arXiv subjects

J. -P. Kneib

Publications and source records attributed to J. -P. Kneib.

At least 181 records · Page 10Linked to original sources

arXiv2004

Star-forming galaxies at z ~ 2: a major science case for the EMIR/GOYA survey on GTC

We present the first results of a project aiming to derive the physical properties of high-redshift lensed galaxies, intrinsically fainter than the Lyman break galaxies currently observed in the field. From FORS and ISAAC spectroscopy on the VLT, we use the full rest-frame UV-to-optical range to derive the physical properties (SFR, extinction, chemical abundances, dynamics, mass, etc) of low-luminosity z ~ 2 star-forming galaxies. Although the sample is still too small for statistical studies, these results give an insight into the nature and evolutionary status of distant star-forming objects and their link with present-day galaxies. Such a project will serve as a basis for the scientific analysis of the EMIR/GOYA survey on the GTC.

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arXiv2004

The nature of a gravitationally lensed sub-millimetre arc in MS0451.6-0305: two interacting galaxies at z~2.9?

We present a new SCUBA image of the cluster MS0451.6-0305, which exhibits strong, extended sub-mm flux at 850 microns. The most striking feature in the map is an elongated region of bright sub-mm emission, with a flux density of >10 mJy over several beam-sizes. This region is apparently coincident with a previously known optical arc (which turns out to be a strongly lensed Lyman Break Galaxy at z=2.911), as well as with a newly identified multiply-imaged ERO (Extremely Red Object) pair predicted to be at a similar, if not identical redshift. By combing a detailed lensing model with deep images from HST, Chandra, CFHT, JCMT, and spectra from the VLT, we conclude that both the strongly lensed optical arc and ERO systems have properties consistent with known sub-mm emitters. Using a simple model for the two sources, we estimate that the multiply-lensed EROs contribute the majority of the flux in the SCUBA lensed arc. Correcting for the lensing amplification, we estimate that the inherent 850 micron fluxes for both objects are ~0.4 mJy. If the LBG and ERO pair are truly at the same redshift, then they are separated by only ~10 kpc in the source plane, and hence constitute an interacting system at z~2.9. Higher angular resolution observations in sub-mm/mm will permit us to more accurately separate the contribution from each candidate, and better understand the nature of this system.

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arXiv2004

Observing z>7 sources with the GTC

We present the first results obtained from our pilot ultra-deep near-IR survey with ISAAC/VLT, aimed at the detection of z>7 sources using lensing clusters as natural Gravitational Telescopes. Evolutionary synthesis models of PopIII and extremely metal-poor starbursts have been used to derive observational properties expected for these high-z galaxies, such as expected magnitudes and colors, line fluxes for the main emission lines, etc. These models have allowed us to define fairly robust selection criteria to find z~ 7-10 galaxies based on broad-band near-IR photometry in combination with the traditional Lyman drop-out technique. The magnification in the core of lensing clusters improves the search efficiency and subsequent spectroscopic follow up. The method used to identify sources and the first results obtained are presented, in particular the first spectroscopic confirmation of a z=10 candidate. The research efficiency will be significantly improved by the future near-IR multi-object facilities such as EMIR/GTC and KMOS/VLT-2, and later by the JWST.

