arXiv subjects

K. Glazebrook

Publications and source records attributed to K. Glazebrook.

At least 127 records · Page 7Linked to original sources

arXiv2009

The Science Case for PILOT I: Summary and Overview

PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5 m optical/infrared telescope to be located at Dome C on the Antarctic plateau. Conditions at Dome C are known to be exceptional for astronomy. The seeing (above ~30 m height), coherence time, and isoplanatic angle are all twice s good as at typical mid-latitude sites, while the water-vapour column, and the atmosphere and telescope thermal emission are all an order of magnitude better. These conditions enable a unique scientific capability for PILOT, which is addressed in this series of papers. The current paper presents an overview of the optical and instrumentation suite for PILO and its expected performance, a summary of the key science goals and observational approach for the facility, a discussion of the synergies between the science goals for PILOT and other telescopes, and a discussion of the future of Antarctic astronomy. Paper II and Paper III present details of the science projects divided, respectively, between the distant Universe (i.e., studies of first light, and the assembly and evolution of structure) and the nearby Universe (i.e., studies of Local Group galaxies, the Milky Way, and the Solar System).

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arXiv2009

GRB 080503: Implications of a Naked Short Gamma-Ray Burst Dominated by Extended Emission

We report on observations of GRB 080503, a short gamma-ray burst with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough comparison to other short Swift events. In spite of the prompt-emission brightness, however, the optical counterpart is extraordinarily faint, never exceeding 25 mag in deep observations starting at ~1 hr after the BAT trigger. The optical brightness peaks at ~1 day and then falls sharply in a manner similar to the predictions of Li & Paczynski (1998) for supernova-like emission following compact-binary mergers. However, a shallow spectral index and similar evolution in X-rays inferred from Chandra observations are more consistent with an afterglow interpretation. The extreme faintness of this probable afterglow relative to the bright gamma-ray emission argues for a very low-density medium surrounding the burst (a "naked" GRB), consistent with the lack of a coincident host galaxy down to 28.5 mag in deep HST imaging. Our observations reinforce the notion that short GRBs generally occur outside regions of active star formation, but demonstrate that in some cases the luminosity of the extended prompt emission can greatly exceed that of the short spike, which may constrain theoretical interpretation of this class of events. Because most previous BAT short bursts without observed extended emission are too faint for this signature to have been detectable even if it were present at typical level, conclusions based solely on the observed presence or absence of extended emission in the existing Swift sample are premature. (abridged)

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arXiv2008

The Galaxy Population Hosting Gamma-Ray Bursts

We present the most extensive and complete study of the properties for the largest sample (46 objects) of gamma-ray burst (GRB) host galaxies. The redshift interval and the mean redshift of the sample are 0<z<6.3 and z=0.96 (look-back time: 7.2 Gyr), respectively; 89% of the hosts are at z <~ 1.6. Optical-near-infrared (NIR) photometry and spectroscopy are used to derive stellar masses, star formation rates (SFRs), dust extinctions and metallicities. The average stellar mass is 10^9.3 M_sun, with a 1 sigma dispersion of 0.8 dex. The average metallicity for a subsample of 17 hosts is about 1/6 solar and the dust extinction in the visual band (for a subsample of 10 hosts) is A_V=0.5. We obtain new relations to derive SFR from [OII] or UV fluxes, when Balmer emission lines are not available. SFRs, corrected for dust extinction, aperture-slit loss and stellar Balmer absorption are in the range 0.01-36 M_sun yr^-1. The median SFR per unit stellar mass (specific SFR) is 0.8 Gyr^-1. Equivalently the inverse quantity, the median formation timescale is 1.3 Gyr. Most GRBs are associated with the death of young massive stars, more common in star-forming galaxies. Therefore GRBs are an effective tool to detect star-forming galaxies in the universe. Star-forming galaxies at z<1.6 are a faint and low-mass population, hard to detect by conventional optical-NIR surveys, unless a GRB event occurs. There is no compelling evidence that GRB hosts are peculiar galaxies. More data on the subclass of short GRB are necessary to establish the nature of their hosts.

