Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userStellar dynamics in the strong-lensing central galaxy of Abell 1201: A low stellar mass-to-light ratio, a large central compact mass, and a standard dark matter halo
124
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We analyse the stellar kinematics of the z=0.169 brightest cluster galaxy (BCG) in Abell 1201, using integral field observations with VLT/MUSE. This galaxy has a gravitationally-lensed arc located at unusually small radius ($sim$5 kpc), allowing us to constrain the mass distribution using lensing and stellar dynamical information over the same radial range. We measure a velocity dispersion profile which is nearly flat at $sigma$ $approx$ 285 km/s in the inner $sim$5 kpc, and then rises steadily to $sigma$ $approx$ 360 km/s at $sim$30 kpc. We analyse the kinematics using axisymmetric Jeans models, finding that the data require both a significant dark matter halo (to fit the rising outer profile) and a compact central component, with mass $M_{rm cen}$ $approx$ 2.5$times$10$^{10}$ $M_odot$ (to fit the flat {sigma} in the inner regions). The latter component could represent a super-massive black hole, in which case it would be among the largest known to date. Alternatively $M_{rm cen}$ could describe excess mass associated with a gradient in the stellar mass-to-light ratio. Imposing a standard NFW dark matter density profile, we recover a stellar mass-to-light ratio $Upsilon$ which is consistent with a Milky-Way-like initial mass function (IMF). By anchoring the models using the lensing mass constraint, we break the degeneracy between $Upsilon$ and the inner slope $gamma$ of the dark matter profile, finding $gamma$=1.0$pm$0.1, consistent with the NFW form. We show that our results are quite sensitive to the treatment of the central mass in the models. Neglecting $M_{rm cen}$ biases the results towards both a heavier-than-Salpeter IMF and a shallower-than-NFW dark matter slope ($gamma$ $approx$ 0.5).
rate research
Read More
We use galaxy-galaxy lensing to study the dark matter halos surrounding a sample of Locally Brightest Galaxies (LBGs) selected from the Sloan Digital Sky Survey. We measure mean halo mass as a function of the stellar mass and colour of the central galaxy. Mock catalogues constructed from semi-analytic galaxy formation simulations demonstrate that most LBGs are the central objects of their halos, greatly reducing interpretation uncertainties due to satellite contributions to the lensing signal. Over the full stellar mass range, $10.3 < log [M_*/M_odot] < 11.6$, we find that passive central galaxies have halos that are at least twice as massive as those of star-forming objects of the same stellar mass. The significance of this effect exceeds $3sigma$ for $log [M_*/M_odot] > 10.7$. Tests using the mock catalogues and on the data themselves clarify the effects of LBG selection and show that it cannot artificially induce a systematic dependence of halo mass on LBG colour. The bimodality in halo mass at fixed stellar mass is reproduced by the astrophysical model underlying our mock catalogue, but the sign of the effect is inconsistent with recent, nearly parameter-free age-matching models. The sign and magnitude of the effect can, however, be reproduced by halo occupation distribution models with a simple (few-parameter) prescription for type-dependence.
Recent observations have been discovering new ultra-faint dwarf galaxies as small as $sim20~{rm pc}$ in half-light radius and $sim3~{rm km~s^{-1}}$ in line-of-sight velocity dispersion. In these galaxies, dynamical friction on a star against dark matter can be significant and alter their stellar density distribution. The effect can strongly depend on a central density profile of dark matter, i.e. cusp or core. In this study, I perform computations using a classical and a modern analytic formulae and $N$-body simulations to study how dynamical friction changes a stellar density profile and how different it is between cuspy and cored dark matter haloes. This study shows that, if a dark matter halo has a cusp, dynamical friction can cause shrivelling instability which results in emergence of a stellar cusp in the central region $simeq2~{rm pc}$. On the other hand, if it has a constant-density core, dynamical friction is significantly weaker and does not generate a stellar cusp even if the galaxy has the same line-of-sight velocity dispersion. In such a compact and low-mass galaxy, since the shrivelling instability by dynamical friction is inevitable if it has a dark matter cusp, absence of a stellar cusp implies that the galaxy has a dark-matter core. I expect that this could be used to diagnose a dark matter density profile in these compact ultra-faint dwarf galaxies.
