An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10

Abstract

Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

Dwarf Galaxies With Optical Signatures of Active Massive Black Holes

“…While optical diagnostics certainly have a role to play, we need to move toward using alternative search techniques and observations at other wavelengths to make further progress (e.g., radio and X-ray; Reines et al 2011;Reines & Deller 2012;Gallo et al 2010;Kamizasa et al 2012). …”

“…These two dwarf galaxies have BH mass estimates of M BH ∼ 3 × 10 5 M (Filippenko & Ho 2003;Peterson et al 2005; Thornton et al 2008). Reines et al (2011) present multi-wavelength evidence for the first example of a massive BH in a dwarf starburst galaxy, Henize 2-10, which has an irregular central morphology and no discernible bulge. The evidence for an accreting massive BH includes Very Large Array radio and Chandra hard X-ray point sources at the center of the galaxy and clearly separated from the bright H ii regions.…”

“…Understanding the radiative properties of BHs in this mass range is important for models of the impact of mini-quasars on reionization and the formation of the first galaxies (e.g., Milosavljević et al 2009). Moreover, the study of BH accretion and star formation in low-mass dwarfs today may prove a good laboratory for understanding their interplay at early times (e.g., Reines et al 2011;Jia et al 2011;Alexandroff et al 2012) and the apparent contribution of obscured AGNs in blue low-mass galaxies to the cosmic X-ray background (Xue et al 2012). Determining the presence of AGNs in lowmass galaxies will also help constrain BH feedback and galaxy formation models at all mass scales.…”

“…The source lies at the center of a ∼250 pc long ionized gas structure that is suggestive of bipolar flow and the position of the central source is consistent with the dynamical center of the galaxy. Reines et al (2011) estimate a BH mass of log (M BH /M ) = 6.3 ± 1.1 using the radio-X-ray-M BH fundamental plane (Merloni et al 2003), and Kormendy & Ho (2013) estimate that Henize 2-10 has a stellar mass of M ∼ 1.4 × 10 9 M with an uncertainty of a factor of three. To determine the frequency of objects like NGC 4395, Pox 52, and Henize 2-10 requires large surveys for AGN signatures in low-mass galaxies.…”

AnXMM-Newtonsearch for X-ray sources in the Fornax dwarf galaxy

“…For example, Reines et al (2011) reported that the nearby dwarf starburst galaxy Henize2-10 harbors a compact radio source at its dynamical center spatially coincident with a hard X-ray source (possibly an 10 6 M accreting black hole). Farrell et al (2009) found the brightest known ultra-luminous X-ray source HLX-1 (see e.g.…”