arXiv subjects

J. Richard

Publications and source records attributed to J. Richard.

At least 91 records · Page 5Linked to original sources

arXiv2014

MUSE observations of the lensing cluster SMACSJ2031.8-4036: new constraints on the mass distribution in the cluster core

We present new observations of the lensing cluster SMACSJ2031.8-4036 obtained with the MUSE integral field spectrograph as part of its commissioning on the Very Large Telescope. By providing medium-resolution spectroscopy over the full 4750-9350 Angstroms domain and a 1x1 arcmin2 field of view, MUSE is ideally suited for identifying lensed galaxies in the cluster core, in particular multiple-imaged systems. We perform a redshift analysis of all sources in the datacube and identify a total of 12 systems ranging from $z=1.46$ to $z=6.4$, with all images of each system confirmed by a spectroscopic redshift. This allows us to accurately constrain the cluster mass profile in this region. We foresee that future MUSE observations of cluster cores should help us discover very faint Lyman-alpha emitters thanks to the strong magnification and the high sensitivity of this instrument.

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arXiv2014

Mass and magnification maps for the Hubble Space Telescope Frontier Fields clusters: implications for high redshift studies

Extending over three Hubble Space Telescope (HST) cycles, the Hubble Frontier Fields (HFF) initiative constitutes the largest commitment ever of HST time to the exploration of the distant Universe via gravitational lensing by massive galaxy clusters. We here present models of the mass distribution in the six HFF cluster lenses, derived from a joint strong- and weak-lensing analysis anchored by a total of 88 multiple-image systems identified in existing HST data. The resulting maps of the projected mass distribution and of the gravitational magnification effectively calibrate the HFF clusters as gravitational telescopes. Allowing the computation of search areas in the source plane, these maps are provided to the community to facilitate the exploitation of forthcoming HFF data for quantitative studies of the gravitationally lensed population of background galaxies. Our models of the gravitational magnification afforded by the HFF clusters allow us to quantify the lensing-induced boost in sensitivity over blank-field observations and predict that galaxies at $z>10$ and as faint as m(AB)=32 will be detectable, up to 2 magnitudes fainter than the limit of the Hubble Ultra Deep Field.

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arXiv2014

Star formation in the massive cluster merger Abell 2744

We present a comprehensive study of star-forming (SF) galaxies in the HST Frontier Field recent cluster merger A2744 (z=0.308). Wide-field, ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFR{UV+IR}=343+/-10 Msun/yr. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFR{UV+IR}=201+/-9 Msun/yr. Focussing on obscured star formation, this core region exhibits a total SFR{IR}=138+/-8 Msun/yr, a mass-normalised SFR{IR} of Sigma{SFR}=11.2+/-0.7 Msun/yr per 10^14 Msun and a fraction of IR-detected SF galaxies f{SF}=0.080(+0.010,-0.037). Overall, the cluster population at z~0.3 exhibits significant intrinsic scatter in IR properties (total SFR{IR}, Tdust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFR{UV}/SFR{IR} up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.

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arXiv2014

Lensed Type Ia Supernovae as Probes of Cluster Mass Models

Using three magnified Type Ia supernovae (SNe Ia) detected behind CLASH clusters, we perform a first pilot study to see whether standardizable candles can be used to calibrate cluster mass maps created from strong lensing observations. Such calibrations will be crucial when next generation HST cluster surveys (e.g. FRONTIER) provide magnification maps that will, in turn, form the basis for the exploration of the high redshift Universe. We classify SNe using combined photometric and spectroscopic observations, finding two of the three to be clearly of type SN Ia and the third probable. The SNe exhibit significant amplification, up to a factor of 1.7 at $\sim5σ$ significance (SN-L2). We conducted this as a blind study to avoid fine tuning of parameters, finding a mean amplification difference between SNe and the cluster lensing models of $0.09 \pm 0.09^{stat} \pm 0.05^{sys}$ mag. This impressive agreement suggests no tension between cluster mass models and high redshift standardized SNe Ia. However, the measured statistical dispersion of $σ_μ=0.21$ mag appeared large compared to the dispersion expected based on statistical uncertainties ($0.14$). Further work with the supernova and cluster lensing models, post unblinding, reduced the measured dispersion to $σ_μ=0.12$. An explicit choice should thus be made as to whether SNe are used unblinded to improve the model, or blinded to test the model. As the lensed SN samples grow larger, this technique will allow improved constraints on assumptions regarding e.g. the structure of the dark matter halo.

