[2]  arXiv:0803.0982 [ps, pdf, other]
    Title: Dark Energy and the Accelerating Universe
    Authors: Joshua Frieman (Chicago/Fermilab), Michael Turner (Chicago), Dragan Huterer (Michigan)
    Comments: Invited review for Annual Reviews of Astronomy and Astrophysics; 53 pages, 18 figures
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    The discovery ten years ago that the expansion of the Universe is accelerating put in place the last major building block of the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. At the same time, it posed one of the most profound mysteries in all of science, with deep connections to both astrophysics and particle physics. Cosmic acceleration could arise from the repulsive gravity of dark energy -- for example, the quantum energy of the vacuum -- or it may signal that General Relativity breaks down on cosmological scales and must be replaced. We review the present observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss the various theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that will shed light on this enigma in the coming years.


[6]  arXiv:0803.1002 [ps, pdf, other]
    Title: The optical spectra of 24 micron galaxies in the COSMOS field: I. Spitzer/MIPS bright sources in the zCOSMOS-bright 10k catalogue
    Authors: K. I. Caputi, S. J. Lilly, H. Aussel, D. Sanders, D. Frayer, O. Le Fevre, A. Renzini, G. Zamorani, M. Scodeggio, T. Contini, N. Scoville, C. M. Carollo, G. Hasinger, A. Iovino, V. Le Brun, E. Le Floc'h, C. Maier, V. Mainieri, M. Mignoli, M. Salvato, D. Schiminovich, J. Silverman, J. Surace, L. Tasca, et al., zCOSMOS, SCOSMOS team members
    Comments: Accepted for publication at the ApJ. 35 pages including 24 figures
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We study zCOSMOS-bright optical spectra for 609 Spitzer/MIPS 24 micron-selected galaxies with S(24um)> 0.30 mJy and I<22.5 (AB mag) over 1.5 sq. deg. of the COSMOS field. From emission-line diagnostics we find that: 1) star-formation rates (SFR) derived from the observed Halpha and Hbeta lines underestimate, on average, the total SFR by factors ~5 and 10, respectively; 2) both the Calzetti et al. and the Milky Way reddening laws are suitable to describe the extinction observed in infrared (IR) sources in most cases; 3) some IR galaxies at z<0.3 have low abundances, but many others with similar IR luminosities and redshifts are chemically enriched; 4) The average [OIII]/Hbeta ratios of nuLnu(24um)>10^11 Lsun galaxies at 0.6<z<0.7 are ~0.6 dex higher than the average ratio of all zCOSMOS galaxies at similar redshifts. Massive star formation and active galactic nuclei (AGN) could simultaneously be present in those galaxies with the highest ionising fluxes; 5) ~1/3 of the galaxies with metallicity measurements at 0.5<z<0.7 lie below the general mass-metallicity relation at the corresponding redshifts. The strengths of the 4000 Angstrom break and the Hdelta EW of our galaxies show that secondary bursts of star formation are needed to explain the spectral properties of most IR sources. The LIRG and ULIRG phases occur, on average, between 10^7 and 10^8 years after the onset of a starburst on top of underlying older stellar populations. These results are valid for galaxies of different IR luminosities at 0.6<z<1.0 and seem independent of the mechanisms triggering star formation.


[17]  arXiv:0803.1066 [ps, pdf, other]
    Title: A 2dF spectroscopic study of globular clusters in NGC 5128: Probing the formation history of the nearest giant Elliptical
    Authors: Michael Beasley, Terry Bridges, Eric Peng, William E. Harris, Gretchen L.H. Harris, Duncan A. Forbes, Glen Mackie
    Comments: 17 figures, some long tables
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We have performed a spectroscopic study of globular clusters (GCs) in the giant elliptical NGC 5128 using the 2dF facility at the Anglo-Australian telescope. We obtained integrated optical spectra for a total of 254 GCs, 79 of which are newly confirmed on the basis of their radial velocities and spectra. In addition, we obtained an integrated spectrum of the galaxy starlight along the southern major axis. We derive an empirical metallicity distribution function (MDF) for 207 GCs (~14 of the estimated total GC system) based upon Milky Way GCs. This MDF is multimodal at high statistical significance with peaks at [Z/H]~-1.3 and -0.5. A comparison between the GC MDF and that of the stellar halo at 20 kpc (~4 Reff) reveals close coincidence at the metal-rich ends of the distributions. However, an inner 8 kpc stellar MDF shows a clear excess of metal-rich stars when compared to the GCs. We compare a higher S/N subsample (147 GCs) with two stellar population models which include non-solar abundance ratio corrections. The vast majority of our sample (~90%) appears old, with ages similar to the Milky Way GC system. There is evidence for a population of intermediate-age (~4-8 Gy) GCs (<15% of the sample) which are on average more metal-rich than the old GCs. We also identify at least one younger cluster (~1-2 Gy) in the central regions of the galaxy. Our observations are consistent with a picture where NGC 5128 has undergone at least two mergers and/or interactions involving star formation and limited GC formation since z=1, however the effect of non-canonical hot stellar populations on the integrated spectra of GCs remains an outstanding uncertainty in our GC age estimates.


