MaNGA AGN dwarf galaxies (MAD) – I. A new sample of AGNs in dwarf galaxies with spatially-resolved spectroscopy

Abstract

The finding of active galactic nuclei (AGN) in dwarf galaxies has important implications for galaxy evolution and supermassive black hole formation models. Yet, how AGN in dwarf galaxies form is still debated, in part due to scant demographics. We make use of the MaNGA survey, comprising ∼10,000 galaxies at z < 0.15, to identify AGN dwarf galaxies using a spaxel by spaxel classification in three spatially-resolved emission line diagnostic diagrams (the [N ii-, [S ii]- and [O i]-BPT) and the WHAN diagram. This yields a sample of 664 AGN dwarf galaxies, the largest to date, and an AGN fraction of $\sim 20~{{\%}}$ that is significantly larger than that of single-fiber-spectroscopy studies (i.e. $\sim 1~{{\%}}$). This can be explained by the lower bolometric luminosity (<1042 erg s−1) and accretion rate (sub-Eddington) of the MaNGA AGN dwarf galaxies. We additionally identify 1,176 SF-AGN (classified as star-forming in the [N ii]-BPT but as AGN in the [S ii]- and [O i]-BPT), 122 Composite, and 173 LINER sources. The offset between the optical center of the galaxy and the median position of the AGN spaxels is more than 3 arcsec for ∼62% of the AGN, suggesting that some could be off-nuclear. We also identify seven new broad-line AGN with log MBH = 5.0–5.9 M⊙. Our results show how integral-field spectroscopy is a powerful tool for uncovering faint and low-accretion AGN and better constraining the demographics of AGN in dwarf galaxies.

Low-mass Galaxy Interactions Trigger Black Hole Activity

“…Some recent works suggest that dwarf galaxies indeed have significantly higher AGN fractions. Mezcua & Sánchez (2024) studied dwarf galaxies from the MaNGA survey using a spaxel-by-spaxel classification in three spatially resolved emission-line diagnostic diagrams. This approach resulted in an AGN fraction of 20%, indicating that integral field spectroscopy is a powerful tool to reveal previously unknown faint and low-accreting dwarf AGN.…”

EMPRESS. XIV. Strong High-ionization Lines of Young Galaxies at z = 0–8: Ionizing Spectra Consistent with the Intermediate-mass Black Holes with M BH ∼ 103–106 M ⊙

“…Although such intermediate-mass BHs (IMBHs; M BH ∼ 10 2 −10 5 M e ) are not well understood both at high redshift and in the local Universe owing to difficulties of observations, recent optical surveys in the local Universe have identified lowmass active galactic nuclei (AGNs) in dwarf galaxies that harbor BHs with masses down to M BH ∼ 10 5 M e (Xiao et al 2011). There are a growing number of IMBH candidates in dwarf galaxies with reports of high-ionization lines or Hα broad lines (Chilingarian et al 2018;Senchyna et al 2020;Berg et al 2021;Bohn et al 2021;Cann et al 2021;Molina et al 2021;Reefe et al 2022;Mezcua & Sánchez 2024). On the other hand, gravitational-wave observations have revealed both IMBHs and stellar BHs with masses up to M BH ∼ 10 2 M e (Abbott et al 2020).…”