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تسجيل مستخدم جديدJoint Gas and Stellar Dynamical Models of WLM: An isolated dwarf galaxy within a cored, prolate DM halo
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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 ($gamma$) and flattening ($q_mathrm{DM}$), and the stellar orbital anisotropy ($beta_{z}, beta_{r}$). 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 $gamma$. The mass-anisotropy degeneracy is also partially broken, leading to reductions on uncertainty by $sim 30%$ on $M_mathrm{vir}$ (and $sim 70%$ at the half-light radius) and $sim 25%$ on anisotropy. Our inferred value of $gamma = 0.3 pm 0.1$ is robust to the halo geometry, and in excellent agreement with predictions of stellar feedback driven DM core creation. The derived prolate geometry of the DM halo with $q_mathrm{DM} = 2 pm 1$ is consistent with $Lambda$CDM simulations of dwarf galaxy halos. While self-interacting DM (SIDM) models with $sigma/m_{X} sim 0.6$ can reproduce this cored DM profile, the interaction events may sphericalise the halo. The simultaneously cored and prolate DM halo may therefore present a challenge for SIDM. Finally we find that the radial profile of stellar anisotropy in WLM ($beta_{r}$) follows a nearly identical trend of increasing tangential anisotropy to the classical dSphs, Fornax and Sculptor. Given WLMs orbital history, this result may call into question whether such anisotropy is a consequence of tidal stripping in only one pericentric passage or if it instead is a feature of the largely self-similar formation and evolutionary pathways for some dwarf galaxies.
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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
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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 rotation in WLM is measured to be $17 pm 1$ km s$^{-1}$, however the ratio of rotation to pressure support for the stars is $V/sigma sim 1$, in contrast to the gas whose ratio is seven times larger. This, along with the structural data and alignment of the kinematic and photometric axes, suggests we are viewing WLM as a highly inclined oblate spheroid. Stellar rotation curves, corrected for asymmetric drift, are used to compute a dynamical mass of $4.3pm 0.3times10^{8} $M$_{odot}$ at the half light radius ($r_{h} = 1656 pm 49$ pc). The stellar velocity dispersion increases with stellar age in a manner consistent with giant molecular cloud and substructure interactions producing the heating in WLM. Coupled with WLMs isolation, this suggests that the extended vertical structure of its stellar and gaseous components and increase in stellar velocity dispersion with age are due to internal feedback, rather than tidally driven evolution. These represent some of the first observational results from an isolated Local Group dwarf galaxy which can offer important constraints on how strongly internal feedback and secular processes modulate SF and dynamical evolution in low mass isolated objects.
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