arXiv subjects

Karl Glazebrook

Publications and source records attributed to Karl Glazebrook.

At least 289 records · Page 16Linked to original sources

arXiv2007

Evidence for a non-universal stellar initial mass function from the integrated properties of SDSS galaxies

This paper revisits the classical Kennicutt method for inferring the stellar initial mass function (IMF) from the integrated light properties of galaxies. The large size, uniform high quality data set from the Sloan Digital Sky Survey DR4 is combined with more in depth modeling and quantitative statistical analysis to search for systematic IMF variations as a function of galaxy luminosity. Galaxy H alpha equivalent widths are compared to a broadband color index to constrain the IMF. This parameter space is useful for breaking degeneracies which are traditionally problematic. Age and dust corrections are largely orthogonal to IMF variations. In addition the effects of metallicity and smooth star formation history e-folding times are small compared to IMF variations. We find that for the sample as a whole the best fitting IMF slope above 0.5 M_sun is Gamma = 1.4535 with a negligible random error of +/- 0.0004 and a systematic error of +/- 0.1. Galaxies brighter than around M_r,0.1 = -20 (including galaxies like the Milky Way which has M_r,0.1 ~ -21) are well fit by a universal Gamma ~ 1.4 IMF, similar to Salpeter, and smooth, exponential star formation histories (SFH). Fainter galaxies prefer steeper IMFs and the quality of the fits reveal that for these galaxies a universal IMF with smooth SFHs is actually a poor assumption. Several sources of sample bias are ruled out as the cause of these luminosity dependent IMF variations. Analysis of bursting SFH models shows that an implausible coordination of burst times is required to fit a universal IMF to the M_r,0.1 = -17 galaxies. This leads to the conclusions that the IMF in low luminosity galaxies has fewer massive stars, either by steeper slope or lower upper mass cutoff, and is not universal.

astro-ph↗

arXiv2007

The Gemini Deep Deep Survey: VIII. When Did Early-type Galaxies Form?

We have used the Hubble Space Telescope's Advanced Camera for Surveys (Ford et al. 2003) to measure the cumulative mass density in morphologically-selected early-type galaxies over the redshift range 0.8 < z < 1.7. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy obtained as part of the Gemini Deep Deep Survey. These images have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-Petrosian' image thresholding technique. We find that at z \~ 1 about 80% of the stars living in the most massive galaxies reside in early-type systems. This fraction is similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 0.8 < z < 1.7, suggesting that over this redshift range the strong morphology-mass relationship seen in the nearby Universe is beginning to fall into place. By comparing our images to published spectroscopic classifications, we show that little ambiguity exists in connecting spectral classes to morphological classes for spectroscopically quiescent systems. However, the mass density function of early-type galaxies is evolving more rapidly than that of spectroscopically quiescent systems, which we take as further evidence that we are witnessing the formation of massive early-type galaxies over the 0.8 < z < 1.7 redshift range.

astro-ph↗

arXiv2007

The WiggleZ project: AAOmega and Dark Energy

We describe the `WiggleZ' spectroscopic survey of 280,000 star-forming galaxies selected from a combination of GALEX ultra-violet and SDSS + RCS2 optical imaging. The fundamental goal is a detection of the baryonic acoustic oscillations in galaxy clustering at high-redshift (0.5 < z < 1) and a precise measurement of the equation of state of dark energy from this purely geometric and robust method. The survey has already started on the 3.9m Anglo-Australian Telescope using the AAOmega spectrograph, and planned to complete during 2009. The WWW page for the survey can be found at http://astronomy.swin.edu.au/wigglez

astro-ph↗

arXiv2007

Optimising Baryon Acoustic Oscillation Surveys - I: Testing the concordance LCDM cosmology

We optimize the design of future spectroscopic redshift surveys for constraining the dark energy via precision measurements of the baryon acoustic oscillations (BAO), with particular emphasis on the design of the Wide-Field Multi-Object Spectrograph (WFMOS). We develop a model that predicts the number density of possible target galaxies as a function of exposure time and redshift. We use this number counts model together with fitting formulae for the accuracy of the BAO measurements to determine the effectiveness of different surveys and instrument designs. We search through the available survey parameter space to find the optimal survey with respect to the dark energy equation-of-state parameters according to the Dark Energy Task Force Figure-of-Merit, including predictions of future measurements from the Planck satellite. We optimize the survey to test the LambdaCDM model, assuming that galaxies are pre-selected using photometric redshifts to have a constant number density with redshift, and using a non-linear cut-off for the matter power spectrum that evolves with redshift. We find that line-emission galaxies are strongly preferred as targets over continuum emission galaxies. The optimal survey covers a redshift range 0.8 < z < 1.4, over the widest possible area (6000 sq. degs from 1500 hours observing time). The most efficient number of fibres for the spectrograph is 2,000, and the survey performance continues to improve with the addition of extra fibres until a plateau is reached at 10,000 fibres. The optimal point in the survey parameter space is not highly peaked and is not significantly affected by including constraints from upcoming supernovae surveys and other BAO experiments.

