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Dave R.,University of the Western Cape | Dave R.,African Institute for Mathematical Sciences | Dave R.,University of Arizona | Katz N.,University of Massachusetts Amherst | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We examine the global HI properties of galaxies in quarter billion particle cosmological simulations using GADGET-2, focusing on howgalactic outflows impactHI content. We consider four outflow models, including a new one (ezw) motivated by recent interstellar medium simulations in which the wind speed and mass loading factor scale as expected for momentumdriven outflows for larger galaxies and energy-driven outflows for dwarfs (s >75 km s-1). To obtain predicted HI masses, we employ a simple but effective local correction for particle selfshielding and an observationally constrained transition from neutral to molecular hydrogen. Our ezw simulation produces an HI mass function whose faint-end slope of -1.3 agrees well with observations from the Arecibo Fast Legacy ALFA survey; other models agree less well. Satellite galaxies have a bimodal distribution in HI fraction versus halo mass, with smaller satellites and/or those in larger haloes more often being HI deficient. At a given stellar mass, HI content correlates with the star formation rate and inversely correlates with metallicity, as expected if driven by stochasticity in the accretion rate. To higher redshifts, massive HI galaxies disappear and the mass function steepens. The global cosmic HI density conspires to remain fairly constant from z ~ 5?0, but the relative contribution from smaller galaxies increases with redshift. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Wong K.C.,University of Arizona | Keeton C.R.,Rutgers University | Williams K.A.,University of Texas at Austin | Momcheva I.G.,Observatories of the Carnegie Institute of Washington | Zabludoff A.I.,University of Arizona
Astrophysical Journal | Year: 2011

Using new photometric and spectroscopic data in the fields of nine strong gravitational lenses that lie in galaxy groups, we analyze the effects of both the local group environment and line-of-sight (LOS) galaxies on the lens potential. We use Monte Carlo simulations to derive the shear directly from measurements of the complex lens environment, providing the first detailed independent check of the shear obtained from lens modeling. We account for possible tidal stripping of the group galaxies by varying the fraction of total mass apportioned between the group dark matter halo and individual group galaxies. The environment produces an average shear of γ = 0.08 (ranging from 0.02 to 0.17), significant enough to affect quantities derived from lens observables. However, the direction and magnitude of the shears do not match those obtained from lens modeling in three of the six four-image systems in our sample (B1422, RXJ1131, and WFI2033). The source of this disagreement is not clear, implying that the assumptions inherent in both the environment and lens model approaches must be reconsidered. If only the local group environment of the lens is included, the average shear is γ = 0.05 (ranging from 0.01 to 0.14), indicating that LOS contributions to the lens potential are not negligible.We isolate the effects of various theoretical and observational uncertainties on our results. Of those uncertainties, the scatter in the Faber-Jackson relation and error in the group centroid position dominate. Future surveys of lens environments should prioritize spectroscopic sampling of both the local lens environment and objects along the LOS, particularly those bright (I <21.5) galaxies projected within 5' of the lens. © 2011 The American Astronomical Society. All rights reserved. Source


Colucci J.E.,University of California at Santa Cruz | Bernstein R.A.,University of California at Santa Cruz | Cameron S.A.,University of Michigan | McWilliam A.,Observatories of the Carnegie Institute of Washington
Astrophysical Journal | Year: 2011

In this paper, we refine our method for the abundance analysis of high-resolution spectroscopy of the integrated light of unresolved globular clusters (GCs). This method was previously demonstrated for the analysis of old (>10Gyr) Milky Way (MW) GCs. Here, we extend the technique to young clusters using a training set of nine GCs in the Large Magellanic Cloud. Depending on the signal-to-noise ratio of the data, we use 20-100 Fe lines per cluster to successfully constrain the ages of old clusters to within a 5Gyr range, the ages of 2Gyr clusters to a 1-2Gyr range, and the ages of the youngest clusters (0.05-1 Gyr) to a 200 Myr range. We also demonstrate that we can measure [Fe/H] in clusters with any age less than 12Gyr with similar or only slightly larger uncertainties (0.1-0.25dex) than those obtained for old MW GCs (0.1dex); the slightly larger uncertainties are due to the rapid evolution in stellar populations at these ages. In this paper, we present only Fe abundances and ages. In the next paper in this series, we present our complete analysis of 20 elements for which we are able to measure abundances. For several of the clusters in this sample, there are no high-resolution abundances in the literature from individual member stars; our results are the first detailed chemical abundances available. The spectra used in this paper were obtained at Las Campanas with the echelle on the du Pont Telescope and with the MIKE spectrograph on the Magellan Clay Telescope. © 2011. The American Astronomical Society. All rights reserved.. Source


Colucci J.E.,University of California at Santa Cruz | Duran M.F.,University of California at Santa Cruz | Bernstein R.A.,University of California at Santa Cruz | McWilliam A.,Observatories of the Carnegie Institute of Washington
Astrophysical Journal Letters | Year: 2013

We present [Fe/H], ages, and Ca abundances for an initial sample of 10 globular clusters in NGC 5128 obtained from high-resolution, high signal-to-noise ratio echelle spectra of their integrated light. All abundances and ages are obtained using our original technique for high-resolution integrated light abundance analysis of globular clusters. The clusters have a range in [Fe/H] between -1.6 and -0.2. In this sample, the average [Ca/Fe] for clusters with [Fe/H] <-0.4 is +0.37 ± 0.07, while the average [Ca/Fe] in our Milky Way (MW) and M31 GC samples is +0.29 ± 0.09 and +0.24 ± 0.10, respectively. This may imply a more rapid chemical enrichment history for NGC 5128 than for either the MW or M31. This sample provides the first quantitative picture of the chemical history of NGC 5128 that is directly comparable to what is available for the MW. Data presented here were obtained with the MIKE echelle spectrograph on the Magellan Clay Telescope. © 2013. The American Astronomical Society. All rights reserved. Source


McWilliam A.,Observatories of the Carnegie Institute of Washington | Zoccali M.,University of Santiago de Chile
Astrophysical Journal | Year: 2010

From Two Micron All Sky Survey infrared photometry, we find two red clump (RC) populations coexisting in fields toward the Galactic bulge at latitudes |b| >5°5, ranging over ∼13° in longitude and 20° in latitude. These RC peaks indicate two stellar populations separated by ∼2.3 kpc; at (l, b) = (+1, -8) the two RCs are located at 6.5 and 8.8 ± 0.2 kpc. The double-peaked RC is inconsistent with a tilted bar morphology. Most of our fields show the two RCs at roughly constant distance with longitude, also inconsistent with a tilted bar; however, an underlying bar may be present. Stellar densities in the two RCs change dramatically with longitude: on the positive longitude side the foreground RC is dominant, while the background RC dominates negative longitudes. A line connecting the maxima of the foreground and background populations is tilted to the line of sight by ∼20° ± 4°, similar to claims for the tilt of a Galactic bar. The distance between the two RCs decreases toward the Galactic plane; seen edge-on the bulge is X-shaped, resembling some extragalactic bulges and the results of N-body simulations. The center of this X is consistent with the distance to the Galactic center, although better agreement would occur if the bulge is 2-3 Gyr younger than 47 Tuc. Our observations may be understood if the two RC populations emanate, nearly tangentially, from the Galactic bar ends, in a funnel shape. Alternatively, the X, or double funnel, may continue to the Galactic center. From the Sun, this would appear peanut/box shaped, but X-shaped when viewed tangentially. © 2010. The American Astronomical Society. Source

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