Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStellar Populations in the Outer Disk and Halo of the Spiral Galaxy M101
454
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We use deep Hubble Space Telescope imaging in the outskirts of the nearby spiral M101 to study stellar populations in the galaxys outer disk and halo. Our ACS field lies 17.6 arcmin (36 kpc) from the center of M101 and targets the blue NE Plume of M101s outer disk, while the parallel WFC3 field lies at a distance of 23.3 arcmin (47 kpc) to sample the galaxys stellar halo. The WFC3 halo field shows a well-defined red giant branch characterized by low metallicity ([M/H]=-1.7 $pm$ 0.2), with no evidence of young stellar populations. In contrast, the ACS disk field shows multiple stellar populations, including a young main sequence, blue and red helium burning stars, and old RGB and AGB populations. The mean metallicity of these disk stars is quite low: [M/H]=-1.3 $pm$ 0.2 for the RGB population, and -1.15 $pm$ 0.2 for the younger helium burning sequences. Of particular interest is a bunching of stars along the BHeB sequence, indicative of an evolving cohort of massive young stars. We show that the young stellar populations in this field are well-described by a decaying burst of star formation that peaked ~ 300-400 Myr ago, along with a more extended star formation history to produce the older RGB and AGB populations. These results confirm and extend the results from our previous deep surface photometry of M101s outer disk, providing an important cross-check on stellar population studies using resolved stellar populations versus integrated light photometry. We discuss our results in the context of halo formation models and the interaction history of M101 and its companions.
rate research
Read More
Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report a few galaxies, including the nearby disk galaxy M101, that have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M101s outskirts by resolving its stars. We present the photometry of its stars based on deep F606W and F814W images taken with Hubble Space Telescope as part of the GHOSTS survey. The constructed CMDs of stars reach down to two magnitudes below the tip of the red giant branch. We derived radial number density profiles of the bright red giant branch (RGB) stars. The mean color of the RGB stars at $R sim$ 40 -- 60 kpc is similar to those of metal-poor globular clusters in the Milky Way. We also derived radial surface brightness profiles using the public image data provided by the Dragonfly team. Both the radial number density and surface brightness profiles were converted to radial mass density profiles and combined. We find that the mass density profiles show a weak upturn at the very outer region, where surface brightness is as faint as $mu_gapprox 34$ mag arcsec$^{-1}$. An exponential disk + power-law halo model on the mass density profiles finds the total stellar halo mass of $M_{halo}=8.2_{-2.2}^{+3.5}times 10^7M_odot$. The total stellar halo mass does not exceed $M_{halo} = 3.2 times 10^8$ $M_{odot}$ when strongly truncated disk models are considered. Combining the halo mass with the total stellar mass of M101, we obtain the stellar halo mass fraction of $M_{halo}/M_{gal} = 0.20_{-0.08}^{+0.10}%$ with an upper limit of 0.78%. We compare the halo properties of M101 with those of six GHOSTS survey galaxies as well as the Milky Way and M31 and find that M101 has an anemic stellar halo.
We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49s stellar halo out to ~ 100 kpc (7 Re), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B-V ~ 0.7); if this is purely a metallicity effect, it argues for extremely metal poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxys surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49s outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49s halo. Thus the extremely metal-poor nature of M49s extended halo provides some tension against current models for elliptical galaxy formation.
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.
The Galaxys stellar populations are naturally classified into six `types, of which five have been observed. These are the thin disk (Pop I in the historical scheme), a discrete thick disk (Pop I.5), the metal-rich bulge, which was not named in the Baade sequence, the rare field halo (Pop II), a population currently being accreted into the very outer halo filed (Pop Sgr?)and a hard to discover initial enriching Pop III. Each of these forms a group with astonishly tight correlations between chemical element ratios and other parameters. It is very hard to understand how the observed properties of any one of these populations can be the sum of many discrete histories, except for the minor continuing outer halo accretion. All these stellar populations are embedded in dark-matter, and allow the properties of dark matter to be measured on small scales. Intriguing and unexpected consistencies in the properties of this dark matter are being revealed.
We investigate the stellar populations of passive spiral galaxies as a function of mass and environment, using integral field spectroscopy data from the Sydney-AAO Multi-object Integral field spectrograph Galaxy Survey. Our sample consists of $52$ cluster passive spirals and $18$ group/field passive spirals, as well as a set of S0s used as a control sample. The age and [Z/H] estimated by measuring Lick absorption line strength indices both at the center and within $1R_{rm e}$ do not show a significant difference between the cluster and the field/group passive spirals. However, the field/group passive spirals with log(M$_star$/M$_odot)gtrsim10.5$ show decreasing [$alpha$/Fe] along with stellar mass, which is $sim0.1$ dex smaller than that of the cluster passive spirals. We also compare the stellar populations of passive spirals with S0s. In the clusters, we find that passive spirals show slightly younger age and lower [$alpha$/Fe] than the S0s over the whole mass range. In the field/group, stellar populations show a similar trend between passive spirals and S0s. In particular, [$alpha$/Fe] of the field/group S0s tend to be flattening with increasing mass above log(M$_star$/M$_odot)gtrsim10.5$, similar to the field/group passive spirals. We relate the age and [$alpha$/Fe] of passive spirals to their mean infall time in phase-space; we find a positive correlation, in agreement with the prediction of numerical simulations. We discuss the environmental processes that can explain the observed trends. The results lead us to conclude that the formation of the passive spirals and their transformation into S0s may significantly depend on their environments.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