astro-ph↗

arXiv2007

The GLARE Survey II. Faint z=6 Ly-alpha Line Emitters in the HUDF

The galaxy population at z~6 has been the subject of intense study in recent years, culminating in the Hubble Ultra Deep Field (HUDF) -- the deepest imaging survey yet. A large number of high redshift galaxy candidates have been identified within the HUDF, but until now analysis of their properties has been hampered by the difficulty of obtaining spectroscopic redshifts for these faint galaxies. Our ''Gemini Lyman-Alpha at Reionisation Era'' (GLARE) project has been designed to undertake spectroscopic follow up of faint (z'<28.5) i'-drop galaxies at z~6 in the HUDF. In a previous paper we presented preliminary results from the first 7.5 hours of data from GLARE. In this paper we detail the complete survey. We have now obtained 36 hours of spectroscopy on a single GMOS slitmask from Gemini-South, with a spectral resolution of lambda/Delta(lambda) ~ 1000. We identify five strong Lyman-alpha emitters at z>5.5, and a further nine possible line emitters with detections at lower significance. We also place tight constraints on the equivalent width of Lyman-alpha emission for a further ten i'-drop galaxies and examine the equivalent width distribution of this faint spectroscopic sample of z~6 galaxies. We find that the fraction of galaxies with little or no emission is similar to that at z~3, but that the z~6 population has a tail of sources with high rest frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass function.

astro-ph↗

arXiv2006

When do early-type galaxies form?

We have used the Hubble Space Telescope's Advanced Camera for Surveys to measure the mass density function of morphologically selected early-type galaxies in the Gemini Deep Deep Survey fields, over the redshift range 0.9 < z < 1.6. Our imaging data set covers four well-separated sight-lines, and is roughly intermediate (in terms of both depth and area) between the GOODS/GEMS imaging data, and the images obtained in the Hubble Deep Field campaigns. Our images contain 144 galaxies with ultra-deep spectroscopy, and they have been analyzed using a new purpose-written morphological analysis code which improves the reliability of morphological classifications by adopting a 'quasi-petrosian' image thresholding technique. We find that at z = 1 approximately 70% of the stars in massive galaxies reside in early-type systems. This fraction is remarkably similar to that seen in the local Universe. However, we detect very rapid evolution in this fraction over the range 1.0 < z < 1.6, suggesting that in this epoch the strong color-morphology relationship seen in the nearby Universe is beginning to fall into place.

astro-ph↗

arXiv2006

Gemini Deep Deep Survey VI: Massive Hdelta-strong galaxies at z=1

We show that there has been a dramatic decline in the abundance of massive galaxies with strong Hdelta stellar absorption lines from z=1.2 to the present. These ``Hdelta-strong'', or HDS, galaxies have undergone a recent and rapid break in their star-formation activity. Combining data from the Gemini Deep Deep and the Sloan Digital Sky Surveys to make mass-matched samples (M*>=10^10.2 Msun), with 25 and 50,255 galaxies, respectively), we find that the fraction of galaxies in an HDS phase has decreased from about 50% at z=1.2 to a few percent today. This decrease in fraction is due to an actual decrease in the number density of massive HDS systems by a factor of 2-4, coupled with an increase in the number density of massive galaxies by about 30 percent. We show that this result depends only weakly on the threshold chosen for the Hdelta equivalent width to define HDS systems (if greater than 4 A) and corresponds to a (1+z)^{2.5\pm 0.7} evolution. Spectral synthesis studies of the high-redshift population using the PEGASE code, treating Hdelta_A, EW[OII], Dn4000, and rest-frame colors, favor models in which the Balmer absorption features in massive Hdelta-strong systems are the echoes of intense episodes of star-formation that faded about 1 Gyr prior to the epoch of observation. The z=1.4-2 epoch appears to correspond to a time at which massive galaxies are in transition from a mode of sustained star formation to a relatively quiescent mode with weak and rare star-formation episodes. We argue that the most likely local descendants of the distant massive HDS galaxies are passively evolving massive galaxies in the field and small groups.

