Publications (134)136.74 Total impact
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Article: NLTT5306: The shortest Period Detached White Dwarf + Brown Dwarf Binary
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ABSTRACT: We have spectroscopically confirmed a brown dwarf mass companion to the hydrogen atmosphere white dwarf NLTT5306. The white dwarf's atmospheric parameters were measured using Sloan Digital Sky Survey and X-Shooter spectroscopy as T_eff=7756+/-35K and log(g)=7.68+/-0.08, giving a mass for the primary of M_WD=0.44+/-0.04 M_sun, at a distance of 71+/-4 pc with a cooling age of 710+/-50 Myr. The existence of the brown dwarf secondary was confirmed through the near-infrared arm of the X-Shooter data and a spectral type of dL4-dL7 was estimated using standard spectral indices. Combined radial velocity measurements from the Sloan Digital Sky Survey, X-Shooter and the Hobby-Eberly Telescope's High Resolution Spectrograph of the white dwarf gives a minimum mass of 56+/-3 M_jup for the secondary, confirming the substellar nature. The period of the binary was measured as 101.88+/-0.02 mins using both the radial velocity data and i'-band variability detected with the INT. This variability indicates 'day' side heating of the brown dwarf companion. We also observe H{\alpha} emission in our higher resolution data in phase with the white dwarf radial velocity, indicating this system is in a low level of accretion, most likely via a stellar wind. This system represents the shortest period white dwarf + brown dwarf binary and the secondary has survived a stage of common envelope evolution, much like its longer period counterpart, WD0137-349. Both systems likely represent bona-fide progenitors of cataclysmic variables with a low mass white dwarf and a brown dwarf donor.12/2012; -
Article: Further evidence for large central mass-to-light ratios in massive early-type galaxies
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ABSTRACT: We studied the stellar populations, distribution of dark matter, and dynamical structure of a sample of 25 early-type galaxies in the Coma and Abell 262 clusters. We derived dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the ages, metallicities, and \alpha-elements abundances of the galaxies from single stellar population models. Most of the galaxies have a significant detection of dark matter and their halos are about 10 times denser than in spirals of the same stellar mass. Calibrating dark matter densities to cosmological simulations we find assembly redshifts z_{DM} \approx 1-3. The dynamical mass that follows the light is larger than expected for a Kroupa stellar initial mass function, especially in galaxies with high velocity dispersion \sigma_{eff} inside the effective radius r_{eff}. We now have 5 of 25 galaxies where mass follows light to 1-3 r_{eff}, the dynamical mass-to-light ratio of all the mass that follows the light is large (\approx 8-10 in the Kron-Cousins R band), the dark matter fraction is negligible to 1-3 r_{eff}. This could indicate a "massive" initial mass function in massive early-type galaxies. Alternatively, some of the dark matter in massive galaxies could follow the light very closely suggesting a significant degeneracy between luminous and dark matter.11/2012; -
Article: Molecular gas in the centre of nearby galaxies from VLT/SINFONI integral field spectroscopy - I. Morphology and mass inventory
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ABSTRACT: We present the first results of an analysis of the properties of the molecular gas in the nuclear regions (r < 300 pc) of a sample of six nearby galaxies, based on new high spatial resolution observations obtained in the K-band with the near-infrared integral field spectrograph SINFONI at the Very Large Telescope. We derive two-dimensional distributions of the warm molecular and ionized gas from the H2, Br_gamma and HeI emission lines present in the spectra of the galaxies. We find a range of morphologies, including bar- and ring-like distributions and either centrally peaked or off-centre emission. The morphologies of the molecular and the ionized gas are not necessarily coincident. The observed emission-line ratios point towards thermal processes as the principal mechanism responsible for the H2 excitation in the nuclear and circumnuclear regions of the galaxies, independently of the presence of an active nucleus. We find that a rescaling of the H2 2.12 microns emission-line luminosity by a factor beta~1200 gives a good estimate (within a factor of 2) of the total (cold) molecular gas mass. The galaxies of the sample contain large quantities of molecular gas in their centres, with total masses in the ~ 105 - 108 Msol range. Never the less, these masses correspond to less than 3 per cent of the stellar masses derived for the galaxies in these regions, indicating that the presence of gas should not affect black hole mass estimates based on the dynamical modelling of the stars. The high-spatial resolution provided by the SINFONI data allowed us to resolve a circumnuclear ring (with a radius of ~270 pc) in the galaxy NGC 4536. The measured values of the Br_gamma equivalent width and the HeI/Br_gamma emission-line ratio suggests that bursts of star formation occurred throughout this ring as recently as 6.5 Myr ago.10/2012; -