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arXiv2014

The first Frontier Fields cluster: 4.5μm excess in a z~8 galaxy candidate in Abell 2744

We present in this letter the first analysis of a z~8 galaxy candidate found in the Hubble and Spitzer imaging data of Abell 2744, as part of the Hubble Frontier Fields legacy program. We applied the most commonly-used methods to select exceptionally high-z galaxies by combining non-detection and color-criteria using seven HST bands. We used GALFIT on IRAC images for fitting and subtracting contamination of bright nearby sources. The physical properties have been inferred from SED-fitting using templates with and without nebular emission. This letter is focussed on the brightest candidate we found (m$_{F160W}$=26.2) over the 4.9 arcmin$^2$ field of view covered by the WFC3. It shows a non-detection in the ACS bands and at 3.6μm whereas it is clearly detected at 4.5μm with rather similar depths. This break in the IRAC data could be explained by strong [OIII]+Hβ lines at z~8 which contribute to the 4.5μm photometry. The best photo-z is found at z~8.0$^{+0.2}_{-0.5}$, although solutions at low-redshift (z~1.9) cannot be completely excluded, but they are strongly disfavoured by the SED-fitting work. The amplification factor is relatively small at μ=1.49$\pm$0.02. The Star Formation Rate in this object is ranging from 8 to 60 Mo/yr, the stellar mass is in the order of M$_{\star}$=(2.5-10) x 10$^{9}$Mo and the size is r~0.35$\pm$0.15 kpc. This object is one of the first z~8 LBG candidates showing a clear break between 3.6μm and 4.5μm which is consistent with the IRAC properties of the first spectroscopically confirmed galaxy at a similar redshift. Due to its brightness, the redshift of this object could potentially be confirmed by near infrared spectroscopy with current 8-10m telescopes. The nature of this candidate will be revealed in the coming months with the arrival of new ACS and Spitzer data, increasing the depth at optical and near-IR wavelengths.

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arXiv2014

[CII] and 12CO(1-0) Emission Maps in HLSJ091828.6+514223: A Strongly Lensed Interacting System at z=5.24

We present Submillimeter Array (SMA) [CII] 158um and Jansky Very Large Array (JVLA) $^{12}$CO(1-0) line emission maps for the bright, lensed, submillimeter source at $z=5.2430$ behind Abell 773: HLSJ091828.6+514223 (HLS0918). We combine these measurements with previously reported line profiles, including multiple $^{12}$CO rotational transitions, [CI], water and [NII], providing some of the best constraints on the properties of the interstellar medium (ISM) in a galaxy at $z>5$. HLS0918 has a total far-infrared (FIR) luminosity L_FIR(8-1000um) = (1.6$\pm$0.1)x10^14 L_sun/mu, where the total magnification mu_total = 8.9$\pm$1.9, via a new lens model from the [CII] and continuum maps. Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local LIRG. We simultaneously fit all of the observed spectral line profiles, finding four components which correspond cleanly to discrete spatial structures identified in the maps. The two most redshifted spectral components occupy the nucleus of a massive galaxy, with a source plane separation <1 kpc. The reddest dominates the continuum map (de-magnified L_FIR = (1.1$\pm$0.2)x10^13 L_sun), and excites strong water emission in both nuclear components via a powerful FIR radiation field from the intense star formation. A third star-forming component is most likely a region of a merging companion (dV ~ 500 km/s) exhibiting generally similar gas properties. The bluest component originates from a spatially distinct region, and photo-dissociation region (PDR) analysis suggests that it is lower density, cooler and forming stars less vigorously than the other components. Strikingly, it has very strong [NII] emission which may suggest an ionized, molecular outflow. This comprehensive view of gas properties and morphology in HLS0918 previews the science possible for a large sample of high-redshift galaxies once ALMA attains full sensitivity.

