Hard X-ray selected AGNs in low-mass galaxies from the NuSTAR serendipitous survey

Understand

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 $L_\star$ galaxy at its redshift.
• The median values of absolute magnitude, stellar mass and 2--10 X-ray luminosity of our sample are $\langle M_r\rangle = -20.03$, $\langle M_\star\rangle = 4.6\times10^{9}M_\odot$, and $\langle L_{2-10\mathrm{keV}}\rangle = 3.1\times10^{42}$ erg s$^{-1}$, respectively.
• Five objects have detectable broad H$\alpha$ emission in their optical spectra, indicating black-hole masses of $(1.1-10.4)\times 10^6 M_\odot$.