P. Jablonka

Paris Diderot University, Lutetia Parisorum, Île-de-France, France

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Publications (155)445.96 Total impact

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    ABSTRACT: Fornax is one of the most massive dwarf spheroidal galaxies in the Local Group. The Fornax field star population is dominated by intermediate age stars but star formation was going on over almost its entire history. It has been proposed that Fornax experienced a minor merger event. Despite recent progress, only the high metallicity end of Fornax field stars ([Fe/H]>-1.2 dex) has been sampled in larger number via high resolution spectroscopy. We want to better understand the full chemical evolution of this galaxy by better sampling the whole metallicity range, including more metal poor stars. We use the VLT-FLAMES multi-fibre spectrograph in high-resolution mode to determine the abundances of several alpha, iron-peak and neutron-capture elements in a sample of 47 individual Red Giant Branch stars in the Fornax dwarf spheroidal galaxy. We combine these abundances with accurate age estimates derived from the age probability distribution from the colour-magnitude diagram of Fornax. Similar to other dwarf spheroidal galaxies, the old, metal-poor stars of Fornax are typically alpha-rich while the young metal-rich stars are alpha-poor. In the classical scenario of the time delay between SNe II and SNe Ia, we confirm that SNe Ia started to contribute to the chemical enrichment at [Fe/H] between -2.0 and -1.8 dex. We find that the onset of SNe Ia took place between 12-10 Gyrs ago. The high values of [Ba/Fe], [La/Fe] reflect the influence of SNe Ia and AGB stars in the abundance pattern of the younger stellar population of Fornax. Our findings of low [alpha/Fe] and enhanced [Eu/Mg] are compatible with an initial mass function that lacks the most massive stars and with star formation that kept going on throughout the whole history of Fornax. We find that massive stars kept enriching the interstellar medium in alpha-elements, although they were not the main contributor to the iron enrichment.
    Astronomy and Astrophysics 09/2014; 572. · 4.48 Impact Factor
  • Matthew Nichols, Yves Revaz, Pascale Jablonka
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    ABSTRACT: The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits, the resulting properties are compared with observations from a dynamical point of view, and from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. This quenching may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher ⟨[Fe/H]⟩/L ratios, but only when they lose ≳20% of stellar mass.Appendices are available in electronic form at http://www.aanda.org
    Astronomy and Astrophysics 03/2014; 564. · 4.48 Impact Factor
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    Matthew Nichols, Yves Revaz, Pascale Jablonka
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    ABSTRACT: The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits the resulting properties are compared with observations from both a dynamical point of view, but also from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. Such quenching, may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher $\langle$[Fe/H]$\rangle$/L ratios, but only when losing $>$$20\%$ of stellar mass.
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    ABSTRACT: We present the first survey of resolved stellar populations in the remote outer halo of our nearest giant elliptical (gE), Centaurus A (D = 3.8 Mpc). Using the VIsible Multi Object Spectrograph (VIMOS)/Very Large Telescope (VLT) optical camera, we obtained deep photometry for four fields along the major and minor axes at projected elliptical radii of ˜30-85 kpc (corresponding to ˜5-14Reff). We use resolved star counts to map the spatial and colour distribution of red giant branch (RGB) stars down to ˜2 mag below the RGB tip. We detect an extended halo out to the furthermost elliptical radius probed (˜85 kpc or ˜14Reff), demonstrating the vast extent of this system. We detect a localized substructure in these parts, visible in both (old) RGB and (intermediate-age) luminous asymptotic giant branch stars, and there is some evidence that the outer halo becomes more elliptical and has a shallower surface brightness profile. We derive photometric metallicity distribution functions for halo RGB stars and find relatively high median metallicity values (<[Fe/H]>med ˜ -0.9 to -1.0 dex) that change very little with radius over the extent of our survey. Radial metallicity gradients are measured to be ≈ -0.002-0.004 dex kpc-1, and the fraction of metal-poor stars (defined as [Fe/H] < -1.0) is ≈40-50 per cent at all radii. We discuss these findings in the context of galaxy formation models for the buildup of gE haloes.
