HST/NICMOS Paschen- alpha Survey of the Galactic Center: Overview

Q. D. Wang1, H. Dong1, A. Cotera,2 S. Stolovy,3 M. Morris,4 C. C. Lang,5 M. P. Muno,6 G. Schneider,7 and D. Calzetti1

(1)Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA,
(2)SETI Institute, 515 North Whisman Road, Mountain View, CA 94043, USA,
(3)Spitzer Science Center, California Institute of Technology, Mail Code 220-6, 1200 East California Boulevard, Pasadena, CA 91125, USA,
(4)Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA,
(5)Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52245, USA,
(6)Space Radiation Laboratory, California Institute of Technology, Pasadena, CA 91125, USA,
(7)Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA

Paper: unknown


We have recently carried out the first wide-field hydrogen Paschen- alpha line imaging survey of the Galactic Center (GC), using the NICMOS instrument aboard the Hubble Space Telescope. The survey maps out a region of 2253 \rm pc2 (416 \rm arcmin2) around the central supermassive black hole (Sgr A*) in the 1.87 and 1.90 micron narrow bands with a spatial resolution of 0.01 pc (0.''2 FWHM) at a distance of 8 kpc. Here we present an overview of the observations, data reduction, preliminary results, and potential scientific implications, as well as a description of the rationale and design of the survey. We have produced mosaic maps of the Paschen- alpha line and continuum emission, giving an unprecedentedly high resolution and high sensitivity panoramic view of stars and photo-ionized gas in the nuclear environment of the Galaxy. We detect a significant number of previously undetected stars with Paschen- alpha in emission. They are most likely massive stars with strong winds, as confirmed by our initial follow-up spectroscopic observations. About half of the newly detected massive stars are found outside the known clusters (Arches, Quintuplet, and Central). the clusters, while many of the others are apparently embedded in distinct HII regions, probably representing massive stellar clusters/groups in formation. Many previously known diffuse thermal features are now resolved into arrays of intriguingly fine linear filaments indicating a profound role of magnetic fields in sculpting the gas. The bright spiral-like Paschen- alpha emission around Sgr A* is seen to be well confined within the known dusty torus. In the directions roughly perpendicular to it, we further detect faint, diffuse Paschen- alpha emission features, which, like earlier radio images, suggest an outflow from the structure. In addition, we detect various compact Paschen- alpha nebulae, probably tracing the accretion and/or ejection of stars at various evolutionary stages. Multi-wavelength comparisons together with follow-up observations are helping us to address such questions as where and how massive stars form, how stellar clusters are disrupted, how massive stars shape and heat the surrounding medium, how various phases of this medium are interspersed, and how the supermassive black hole interacts with its environment.

Preprints available from the authors at wqd@astro.umass.edu , or the raw TeX (no figures) if you click here.

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