Extended Structure and Fate of the Nucleus in Henize 2-10

Abstract

We investigate the structure and nuclear region of the black hole (BH) hosting galaxy Henize2-10. Surface brightness (SB) profiles are analyzed using Magellan/Megacam $g$- and $r$-band images. Excluding the central starburst, we find a best-fit two component Sérsic profile with $n_{\mathrm{in}}\sim 0.6$, $r_{\text{eff,in}}\sim$ 260~pc, and $n_{\mathrm{out}}\sim 1.8$, $r_{\text{eff, out}}\sim$ 1 kpc. Integrating out to our outer most data point (100 arc sec $\sim$ 4.3 kpc), we calculate $M_g=-19.2$ and $M_r=-19.8$. The corresponding enclosed stellar mass is $M_{\star }\sim (10\pm 3)\times 10^9$ M${}_{\odot }$, $\sim 3\times$ larger than previous estimates. Apart from the central $\lesssim$500 pc, with blue colors and an irregular morphology, the galaxy appears to be an early-type system. The outer color is quite red, $(g-r{)}_0=0.75$, suggesting a dominant old population. We study the nuclear region of the galaxy using archival Gemini/NIFS $K$-band adaptive optics spectroscopy and {\it Hubble Space Telescope} imaging. We place an upper limit on the BH mass of $\sim 10^7{M}_{\odot }$ from the NIFS data, consistent with that from the $M_{\mathrm{BH}}$-radio-X-ray fundamental plane. No coronal lines are seen, but a Br${\hat{I}}^3$ source is located at the position of the BH with a luminosity consistent with the X-ray emission. The starburst at the center of Henize 2-10 has led to the formation of several super star clusters, which are within $\sim$100 pc of the BH. We examine the fate of the nucleus by estimating the dynamical masses and dynamical friction timescales of the clusters. The most massive clusters ($\sim 10^6{M}_{\odot }$) have $\ddot{I}{„}_{\mathrm{dyn}}\lesssim 200$ Myr, and thus Henize 2-10 may represent a rare snapshot of nuclear star cluster formation around a pre-existing massive BH.

15 pages, 9 figures, ApJ accepted