arXiv subjects

Chris Lidman

Publications and source records attributed to Chris Lidman.

At least 55 records · Page 3Linked to original sources

arXiv2016

The 2-degree Field Lensing Survey: photometric redshifts from a large new training sample to r<19.5

We present a new training set for estimating empirical photometric redshifts of galaxies, which was created as part of the 2dFLenS project. This training set is located in a 700 sq deg area of the KiDS South field and is randomly selected and nearly complete at r<19.5. We investigate the photometric redshift performance obtained with ugriz photometry from VST-ATLAS and W1/W2 from WISE, based on several empirical and template methods. The best redshift errors are obtained with kernel-density estimation, as are the lowest biases, which are consistent with zero within statistical noise. The 68th percentiles of the redshift scatter for magnitude-limited samples at r<(15.5, 17.5, 19.5) are (0.014, 0.017, 0.028). In this magnitude range, there are no known ambiguities in the colour-redshift map, consistent with a small rate of redshift outliers. In the fainter regime, the KDE method produces p(z) estimates per galaxy that represent unbiased and accurate redshift frequency expectations. The p(z) sum over any subsample is consistent with the true redshift frequency plus Poisson noise. Further improvements in redshift precision at r<20 would mostly be expected from filter sets with narrower passbands to increase the sensitivity of colours to small changes in redshift.

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arXiv2016

2dFLenS and KiDS: Determining source redshift distributions with cross-correlations

We develop a statistical estimator to infer the redshift probability distribution of a photometric sample of galaxies from its angular cross-correlation in redshift bins with an overlapping spectroscopic sample. This estimator is a minimum variance weighted quadratic function of the data: a quadratic estimator. This extends and modifies the methodology presented by McQuinn & White (2013). The derived source redshift distribution is degenerate with the source galaxy bias, which must be constrained via additional assumptions. We apply this estimator to constrain source galaxy redshift distributions in the Kilo-Degree imaging survey through cross-correlation with the spectroscopic 2-degree Field Lensing Survey, presenting results first as a binned step-wise distribution in the range z < 0.8, and then building a continuous distribution using a Gaussian process model. We demonstrate the robustness of our methodology using mock catalogues constructed from N-body simulations, and comparisons with other techniques for inferring the redshift distribution.

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arXiv2016

Evidence for strong evolution in galaxy environmental quenching efficiency between z = 1.6 and z = 0.9

We analyse the evolution of environmental quenching efficiency, the fraction of quenched cluster galaxies that would be star-forming if they were in the field, as a function of redshift in 14 spectroscopically confirmed galaxy clusters with 0.87 < z < 1.63 from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS). The clusters are the richest in the survey at each redshift. Passive fractions rise from $42_{-13}^{+10}$\% at z ~ 1.6 to $80_{-9}^{+12}$\% at z ~ 1.3 and $88_{-3}^{+4}$\% at z < 1.1, outpacing the change in passive fraction in the field. Environmental quenching efficiency rises dramatically from $16_{-19}^{+15}$ at z ~ 1.6 to $62_{-15}^{+21}\% at z ~ 1.3 and $73_{-7}^{+8}$\% at z $\lesssim$ 1.1. This work is the first to show direct observational evidence for a rapid increase in the strength of environmental quenching in galaxy clusters at z ~ 1.5, where simulations show cluster-mass halos undergo non-linear collapse and virialisation.

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arXiv2016

High-redshift supernova rates measured with the gravitational telescope A1689

We present a ground-based near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z=0.18, one of the most powerful gravitational telescopes that nature provides. Our survey was based on multi-epoch $J$-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Our search resulted in the discovery of five high-redshift, $0.671<z<1.703$, photometrically classified core-collapse supernovae with magnifications in the range $Δm$ = $-0.31$ to $-1.58$ mag, as calculated from lensing models in the literature. Thanks to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high-redshifts, $z$$\sim$$3$, albeit for a limited region of space. We present a study of the core-collapse supernova rates for $0.4\leq z< 2.9$, and find good agreement with both previous estimates, and the predictions from the star formation history. During our survey, we also discovered 2 type Ia supernovae in A1689 cluster members, which allowed us to determine the cluster Ia rate to be $0.14^{+0.19}_{-0.09}\pm0.01$ $\rm{SNuB}$$\,h^2$ (SNuB$\equiv 10^{-12} \,\rm{SNe} \, L^{-1}_{\odot,B} yr^{-1}$). The cluster rate normalized by the stellar mass is $0.10^{+0.13}_{-0.06}\pm0.02$ in $\rm SNuM$$\,h^2$ (SNuM$\equiv 10^{-12} \,\rm{SNe} \, M^{-1}_{\odot} yr^{-1}$). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at $z\gtrsim2$ using gravitational telescopes, as well as for the detections with multiply lensed images, and find that the planned WFIRST space mission has excellent prospects. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-$z$ transient universe.