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arXiv2004

ISAAC/VLT observations of a lensed galaxy at z=10.0

We report the first likely spectroscopic confirmation of a z 10.0 galaxy from our ongoing search for distant galaxies with ISAAC/VLT. Galaxy candidates at z >~ 7 are selected from ultra-deep JHKs images in the core of gravitational lensing clusters for which deep optical imaging is also available, including HST data. The object reported here, found behind Abell 1835, exhibits a faint emission line detected in the J band, leading to z=10.0 when identified as Ly-a, in excellent agreement with the photometric redshift determination. Redshifts z < 7 are very unlikely for various reasons we discuss. The object is located on the critical lines corresponding to z=9 to 11. The magnification factor μranges from 25 to 100. For this object we estimate SFR(Ly-a) (0.8-2.2) Msun/yr and SFR(UV) (47-75) Msun/yr, both uncorrected for lensing. The steep UV slope indicates a young object with negligible dust extinction. SED fits with young low-metallicity stellar population models yield (adopting mu=25) a lensing corrected stellar mass of M*~8.e+6 Msun, and luminosities of 2.e+10 Lsun, corresponding to a dark matter halo of a mass of typically M_tot>~ 5.e+8 Msun. In general our observations show that under excellent conditions and using strong gravitational lensing direct observations of galaxies close to the ``dark ages'' are feasible with ground-based 8-10m class telescopes.

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arXiv2003

Discovery of a faint R-band drop-out: a strongly reddened lensed star forming galaxy at z=1.68

We report the discovery of an unusual emission line galaxy at redshift z=1.68 found from near-IR imaging and spectroscopic observations with ISAAC/VLT of a faint gravitationally lensed R-band drop-out behind the lensing cluster Abell 1835. From the emission lines of [O_III], and H_beta this galaxy shows a moderate to high excitation and line equivalent widths typical of relatively metal-poor HII galaxies. Its apparent J magnitude translates to an absolute B-band magnitude M_B ~ -16.4 once corrected for a gravitational magnification of 1.8 magnitudes. This makes it one of the faintest intermediate redshift galaxiesknown so far. From the presence of emission lines and the available VRIJHK photometry we determine constraints on its dominant stellar population. The only viable fit found is for a fairly young (~ 6-9 Myr) burst suffering from a considerable extinction (A_v ~ 1.2-1.8 mag). We find that this object resembles strongly HII galaxies and intermediate redshift compact emission line galaxies, albeit suffering from a larger extinction than usual. We also discuss the possible contamination introduced by such R-band drop-out galaxies in searches for z > 5 galaxies.

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arXiv2003

Measuring the matter distribution within z=0.2 cluster lenses with XMM-Newton

We present an analysis of 7 clusters observed by XMM as part of our survey of 17 most X-ray luminous clusters of galaxies at z=0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using public software, we have set up an automated pipeline to reduce the EPIC MOS & pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM deep spectro-imaging of these clusters allowed us to fit a standard beta-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations.

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arXiv2003

Searches for high redshift galaxies using gravitational lensing

We present different methods used to identify high redshift (z>5) objects in the high-magnification regions of lensing galaxy clusters, taking advantage of very well constrained lensing models. The research procedures are explained and discussed. The detection of emission lines in the optical/NIR spectra, such as Lyman-alpha, allows us to determine the redshift of these sources. Thanks to the lensing magnification, it is possible to identify and to study more distant or intrinsically fainter objects with respect to standard field surveys.

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arXiv2003

An ISOCAM survey through gravitationally lensing galaxy clusters

ISOCAM was used to perform a deep survey through three gravitationally lensing clusters of galaxies. Nearly seventy sq. arcmin were covered over the clusters A370, A2218 and A2390. We present maps and photometry at 6.7 & 14.3 microns, showing a total of 145 mid-IR sources and the associated source counts. The 15 micron counts reach the faintest level yet recorded. All sources have counterparts in the optical or near-IR. Models of the clusters were used to correct for the effects of lensing, which increases the sensitivity of the survey. Seven of fifteen SCUBA sources were detected at 15 microns. Five have redshift between 0.23 & 2.8, with a median of 0.9. The field sources were counted to a lensing-corrected sensitivity of 30 microJy at 15 microns, and 14 microJy at 7 microns. The counts, corrected for completeness, contamination by cluster sources and lensing, confirm and extend findings of an excess by a factor of ten in the 15 micron population with respect to source models with no evolution. Source redshifts are mostly between 0.4 and 1.5. For the counts at 7 microns, integrating from 14 microJy to 460 microJy, we resolve 0.49+/-0.2 nW.m^(-2).sr^(-1) of the infrared background light (IBL) into discrete sources. At 15 microns we include the counts from other ISOCAM surveys to integrate from 30 microJy to 50 mJy, two to three times deeper than unlensed surveys, to resolve 2.7+/-0.62 nW.m^(-2).sr^(-1) of the IBL. These values are 10% and 55%, respectively, of the upper limit to the IBL, derived from photon-photon pair production of the TeV gamma rays from BL-Lac sources on the IBL photons. However, recent detections of TeV gamma rays from the z=0.129 BL Lac H1426+428 suggest that the 15 micron background reported implies substantial absorption of TeV photons from that source.

