Laboratoire Dastrophysique Of Marseille

Saint-Rémy-de-Provence, France

Laboratoire Dastrophysique Of Marseille

Saint-Rémy-de-Provence, France
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Peschken N.,Laboratoire Dastrophysique Of Marseille | Peschken N.,Polish Academy of Sciences | Athanassoula E.,Laboratoire Dastrophysique Of Marseille | Rodionov S.A.,Laboratoire Dastrophysique Of Marseille
Monthly Notices of the Royal Astronomical Society | Year: 2017

We study the effect of angular momentum on the surface density profiles of disc galaxies, using high-resolution simulations of major mergers whose remnants have downbending radial density profiles (type II). As described in the previous papers of this series, in this scenario, most of the discmass is acquired after the collision via accretion from a hot gaseous halo. We find that the inner and outer disc scalelengths, as well as the break radius, correlate with the total angular momentum of the initial merging system, and are larger for high-angular momentum systems. We follow the angular momentum redistribution in our simulated galaxies, and find that like the mass, the disc angular momentum is acquired via accretion, i.e. to the detriment of the gaseous halo. Furthermore, high-angular momentum systems give more angular momentum to their discs, which directly affects their radial density profile. Adding simulations of isolated galaxies to our sample, we find that the correlations are valid also for disc galaxies evolved in isolation. We show that the outer part of the disc at the end of the simulation is populated mainly by inside-out stellar migration, and that in galaxies with higher angular momentum, stars travel radially further out. This, however, does not mean that outer disc stars (in type II discs) were mostly born in the inner disc. Indeed, generally the break radius increases over time, and not taking this into account leads to overestimating the number of stars born in the inner disc. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Popping A.,Laboratoire Dastrophysique Of Marseille | Popping A.,NOVA Kapteyn Astronomical Institute | Popping A.,CSIRO | Braun R.,CSIRO
Astronomy and Astrophysics | Year: 2011

Context. Observations of neutral hydrogen can provide a wealth of information about the kinematics of galaxies. To learn more about the large-scale structures and accretion processes, the extended environment of galaxies have to be observed. Numerical simulations predict a cosmic web of extended structures and gaseous filaments.Aims. To observe the direct vicinity of galaxies, column densities have to be achieved that probe the regime of Lyman limit systems. Typically, Hi observations are limited to a brightness sensitivity of NHI ∼ 1019 cm-2, but this has to be improved by ∼2 orders of magnitude.Methods. With the Westerbork Synthesis Radio Telescope (WSRT), we mapped the galaxy filament connecting the Virgo Cluster with the Local Group. About 1500 square degrees on the sky was surveyed with Nyquist sampled pointings. By using the WSRT antennas as single-dish telescopes instead of the more conventional interferometer, we were very sensitive to extended emission. The survey consists of a total of 22 000 pointings, and each pointing was observed for two minutes with 14 antennas.Results. We reached a flux sensitivity of 16 mJy beam-1 over 16 kms-1, corresponding to a brightness sensitivity of NHI ∼ 3.5 × 1016 cm-2 for sources that fill the beam. At a typical distance of ten Mpc probed by this survey, the beam extent corresponds to about 145 kpc on linear scale. Although the processed data cubes are affected by confusion owing to the very large beam size, we can identify most of the galaxies that have been observed in HIPASS. Furthermore we made 20 new candidate detections of neutral hydrogen. Several of the candidate detections can be linked to an optical counterpart. The majority of the features, however, do not show any signs of stellar emission. Their origin is investigated further with accompanying Hi surveys, which will be published in follow-up papers. © ESO 2011.