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arXiv2013

Star formation histories, extinction, and dust properties of strongly lensed z~1.5-3 star-forming galaxies from the Herschel Lensing Survey

Multi-wavelength, optical to IR/sub-mm observations of 5 strongly lensed galaxies identified by the Herschel Lensing Survey, plus two well-studied lensed galaxies, MS1512-cB58 and the Cosmic Eye, for which we also provide updated Herschel measurements, are used to determine the physical properties of z~1.5-3 star-forming galaxies close to or below the detection limits of blank fields. We constrain their stellar and dust content, determine star formation rates and histories, dust attenuation and extinction laws, and other related properties. We perform SED-fits of the full photometry of each object as well for the optical and infrared parts separately, exploring various parameters, including nebular emission. The IR observations and emission line measurements, where available, are used a posteriori constraints on the models. Besides the various stellar population models we explore, we use the observed IR/UV ratio to estimate the extinction and create "energy conserving models", that constrain most accurately the physical properties of our sources. Our sample has a median lensing-corrected IR luminosity ~ 3e11 Lsun, stellar masses between 2e9 and 2e11 Msun, and IR/UV luminosity ratios spanning a wide range. The dust masses of our galaxies are in the range 2 to 17e7 Msun, extending previous studies at the same redshift down to lower masses. We do not find any particular trend of the dust temperature Tdust with IR luminosity, suggesting an overall warmer dust regime at our redshift regardless of luminosity. Lensing enables us to study the detailed physical properties of individual IR-detected z~1.5-3 galaxies up to a factor ~10 fainter than achieved with deep blank field observations. We demonstrate that multi-wavelength observations combining stellar and dust emission can constrain star formation histories and extinction laws of star-forming galaxies.

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arXiv2013

An extended Herschel drop-out source in the center of AS1063, a 'normal' dusty galaxy at z=6.1 or SZ substructures?

In the course of our 870um APEX/LABOCA follow up of the Herschel Lensing Survey we have detected a source in AS1063 (RXC J2248.7-4431), that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel 'drop-out' with S_870/S_500>0.5. The 870um emission is extended and centered on the brightest cluster galaxy suggesting either a multiply imaged background source or substructure in the Sunyaev-Zel'dovich (SZ) increment due to inhomogeneities in the hot cluster gas of this merging cluster. We discuss both interpretations with emphasis on the putative lensed source. Based on the observed properties and on our lens model we find that this source could be the first SMG with a moderate far infrared luminosity (L_FIR<10^12 L_sol) detected so far at z>4. In deep HST observations we identified a multiply imaged z~6 source and we measured its spectroscopic redshift z=6.107 with VLT/FORS. This source could be associated with the putative SMG but it is most likely offset spatially by 10-30kpc and they could be interacting galaxies. With a FIR luminosity in the range [5-15]x10^{11} L_sol corresponding to a star formation rate in the range [80-260]M_sol/yr, this SMG would be more representative than the extreme starbursts usually detected at z>4. With a total magnification of ~25 it would open a unique window to the 'normal' dusty galaxies at the end of the epoch of reionization.

