arXiv subjects

J. -P. Kneib

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

At least 163 records · Page 9Linked to original sources

arXiv2006

An ISOCAM survey through gravitationally lensing galaxy clusters. IV. Luminous infrared galaxies in Cl 0024+1654 and the dynamical status of clusters

Observations of the core of the massive cluster Cl 0024+1654, at a redshift z=0.39, were obtained with the Infrared Space Observatory using ISOCAM at 6.7 mum and 14.3 mum (hereafter 15 mum). Thirty five sources were detected at 15 mum and thirteen of them are spectroscopically identified with cluster galaxies. The remaining sources consist of four stars, one quasar, one foreground galaxy, three background galaxies and thirteen sources with unknown redshift. The ISOCAM sources have best-fit SEDs typical of spiral or starburst models observed 1 Gyr after the main starburst event. The median infrared luminosity of the twelve cluster galaxies is 1.0x10^11 Lsun, with 10 having infrared luminosity above 9x10^10 Lsun, and so lying near or above the 1x10^11 Lsun threshold for identification as a luminous infrared galaxy (LIRG). The [OII] star formation rates obtained for 3 cluster galaxies are one to two orders of magnitude lower than the infrared values, implying that most of the star formation is missed in the optical because it is enshrouded by dust in the starburst galaxy. The counterparts of about half of the 15 mum cluster sources are blue, luminous, star-forming systems and the type of galaxy that is usually associated with the Butcher-Oemler effect. Dust obscuration may be a major cause of the 15 mum sources appearing on the cluster main sequence. The majority of the ISOCAM sources in the Butcher-Oemler region of the colour-magnitude diagram are best fit by spiral-type SEDs whereas post-starburst models are preferred on the main sequence, with the starburst event probably triggered by interaction with one or more galaxies. Finally, the mid-infrared results on Cl 0024+1654 are compared with four other clusters observed with ISOCAM.

astro-ph↗

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.

astro-ph↗

arXiv2006

The evolution of the number density of large disk galaxies in COSMOS

We study a sample of approximately 16,500 galaxies with I_AB <= 22.5 in the COSMOS field. Structural information on the galaxies is derived by fitting single Sersic models to their two-dimensional surface brightness distributions. We investigate the evolution of the number density of disk galaxies larger than 5 kpc between redshift z~1 and the present epoch. To this end, we use the measurements of the half-light radii to construct, as a function of redshift, the size function of both the total disk galaxy population and of disk galaxies split in four bins of bulge-to-disk ratio. Furthermore, we use a selected sample of roughly 1800 SDSS galaxies to calibrate our results with respect to the local universe. We find that: (i) The number density of disk galaxies with intermediate sizes (r_{1/2}~5-7 kpc) remains nearly constant from z~1 to today. (ii) The number density of the largest disks (r_{1/2}>7 kpc) decreases by a factor of about two out to z~1. (iii) There is a constancy in the number density of large bulgeless disks out to z~1; the deficit of large disks at early epochs seems to arise from a smaller number of bulged disks. Our results indicate that the bulk of the large disk galaxy population has completed its growth by z~1, and support the hypothesis that secular evolution processes produce - or at least add stellar mass to - the bulge components of disk galaxies.

astro-ph↗

arXiv2006

A Panoramic Mid-infrared Survey of Two Distant Clusters

(abridged) We present panoramic Spitzer MIPS 24um observations covering 9x9Mpc (25'x25') fields around two massive clusters, Cl0024+16 and MS0451-03, at z=0.39 and z=0.55. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turn-around radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24um members. The much more significant excess is associated with Cl0024+16, whereas MS0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to A_V~1-2 mags) rather than emission from dusty tori around active galactic nuclei (AGN) in early-type hosts. The inferred total-infrared star-formation rates in Cl0024+16 are typically >5x greater than those found from a similar Halpha survey, indicating significant obscured activity in the cluster population. We find evidence for strong evolution of the level of dust-obscured star-formation in dense environments out to z=0.5, analogous to the rise in fraction of optically-selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.

