Stellar populations of the Sagittarius dwarf irregular galaxy

摘要

We present deep BVRI CCD photometry of the stars in the dwarf irregular galaxy SagDIG. The color-magnitude diagrams of the measured stars in SagDIG show a blue plume that consists mostly of young stellar populations and a well-defined red giant branch (RGB). The foreground reddening of SagDIG is estimated to be E(B - V) = 0.06. The tip of the RGB is found to be at I-TRGB = 21.55 +/- 0.10 mag. From this the distance to this galaxy is estimated to be d = 1.18 +/- 0.10 Mpc. This result, combined with its velocity information, shows that it is a member of the Local Group. The mean metallicity of the red giant branch is estimated to be Fe/H (BSG) = 19.89 +/- 0.13 mag, (BSG) = 0.08 +/- 0.07 mag, (RSG) = 20.39 +/- 0.10 mag, and (RSG) = 1.29 +/- 0.12 mag. The corresponding absolute magnitudes are derived to be (BSG) = -5.66 mag and (RSG) = -5.16 mag, which are about 1 mag fainter than those expected from conventional correlations with galaxy luminosity. References: 29