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arXiv2003

LBQS 1429-0053: a binary quasar rather than a lensed quasar

Very deep ESO/VLT FORS1 and ISAAC images, as well as HST NICMOS2 data are used to infer the nature of the quasar pair LBQS 1429-0053 A and B, either a binary quasar or a doubly-imaged lensed quasar. Direct search of a putative lensing galaxy is unsuccessful . Moreover, no galaxy overdensity close to the quasar pair is found. A weak shear analysis of the field also fails at detecting any concentration of dark matter and weakens the hypothesis of a dark lens. The only sign of a possible lens consists in a group of 5 objects at z~1, within a radius of 5'', from the quasar pair. Considering this group as the lensing potential does not allow to reproduce the image position and flux ratio of the quasars. Our deep R-band image shows a blue, extended object at the position of quasar A, which is consistent with either being the lensed quasar A host, or being an intervening galaxy at lower redshift. Unless future very deep optical images demonstrate that this object is actually the lensed host of LBQS 1429-0053, we conclude that there is very little evidence for this quasar being lensed. Therefore, we are led to declare LBQS 1429-0053 A and B a genuine binary quasar.

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arXiv2003

A wide field Hubble Space Telescope study of the cluster CL0024+16 at z=0.4. I: morphological distributions to 5 Mpc radius

We describe a new wide field Hubble Space Telescope survey of the galaxy cluster Cl0024+16 (z~0.4) consisting of a sparse-sampled mosaic of 39 Wide Field and Planetary Camera 2 images which extends to a cluster radius of 5 Mpc. [Abridged] We examine both the morphology-radius (T-R) and morphology-density (T-Sigma) relations and demonstrate sensitivities adequate for measures from the core to a radius of 5 Mpc, spanning over 3 decades in local projected density. The fraction of early-type galaxies declines steeply from the cluster center to 1 Mpc radius and more gradually thereafter, asymptoting towards the field value at the periphery. We discuss our results in the context of three distinct cluster zones, defined according to different physical processes that may be effective in transforming galaxy morphology in each. By treating infalling galaxies as isolated test particles, we deduce that the most likely processes responsible for the mild gradient in the morphological mix outside the virial radius are harassment and starvation. Although more data are needed to pin down the exact mechanisms, starvation seems more promising in that it would naturally explain the stellar and dynamical homogeneity of cluster E/S0s. However, we find significant scatter in the local density at any given radius outside 0.5 Mpc, and that the same T-Sigma relation holds in subregions of the cluster, independent of location. In this hitherto unprobed region, where the potential of the cluster is weak, galaxies apparently retain their identities as members of infalling sub-groups whose characteristic morphological properties remain intact. Only upon arrival in the central regions is the substructure erased, as indicated by the tight correlation between cluster radius and Sigma.

