arXiv subjects

P. Jablonka

Publications and source records attributed to P. Jablonka.

At least 91 records · Page 5Linked to original sources

arXiv2006

The X-ray properties of optically-selected z>0.6 clusters in the ESO Distant Cluster Survey

We present XMM-Newton observations of three optically-selected z > 0.6 clusters from the ESO Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and -- unlike other high-redshift, optically-selected clusters -- are consistent with the T - sigma and L_x - sigma relations determined from X-ray selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalog may, like selection by X-ray luminosity, be well-suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ~ 0.8.

astro-ph↗

arXiv2005

The evolution of the star formation activity in galaxies and its dependence on environment

We study how the proportion of star-forming galaxies evolves between z=0.8 and z=0 as a function of galaxy environment, using the [OII] line in emission as a signature of ongoing star formation. Our high-z dataset comprises 16 clusters, 10 groups and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters at similar redshifts. As a local comparison, we use samples of galaxy systems selected from the Sloan Digital Sky Survey at 0.04< z < 0.08. At high-z most systems follow a broad anticorrelation between the fraction of star-forming galaxies and the system velocity dispersion. At face value, this suggests that at z=0.4-0.8 the mass of the system largely determines the proportion of galaxies with ongoing star formation. At these redshifts the strength of star formation (as measured by the [OII] equivalent width) in star-forming galaxies is also found to vary systematically with environment. Sloan clusters have much lower fractions of star-forming galaxies than clusters at z=0.4-0.8 and, in contrast with the distant clusters, show a plateau for velocity dispersions $ \ge 550 km s^-1$, where the fraction of galaxies with [OII] emission does not vary systematically with velocity dispersion. We quantify the evolution of the proportion of star-forming galaxies as a function of the system velocity dispersion and find it is strongest in intermediate-mass systems (sigma ~ 500-600 km s^-1 at z=0). To understand the origin of the observed trends, we use the Press-Schechter formalism and the Millennium Simulation and show that galaxy star formation histories may be closely related to the growth history of clusters and groups. We propose a scheme that is able to account for the observed relations between the star-forming fraction and σ[abridged].

astro-ph↗

arXiv2005

Weak lensing mass reconstructions of the ESO Distant Cluster Survey

We present weak lensing mass reconstructions for the 20 high-redshift clusters i n the ESO Distant Cluster Survey. The weak lensing analysis was performed on deep, 3-color optical images taken with VLT/FORS2, using a composite galaxy catalog with separate shape estimators measured in each passband. We find that the EDisCS sample is composed primarily of clusters that are less massive than t hose in current X-ray selected samples at similar redshifts, but that all of the fields are likely to contain massive clusters rather than superpositions of low mass groups. We find that 7 of the 20 fields have additional massive structures which are not associated with the clusters and which can affect the weak lensing mass determination. We compare the mass measurements of the remaining 13 clusters with luminosity measurements from cluster galaxies selected using photometric redshifts and find evidence of a dependence of the cluster mass-to-light ratio with redshift. Finally we determine the noise level in the shear measurements for the fields as a function of exposure time and seeing and demonstrate that future ground-based surveys which plan to perform deep optical imaging for use in weak lensing measurements must achieve point-spread functions smaller than a median of 0.6" FWHM.

astro-ph↗

arXiv2005

EDisCS -- the ESO Distant Cluster Survey -- Sample Definition and Optical Photometry

We present the ESO Distant Cluster Survey (EDisCS) a survey of 20 fields containing distant galaxy clusters with redshifts ranging from 0.4 to almost 1.0. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey, half with estimated redshift z_est~0.5 and half with z_est~0.8. They were confirmed by identifying red sequences in moderately deep two colour data from VLT/FORS2. For confirmed candidates we have assembled deep three-band optical photometry using VLT/FORS2, deep near-infrared photometry in one or two bands using NTT/SOFI, deep optical spectroscopy using VLT/FORS2, wide field imaging in two or three bands using the ESO Wide Field Imager, and HST/ACS mosaic images for 10 of the most distant clusters. This first paper presents our sample and the VLT photometry we have obtained. We present images, colour-magnitude diagrams and richness estimates for our clusters, as well as giving redshifts and positions for the brightest cluster members. Subsequent papers will present our infrared photometry, spectroscopy, HST and wide-field imaging, as well as a wealth of further analysis and science results. Our reduced data become publicly available as these papers are accepted.

astro-ph↗

arXiv2004

Subaru/HDS Abundances in Three Giant Stars in the Ursa Minor Dwarf Spheroidal Galaxy