Article: The first planet detected in the WTS: an inflated hot-Jupiter in a 3.35 day orbit around a late F-star
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ABSTRACT: We report the discovery of WTS-1b, the first extrasolar planet found by the WFCAM Transit Survey, which began observations at the 3.8-m United Kingdom Infrared Telescope. Light curves comprising almost 1200 epochs with a photometric precision of better than 1 per cent to J=16 were constructed for 60000 stars and searched for periodic transit signals. For one of the most promising transiting candidates, high-resolution spectra taken at the Hobby-Eberly Telescope allowed us to estimate the spectroscopic parameters of the host star, a late-F main sequence dwarf (V=16.13) with possibly slightly subsolar metallicity, and to measure its radial velocity variations. The combined analysis of the light curves and spectroscopic data resulted in an orbital period of the substellar companion of 3.35 days, a planetary mass of 4.01+-0.35 Mj and a planetary radius of 1.49+-0.17 Rj. WTS-1b has one of the largest radius anomalies among the known hot Jupiters in the mass range 3-5 Mj.10/2012; -
Article: Further evidence for large central mass-to-light ratios in early-type galaxies: the case of ellipticals and lenticulars in the Abell~262 cluster
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ABSTRACT: We present radially resolved spectroscopy of 8 early-type galaxies in Abell~262, measuring rotation, velocity dispersion, $H_3$ and $H_4$ coefficients along three axes, and line-strength index profiles of Mg, Fe and H$\beta$. Ionized-gas velocity and velocity dispersion is included for 6 galaxies. We derive dynamical mass-to-light ratios and dark matter densities from orbit-based dynamical models, complemented by the galaxies' ages, metallicities, and $\alpha$-elements abundances. Four galaxies have significant dark matter with halos about 10 times denser than in spirals of the same stellar mass. Using dark matter densities and cosmological simulations, assembly redshifts $\zdm\approx 1-3$, which we found earlier for Coma. The dynamical mass following the light is larger than expected for a Kroupa stellar IMF, especially in galaxies with high velocity dispersion $\sigeff$ inside the effective radius $\reff$. This could indicate a `massive' IMF in massive galaxies. Alternatively, some dark matter in massive galaxies could follow the light closely. Combining with our comparison sample of Coma early-types, we now have 5 of 24 galaxies where (1) mass follows light to $1-3\,\reff$, (2) the dynamical mass-to-light ratio {of all the mass that follows the light is large ($\approx\,8-10$ in the Kron-Cousins $R$ band), (3) the dark matter fraction is negligible to $1-3\,\reff$. Unless the IMF in these galaxies is particularly `massive' and somehow coupled to the dark matter content, there seems a significant degeneracy between luminous and dark matter in some early-type galaxies. The role of violent relaxation is briefly discussed.06/2012; -
Article: Four ultra-short period eclipsing M-dwarf binaries in the WFCAM Transit Survey
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ABSTRACT: We report on the discovery of four ultra-short period (P<0.18 days) eclipsing M-dwarf binaries in the WFCAM Transit Survey. Their orbital periods are significantly shorter than of any other known main-sequence binary system, and are all significantly below the sharp period cut-off at P~0.22 days as seen in binaries of earlier type stars. The shortest-period binary consists of two M4 type stars in a P=0.112 day orbit. The binaries are discovered as part of an extensive search for short-period eclipsing systems in over 260,000 stellar lightcurves, including over 10,000 M-dwarfs down to J=18 mag, yielding 25 binaries with P<0.23 days. In a popular paradigm, the evolution of short period binaries of cool main-sequence stars is driven by loss of angular momentum through magnetised winds. In this scheme, the observed P~0.22 day period cut-off is explained as being due to timescales that are too long for lower-mass binaries to decay into tighter orbits. Our discovery of low-mass binaries with significantly shorter orbits implies that either these timescales have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic activity, or that the mechanism for forming these tight M-dwarf binaries is different from that of earlier type main-sequence stars.06/2012; -