Schenker M.A.,California Institute of Technology | Stark D.P.,University of Cambridge | Ellis R.S.,California Institute of Technology | Robertson B.E.,California Institute of Technology | And 4 more authors.
Astrophysical Journal | Year: 2012

Using deep Keck spectroscopy of Lyman break galaxies selected from infrared imaging data taken with the Wide Field Camera 3 on board the Hubble Space Telescope, we present new evidence for a reversal in the redshift-dependent fraction of star-forming galaxies with detectable Lyman alpha (Lyα) emission in the redshift range 6.3 < z < 8.8. Our earlier surveys with the DEIMOS spectrograph demonstrated a significant increase with redshift in the fraction of line emitting galaxies over the interval 4 < z < 6, particularly for intrinsically faint systems which dominate the luminosity density. Using the longer wavelength sensitivities of Low Resolution Imaging Spectrometer and NIRSPEC, we have targeted 19 Lyman break galaxies selected using recent WFC3/IR data whose photometric redshifts are in the range 6.3 < z < 8.8 and which span a wide range of intrinsic luminosities. Our spectroscopic exposures typically reach a 5σ sensitivity of <50 Å for the rest-frame equivalent width (EW) of Lyα emission. Despite the high fraction of emitters seen only a few hundred million years later, we find only two convincing and one possible line emitter in our more distant sample. Combining with published data on a further seven sources obtained using FORS2 on the ESO Very Large Telescope, and assuming continuity in the trends found at lower redshift, we discuss the significance of this apparent reversal in the redshift-dependent Lyα fraction in the context of our range in continuum luminosity. Assuming all the targeted sources are at their photometric redshift and our assumptions about the Lyα EW distribution are correct, we would expect to find so few emitters in less than 1% of the realizations drawn from our lower redshift samples. Our new results provide further support for the suggestion that, at the redshifts now being probed spectroscopically, we are entering the era where the intergalactic medium is partially neutral. With the arrival of more sensitive multi-slit infrared spectrographs, the prospects for improving the statistical validity of this result are promising. © 2012 The American Astronomical Society. All rights reserved.

Guo Y.,University of Massachusetts Amherst | Giavalisco M.,University of Massachusetts Amherst | Ferguson H.C.,US Space Telescope Science Institute | Cassata P.,University of Massachusetts Amherst | And 2 more authors.
Astrophysical Journal | Year: 2012

This paper studies the properties of kiloparsec-scale clumps in star-forming galaxies at z∼2 through multi-wavelength broadband photometry. A sample of 40 clumps is identified from Hubble Space Telescope (HST)/Advanced Camera for Surveys (ACS) z-band images through auto-detection and visual inspection from 10galaxies with 1.5 < z < 2.5 in the Hubble Ultra Deep Field, where deep and high-resolution HST/WFC3 and ACS images enable us to resolve structures of z∼2 galaxies down to the kiloparsec scale in the rest-frame UV and optical bands and to detect clumps toward the faint end. The physical properties of clumps are measured through fitting spatially resolved seven-band (BVizYJH) spectral energy distribution to models. On average, the clumps are blue and have similar median rest-frame UV-optical color as the diffuse components of their host galaxies, but the clumps have large scatter in their colors. Although the star formation rate (SFR)-stellar mass relation of galaxies is dominated by the diffuse components, clumps emerge as regions with enhanced specific star formation rates, contributing individually ∼10% and together ∼50% of the SFR of the host galaxies. However, the contributions of clumps to the rest-frame UV/optical luminosity and stellar mass are smaller, typically a few percent individually and ∼20% together. On average, clumps are younger by 0.2dex and denser by a factor of eight than diffuse components. Clump properties have obvious radial variations in the sense that central clumps are redder, older, more extincted, denser, and less active on forming stars than outskirt clumps. Our results are broadly consistent with a widely held view that clumps are formed through gravitational instability in gas-rich turbulent disks and would eventually migrate toward galactic centers and coalesce into bulges. Roughly 40% of the galaxies in our sample contain a massive clump that could be identified as a proto-bulge, which seems qualitatively consistent with such a bulge-formation scenario. © © 2012. The American Astronomical Society. All rights reserved.