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arXiv2013

Mass assembly in quiescent and star-forming galaxies since z=4 from UltraVISTA

We estimate the galaxy stellar mass function and stellar mass density for star-forming and quiescent galaxies with 0.2 10^10.7Msun. For the mass function of the quiescent galaxies, we do not find any significant evolution of the high-mass end at z<1; however we observe a clear flattening of the faint-end slope. From z~3 to z~1, the density of quiescent galaxies increases over the entire mass range. Their comoving stellar mass density increases by 1.6 dex between z~3 and z~1 and by less than 0.2dex at z<1. We infer the star formation history from the mass density evolution and we find an excellent agreement with instantaneous star formation rate measurements at z<1.5, while we find differences of 0.2dex at z>1.5 consistent with the expected uncertainties. We also develop a new method to infer the specific star formation rate from the mass function of star-forming galaxies. We find that the specific star formation rate of 10^10Msun galaxies increases continuously in the redshift range 1<z<4. Finally, we compare our results with a semi-analytical model and find that these models overestimate the density of low mass quiescent galaxies by an order of magnitude, while the density of low-mass star-forming galaxies is successfully reproduced.

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arXiv2013

Herschel-ATLAS: a binary HyLIRG pinpointing a cluster of starbursting proto-ellipticals

Panchromatic observations of the best candidate HyLIRG from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z=2.41 galaxies across a ~100-kpc region - a cluster of starbursting proto-ellipticals. Via sub-arcsecond interferometric imaging we have measured accurate gas and star-formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submm/radio continuum and CO J=4-3, and double that in CO J=1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks -- a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have M(dyn) of several x 10^11 Msun, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star-formation rates place them ~>5x above the main sequence, which supposedly comprises large gas disks like these. Their high star-formation efficiencies are difficult to reconcile with a simple volumetric star-formation law. N-body and dark matter simulations suggest this system is the progenitor of a B(inary)-type ~10^14.6-Msun cluster.

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arXiv2013

The structure of the merging RCS 231953+00 Supercluster at z ~ 0.9

The RCS 2319+00 supercluster is a massive supercluster at z=0.9 comprising three optically selected, spectroscopically confirmed clusters separated by <3 Mpc on the plane of the sky. This supercluster is one of a few known examples of the progenitors of present-day massive clusters (10^{15} Msun by z~0.5). We present an extensive spectroscopic campaign carried out on the supercluster field resulting, in conjunction with previously published data, in 1961 high confidence galaxy redshifts. We find 302 structure members spanning three distinct redshift walls separated from one another by ~65 Mpc. The component clusters have spectroscopic redshifts of 0.901, 0.905 and 0.905. The velocity dispersions are consistent with those predicted from X-ray data, giving estimated cluster masses of ~10^{14.5} - 10^{14.9} Msun. The Dressler-Shectman test finds evidence of substructure in the supercluster field and a friends-of-friends analysis identified 5 groups in the supercluster, including a filamentary structure stretching between two cluster cores previously identified in the infrared by Coppin et al. (2012). The galaxy colors further show this filamentary structure to be a unique region of activity within the supercluster, comprised mainly of blue galaxies compared to the ~43-77% red-sequence galaxies present in the other groups and cluster cores. Richness estimates from stacked luminosity function fits results in average group mass estimates consistent with ~10^{13} Msun halos. Currently, 22% of our confirmed members reside in >~10^{13} Msun groups/clusters destined to merge onto the most massive cluster, in agreement with the massive halo galaxy fractions important in cluster galaxy pre-processing in N-body simulation merger tree studies.

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arXiv2012

Dynamical analysis of strong-lensing galaxy groups at intermediate redshift

We present VLT spectroscopic observations of 7 discovered galaxy groups between 0.3<z<0.7. The groups were selected from the Strong Lensing Legacy Survey (SL2S), a survey that consists in a systematic search for strong lensing systems in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We give details about the target selection, spectroscopic observations and data reduction for the first release of confirmed SL2S groups. The dynamical analysis of the systems reveals that they are gravitationally bound structures, with at least 4 confirmed members and velocity dispersions between 300 and 800 km/s. Their virial masses are between 10^13 and 10^14 M_sun, and so can be classified as groups or low mass clusters. Most of the systems are isolated groups, except two of them that show evidence of an ongoing merger of two sub-structures. We find a good agreement between the velocity dispersions estimated from the analysis of the kinematics of group galaxies and the weak lensing measurements, and conclude that the dynamics of baryonic matter is a good tracer of the total mass content in galaxy groups.

