Guo, Hengxiao, Burke, Colin J, Liu, Xin, Phadke, Kedar A, Zhang, Kaiwen, Chen, Yu-Ching, Gruendl, Robert A, Lidman, Christopher, Shen, Yue, Morganson, Eric, Aguena, Michel, Allam, Sahar, Avila, Santiago, Bertin, Emmanuel, Romer, Anita K, DES Collaboration, and others, (2020) Dark Energy Survey identification of a low-mass active galactic nucleus at redshift 0.823 from optical variability. Monthly Notices of the Royal Astronomical Society, 496 (3). pp. 3636-3647. ISSN 0035-8711

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Abstract

We report the identification of a low-mass active galactic nucleus (AGN), DES J0218−0430, in a redshift z = 0.823 galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218−0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning over 6 yr. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg II and broad H β lines, confirming its nature as a broad-line AGN. Archival XMM–Newton X-ray observations suggest an intrinsic hard X-ray luminosity of L2−12keV≈7.6±0.4×1043 erg s−1, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H β from SDSS spectrum, we estimate a virial black hole (BH) mass of M• ≈ 106.43–106.72 M⊙ (with the error denoting the systematic uncertainty from different calibrations), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift > 0.4 detected in optical. We estimate the host galaxy stellar mass to be M* ≈ 1010.5 ± 0.3 M⊙ based on modelling the multiwavelength spectral energy distribution. DES J0218−0430 extends the M•–M* relation observed in luminous AGNs at z ∼ 1 to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.

Item Type:	Article
Keywords:	Surveys, galaxies, high-redshift, active, Black hole physics, nuclei, quasars, general, Astrophysics - Astrophysics of Galaxies
Schools and Departments:	School of Mathematical and Physical Sciences > Physics and Astronomy
SWORD Depositor:	Mx Elements Account
Depositing User:	Mx Elements Account
Date Deposited:	04 Aug 2020 07:26
Last Modified:	05 Aug 2020 15:42
URI:	http://sro.sussex.ac.uk/id/eprint/92911

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