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 Henize 2-10. Surface brightness 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 _in ~ 0.6, r _{eff, in} ~ 260 pc and n _out ~ 1.8, r ~ 1 kpc. Integrating out to our outermost data point (100'' ~ 4.3 kpc), we calculate M_g = -19.2 and M_r = -19.8. The corresponding enclosed stellar mass is M _sstarf ~ (10 ± 3) × 10⁹ M _⊙, ~3 × larger than previous estimates. Apart from the central lsim500 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 Hubble Space Telescope imaging. We place an upper limit on the BH mass of ~10⁷ M _⊙ from the NIFS data, consistent with that from the M _BH-radio-X-ray fundamental plane. No coronal lines are seen, but a Brγ 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 ~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 (~10⁶ M _⊙) have τ_dyn <~ 200 Myr, and thus Henize 2-10 may represent a rare snapshot of nuclear star cluster formation around a preexisting massive BH.