Article: The Photometric Classification Server for Pan-STARRS1
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ABSTRACT: The Pan-STARRS1 survey is obtaining multi-epoch imaging in five bands (g P1 r P1 i P1 z P1 y P1) over the entire sky north of declination –30 deg. We describe here the implementation of the Photometric Classification Server (PCS) for Pan-STARRS1. PCS will allow the automatic classification of objects into star/galaxy/quasar classes based on colors and the measurement of photometric redshifts for extragalactic objects, and will constrain stellar parameters for stellar objects, working at the catalog level. We present tests of the system based on high signal-to-noise photometry derived from the Medium-Deep Fields of Pan-STARRS1, using available spectroscopic surveys as training and/or verification sets. We show that the Pan-STARRS1 photometry delivers classifications and photometric redshifts as good as the Sloan Digital Sky Survey (SDSS) photometry to the same magnitude limits. In particular, our preliminary results, based on this relatively limited data set down to the SDSS spectroscopic limits, and therefore potentially improvable, show that stars are correctly classified as such in 85% of cases, galaxies in 97%, and QSOs in 84%. False positives are less than 1% for galaxies, 19% for stars, and 28% for QSOs. Moreover, photometric redshifts for 1000 luminous red galaxies up to redshift 0.5 are determined to 2.4% precision (defined as 1.48 × Median|z phot – z spec|/(1 + z)) with just 0.4% catastrophic outliers and small (–0.5%) residual bias. For bluer galaxies up to the same redshift, the residual bias (on average –0.5%) trend, percentage of catastrophic failures (1.2%), and precision (4.2%) are higher, but still interestingly small for many science applications. Good photometric redshifts (to 5%) can be obtained for at most 60% of the QSOs of the sample. PCS will create a value-added catalog with classifications and photometric redshifts for eventually many millions of sources.The Astrophysical Journal 01/2012; 746(2):128. · 6.02 Impact Factor -
Article: MDia and POTS - The Munich Difference Imaging Analysis for the pre-OmegaTranS Project
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ABSTRACT: We describe the Munich Difference Imaging Analysis pipeline that we developed and implemented in the framework of the Astro-WISE package to automatically measure high precision light curves of a large number of stellar objects using the difference imaging approach. Combined with programs to detect time variability, this software can be used to search for planetary systems or binary stars with the transit method and for variable stars of different kinds. As a first scientific application, we discuss the data reduction and analysis performed with Astro-WISE on the pre-OmegaTranS data set, that we collected during a monitoring campaign of a dense stellar field with the Wide Field Imager at the ESO 2.2m telescope.12/2011; -
Article: Implementation of PhotoZ under Astro-WISE - A photometric redshift code for large datasets
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ABSTRACT: We describe the implementation of the PhotoZ code in the framework of the Astro-WISE package and as part of the Photometric Classification Server of the PanSTARRS pipeline. Both systems allow the automatic measurement of photometric redshifts for the millions of objects being observed in the PanSTARRS project or expected to be observed by future surveys like KIDS, DES or EUCLID.10/2011; -
Article: PAndromeda - first results from the high-cadence monitoring of M31 with Pan-STARRS 1
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ABSTRACT: The Pan-STARRS 1 (PS1) survey of M31 (PAndromeda) is designed to identify gravitational microlensing events, caused by bulge and disk stars (self-lensing) and by compact matter in the halos of M31 and the Milky Way (halo lensing, or lensing by MACHOs). With the 7 deg2 FOV of PS1, the entire disk of M31 can be imaged with one single pointing. Our aim is to monitor M31 with this wide FOV with daily sampling (20 mins/day). In the 2010 season we acquired in total 91 nights towards M31, with 90 nights in the rP1 and 66 nights in the iP1. The total integration time in rP1 and iP1 are 70740s and 36180s, respectively. As a preliminary analysis, we study a 40'\times40' sub-field in the central region of M31, a 20'\times20' sub-field in the disk of M31 and a 20'\times20' sub-field for the investigation of astrometric precision. We demonstrate that the PSF is good enough to detect microlensing events. We present light curves for 6 candidate microlensing events. This is a competitive rate compared to previous M31 microlensing surveys. We finally also present one example light curve for Cepheids, novae and eclipsing binaries in these sub-fields.09/2011; -
