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Abstract We study the black hole mass–host galaxy stellar mass relation,MBH–M*, for a sample of 706z ≲ 1.5 andi ≲ 24 optically variable active galactic nuclei (AGNs) in three Dark Energy Survey (DES) Deep Fields: C3, X3, E2, which partially cover Chandra Deep Field-South, XMM Large Scale Structure survey, and European Large Area ISO Survey, respectively. The parent sample was identified by optical variability from the DES supernova survey program imaging. Using publicly available spectra and photometric catalogs, we consolidate their spectroscopic redshifts, estimate their black hole masses using broad line widths and luminosities, and obtain improved stellar masses using spectral energy distribution fitting from X-ray to mid-infrared wavelengths. Our results confirm previous work from Hyper-Suprime Camera imaging that variability searches with deep, high-precision photometry can reliably identify AGNs in low-mass galaxies up toz ∼ 1. However, we find that the hosted black holes are more massive than predicted by the local AGN relation, fixing host galaxy stellar mass. Instead,z ∼ 0.1–1.5 variability-selected AGNs lie in between theMBH–M*relation for local inactive early-type galaxies and local active galaxies. This result agrees with most previous studies of theMBH–M*relation for AGNs at similar redshifts, regardless of the selection technique. We demonstrate that studies of variability-selected AGN provide critical insights into the low-mass end of theMBH–M*relation, shedding light on the occupation fraction of that provides constraints on early black hole seeding mechanisms and self-regulated feedback processes during their growth and coevolution with their hosts.
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Dwarf AGNs from variability for the origins of seeds (DAVOS): Intermediate-mass black hole demographics from optical synoptic surveys
ABSTRACT We present a phenomenological forward Monte Carlo model for forecasting the population of active galactic nuclei (AGNs) in dwarf galaxies observable via their optical variability. Our model accounts for expected changes in the spectral energy distribution of AGNs in the intermediate-mass black hole (IMBH) mass range and uses observational constraints on optical variability as a function of black hole (BH) mass to generate mock light curves. Adopting several different models for the BH occupation function, including one for off-nuclear IMBHs, we quantify differences in the predicted local AGN mass and luminosity functions in dwarf galaxies. As a result, we are able to model the fraction of variable AGNs as a function of important galaxy host properties, such as host galaxy stellar mass, in the presence of selection effects. We find that our adopted occupation fractions for the ‘heavy’ and ‘light’ initial BH seeding scenarios can be distinguished with variability at the 2–3σ level for galaxy host stellar masses below ∼108M⊙ with data from the upcoming Vera C. Rubin Observatory. We also demonstrate the prevalence of a selection bias whereby recovered IMBH masses fall, on average, above the predicted value from the local host galaxy–BH mass scaling relation with the strength of this bias dependent on the survey sensitivity. Our methodology can be used more broadly to calibrate AGN demographic studies in synoptic surveys. Finally, we show that a targeted ∼ hourly cadence program over a few nights with the Rubin Observatory can provide strong constraints on IMBH masses given their expected rapid variability time-scales.
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- Award ID(s):
- 2108162
- PAR ID:
- 10464810
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 518
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 1880-1904
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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