2 um Narrow-Band Imaging of the Sagittarius D H II region

Abstract

We present 2 um narrow-band images of the core H II region in the Galactic star forming region Sagittarius D. The emission-line images are centered on 2.17 um (Brgamma) and 2.06 um (He I). The H II region appears at the edge of a well defined dark cloud, and the morphology suggests a blister geometry as pointed out in earlier radio continuum work. There is a deficit of stars in general in front of the associated dark cloud indicating the H II region is located in-between the Galactic center and the sun. The lesser spatial extent of the He I line emission relative to Brgamma places the effective temperature of the ionizing radiation field below 40,000 K. The He I 2.06 um to Brgamma ratio and Brgamma / far infrared dust emission put Teff at about 36,500 K to 40,000 K as derived from ionization models.