27]  arXiv:0803.1130 [ps, pdf, other]
    Title: The Extended HST Supernova Survey: The Rate of SNe Ia at z>1.4 Remains Low
    Authors: Tomas Dahlen (1), Louis-Gregory Strolger (1,2), Adam G. Riess (1,3) ((1) Space Telescope Science Institute, (2) Western Kentucky University, (3) Johns Hopkins University)
    Comments: Accepted for publication in ApJ
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We use the HST ACS imaging of the two GOODS fields during Cycles 11, 12, and 13 to derive the Type Ia supernova rate in four redshift intervals in the range 0.2<z<1.8. Compared to our previous results based on Cycle 11 observations only, we have increased the coverage of the search by a factor 2.7, making the total area searched equivalent to one square degree. The sample now consists of 56 Type Ia supernovae. The rates we derive are consistent with our results based on the Cycle 11 observations. In particular, the few detected supernovae at z>1.4 supports our previous result that there is a drop in the Type Ia supernova rate at high redshift, suggesting a long time delay between the formation of the progenitor star and the explosion of the supernova. If described by a simple one-parameter model, we find a characteristic delay time of 2-3 Gyr. However, a number of recent results based on e.g., low redshift supernova samples and supernova host galaxy properties suggest that the supernova delay time distribution is bimodal. In this model, a major fraction of the Type Ia supernova rate is 'prompt' and follows the star formation rate, while a smaller fraction of the rate has a long delay time, making this channel proportional to mass. While our results are fully consistent with the bimodal model at low redshifts, the low rate we find at z>1.4 appears to contradict these results. Models that corrects for star formation hidden by dust may explain at least part of the differences. Here we discuss this possibility together with other ways to reconcile data and models.


35]  arXiv:0803.1174 [ps, pdf, other]
    Title: The Lyman alpha morphology of local starburst galaxies: release of calibrated images
    Authors: Goran Ostlin (1), Matthew Hayes (1 and 2), Daniel Kunth (3), J. Miguel Mas-Hesse (4), Claus Leitherer (5), Artashes Petrosian (6), Hakim Atek (3) ((1) Stockholm Observatory, (2) Geneva Observatory, (3) IAP, (4) CSIC-INTA, (5) STScI, (6) BAO)
    Comments: Submitted to AJ. Full resolution version available from this http URL
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We present reduced and calibrated high resolution Lyman-alpha (Lya) images for a sample of six local star forming galaxies. Targets were selected to represent a range in luminosity and metallicity and to include both known Lya emitters and non-emitters. Far ultraviolet imaging was carried out with the Solar Blind Channel of the Advanced Camera for Surveys on Hubble Space Telescope in the F122M (Lya on-line) and F140LP (continuum) filters. The resulting Lya images are the product of careful modeling of both the stellar and nebular continua, facilitated by supporting HST imaging at lambda=2200, 3300, 4400, 5500, H-alpha and 8000AA, combined with Starburst 99 evolutionary synthesis models. In all, the resulting morphologies in Lya, Ha, and UV-continuum are qualitatively very different and we show that the bulk of Lya emerges in a diffuse component resulting from resonant scattering events. Lya escape fractions, computed from Ha luminosities and recombination theory, are found never to exceed 14%. Even after corrections for internal dust extinction, the highest escape fraction in the sample is found to be 40%, with the remainder falling significantly short of the case B ratio. The images presented have a physical resolution 3 orders of magnitude better than attainable at high redshifts from the ground with current instrumentation and our images may therefore serve as useful templates for comparing with observations and modeling of primeval galaxy formation. We therefore provide the reduced Lya, Ha, and continuum images to the community.


