Gravitationally lensed image simulations for the study of the substructure in galaxy clusters

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 49-50).As gravitational lensing is susceptible to all gravitating matter-both baryonic and dark-it provides a potentially clean way to study the mass distribution of galaxy clusters. We are particularly interested in the substructure of dark matter in galaxy clusters as it signals constraints on various cosmological parameters as well as cluster evolution. Gravitationally lensed image simulations are needed in order to determine just how much can be learned from current mass reconstruction methods. We present here a comprehensive procedure for generating such a set of simulated images using shapelets (Massey et al. (2005)). These images use a catalog of galaxies from the Hubble Space Telescope data taken as part of the Cosmos Evolution Survey (COSMOS). The background galaxies are then lensed by a 1015M galaxy cluster set at a redshift of z = 0.4. Noise and a point spread function (PSF) can also be added to the images; we chose to emulate the set of COSMOS pointings from the Subaru Telescope. As the shapelets simulation software allows complete freedom over all background galaxy, noise, and PSF parameters, the methods presented here have the potential to be used to not only verify that existing mass reconstruction algorithms work, but also to help optimize specifications on future telescopes.(cont.) We also present a preliminary strong lensing analysis of two noise- and PSF-free simulated images according to the algorithm presented in Diego et al. (2005). We found that while this procedure was able to accurately reproduce the surface mass density profile for radii greater than that of the outermost arcs used in the analysis, it failed in unexpected ways for the inner radii.by Mossy S. Peeples.S.B

A Budget and Accounting of Metals at z~0: Results from the COS-Halos Survey

We present a budget and accounting of metals in and around star-forming galaxies at $z\sim 0$. We combine empirically derived star formation histories with updated supernova and AGB yields and rates to estimate the total mass of metals produced by galaxies with present-day stellar mass of $10^{9.3}$--$10^{11.6} M_{\odot}$. On the accounting side of the ledger, we show that a surprisingly constant 20--25% mass fraction of produced metals remain in galaxies' stars, interstellar gas and interstellar dust, with little dependence of this fraction on the galaxy stellar mass (omitting those metals immediately locked up in remnants). Thus, the bulk of metals are outside of galaxies, produced in the progenitors of today's $L^*$ galaxies. The COS-Halos survey is uniquely able to measure the mass of metals in the circumgalactic medium (to impact parameters of $< 150$ kpc) of low-redshift $\sim L^*$ galaxies. Using these data, we map the distribution of CGM metals as traced by both the highly ionized OVI ion and a suite of low-ionization species; combined with constraints on circumgalactic dust and hotter X-ray emitting gas out to similar impact parameters, we show that $\sim 40$% of metals produced by $M_{\star}\sim 10^{10}M_{\odot}$ galaxies can be easily accounted for out to 150 kpc. With the current data, we cannot rule out a constant mass of metals within this fixed physical radius. This census provides a crucial boundary condition for the eventual fate of metals in galaxy evolution models.Comment: 19 pages, 12 figures, 2 tables. ApJ, in pres

Outliers from the Mass--Metallicity Relation II: A Sample of Massive Metal-Poor Galaxies from SDSS

We present a sample of 42 high-mass low-metallicity outliers from the mass--metallicity relation of star-forming galaxies. These galaxies have stellar masses that span log(M_*/M_sun) ~9.4 to 11.1 and are offset from the mass--metallicity relation by -0.3 to -0.85 dex in 12+log(O/H). In general, they are extremely blue, have high star formation rates for their masses, and are morphologically disturbed. Tidal interactions are expected to induce large-scale gas inflow to the galaxies' central regions, and we find that these galaxies' gas-phase oxygen abundances are consistent with large quantities of low-metallicity gas from large galactocentric radii diluting the central metal-rich gas. We conclude with implications for deducing gas-phase metallicities of individual galaxies based solely on their luminosities, specifically in the case of long gamma-ray burst host galaxies.Comment: Accepted for publication in ApJ; 11 pages, 11 figure