Maksym W.P.,Northwestern University | Maksym W.P.,University of Alabama | Ulmer M.P.,Northwestern University | Eracleous M.C.,Pennsylvania State University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

As part of our ongoing archival X-ray survey of galaxy clusters for tidal flares, we present evidence of an X-ray transient source within 1 arcmin of the core of Abell 1795. The extreme variability (a factor of nearly 50), luminosity (>2 × 1042 erg s-1), long duration (>5 yr) and supersoft X-ray spectrum (>0.1 keV) are characteristic signatures of a stellar tidal disruption event according to theoretical predictions and to existing X-ray observations, implying a massive {greater-than or approximate}105Ṁ black hole at the centre of that galaxy. The large number of X-ray source counts (~700) and long temporal baseline (~12yr with Chandra and XMM-Newton) make this one of the best sampled examples of any tidal flare candidate to date. The transient may be the same EUV source originally found contaminating the diffuse intracluster medium observations of Bowyer, Berghöfer and Korpela, which would make it the only tidal flare candidate with reported EUV observations and implies an early source luminosity 1-2 orders of magnitude greater. If the host galaxy is a clustermember then it must be a dwarf galaxy, an order of magnitude less massive than the quiescent galaxy Henize 2-10 which hosts a massive black hole that is difficult to reconcile with its low mass. The unusual faintness of the host galaxy may be explained by tidal stripping in the cluster core. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Giordano S.,National institute for astrophysics | Raymond J.C.,Harvard - Smithsonian Center for Astrophysics | Lamy P.,Laboratoire Dastrophysique Of Marseille | Uzzo M.,Computer Sciences Corp. | Dobrzycka D.,European Southern Observatory
Astrophysical Journal | Year: 2015

Comet C/2002 S2, amember of the Kreutz family of sungrazing comets,was discovered inwhite-light images of the Large Angle and Spectromeric Coronagraph Experiment coronagraph on the Solar and Heliospheric Observatory (SOHO) on 2002 September 18 and observed in H I Lyα emission by the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) instrument at four different heights as it approached the Sun. The H I Lyα line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width, and Doppler shift with respect to the coronal background. Two-dimensional comet images of these parameters are reconstructed at the different heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from most of the tail is blueshifted, that along one edge of the tail is redshifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature, and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the H I Lyα emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9m. This rate steadily increases as the comet approaches the Sun, while the optical brightness decreases by more than a factor of 10 and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms, and molecules produced by the comet. © 2015. The American Astronomical Society. All rights reserved.

Cebron D.,Aix - Marseille University | Le Bars M.,Aix - Marseille University | Moutou C.,Laboratoire Dastrophysique Of Marseille | Le Gal P.,Aix - Marseille University
Astronomy and Astrophysics | Year: 2012

Context. The presence of celestial companions means that any planet may be subject to three kinds of harmonic mechanical forcing: tides, precession/nutation, and libration. These forcings can generate flows in internal fluid layers, such as fluid cores and subsurface oceans, whose dynamics then significantly differ from solid body rotation. In particular, tides in non-synchronized bodies and libration in synchronized ones are known to be capable of exciting the so-called elliptical instability, i.e. a generic instability corresponding to the destabilization of two-dimensional flows with elliptical streamlines, leading to three-dimensional turbulence. Aims. We aim here at confirming the relevance of such an elliptical instability in terrestrial bodies by determining its growth rate, as well as its consequences on energy dissipation, on magnetic field induction, and on heat flux fluctuations on planetary scales. Methods. Previous studies and theoretical results for the elliptical instability are re-evaluated and extended to cope with an astrophysical context. In particular, generic analytical expressions of the elliptical instability growth rate are obtained using a local WKB approach, simultaneously considering for the first time (i) a local temperature gradient due to an imposed temperature contrast across the considered layer or to the presence of a volumic heat source and (ii) an imposed magnetic field along the rotation axis, coming from an external source. Results. The theoretical results are applied to the telluric planets and moons of the solar system as well as to three Super-Earths: 55 CnC e, CoRoT-7b, and GJ 1214b. For the tide-driven elliptical instability in non-synchronized bodies, only the early Earth core is shown to be clearly unstable. For the libration-driven elliptical instability in synchronized bodies, the core of Io is shown to be stable, contrary to previously thoughts, whereas Europa, 55 CnC e, CoRoT-7b, and GJ 1214b cores can be unstable. The subsurface ocean of Europa is slightly unstable. However, these present states do not preclude more unstable situations in the past. © ESO, 2012.