    Monthly Notices of the Royal Astronomical Society 06/2013; 432(1):832-847. · 5.23 Impact Factor
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    ABSTRACT: We use OSIRIS in its long-slit mode to look for mass transfer and induced star formation in the interacting galaxy pair KPG 468.
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    ABSTRACT: Determining gas content and star formation rate has known remarkable progress in field galaxies, but has been much less investigated in galaxies inside clusters. We present the first CO observations of luminous infrared galaxies (LIRGs) inside the virial radii of two intermediate redshift clusters, CL1416+4446 (z=0.397) and CL0926+1242 (z=0.489). We detect three galaxies at high significance (5 to 10 sigma), and provide robust estimates of their CO luminosities, L'CO. In order to put our results into a general context, we revisit the relation between cold and hot gas and stellar mass in nearby field and cluster galaxies. We find evidence that at fixed LIR (or fixed stellar mass), the frequency of high L'CO galaxies is lower in clusters than in the field, suggesting environmental depletion of the reservoir of cold gas. The level of star formation activity in a galaxy is primarily linked to the amount of cold gas, rather than to the galaxy mass or the lookback time. In clusters, just as in the field, the conversion between gas and stars seems universal. The relation between LIR and L'CO for distant cluster galaxies extends the relation of nearby galaxies to higher IR luminosities. Nevertheless, the intermediate redshift galaxies fall well within the dispersion of the trend defined by local systems. Considering that L'CO is generally derived from the CO(1-0) line and sensitive to the vast majority of the molecular gas in the cold interstellar medium of galaxies, but less to the part which will actually be used to form stars, we suggest that molecular gas can be stripped before the star formation rate is affected. Combining the sample of Geach et al. (2009, 2011) and ours, we find evidence for a decrease in CO towards the cluster centers. This is the first hint of an environmental impact on cold gas at intermediate redshift.
    Astronomy and Astrophysics 03/2013; · 4.48 Impact Factor
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    ABSTRACT: Despite decades of work, it is still unclear whether a galaxy's properties are affected by environment or whether they are determined solely by the galaxy's mass. I will present new results that shed light on the key question of how the gas supplies of galaxies may be altered by dense environments. We use a stellar mass selected sample consisting of hundreds of cluster, group, and field galaxies at 0.4<z<0.8 with multi-wavelength imaging and deep spectroscopy. Using these data, we identify galaxies whose light is dominated by old stellar populations, as determined by the 4000 Angstrom Break and Balmer absorption line strengths. Contrary to expectations, we find that these "old" galaxies at intermediate redshift have a high likelihood of hosting weak [OII] emission. In contrast, analogously old galaxies in clusters and groups are significantly less likely to have activity. Based on the limited line ratio information that we have, the source of the emission in these galaxies is probably a weak AGN or gas heated by evolved stellar populations. Our results therefore imply that the cluster and group environments are effective at either stripping out gas from deep in the potential wells of galaxies or at cutting off their fuel supply of fresh new gas. Our work is possible because we probe a large number of clusters (not available in DEEP2 or COSMOS) as well as coeval group and field galaxies, and use deep Spitzer observations to search for dust-obscured star formation.
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    ABSTRACT: We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the Dwarf Abundances and Radial Velocities Team (DART) using the latest calibration. Of the seven extremely metal-poor candidates, five stars are confirmed to be extremely metal-poor (i.e., [Fe/H]<-3 dex), with [Fe/H]=-3.47 +/- 0.07 for our most metal-poor star. All are around or below [Fe/H]=-2.5 dex from the measurement of individual Fe lines. These values are in agreement with the CaT predictions to within error bars. None of the seven stars is found to be carbon-rich. We estimate a 2-13% possibility of this being a pure chance effect, which could indicate a lower fraction of carbon-rich extremely metal-poor stars in Sculptor compared to the Milky Way halo. The [alpha/Fe] ratios show a range from +0.5 to -0.5, a larger variation than seen in Galactic samples although typically consistent within 1-2sigma. One star seems mildly iron-enhanced. Our program stars show no deviations from the Galactic abundance trends in chromium and the heavy elements barium and strontium. Sodium abundances are, however, below the Galactic values for several stars. Overall, we conclude that the CaT lines are a successful metallicity indicator down to the extremely metal-poor regime and that the extremely metal-poor stars in the Sculptor dwarf galaxy are chemically more similar to their Milky Way halo equivalents than the more metal-rich population of stars.