astro-ph↗

arXiv2006

Diffuse light and building history of the galaxy cluster Abell 2667

We have searched for diffuse intracluster light in the galaxy cluster Abell 2667 (z=0.233) from HST images in three filters. We have applied to these images an iterative multi-scale wavelet analysis and reconstruction technique, which allows to subtract stars and galaxies from the original images. We detect a zone of diffuse emission south west of the cluster center (DS1), and a second faint object (ComDif), within DS1. Another diffuse source (DS2) may be detected, at lower confidence level, north east of the center. These sources of diffuse light contribute to 10-15% of the total visible light in the cluster. Whether they are independent entities or are part of the very elliptical external envelope of the central galaxy remains unclear. VLT VIMOS integral field spectroscopy reveals a faint continuum at the positions of DS1 and ComDif but do not allow to compute a redshift. A hierarchical substructure detection method reveals the presence of several galaxy pairs and groups defining a similar direction as the one drawn by the DS1-central galaxy-DS2 axis. The analysis of archive XMM-Newton and Chandra observations shows X-ray emission elongated in the same direction. The X-ray temperature map shows the presence of a cool core, a broad cool zone stretching from north to south and hotter regions towards the north east, south west and north west. This possibly suggests shock fronts along these directions produced by infalling material. These various data are consistent with a picture in which diffuse sources are concentrations of tidal debris and harassed matter expelled from infalling galaxies by tidal stripping and undergoing an accretion process onto the central cluster galaxy; as such, they are expected to be found along the main infall directions.

astro-ph↗

arXiv2006

The dynamical state of massive galaxy clusters

We study the mass distribution of a sample of 24 X-ray bright Abell clusters through weak gravitational lensing. This method is independent of the dynamical state of the galaxy cluster. Hence, by comparing dynamical and lensing mass estimators, we can access the dynamical state of these clusters. We have found that clusters with ICM temperatures above 8 keV show strong deviations from the relaxation, as well as the presence of prominent sub-structures. For the remaining clusters (the majority of the sample) we have found agreement among the several mass estimators, which indicates that most of the clusters are in or close to a state of dynamical equilibrium.

astro-ph↗

arXiv2006

Extending the redshift distribution of submm galaxies: Identification of a z~4 submm galaxy

We present the identification of a bright submillimeter galaxy (SMG) in the field of Abell 2218. The galaxy has a spectroscopic redshift of ~4, and is currently the highest redshift SMG known. It is detected at all wavelengths from optical to submm, including the Spitzer IRAC bands. We discuss the properties of this galaxy, which is undergoing intense star formation at a rate~600 Msun/yr. We also compare the properties to those of radio-preselected submm-bright galaxies. The z~4 result extends the redshift distribution of SMGs.

astro-ph↗

arXiv2006

Spitzer Massive Lensing Cluster Survey

We are currently undertaking a Spitzer GTO program to image ~30 massive lensing clusters at moderate redshift with both IRAC and MIPS. By taking advantage of the gravitatinoal lensing power of these clusters, we will study the population of faint galaxies that are below the nominal Spitzer detection limits. Here, we present a few examples of our science programs.

astro-ph↗

arXiv2006

Spitzer Observations of the Brightest Galaxies in X-ray-Luminous Clusters

We have studied the infrared properties of the brightest cluster galaxies (BCGs) located in the cores of X-ray-luminous clusters at 0.15 < z < 0.35. The majority of the BCGs are not particularly infrared-luminous compared with other massive early-type galaxies, suggesting that the cluster environment has little influence on the infrared luminosities of the BCGs. The exceptions, however, are the BCGs in the three X-ray-brightest clusters in the sample, A1835, Z3146, and A2390. These BCGs have a prominent far-infrared peak in their spectral energy distributions (SEDs), and two of them (those in A1835 and Z3146) can be classified as luminous infrared galaxies (LIRGs: L_{IR} > 10^{11} L_{sun}). Although radio AGNs are found to be prevalent among the BCGs, the infrared luminosities of these three BCGs, judged from the infrared SED signatures, are likely to be powered by star formation. Considering the overall trend that clusters with shorter radiative gas cooling times harbor more infrared-luminous BCGs, the enhanced star formation may be caused by the cooling cluster gas accreting onto the BCGs.

astro-ph↗

arXiv2006

Galaxies Under the Cosmic Microscope: Resolved Spectroscopy and New Constraints on the z=1 Tully-Fisher relation

