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Register a new userSeparating Galaxies from the Cluster Dark Matter Halo in Abell 611
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We investigate the mass content of galaxies in the core of the galaxy cluster Abell 611. We perform a strong lensing analysis of the cluster core and use velocity dispersion measurements for individual cluster members as additional constraints. Despite the small number of multiply-imaged systems and cluster members with central velocity dispersions available in the core of A611, the addition of velocity dispersion measurements leads to tighter constraints on the mass associated with the galaxy component, and as a result, on the mass associated with the dark matter halo. Without the spectroscopic velocity dispersions, we would overestimate the mass of the galaxy component by a factor of $sim1.5$, or, equivalently, we would underestimate the mass of the cluster dark halo by $sim5%$. We perform an additional lensing analysis using surface brightness (SB) reconstruction of the tangential giant arc. This approach improves the constraints on the mass parameters of the 5 galaxies close to the arc by up to a factor $sim10$. The galaxy velocity dispersions resulting from the SB analysis are consistent at the 1$sigma$ confidence level with the spectroscopic measurements and with the prediction from the simple pointlike analysis. In contrast the truncation radii for 2-3 galaxies depart significantly from the galaxy scaling relation and suggest differences in the stripping history from galaxy to galaxy.
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We present a detailed analysis of the baryonic and dark matter distribution in the lensing cluster Abell 611 (z=0.288), with the goal of determining the dark matter profile over an unprecedented range of cluster-centric distance. By combining three complementary probes of the mass distribution, weak lensing from deep multi-color imaging, strong lensing constraints based on the identification of multiply-imaged sources, and resolved stellar velocity dispersion measures for the brightest cluster galaxy (BCG), we extend the methodology for separating the dark and baryonic mass components introduced by Sand et al. (2008). Our resulting dark matter profile samples the cluster from ~3 kpc to 3.25 Mpc, thereby providing an excellent basis for comparisons with recent numerical models. We demonstrate that only by combining our three observational techniques can degeneracies in constraining the form of the dark matter profile be broken on scales crucial for detailed comparisons with numerical simulations. Our analysis reveals that a simple Navarro, Frenk, and White (NFW) profile is an unacceptable fit to our data. We confirm earlier claims that the inner profile of the dark matter profile deviates significantly from the NFW form and find a inner logarithmic slope beta flatter than 0.3 (68%; where rho_DM ~ r^{-beta} at small radii). In order to reconcile our data with cluster formation in a LambdaCDM cosmology, we speculate that it may be necessary to revise our understanding of the nature of baryon--dark matter interactions in cluster cores. Comprehensive weak and strong lensing data, when coupled with kinematic information on the brightest cluster galaxy, can readily be applied to a larger sample of clusters to test the universality of these results.
I present a simple phenomenological model for the observed linear scaling of the stellar mass in old globular clusters (GCs) with $z=0$ halo mass in which the stellar mass in GCs scales linearly with progenitor halo mass at $z=6$ above a minimum halo mass for GC formation. This model reproduces the observed $M_{rm GCs}-M_{rm halo}$ relation at $z=0$ and results in a prediction for the minimum halo mass at $z=6$ required for hosting one GC: $M_{rm min}(z=6)=1.07 times 10^9,M_{odot}$. Translated to $z=0$, the mean threshold mass is $M_{rm halo}(z=0) approx 2times 10^{10},M_{odot}$. I explore the observability of GCs in the reionization era and their contribution to cosmic reionization, both of which depend sensitively on the (unknown) ratio of GC birth mass to present-day stellar mass, $xi$. Based on current detections of $z gtrsim 6$ objects with $M_{1500} < -17$, values of $xi > 10$ are strongly disfavored; this, in turn, has potentially important implications for GC formation scenarios. Even for low values of $xi$, some observed high-$z$ galaxies may actually be GCs, complicating estimates of reionization-era galaxy ultraviolet luminosity functions and constraints on dark matter models. GCs are likely important reionization sources if $5 lesssim xi lesssim 10$. I also explore predictions for the fraction of accreted versus in situ GCs in the local Universe and for descendants of systems at the halo mass threshold of GC formation (dwarf galaxies). An appealing feature of the model presented here is the ability to make predictions for GC properties based solely on dark matter halo merger trees.
The cusp-core problem is one of the main challenges of the cold dark matter paradigm on small scales: the density of a dark matter halo is predicted to rise rapidly toward the center as rho ~ r^alpha with alpha between -1 and -1.5, while such a cuspy profile has not been clearly observed. We have carried out the spatially-resolved mapping of gas dynamics toward a nearby ultra-diffuse galaxy (UDG), AGC 242019. The derived rotation curve of dark matter is well fitted by the cuspy profile as described by the Navarro-Frenk-White model, while the cored profiles including both the pseudo-isothermal and Burkert models are excluded. The halo has alpha=-(0.90+-0.08) at the innermost radius of 0.67 kpc, Mhalo=(3.5+-1.2)E10 Msun and a small concentration of 2.0+-0.36. AGC 242019 challenges alternatives of cold dark matter by constraining the particle mass of fuzzy dark matter to be < 0.11E-22 eV or > 3.3E-22 eV , the cross section of self-interacting dark matter to be < 1.63 cm2/g, and the particle mass of warm dark matter to be > 0.23 keV, all of which are in tension with other constraints. The modified Newtonian dynamics is also inconsistent with a shallow radial acceleration relationship of AGC 242019. For the feedback scenario that transforms a cusp to a core, AGC 242019 disagrees with the stellar-to-halo-mass-ratio dependent model, but agrees with the star-formation-threshold dependent model. As a UDG, AGC 242019 is in a dwarf-size halo with weak stellar feedback, late formation time, a normal baryonic spin and low star formation efficiency (SFR/gas).
We present rotation curve fits to 175 late-type galaxies from the Spitzer Photometry & Accurate Rotation Curves (SPARC) database using seven dark matter (DM) halo profiles: pseudo-isothermal (pISO), Burkert, Navarro-Frenk-White (NFW), Einasto, Di Cintio (2014, DC14), coreNFW, and a new semi-empirical profile named Lucky13. We marginalize over stellar mass-to-light ratio, galaxy distance, disk inclination, halo concentration and halo mass (and an additional shape parameter for Einasto) using a Markov Chain Monte Carlo method. We find that cored halo models such as the DC14 and Burkert profiles generally provide better fits to rotation curves than the cuspy NFW profile. The stellar mass-halo mass relation from abundance matching is recovered by all halo profiles once imposed as a Bayesian prior, whereas the halo mass-concentration relation is not reproduced in detail by any halo model. We provide an extensive set of figures as well as best-fit parameters in machine-readable tables to facilitate model comparison and the exploration of DM halo properties.
A recently discovered young, high-velocity giant star J01020100-7122208 is a good candidate of hypervelocity star ejected from the Galactic center, although it has a bound orbit. If we assume that this star was ejected from the Galactic center, it can be used to constrain the Galactic potential, because the deviation of its orbit from a purely radial orbit informs us of the torque that this star has received after its ejection. Based on this assumption, we estimate the flattening of the dark matter halo of the Milky Way by using the Gaia DR2 data and the circular velocity data from Eilers et al. (2019). Our Bayesian analysis shows that the orbit of J01020100-7122208 favors a prolate dark matter halo within $sim$ 10 kpc from the Galactic center. The posterior distribution of the density flattening $q$ shows a broad distribution at $q gtrsim1$ and peaks at $q simeq 1.5$. Also, 98.5% of the posterior distribution is located at $q>1$, highly disfavoring an oblate halo.
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