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

TL;DR

This paper presents the first wide-field hydrogen Paschen-alpha imaging survey of the Galactic Center using HST/NICMOS, revealing new stars, detailed gas structures, and insights into the nuclear environment of the Galaxy.

Contribution

It provides high-resolution, high-sensitivity panoramic Paschen-alpha maps of the Galactic Center, detecting new stars and detailed gas features, advancing understanding of the region's stellar and gas dynamics.

Findings

Detection of numerous previously unknown Paschen-alpha emitting stars.

Resolution of diffuse thermal features into fine linear filaments indicating magnetic fields.

Observation of spiral-like emission confined within the dusty torus around Sgr A*.

Abstract

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 pc^2 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 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). 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.