Article: Dynamical masses of early‐type galaxies: a comparison to lensing results and implications for the stellar initial mass function and the distribution of dark matter
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ABSTRACT: This work aims to study the distribution of the luminous and dark matter in Coma early-type galaxies. Dynamical masses obtained under the assumption that mass follows light do not match with the masses of strong gravitational lens systems of similar velocity dispersions. Instead, dynamical fits with dark matter haloes are in good agreement with lensing results. We derive mass-to-light ratios of the stellar populations from Lick absorption line indices, reproducing well the observed galaxy colours. Even in dynamical models with dark matter haloes the amount of mass that follows the light increases more rapidly with the galaxy velocity dispersion than expected for a constant stellar initial mass function (IMF). While galaxies around σeff≈ 200 km s−1 are consistent with a Kroupa IMF, the same IMF underpredicts luminous dynamical masses of galaxies with σeff≈ 300 km s−1 by a factor of 2 and more. A systematic variation in the stellar IMF with the galaxy velocity dispersion could explain this trend with a Salpeter IMF for the most massive galaxies. If the IMF is instead constant, then some of the dark matter in high-velocity-dispersion galaxies must follow a spatial distribution very similar to that of the light. A combination of both, a varying IMF and a component of dark matter that follows the light is possible as well. For a subsample of galaxies with old stellar populations, we show that the tilt in the Fundamental Plane can be explained by systematic variations of the total (stellar + dark) mass inside the effective radius. We tested commonly used mass estimator formulae, finding them accurate at the 20–30 per cent level.Monthly Notices of the Royal Astronomical Society 07/2011; 415(1):545 - 562. · 4.90 Impact Factor -
Article: Dynamical masses of early-type galaxies: a comparison to lensing results and implications for the stellar IMF and the distribution of dark matter
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ABSTRACT: This work aims to study the distribution of luminous and dark matter in Coma early-type galaxies. Dynamical masses obtained under the assumption that mass follows light do not match with the masses of strong gravitational lens systems of similar velocity dispersions. Instead, dynamical fits with dark matter halos are in good agreement with lensing results. We derive mass-to-light ratios of the stellar populations from Lick absorption line indices, reproducing well the observed galaxy colours. Even in dynamical models with dark matter halos the amount of mass that follows the light increases more rapidly with galaxy velocity dispersion than expected for a constant stellar initial mass function (IMF). While galaxies around sigma ~ 200 km/s are consistent with a Kroupa IMF, the same IMF underpredicts luminous dynamical masses of galaxies with sigma ~ 300 km/s by a factor of two and more. A systematic variation of the stellar IMF with galaxy velocity dispersion could explain this trend with a Salpeter IMF for the most massive galaxies. If the IMF is instead constant, then some of the dark matter in high velocity dispersion galaxies must follow a spatial distribution very similar to that of the light. A combination of both, a varying IMF and a component of dark matter that follows the light is possible as well. For a subsample of galaxies with old stellar populations we show that the tilt in the fundamental plane can be explained by systematic variations of the total (stellar + dark) mass inside the effective radius. We tested commonly used mass estimator formulae, finding them accurate at the 20-30% level.03/2011; -
Article: The central black hole mass of the high‐σ but low‐bulge‐luminosity lenticular galaxy NGC 1332★