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arXiv2012

The Metallicity Evolution of Star-Forming Galaxies from Redshift 0 to 3: Combining Magnitude Limited Survey with Gravitational Lensing

We present a comprehensive observational study of the gas phase metallicity of star-forming galaxies from z ~ 0 -> 3. We combine our new sample of gravitationally lensed galaxies with existing lensed and non-lensed samples to conduct a large investigation into the mass-metallicity (MZ) relation at z > 1. We apply a self-consistent metallicity calibration scheme to investigate the metallicity evolution of star-forming galaxies as a function of redshift. The lensing magnification ensures that our sample spans an unprecedented range of stellar mass (3*10^{7}-6*10^{10} M_sun). We find that at the median redshift of z=2.07, the median metallicity of the lensed sample is 0.35 dex lower than the local SDSS star-forming galaxies and 0.18 dex lower than the z ~ 0.8 DEEP2 galaxies. We also present the z ~ 2 MZ relation using 19 lensed galaxies. A more rapid evolution is seen between z ~ 1->3 than z ~ 0 -> 1 for the high-mass galaxies (10^{9.5-11} M_sun), with almost twice as much enrichment between z ~ 1 -> 3 than between z ~ 1 -> 0. We compare this evolution with the most recent cosmological hydrodynamic simulations with momentum driven winds. We find that the model metallicity is consistent with the observed metallicity within the observational error for the low mass bins. However, for higher masses, the model over-predicts the metallicity at all redshifts. The over-prediction is most significant in the highest mass bin of 10^{10-11} M_sun.

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arXiv2012

Reduction and analysis of MUSE data

MUSE, the Multi Unit Spectroscopic Explorer, is a 2nd generation integral-field spectrograph under final assembly to see first light at the Very Large Telescope in 2013. By capturing ~ 90000 optical spectra in a single exposure, MUSE represents a challenge for data reduction and analysis. We summarise here the main features of the Data Reduction System, as well as some of the tools under development by the MUSE consortium and the DAHLIA team to handle the large MUSE datacubes (about 4x?10^8 pixels) to recover the original astrophysical signal.

astro-ph.IM↗

arXiv2012

Observational limits on the gas mass of a z=4.9 galaxy

We present the results of a search for molecular gas emission from a star-forming galaxy at z = 4.9. The galaxy benefits from magnification of 22 +/- 5x due to strong gravitational lensing by the foreground cluster MS1358+62. We target the CO(5-4) emission at a known position and redshift from existing Hubble Space Telescope/ACS imaging and Gemini/NIFS [OII]3727 imaging spectroscopy, and obtain a tentative detection at the 4.3sigma level with a flux of 0.104 +/- 0.024Jkm/s. From the CO line luminosity and assuming a CO-to-H2 conversion factor alpha=2, we derive a gas mass M_gas ~ 1^{+1}_{-0.6} x 10^9 M_sun. Combined with the existing data, we derive a gas fraction Mgas/(Mgas + M*) = 0.59^{+0.11}_{-0.06}. The faint line flux of this galaxy highlights the difficulty of observing molecular gas in representative galaxies at this epoch, and suggests that routine detections of similar galaxies in the absence of gravitational lensing will remain challenging even with ALMA in full science operations.