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arXiv2002

Physical properties of two low-luminosity z ~ 1.9 galaxies behind the lensing cluster AC 114

We present VLT/ISAAC near-infrared spectroscopy of two gravitationally-lensed z ~ 1.9 galaxies, A2 and S2, located behind the cluster AC 114. Thanks to large magnification factors, we have been successful in detecting rest-frame optical emission lines in star-forming galaxies 1 to 2 magnitudes fainter than in previous studies of Lyman break galaxies (LBGs) at z ~ 3. From the Ha luminosity, we estimate star formation rates (SFRs) which are 7 to 15 times higher than those inferred from the UV continuum flux at 1500 ang without dust extinction correction. The behavior of S2 and A2 in terms of O/H and N/O abundance ratios are very different, and they are also different from typical LBGs at z ~ 3. S2 is a low-metallicity object (Z ~ 0.03 Zsun) with a low N/O ratio, similar to those derived in the most metal-poor nearby HII galaxies. In contrast, A2 is a high-metallicity galaxy (Z ~ 1.3 Zsun) with a high N/O abundance ratio, similar to those derived in the most metal-rich starburst nucleus galaxies. The virial masses, derived from emission-line widths, are 0.5 and 2.4 x 10^10 Msun, for S2 and A2 respectively. Thanks to the gravitational amplification, the line profiles of S2 are spatially resolved, leading to a velocity gradient of +- 240 km/s, which yields a dynamical mass of ~ 1.3 x 10^10 Msun within the inner 1 kpc radius. Combining these new data with the sample of LBGs at z ~ 3, we conclude that these three galaxies exhibit different physical properties in terms of SFRs, abundance and mass-to-light ratios, and reddening. High-redshift galaxies of different luminosities could thus have quite different star formation histories (abridged version).

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arXiv2002

The Submillimeter Properties of Extremely Red Objects

We use deep near-infrared and submillimeter observations of three massive lensing cluster fields, A370, A851, and A2390, to determine the average submillimeter properties of a K'-selected sample. The 38 Extremely Red Objects (EROs; I-K'>4) with K'<21.25 have a very significant error-weighted mean 850-micron flux of 1.58 +/- 0.13 mJy. The ERO contribution to the 850-micron background is 1.88 +/- 0.16 x 10^4 mJy per square degree, or about half the background light. The 17 Very Red Objects (VROs; 3.5<I-K'<4) are also significantly detected (1.32 +/- 0.19 mJy), bringing the combined VRO and ERO contribution to 2.59 +/- 0.19 x 10^4 mJy per square degree. There is a substantial systematic uncertainty (about a factor of two) in this value due to field-to-field variation, but even with this uncertainty it is clear that a large fraction of the 850-micron background arises from red objects. An analysis of the VRO and ERO number counts shows that half of the population's 850-micron light arises in objects with demagnified magnitudes K'<20 and half in fainter objects. On the basis of the I-J versus J-K' colors of the galaxies, the bulk of the submillimeter signal appears to arise from the dusty starburst galaxies in the red object population rather than from the high-redshift elliptical galaxies.

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arXiv2002

Pseudo Elliptical Lensing Mass Model: Application to the NFW Mass Distribution

We introduce analytical expressions for a pseudo fully analytical elliptical projected Navarro, Frenk & White (NFW) mass profile to be used in lensing equations. We propose a formalism that incorporates the ellipticity into the expression for the lens potential, producing a pseudo-elliptical mass distribution. This approach can be implemented to any circular mass profile for which the projected mass profile Sigma(r) and the deflection angle profile alpha(r) both have analytical expressions; however the potential does not necessarily need to take an analytical form. We apply this new formalism to the NFW mass distribution and study how well this pseudo-elliptical NFW model describes an elliptical mass distribution. We conclude that the pseudo-elliptical NFW model is a good description of elliptical mass distributions provided that the ellipticity of the projected mass distribution is <~ 0.4, although with a slightly boxy distribution.

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arXiv2002

Physical Properties of Low-Luminosity Galaxies at z ~ 2

We report the results obtained from ISAAC/VLT near-IR spectroscopy of two low-luminosity z ~ 1.9 galaxies located in the core of the lensing cluster AC114. The amplification factor allowed to obtain, for the first time, physical properties (SFR, abundance ratios, mass, etc) of star-forming galaxies, 1 to 2 magnitudes fainter than in previous studies of Lyman-break galaxies at z ~ 3.