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arXiv2008

Observations of the Naked-Eye GRB 080319B: Implications of Nature's Brightest Explosion

The first gamma-ray burst (GRB) confirmed to be bright enough to be seen with the naked eye, GRB 080319B at redshift z = 0.937, allowed for exquisite follow-up observations across the electromagnetic spectrum. We present our detailed optical and infrared observations of the afterglow, consisting of over 5000 images starting 51 s after the GRB trigger, in concert with our own analysis of the Swift data. The event is extreme not only in observed properties but intrinsically: it was the most luminous event ever recorded at optical and infrared wavelengths and had an exceedingly high isotropic-equivalent energy release in gamma-rays. At early times, the afterglow evolution is broadly consistent with being reverse-shock dominated, but then is subsumed by a forward shock at around 1000 s. The overall spectral energy distribution, spanning from ultraviolet through near-infrared wavelengths, shows no evidence for a significant amount of dust extinction in the host frame. The afterglow evolution, however, is highly chromatic: starting at about 1000 s the index shifts blueward before shifting back to the red at late times. In our deepest late-time observations, we find tentative evidence for an optical jet break and a luminous supernova. Finally, we examine the detectability of such events with current and future facilities and find that such an event could be detected in gamma-rays by BAT out to z = 10.7 (8 sigma), while the nominal EXIST sensitivity would allow detection to z ~ 32. At K band, this source would have been easily detected with meter-class telescopes to z ~ 17.

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arXiv2008

On the galaxy stellar mass function, the mass-metallicity relation, and the implied baryonic mass function

A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4--8 per cent of the baryon density (assuming Omega_b = 0.045). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the z < 0.05 GSMF using the New York University - Value-Added Galaxy Catalog sample of 49968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has alpha_2 =~ -1.6. At masses below ~ 10^8.5 Msun, the GSMF may be significantly incomplete because of missing low surface-brightness galaxies. One interpretation of the stellar mass-metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principal, we determine a simple relationship between baryonic mass and stellar mass and present an `implied baryonic mass function'. This function has a faint-end slope, alpha_2 =~ -1.9. Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function --> galaxy baryonic mass function --> GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses ~ 10^11 Msun corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.

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arXiv2007

A Compact Cluster of Massive Red Galaxies at a Redshift of 1.51

We describe a compact cluster of massive red galaxies at z=1.51 discovered in one of the Gemini Deep Deep Survey (GDDS) fields. Deep imaging with the Near Infrared Camera and Multi Object Spectrometer (NICMOS) on the Hubble Space Telescope reveals a high density of galaxies with red optical to near-IR colors surrounding a galaxy with a spectroscopic redshift of 1.51. Mid-IR imaging with Infrared Array Camera (IRAC) on the Spitzer Space telescope shows that these galaxies have spectral energy distributions that peak between 3.6 and 4.5 microns. Fits to 12-band photometry reveal 12 or more galaxies with spectral shapes consistent with z = 1.51. Most are within ~170 co-moving kpc of the GDDS galaxy. Deep F814W images with the Advanced Camera for Surveys (ACS) on HST reveal that these galaxies are a mix of early-type galaxies, disk galaxies and close pairs. The total stellar mass enclosed within a sphere of 170 kpc in radius is > 8E+11 solar masses. The colors of the most massive galaxies are close to those expected from passive evolution of simple stellar populations (SSP) formed at much higher redshifts. We suggest that several of these galaxies will merge to form a single, very massive galaxy by the present day. This system may represent an example of a short-lived dense group or cluster core typical of the progenitors of massive clusters in the present day and suggests the red sequence was in place in over-dense regions at early times.

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arXiv2006

Galaxy bimodality versus stellar mass and environment

We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation of the galaxy colour bimodality with stellar mass and projected neighbour density Sigma, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour-mass and colour-concentration index not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and log mass (12 x 13 bins). The red fraction f_r generally increases continuously in both Sigma and mass such that there is a unified relation: f_r = F(Sigma,mass). Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N-body simulation: the Bower et al. (2006) and Croton et al. (2006) models that incorporate AGN feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies.