    Astronomy and Astrophysics 11/2012; 549. · 4.48 Impact Factor
  • 10/2012;
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    ABSTRACT: We present a deep, wide-field optical study of the M81 group dwarf galaxy Holmberg II (HoII) based on Subaru/Suprime-Cam imaging. Individual stars are resolved down to I~25.2, i.e. about 1.5 mag below the tip of the red giant branch (RGB). We use resolved star counts in the outskirts of the galaxy to measure the radial surface brightness profile down to \mu_V~32 mag arcsec^-2, from which we determine a projected exponential scalelength of 0.70'+-0.01' (i.e. 0.69+-0.01 kpc). The composite profile, ranging from the cored centre out to R=7', is best fit by an EFF profile which gives a half-light radius of 1.41'+-0.04' (i.e. 1.39+-0.04 kpc), and an absolute magnitude M_V=-16.3. The low surface-brightness stellar component of HoII is regular and symmetric and has an extent much smaller than the vast HI cloud in which it is embedded. We compare the spatial distribution of the young, intermediate age, and old stellar populations, and find that the old RGB stars are significantly more centrally concentrated than the young stellar populations, contrary to what is observed in most dwarf galaxies of the Local Universe. We discuss these properties in the context of the comet-like distribution of HI gas around HoII, and argue for the presence of a hot intragroup medium in the vicinity of HoII to explain the contrasting morphologies of the gas and stars.
    Monthly Notices of the Royal Astronomical Society 08/2012; 426(4). · 5.23 Impact Factor
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    ABSTRACT: We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl1103.7$-$1245 (z=0.9580; sigma_{clus} = 522 +/- 111 km/s) we find a secondary structure at z=0.9830, Cl1103.7-1245c. We then characterize the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl1103.7-1245 z=0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z~1.
    Astronomy and Astrophysics 07/2012; · 4.48 Impact Factor
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    ABSTRACT: The target selection strategy, mask design procedure and observations are similar to those adopted for the EDisCS spectroscopy, described in detail in Halliday et al. (2004, Cat. J/A+A/427/397) and Milvang-Jensen et al. (2008, Cat. J/A+A/482/419). The target selection was based on the available VLT/FORS2 optical photometry (White et al., 2005, Cat. J/A+A/444/365) and the NTT/SOFI NIR photometry (Aragon-Salamanca et al., in preparation). The optical data cover 6.5'x6.5' and are well-matched to the FORS2 spectrograph field-of-view. The NIR data cover a somewhat smaller region of 4.2'x5.4'. Spectroscopic observations were completed using the FORS2 spectrograph (cf. Appenzeller et al., 1998Msngr..94....1A) on the VLT, during one observing run in March 2008, comprised of 3 half-nights. A high-efficiency grism was used (grism 600RI+19, λcentral=6780Å, resolution FWHM~6Å). The exposure time was 1800 seconds per frame, for a total of 8 frames per mask. A total of 3 masks were observed, for a total of 94 slits (33 slits in mask 1 and 2 and 28 slits in mask 3). The reduction was performed using an "improved sky subtraction", whose properties and advantages have been largely described and discussed in Milvang-Jensen et al. (2008, Cat. J/A+A/482/419). Galaxy redshifts were measured from the reduced 1D spectra, using emission lines where possible, as done in Poggianti et al. (2006ApJ...642..188P). In addition, when possible, we also measured the equivalent width of [OII] and Hδ. Note that for star-forming galaxies the Hδ absorption line may be affected by emission in-filling. We have not attempted to correct for this effect. (1 data file).