With the HDS (High Dispersion Spectrograph) on the Subaru telescope, we obtained high resolution optical region spectra of three red giant stars (cos 4, cos 82, and cos 347) in the Ursa Minor dwarf spheriodal galaxy. Chemical abundances in these stars have been analysed for 26 elements including alpha-, iron-peak, and neutron capture elements. All three stars show low abundances of alpha-elements (Mg, Si, and Ca) and two stars (cos 82 and cos 347) show high abundance of Mn compared to Galactic halo stars of similar metallicity. One star (cos 4) has been confirmed to be very metal deficient ([Fe/H]=-2.7) and found to show anomalously low abundances of Mn, Cu, and Ba. In another star cos 82 ([Fe/H]=-1.5), we have found large excess of heavy neutron-capture elements with the general abundance pattern similar to the scaled solar system r-process abundance curve. These observational results are rather puzzling: low abundances of alpha-elements and high abundance of Mn seem to sugggest a significant contribution of SNe Ia at low metallicity, while there is no hint of s-process (i.e., AGB stars) contribution even at [Fe/H]=-1.5, suggesting a peculiar nucleosynthetic history of the UMi dSph galaxy.

astro-ph↗

arXiv2004

Two distinct ancient components in the Sculptor Dwarf Spheroidal Galaxy: First Results from DART

We have found evidence for the presence of two distinct ancient stellar components (both geq 10 Gyr old) in the Sculptor dwarf spheroidal galaxy. We used the ESO Wide Field Imager (WFI) in conjunction with the VLT/FLAMES spectrograph to study the properties of the resolved stellar population of Sculptor out to and beyond the tidal radius. We find that two components are discernible in the spatial distribution of Horizontal Branch stars in our imaging, and in the [Fe/H] and v_hel distributions for our large sample of spectroscopic measurements. They can be generally described as a ``metal-poor'' component ([Fe/H]< -1.7) and a ``metal-rich'' component ([Fe/H]> -1.7). The metal-poor stars are more spatially extended than the metal-rich stars, and they also appear to be kinematically distinct. These results provide an important insight into the formation processes of small systems in the early universe and the conditions found there. Even this simplest of galaxies appears to have had a surprisingly complex early evolution.

astro-ph↗

arXiv2004

Spectroscopy of clusters in the ESO Distant Cluster Survey (EDisCS)

We present spectroscopic observations of galaxies in 4 clusters at z = 0.7-0.8 and in one cluster at z~0.5 obtained with the FORS2 spectrograph on the VLT as part of the ESO Distant Cluster Survey (EDisCS), a photometric and spectroscopic survey of 20 intermediate to high redshift clusters. We describe our target selection, mask design, observation and data reduction procedures, using these first 5 clusters to demonstrate how our strategies maximise the number of cluster members for which we obtain spectroscopy. We present catalogues containing positions, I-band magnitudes and spectroscopic redshifts for galaxies in the fields of our 5 clusters. These contain 236 cluster members, with the number of members per cluster ranging from 30 to 67. Our spectroscopic success rate, i.e. the fraction of spectroscopic targets which are cluster members, averages 50% and ranges from 30% to 75%. We use a robust biweight estimator to measure cluster velocity dispersions from our spectroscopic redshift samples. We also make a first assessment of substructure within our clusters. The velocity dispersions range from 400 to 1100 km s-1. Some of the redshift distributions are significantly non-Gaussian and we find evidence for significant substructure in two clusters, one at z~0.79 and the other at z~0.54. Both have velocity dispersions exceeding 1000 km s-1 but are clearly not fully virialised; their velocity dispersions may thus be a poor indicator of their masses. The properties of these first 5 EDisCS clusters span a wide range in redshift, velocity dispersion, richness and substructure, but are representative of the sample as a whole. Spectroscopy for the full dataset will allow a comprehensive study of galaxy evolution as a function of cluster environment and redshift.

astro-ph↗

arXiv2004

The build-up of the red-sequence in galaxy clusters since z~0.8

We study the rest-frame (U-V) color-magnitude relation in 4 clusters at redshifts 0.7-0.8, drawn from the ESO Distant Cluster Survey. We confirm that red-sequence galaxies in these clusters can be described as an old, passively-evolving population and we demonstrate, by comparison with the Coma cluster, that there has been significant evolution in the stellar mass distribution of red-sequence galaxies since z~0.75. The EDisCS clusters exhibit a deficiency of low luminosity passive red galaxies. Defining as `faint' all galaxies in the passive evolution corrected range 0.4>~ L/L*>~0.1, the luminous-to-faint ratio of red-sequence galaxies varies from 0.34+/-0.06 for the Coma cluster to 0.81+/-0.18 for the high redshift clusters. These results exclude a synchronous formation of all red-sequence galaxies and suggest that a large fraction of the faint red galaxies in current clusters moved on to the red-sequence relatively recently. Their star formation activity presumably came to an end at z<~0.8.

