The ALMA View of Positive Black Hole Feedback in the Dwarf Galaxy Henize 2-10 (2401.02486v1)

Abstract: Henize 2-10 is a dwarf starburst galaxy hosting a $\sim10^{6}~M_{\odot}$ black hole (BH) that is driving an ionized outflow and triggering star formation within the central $\sim100$ pc of the galaxy. Here we present ALMA continuum observations from 99 to 340 GHz, as well as spectral line observations of the molecules CO (1-0, 3-2), HCN (1-0, 3-2), and HCO$^{+}$ (1-0, 3-2), with a focus on the BH and its vicinity. Incorporating cm-wave radio measurements from the literature, we show that the spectral energy distribution of the BH is dominated by synchrotron emission from 1.4 to~340 GHz with a spectral index of $\alpha\approx-0.5$. We analyze the spectral line data and identify an elongated molecular gas structure around the BH with a velocity distinct from the surrounding regions. The physical extent of this molecular gas structure is $\approx130~{\rm pc}\times30$ pc and the molecular gas mass is $\sim10^{6}~M_{\odot}$. Despite an abundance of molecular gas in this general region, the position of the BH is significantly offset from the peak intensity, which may explain why the BH is radiating at a very low Eddington ratio. Our analysis of the spatially-resolved line ratio between CO J=3-2 and J=1-0 implies that the CO gas in the vicinity of the BH is highly excited, particularly at the interface between the BH outflow and the regions of triggered star formation. This suggests that the cold molecular gas is being shocked by the bipolar outflow from the BH, supporting the case for positive BH feedback.