A Nearby Isolated Dwarf: Star Formation and Structure of ESO 006–001

Abstract

Abstract Observations with the Hubble Space Telescope unexpectedly revealed that the dwarf galaxy ESO 006–001 is a near neighbor to the Local Group at a distance of 2.70 ± 0.11 Mpc. The stellar population in the galaxy is well resolved into individual stars to a limit of M I ∼ − 0.5 mag. The dominant population is older than 12 Gyr yet displays a significant range in metallicity of −2 < [Fe/H] < − 1, as evidenced by a red giant branch with substantial width. Superimposed on the dominant population are stars on the main sequence with ages less than 100 Myr and helium burning blue loop stars with ages of several hundred Myr. ESO 006–001 is an example of a transition dwarf; a galaxy dominated by old stars but one that has experienced limited recent star formation in a swath near the center. No H i gas is detected at the location of the optical galaxy in spite of the evidence for young stars. Intriguingly, an H i cloud with a similar redshift is detected 9 kpc away in projection. Otherwise, ESO 006–001 is a galaxy in isolation with its nearest known neighbor IC 3104, itself a dwarf, at a distance of ∼500 kpc.