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ABSTRACT: The masses of the most massive supermassive black holes (SMBHs) predicted by the MBH–σ and MBH–L relations appear to be in conflict. Which of the two relations is the more fundamental one remains an open question. NGC 1332 is an excellent example that represents the regime of conflict. It is a massive lenticular galaxy which has a bulge with a high velocity dispersion σ of ∼320 km s−1; bulge–disc decomposition suggests that only 44 per cent of the total light comes from the bulge. The MBH–σ and the MBH–L predictions for the central black hole mass of NGC 1332 differ by almost an order of magnitude. We present a stellar dynamical measurement of the SMBH mass using an axisymmetric orbit superposition method. Our SINFONI integral-field unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence which has a diameter of ∼0.76 arcsec. The σ inside 0.2 arcsec reaches ∼400 km s−1. The IFU data allow us to increase the statistical significance of our results by modelling each of the four quadrants separately. We measure an SMBH mass of (1.45 ± 0.20) × 109 M⊙ with a bulge mass-to-light ratio of 7.08 ± 0.39 in the R band. With this mass, the SMBH of NGC 1332 is offset from the MBH–L relation by a full order of magnitude but is consistent with the MBH–σ relation.Monthly Notices of the Royal Astronomical Society 01/2011; 410(2):1223 - 1236. · 4.90 Impact Factor -
Article: Superdense Massive Galaxies in the ESO Distant Cluster Survey (EDisCS)
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ABSTRACT: We find a significant number of massive and compact galaxies in clusters from the ESO Distant Clusters Survey (EDisCS) at 0.4 < z < 1. They have similar stellar masses, ages, sizes, and axial ratios to local z ~ 0.04 compact galaxies in WIde field Nearby Galaxy clusters Survey (WINGS) clusters, and to z = 1.4-2 massive and passive galaxies found in the general field. If non-brightest cluster galaxies of all densities, morphologies, and spectral types are considered, the median size of EDisCS galaxies is only a factor 1.18 smaller than in WINGS. We show that for morphologically selected samples, the morphological evolution taking place in a significant fraction of galaxies during the last Gyr may introduce an apparent, spurious evolution of size with redshift, which is actually due to intrinsic differences in the selected samples. We conclude that the median mass-size relation of cluster galaxies does not evolve significantly from z ~ 0.7 to z ~ 0.04. In contrast, the masses and sizes of BCGs and galaxies with M *>4 × 1011 M ☉ have significantly increased by a factor of 2 and 4, respectively, confirming the results of a number of recent works on the subject. Our findings show that progenitor bias effects play an important role in the size-growth paradigm of massive and passive galaxies.The Astrophysical Journal Letters 08/2010; 721(1):L19. · 5.53 Impact Factor -
Article: Radially extended kinematics and stellar populations of the massive ellipticals NGC1600, NGC4125 and NGC7619. Constraints on the outer dark halo density profile
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ABSTRACT: We present high quality long slit spectra along the major and minor axes out to 1.5-2 Re (14-22 kpc) of three bright elliptical galaxies (NGC1600, NGC4125, NGC7619) obtained at the Hobby-Eberly Telescope (HET). We derive stellar kinematic profiles and Lick/IDS indices (Hbeta, Mgb, Fe5015, Fe5270, Fe5335, Fe5406). Moreover, for NGC4125 we derive gas kinematics and emission line strengths. We model the absorption line strengths using Simple Stellar Populations models that take into account the variation of [\alpha/Fe] and derive ages, total metallicity and element abundances. Overall, we find that the three galaxies have old and [\alpha/Fe] overabundant stellar populations with no significant gradients. The metallicity is supersolar at the center with a strong negative radial gradient. For NGC4125, several pieces of evidence point to a recent dissipational merger event. We calculate the broad band color profiles with the help of SSP models. All of the colors show sharp peaks at the center of the galaxies, mainly caused by the metallicity gradients, and agree well with the measured colors. Using the Schwarzschild's axisymmetric orbit superposition technique, we model the stellar kinematics to constrain the dark halos of the galaxies. We use the tight correlation between the Mgb strength and local escape velocity to set limits on the extent of the halos by testing different halo sizes. Logarithmic halos - cut at 60 kpc -minimize the overall scatter of the Mgb-Vesc relation. Larger cutoff radii are found if the dark matter density profile is decreasing more steeply at large radii. Comment: Accepted for publication in Astronomy and Astrophysics04/2010; -
Article: Do black hole masses scale with classical bulge luminosities only? The case of the two composite pseudo‐bulge galaxies NGC 3368 and NGC 3489★
