arXiv subjects

Luc Simard

Publications and source records attributed to Luc Simard.

At least 91 records · Page 5Linked to original sources

arXiv2007

Rest-Frame Ultraviolet to Near Infrared Observations of an Interacting Lyman Break Galaxy at z = 4.42

We present the rest-frame ultraviolet through near infrared spectral energy distribution for an interacting Lyman break galaxy at a redshift z=4.42, the highest redshift merging system known with clearly resolved tidal features. The two objects in this system - HDF-G4 and its previously unidentified companion - are both B_{435} band dropouts, have similar V_{606}-i_{775} and i_{775}-z_{850} colors, and are separated by 1", which at z=4.42 corresponds to 7 kpc projected nuclear separation; all indicative of an interacting system. Fits to stellar population models indicate a stellar mass of M_\star = 2.6\times 10^{10} M_\odot, age of τ_\star = 720 My, and exponential star formation history with an e-folding time τ_0 = 440 My. Using these derived stellar populations as constraints, we model the HDF-G4 system using hydrodynamical simulations, and find that it will likely evolve into a quasar by z\sim3.5, and a quiescent, compact spheroid by z\sim 2.5 similar to those observed at z > 2. And, the existence of such an object supports galaxy formation models in which major mergers drive the high redshift buildup of spheroids and black holes.

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arXiv2007

Observing GRBs with TMT

The Thirty-Meter Telescope is an ambitious project to build a giant segmented mirror telescope with fully integrated adaptive optics systems that will produce diffraction-limited images. A powerful suite of instruments is being developed that, coupled with the ability to rapidly switch between targets and instruments, will allow TMT to take advantage of GRBs to probe fundamental physics in extreme conditions and as the ultimate tomographic beacons, especially if some are as far as z ~ 10. This article gives a brief summary of TMT and its instruments, and some examples of the potential offered by observation of GRBs.

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arXiv2006

The build-up of the colour-magnitude relation in galaxy clusters since z~0.8

Using galaxy clusters from the ESO Distant Cluster Survey, we study how the distribution of galaxies along the colour-magnitude relation has evolved since z~0.8. While red-sequence galaxies in all these clusters are well described by an old, passively evolving population, we confirm our previous finding of a significant evolution in their luminosity distribution as a function of redshift. When compared to galaxy clusters in the local Universe, the high redshift EDisCS clusters exhibit a significant "deficit" of faint red galaxies. Combining clusters in three different redshift bins, and defining as `faint' all galaxies in the range 0.4 > L/L* > 0.1, we find a clear decrease in the luminous-to-faint ratio of red galaxies from z~0.8 to z~0.4. The amount of such a decrease appears to be in qualitative agreement with predictions of a model where the blue bright galaxies that populate the colour-magnitude diagram of high redshift clusters, have their star formation suppressed by the hostile cluster environment. Although model results need to be interpreted with caution, our findings clearly indicate that the red-sequence population of high-redshift clusters does not contain all progenitors of nearby red-sequence cluster galaxies. A significant fraction of these must have moved onto the red-sequence below z~0.8.

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arXiv2006

The Tully-Fisher Relation in Cluster Cl0024+1654 at z=0.4

Using moderate-resolution Keck spectra, we have examined the velocity profiles of 15 members of cluster Cl0024+1654 at z=0.4. WFPC2 images of the cluster members have been used to determine structural parameters, including disk sizes, orientations, and inclinations. We compare two methods of optical rotation curve analysis for kinematic measurements. Both methods take seeing, slit size and orientation, and instrumental effects into account and yield similar rotation velocity measurements. Four of the galaxies in our sample exhibit unusual kinematic signatures, such as non-circular motions. Our key result is that the Cl0024 galaxies are marginally underluminous (0.50 +/- 0.23 mag), given their rotation velocities, as compared to the local Tully-Fisher relation. In this analysis, we assume no slope evolution, and take into account systematic differences between local and distant velocity and luminosity measurements. Our result is particularly striking considering the Cl0024 members have very strong emission lines, and local galaxies with similar Halpha equivalent widths tend to be overluminous on the Tully-Fisher relation. Cl0024 Tully-Fisher residuals appear to be correlated most strongly with galaxy rotation velocities, indicating a possible change in the slope of the Tully-Fisher relation. However, we caution that this result may be strongly affected by magnitude selection and by the original slope assumed for the analysis. Cl0024 residuals also depend weakly on color, emission line strength and extent, and photometric asymmetry. In a comparison of stellar and gas motions in two Cl0024 members, we find no evidence for counter-rotating stars and gas, an expected signature of mergers.