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arXiv2002

Submillimeter Galaxies

A cosmologically significant population of very luminous high-redshift galaxies has recently been discovered at submm wavelengths. Advances in submm detector technologies have opened this new window on the distant Universe. Here we discuss the properties of the high-redshift submm galaxies, their significance for our understanding of the process of galaxy formation, and the selection effects that apply to deep submm surveys. The submm galaxies generate a significant fraction of the energy output of all galaxies in the early Universe. We emphasize the importance of studying a complete sample of submm galaxies, and stress that because they are typically very faint in other wavebands, these follow-up observations are very challenging. Finally, we discuss the surveys that will be made using the next generation of submm-wave instruments under development.

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arXiv2002

Constraining the Cosmological Parameters using Strong Lensing

We investigate the potentiality of using strong lensing clusters to constrain the cosmological parameters Omega_m and Omega_lambda. The existence of a multiple image system with known redshift allows, for a given (Omega_m, Omega_lambda) cosmology, absolute calibration of the total mass deduced from lens modelling. Recent Hubble Space Telescope (HST) observations of galaxy clusters reveal a large number of multiple images, which are predicted to be at different redshifts. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Omega_m,Omega_lambda) through ratios of angular diameter distances, independently of any external assumptions. For a regular/relaxed cluster observed by HST with 3 multiple image systems, each with different spectroscopic redshifts, we show by analytic calculation that the following uncertainties can be expected: Omega_m=0.30 +/- 0.11, Omega_lambda=0.70 +/- 0.23 or Omega_m=1.00 +/- 0.17, Omega_lambda=0.00 +/- 0.48 for the two most popular world models. Numerical tests on simulated data confirm these good constraints, even in the case of more realistic cluster potentials, such as bimodal clusters, or when including perturbations by galaxies. To investigate the sensitivity of the method to different mass profiles, we also use an analytic ``pseudo-elliptical'' Navarro, Frenk & White profile in the simulations. These constraints can be improved if more than 3 multiple images with spectroscopic redshifts are observed, or by combining the results from different clusters. Some prospects on the determination of the cosmological parameters with gravitational lensing are given.

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arXiv2002

Constraints on (Omega_M0, Omega_Lambda) from strong lensing in AC 114

We use a strong lensing inversion in the cluster of galaxies AC 114 to derive constraints on the cosmological parameters Omega_M0 and Omega_Lambda. If it is possible to measure spectroscopically the redshifts of many multiple images then one can in principle constrain (Omega_M0,Omega_Lambda) through ratios of angular diameter distances, independently of any external assumptions. Numerical tests on simulated data show rather good constraints from this test. We also use an analytic ``pseudo-elliptical'' NFW profile in the simulations, following the general new formalism we present. An application to AC 114 favors a flat Universe, an EdS model being marginally ruled out.

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arXiv2002

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: III. A Multiply-imaged Extremely Red Galaxy at z=1.6

We present near-infrared spectroscopy and Hubble Space Telescope (HST) imaging of EROJ003707+0909.5, the brightest of three gravitationally-lensed images of an Extremely Red Object (ERO) at z=1.6, in the field of the massive cluster A68 (z=0.255). We exploit the superlative resolution of our HST data and the enhanced spatial resolution and sensitivity afforded by the lens amplification to reconstruct the source-plane properties of this ERO. Our morphological and photometric analysis reveals that EROJ003707 is an L* early-type disk-galaxy and we estimate that ~10 per cent of EROs with (R-K)>=5.3 and K<=21 may have similar properties. The unique association of passive EROs with elliptical galaxies therefore appears to be too simplistic. We speculate on the evolution of EROJ003707: if gas continues to cool onto this galaxy in the manner predicted by hierarchical galaxy formation models, then by the present day, EROJ003707 could evolve into a very luminous spiral galaxy.

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