern, D., Alexander, D., …Trump, J. (2017). Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey. Astrophysical Journal, 837(1), Article 48. https://doi.org/10.3847/1538-4357/aa5d5b

Journal Article Type	Article
Acceptance Date	Jan 27, 2017
Online Publication Date	Mar 1, 2017
Publication Date	Mar 1, 2017
Deposit Date	Jun 21, 2017
Publicly Available Date	Jul 3, 2017
Journal	Astrophysical Journal
Print ISSN	0004-637X
Electronic ISSN	1538-4357
Publisher	American Astronomical Society
Peer Reviewed	Peer Reviewed
Volume	837
Issue	1
Article Number	48
DOI	https://doi.org/10.3847/1538-4357/aa5d5b