Meimon S.,ONERA | Fusco T.,ONERA | Fusco T.,Laboratoire Dastrophysique Of Marseille | Michau V.,ONERA | Plantet C.,ONERA
Optics Letters | Year: 2014

We propose here a novel way to analyze Shack-Hartmann wavefront sensor images in order to retrieve more modes than the two centroid coordinates per sub-aperture. To do so, we use the linearized focal-plane technique (LIFT) phase retrieval method for each sub-aperture. We demonstrate that we can increase the number of modes sensed with the same computational burden per mode. For instance, we show the ability to control a 21 × 21 actuator deformable mirror using a 10 × 10 lenslet array. © 2014 Optical Society of America.

Rozelot J.P.,University of Nice Sophia Antipolis | Damiani C.,National institute for astrophysics | Damiani C.,Laboratoire Dastrophysique Of Marseille
European Physical Journal H | Year: 2012

From time immemorial men have strived to measure the size of celestial bodies. Among them, the diameter of the Sun was a source of curiosity and study. Tackled by Greek astronomers from a geometric point of view, an estimate, although incorrect, has been first determined, not truly called into question for several centuries. One must wait up to the XVIIth century to get the first precise determinations made by the French school of astronomy. Gradually, as the techniques were more and more sophisticated, many other solar diameter measurements were carried out, notably in England, Germany, Italy and US. However, even with instruments at the cutting edge of progress, no absolute value of the solar diameter has been provided yet, even if the community has adopted a canonical radius of 959.″63, given in all ephemeris since the end of the XIXth century. One of the major difficulties is to define a correct solar diameter. Another issue is the possible temporal variability of the size of the Sun, as first advocated at the end of the XIXth century by the Italian school. Today, this question is just on the way to being solved in spite of considerable efforts developed on ground-based facilities or on board space experiments. We will here give a review of some of the most remarkable techniques used in the past, emphasising how incorrect measurements have driven new ideas, leading to develop new statements for the underlying physics. On such new grounds, it can be speculated that the roundness of the Sun is not perfect, but developing a thin "cantaloupe skin" in periods of higher activity, with departures from sphericity being inevitably bounded by a few kilometers (around 80 km or 10 to 15 mas). © 2012 EDP Sciences and Springer.

Vasiliev E.,Rochester Institute of Technology | Vasiliev E.,Laboratoire Dastrophysique Of Marseille
Monthly Notices of the Royal Astronomical Society | Year: 2013

We review the methods used to study the orbital structure and chaotic properties of various galactic models and to construct self-consistent equilibrium solutions by Schwarzschild's orbit superposition technique. These methods are implemented in a new publicly available software tool, SMILE, which is intended to be a convenient and interactive instrument for studying a variety of 2D and 3D models, including arbitrary potentials represented by a basis-set expansion, a spherical-harmonic expansion with coefficients being smooth functions of radius (splines) or a set of fixed point masses. We also propose two new variants of Schwarzschild modelling, in which the density of each orbit is represented by the coefficients of the basis-set or spline spherical-harmonic expansion, and the orbit weights are assigned in such a way as to reproduce the coefficients of the underlying density model. We explore the accuracy of these general-purpose potential expansions and show that they may be efficiently used to approximate a wide range of analytic density models and serve as smooth representations of discrete particle sets (e.g. snapshots from an N-body simulation), for instance, for the purpose of orbit analysis of the snapshot. For the variants of Schwarzschild modelling, we use two test cases - a triaxial Dehnen model containing a central black hole and a model re-created from an N-body snapshot obtained by a cold collapse. These tests demonstrate that all modelling approaches are capable of creating equilibrium models. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

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