3]  arXiv:0803.1199 [ps, pdf, other]
    Title: LensPerfect: Gravitational Lens Massmap Reconstructions Yielding Exact Reproduction of All Multiple Images
    Authors: D. Coe, E. Fuselier, N. Benitez, T. Broadhurst, B. Frye, H. Ford
    Comments: 17 pages, 18 figures, accepted by ApJ. Software and full-color version of paper available at this http URL
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We present a new approach to gravitational lens massmap reconstruction. Our massmap solutions perfectly reproduce the positions, fluxes, and shears of all multiple images. And each massmap accurately recovers the underlying mass distribution to a resolution limited by the number of multiple images detected. We demonstrate our technique given a mock galaxy cluster similar to Abell 1689 which gravitationally lenses 19 mock background galaxies to produce 93 multiple images. We also explore cases in which far fewer multiple images are observed, such as four multiple images of a single galaxy. Massmap solutions are never unique, and our method makes it possible to explore an extremely flexible range of physical (and unphysical) solutions, all of which perfectly reproduce the data given. Each reconfiguration of the source galaxies produces a new massmap solution. An optimization routine is provided to find those source positions (and redshifts, within uncertainties) which produce the "most physical" massmap solution, according to a new figure of merit developed here. Our method imposes no assumptions about the slope of the radial profile nor mass following light. But unlike "non-parametric" grid-based methods, the number of free parameters we solve for is only as many as the number of observable constraints (or slightly greater if fluxes are constrained). For each set of source positions and redshifts, massmap solutions are obtained "instantly" via direct matrix inversion by smoothly interpolating the deflection field using a recently developed mathematical technique. Our LensPerfect software is straightforward and easy to use and is made publicly available via our website.


[15]  arXiv:0803.1274 [ps, pdf, other]
    Title: Inclination-Independent Galaxy Classification
    Authors: Jeremy Bailin, William E. Harris (McMaster University)
    Comments: Accepted for publication in ApJ. 7 pages in emulateapj
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round; Late-type galaxies, which are blue, have low concentrations, and are disk dominated; and Intermediate-type galaxies, which are red, have intermediate concentrations, and have disks. We have validated our method by comparing to visual classifications of high-quality imaging data from the Millennium Galaxy Catalogue. The inclination correction is crucial to unveiling the previously unrecognized Intermediate class. Intermediate-type galaxies, roughly corresponding to lenticulars and early spirals, lie on the red sequence. The red sequence is therefore composed of two distinct morphological types, suggesting that there are two distinct mechanisms for transiting to the red sequence. We propose that Intermediate-type galaxies are those that have lost their cold gas via strangulation, while Early-type galaxies are those that have experienced a major merger that either consumed their cold gas, or whose merger progenitors were already devoid of cold gas (the ``dry merger'' scenario).


[5]  arXiv:0803.1489 [ps, pdf, other]
    Title: The contribution of star formation and merging to stellar mass buildup in galaxies
    Authors: Niv Drory (1), Marcelo Alvarez (2) ((1) MPE, Garching, Germany, (2) KIPAC-Stanford, USA)
    Comments: Accepted for publication in ApJ
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    We present a formalism to infer the presence of merging by comparing the time derivative of the observed galaxy stellar mass function (MF) to the change of the MF expected from the star formation rate (SFR) in galaxies as a function of mass and time. We present the SFR in as a function of stellar mass and time spanning 9<logM<12 and 0<z<5. We show that at z>=3 the average SFR, is a power law of stellar mass (SFR~M^0.6). The average SFR in the most massive objects at this redshift is 100-500 Msun/yr. At z~3, the SFR starts to drop at the high mass end. As z decreases further, the SFR drops at progressively lower masses (downsizing), dropping most rapidly for high mass (logM>11) galaxies. The mass at which the SFR starts to deviate from the power-law form (break mass) progresses smoothly from logM~13 at z~5 to logM~10.9 at z~0.5. The break mass evolves with redshift as M(z)=2.7x10^10 (1+z)^2.1. We directly observe a relationship between SFH and mass. More massive galaxies have steeper and earlier onsets of SF, their SFR peaks earlier and higher, and the following decay has a shorter e-folding time. The SFR observed in high mass galaxies at z~4 is sufficient to explain their rapid increase in number density. Within large uncertainties, at most 0.8 major mergers per Gyr are consistent with the high-z data, yet enough to transform most high mass objects into ellipticals contemporaneously with their major star formation episode. In contrast, at z<1.5 and at logM>11, mergers contribute 0.1-0.2 Gyr^-1 to the relative increase in number density (~1 major merger per massive object at 1.5>z>0). At 10<logM<11, galaxies are being preferably destroyed in mergers at high z, while at later times the change in their numbers turns positive. This shows the top-down buildup of the red sequence suggested by other observations.