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ABSTRACT: It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge mass and the velocity dispersion, which implies that the bulge and the central BH of a galaxy have grown together during the formation process. As part of an investigation of the dependence of the SMBH mass on bulge types and formation mechanisms, we present measurements of SMBH masses in two pseudo-bulge galaxies. The spiral galaxy NGC 3368 is double-barred and hosts a large pseudo-bulge with a tiny classical bulge component at the very centre. The S0 galaxy NGC 3489 has only a weak large-scale bar, a small pseudo-bulge and a small classical bulge. Both galaxies show weak nuclear activity in the optical, indicative of the presence of an SMBH. We present high-resolution, adaptive-optics-assisted, near-IR integral-field data of these two galaxies, taken with SINFONI at the Very Large Telescope, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC 3368, averaged over the four quadrants, is 〈M•〉= 7.5 × 106 M⊙ with an error of 1.5 × 106 M⊙, which mostly comes from the non-axisymmetry in the data. For NGC 3489, a solution without a BH cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M•= (6.00+0.56−0.54∣stat± 0.64∣sys) × 106 M⊙. Although both galaxies seem to be consistent with the M•–σ relation, at face value they do not agree with the relation between bulge magnitude and BH mass when the total bulge magnitude (i.e. including both classical bulge and pseudo-bulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion.Monthly Notices of the Royal Astronomical Society 03/2010; 403(2):646 - 672. · 4.90 Impact Factor -
Article: The old and heavy bulge of M31 I. Kinematics and stellar populations
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ABSTRACT: We present new optical long-slit data along 6 position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin from the center, where the disk light contribution is always less than 30%, and out to 8 arcmin along the major axis, where the disk makes 55% of the total light. We show that the velocity dispersions of McElroy (1983) are severely underestimated (by up to 50 km/s) and previous dynamical models have underestimated the stellar mass of M31's bulge by a factor 2. Moreover, the light-weighted velocity dispersion of the galaxy grows to 166 km/s, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31. The kinematic position angle varies with distance, pointing to triaxiality. We detect gas counterrotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. We derive the age, metallicity and alpha-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (>12 Gyr, with many best-fit ages at the model grid limit of 15 Gyr), slightly alpha-elements overabundant ([alpha/Fe]~0.2) and at solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match reasonably well the dust-corrected observations. The stellar populations have approximately radially constant mass-to-light ratios (M/L_R ~ 4-4.5 for a Kroupa IMF), in agreement with stellar dynamical estimates based on our new velocity dispersions. In the inner arcsecs the luminosity-weighted age drops to 4-8 Gyr, while the metallicity increases to above 3 times the solar value. Comment: Accepted for publication in A&A10/2009; -
Article: Photometric redshifts and cluster tomography in the ESO Distant Cluster Survey
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ABSTRACT: This paper reports the results obtained on the photometric redshifts measurement and accuracy, and cluster tomography in the ESO Distant Cluster Survey (EDisCS) fields. Photometric redshifts were computed using two independent codes (Hyperz and G. Rudnick's code). The accuracy of photometric redshifts was assessed by comparing our estimates with the spectroscopic redshifts of ~1400 galaxies in the 0.3<z<1.0 domain. The accuracy for galaxies fainter than the spectroscopic control sample was estimated using a degraded version of the photometric catalog for the spectroscopic sample. The accuracy of photometric redshifts is typically sigma(Delta z/(1+z)) ~ 0.05+/-0.01, depending on the field, the filter set, and the spectral type of the galaxies. The quality of the photometric redshifts degrades by a factor of two in sigma(Delta z/(1+z)) between the brightest (I~22) and the faintest (I~24-24.5) galaxies in the EDisCS sample. The photometric determination of cluster redshifts in the EDisCS fields using a simple algorithm based on photoz is in excellent agreement with the spectroscopic values (delta(z) ~0.03-0.04 in the high-z sample and ~0.05 in the low-z sample). We also developed a method that uses both photz codes jointly to reject interlopers at