On the AGN Nature of Broad Balmer Emission in Four Low-Redshift Metal-Poor Galaxies

Abstract

We report on continued, $\sim$15 year-long, broad Balmer emission lines in three metal-poor dwarf emission-line galaxies selected from Sloan Digital Sky Survey spectroscopy. The persistent luminosity of the broad Balmer emission indicates the galaxies are active galactic nuclei (AGNs) with virial black hole masses of $\sim 10^{6.7}-10^{7.0}{M}_{\odot }$. The lack of observed hard X-ray emission and the possibility that the Balmer emission could be due to a long-lived stellar transient motivated additional follow-up spectroscopy. We also identify a previously-unreported blueshifted narrow absorption line in the broad H$\alpha$ feature in one of the AGNs, indicating an AGN-driven outflow with hydrogen column densities of order $10^{17}$ cm${}^{-2}$. We also extract light curves from the Catalina Real-Time Transient Survey and the Zwicky Transient Facility. We detect probable AGN-like variability in three galaxies, further supporting the AGN scenario. This also suggests the AGNs are not strongly obscured. This sample of galaxies are among the most metal-poor which host an AGN ($Z=0.05-0.16Z_{\odot }$). We speculate they may be analogues to seed black holes which formed in unevolved galaxies at high redshift. Given the rarity of metal-poor AGNs and small sample size available, we investigate prospects for their identification in future spectroscopic and photometric surveys.

8 pages, 4 figures, 1 table, 1 appendix; accepted for publication in MNRAS

References in corpus (19)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• Dust Masses, PAH Abundances, and Starlight Intensities in the SINGS Galaxy Sample
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• On the X-ray, optical emission line and black hole mass properties of local Seyfert galaxies
• The evolution of massive black hole seeds
• X-CIGALE: fitting AGN/galaxy SEDs from X-ray to infrared
• Emission-line Diagnostics of Low Metallicity AGN
• Constraining the properties of AGN host galaxies with Spectral Energy Distribution modeling
• A Candidate Massive Black Hole in the Low-metallicity Dwarf Galaxy Pair Mrk 709
• Endurance of SN 2005ip after a decade: X-rays, radio, and H-alpha like SN 1988Z require long-lived pre-supernova mass loss
• Preliminary Target Selection for the DESI Emission Line Galaxy (ELG) Sample
• A Balmer-line Broad Absorption Line Quasar
• X-ray emission from active galactic nuclei with intermediate mass black holes
• Do Some AGN Lack X-ray Emission?
• Dwarf galaxies might not be the birth sites of supermassive black holes
• Optical Variability of the Dwarf AGN NGC 4395 from the Transiting Exoplanet Survey Satellite
• Multi-wavelength observations of SDSS J105621.45+313822.1, a broad-line, low-metallicity AGN
• Identifying AGN's Balmer-Absorptions and stratified NLR kinematics in SDSSJ112611.63+425246.4

Cited by in corpus (14)

• GA-NIFS: A massive black hole in a low-metallicity AGN at $z\sim 5.55$ revealed by JWST/NIRSpec IFS
• JADES -- The Rosetta Stone of JWST-discovered AGN: deciphering the intriguing nature of early AGN
• Dwarf AGNs from Variability for the Origins of Seeds (DAVOS): Intermediate-mass black hole demographics from optical synoptic surveys
• The radio properties of the JWST-discovered AGN
• Nuclear Activity in the Low Metallicity Dwarf Galaxy SDSS J0944-0038: A Glimpse into the Primordial Universe
• The missing FeII bump in faint JWST AGN: possible evidence for metal-poor broad-line regions at early cosmic times
• Variable AGN in the GALEX Time Domain Survey
• A candidate of binary black hole system in AGN with broad Balmer emission lines having quite different line widths
• Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV candidate SDSS1133
• Decade-long time-monitoring of candidate Luminous Blue Variable Stars in the two very metal-deficient compact dwarf galaxies DDO 68 and PHL 293B
• Monitoring broad emission-line components in spectra of the two low-metallicity dwarf compact star-forming galaxies SBS 1420+540 and J1444+4840
• Overmassive black holes in the early Universe can be explained by gas-rich, dark matter-dominated galaxies
• X-ray Analysis of AGN from the GALEX Time Domain Survey
• X-ray Properties of Optically Variable Low-mass AGN Candidates