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arXiv2016

The 2-degree Field Lensing Survey: design and clustering measurements

We present the 2-degree Field Lensing Survey (2dFLenS), a new galaxy redshift survey performed at the Anglo-Australian Telescope. 2dFLenS is the first wide-area spectroscopic survey specifically targeting the area mapped by deep-imaging gravitational lensing fields, in this case the Kilo-Degree Survey. 2dFLenS obtained 70,079 redshifts in the range z < 0.9 over an area of 731 sq deg, and is designed to extend the datasets available for testing gravitational physics and promote the development of relevant algorithms for joint imaging and spectroscopic analysis. The redshift sample consists first of 40,531 Luminous Red Galaxies (LRGs), which enable analyses of galaxy-galaxy lensing, redshift-space distortion, and the overlapping source redshift distribution by cross-correlation. An additional 28,269 redshifts form a magnitude-limited (r < 19.5) nearly-complete sub-sample, allowing direct source classification and photometric-redshift calibration. In this paper, we describe the motivation, target selection, spectroscopic observations, and clustering analysis of 2dFLenS. We use power spectrum multipole measurements to fit the redshift-space distortion parameter of the LRG sample in two redshift ranges 0.15 < z < 0.43 and 0.43 < z < 0.7 as beta = 0.49 +/- 0.15 and beta = 0.26 +/- 0.09, respectively. These values are consistent with those obtained from LRGs in the Baryon Oscillation Spectroscopic Survey. 2dFLenS data products will be released via our website http://2dflens.swin.edu.au.

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arXiv2016

Stellar mass function of cluster galaxies at z $\sim$ 1.5: evidence for reduced quenching efficiency at high redshift

We present the stellar mass functions (SMFs) of passive and star-forming galaxies with a limiting mass of 10$^{10.1}$ M$_{\odot}$ in four spectroscopically confirmed Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) galaxy clusters at 1.37 $<$ z $<$ 1.63. The clusters have 113 spectroscopically confirmed members combined, with 8-45 confirmed members each. We construct $Ks$-band-selected photometric catalogs for each cluster with an average of 11 photometric bands ranging from $u$ to 8 $μ$m. We compare our cluster galaxies to a field sample derived from a similar $Ks$-band-selected catalog in the UltraVISTA/COSMOS field. The SMFs resemble those of the field, but with signs of environmental quenching. We find that 30 $\pm$ 20\% of galaxies that would normally be forming stars in the field are quenched in the clusters. The environmental quenching efficiency shows little dependence on projected cluster-centric distance out to $\sim$ 4 Mpc, providing tentative evidence of pre-processing and/or galactic conformity in this redshift range. We also compile the available data on environmental quenching efficiencies from the literature, and find that the quenching efficiency in clusters and in groups appears to decline with increasing redshift in a manner consistent with previous results and expectations based on halo mass growth.

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arXiv2016

Discovery of a z=0.65 Post-Starburst BAL Quasar in the DES Supernova Fields

We present the discovery of a z=0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad FeII (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario.

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arXiv2016

The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years

Using a sample of 98 galaxy clusters recently imaged in the near infra-red with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from the ESO archive, we measure how the stellar mass of the most massive galaxies in the universe, namely Brightest Cluster Galaxies (BCG), increases with time. Most of the BCGs in this new sample lie in the redshift range $0.2<z<0.6$, which has been noted in recent works to mark an epoch over which the growth in the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass. We combine the BCGs in this subsample with BCGs from the literature, and find that the growth in stellar mass of BCGs from 10 billion years ago to the present epoch is broadly consistent with recent semi-analytic and semi-empirical models. As in other recent studies, tentative evidence indicates that the stellar mass growth rate of BCGs may be slowing in the past 3.5 billion years. Further work in collecting larger samples, and in better comparing observations with theory using mock images is required if a more detailed comparison between the models and the data is to be made.

