The Star Formation Histories of Four Fields Spanning the Minor Axis of NGC 6822

Abstract

The star formation histories of four fields within the Local Group dwarf irregular galaxy NGC 6822 are presented. Each of the fields was imaged by the WFPC2 aboard the {\it Hubble Space Telescope} and were used to obtain $VI$ color-magnitude diagrams for each field reaching $V\simeq 26$. The magnitude of the tip of the red giant branch and the red clump were used to determine distances to NGC 6822 that are consistent with previous ground-based measurements. The distance, extinction and star formation history were also determined by fitting the entire color-magnitude diagram in each field. The distances from these fits are consistent with the other determinations within the estimated errors once the systematic effects of uncertainties in the age-metallicity relation are taken into account. The extinction varies among the four fields from approximately the foreground Galactic value to $\approx 0.4$ mag higher in $V$ and roughly correlates with the $60\micron$ surface brightness. The star formation histories in the four fields are similar for ages $\gtrsim 1$ Gyr and are relatively constant or somewhat increasing with time. These old star formation rates are comparable to that expected from the typical gas surface densities at these galactocentric radii and suggest that no large scale redistribution of gas or stars is required to account for the inferred star formation rates. Three of the fields show a drop of a factor of $\sim 2-4$ in the star formation rate about 600 Myr ago while the remaining field centered on the bar shows an increase.

29 pages, 10 figures, accepted by the Astronomical Journal (June 2003 issue)

References in corpus (2)

• A High-Resolution Rotation Curve of NGC 6822: A Test-case for Cold Dark Matter
• Testing intermediate-age stellar evolution models with VLT photometry of LMC clusters. I. The data

Cited by in corpus (18)

• Star Formation Histories, Abundances and Kinematics of Dwarf Galaxies in the Local Group
• Evidence for a non-universal stellar initial mass function from the integrated properties of SDSS galaxies
• Identifying Local Group Field Galaxies which have interacted with the Milky Way
• The stellar population and interstellar medium in NGC 6822
• The Stellar Populations of M33's Outer Regions III: Star Formation History
• The Stellar Populations of M33's Outer Regions IV: Inflow History and Chemical Evolution
• The Nature of Infrared Emission in the Local Group Dwarf Galaxy NGC 6822 As Revealed by Spitzer
• A New Cepheid Distance Measurement and Method for NGC 6822
• Astrophysical Distance Scale II. Application of the JAGB Method: A Nearby Galaxy Sample
• Chemical and Photometric Evolution of the Local Group Galaxy NGC 6822 in a Cosmological Context
• The PNe and H II regions in NGC 6822 revisited. Clues to AGB nucleosynthesis
• The recent star formation in NGC 6822 from HST imaging
• Near-infrared spectroscopy of AGB star candidates in Fornax, Sculptor and NGC 6822
• The Young Stellar Population of the metal-poor galaxy NGC 6822
• Light and Motion in the Local Volume
• A two-mode planetary nebula luminosity function
• Stripping of nitrogen-rich AGB ejecta from interacting dwarf irregular galaxies
• The dwarf irregular galaxy NGC 6822. II. Young, intermediate and old stellar populations: comparison between theory and observations