Spectroscopic follow up of arclets in AC114 with the VLT

We present the first results on the VLT/FORS-1 spectroscopic survey of amplified sources and multiple images in the lensing cluster AC114. Background sources were selected in the cluster core, close to the critical lines, using photometric redshifts combined with lensing inversion criteria. Spectroscopic results are given, together with a brief summary of the properties of some of these high-z galaxies.Comment: 4pages. To appear in the Proceedings of the XXth Moriond Astrophysics Meeting "Cosmological Physics with Gravitational Lensing", eds. J.-P. Kneib, Y. Mellier, M. Moniez and J. Tran Thanh Van, Les Arcs, France, March 11th-18th 200

Properties of high-z galaxies as seen through lensing clusters

We discuss the first results obtained on the study of a sample of high-z galaxies (2 < z < 7), using the gravitational amplification effect in the core of lensing clusters. Sources are located close to the critical lines in clusters with well constrained mass distributions, and selected through photometric redshifts, computed on a large wavelength domain, and lens inversion techniques.Comment: 5 pages, 3 figures, Conference Proceedings of the "Clustering at High Redshift" Conference, June 29 to July 2, 1999, Marseille (France

ZEN2: A narrow J-band search for z~9 Lya emitting galaxies directed towards three lensing clusters

We present the results of a continuing survey to detect Lya emitting galaxies at redshifts z~9: the ZEN ("z equals nine'') survey. We have obtained deep VLT/ISAAC observations in the narrow J-band filter NB119 directed towards three massive lensing clusters: Abell clusters 1689, 1835, and 114. The foreground clusters provide a magnified view of the distant universe and permit a sensitive test for the presence of very high-redshift galaxies. We search for z~9 Lya emitting galaxies displaying a significant narrow-band excess relative to accompanying J-band observations that remain undetected in HST/ACS optical images of each field. No sources consistent with this criterion are detected above the unlensed 90% point-source flux limit of the narrow-band image, F_NB=3.7e-18 ergs/s/cm2. To date, the total coverage of the ZEN survey has sampled a volume at z~9 of approximately 1700 co-moving Mpc3 to a Lya emission luminosity of 1e43 erg/s. We conclude by considering the prospects for detecting z~9 Lya emitting galaxies in light of both observed galaxy properties at z7.Comment: 7 pages, MNRAS accepte

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).Comment: 11 pages, 8 figures. Accepted for publication in A&

Constraining the population of 6 < z < 10 star-forming galaxies with deep near-IR images of lensing clusters

(abridged) We present the first results of our deep survey of lensing clusters aimed at constraining the abundance of star-forming galaxies at z~6-10. Deep near-IR photometry of two lensing clusters (A1835 and AC114) was obtained with ISAAC/VLT. These images, combined with existing data in the optical bands, including HST images, were used to select very high redshift candidates at z>~6 among the optical-dropouts. We have identified 18(8) first and second-category optical dropouts in A1835 (AC114), detected in more than one filter up to H(Vega)~23.8 (AB~25.2,uncorrected for lensing). Among them, 8(5) exhibit homogeneous SEDs compatible with star-forming galaxies at z>~6, and 5(1) are more likely intermediate-redshift EROs based on luminosity considerations. We have also identified a number of fainter sources in these fields fulfilling our photometric selection and located around the critical lines. We use all these data to make a first attempt at constraining the density of star-forming galaxies present at 6<z<10 using lensing clusters. Taken at face value, it appears that the number of candidates found seems to be higher than the one achieved in blank fields with similar photometric depth in the near-IR. The luminosity function derived for z>6 candidates appears compatible with that of LBGs at z~3. The turnover observed by Bouwens et al. (2005) towards the bright end relative to the z~3 LF is not observed in this sample. Also the upper limit for the UV SFR density at z~6-10 is compatible with the usual values derived at z~5-6, but higher than the estimates obtained in the NICMOS Ultra Deep Field (UDF). Increasing the number of blank and lensing fields with ultra-deep near-IR photometry is essential to get more accurate constraints on the abundance of z>6 galaxies.Comment: 35 pages, 19 figures; Accepted for publication in A&A; Corrected missing separation line between First/Second candidates in Table C.2 and added corrections from language editor. Full version with high resolution figures available at http://astro.caltech.edu/~johan/publi.htm

EROs found behind lensing clusters. II. Stellar populations and dust properties of optical dropout EROs and comparison with related objects

We determine the nature, redshift, stellar populations and dust properties of optically faint or non-detected extremely red objects (ERO) found from our survey of the lensing clusters A1835 and AC114. We perform SED fitting and use deep optical, HST, VLT, Spitzer data, and for some objects and sub-mm data. For most of the lensed EROs we find photometric redshifts showing a strong degeneracy between "low-z" (z~1-3) and high-z (z~6-7). Although formally best fits are often found at high-z, their resulting bright absolute magnitudes, the number density of these objects, and in some cases Spitzer photometry or longer wavelength observations, suggest strongly that all of these objects are at "low-z". The majority of these objects are best fitted with young (<~ 0.5-0.7 Gyr) and dusty starbursts. Indications for strong extinction, with A_V~2.4-4, are found in some objects. For dusty objects star formation rates (SFR) have been estimated from the bolometric luminosity determined after fitting of semi-empirical starburst, ERO, and ULIRG templates. Typically we find SFR~(1-18) Msun/yr. Again, SMMJ14009+0252 stands out as a LIRG with SFR 1000 Msun/yr. Concerning the comparison objects, we argue that the massive post-starburst z~6.5 galaxy candidate HUDF-J2 showing observed properties very similar to our EROs, is more likely a dusty starburst at z~2.3-2.6. This interpretation also naturally explains the observed 24 micron emission. Both empirically and from our SED fits we find that the IRAC selectec EROs from Yan et al (2004) show very similar properties to our lensed EROs. Reasonable fits are found for most of them with relatively young and dusty stellar populations.Comment: 18 pages, 17 figures, accepted for publication in Astronomy and Astrophysic