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arXiv2016

MARZ: Manual and Automatic Redshifting Software

The Australian Dark Energy Survey (OzDES) is a 100-night spectroscopic survey underway on the Anglo-Australian Telescope using the fibre-fed 2-degree-field (2dF) spectrograph. We have developed a new redshifting application Marz with greater usability, flexibility, and the capacity to analyse a wider range of object types than the Runz software package previously used for redshifting spectra from 2dF. Marz is an open-source, client-based, Javascript web-application which provides an intuitive interface and powerful automatic matching capabilities on spectra generated from the AAOmega spectrograph to produce high quality spectroscopic redshift measurements. The software can be run interactively or via the command line, and is easily adaptable to other instruments and pipelines if conforming to the current FITS file standard is not possible. Behind the scenes, a modified version of the Autoz cross-correlation algorithm is used to match input spectra against a variety of stellar and galaxy templates, and automatic matching performance for OzDES spectra has increased from 54% (Runz) to 91% (Marz). Spectra not matched correctly by the automatic algorithm can be easily redshifted manually by cycling automatic results, manual template comparison, or marking spectral features.

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arXiv2016

UNITY: Confronting Supernova Cosmology's Statistical and Systematic Uncertainties in a Unified Bayesian Framework

While recent supernova cosmology research has benefited from improved measurements, current analysis approaches are not statistically optimal and will prove insufficient for future surveys. This paper discusses the limitations of current supernova cosmological analyses in treating outliers, selection effects, shape- and color-standardization relations, unexplained dispersion, and heterogeneous observations. We present a new Bayesian framework, called UNITY (Unified Nonlinear Inference for Type-Ia cosmologY), that incorporates significant improvements in our ability to confront these effects. We apply the framework to real supernova observations and demonstrate smaller statistical and systematic uncertainties. We verify earlier results that SNe Ia require nonlinear shape and color standardizations, but we now include these nonlinear relations in a statistically well-justified way. This analysis was primarily performed blinded, in that the basic framework was first validated on simulated data before transitioning to real data. We also discuss possible extensions of the method.

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arXiv2016

Rapidly Rising Transients in the Supernova - Superluminous Supernova Gap

We present observations of four rapidly rising (t_{rise}~10d) transients with peak luminosities between those of supernovae (SNe) and superluminous SNe (M_{peak}~-20) - one discovered and followed by the Palomar Transient Factory (PTF) and three by the Supernova Legacy Survey (SNLS). The light curves resemble those of SN 2011kl, recently shown to be associated with an ultra-long-duration gamma ray burst (GRB), though no GRB was seen to accompany our SNe. The rapid rise to a luminous peak places these events in a unique part of SN phase space, challenging standard SN emission mechanisms. Spectra of the PTF event formally classify it as a Type II SN due to broad Halpha emission, but an unusual absorption feature, which can be interpreted as either high velocity Halpha (though deeper than in previously known cases) or Si II (as seen in Type Ia SNe), is also observed. We find that existing models of white dwarf detonations, CSM interaction, shock breakout in a wind (or steeper CSM) and magnetar spindown can not readily explain the observations. We consider the possibility that a "Type 1.5 SN" scenario could be the origin of our events. More detailed models for these kinds of transients and more constraining observations of future such events should help better determine their nature.

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arXiv2015

Evidence for a change in the dominant satellite galaxy quenching mechanism at z=1

We present an analysis of galaxies in groups and clusters at $0.8 10^{10.3}M_\odot$, we find $f_{\rm convert}\sim 0.4$ in the groups and $\sim 0.6$ in the clusters, similar to comparable measurements at $z=0$. This means the time between first accretion into a more massive halo and final star formation quenching is $t_p\sim 2$ Gyr. This is substantially longer than the estimated time required for a galaxy's star formation rate to become zero once it starts to decline, suggesting there is a long delay time during which little differential evolution occurs. In contrast with local observations we find evidence that this delay timescale may depend on stellar mass, with $t_p$ approaching $t_{\rm Hubble}$ for $M_{\rm star}\sim 10^{9.5}M_\odot$. The result suggests that the delay time must not only be much shorter than it is today, but may also depend on stellar mass in a way that is not consistent with a simple evolution in proportion to the dynamical time. Instead, we find the data are well-matched by a model in which the decline in star formation is due to "overconsumption", the exhaustion of a gas reservoir through star formation and expulsion via modest outflows in the absence of cosmological accretion. Dynamical gas removal processes, which are likely dominant in quenching newly accreted satellites today, may play only a secondary role at $z=1$.

