Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDissecting the stellar content of Leo I: a dwarf irregular caught in transition
247
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Leo I is considered one of the youngest dwarf spheroidals (dSph) in the Local Group. Its isolation, extended star formation history (SFH), and recent perigalacticon passage (~1 Gyr ago) make Leo~I one of the most interesting nearby stellar systems. Here, we analyse deep photometric Hubble Space Telescope data via colour-magnitude diagram fitting techniques to study its global and radially-resolved SFH. We find global star formation enhancements in Leo I ~13, 5.5, 2.0, and 1.0 Gyr ago, after which it was substantially quenched. Within the context of previous works focused on Leo I, we interpret the most ancient and the youngest ones as being linked to an early formation (surviving reionisation) and the latest perigalacticon passage (transition from dIrr to dSph), respectively. We clearly identify the presence of very metal poor stars ([Fe/H]~-2) ageing ~5-6 and ~13 Gyr old. We speculate with the possibility that this metal-poor population in Leo I is related to the merging with a low mass system (possibly an ultra-faint dwarf). This event would have triggered star formation (peak of star formation ~5.5 Gyr ago) and accumulated old, metal poor stars from the accreted system in LeoI. Some of the stars born during this event would also form from accreted gas of low-metallicity (giving rise to the 5-6 Gyr low-metallicity tail). Given the intensity and extension of the 2.0 Gyr burst, we hypothesise that this enhancement could also have an external origin. Despite the quenching of star formation around 1 Gyr ago (most probably induced by ram pressure stripping with the Milky Way halo at pericentre), we report the existence of stars as young as 300-500 Myr. We also distinguish two clear spatial regions: the inner ~190 pc presents an homogeneous stellar content (size of the gaseous star forming disc in LeoI from ~4.5 to 1 Gyr ago), whereas the outer regions display a clear positive age gradient.
rate research
Read More
We have surveyed a complete extent of Leo A - an apparently isolated gas-rich low-mass dwarf irregular galaxy in the Local Group. The $B$, $V$, and $I$ passband CCD images (typical seeing $sim$0.8) were obtained with Subaru Telescope equipped with Suprime-Cam mosaic camera. The wide-field ($20 times 24$) photometry catalog of 38,856 objects ($V sim 16-26$ mag) is presented. This survey is also intended to serve as a finding chart for future imaging and spectroscopic observation programs of Leo A.
We analysed a population of bright-red (BR) stars in the dwarf irregular galaxy Leo A by using multicolour photometry data obtained with the Subaru/Suprime-Cam ($B$, $V$, $R$, $I$, $Halpha$) and HST/ACS ($F475W$ & $F814W$) instruments. In order to separate the Milky Way (MW) and Leo A populations of red stars, we developed a photometric method, which enabled us to study the spatial distribution of BR stars within the Leo A galaxy. We found a significant difference in the scale-length (S-L) of radial distributions of the young and old red giant branch (RGB) stars -- $0.82 pm 0.04$ and $1.53 pm 0.03$, respectively. Also, we determined the S-L of BR stars of $0.85 pm 0.05$, which closely matches that of the young RGB stars. Additionally, we found a sequence of peculiar RGB stars and 8 dust-enshrouded stars in the Leo A galaxy.
We have studied Leo A - the isolated and extremely gas rich dwarf irregular galaxy of very low stellar mass and metallicity. Ages of the stellar populations in Leo A are ranging from ~10 Myr to ~10 Gyr. Here we report the discovery of an old stellar halo and a sharp stellar edge. Also we find the distribution of stars extending beyond the gaseous envelope of the galaxy. Therefore, Leo A by its structure as well as stellar and gaseous content is found to resemble massive disk galaxies. This implies that galaxies of very low stellar mass are also able to develop complex structures, challenging contemporary understanding of galaxy evolution.
We present the results of a detailed optical and near-IR study of the nearby star-forming dwarf galaxy NGC4214. We discuss the stellar content, drawing particular attention to the intermediate-age and/or old field stars, which are used as a distance indicator. On images obtained with the Hubble Space Telescope WFPC2 and NICMOS instruments in the equivalents of the V, R, I, J and H bands, the galaxy is well resolved into stars. We achieve limiting magnitudes of F814W ~27 in the WF chips and F110W ~25 in the NIC2. The optical and near-infrared color-magnitude diagrams confirm a core-halo galaxy morphology: an inner high surface-brightness young population within ~1.5 (~1 kpc) from the center of the galaxy, where the stars are concentrated in bright complexes along a bar-like structure; and a relatively low-surface-brightness, field-star population extending out to at least 8 (7 kpc). The color-magnitude diagrams of the core region show evidence of blue and red supergiants, main-sequence stars, asymptotic giant branch stars and blue loop stars. We identify some candidate carbon stars from their extreme near-IR color. The field-star population is dominated by the red tangle, which contains the red giant branch. We use the I-band luminosity function to determine the distance based on the tip-of-the-red-giant-branch method: 2.7pm0.3 Mpc. This is much closer than the values usually assumed in the literature, and we provide revised distance dependent parameters such as physical size, luminosity, HI mass and star-formation rate.
We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A, Aquarius, and the Sagittarius dwarf irregular galaxy. The three galaxies--but especially Leo A and Aquarius--share in common delayed star formation histories relative to many other isolated dwarf galaxies. The stars in all three galaxies are supported by dispersion. We found no evidence of stellar velocity structure, even for Aquarius, which has rotating HI gas. The velocity dispersions indicate that all three galaxies are dark matter-dominated, with dark-to-baryonic mass ratios ranging from $4.4^{+1.1}_{-0.8}$ (SagDIG) to $9.6^{+2.5}_{-1.8}$ (Aquarius). Leo A and SagDIG have lower stellar metallicities than Aquarius, and they also have higher gas fractions, both of which would be expected if Aquarius were farther along in its chemical evolution. The metallicity distribution of Leo A is inconsistent with a Closed or Leaky Box model of chemical evolution, suggesting that the galaxy was pre-enriched or acquired external gas during star formation. The metallicities of stars increased steadily for all three galaxies, but possibly at different rates. The [$alpha$/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended star formation histories than Sculptor, consistent with photometrically derived star formation histories. Overall, the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies, including dwarf spheroidal galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