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arXiv2006

GRB Host Studies (GHostS)

The GRB Host Studies (GHostS) is a public archive collecting observed quantities of GRB host galaxies. At this time (January 2006) it contains information on 32 GRB hosts, i.e. about half of the total number of GRBs with known redshift. Here we present some preliminary statistical analysis of the sample, e.g. the total stellar mass, metallicity and star formation rate for the hosts. We found that these are generally low-mass objects, with 79% having M_*<10^10 M_sun. The total stellar mass and the metallicity for a subsample of 7 hosts at 0.4<z<1 are consistent with the mass-metallicity relation recently found for normal star-forming galaxies in the same redshift interval. At least 56% of the total sample are bursty galaxies: their growth time-scale (the time required to form the observed stellar mass assuming that the observed SFR is constant over the entire life of the galaxy) is shorter than 400 Myr.

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arXiv2005

The Gemini Deep Deep Survey. VII. The Redshift Evolution of the Mass-Metallicity Relation

We have investigated the mass-metallicity (M-Z) relation using galaxies at 0.4<z<1.0 from the Gemini Deep Deep Survey and Canada-France Redshift Survey. Deep K and z' band photometry allowed us to measure stellar masses for 69 galaxies. From a subsample of 56 galaxies, for which metallicity of the interstellar medium is also measured, we identified a strong correlation between mass and metallicity, for the first time in the distant Universe. This was possible because of the larger base line spanned by the sample in terms of metallicity (a factor of 7) and mass (a factor of 400) than in previous works. This correlation is much stronger and tighter than the luminosity-metallicity, confirming that stellar mass is a more meaningful physical parameter than luminosity. We find clear evidence for temporal evolution in the M-Z relation in the sense that at a given mass, a galaxy at z=0.7 tends to have lower metallicity than a local galaxy of similar mass. We use the z=0.1 SDSS M-Z relation, and a small sample of z=2.3 Lyman break galaxies with known mass and metallicity, to propose an empirical redshift-dependent M-Z relation, according to which the stellar mass and metallicity in small galaxies evolve for a longer time than in massive galaxies. This relation predicts that the generally metal poor damped Lyman-alpha galaxies have stellar masses of the order of 10^8.8 M_sun (with a dispersion of 0.7 dex) all the way from z=0.2 to z=4. The observed redshift evolution of the M-Z relation can be reproduced remarkably well by a simple closed-box model where the key assumption is an e-folding time for star formation which is higher or, in other words, a period of star formation that lasts longer in less massive galaxies than in more massive galaxies. Such a picture supports the downsizing scenario for galaxy formation.

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arXiv2005

The 2dF Galaxy Redshift Survey: Power-spectrum analysis of the final dataset and cosmological implications

We present a power spectrum analysis of the final 2dF Galaxy Redshift Survey, employing a direct Fourier method. The sample used comprises 221,414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys which are used to demonstrate that the input cosmological model can be correctly recovered. We are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the `baryon oscillations' that are predicted in CDM models. Fitting to a CDM model, assuming a primordial $n_{s}=1$ spectrum, $h=0.72$ and negligible neutrino mass, the preferred parameters are $Ω_{M} h = 0.168 \pm 0.016$ and a baryon fraction $Ω_{b} /Ω_{M} = 0.185\pm0.046$ (1$σ$ errors). The value of $Ω_{M} h$ is $1σ$ lower than the $0.20 \pm 0.03$ in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly-sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard $Ω_{M} =0.3$: in combination with CMB data from WMAP, we infer $Ω_{M} =0.231\pm 0.021$. (Abridged.)

