Star formation at the edge of the Local Group: a rising star formation history in the isolated galaxy WLM
Saundra M. Albers, Daniel R. Weisz, Andrew A. Cole, Andrew E. Dolphin, Evan D. Skillman, Benjamin F. Williams, Michael Boylan-Kolchin, James S. Bullock, Juliann… 展开作者
Saundra M. Albers, Daniel R. Weisz, Andrew A. Cole, Andrew E. Dolphin, Evan D. Skillman, Benjamin F. Williams, Michael Boylan-Kolchin, James S. Bullock, Julianne J. Dalcanton, Philip F. Hopkins, Ryan Leaman, Alan W. McConnachie, Mark Vogelsberger, Andrew Wetzel
备注：
13 pages, 13 Figures, 4 Tables. Re-submitted to MNRAS after addressing the referee's comments
We present the star formation history (SFH) of the isolated (D~970 kpc) Local Group dwarf galaxy WLM measured from color-magnitude diagrams constructed from deep Hubble Space Telescope imaging. Our observations include a central (0.5 $r_h$) and outer field (0.7 $ r_h$) that reach below the oldest main sequence turnoff. WLM has no early dominant episode of star formation: 20% of its stellar mass formed by ~12.5 Gyr ago (z~5). It also has an SFR that rises to the present with 50% of the stellar mass within the most recent 5 Gyr (z<0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark matter core creation. The SFHs of real isolated dwarf galaxies and those from the the Feedback In Realistic Environment suite are in good agreement for $M_{\star}(z=0) \sim 10^7-10^9 M_{\odot}$, but in worse agreement at lower masses ($M_{\star}(z=0) \sim 10^5-10^7 M_{\odot}$). These differences may be explainable by systematics in the models (e.g., reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.
WLM: Dynamics of an isolated Dwarf Irregular Galaxy Under Ram Pressure in the Local Group
LIRA, Observatoire de Paris, Universite PSL, CNRS（巴黎天文台）；Instituto de Astrofísica de Andalucía (CSIC)（安达卢西亚天体物理研究所）；Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg（斯特拉斯堡大学）；Aix Marseille Univ, CNRS, CNES, LAM（艾克斯马赛大学）；University of Cape Town（开普敦大学）；Université de Montréal（蒙特利尔大学）；Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo（瓦加杜古第一大学约瑟夫·基泽博天体物理观测站）
We report a tentative detection of the circumgalactic medium (CGM) of WLM, an isolated, low-mass (log$M_*/M_\odot\approx7.6$), dwarf irregular galaxy in the Local Group (LG). We analyze an HST/COS archival spectrum of a quasar sightline (PHL2525), which is 45 kpc (0.5 virial radius) from WLM and close to the Magellanic Stream (MS). Along this sightline, two ion absorbers are detected in Si II, Si III, Si IV, C II, and C IV at velocities of $\sim$-220 km s$^{-1}$ (Component v-220) and $\sim$-150 km s$^{-1}$ (Component v-150). To identify their origins, we study the position-velocity alignment o…
Building on our previous spectroscopic and photometric analysis of the isolated Local Group dwarf irregular (dIrr) galaxy WLM, we present a comparison of the metallicities of its RGB stars with respect to the well studied Local Group dwarf spheroidal galaxies (dSphs) and Magellanic Clouds. We calculate a mean metallicity of [Fe/H]$ = -1.28 \pm 0.02$, and intrinsic spread in metallicity of $σ= 0.38 \pm 0.04$ dex, similar to the mean and spread observed in the massive dSph Fornax and the Small Magellanic Cloud. Thus, despite its isolated environment the global metallicity still follows expectati…
We present multi-tracer dynamical models of the low mass ($M_{*} \sim 10^{7}$), isolated dwarf irregular galaxy WLM in order to simultaneously constrain the inner slope of the dark matter (DM) halo density profile ($γ$) and flattening ($q_\mathrm{DM}$), and the stellar orbital anisotropy ($β_{z}, β_{r}$). For the first time, we show how jointly constraining the mass distribution from the HI gas rotation curve and solving the Jeans' equations with discrete stellar kinematics leads to a factor of $\sim2$ reduction in the uncertainties on $γ$. The mass-anisotropy degeneracy is also partially brok…
We present spectroscopic data for 180 red giant branch stars in the isolated dwarf irregular galaxy WLM. Observations of the Calcium II triplet lines in spectra of RGB stars covering the entire galaxy were obtained with FORS2 at the VLT and DEIMOS on Keck II allowing us to derive velocities, metallicities, and ages for the stars. With accompanying photometric and radio data we have measured the structural parameters of the stellar and gaseous populations over the full galaxy. The stellar populations show an intrinsically thick configuration with $0.39 \leq q_{0} \leq 0.57$. The stellar rotatio…
We measure systemic proper motions for distant dwarf galaxies in the Local Group and investigate if these isolated galaxies have ever had an interaction with the Milky Way or M31. We cross-match photometry of isolated, star forming, dwarf galaxies in the Local Group, taken as part of the {\it Solo} survey, with astrometric measurements from Gaia Data Release 2. We find that NGC 6822, Leo A, IC 1613 and WLM have sufficient supergiants with reliable astrometry to derive proper motions. An additional three galaxies (Leo T, Eridanus 2 and Phoenix) are close enough that their proper motions have al…
We present observations and models of the kinematics and the distribution of the neutral hydrogen (HI) in the isolated dwarf irregular galaxy, Wolf-Lundmark-Melotte (WLM). We observed WLM with the Green Bank Telescope (GBT) and as part of the MeerKAT Early Science Programme, where 16 dishes were available. The HI disc of WLM extends out to a major axis diameter of 30 arcmin (8.5 kpc), and a minor axis diameter of 20 arcmin (5.6 kpc) as measured by the GBT. We use the MeerKAT data to model WLM using the TiRiFiC software suite, allowing us to fit different tilted-ring models and select the one t…