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arXiv2005

Colors of Luminous Bulges in Cluster MS1054-03 and Field Galaxies at Redshifts z ~ 0.83

Using HST images, we separate the bulge-like (pbulge) and disk-like (pdisk) components of 71 galaxies in the rich cluster MS1054-03 and of 21 in the field. Our key finding is that luminous pbulges are very red with restframe U-B ~ 0.45, while predicted colors are bluer by 0.20 mag. Moreover, these very red colors appear to be independent of environment, pbulge luminosity, pdisk color, and pbulge fraction. These results challenge any models of hierarchical galaxy formation that predict the colors of distant (z ~ 0.8) luminous field and cluster bulges would differ. Our findings also disagree with other claims that 30% to 50% of bright bulges and ellipticals at z ~ 1 are very blue (U-B < 0).

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arXiv2005

The Evolution of Stellar Mass in the NICMOS UDF and the CFHTLS Deep Fields

We measure the build-up of the stellar mass of galaxies from z=6 to z=1. Using 15 band multicolour imaging data in the NICMOS Ultra Deep Field we derive photometric redshifts and masses for 796 galaxies down to H_AB=26.5. The derived evolution of the global stellar mass density of galaxies is consistent with previous star formation rate density measurements over the observed range of redshifts. Ongoing research in the CFHTLS Deep Fields confirms this result at lower redshifts. Further, if the sample is split by morphological type, a substantial increase is seen in the number of bulge dominated galaxies relative to disk-dominated galaxies since z=1.

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arXiv2005

Halpha-Derived Star-Formation Rates For Three z ~ 0.75 EDisCS Galaxy Clusters

We present Halpha-derived star-formation rates (SFRs) for three z ~ 0.75 galaxy clusters. Our 1 sigma flux limit corresponds to a star-formation rate of 0.10-0.24 solar mass per year, and our minimum reliable Halpha + [N II] rest-frame equivalent width is 10Å. We show that Halpha narrowband imaging is an efficient method for measuring star formation in distant clusters. In two out of three clusters, we find that the fraction of star-forming galaxies increases with projected distance from the cluster center. We also find that the fraction of star-forming galaxies decreases with increasing local galaxy surface density in the same two clusters. We compare the median rate of star formation among star-forming cluster galaxies to a small sample of star-forming field galaxies from the literature and find that the median cluster SFRs are \~50% less than the median field SFR. We characterize cluster evolution in terms of the mass-normalized integrated cluster SFR and find that the z ~ 0.75 clusters have more SFR per cluster mass on average than the z <= 0.4 clusters from the literature. The interpretation of this result is complicated by the dependence of the mass-normalized SFR on cluster mass and the lack of sufficient overlap in the mass ranges covered by the low and high redshift samples. We find that the fraction and luminosities of the brightest starburst galaxies at z ~ 0.75 are consistent with their being progenitors of the post-starburst galaxies at z ~ 0.45 if the post-starburst phase lasts several (~5) times longer than the starburst phase.

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arXiv2005

The DEEP Groth Strip Survey. I. The Sample

The Deep Extragalactic Exploratory Probe (DEEP) is a multi-phase research program dedicated to the study of the formation and evolution of galaxies and of large scale structure in the distant Universe. This paper describes the first five-year phase, denoted DEEP1. A series of ten DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127 square arcminute region which has been observed with the Hubble Space Telescope in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects. We evaluate three independent techniques for constructing an imaging catalog for the field from the HST data, and discuss the depth and sampling of the resultant catalogs. The selection of the spectroscopic subsample is discussed, and we describe the multifaceted approach taken to prioritizing objects of interest for a variety of scientific subprograms. A series of Monte Carlo simulations then demonstrates that the spectroscopic subsample can be adequately modeled as a simple function of magnitude and color cuts in the imaging catalog.