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arXiv2005

Science Programs for a 2 m-class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope

The cold, dry and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-mm wavelengths to be found on the Earth. PILOT is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of science projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near-diffraction limited performance with simple tip-tilt wavefront correction. PILOT would also be capable of near-diffraction limited performance in the optical wavebands, as well be able to open new wavebands for regular ground based observation; in the mid-IR from 17 to 40 microns and in the sub-mm at 200 microns.

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arXiv2005

The 2dF Galaxy Redshift Survey: luminosity functions by density environment and galaxy type

We use the 2dF Galaxy Redshift Survey to measure the dependence of the bJ-band galaxy luminosity function on large-scale environment, defined by density contrast in spheres of radius 8h-1Mpc, and on spectral type, determined from principal component analysis. We find that the galaxy populations at both extremes of density differ significantly from that at the mean density. The population in voids is dominated by late types and shows, relative to the mean, a deficit of galaxies that becomes increasingly pronounced at magnitudes brighter than M_bJ-5log10h <-18.5. In contrast, cluster regions have a relative excess of very bright early-type galaxies with M_bJ-5log10h < -21. Differences in the mid to faint-end population between environments are significant: at M_bJ-5log10h=-18 early and late-type cluster galaxies show comparable abundances, whereas in voids the late types dominate by almost an order of magnitude. We find that the luminosity functions measured in all density environments, from voids to clusters, can be approximated by Schechter functions with parameters that vary smoothly with local density, but in a fashion which differs strikingly for early and late-type galaxies. These observed variations, combined with our finding that the faint-end slope of the overall luminosity function depends at most weakly on density environment, may prove to be a significant challenge for models of galaxy formation.

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arXiv2005

Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies

We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16<z<0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute distance to z=0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density Omega_mh^2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273 +- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties.

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arXiv2005

The SDSS u-band Galaxy Survey: Luminosity functions and evolution

We construct and analyze a u-band selected galaxy sample from the SDSS Southern Survey, which covers 275 sq. deg. The sample includes 43223 galaxies with spectroscopic redshifts in the range 0.005<z<0.3 and with 14.5<u<20.5. The S/N in the u-band Petrosian aperture is improved by coadding multiple epochs of imaging data and by including sky-subtraction corrections. Luminosity functions for the near-UV ^{0.1}u band (322+-26 nm) are determined in redshift slices of width 0.02, which show a highly significant evolution in M^{star} of -0.8+-0.1 mag between z=0 and 0.3; with M^{star} = -18.84+-0.05 (AB mag), log phi^{star} = -2.06+-0.03 (Mpc^{-3}) and log rho_L = 19.11+-0.02 (W Hz^{-1} Mpc^{-3}) at z=0.1. The faint-end slope determined for z<0.06 is given by alpha=-1.05+-0.08. This is in agreement with recent determinations from GALEX at shorter wavelengths. Comparing our z<0.3 luminosity density measurements with 0.2<z<1.2 from COMBO-17, we find that the 280-nm density evolves as rho_L proportional to (1+z)^{beta} with beta=2.1+-0.2; and find no evidence for any change in slope over this redshift range. By comparing with other measurements of cosmic star formation history, we estimate that the effective dust attenuation at 280 nm has increased by 0.8+-0.3 mag between z=0 and 1.

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arXiv2004

Color bimodality: Implications for galaxy evolution

We use a sample of 69726 galaxies from the SDSS to study the variation of the bimodal color-magnitude (CM) distribution with environment. Dividing the galaxy population by environment (Sigma_5) and luminosity (-23<M_r<-17), the u-r color functions are modeled using double-Gaussian functions. This enables a deconvolution of the CM distributions into two populations: red and blue sequences. The changes with increasing environmental density can be separated into two effects: a large increase in the fraction of galaxies in the red distribution, and a small color shift in the CM relations of each distribution. The average color shifts are 0.05+-0.01 and 0.11+-0.02 for the red and blue distributions, respectively, over a factor of 100 in projected neighbor density. The red fraction varies between about 0% and 70% for low-luminosity galaxies and between about 50% and 90% for high-luminosity galaxies. This difference is also shown by the variation of the luminosity functions with environment. We demonstrate that the effects of environment and luminosity can be unified. A combined quantity, Sigma_mod = Sigma_5/Mpc^{-2} + L_r/L_{-20.2}, predicts the fraction of red galaxies, which may be related to the probability of transformation events. Our results are consistent with major interactions (mergers and/or harassment) causing galaxies to transform from the blue to the red distribution. We discuss this and other implications for galaxy evolution from earlier results and model the effect of slow transformations on the color functions.