We exploit the gravitational potential of massive cluster lenses to probe the emission line properties of six z=1 galaxies which appear as highly magnified luminous arcs. Using the GMOS integral field spectrograph together with detailed cluster lens models we reconstruct the intrinsic morphologies and two-dimensional velocity fields in these galaxies on scales corresponds to \~0.5kpc (unlensed) at z=1. Four of the galaxies have stable disk-like kinematics, whilst the other two resemble interacting or starburst galaxies. These galaxies lie close to the mean rest-frame I-band Tully-Fisher relation for nearby spirals suggesting a clear preference for hierarchical growth of structure. In the rest-frame B-band, the observations suggest 0.5+/-0.3mag of brightening, consistent with increased star-formation activity at z=1. However, the galaxies with stable disk kinematics have more slowly rising rotation curves than expected from galaxies with similar surface brightness in the local Universe. We suggest that this may arise because the distant galaxies have lower bulge masses than their local counter-parts. Whilst this study is based on only six galaxies, the gain in flux and in spatial resolution achieved via gravitational magnification provides a much more detailed view of the high redshift Universe than possible with conventional surveys.

astro-ph↗

arXiv2006

An ultradeep submillimetre map: beneath the SCUBA confusion limit with lensing and robust source extraction

Extracting sources with low signal-to-noise from maps with structured background is a non-trivial task which has become important in studying the faint end of the submillimetre number counts. In this article we study source extraction from submillimetre jiggle-maps from the Submillimetre Common-User Bolometer Array (SCUBA) using the Mexican Hat Wavelet (MHW), an isotropic wavelet technique. As a case study we use a large (11.8 arcmin^2) jiggle-map of the galaxy cluster Abell 2218, with a 850um 1sigma r.m.s. sensitivity of 0.6-1mJy. We show via simulations that MHW is a powerful tool for reliable extraction of low signal-to-noise sources from SCUBA jiggle-maps and nine sources are detected in the A2218 850um image. Three of these sources are identified as images of a single background source with an unlensed flux of 0.8mJy. Further, two single-imaged sources also have unlensed fluxes <2mJy, below the blank-field confusion limit. In this ultradeep map, the individual sources detected resolve nearly all of the extragalactic background light at 850um, and the deep data allow to put an upper limit of 44 sources per arcmin^2 to 0.2mJy at 850um.

astro-ph↗

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.

astro-ph↗

arXiv2005

Confirmation of two extended objects along the line of sight to PKS1830-211 with ESO-VLT adaptive optics imaging

We report on new high-resolution near-infrared images of the gravitationally lensed radio source PKS1830-211, a quasar at z=2.507. These adaptive optics observations, taken with the Very Large Telescope (VLT), are further improved through image deconvolution. They confirm the presence of a second object along the line of sight to the quasar, in addition to the previously known spiral galaxy. This additional object is clearly extended in our images. However, its faint luminosity does not allow to infer any photometric redshift. If this galaxy is located in the foreground of PKS1830-211, it complicates the modeling of this system and decreases the interest in using PKS1830-211 as a means to determine H0 via the time delay between the two lensed images of the quasar.

astro-ph↗

arXiv2005

An interferometric CO survey of luminous submm galaxies

In this paper we present results from an IRAM Plateau de Bure millimetre-wave Interferometer (PdBI) survey for CO emission towards radio-detected submillimetre galaxies (SMGs) with known optical and near-infrared spectroscopic redshifts. Five sources in the redshift range z~1-3.5 were detected, nearly doubling the number of SMGs detected in CO. We summarise the properties of all 12 CO-detected SMGs, as well as 6 sources not detected in CO by our survey, and use this sample to explore the bulk physical properties of the SMG population as a whole. The median CO line luminosity of the SMGs is = (3.8 +- 2.0) x 10^10 K km/s pc^2. Using a CO-to-H_2 conversion factor appropriate for starburst galaxies, this corresponds to a molecular gas mass = (3.0 +- 1.6) x 10^10 Msun within a ~2kpc radius, about four times greater than the most luminous local ultraluminous infrared galaxies (ULIRGs) but comparable to that of the most extreme high-redshift radio galaxies and QSOs. The median CO fwhm linewidth is broad, = 780 +- 320 km/s, and the SMGs often have double peaked line profiles, indicative of either a merger or a disk. From their median gas reservoirs (~3 x 10^10 Msun) and star-formation rates (>700 Msun/yr) we estimate a lower limit on the typical gas-depletion time scale of >40Myr in SMGs. This is marginally below the typical age expected for the starbursts in SMGs, and suggests that negative feedback processes may play an important role in prolonging the gas consumption time scale. We find a statistically-significant correlation between the far-infrared and CO luminosities of the SMGs which extends the observed correlation for local ULIRGs to higher luminosities and higher redshifts. [ABRIDGED]

astro-ph↗

arXiv2005

A CFH12k lensing survey of X-ray luminous galaxy clusters - I: Weak lensing methodology

