Faint jewels: discovering the brilliance of dwarf galaxies

Most AGN are suspected to feature supermassive black holes with masses greater than one million solar masses at their centers; however, today’s authors present exciting evidence, in tandem with previous studies that have uncovered hundreds of AGN within dwarf galaxies that harbor lower mass black holes, that is compelling astronomers to return to the drawing board.

Previous studies of AGN in dwarf galaxies primarily relied upon single-fiber (3-arcsecond aperture) spectroscopic measurements taken at the galactic center. Prominent emission lines were then identified in these spectra and their flux ratios plotted in a BPT diagram. Depending on a galaxy’s location on a BPT diagram, the primary emission source for each galaxy was then classified as star formation, AGN, Low-Ionization Nuclear Emission-Line Regions (LINERs), or a composite of multiple ionization mechanisms.

However, these single-fiber measurements are often biased towards identifying central AGN, and they can fail at AGN identification if there is abundant star formation in the center of a galaxy. Moreover, strong host galaxy light can diminish AGN signatures.

Alternatively, spatially resolved spectroscopic measurements can provide more definitive evidence of AGN activity. In particular, integral field unit (IFU) spectroscopy traces emission line features from varying physical regions of a galaxy.

The SDSS/Mapping Nearby Galaxies at APO (MaNGA) survey is a critical step forward in this direction. This survey will provide IFU data for nearly 10,000 galaxies by the end of 2020, which will make it the largest such catalog. Today’s authors leverage MaNGA to conduct the largest dedicated study of dwarf galaxies that host AGN within the survey.

Source: “Faint Jewels: Discovering The Brilliance of Dwarf Galaxies” AASNOVA, 4 August 2020

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