Hubble Space Telescope Paα and 1.9 micron imaging of Sagittarius A West

We present Hubble Space Telescope/NICMOS images at 0.2 resolution (Nyquist-sampled in the central 19) of the H I Paalpha emission line in a 70(alpha) x 90(delta) region of the Galactic center centered on the nonthermal radio source Sgr A*. The majority of the emission arises from ionized gas in the minispiral in the central parsec. Paalpha emission is also seen from 26 stellar sources, presumably early-type stars with mass-loss winds. The new data reveal significant small-scale structure (less than or equal to 1 similar to 1.2 x 10(17) cm) in the ionized gas of the mini-spiral; low surface brightness emission features are also seen for the first time. The ratio of observed Paalpha emission to 6 cm radio continuum emission is used to derive an extinction map for the ionized gas over the central parsec. A(V) varies from 20 to 50 mag with a median value of A(V) = 31.1 mag, in excellent agreement with earlier estimates derived for the stellar sources. Extinctions, independently derived using H92alpha recombination-line data, were in excellent agreement with those derived from the 6 cm continuum. A broad minimum in the extinction extends similar to30 northeast-southwest over the area of the IRS 16 cluster, including the area of peak flux in Paalpha and radio continuum. 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; however, the H II cannot be entirely behind the molecular clouds since the extinctions would then be much greater. The minimum Lyman continuum emission rate within 40 radius of Sgr A* is 3.9 x 10(50) s(-1) or L-LyC similar or equal to 2.7 x 10(6) L-., half of this within 20 radius. The small-scale, filamentary structures in the ionized gas have a free thermal expansion time of only similar to3000 yr; either magnetic fields or mass-loss winds from the hot emission line stars may contain the ionized. laments. (Eight new emission-line stars were also detected in Paalpha.) For both the ionized gas and stellar continuum, the centroids of the emission (corrected for extinction) remain within similar to+/-1 from a radius of 2 out to 40. This provides further evidence that Sgr A* (the putative central black hole) is indeed at or extremely close (less than or equal to0.04 pc or 1.2 x 10(17) cm) to the center of the Galactic nucleus stellar distribution and presumably the dynamical center of the Galaxy. The 1.9 mum surface brightness increases inwards to 0.9 radius and exhibits a decrease or leveling off closer to Sgr A*, possibly indicating the core radius of the central stellar distribution or depletion of the late-type stars by stellar collisions near the central black hole.