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arXiv2004

The mass-metallicity relation at z~0.7

The ISM metallicity and the stellar mass are examined in a sample of 66 galaxies at 0.4<z<1, selected from the Gemini Deep Deep Survey (GDDS) and the Canada-France Redshift Survey (CFRS). We observe a mass-metallicity relation similar to that seen in z~0.1 SDSS galaxies, but displaced towards higher masses and/or lower metallicities. Using this sample, and a small sample of z~2.3 LBGs, a redshift dependent mass-metallicity relation is proposed which describes the observed results.

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arXiv2004

Cosmic Star Formation History and its Dependence on Galaxy Stellar Mass

We examine the cosmic star formation rate (SFR) and its dependence on galaxy stellar mass over the redshift range 0.8 < z < 2 using data from the Gemini Deep Deep Survey (GDDS). The SFR in the most massive galaxies (M > 10^{10.8} M_sun) was six times higher at z = 2 than it is today. It drops steeply from z = 2, reaching the present day value at z ~ 1. In contrast, the SFR density of intermediate mass galaxies (10^{10.2} < M < 10^{10.8} M_sun) declines more slowly and may peak or plateau at z ~ 1.5. We use the characteristic growth time t_SFR = rho_M / rho_SFR to provide evidence of an associated transition in massive galaxies from a burst to a quiescent star formation mode at z ~ 2. Intermediate mass systems transit from burst to quiescent mode at z ~ 1, while the lowest mass objects undergo bursts throughout our redshift range. Our results show unambiguously that the formation era for galaxies was extended and proceeded from high to low mass systems. The most massive galaxies formed most of their stars in the first ~3 Gyr of cosmic history. Intermediate mass objects continued to form their dominant stellar mass for an additional ~2 Gyr, while the lowest mass systems have been forming over the whole cosmic epoch spanned by the GDDS. This view of galaxy formation clearly supports `downsizing' in the SFR where the most massive galaxies form first and galaxy formation proceeds from larger to smaller mass scales.

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arXiv2004

The 2dF Galaxy Redshift Survey: stochastic relative biasing between galaxy populations

It is well known that the clustering of galaxies depends on galaxy type.Such relative bias complicates the inference of cosmological parameters from galaxy redshift surveys, and is a challenge to theories of galaxy formation and evolution. In this paper we perform a joint counts-in-cells analysis on galaxies in the 2dF Galaxy Redshift Survey, classified by both colour and spectral type, eta, as early or late type galaxies. We fit three different models of relative bias to the joint probability distribution of the cell counts, assuming Poisson sampling of the galaxy density field. We investigate the nonlinearity and stochasticity of the relative bias, with cubical cells of side 10Mpc \leq L \leq 45Mpc (h=0.7). Exact linear bias is ruled out with high significance on all scales. Power law bias gives a better fit, but likelihood ratios prefer a bivariate lognormal distribution, with a non-zero `stochasticity' - i.e. scatter that may result from physical effects on galaxy formation other than those from the local density field. Using this model, we measure a correlation coefficient in log-density space (r_LN) of 0.958 for cells of length L=10Mpc, increasing to 0.970 by L=45Mpc. This corresponds to a stochasticity sigma_b/bhat of 0.44\pm0.02 and 0.27\pm0.05 respectively. For smaller cells, the Poisson sampled lognormal distribution presents an increasingly poor fit to the data, especially with regard to the fraction of completely empty cells. We compare these trends with the predictions of semianalytic galaxy formation models: these match the data well in terms of overall level of stochasticity, variation with scale, and fraction of empty cells.

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