    VizieR Online Data Catalog. 07/2012;
  • Y. Revaz, P. Jablonka
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    ABSTRACT: GEAR is a new fully parallel chemodynamical Tree/SPH code designed to study the formation and evolution of galaxies. GEAR treats the complex physics of baryons, such as radiative cooling and feedback, star formation, and chemical evolution. It has been fully characterized by performing hundreds of simulations, including convergence tests with the spatial resolution varying from 100 pc down to 12 pc. We demonstrate here the performance of GEAR in the context of the evolution of the dwarf spheroidal galaxies. Our models, combined with the stellar chemical abundances derived from high resolution spectroscopy in a sample of dSphs (The ESO Large Programme DART), bring crucial clues on otherwise poorly constrained physical parameters, such as the supernova feedback, star formation efficiency or galaxy mass profiles. Moreover, these new simulations allow to predict the number of stars formed in a given dark matter halo mass, providing a crucial test for cosmology.
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    ABSTRACT: The detailed abundances of 23 chemical elements in nine bright red giant branch stars in the Carina dwarf spheroidal galaxy are presented based on high-resolution spectra gathered at the Very Large Telescope (VLT) and Magellan telescopes. A spherical model atmospheres analysis is applied using standard methods (local thermodynamic equilibrium and plane-parallel radiative transfer) to spectra ranging from 380 to 680 nm. Stellar parameters are found to be consistent between photometric and spectroscopic analyses, both at moderate and high resolution. The stars in this analysis range in metallicity from –2.9 < [Fe/H] <–1.3, and adopting the ages determined by Lemasle et al., we are able to examine the chemical evolution of Carina's old and intermediate-aged populations. One of the main results from this work is the evidence for inhomogeneous mixing in Carina and therefore for a poor statistical sampling of the supernova contributions when forming stars; a large dispersion in [Mg/Fe] indicates poor mixing in the old population, an offset in the [α/Fe] ratios between the old and intermediate-aged populations (when examined with previously published results) suggests that the second star formation event occurred in α-enriched gas, and one star, Car-612, seems to have formed in a pocket enhanced in SN Ia/II products. This latter star provides the first direct link between the formation of stars with enhanced SN Ia/II ratios in dwarf galaxies to those found in the outer Galactic halo (Ivans et al.). Another important result is the potential evidence for SN II driven winds. We show that the very metal-poor stars in Carina have not been enhanced in asymptotic giant branch or SN Ia products, and therefore their very low ratios of [Sr/Ba] suggests the loss of contributions from the early SNe II. Low ratios of [Na/Fe], [Mn/Fe], and [Cr/Fe] in two of these stars support this scenario, with additional evidence from the low [Zn/Fe] upper limit for one star. It is interesting that the chemistry of the metal-poor stars in Carina is not similar to those in the Galaxy, most of the other dwarf spheroidal galaxies, or the ultra faint dwarfs, and suggests that Carina may be at the critical mass where some chemical enrichments are lost through SN II driven winds.
    The Astrophysical Journal 05/2012; 751(2):102. · 6.28 Impact Factor
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    ABSTRACT: We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other elements in these galaxies, including alpha and iron-peak ones, which allowed us to build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\sim -1.8 and -1.4 and decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the dSph galaxies is clearly systematically offset from that for the Milky Way, which reflects the different star formation histories of the respective galaxies. The [Mn/alpha] behavior can be interpreted as a result of the metal-dependent Mn yields of type II and type Ia supernovae. We also computed chemical evolution models for star formation histories matching those determined empirically for Sculptor, Fornax, and Carina, and for the Mn yields of SNe Ia, which were assumed to be either constant or variable with metallicity. The observed [Mn/Fe] versus [Fe/H] relation in Sculptor, Fornax, and Carina can be reproduced only by the chemical evolution models that include a metallicity-dependent Mn yield from the SNe Ia.
