Brackett Lines from the Super Star Cluster Nebulae in HE 2-10

We present high spectral resolution (v ∼ 12-16 km s-1) Brackett line spectroscopy of the blue compact dwarf galaxy Henize 2-10 made with NIRSPEC on the Keck telescope. The spatial resolution is seeing-limited, at 1″. We detect two distinct kinematic features separated by approximately 3″, with heliocentric velocities of ∼860 and ∼890 km s-1. In addition to a narrow core, the line profiles also display a broad, low-intensity feature on the blue side of the centroid, which we attribute to an outflow. This may be a sign of aging in the clusters. We compare to archival high-resolution Very Large Array data at 1.3 cm and find that the centimeter-wavelength emission is resolved into six sources. These radio sources are organized into two larger groups, which we associate with the two kinematic peaks in the Brackett spectrum. We estimate a Lyman continuum rate of at least 7 × 1052 s-1, with a corresponding stellar mass of 6 × 106 M⊙ required to ionize the nebulae. We also estimate the size of the nebulae from the radio continuum brightness and find that the observed sources probably contain many H II regions in smaller, unresolved clumps. Brackett line profiles have supersonic line widths but, aside from the blue wing, are comparable to line widths observed in Galactic ultracompact H II regions, which are excited by a single star or a few stars.