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arXiv2005

Imaging of SDSS z>6 quasar fields: gravitational lensing, companion galaxies and the host dark matter halos

We have undertaken deep optical imaging observations of three 6.2<z<6.5 quasar fields in the i' and z' filters. These data are used to search for foreground galaxies which are gravitationally lensing the quasars and distant galaxies physically associated with the quasars. Foreground galaxies are found closer than 5 arcsec from the lines-of-sight of two of the three quasars. However, the faintness of these galaxies suggests they have fairly low masses and provide only weak magnifications (mu<1.1). No convincing galaxies physically associated with the quasars are found and the number of i'-band dropouts is consistent with that found in random fields. We consider the expected dark matter halo masses which host these quasars under the assumption that a correlation between black hole mass and dark matter halo mass exists. We show that the steepness of the high-mass tail of the halo mass function at this redshift, combined with realistic amounts of scatter in this correlation, lead to expected halo masses substantially lower than previously believed. This analysis can explain the lack of companion galaxies found here and the low dynamical mass recently published for one of the quasars.

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arXiv2004

The DEEP Groth Strip Galaxy Redshift Survey. VIII. The Evolution of Luminous Field Bulges at Redshift z ~ 1

We present a sample of over 50 luminous field bulges (including ellipticals) found in the Groth Strip Survey (GSS), with 0.73< z < 1.04 and with bulge magnitudes I <= 23. The exponential disk light is removed via decomposition of HST images using GIM2D. We find that 85% of these bulges are nearly as red as local E/S0's and have a shallow slope and a small color dispersion in the color-luminosity relation, suggesting roughly coeval formation. The surface brightnesses of these bulges are about 1 mag higher than local bulges. These results are explained adopting a "drizzling" scenario where a metal-rich early formation is later polluted by small amounts of additional star formation. Almost all disks have the same or bluer colors than their accompanying bulges, regardless of the bulge-disk ratio and bulge luminosity, as expected from semi-analytic hierarchical galaxy formation models. We present evidence that the few blue bulge candidates are not likely to be genuine blue ellipticals or bulges. Our deeper, more extensive, and less disk-contaminated observations challenge prior claims that 30% to 50% of field bulges or ellipticals are in a blue, star-forming phase at z < 1. We conclude that field bulges and ellipticals at z ~ 1, like luminous early- type cluster galaxies at the same redshift, are already dominated by metal-rich, old stellar populations that have been fading from a formation epoch earlier than z ~ 1.5. (abridged)

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arXiv2004

The DEEP Groth Strip Galaxy Redshift Survey. III. Redshift Catalog and Properties of Galaxies

The Deep Extragalactic Evolutionary Probe (DEEP) is a series of spectroscopic surveys of faint galaxies, targeted at the properties and clustering of galaxies at redshifts z ~ 1. We present the redshift catalog of the DEEP 1 GSS pilot phase of this project, a Keck/LRIS survey in the HST/WFPC2 Groth Survey Strip. The redshift catalog and data, including reduced spectra, are publicly available through a Web-accessible database. The catalog contains 658 secure galaxy redshifts with a median z=0.65, and shows large-scale structure walls to z = 1. We find a bimodal distribution in the galaxy color-magnitude diagram which persists to z = 1. A similar color division has been seen locally by the SDSS and to z ~ 1 by COMBO-17. For red galaxies, we find a reddening of only 0.11 mag from z ~ 0.8 to now, about half the color evolution measured by COMBO-17. We measure structural properties of the galaxies from the HST imaging, and find that the color division corresponds generally to a structural division. Most red galaxies, ~ 75%, are centrally concentrated, with a red bulge or spheroid, while blue galaxies usually have exponential profiles. However, there are two subclasses of red galaxies that are not bulge-dominated: edge-on disks and a second category which we term diffuse red galaxies (DIFRGs). The distant edge-on disks are similar in appearance and frequency to those at low redshift, but analogs of DIFRGs are rare among local red galaxies. DIFRGs have significant emission lines, indicating that they are reddened mainly by dust rather than age. The DIFRGs in our sample are all at z>0.64, suggesting that DIFRGs are more prevalent at high redshifts; they may be related to the dusty or irregular extremely red objects (EROs) beyond z>1.2 that have been found in deep K-selected surveys. (abridged)

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arXiv2004

A search for the first massive galaxy clusters

We have obtained deep, multi-band imaging observations around three of the most distant known quasars at redshifts z>6. Standard accretion theory predicts that the supermassive black holes present in these quasars were formed at a very early epoch. If a correlation between black hole mass and dark matter halo mass is present at these early times, then these rare supermassive black holes will be located inside the most massive dark matter halos. These are therefore ideal locations to search for the first clusters of galaxies. We use the Lyman-break technique to identify star-forming galaxies at high redshifts. Our observations show no overdensity of star-forming galaxies in the fields of these quasars. The lack of (dust-free) luminous starburst companions indicates that the quasars may be the only massive galaxies in their vicinity undergoing a period of intense activity.