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arXiv2015

Evidence for the Universality of Properties of Red-Sequence Galaxies in X-ray- and Red-Sequence-Selected Clusters at z ~ 1

We study the slope, intercept, and scatter of the color-magnitude and color-mass relations for a sample of ten infrared red-sequence-selected clusters at z ~ 1. The quiescent galaxies in these clusters formed the bulk of their stars above z ~ 3 with an age spread Δt ~ 1 Gyr. We compare UVJ color-color and spectroscopic-based galaxy selection techniques, and find a 15% difference in the galaxy populations classified as quiescent by these methods. We compare the color-magnitude relations from our red-sequence selected sample with X-ray- and photometric- redshift-selected cluster samples of similar mass and redshift. Within uncertainties, we are unable to detect any difference in the ages and star formation histories of quiescent cluster members in clusters selected by different methods, suggesting that the dominant quenching mechanism is insensitive to cluster baryon partitioning at z ~ 1.

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arXiv2015

The Star-Formation History of BCGs to z = 1.8 from the SpARCS/SWIRE Survey: Evidence for significant in-situ star formation at high-redshift

We present the results of a MIPS-24um study of the Brightest Cluster Galaxies (BCGs) of 535 high-redshift galaxy clusters. The clusters are drawn from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), which effectively provides a sample selected on total stellar mass, over 0.2 < z < 1.8 within the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey fields. 20%, or 106 clusters have spectroscopically confirmed redshifts, and the rest have redshifts estimated from the color of their red sequence. A comparison with the public SWIRE images detects 125 individual BCGs at 24um > 100uJy, or 23%. The luminosity-limited detection rate of BCGs in similar richness clusters (Ngal> 12) increases rapidly with redshift. Above z ~ 1, an average of ~20\% of the sample have 24um-inferred infrared luminosities of LIR > 10^12 Lsun, while the fraction below z ~ 1 exhibiting such luminosities is < 1 \%. The Spitzer-IRAC colors indicate the bulk of the 24um-detected population is predominantly powered by star formation, with only 7/125 galaxies lying within the color region inhabited by Active Galactic Nuclei (AGN). Simple arguments limit the star-formation activity to several hundred million years and this may therefore be indicative of the timescale for AGN feedback to halt the star formation. Below redshift z ~ 1 there is not enough star formation to significantly contribute to the overall stellar mass of the BCG population, and therefore BCG growth is likely dominated by dry-mergers. Above z~ 1, however, the inferred star formation would double the stellar mass of the BCGs and is comparable to the mass assembly predicted by simulations through dry mergers. We cannot yet constrain the process driving the star formation for the overall sample, though a single object studied in detail is consistent with a gas-rich merger.

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arXiv2015

An Extreme Starburst in Close Proximity to the Central Galaxy of a Rich Galaxy Cluster at z=1.7

We have discovered an optically rich galaxy cluster at z=1.7089 with star formation occurring in close proximity to the central galaxy. The system, SpARCS104922.6+564032.5, was detected within the Spitzer Adaptation of the red-sequence Cluster Survey, (SpARCS), and confirmed through Keck-MOSFIRE spectroscopy. The rest-frame optical richness of Ngal(500kpc) = 30+/-8 implies a total halo mass, within 500kpc, of ~3.8+/-1.2 x 10^14 Msun, comparable to other clusters at or above this redshift. There is a wealth of ancillary data available, including Canada-France-Hawaii Telescope optical, UKIRT-K, Spitzer-IRAC/MIPS, and Herschel-SPIRE. This work adds submillimeter imaging with the SCUBA2 camera on the James Clerk Maxwell Telescope and near-infrared imaging with the Hubble Space Telescope (HST). The mid/far-infrared (M/FIR) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy, with LIR = 6.2+/-0.9 x 10^12 Lsun. The detection of polycyclic aromatic hydrocarbons (PAHs) at z=1.7 in a Spitzer-IRS spectrum of the source implies the FIR luminosity is dominated by star formation (an Active Galactic Nucleus contribution of 20%) with a rate of ~860+/-30 Msun/yr. The optical source corresponding to the IR emission is likely a chain of of > 10 individual clumps arranged as "beads on a string" over a linear scale of 66 kpc. Its morphology and proximity to the Brightest Cluster Galaxy imply a gas-rich interaction at the center of the cluster triggered the star formation. This system indicates that wet mergers may be an important process in forming the stellar mass of BCGs at early times.

