Sloan Fellows

About: Sloan Fellows is a based out in . It is known for research contribution in the topics: Galaxy & Star formation. The organization has 55 authors who have published 253 publications receiving 35008 citations. The organization is also known as: Sloan Fellows.

Photoionization, numerical resolution, and galaxy formation

Abstract: Using cosmological simulations that incorporate gasdynamics and gravitational forces, we investigate the influence of photoionization by an ultraviolet radiation background on the formation of galaxies. In our highest resolution simulations, we find that photoionization has essentially no effect on the baryonic mass function of galaxies at z = 2, down to our resolution limit of ~5 × 109 M☉. We do, however, find a strong interplay between the mass resolution of a simulation and the microphysics included in the computation of heating and cooling rates. At low resolution, a photoionizing background can appear to suppress the formation of even relatively massive galaxies. However, when the same initial conditions are evolved with a factor of 8 improvement in mass resolution, this effect disappears. Our results demonstrate the need for care in interpreting the results of cosmological simulations that incorporate hydrodynamics and radiation physics. For example, we conclude that a simulation with limited resolution may yield more accurate results if it ignores some relevant physical processes, such as photoionization. At higher resolution, the simulated population of massive galaxies is insensitive to the treatment of photoionization or the inclusion of star formation in the simulations, but it does depend significantly on the amplitude of the initial density fluctuations. By z = 2, an Ω = 1 cold dark matter model normalized to produce the observed masses of present-day clusters has already formed galaxies with baryon masses exceeding 1011 M☉.

SPECTROSCOPIC CONFIRMATION OF A MASSIVE RED-SEQUENCE-SELECTED GALAXY CLUSTER AT z = 1.34 IN THE SpARCS-SOUTH CLUSTER SURVEY

Abstract: The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a z ′ -passband imaging survey, consisting of deep (z ′ ≃ 24 AB) observations made from both hemispheres using the CFHT 3.6m and CTIO 4m telescopes. The survey was designed with the primary aim of detecting galaxy clusters at z > 1. In tandem with pre-existing 3.6µm observations from the Spitzer Space Telescope SWIRE Legacy Survey, SpARCS detects clusters using an infrared adaptation of the two-filter redsequence cluster technique. The total effective area of the SpARCS cluster survey is 41.9 deg 2 . In this paper, we provide an overview of the 13.6 deg 2 Southern CTIO/MOSAICII observations. The 28.3 deg 2 Northern CFHT/MegaCam observations are summarized in a companion paper by Muzzin et al. (2008a). In this paper, we also report spectroscopic confirmation of SpARCS J003550431224, a very rich galaxy cluster at z = 1.335, discovered in the ELAIS-S1 field. To date, this is the highest spectroscopically confirmed redshift for a galaxy cluster discovered using the red-sequence technique. Based on nine confirmed members, SpARCS J003550-431224 has a preliminary velocity dispersion of 1050 ±230 km s −1 . With its proven capability for efficient cluster detection,SpARCS is a demonstration that we have entered an era of large, homogeneously-selected z > 1 cluster surveys. Subject headings: surveys — cosmology: observations — galaxies: clusters: general — galaxies: highredshift — infrared: galaxies

Constraints on the Mass of Warm Dark Matter Particles and the Shape of the Linear Power Spectrum from the Lyα Forest

Abstract: High-resolution N-body simulations of cold dark matter (CDM) models predict that galaxies and clusters have cuspy halos with considerable substructure. Observations reveal smooth halos with central density cores. One possible resolution of the substructure problem is that the dark matter is warm; this will suppress the power spectrum on small scales. The Lyα forest is a powerful probe of the linear power spectrum on these scales. We use collisionless N-body simulations to follow the evolution of structure in warm dark matter (WDM) models and analyze artificial Lyα forest spectra extracted from them. By requiring that there be enough small-scale power in the linear power spectrum to reproduce the observed properties of the Lyα forest in quasar spectra, we derive a lower limit to the mass of the WDM particle of 750 eV. This limit is robust to reasonable uncertainties in our assumption about the temperature of the gas at mean density (T0) at z = 3. We argue that any model that suppresses the CDM linear theory power spectrum more severely than a 750 eV WDM particle cannot produce the Lyα forest.