Cluster Lenses

Clusters of galaxies are the most recently assembled, massive, bound structures in the Universe. As predicted by General Relativity, given their masses, clusters strongly deform space-time in their vicinity. Clusters act as some of the most powerful gravitational lenses in the Universe. Light rays traversing through clusters from distant sources are hence deflected, and the resulting images of these distant objects therefore appear distorted and magnified. Lensing by clusters occurs in two regimes, each with unique observational signatures. The strong lensing regime is characterized by effects readily seen by eye, namely, the production of giant arcs, multiple-images, and arclets. The weak lensing regime is characterized by small deformations in the shapes of background galaxies only detectable statistically. Cluster lenses have been exploited successfully to address several important current questions in cosmology: (i) the study of the lens(es) - understanding cluster mass distributions and issues pertaining to cluster formation and evolution, as well as constraining the nature of dark matter; (ii) the study of the lensed objects - probing the properties of the background lensed galaxy population - which is statistically at higher redshifts and of lower intrinsic luminosity thus enabling the probing of galaxy formation at the earliest times right up to the Dark Ages; and (iii) the study of the geometry of the Universe - as the strength of lensing depends on the ratios of angular diameter distances between the lens, source and observer, lens deflections are sensitive to the value of cosmological parameters and offer a powerful geometric tool to probe Dark Energy. In this review, we present the basics of cluster lensing and provide a current status report of the field.Comment: About 120 pages - Published in Open Access at: http://www.springerlink.com/content/j183018170485723/ . arXiv admin note: text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author

Motor-Coordination-Dependent Learning, More than Others, Is Impaired in Transgenic Mice Expressing Pseudorabies Virus Immediate-Early Protein IE180

The cerebellum in transgenic mice expressing pseudorabies virus immediate-early protein IE180 (TgIE96) was substantially diminished in size, and its histoarchitecture was severely disorganized, resulting in severe ataxia. TgIE96 mice can therefore be used as an experimental model to study the involvement of cerebellar circuits in different learning tasks. The performance of three-month-old TgIE96 mice was studied in various behavioral tests, including associative learning (classical eyeblink conditioning), object recognition, spatial orientation (water maze), startle response and prepulse inhibition, and passive avoidance, and compared with that of wild-type mice. Wild-type and TgIE96 mice presented similar reflexively evoked eyeblinks, and acquired classical conditioned eyelid responses with similar learning curves for both trace and delay conditioning paradigms. The two groups of mice also had similar performances during the object recognition test. However, they showed significant differences for the other three tests included in this study. Although both groups of animals were capable of swimming, TgIE96 mice failed to learn the water maze task during the allowed time. The startle response to a severe tone was similar in both control and TgIE96 mice, but the latter were unable to produce a significant prepulse inhibition. TgIE96 mice also presented evident deficits for the proper accomplishment of a passive avoidance test. These results suggest that the cerebellum is not indispensable for the performance of classical eyeblink conditioning and for object recognition tasks, but seems to be necessary for the proper performance of water maze, prepulse inhibition, and passive avoidance tests

Relation of radio-quiet quasars to galaxy clusters at z &lt; 0.3

We investigate whether radio-quiet quasars (RQQs) with z &lt; 0.3 (and predominantly of low luminosity) are located preferentially in specific regions with respect to the centres and boundaries of neighbouring galaxy clusters. This way of characterizing the environment of RQQs differs from previous studies, which relied on the galaxy excess statistics within small radii around the quasars. For the detection of galaxy clusters we use a robust, semiparametric method based on a maximum likelihood estimate applied to Voronoi tessellation and enhanced by a colour-cut approach, allowing boundary determination and redshift estimates. We find that most of the RQQs reside within 3 h -1 Mpc of the centre of a galaxy cluster with comparable redshift and that none of them lies in the core itself. About 20 per cent of the investigated quasars reside between two galaxy clusters, which are possibly at an early stage of merger. Consequently, we suggest that quasars found in rich environments are associated with cluster mergers whereas those found in poorer environments are associated with infall towards a cluster. The information on larger scales provided by our analysis thus allows a clearer interpretation of the diverse environments that have for many years been reported in the literature for smaller scales. We discuss our findings in the context of existing quasar formation models and suggest that at least two formation mechanisms coexist. Additionally, we confirm, using multiple data sets, that low-redshift quasars follow a narrow channel of width ∼10 h -1 Mpc around the large-scale structure (LSS) traced by galaxy clusters, in agreement with the first report of this effect by Söchting, Clowes and Campusano. Such a result, if it applies to quasars at higher redshifts, has the potential to explain the clustering of quasars on scales &lt;10 h -1 Mpc found initially by Shanks et al. The association of the LSS in clusters with the spatial distribution of quasars is not reproduced by samples of narrow emission-line galaxies (NELGs), indicating that the occurrence of NELGs does not require the same environmental conditions as that of quasars