HST P alpha Imaging of Sgr A

N. Z. Scoville1, S. R. Stolovy1, M. Rieke2, M. Christopher1, and F. Yusef-Zadeh3

1 Astronomy Department, California Institute of Technology, Pasadena, CA 91125
2 Steward Observatory, University of Arizona, Tucson, AZ 85721
3 Astronomy Department, Northwestern University

E-mail contact: nzs@astro.caltech.edu

We present HST/NICMOS images at 0.2 arcsec resolution of the HI P alpha emission line in a 70 arcsec x 90 arcsec region centered on the non-thermal source Sgr A*. The ratio of observed P alpha emission to 6-cm radio continuum is used to derive an extinction map for the ionized gas over the central parsec. AV varies from 20 to 50 mag with a median pixel value of AV = 31.1 mag, in excellent agreement with earlier estimates derived for the stellar sources. A broad minimum in the extinction extends 30 arcsec NE-SW over the area of the IRS 16 cluster, south of Sgr A*. Large increases in extinction are seen along the periphery of the ionized gas, particularly in the direction of the western arm, suggesting that the ionized gas is partially extincted by dust in the molecular clouds at the outside of the ionized region. The minimum Lyman continuum emission rate from within 40 arcsec radius of Sgr A* is 3.9 x 1050 sec-1 or L . The requirement is half of this within 20 arcsec radius. For both the ionized gas and the stellar continuum, we analyze the spatial distribution relative to Sgr A*.