astro-ph↗

arXiv2006

AAT Imaging and Microslit Spectroscopy in the Southern Hubble Deep Field

We present a deep photometric (B- and R-band) catalog and an associated spectroscopic redshift survey conducted in the vicinity of the Hubble Deep Field South. The spectroscopy yields 53 extragalactic redshifts in the range 0<z<1.4 substantially increasing the body of spectroscopic work in this field to over 200 objects. The targets are selected from deep AAT prime focus images complete to R<24 and spectroscopy is 50% complete at R=23. There is now strong evidence for a rich cluster at z\simeq 0.58 flanking the WFPC2 field which is consistent with a known absorber of the bright QSO in this field. We find that photometric redshifts of z<1 galaxies in this field based on HST data are accurate to σ_z/(1+z)=0.03 (albeit with small number statistics). The observations were carried out as a community service for Hubble Deep Field science, to demonstrate the first use of the `nod & shuffle' technique with a classical multi-object spectrograph and to test the use of `microslits' for ultra-high multiplex observations along with a new VPH grism and deep-depletion CCD. The reduction of this new type of data is also described.

astro-ph↗

arXiv2005

Monster Redshift Surveys through Dispersive Slitless Imaging: The Baryon Oscillation Probe

Wide-field imaging from space should not forget the dispersive dimension. We consider the capability of space-based imaging with a slitless grism: because of the low near-infrared background in space and the high sky-density of high redshift emission line galaxies this makes for a very powerful redshift machine with no moving parts. A small 1m space telescope with a 0.5 degree field of view could measure redshifts for 10^7 galaxies at 0.5<z<2 per year, this is a MIDEX class concept which we have dubbed `The Baryon Oscillation Probe' as the primary science case would be constraining dark energy evolution via measurement of the baryonic oscillations in the galaxy power spectrum. These ideas are generalizable to other missions such as SNAP and DESTINY.

astro-ph↗

arXiv2005

Dark Energy and Cosmic Sound: w(z) Surveys with the Gemini/Subaru Wide-Field Multi-Object Spectrograph

This white paper gives an overview of the proposed Gemini/Subaru Wide-Field Multi-Object Spectrograph (WFMOS) and the proposed redshift surveys of 2.6 million galaxies with 0.5<z<3.3 over 2000 deg^2 of sky. These surveys will probe the baryonic acoustic oscillations in the galaxy power spectrum with unprecedented precision and over a range of redshifts and deliver dark energy w(z) constraints an order of magnitude better than current limits. We discuss the requirements on precursor observations and on calibrations, the systematics in the method and the quantitative precision obtainaible in distance-redshift and expansion-rate-redshift measurements which feed in to the w(z) precision. We also outline the technological and scientific strengths and risks which might be associated with the project and the relationship of WFMOS to other baryon oscillation experiments.

astro-ph↗

arXiv2005

Universal fitting formulae for baryon oscillation surveys

The next generation of galaxy surveys will attempt to measure the baryon oscillations in the clustering power spectrum with high accuracy. These oscillations encode a preferred scale which may be used as a standard ruler to constrain cosmological parameters and dark energy models. In this paper we present simple analytical fitting formulae for the accuracy with which the preferred scale may be determined in the tangential and radial directions by future spectroscopic and photometric galaxy redshift surveys. We express these accuracies as a function of survey parameters such as the central redshift, volume, galaxy number density and (where applicable) photometric redshift error. These fitting formulae should greatly increase the efficiency of optimizing future surveys, which requires analysis of a potentially vast number of survey configurations and cosmological models. The formulae are calibrated using a grid of Monte Carlo simulations, which are analyzed by dividing out the overall shape of the power spectrum before fitting a simple decaying sinusoid to the oscillations. The fitting formulae reproduce the simulation results with a fractional scatter of 7% (10%) in the tangential (radial) directions over a wide range of input parameters. We also indicate how sparse-sampling strategies may enhance the effective survey area if the sampling scale is much smaller than the projected baryon oscillation scale.

astro-ph↗

arXiv2005

The 2dF Galaxy Redshift Survey: correlation with the ROSAT-ESO Flux Limited X-ray (REFLEX) galaxy cluster survey