We present the weak lensing methodology applied to our multi-colour imaging survey of X-ray luminous galaxy clusters conducted with the wide field CFH12k camera. This method, which is converting a fully reduced CFH12k image into cluster mass constraints, is done in two steps that we explain in detail: (1) determination of the "true" shape of faint (lensed) galaxies which involves: object detection strategy, point spread function (PSF) determination, galaxy shapes measurements with errors; (2) conversion of the faint galaxies catalogue into useful mass constraints which is done by different lensing techniques using 1D and/or 2D mass estimates. Finally, we compare the cluster mass model to the light distribution of cluster members as observed on our imaging data. To illustrate the method, we apply it to the well studied cluster Abell 1689 (z=0.184). In this cluster, we detect the gravitational shear signal to the edge of the image at 3 sigma significance. The two-dimensional mass reconstruction has a ~10 sigma significance mass peak centered on the brightest cluster galaxy. The weak lensing constraints are well fitted by a NFW mass profile with $M_{200} = 14.1^{+6.3}_{-4.7}\times 10^{14} M_\sun$, and $c = 3.5^{+0.5}_{-0.3}$ (chi^2=0.33), or by a power law (PL) profile with q=0.75 +- 0.07 and theta_E = 14.6"+-0.3" (chi^2=0.64). The mass-to-light ratio is found to be almost constant with radius with a mean value of M/L_R = 150 h (M/L)_\sun. We compare these results to other weak lensing analyses of Abell 1689 presented in the literature and find good agreements in terms of the shear measurement as well as the final mass estimate.

astro-ph↗

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.

astro-ph↗

arXiv2004

A search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars

In this paper we present new ESO/VLT FORS1 and ISAAC images of the fields around eight gravitationally lensed quasars: CTQ414, HE0230-2130, LBQS1009-0252, B1030+074, HE1104-1805, B1359+154, H1413+117 and HE2149-2745. When available and deep enough, HST/WFPC2 data were also used to infer the photometric redshifts of the galaxies around the quasars. The search of galaxy overdensities in space and redshift, as well as a weak-shear analysis and a mass reconstruction are presented in this paper. We find that there are most probably galaxy groups towards CTQ414, HE0230-2130, B1359+154, H1413+117 and HE2149-2745, with a mass ~ 4x10^14 M_sol h^-1. Considering its photometric redshift, the galaxy group discovered in the field around HE1104-1805 is associated with the quasar rather than with the lensing potential.

astro-ph↗

arXiv2004

Discovery of a Transient U-band Dropout in a Lyman-Break Survey: A Tidally-Disrupted Star at z = 3.3?

We report the discovery of a transient source in the central regions of galaxy cluster Abell 267. The object, which we call "PALS1", was found in a survey aimed at identifying highly-magnified Lyman-break galaxies in the fields of intervening rich clusters. At discovery, the source had U>24.7 (2-sigma; AB), g=21.96, and very blue g-r and r-i colors; i.e., PALS1 was a U-band drop-out, characteristic of star-forming galaxies and quasars at z~3. However, three months later the source had faded by more than three magnitudes. Further observations showed a continued decline in luminosity, to R>26.4 seven months after discovery. Though the apparent brightness is suggestive of a supernova at roughly the cluster redshift, we show that the photometry and light curve argue against any known type of supernova at any redshift. The spectral energy distribution and location near the center of a galaxy cluster are consistent with the hypothesis that PALS1 is a gravitationally-lensed transient at z~3.3. If this interpretation is correct, the source is magnified by a factor of 4-7 and two counterimages are predicted. Our lens model predicts time delays between the three images of 1-10 years and that we have witnessed the final occurrence of the transient. The intense luminosity (M(AB) ~ -23.5 after correcting for lensing) and blue UV continuum (implying T>50,000 K) argue the source may have been a flare resulting from the tidal disruption of a star by a 10^6-10^8 solar-mass black hole. Regardless of its physical nature, PALS1 highlights the importance of monitoring regions of high magnification in galaxy clusters for distant, time-varying phenomena.

astro-ph↗