magnitudes fainter than the spectroscopic limit. When applied to the spectroscopic sample, this method rejects ~50-90% of all spectroscopically confirmed non-members, while retaining at least 90% of all confirmed members. Photometric redshifts are found to be particularly useful for the identification and study of clusters of galaxies in large surveys. They enable efficient and complete pre-selection of cluster members for spectroscopy, allow accurate determinations of the cluster redshifts, and provide a means of determining cluster membership. (Abridged) Comment: 26 pages, 22 figures, accepted for publication in A&A High-resolution version of the paper and figures can be found at http://www.ast.obs-mip.fr/users/roser/photoz_EDISCS/10/2009; -
Article: The flattening and the orbital structure of early‐type galaxies and collisionless N‐body binary disc mergers
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ABSTRACT: We use oblate axisymmetric dynamical models including dark haloes to determine the orbital structure of intermediate mass to massive early-type galaxies in the Coma galaxy cluster. We find a large variety of orbital compositions. Averaged over all sample galaxies the unordered stellar kinetic energy in the azimuthal and the radial direction are of the same order, but they can differ by up to 40 per cent in individual systems. In contrast, both for rotating and non-rotating galaxies the vertical kinetic energy is on average smaller than in the other two directions. This implies that even most of the rotating ellipticals are flattened by an anisotropy in the stellar velocity dispersions. Using three-integral axisymmetric toy models, we show that flattening by stellar anisotropy maximizes the entropy for a given density distribution. Collisionless disc merger remnants are radially anisotropic. The apparent lack of strong radial anisotropy in observed early-type galaxies implies that they may not have formed from mergers of discs unless the influence of dissipational processes was significant.Monthly Notices of the Royal Astronomical Society 02/2009; 393(2):641 - 652. · 4.90 Impact Factor -
Article: Exploring Cluster Elliptical Galaxies as Cosmological Standard Rods
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ABSTRACT: We explore the possibility of calibrating massive cluster elliptical galaxies as cosmological standard rods using the fundamental plane relation combined with a correction for luminosity evolution. Although cluster ellipticals certainly formed in a complex way, their passive evolution out to redshifts of about 1 indicates that basically all major merging and accretion events took place at higher redshifts. Therefore, a calibration of their luminosity evolution can be attempted. We propose to use the Mg-σ relation for that purpose because it is independent of distance and cosmology. We discuss a variety of possible caveats, ranging from dynamical evolution to uncertainties in stellar population models and evolution corrections to the presence of age spread. Sources of major random and systematic errors are analyzed as well. We apply the described procedure to nine elliptical galaxies in two clusters at z = 0.375 and derive constraints on the cosmological model. For the best-fitting Λ-free cosmological model we obtain q0 ≈ 0.1, with 90% confidence limits being 0 < q0 < 0.7 (the lower limit being due to the presence of matter in the universe). If the inflationary scenario applies (i.e., the universe has flat geometry), then, for the best-fitting model, matter and Λ contribute about equally to the critical cosmic density (i.e., Ωm ≈ ΩΛ ≈ 0.5). With 90% confidence, ΩΛ should be smaller than 0.9.The Astrophysical Journal 01/2009; 493(2):529. · 6.02 Impact Factor
Top co-authors
Top Journals
Institutions
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2005–2011
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Max-Planck-Institut für extraterrestrische Physik
Garching bei München, Bavaria, Germany
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1996
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Ghent University
Gent, VLG, Belgium
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1993
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Carnegie Institute
Pasadena, TX, USA -
University of Padua
Padova, Veneto, Italy
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1989
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California Institute of Technology
Pasadena, CA, USA
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1988
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Scuola Normale Superiore di Pisa
Pisa, Tuscany, Italy
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