67 research outputs found
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 . 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
--. 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 galaxies. The COS-Halos
survey is uniquely able to measure the mass of metals in the circumgalactic
medium (to impact parameters of kpc) of low-redshift
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 % of metals produced by
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
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