THE PROPERTIES AND PREVALENCE OF GALACTIC OUTFLOWS AT z ∼ 1 IN THE EXTENDED GROTH STRIP*

Abstract: We investigate galactic-scale outflowing winds in 72 star-forming galaxies at z ~ 1 in the Extended Groth Strip. Galaxies were selected from the DEEP2 survey and follow-up LRIS spectroscopy was obtained covering Si II, C IV, Fe II, Mg II, and Mg I lines in the rest-frame ultraviolet. Using Galaxy Evolution Explorer (GALEX), Hubble Space Telescope (HST), and Spitzer imaging available for the Extended Groth Strip, we examine galaxies on a per-object basis in order to better understand both the prevalence of galactic outflows at z ~ 1 and the star-forming and structural properties of objects experiencing outflows. Gas velocities, measured from the centroids of Fe II interstellar absorption lines, are found to span the interval [–217, +155] km s–1. We find that ~40% (10%) of the sample exhibits blueshifted Fe II lines at the 1σ (3σ) level. We also measure maximal outflow velocities using the profiles of the Fe II and Mg II lines; we find that Mg II frequently traces higher velocity gas than Fe II. Using quantitative morphological parameters derived from the HST imaging, we find that mergers are not a prerequisite for driving outflows. More face-on galaxies also show stronger winds than highly inclined systems, consistent with the canonical picture of winds emanating perpendicular to galactic disks. In light of clumpy galaxy morphologies, we develop a new physically motivated technique for estimating areas corresponding to star formation. We use these area measurements in tandem with GALEX-derived star formation rates (SFRs) to calculate SFR surface densities. At least 70% of the sample exceeds an SFR surface density of 0.1 M ☉ yr–1 kpc–2, the threshold necessary for driving an outflow in local starbursts. At the same time, the outflow detection fraction of only 40% in Fe II absorption provides further evidence for an outflow geometry that is not spherically symmetric. We see a ~3σ trend between outflow velocity and SFR surface density, but no significant trend between outflow velocity and SFR. Higher resolution data are needed in order to test the scaling relations between outflow velocity and both SFR and SFR surface density predicted by theory.

The MOSDEF Survey: Mass, Metallicity, and Star-formation Rate at z~2.3

Abstract: We present results on the z~2.3 mass-metallicity relation (MZR) using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. We use an initial sample of 87 star-forming galaxies with spectroscopic coverage of H\beta, [OIII]\lambda 5007, H\alpha, and [NII]\lambda 6584 rest-frame optical emission lines, and estimate the gas-phase oxygen abundance based on the N2 and O3N2 strong-line indicators. We find a positive correlation between stellar mass and metallicity among individual z~2.3 galaxies using both the N2 and O3N2 indicators. We also measure the emission-line ratios and corresponding oxygen abundances for composite spectra in bins of stellar mass. Among composite spectra, we find a monotonic increase in metallicity with increasing stellar mass, offset ~0.15-0.3 dex below the local MZR. When the sample is divided at the median star-formation rate (SFR), we do not observe significant SFR dependence of the z~2.3 MZR among either individual galaxies or composite spectra. We furthermore find that z~2.3 galaxies have metallicities ~0.1 dex lower at a given stellar mass and SFR than is observed locally. This offset suggests that high-redshift galaxies do not fall on the local "fundamental metallicity relation" among stellar mass, metallicity, and SFR, and may provide evidence of a phase of galaxy growth in which the gas reservoir is built up due to inflow rates that are higher than star-formation and outflow rates. However, robust conclusions regarding the gas-phase oxygen abundances of high-redshift galaxies await a systematic reappraisal of the application of locally calibrated metallicity indicators at high redshift.