[20]  arXiv:0803.1615 [ps, pdf, other]
    Title: Submillimeter observations of the J2142-4423 Lya protocluster at z = 2.38
    Authors: A. Beelen, N. Bavouzet, A. Kovacs, G. Lagache, C. de Breuck, A. Weiss, K.M. Menten, J.W. Colbert, H. Dole, G. Siringo, E. Kreysa
    Comments: 14 pages, 9 figures, accepted for publication in A&A
    License: http://creativecommons.org/licenses/by-nc-sa/3.0/
    Subjects: Astrophysics (astro-ph)

    We present observations aimed at exploring both the nature of Lya emitting nebulae (Lya blobs) at z=2.38 and the way they trace large scale structure (LSS), by exploring their proximity to maximum starbursts through submillimeter emission. Our most important objectives are to make a census of associated submillimeter galaxies (SMGs), check their properties, and look for a possible overdensity in the protocluster J2142-4426 at z=2.38.
    We used the newly commissioned Large APEX Bolometer Camera (LABoCa) on the Atacama Pathfinder EXperiment (APEX) telescope, in its Science Verification phase, to carry out a deep 10'x10' map at 870 micron, and we performed multiple checks of the quality of data processing and source extraction.
    Our map, the first published deep image, confirms the capabilities of APEX/LABoCa as the most efficient current equipment for wide and deep submm mapping. Twenty-two sources were securely extracted with 870 micron flux densities in the range 3-21 mJy, rms noise 0.8-2.4 mJy, and far-IR luminosities probably in the range ~5-20 x 10(12) Lo. Only one of the four 50 kpc-extended Lya blobs has a secure 870 micron counterpart. The 870 micron source counts in the whole area are marginally higher than in the SHADES SCUBA survey, with a possible over-density around this blob. The majority of the 3.6-24 micron SEDs of the submillimeter sources indicate they are starburst dominated, with redshifts mostly >2. However, there is evidence of a high-z AGN in ~30% of the sources.


23]  arXiv:0803.1772 [ps, pdf, other]
    Title: An Infrared Survey of Brightest Cluster Galaxies. II: Why are Some Brightest Cluster Galaxies Forming Stars?
    Authors: Christopher P. O'Dea, Stefi A. Baum, George Privon, Jacob Noel-Storr, Alice C. Quillen, Nicholas Zufelt, Jaehong Park, Alastair Edge, Helen Russell, Andrew C. Fabian, Megan Donahue, Craig L. Sarazin, Brian McNamara, Joel N. Bregman, Eiichi Egami
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    Quillen et al.(2007) presented an imaging survey with the {\it Spitzer Space Telescope} of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray luminous clusters. They found that at least half of these sources have signs of excess infrared emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-infrared emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star forming galaxies. The gas depletion time scale is about 1 Gyr. The physical extent of the infrared excess is consistent with that of the optical emission line nebulae. This supports the hypothesis that the star formation occurs in molecular gas associated with the emission line nebulae and with evidence that the emission line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates (${\dot M}_X$) estimated from the X-ray emission and the star formation rate estimated from the infrared luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates suggesting that the re-heating of the ICM is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.