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arXiv2004

Structural properties of discs and bulges of early-type galaxies

We have used the EFAR sample of galaxies to study the light distributions of early-type galaxies. We decompose the 2D light distribution of the galaxies in a flattened spheroidal component with a Sersic radial light profile and an inclined disc component with an exponential light profile. We show that the brightest, bulge dominated elliptical galaxies have a fairly broad distribution in the Sersic profile shape parameter n_B, with a median of about 3.7 and a sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids are in general less concentrated than the n_B=4 de Vaucouleurs-law profile. The results of our light decompositions are robust, even though without kinematic information we cannot prove that the spheroids and discs are really pressure- and rotation-supported stellar systems. If we assume that the detected spheroids and discs are indeed separate components, we can draw the following conclusions: 1) the spheroid and disc scale sizes are correlated; 2) bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values are all positively correlated; 3) the bivariate space density distribution of elliptical galaxies in the (luminosity, scale size)-plane is well described by a Schechter luminosity function in and a log-normal scale-size distribution at a given luminosity; 4) at the brightest luminosities, the scale size distribution of elliptical galaxies is similar to those of bright spiral galaxies; at fainter luminosities the elliptical scale size distribution peaks at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge components of early-type galaxies are typically a factor 1.5 to 2.5 smaller than the disks of spiral galaxies, while disc components of early-type galaxies are typically twice as large as the discs of spiral galaxies. [abridged]

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arXiv2003

The DEEP Groth Strip Survey VII: The Metallicity of Field Galaxies at 0.26<z<0.82 and the Evolution of the Luminosity-Metallicity Relation

Using spectroscopic data from the Deep Extragalactic Evolutionary Probe (DEEP) Groth Strip survey (DGSS), we analyze the gas-phase oxygen abundances in the warm ionized medium for 64 emission-line field galaxies in the redshift range 0.26 -19) end of the sample and vanishingly small for objects at the high-luminosity end of the sample (M_B ~ -22). Simple galaxy evolution models can produce reasonable agreement with observations for low-mass galaxies when least two of the following are true: 1) low-mass galaxies have lower effective chemical yields than massive galaxies, 2) low-mass galaxies assemble on longer timescales than massive galaxies, 3) low-mass galaxies began the assembly process at a later epoch than massive galaxies. (abridged)

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arXiv2003

The DEEP Groth Strip Survey IX: Evolution of the Fundamental Plane of Field Galaxies

Fundamental Plane studies provide an excellent means of understanding the evolutionary history of early-type galaxies. Using the Low Resolution Imaging Spectrograph on the Keck telescope, we obtained internal stellar kinematic information for 36 field galaxies in the Groth Strip--21 early-type and 15 disk galaxies. Their redshifts range from 0.3--1.0, with a median redshift 0.8. The slope of the relation shows no difference compared with the local slope. However, there is significant evolution in the zero-point offset; an offset due to evolution in magnitude requires a 2.4 magnitude luminosity brightening at z=1. We see little differences of the offset with bulge fraction, which is a good surrogate for galaxy type. Correcting for the luminosity evolution reduces the orthogonal scatter in the Fundamental Plane to 8%, consistent with the local scatter. This scatter is measured for our sample, and does not include results from other studies which may have different selection effects. The difference in the degree of evolution between our field sample and published cluster galaxies suggests a more recent formation epoch--around z=1.5 for field galaxies compared to z>2.0 for cluster galaxies. The magnitude difference implies that the field early-type galaxies are about 2 Gyr younger than the cluster ellipticals using standard single-burst models. However, the same models imply a significant change in the rest-frame U-B color from then to present, which is not seen in our sample. Continuous low-level star formation, however, would serve to explain the constant colors over this large magnitude change. A consistent model has 7% of the stellar mass created after the initial burst, using an exponentially decaying star formation rate with an e-folding time of 5 Gyr.