    Astronomy and Astrophysics 03/2012; · 4.48 Impact Factor
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    ABSTRACT: The primary goal of the Local Cluster Survey is to measure the variations in the spatial extent of cold disk gas relative to the stellar disk for approximately 400 low-redshift group and cluster galaxies (z < 0.037) in order to quantify the relative importance of the physical mechanisms that cause galaxies to evolve from blue, actively star-forming galaxies to red, passive galaxies. The sample consists of 9 groups and clusters that span a range of X-ray luminosities, and all have optical photometry and spectroscopy from the SDSS, infrared 24-micron imaging from the Spitzer Space Telescope, and radio data from the ALFALFA survey. The wide areal coverage of these data allows us to track the evolution of disk gas from the dense cluster core to the surrounding field. Here we present a preliminary analysis of the stellar and gas radial profiles for the group and cluster galaxies. We compare with those of the surrounding field galaxies to look for signatures of environmentally-driven gas depletion.
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    ABSTRACT: The spectroscopic observations were carried out at VLT/FLAMES between 2003 and 2004, with the exception of one pointing which was re-observed in 2008 May, during the commissioning of the upgraded Grating Instrument for Radiation Analysis with a Fiber-FedEchelle (GIRAFFE) spectrograph CCD. (1 data file).
    VizieR Online Data Catalog. 10/2011;
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    ABSTRACT: The sample of galaxies analyzed in this paper consists of spectroscopic early-type objects. We considered the flux-calibrated spectra reduced in Halliday et al. (2004, Cat. J/A+A/427/397) and Milvang-Jensen et al. (2008, Cat. J/A+A/482/419) of galaxies with early spectral type (1 or 2). (3 data files).
    VizieR Online Data Catalog. 04/2011;
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    ABSTRACT: Observations were made in 12 runs, from 2003-09-29 to 2004-01-26. (5 data files).
    VizieR Online Data Catalog. 03/2011;
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    ABSTRACT: We present the results of a dedicated search for extremely metal-poor stars in the Fornax, Sculptor and Sextans dSphs. Five stars were selected from two earlier VLT/Giraffe and HET/HRS surveys and subsequently followed up at high spectroscopic resolution with VLT/UVES. All of them turned out to have [Fe/H] <= -3 and three stars are below [Fe/H]~-3.5. This constitutes the first evidence that the classical dSphs Fornax and Sextans join Sculptor in containing extremely metal-poor stars and suggests that all of the classical dSphs contain extremely metal-poor stars. One giant in Sculptor at [Fe/H]=-3.96 +- 0.10 is the most metal-poor star ever observed in an external galaxy. We carried out a detailed analysis of the chemical abundances of the alpha, iron peak, and the heavy elements, and we performed a comparison with the Milky Way halo and the ultra faint dwarf stellar populations. Carbon, barium and strontium show distinct features characterized by the early stages of galaxy formation and can constrain the origin of their nucleosynthesis. Comment: Accepted for publication in A&A
    Astronomy and Astrophysics 02/2011; 527:1. · 4.48 Impact Factor

Publication Stats

2k Citations
445.96 Total Impact Points


  • 2008–2014
    • Paris Diderot University
      Lutetia Parisorum, Île-de-France, France
  • 2005–2012
    • École Polytechnique Fédérale de Lausanne
      • Psychophysics Laboratory
      Lausanne, Vaud, Switzerland
  • 2009
    • The Graduate University for Advanced Studies
      • Department of Astronomical Science
      Миура, Kanagawa, Japan
  • 2006–2009
    • University of Geneva
      Genève, Geneva, Switzerland
  • 1991–2007
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France
  • 2004
    • University of Nottingham
      • School of Physics and Astronomy
      Nottingham, ENG, United Kingdom
  • 2003
    • University of Liège
      • Department of Astrophysics, Geophysics and Oceanography
      Luik, Walloon Region, Belgium
  • 1990
    • Universidade Federal do Rio Grande do Sul
      • Departamento de Astronomia
      Pôrto de São Francisco dos Casaes, Rio Grande do Sul, Brazil