[2]  arXiv:0803.1833 [ps, pdf, other]
    Title: Dense Stellar Populations: Initial Conditions
    Authors: Pavel Kroupa (AIfA, Bonn)
    Comments: 85 pages. To appear in The Cambridge N-body Lectures, Sverre Aarseth, Christopher Tout, Rosemary Mardling (eds), Lecture Notes in Physics Series, Springer Verlag
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    This chapter is based on four lectures given at the Cambridge N-body school "Cambody". The material covered includes the IMF, the 6D structure of dense clusters, residual gas expulsion and the initial binary population. It is aimed at those needing to initialise stellar populations for a variety of purposes (N-body experiments, stellar population synthesis).


7]  arXiv:0803.1843 [ps, pdf, other]
    Title: WMAP5 and the Cluster Mass Function
    Authors: Kenneth Rines, Antonaldo Diaferio, Priyamvada Natarajan
    Comments: 4 pages, 2 color figures, submitted to ApJ Letters
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    The recently revised cosmological constraints from the Five-Year WMAP data ameliorate previous tension between cosmological constraints from the microwave background and from cluster abundances. We demonstrate that the revised estimates of cosmological parameters are in excellent agreement with the mass function of X-ray clusters in the Sloan Digital Sky Survey. Velocity segregation between galaxies and the underlying dark matter could cause virial mass estimates to be biased, causing the mass scale of the mass function to be offset from the true value. Modest velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.13$^{+0.06}_{-0.05}$) is sufficient to match the mass function to the Five-Year WMAP results. When the new WMAP results are combined with constraints from supernovae and baryon acoustic oscillations, there is no need for velocity segregation ($\sigma_{gxy}/\sigma_{DM}$=1.05$\pm$0.05). This result agrees with expectations for velocity segregation from state-of-the-art numerical simulations of clusters. Together with the improved agreement between the new WMAP results and recent cosmic shear measurements, this result demonstrates that the amplitude of large-scale structure in the nearby universe matches that predicted from the structure seen in the microwave background. The new constraint we place on velocity segregation in clusters indicates that virial mass estimates for clusters are reasonably accurate. This result suggests that future cluster surveys will be able to probe both cosmological parameters and fundamental cluster physics.


[19]  arXiv:0803.1924 [ps, pdf, other]
    Title: Lyman alpha emitting galaxies at 0.2 < z < 0.35 from GALEX spectroscopy
    Authors: Jean-Michel Deharveng, Todd Small, Tom A. Barlow, Celine Peroux, Bruno Milliard, Peter G. Friedman, D. Christopher Martin, Patrick Morrissey, David Schiminovich, Karl Forster, Mark Seibert, Ted K. Wyder, Luciana Bianchi, Jose Donas, Timothy M. Heckman, Young-Wook Lee, Barry F. Madore, Susan G. Neff, R. Michael Rich, Alex S. Szalay, Barry Y. Welsh, Sukyoung K. Yi
    Comments: 18 pages, 9 figures, accepted for publication in ApJ
    License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
    Subjects: Astrophysics (astro-ph)

    The GALEX (Galaxy Evolution Explorer) spectroscopic survey mode, with a resolution of about 8 A in the FUV (1350 - 1750 A) and about 20 A in the NUV (1950 - 2750 A) is used for a systematic search of Ly-a emitting galaxies at low redshift. This aims at filling a gap between high-redshift surveys and a small set of objects studied in detail in the nearby universe. A blind search of 7018 spectra extracted in 5 deep exposures (5.65 sq.deg) has resulted in 96 Ly-a emitting galaxy candidates in the FUV domain, after accounting for broad-line AGNs. The Ly-a EWs (equivalent width) are consistent with stellar population model predictions and show no trends as a function of UV color or UV luminosity, except a possible decrease in the most luminous that may be due to small-number statistics. Their distribution in EW is similar to that at z about 3 but their fraction among star-forming galaxies is smaller. Avoiding uncertain candidates, a sub-sample of 66 objects in the range 0.2 < z < 0.35 has been used to build a Ly-a LF (luminosity function). The incompleteness due to objects with significant Ly-a emission but a UV continuum too low for spectral extraction has been evaluated. A comparison with H-a LF in the same redshift domain is consistent with an average Ly-a/H-a of about 1 in about 15 % of the star-forming galaxies. A comparison with high-redshift Ly-a LFs implies an increase of the Ly-a luminosity density by a factor of about 16 from z about 0.3 to z about 3. By comparison with the factor 5 increase of the UV luminosity density in the same redshift range, this suggests an increase of the average Ly-a escape fraction with redshift.
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