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arXiv2012

Hubble Space Telescope H-alpha imaging of star-forming galaxies at z = 1-1.5: evolution in the size and luminosity of giant HII regions

We present HST/WFC3 narrowband imaging of the H-alpha emission in a sample of eight gravitationally-lensed galaxies at z = 1 - 1.5. The magnification caused by the foreground clusters enables us to obtain a median source plane spatial resolution of 360pc, as well as providing magnifications in flux ranging from ~10x to ~50x. This enables us to identify resolved star-forming HII regions at this epoch and therefore study their H-alpha luminosity distributions for comparisons with equivalent samples at z ~ 2 and in the local Universe. We find evolution in the both luminosity and surface brightness of HII regions with redshift. The distribution of clump properties can be quantified with an HII region luminosity function, which can be fit by a power law with an exponential break at some cut-off, and we find that the cut-off evolves with redshift. We therefore conclude that `clumpy' galaxies are seen at high redshift because of the evolution of the cut-off mass; the galaxies themselves follow similar scaling relations to those at z = 0, but their HII regions are larger and brighter and thus appear as clumps which dominate the morphology of the galaxy. A simple theoretical argument based on gas collapsing on scales of the Jeans mass in a marginally unstable disk shows that the clumpy morphologies of high-z galaxies are driven by the competing effects of higher gas fractions causing perturbations on larger scales, partially compensated by higher epicyclic frequencies which stabilise the disk.

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arXiv2012

The A2667 Giant Arc at z=1.03: Evidence for Large-scale Shocks at High Redshift

We present the spatially resolved emission line ratio properties of a ~10^10 M_sun star-forming galaxy at redshift z=1.03. This galaxy is gravitationally lensed as a triple-image giant arc behind the massive lensing cluster Abell 2667. The main image of the galaxy has magnification factors of 14+/-2.1 in flux and ~ 2 by 7 in area, yielding an intrinsic spatial resolution of 115-405 pc after AO correction with OSIRIS at KECK II. The HST morphology shows a clumpy structure and the Hα kinematics indicates a large velocity dispersion with V_{max} sin(i)/σ~ 0.73, consistent with high redshift disk galaxies of similar masses. From the [NII]/Hα line ratios, we find that the central 350 parsec of the galaxy is dominated by star formation. The [NII]/Hα line ratios are higher in the outer-disk than in the central regions. Most noticeably, we find a blue-shifted region of strong [NII]/Hα emission in the outer disk. Applying our recent HII region and slow-shock models, we propose that this elevated [NII]/Hα ratio region is contaminated by a significant fraction of shock excitation due to galactic outflows. Our analysis suggests that shocked regions may mimic flat or inverted metallicity gradients at high redshift.

astro-ph.CO↗

arXiv2012

Strong Lensing by a Node of the Cosmic Web. The Core of MACS J0717.5+3745 at z=0.55

We present results of a strong-lensing analysis of MACS J0717.5+3745 (hereafter MACS J0717), an extremely X-ray luminous galaxy cluster at z=0.55. Observations at different wavelengths reveal a complex and dynamically very active cluster, whose core is connected to a large scale filament extended over several Mpc. Using multi-passband imaging data obtained with the Hubble Space Telescope Advanced Camera for Surveys (ACS), we identify 15 multiply imaged systems across the full field of view of ACS, five of which we confirmed spectroscopically in groundbased follow-up observations with the Keck telescope. We use these multiply imaged systems to constrain a parametric model of the mass distribution in the cluster core, employing a new parallelized version of the Lenstool software. The main result is that the most probable description of the mass distribution comprises four cluster-scale dark matter haloes. The total mass distribution follows the light distribution but strongly deviates from the distribution of the intra-cluster gas as traced by the X-ray surface brightness. This confirms the complex morphology proposed by previous studies. We interpret this segregation of collisional and collisionless matter as strong evidence of multiple mergers and ongoing dynamical activity. MACS J0717 thus constitutes one of the most disturbed clusters presently known and, featuring a projected mass within the ACS field of view (R=150"=960 kpc) of 2.11 +- 0.23 x 10^{15} M_{sun}, the system is also one of the most massive known.

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