The ROSAT-ESO Flux Limited X-ray (REFLEX) galaxy cluster survey and the 2dF Galaxy Redshift Survey (2dFGRS) respectively comprise the largest, homogeneous X-ray selected cluster catalogue and completed galaxy redshift survey. In this work we combine these two outstanding datasets in order to study the effect of the large-scale cluster environment, as traced by X-ray luminosity, on the properties of the cluster member galaxies. We measure the LX-sigma relation from the correlated dataset and find it to be consistent with recent results found in the literature. Using a sample of 19 clusters with LX>=0.36*10^44 erg s^-1 in the (0.1-2.4 keV) band, and 49 clusters with lower X-ray luminosity, we find that the fraction of early spectral type (eta<=-1.4), passively-evolving galaxies is significantly higher in the high-LX sample within R200. We extend the investigation to include composite bJ cluster luminosity functions, and find that the characteristic magnitude of the Schechter-function fit to the early-type luminosity function is fainter for the high-LX sample compared to the low-LX sample (Delta M*=0.58+/-0.14). This seems to be driven by a deficit of such galaxies with M_bJ ~ -21. In contrast, we find no significant differences between the luminosity functions of star-forming, late-type galaxies. We believe these results are consistent with a scenario in which the high-LX clusters are more dynamically evolved systems than the low-LX clusters.

astro-ph↗

arXiv2005

Measuring the cosmic evolution of dark energy with baryonic oscillations in the galaxy power spectrum

We use Monte Carlo techniques to simulate the ability of future large high-redshift galaxy surveys to measure the temporal evolution of the dark energy equation-of-state w(z), using the baryonic acoustic oscillations in the clustering power spectrum as a 'standard ruler'. Our analysis only utilizes the oscillatory component of the power spectrum and not its overall shape, which is potentially susceptible to broadband tilts induced by a host of model-dependent systematic effects. Our results are therefore robust and conservative. We show that baryon oscillation constraints can be thought of, to high accuracy, as a direct probe of the distance - redshift and expansion rate - redshift relations where distances are measured in units of the sound horizon. Distance precisions of 1% are obtainable for a fiducial redshift survey covering 10,000 deg^2 and redshift range 0.5 < z < 3.5. If the dark energy is further characterized by w(z) = w_0 + w_1 z (with a cut-off in the evolving term at z = 2), we can then measure the parameters w_0 and w_1 with a precision exceeding current knowledge by a factor of ten: 1 sigma accuracies Delta w_0 ~ 0.03 and Delta w_1 ~ 0.06 are obtainable (assuming a flat universe and that the other cosmological parameters Omega_m} and h could be measured independently to a precision of +/- 0.01 by combinations of future CMB and other experiments). We quantify how this performance degrades with redshift/areal coverage and knowledge of Omega_m and h, and discuss realistic observational prospects for such large-scale spectroscopic redshift surveys, with a variety of diverse techniques. We also quantify how large photometric redshift imaging surveys could be utilized to produce measurements of (w_0,w_1) with the baryonic oscillation method which may be competitive in the short term.

astro-ph↗

arXiv2005

The Color Selection of Quasars from Redshifts 5 to 10: Cloning and Discovery

We present simulations of quasar colors, magnitudes, and numbers at redshifts 5 6 epoch taking advantage of the new UKIDSS near-infrared filter set, and we examine the redshift intervals of maximum productivity, discussing color selection and survey depth issues. On the basis of the SDSS sample, we find that the surface density of z>4.7 quasars increases by a factor of 3X by extending 0.7 i-magnitudes deeper than the SDSS spectroscopic survey limit of i=20.2 -- correspondingly we predict a total of ~400 faint quasars in the SDSS main area that have redshift z>4.7 and magnitudes $<20.9.

astro-ph↗

arXiv2004

The 2dF Galaxy Redshift Survey: the local E+A galaxy population

We select a sample of low-redshift (z ~ 0.1) E+A galaxies from the 2dF Galaxy Redshift Survey (2dFGRS). The spectra of these objects are defined by strong hydrogen Balmer absorption lines (H-delta, H-gamma, H-beta) combined with a lack of [OII] 3727A emission, together implying a recently-truncated burst of star formation. The E+A spectrum is thus a signpost to galaxies in the process of evolution. We quantify the local environments, clustering properties and luminosity function of the E+A galaxies. We find that the environments are consistent with the ensemble of 2dFGRS galaxies: low-redshift E+A systems are located predominantly in the field, existing as isolated objects or in poor groups. However, the luminosity distribution of galaxies selected using three Balmer absorption lines H-delta-gamma-beta appears more typical of ellipticals. Indeed, morphologically these galaxies are preferentially spheroidal (E/S0) systems. In a small but significant number we find evidence for recent major mergers, such as tidal tails. We infer that major mergers are one important formation mechanism for E+A galaxies, as suggested by previous studies. At low redshift the merger probability is high in the field and low in clusters, thus these recently-formed spheroidal systems do not follow the usual morphology-density relation for ellipticals. Regarding the selection of E+A galaxies: we find that basing the Balmer-line criterion solely on H-delta absorption leads to a significant sub-population of disk systems with detectable H-alpha emission. In these objects the [OII] emission is presumably either obscured by dust or present with a low signal-to-noise ratio, whilst the (H-gamma, H-beta) absorption features are subject to emission-filling.