Dwarf galaxies are affected by all the evolutionary processes normally at work in galaxies of any mass. As fainter and less massive galaxies, however, dwarf galaxies are particularly susceptible to environmental mechanisms that can more easily perturb these systems. Importantly, the presence of nearby large galaxies are expected to have a profound effect on dwarf galaxies. Gravitational (especially tidally-induced) effects from the large galaxy can cause mass to be lost from the dwarf, and the passage of the dwarf through the gaseous medium surrounding the large galaxy can additionally cause t…
We present the first determination of the radial velocities and metallicities of 78 red giant stars in the isolated dwarf irregular galaxy WLM. Observations of the calcium II triplet in these stars were made with FORS2 at the VLT-UT2 in two separated fields of view in WLM, and the [Fe/H] values were conformed to the Carretta & Gratton (1997) metallicity scale. The mean metallicity is <[Fe/H]> = -1.27 +/- 0.04 dex, with a standard deviation of 0.37. We find that the stars in the inner field are more metal rich by [Fe/H] =0.30 +/- 0.06 dex. These results are in agreement with previous photometri…
The shape and diversity of dwarf galaxy rotation curves is at apparent odds with dark matter halos in a $Λ$ Cold Dark Matter ($Λ$CDM) cosmology. We use mock data from isolated dwarf galaxy simulations to show that this owes to three main effects. Firstly, stellar feedback heats dark matter, leading to a 'coreNFW' dark matter density profile with a slowly rising rotation curve. Secondly, if close to a recent starburst, large HI bubbles push the rotation curve out of equilibrium, deforming the rotation curve shape. Thirdly, when galaxies are viewed near face-on, their best fit inclination is bia…
Ghostly stellar haloes are extended haloes of stars composed solely of debris of pre-reionization fossil galaxies and should exist in dwarf galaxies with total masses $<10^{10}$ M$_\odot$. Fossil galaxies are even smaller mass dwarf galaxies that stopped forming stars after the epoch of reionization and have been identified in the Local Group as the ultra-faint dwarf satellites. Using cosmological N-body simulations we present an empirical model for the shapes and masses of ghostly stellar haloes. We compare the model to available observations of stellar haloes in six isolated dwarf galaxies i…
We measure the radial profiles of the stellar velocity dispersions, $σ(R)$, for 90 early-type galaxies (ETGs) in the MASSIVE survey, a volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all northern-sky ETGs with absolute $K$-band magnitude $M_K < -25.3$ mag, or stellar mass $M_* > 4 \times 10^{11} M_\odot$, within 108 Mpc. Our wide-field 107" $\times$ 107" IFS data cover radii as large as 40 kpc, for which we quantify separately the inner (2 kpc) and outer (20 kpc) logarithmic slopes $γ_{\rm inner}$ and $γ_{\rm outer}$ of $σ(R)$. While $γ_{\rm inner}$ is mostly negative…
The shallow faint-end slope of the galaxy mass function is usually reproduced in $Λ$CDM galaxy formation models by assuming that the fraction of baryons that turns into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities $V_{\rm max}<20$-$30$ km/s. Dark matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e., half-mass radii, $r_{1/2}\ll 1$ kpc). Many dwarfs have properties in disagreement with th…
Compared with numerous X-ray dominant active galactic nuclei (AGNs) without emission-line signatures in their optical spectra, the X-ray selected AGNs with optical emission lines are probably still in the high-accretion phase of black hole growth. This paper presents an investigation on the fraction of these X-ray detected AGNs with optical emission-line spectra in 198 galaxy groups at $z<1$ in a rest frame 0.1-2.4 keV luminosity range 41.3 <log(L_X/erg s-1) < 44.1 within the COSMOS field, as well as its variations with redshift and group richness. For various selection criteria of member gala…
We present spatially-resolved two-dimensional stellar kinematics for the 41 most massive early-type galaxies (MK <~ -25.7 mag, stellar mass M* >~ 10^11.8 Msun) of the volume-limited (D < 108 Mpc) MASSIVE survey. For each galaxy, we obtain high-quality spectra in the wavelength range of 3650 to 5850 A from the 246-fiber Mitchell integral-field spectrograph (IFS) at McDonald Observatory, covering a 107" x 107" field of view (often reaching 2 to 3 effective radii). We measure the 2-D spatial distribution of each galaxy's angular momentum (lambda and fast or slow rotator status), velocity dispersi…
The study of velocity fields of the hot gas in galaxy clusters can help to unravel details of microphysics on small-scales and to decipher the nature of feedback by active galactic nuclei (AGN). Likewise, magnetic fields as traced by Faraday rotation measurements (RMs) inform about their impact on gas dynamics as well as on cosmic ray production and transport. We investigate the inherent relationship between large-scale gas kinematics and magnetic fields through non-radiative magnetohydrodynamical simulations of the creation, evolution and disruption of AGN jet-inflated lobes in an isolated Pe…
