arXiv subjects

J. Richard

Publications and source records attributed to J. Richard.

137 records · Page 8Linked to original sources

arXiv2006

Searching for the first galaxies through gravitational lenses

Observing the first galaxies formed during the reionisation epoch, i.e. approximately within the first billion years after the Big Bang, remains one of the challenges of contemporary astrophysics. Several efforts are being undertaken to search for such remote objects. Combining the near-IR imaging power of the VLT and the natural effect of strong gravitational lensing our pilot program has allowed us to identify several galaxy candidates at redshift 6 <~ z <~ 10. The properties of these objects and the resulting constraints on the star formation rate density at high redshift are discussed. Finally we present the status of follow-up observations (ISAAC spectroscopy, HST and Spitzer imaging) and discuss future developments.

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arXiv2005

VIMOS-IFU survey of z~0.2 massive galaxy clusters. I. Observations of the strong lensing cluster Abell 2667

(abridged) We present extensive multi-color imaging and low resolution VIMOS Integral Field Unit spectroscopic observations of the X-ray luminous cluster Abell 2667 (z=0.233). An extremely bright giant gravitational arc (z=1.0334) is easily identified as part of a triple image system and other fainter multiple images are also revealed by the HST-WFPC2 images. The VIMOS-IFU observations cover a field of view of 54'' x 54'' and enable us to determine the redshift of all galaxies down to V=22.5. Furthermore, redshifts could be identified for some sources down to V=23.2. In particular we identify 21 cluster members in the cluster inner region, from which we derive a velocity dispersion of σ=960 km/s, corresponding to a total mass of 7.1 x 10^{13} solar masses within a 110 kpc radius. Using the multiple images constraints and priors on the mass distribution of cluster galaxy halos we construct a detailed lensing mass model leading to a total mass of 2.9 x 10^{13} solar masses within the Einstein radius (16 arcsec). The lensing mass and dynamical mass are in good agreement although the dynamical one is much less accurate. Comparing these measurements with published X-ray analysis, is however less conclusive. Although the X-ray temperature matches the dynamical and lensing estimates, the published NFW mass model derived from the X-ray measurement with its small concentration of c ~3 can not account for the large Einstein radius observed in this cluster. A larger concentration of ~6 would however match the strong lensing measurements. These results are likely reflecting the complex structure of the cluster mass distribution, underlying the importance of panchromatic studies from small to large scale in order to better understand cluster physics.

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arXiv2005

Looking for z>7 galaxies with the Gravitational Telescope

We summarize the main results obtained recently by our group on the identification and study of very high-z galaxies (z>7) using lensing clusters as natural gravitational telescopes. A description of our pilot survey with ISAAC/VLT is presented, aimed at the spectroscopic confirmation of z>7 candidate galaxies photometrically selected from deep near-IR, HST and optical ground-based imaging. The first results issued from this survey are discussed, in particular the global photometric properties of our high-z candidates, and the implications for the global star formation rate at very high-z.

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arXiv2004

Spitzer and Hubble Constraints on the Physical Properties of the z~7 Galaxy Strongly Lensed by Abell 2218

We report the detection of a z~7 galaxy strongly lensed by the massive galaxy cluster Abell 2218 (z=0.175) at 3.6 and 4.5 um using the Spitzer Observatory and at 1.1 um using the Hubble Space Telescope. The new data indicate a refined photometric redshift in the range of 6.6-6.8 depending on the presence of Ly-alpha emission. The spectral energy distribution is consistent with having a significant Balmer break, suggesting that the galaxy is in the poststarburst stage with an age of at least ~50 Myr and quite possibly a few hundred Myr. This suggests the possibility that a mature stellar population is already in place at such a high redshift. Compared with typical Lyman break galaxies at z~3-4, the stellar mass is an order of magnitude smaller (~10^{9} Msun), but the specific star formation rate (star formation rate/M_{star}) is similarly large (> 10^{-9} yr^{-1}), indicating equally vigorous star-forming activity.

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arXiv2004

Very High-Redshift Lensed Galaxies

We review in this paper the main results recently obtained on the identification and study of very high-z galaxies usinglensing clusters as natural gravitational telescopes. We present in detail our pilot survey with ISAAC/VLT, aimed at the detection of z>7 sources. Evolutionary synthesis models for extremely metal-poor and PopIII starbursts have been used to derive the 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 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 first results issued from our photometric and spectroscopic survey are discussed, in particular the preliminary confirmation rate, and the global properties of our high-z candidates, including the latest results on the possible z=10.0 candidate A1835-1916. The search efficiency should be significantly improved by the future near-IR multi-object ground-based and space facilities. However, strong lensing clusters remain a factor of ~5-10 more efficient than blank fields in this redshift domain, within the FOV of a few arcminutes around the cluster core, for the typical depth required for this survey project.

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arXiv2004

Response to "Reanalysis of the spectrum of the z=10 galaxy ISAAC/VLT observations of a lensed galaxy at z=10.0" by Weatherley et al. (astro-ph/0407150)

In a recent posting of a submitted paper Weatherley et al. re-analyse the spectroscopic data from our observations of Abell 1835 IR 1916, a galaxy we claimed to be at redshift z=10.0 (Pello et al., 2004, A&A, 416, L35). They conclude that the emission line is not detected in their analysis. Although their reduction procedure is accurate and robust, there are several differences with ours. The most important one concerns the stacking of the spectral frames. In the case of compact target sources [here: seeing-limited object,~3 pixels FWHM in the spectral direction, on a 1" (~7 pixels) wide slit] spectral shifts occur between individual frames. Our reduction corrects for this effect using a nearby strong emission line from a compact reference object, as described in Pello et al. However, Weatherley et al. neglect this effect. This difference turns out to be crucial. E.g. adopting their combination scheme as closely as possible but correcting for the spectral drifts we recover the line detection. We conclude that more work is needed to fully understand the origin of our differences. However, their non-detection claim needs further investigation and cannot be uphold based on the arguments presented in their original version of the paper. More information is beeing posted on http://webast.ast.obs-mip.fr/people/roser/z10_spectroscopy_discussion. With this material we also invite other researchers to re-analyse independently the ISAAC spectroscopic observations.

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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

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

Properties of Faint Distant Galaxies as seen through Gravitational Telescopes

This paper reviews the most recent developments related to the use of lensing clusters of galaxies as Gravitational Telescopes in deep Universe studies. We summarize the state of the art and the most recent results aiming at studying the physical properties of distant galaxies beyond the limits of conventional spectroscopy. The application of photometric redshift techniques in the context of gravitational lensing is emphasized for the study of both lensing structures and the background population of lensed galaxies. A presently ongoing search for the first building blocks of galaxies behind lensing clusters is presented and discussed.

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