astro-ph↗

arXiv2004

Cosmic Star Formation History to z=1 from a Narrow Emission Line Selected Tunable Filter Survey

We report the results of a deep 3D imaging survey of the Hubble Deep Field North using the Taurus Tunable Filter and the William Herschel Telescope. This survey was designed to search for new line emitting populations of objects missed by other techniques and to measure the cosmic star-formation rate density from a line-selected survey. We observed in three contiguous sequences of narrow band slices in the 7100, 8100 and 9100A regions of the spectrum, corresponding to a cosmological volume of up to 1000 Mpc^3 at z=1, down to a flux limit of 2x 10^-17 ergs cm^-2 s^-1. The survey is deep enough to be highly complete for low line luminosity galaxies. Cross-matching with existing spectroscopy in the field results in a small line-luminosity limited sample, with very highly redshift identification completeness containing seven [OII], Hbeta and Halpha emitters over the redshift range 0.3 - 0.9. Treating this as a direct star-formation rate selected sample we estimate the star-formation history of the Universe to z=1. We find no evidence for any new population of line emitting objects contributing significantly to the cosmological star-formation rate density. Rather from our complete narrow-band sample we find the star-formation history is consistent with earlier estimates from broad-band imaging surveys and other less deep line-selected surveys.

astro-ph↗

arXiv2004

Evolved Galaxies at z > 1.5 from the Gemini Deep Deep Survey: The Formation Epoch of Massive Stellar Systems

We present spectroscopic evidence from the Gemini Deep Deep Survey (GDDS) for a significant population of color-selected red galaxies at 1.3 < z < 2.2 whose integrated light is dominated by evolved stars. Unlike radio-selected objects, the z > 1.5 old galaxies have a sky density > 0.1 per sq. arcmin. Conservative age estimates for 20 galaxies with z > 1.3; = 1.49, give a median age of 1.2 Gyr and = 2.4. One quarter of the galaxies have inferred z_f > 4. Models restricted to abundances less than or equal to solar give median ages and z_f of 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute approximately 50% of the stellar mass density at 1 < z < 2. The derived ages and most probable star formation histories suggest a high star-formation-rate (300-500 solar masses per year) phase in the progenitor population. We argue that most of the red galaxies are not descendants of the typical z=3 Lyman break galaxies. Galaxies associated with luminous sub-mm sources have the requisite star formation rates to be the progenitor population. Our results point toward early and rapid formation for a significant fraction of present day massive galaxies.

astro-ph↗

arXiv2004

FORTIS: Pathfinder to the Lyman Continuum

Shull et al. (1999) have asserted that the contribution of stars, relative to quasars, to the metagalactic background radiation that ionizes most of the baryons in the universe remains almost completely unknown at all epochs. The potential to directly quantify this contribution at low redshift has recently become possible with the identification by GALEX of large numbers of sparsely distributed faint ultraviolet galaxies. Neither STIS nor FUSE nor GALEX have the ability to efficiently survey these sparse fields and directly measure the Lyman continuum radiation that may leak into the low redshift (z < 0.4) intergalactic medium. We present here a design for a new type of far ultraviolet spectrograph, one that is more sensitive, covers wider fields, and can provide spectra and images of a large number of objects simultaneously, called the Far-ultraviolet Off Rowland-circle Telescope for Imaging and Spectroscopy (FORTIS). We intend to use a sounding rocket flight to validate the new instrument with a simple long-slit observation of the starburst populations in the galaxy M83. If however, the long-slit were replaced with microshutter array, this design could isolate the chains of blue galaxies found by GALEX over an ~30' diameter field-of-view and directly address the Lyman continuum problem in a long duration orbital mission. Thus, our development of the sounding rocket instrument is a pathfinder to a new wide field spectroscopic technology for enabling the potential discovery of the long hypothesized but elusive Lyman continuum radiation that is thought to leak from low redshift galaxies and contribute to the ionization of the universe.

astro-ph↗