We analyze the correlations between central dark matter (DM) content of early-type galaxies and their sizes and ages, using a sample of intermediate-redshift (z ~ 0.2) gravitational lenses from the SLACS survey, and by comparing them to a larger sample of z ~ 0 galaxies. We decompose the deprojected galaxy masses into DM and stellar components using combinations of strong lensing, stellar dynamics, and stellar populations modeling. For a given stellar mass, we find that for galaxies with larger sizes, the DM fraction increases and the mean DM density decreases, consistently with the cuspy halos expected in cosmological formation scenarios. The DM fraction also decreases with stellar age, which can be partially explained by the inverse correlation between size and age. The residual trend may point to systematic dependencies on formation epoch of halo contraction or stellar initial mass functions. These results are in agreement with recent findings based on local galaxies by Napolitano, Romanowsky & Tortora (2010) and suggest negligible evidence of galaxy evolution over the last ~ 2.5 Gyr other than passive stellar aging.
Using deep images from the Hyper Suprime-Cam (HSC) survey and taking advantage of its unprecedented weak lensing capabilities, we reveal a remarkably tight connection between the stellar mass distribution of massive central galaxies and their host dark matter halo mass. Massive galaxies with more extended stellar mass distributions tend to live in more massive dark matter haloes. We explain this connection with a phenomenological model that assumes, (1) a tight relation between the halo mass and the total stellar content in the halo, (2) that the fraction of in-situ and ex-situ mass at $r<10$ kpc depends on halo mass. This model provides an excellent description of the stellar mass functions (SMF) of total stellar mass ($M_{star}^{rm Max}$) and stellar mass within inner 10 kpc ($M_{star}^{10}$) and also reproduces the HSC weak lensing signals of massive galaxies with different stellar mass distributions. The best-fit model shows that halo mass varies significantly at fixed total stellar mass (as much as 0.4 dex) with a clear dependence on $M_{star}^{10}$. Our two-parameter $M_{star}^{rm Max}$-$M_{star}^{10}$ description provides a more accurate picture of the galaxy-halo connection at the high-mass end than the simple stellar-halo mass relation (SHMR) and opens a new window to connect the assembly history of halos with those of central galaxies. The model also predicts that the ex-situ component dominates the mass profiles of galaxies at $r< 10$ kpc for $log M_{star} ge 11.7$). The code used for this paper is available online: https://github.com/dr-guangtou/asap
We present a new gravitational lens model of the Hubble Frontier Fields cluster Abell 370 ($z = 0.375$) using imaging and spectroscopy from Hubble Space Telescope and ground-based spectroscopy. We combine constraints from a catalog of 1344 weakly lensed galaxies and 39 multiply-imaged sources comprised of 114 multiple images, including a system of multiply-imaged candidates at $z=7.93 pm 0.02$, to obtain a best-fit mass distribution using the cluster lens modeling code Strong and Weak Lensing United. As the only analysis of A370 using strong and weak lensing constraints from Hubble Frontier Fields data, our method provides an independent check on assumptions in other methods on the mass distribution. Convergence, shear, and magnification maps are made publicly available through the HFF website. We find that the model we produce is similar to models produced by other groups, with some exceptions due to the differences in lensing code methodology. In an effort to study how our total projected mass distribution traces light, we measure the stellar mass density distribution using Spitzer/Infrared Array Camera imaging. Comparing our total mass density to our stellar mass density in a radius of 0.3 Mpc, we find a mean projected stellar to total mass ratio of $langle f* rangle = 0.011 pm 0.003$ (stat.) using the diet Salpeter initial mass function. This value is in general agreement with independent measurements of $langle f* rangle$ in clusters of similar total mass and redshift.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