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arXiv2015

The accretion histories of brightest cluster galaxies from their stellar population gradients

We analyse the spatially-resolved stellar populations of 9 local ($z<0.1$) Brightest Cluster Galaxies (BCGs) observed with VIMOS in IFU mode. Our sample is composed of 7 slow-rotating and 2 fast-rotating BCGs. We do not find a connection between stellar kinematics and stellar populations in this small sample. The BCGs have shallow metallicity gradients (median $Δ$[Fe/H] $= -0.11\pm0.1$), high central metallicities (median $[$Fe/H]$_{[α/Fe]=0} = 0.13\pm0.07$), and a wide range of central ages (from 5 to 15 Gyr). We propose that the reason for this is diverse evolutionary paths in BCGs. 67 per cent of the sample (6/9) show $\sim 7$ Gyr old central ages, which reflects an active accretion history, and 33 per cent of the sample (3/9) have central ages older than 11 Gyr, which suggest no star formation since $z=2$. The BCGs show similar central stellar populations and stellar population gradients to early-type galaxies of similar mass (M$_{dyn}> 10^{11.3}$M$_{\odot}$) from the ATLAS$^{3D}$ survey (median [Z/H] $= 0.04\pm0.07$, $Δ$[Z/H] $= -0.19\pm0.1$). However, massive early-type galaxies from ATLAS$^{3D}$ have consistently old ages (median Age $=12.0\pm3.8$Gyr). We also analyse the close massive companion galaxies of two of the BCGs. These galaxies have similar stellar populations to their respective BCGs.

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arXiv2014

The Type Ia supernovae rate with Subaru/XMM-Newton Deep Survey

We present measurements of the rates of high-redshift Type Ia supernovae derived from the Subaru/XMM-Newton Deep Survey (SXDS). We carried out repeat deep imaging observations with Suprime-Cam on the Subaru Telescope, and detected 1040 variable objects over 0.918 deg$^2$ in the Subaru/XMM-Newton Deep Field. From the imaging observations, light curves in the observed $i'$-band are constructed for all objects, and we fit the observed light curves with template light curves. Out of the 1040 variable objects detected by the SXDS, 39 objects over the redshift range $0.2 < z < 1.4$ are classified as Type Ia supernovae using the light curves. These are among the most distant SN Ia rate measurements to date. We find that the Type Ia supernova rate increase up to $z \sim 0.8$ and may then flatten at higher redshift. The rates can be fitted by a simple power law, $r_V(z)=r_0(1+z)^α$ with $r_0=0.20^{+0.52}_{-0.16}$(stat.)$^{+0.26}_{-0.07}$(syst.)$\times 10^{-4} {\rm yr}^{-1}{\rm Mpc}^{-3}$, and $α=2.04^{+1.84}_{-1.96}$(stat.)$^{+2.11}_{-0.86}$(syst.).

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arXiv2013

A Census of Stellar Mass in 10 Massive Haloes at z~1 from the GCLASS Survey

We study the stellar mass content of massive haloes in the redshift range 0.86<z<1.34, by measuring: (1) The stellar mass in the central galaxy versus total dynamical halo mass. (2) The total stellar mass (including satellites) versus total halo mass. (3) The radial stellar mass and number density profiles for the ensemble halo. We use a Ks-band selected catalogue for the 10 clusters in the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), with photometric redshifts and stellar masses measured from 11-band SED fitting. Combining the photometric catalogues with the deep spectroscopic component of GCLASS, we correct the cluster galaxy sample for interlopers. We also perform a dynamical analysis of the cluster galaxies to estimate the halo mass M200 for each cluster based on a measurement of its velocity dispersion. (1) We find that the central galaxy stellar mass fraction decreases with total halo mass, and that this is in reasonable quantitative agreement with measurements from abundance matching studies at z~1. (2) The total stellar mass fractions of these systems decrease with halo mass, indicating that lower mass systems are more efficient at transforming baryons into stars. We find the total stellar mass to be a good proxy for total halo mass, with a small intrinsic scatter. When we compare these results with literature measurements, we find that the stellar mass fraction at fixed halo mass shows no significant evolution in the range 0<z<1. (3) We measure a relatively high NFW concentration parameter c ~ 7 for the stellar mass distribution in these clusters. A simple model shows that the stellar mass content of GCLASS can evolve in typical distributions observed at lower redshifts if the clusters primarily accrete stellar mass onto the outskirts. [Abridged]

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