The H i hole and AGB stellar population of the Sagittarius dwarf irregular galaxy

Abstract

Using two HST/ACS data sets that are separated by about two years has allowed us to derive the relative proper motion for the Sagittarius dwarf irregular (SagDIG) and reduce the heavy foreground Galactic contamination. The proper-motion decontaminated SagDIG catalog provides a much clearer view of the young red-supergiant and intermediate-age asymptotic giant branch populations. Previously identified carbon-and oxygen-rich star samples, which are based on narrow-band filter photometry, were complemented by membership criteria. We report identifying three Milky Way carbon-rich dwarf stars, which probably belong to the thin disk, and pointing to the high incidence of this class at low Galactic latitudes. A subgroup of four oxygen-rich candidate stars depicts a faint, red extension of the well-defined SagDIG carbon-rich sequence. The origin of these oxygen-rich candidate stars remains unclear, reflecting the uncertainty in the ratio of carbon-and oxygen-rich stars. Finally, SagDIG is a gas-rich galaxy characterized by a single large cavity in the gas disk (H  hole), which is offset by ∼360 pc from the optical center of the galaxy. We nonetheless investigate the stellar feedback hypothesis by comparing the proper-motion cleaned stellar populations within the H  hole with appropriately selected comparison regions that have higher H  densities external to the hole. The comparison shows no significant differences. In particular, the center of the H  hole (and the comparison regions) lack stellar populations younger than ∼400 Myr, which are otherwise abundant in the inner body of the galaxy. We conclude that there is no convincing evidence that the SagDIG H  hole is the result of stellar feedback and that gravitational and thermal instabilities in the gas are the most likely mechanism for its formation.

Chemistry and Kinematics of the Late-Forming Dwarf Irregular Galaxies Leo A, Aquarius, and Sagittarius Dig*

“…The explosion would not have affected the positions of the stars, which fill the hole. However, Momany et al (2014) found that even young stars can be found in the hole, which could indicate that the hole was formed by gravitational instability rather than stellar feedback. On the other hand, a study of similar kiloparsec-sized H I holes in five nearby dIrrs found that the underlying stellar population produced sufficient energy to create the holes (Warren et al 2011).…”

An Infrared Census of DUST in Nearby Galaxies with Spitzer (DUSTiNGS). IV. Discovery of High-redshift AGB Analogs*

“…Both of these characteristics point to an AGB nature. Three additional confirmed O-rich stars in Sag DIG that were identified by Momany et al (2014) are included in our near-IR HST coverage. These three stars have very red F606W-F814W colors, suggesting substantial circumstellar dust, but we do not detect dust around these stars.…”

A remarkable oxygen-rich asymptotic giant branch variable in the Sagittarius Dwarf Irregular Galaxy

“…As noted above, Gullieuszik et al (2007) find V1 to be blended. In the Momany et al (2014) catalogue, there are measurements in 3 bands for 11 stars inside a circle of diameter 3 arcsec centred on the variable. Using these data we estimate that the neighbouring stars contribute only about 0.1 mag to the J mean magnitude of the variable, and probably somewhat less to K S , so its position in the K S , J − K S (Fig.…”