Overview
The study of nearby galaxies has been revolutionized by the Hubble Space Telescope. The high spatial resolutions of WFPC2 and ACS reveal individual stars and parsec-scale structures, permitting studies of stellar populations, star formation histories, and stellar clusters for galaxies out to several megaparsecs.
The ACS Nearby Galaxy Survey Treasury (ANGST) is creating a uniform, multi-color archive of observations of resolved stellar populations within a volume-limited sample of nearby galaxies. The survey provides complete and unbiased sampling of the local universe, thereby maximizing the legacy impact of the resulting data set, and enabling meaningful comparisons among galaxies in the sample and with cosmological simulations. Within this volume, ANGST adds more than a hundred orbits of new high-quality observations, and provides uniform reduction and photometry of both the new and archival observations. The resulting survey now offers superb targets for future multi-wavelength surveys, including the VLA-ANGST survey and the Spitzer Local Volume Legacy Survey (LVL), which allow the local star formation history revealed by ANGST to be tied to fluxes at other wavelengths.
Sample Selection
| The initial ANGST sample was selected from the Catalog of Neighboring Galaxies, updated with revised distances provided by I. Karachentsev. The sample was restricted to galaxies found beyond the zero velocity surface of the Local Group and above the Galactic plane (|b|>20o). The maximum distance of the sample is 3.5 Mpc, with cones out to 4 Mpc in the direction of the M81 group and the Sculptor filament. |
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Galaxy Properties
The resulting sample contains a rich assortment of galaxies. The absolute magnitudes span from brighter than MB=-20 (M81 and NGC 253, the dominant galaxies in the M81 group and the Sculptor filament), down to fainter than MB=-9, comparable to the Carina dwarf spheroidal in the Local Group. Due to the volume-limited nature of the sample, roughly 90% of the galaxies in the ANGST volume are fainter than the Large Magellanic Cloud (LMC), and 80% are fainter than the Small Magellanic Cloud. Only 17% of the galaxies have morphological types characteristic of spirals, while 58% are classified as dwarf irregulars and 25% as dwarf ellipticals.
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Observations
The new ACS observations include 104 orbits that were executed before the ACS failure (out of 295 awarded; GO-10915). Subsequent WFPC2 observations include 141 orbits on the closest galaxies, 25 of which were allocated through a Director's Discretionary request (DD-11307). The default filters were F475W+F606W+F814W for the ACS observations (and F475W+F814W for the dwarfs), and F606+F814W for the WFPC2 observations. These new observations were supplemented with extensive archival data. For large galaxies, the new observations tile a radial strip from the center of the galaxy to the outskirts. The most massive and/or the nearest galaxies were also targetted for a single deep observation in the outskirts, where errors due to crowding were minimized.
Data Products
The first data release includes tables of all photometric measurements for the ANGST survey, comprising ~34 million measurements of ~14 million stars. Also included are completeness as a function of color and magnitude, drizzled reference images, and processing information. The majority of the data is accessible through MAST, or through this web site.