astro-ph↗

arXiv2004

On-axis spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600: an elliptical host with a highly ionized ISM

VLT on-axis optical spectroscopy of the z=0.144 radio-loud quasar HE 1434-1600 is presented. The spatially resolved spectra of the host galaxy are deconvolved and separated from those of the central quasar in order to study the dynamics of the stars and gas as well as the physical conditions of the ISM. We find that the host of HE 1434-1600 is an elliptical galaxy that resides in a group of at least 5 member galaxies, and that most likely experienced a recent collision with its nearest companion. Compared with other quasar host galaxies, HE 1434-1600 has a highly ionized ISM. The ionization state corresponds to that of typical Seyferts, but the ionized regions are not distributed in a homogeneous way around the QSO, and are located preferentially several kiloparsecs away from it. While the stellar absorption lines do not show any significant velocity field, the gas emission lines do. The observed gas velocity field is hard to reconcile with dynamical models involving rotating disk, modified Hubble laws or power laws, that all require extreme central masses (M > 10^9 M_sun) to provide only poor fit to the data. Power law models, which best fit the data, provide a total mass of M(< 10 kpc)=9.2 10^10 M_sun. We conclude that the recent interaction between HE 1434-1600 and its closest companion has strongly affected the gas velocity and ionization state, from the center of the galaxy to its most external parts.

astro-ph↗

arXiv2004

Observing the build-up of the colour-magnitude relation at redshift ~0.8

We analyse the rest-frame (U-V) colour-magnitude relation for 2 clusters at redshift 0.7 and 0.8, drawn from the ESO Distant Cluster Survey. By comparing with the population of red galaxies in the Coma cluster, we show that the high redshift clusters exhibit a deficit of passive faint red galaxies. Our results show that the red-sequence population cannot be explained in terms of a monolithic and synchronous formation scenario. A large fraction of faint passive galaxies in clusters today has moved onto the red sequence relatively recently as a consequence of the fact that their star formation activity has come to an end at z<0.8.

astro-ph↗

arXiv2002

On-axis spatially resolved spectroscopy of low redshift quasar host galaxies: HE 1503+0228 at z=0.135

We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the ``MCS deconvolution algorithm''. The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE1503+0228, at z=0.135 (M_B=-23.0), it provides us with the spectrum of the host galaxy between 3600A, and 8500A, (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE1503+0228, are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 4arcsec, away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r<1kpc) = (2.0 +- 0.3) 10^{10} solar mass within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r<10kpc) = (1.9 +- 0.3) 10^{11} solar mass, with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE1503+0228, is a normal spiral galaxy.

astro-ph↗

arXiv2002

Stellar Populations in Bulges of Spiral Galaxies

We have conducted a spectroscopic analysis of the bulges of a sample of 31 spiral galaxies, spanning the Hubble sequence from S0 to Scd type, in order to study the radial distribution of their stellar population properties.

astro-ph↗

arXiv2001

The globular cluster system of M31

This review presents the current status of our knowledge of M31 star clusters. Given the broadness of the subject, I chose to focus on some of its aspects which are not covered by the other participants in this conference.

astro-ph↗

arXiv2001

Mayall II = G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy ?

(Abridged version) Mayall II = G1 is one of the brightest globular clusters belonging to M31, the Andromeda galaxy. Our observations with HST/WFPC2 provide data for the (I vs. V-I) and (V vs. V-I) color-magnitude diagrams. From model fitting, we determine a rather high mean metallicity of [Fe/H] = --0.95 +- 0.09, somewhat similar to 47 Tucanae. We find a larger spread in V-I than can be explained by the measurement errors, and we attribute this to an intrinsic metallicity dispersion amongst the stars of G1. So far, only omega Centauri, the giant Galactic globular cluster, has been known to exhibit such an intrinsic metallicity dispersion. Three estimates of the total mass of this globular cluster can be obtained: King mass = 15 x 10^6 with M/Lv ~ 7.5, Virial mass = 7.3 x 10^6 with M/Lv ~ 3.6, and King-Michie mass range from 14 to 17 x 10^6. Although uncertain, all of these mass estimates make G1 more than twice as massive as omega Centauri. Such large masses relate to the metallicity spread whose origin is still unknown (either self-enrichment, an inhomogeneous proto-cluster cloud, or remaining core of a dwarf galaxy). When considering the positions of G1 in the different diagrams defined by Kormendy (1985), G1 always appears on the sequence defined by globular clusters, and definitely away from the other sequences defined by elliptical galaxies, bulges, and dwarf spheroidal galaxies. The same is true for omega Centauri and for the nucleus of the dwarf elliptical NGC 205. This does not prove that all (massive) globular clusters are the remnant cores of nucleated dwarf galaxies.

