Variability-selected Intermediate-mass Black Hole Candidates in Dwarf Galaxies from ZTF and WISE

September 2022 • 2022ApJ...936..104W

Authors • Ward, Charlotte • Gezari, Suvi • Nugent, Peter • Bellm, Eric C. • Dekany, Richard • Drake, Andrew • Duev, Dmitry A. • Graham, Matthew J. • Kasliwal, Mansi M. • Kool, Erik C. • Masci, Frank J. • Riddle, Reed L.

Abstract • While it is difficult to observe the first black hole seeds in the early universe, we can study intermediate-mass black holes (IMBHs) in local dwarf galaxies for clues about their origins. In this paper we present a sample of variability-selected active galactic nuclei (AGN) in dwarf galaxies using optical photometry from the Zwicky Transient Facility (ZTF) and forward-modeled mid-IR photometry of time-resolved Wide-field Infrared Survey Explorer (WISE) co-added images. We found that 44 out of 25,714 dwarf galaxies had optically variable AGN candidates and 148 out of 79,879 dwarf galaxies had mid-IR variable AGN candidates, corresponding to active fractions of 0.17% ± 0.03% and 0.19% ± 0.02%, respectively. We found that spectroscopic approaches to AGN identification would have missed 81% of our ZTF IMBH candidates and 69% of our WISE IMBH candidates. Only nine candidates have been detected previously in radio, X-ray, and variability searches for dwarf galaxy AGN. The ZTF and WISE dwarf galaxy AGN with broad Balmer lines have virial masses of 10⁵ M _⊙ < M _BH < 10⁷ M _⊙, but for the rest of the sample, BH masses predicted from host galaxy mass range between 10^5.2 M _⊙ < M _BH < 10^7.25 M _⊙. We found that only 5 of 152 previously reported variability-selected AGN candidates from the Palomar Transient Factory in common with our parent sample were variable in ZTF. We also determined a nuclear supernova fraction of 0.05% ± 0.01% yr^-1 for dwarf galaxies in ZTF. Our ZTF and WISE IMBH candidates show the promise of variability searches for the discovery of otherwise hidden low-mass AGN.

Links

• PREPRINT http://arxiv.org/abs/2110.13098
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2022ApJ...936..104W
• ELECTR https://doi.org/10.3847%2F1538-4357%2Fac8666
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2022ApJ...936..104W
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/ac8666/pdf
• DATA https://irsa.ipac.caltech.edu/bibdata/2022/W/2022ApJ...936..104W.html