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arXiv2003

The DEEP Groth Strip Survey XII: The Metallicity of Field Galaxies at 0.26<z<0.82 and the Evolution of the Luminosity-Metallicity Relation

Using spectroscopic data from the Deep Extragalactic Evolutionary Probe (DEEP) Groth Strip survey (DGSS), we analyze the gas-phase oxygen abundances for 56 emission-line field galaxies in the redshift range 0.26<z<0.82. Oxygen abundances relative to hydrogen range between 8.4<12+log(O/H)<9.0 with typical uncertainties of 0.17 dex. The 56 DGSS galaxies collectively exhibit a correlation between B-band luminosity and metallicity, i.e., an L-Z relation. Subsets of DGSS galaxies binned by redshift also exhibit L-Z correlations but with different zero points. Galaxies in the highest redshift bin (z=0.6-0.82) are brighter by ~1 mag compared to the lowest redshift bin (z=0.26-0.40) and brighter by ~1-2 mag compared to local (z<0.1) field galaxies. This offset from the local L-Z relation is greatest for objects at the low-luminosity (M_B ~ -19) end of the sample, and vanishingly small for objects at the high-luminosity end of the sample (M_B ~ -22). Thus, both the slope and zero point of the L-Z relation appear to evolve. Either the least-luminous DGSS field galaxies have faded by 1--2 mag due to decreasing levels of star formation, or they have experienced an increase in the mean metallicity of the interstellar medium by factors of 1.3--2 (0.1-0.3 dex). The relatively greater degree of luminosity and metallicity evolution seen among the lower luminosity (sub L*) galaxies in the last 8 Gyr implies either a more protracted assembly process, or a more recent formation epoch compared to more luminous L* galaxies. (abridged)

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arXiv2003

CL 1358+62: Characterizing the Physical Properties of Cluster Galaxies at z=0.33

[Abridged] We examine the physical properties of 173 cluster members in CL1358+62 (z=0.33) from HST WFPC2 imaging taken in the F606W & F814W filters (rest-frame B & V) over a 2.2x2.2 Mpc^2 field. Structural parameters are measured for each member by fitting a PSF-convolved, two component model to their 2D surface brightness distribution. We examine bulge+disk models using three different bulge profiles (de Vaucouleurs, Sersic, and exponential), and rigorously test the robustness of our results by analyzing several thousand artificial galaxies in the same manner as the cluster data. Combining structural parameters with ground-based spectroscopy, we test for correlations between morphological characteristics, current star formation, total galaxy colors, and cluster substructure. We find that: (1) Using a de Vaucouleurs bulge, bulge-to-total ratios and Hubble type (-5<T<8) are strongly correlated (99% CL), but the scatter is large and early-type spirals are not reliably distinguished from E's and S0's based on (B/T). (2) The low luminosity ellipticals in our sample are likely to be face-on S0 galaxies. (3) High galaxy asymmetry and strong [OII] emission are strongly correlated for disk-dominated members. (4) There exists a small population (~5%) of bulge-dominated members whose significant [OII] emission (<-5A) suggest they harbor AGN. (5) At these redshifts, determining the correct Sersic index can be highly unreliable.

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arXiv2002

Tests of the Las Campanas Distant Cluster Survey from Confirmation Observations for the ESO Distant Cluster Survey

The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic study of the galaxy cluster population at two epochs, z~0.5 and z~0.8, drawn from the Las Campanas Distant Cluster Survey (LCDCS). We report results from the initial candidate confirmation stage of the program and use these results to probe the properties of the LCDCS. Of the 30 candidates targeted, we find statistically significant overdensities of red galaxies near 28. Of the ten additional candidates serendipitously observed within the fields of the targeted 30, we detect red galaxy overdensities near six. We test the robustness of the published LCDCS estimated redshifts to misidentification of the brighest cluster galaxy (BCG) in the survey data, and measure the spatial alignment of the published cluster coordinates, the peak red galaxy overdensity, and the brightest cluster galaxy. We conclude that for LCDCS clusters out to z~0.8, 1) the LCDCS coordinates agree with the centroid of the red galaxy overdensity to within 25'' (~150 h^{-1} kpc) for 34 out of 37 candidates with 3σgalaxy overdensities, 2) BCGs are typically coincident with the centroid of the red galaxy population to within a projected separation of 200 h^{-1} kpc (32 out of 34 confirmed candidates), 3) the red galaxy population is strongly concentrated, and 4) the misidentification of the BCG in the LCDCS causes a redshift error >0.1 in 15-20% of the LCDCS candidates. These findings together help explain the success of the surface brightness fluctuations detection method.

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