astro-ph↗

arXiv2000

HST-NICMOS Observations of M31's Metal Rich Globular Clusters and Their Surrounding Fields: I. Techniques

We have obtained HST-NICMOS observations of five of M31's most metal rich globular clusters. These data allow photometry of individual stars in the clusters and their surrounding fields. However, to achieve our goals -- obtain accurate luminosity functions to compare with their Galactic counterparts, determine metallicities from the slope of the giant branch, identify long period variables, and estimate ages from the AGB tip luminosity, we must be able to disentangle the true properties of the population from the observational effects associated with measurements made in very crowded fields. In this paper we present a careful analysis of photometry in crowded regions, and show how image blending affects the results and interpretation of such data. Although this analysis is specifically for our NICMOS observations in M31, the techniques we develop can be applied to any imaging data taken in crowded fields; we show how the effects of image blending will even limit NGST. We use three different techniques to analyze the effects of crowding on our data, including the insertion of artificial stars (traditional completeness tests) and the creation of completely artificial clusters. They are used to derive threshold- and critical-blending radii for each cluster, which determine how close to the cluster center reliable photometry can be achieved. The simulations also allow us to quantify and correct for the effects of blending on the slope and width of the RGB at different surface brightness levels.

astro-ph↗

arXiv2000

HST-NICMOS Observations of M31's Metal Rich Globular Clusters and Their Surrounding Fields: II. Results

We have obtained HST-NICMOS observations of five of M31's most metal rich globular clusters: G1, G170, G174, G177 & G280. For the two clusters farthest from the nucleus we statistically subtract the field population and estimate metallicities using K-(J-K) color-magnitude diagrams (CMDs). Based on the slopes of their infrared giant branches we estimate [Fe/H]=-1.22+/-0.43 for G1 and -0.15+/-0.37 for G280. We combine our infrared observations of G1 with two epochs of optical HST-WFPC2 V-band data and identify at least one LPV based on color and variability. The location of G1's giant branch in the K-(V-K) CMD is very similar to that of M107, indicating a higher metallicity than our purely infrared CMD: [Fe/H]=-0.9+/-0.2. For the field surrounding G280, we estimate the metallicity to be -1.3 with a spread of 0.5 from the slope and width of the giant branch. Based on the numbers and luminosities of the brightest giants, we conclude that only a small fraction of the stars in this field could be as young as 2 Gyr, while the majority have ages closer to 10 Gyr. The K-band luminosity functions (LFs) of the upper few magnitudes of G1 and G280, as well as for the fields surrounding all clusters, are indistinguishable from the LF measured in the bulge of our Galaxy. This indicates that these clusters are very similar to Galactic clusters, and at least in the surrounding fields observed, there are no significant populations of young luminous stars.

astro-ph↗

arXiv2000

Resolved Stellar Populations of Super-Metal-Rich Star Clusters in the Bulge of M31

We have applied the MCS image deconvolution algorithm (Magain, Courbin & Sohy 1998) to HST/WFPC2 V, I data of three M31 bulge globular clusters (G170, G177, and G198) and control fields near each cluster. All three clusters are clearly detected, with an increase in stellar density with decreasing radius from the cluster centers; this is the first time that stars have been resolved in bulge clusters in the inner regions of another galaxy. From the RGB slopes of the clusters and the difference in I magnitude between the HB and the top of the RGB, we conclude that these three clusters all have roughly solar metallicity, in agreement with earlier integrated-light spectroscopic measurements. Our data support a picture whereby the M31 bulge clusters and field stars were born from the same metal-rich gas, early in the galaxy formation.

astro-ph↗

arXiv1999

Line Strengths and Line Strength Gradients in Bulges along the Hubble Sequence

We present first results of a comprehensive survey of deep long-slit spectra along the minor axis of bulges of edge-on spiral galaxies. Our results indicate that stellar populations in bulges are fairly old and encompass a range of metallicities. The luminosity-weighted ages of bulges range from those found for cluster ellipticals to slightly ``younger'' (by up to only a few Gyr, however). Their $α$/Fe element ratio is typically supersolar, consistent with those found in giant ellipticals. The radial line-strength gradients in bulges correlate with bulge luminosity. Generally, these findings are more compatible with predictions of the ``dissipative collapse'' model than with those of the ``secular evolution'' model.

astro-ph↗