Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe evolution of stellar structures in dwarf galaxies
332
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a study of the variation of spatial structure of stellar populations within dwarf galaxies as a function of the population age. We use deep Hubble Space Telescope/Advanced Camera for Surveys imaging of nearby dwarf galaxies in order to resolve individual stars and create composite colour-magnitude diagrams (CMDs) for each galaxy. Using the obtained CMDs, we select Blue Helium Burning stars (BHeBs), which can be unambiguously age-dated by comparing the absolute magnitude of individual stars with stellar isochrones. Additionally, we select a very young (<10 Myr) population of OB stars for a subset of the galaxies based on the tip of the young main-sequence. By selecting stars in different age ranges we can then study how the spatial distribution of these stars evolves with time. We find, in agreement with previous studies, that stars are born within galaxies with a high degree of substructure which is made up of a continuous distribution of clusters, groups and associations from parsec to hundreds of parsec scales. These structures disperse on timescales of tens to hundreds of Myr, which we quantify using the two-point correlation function and the Q-parameter developed by Cartwright & Whitworth (2004). On galactic scales, we can place lower limits on the time it takes to remove the original structure (i.e., structure survives for at least this long), tevo, which varies between ~100~Myr (NGC~2366) and ~350 Myr (DDO~165). This is similar to what we have found previously for the SMC (~80~Myr) and the LMC (~175 Myr). We do not find any strong correlations between tevo and the luminosity of the host galaxy.
rate research
Read More
Using a suite of simulations (Governato et al. 2010) which successfully produce bulgeless (dwarf) disk galaxies, we provide an analysis of their associated cold interstellar media (ISM) and stellar chemical abundance patterns. A preliminary comparison with observations is undertaken, in order to assess whether the properties of the cold gas and chemistry of the stellar components are recovered successfully. To this end, we have extracted the radial and vertical gas density profiles, neutral hydrogen velocity dispersion, and the power spectrum of structure within the ISM. We complement this analysis of the cold gas with a brief examination of the simulations metallicity distribution functions and the distribution of alpha-elements-to-iron.
We have used V- and I- band images from the Hubble Space Telescope (HST) to identify compact stellar clusters within the tidal tails of twelve different interacting galaxies. The seventeen tails within our sample span a physical parameter space of HI/stellar masses, tail pressure and density through their diversity of tail lengths, optical brightnesses, mass ratios, HI column densities, stage on the Toomre sequence, and tail kinematics. Our preliminary findings in this study indicate that star cluster demographics of the tidal tail environment are compatible with the current understanding of star cluster formation in quiescent systems, possibly only needing changes in certain parameters or normalization of the Schechter cluster initial mass function (CIMF) to replicate what we observe in color-magnitude diagrams and a brightest absolute magnitude -- log N plot.
We investigate recent star formation in the extended ultraviolet (XUV) disks of five nearby galaxies (NGC 0628, NGC 2090, NGC 2841, NGC 3621, and NGC 5055) using a long wavelength baseline comprised of ultraviolet and mid-infrared imaging from the Galaxy Evolution Explorer and the Spitzer Infrared Array Camera. We identify 229 unresolved stellar complexes across targeted portions of their XUV disks and utilize spectral energy distribution fitting to measure their stellar ages and masses through comparison with Starburst99 population synthesis models of instantaneous burst populations. We find that the median age of outer disk associations in our sample is ~100 Myr with a large dispersion that spans the entire range of our models (1 Myr-1 Gyr). This relatively evolved state for most associations addresses the observed dearth of Halpha emission in some outer disks, as Halpha can only be observed in star forming regions younger than ~10 Myr. The large age dispersion is robust against variations in extinction (in the range E(B-V)=0-0.3 mag) and variations in the upper end of the stellar Initial Mass Function (IMF). In particular, we demonstrate that the age dispersion is insensitive to steepening of the IMF, up to extreme slopes.
We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (~3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting discs are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment and ram pressure stripping).
The formation mechanism of tidal dwarf galaxies means they are expected to contain little or no dark matter. As such, they might be expected to be very sensitive to their environment. We investigate the impact of ram pressure on tidal dwarf galaxies in a parameter study, varying dwarf galaxy properties and ram pressures. We submit model tidal dwarf galaxies to wind-tunnel style tests using a toy ram pressure model. The effects of ram pressure are found to be substantial. If tidal dwarf galaxies have their gas stripped, they may be completely destroyed. Ram pressure drag causes acceleration of our dwarf galaxy models, and this further enhances stellar losses. The dragging can also cause stars to lie in a low surface brightness stellar stream that points in the opposite direction to the stripped gas, in a manner distinctive from tidal streams. We investigate the effects of ram pressure on surface density profiles, the dynamics of the stars, and discuss the consequences for dynamical mass measurements.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
