Observatoire de Strasbourg

Strasbourg, France

Observatoire de Strasbourg

Strasbourg, France
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Zwitter T.,University of Ljubljana | Matijevic G.,University of Ljubljana | Breddels M.A.,University of Groningen | Smith M.C.,University of Groningen | And 24 more authors.
Astronomy and Astrophysics | Year: 2010

The RAdial Velocity Experiment (RAVE) is a spectroscopic survey of the Milky Way which already collected over 400000 spectra of ∼330000 different stars. We use the subsample of spectra with spectroscopically determined values of stellar parameters to determine the distances to these stars. The list currently contains 235  064 high quality spectra which show no peculiarities and belong to 21872 different stars. The numbers will grow as the RAVE survey progresses. The public version of the catalog will be made available through the CDS services along with the ongoing RAVE public data releases. The distances are determined with a method based on the work by Breddels et al. (2010, A&A, 511, A16). Here we assume that the star undergoes a standard stellar evolution and that its spectrum shows no peculiarities. The refinements include: the use of either of the three isochrone sets, a better account of the stellar ages and masses, use of more realistic errors of stellar parameter values, and application to a larger dataset. The derived distances of both dwarfs and giants match within ∼ 21% to the astrometric distances of Hipparcos stars and to the distances of observed members of open and globular clusters. Multiple observations of a fraction of RAVE stars show that repeatability of the derived distances is even better, with half of the objects showing a distance scatter of ≲ 11%. RAVE dwarfs are ∼ 300 pc from the Sun, and giants are at distances of 1 to 2 kpc, and up to 10 kpc. This places the RAVE dataset between the more local Geneva-Copenhagen survey and the more distant and fainter SDSS sample. As such it is ideal to address some of the fundamental questions of Galactic structure and evolution in the pre-Gaia era. Individual applications are left to separate papers, here we show that the full 6-dimensional information on position and velocity is accurate enough to discuss the vertical structure and kinematic properties of the thin and thick disks. © 2010 ESO.

Kewley L.J.,Research School for Astronomy and Astrophysics | Kewley L.J.,University of Hawaii at Manoa | Dopita M.A.,Research School for Astronomy and Astrophysics | Dopita M.A.,King Abdulaziz University | And 8 more authors.
Astrophysical Journal | Year: 2013

We use the chemical evolution predictions of cosmological hydrodynamic simulations with our latest theoretical stellar population synthesis, photoionization, and shock models to predict the strong line evolution of ensembles of galaxies from z = 3 to the present day. In this paper, we focus on the brightest optical emission-line ratios, [N II]/Hα and [O III]/Hβ. We use the optical diagnostic Baldwin-Phillips-Terlevich (BPT) diagram as a tool for investigating the spectral properties of ensembles of active galaxies. We use four redshift windows chosen to exploit new near-infrared multi-object spectrographs. We predict how the BPT diagram will appear in these four redshift windows given different sets of assumptions. We show that the position of star-forming galaxies on the BPT diagram traces the interstellar medium conditions and radiation field in galaxies at a given redshift. Galaxies containing active galactic nucleus (AGN) form a mixing sequence with purely star-forming galaxies. This mixing sequence may change dramatically with cosmic time, due to the metallicity sensitivity of the optical emission-lines. Furthermore, the position of the mixing sequence may probe metallicity gradients in galaxies as a function of redshift, depending on the size of the AGN narrow-line region. We apply our latest slow shock models for gas shocked by galactic-scale winds. We show that at high redshift, galactic wind shocks are clearly separated from AGN in line ratio space. Instead, shocks from galactic winds mimic high metallicity starburst galaxies. We discuss our models in the context of future large near-infrared spectroscopic surveys. © 2013. The American Astronomical Society. All rights reserved.

Evans C.J.,Astronomy Technology Center | Puech M.,University Paris Diderot | Barbuy B.,University of Sao Paulo | Bonifacio P.,University Paris Diderot | And 55 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for two observational modes to best exploit the large (≥40 arcmin2) patrol field of the E-ELT. The first mode ('high multiplex') requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously. The second ('high definition'), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10 objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the toplevel requirements from each case and introduce the next steps in the design process. © 2014 SPIE.

Lockhart K.E.,Institute for Astronomy | Kewley L.J.,Australian National University | Lu J.R.,Institute for Astronomy | Allen M.G.,Observatoire de Strasbourg | And 8 more authors.
Astrophysical Journal | Year: 2015

We present a high spatial resolution optical and infrared study of the circumnuclear region in Arp 220, a late-stage galaxy merger. Narrowband imaging using Hubble Space Telescope/WFC3 has resolved the previously observed peak in Hα+[N ii] emission into a bubble-shaped feature. This feature measures 1.″6 in diameter, or 600 pc, and is only 1″ northwest of the western nucleus. The bubble is aligned with the western nucleus and the large-scale outflow axis seen in X-rays. We explore several possibilities for the bubble origin, including a jet or outflow from a hidden active galactic nucleus (AGN), outflows from high levels of star formation within the few hundred pc nuclear gas disk, or an ultraluminous X-ray source. An obscured AGN or high levels of star formation within the inner ∼100 pc of the nuclei are favored based on the alignment of the bubble and energetics arguments. © 2015. The American Astronomical Society. All rights reserved.

Fathi K.,Albanova University Center | Fathi K.,The Oskar Klein Center | Allen M.,Observatoire de Strasbourg | Boch T.,Observatoire de Strasbourg | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We have derived disc scalelengths for 30 374 non-interacting disc galaxies in all five Sloan Digital Sky Survey (SDSS) bands. Virtual Observatory methods and tools were used to define, retrieve and analyse the images for this unprecedentedly large sample classified as disc/spiral galaxies in the LEDA catalogue. Cross-correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scalelengths for different types of disc/spiral galaxies. We further investigate asymmetry, concentration and central velocity dispersion as indicators of morphological type, and are able to assess how the scalelength varies with respect to galaxy type. We note, however, that the concentration and asymmetry parameters have to be used with caution when investigating type dependence of structural parameters in galaxies. Here, we present the scalelength derivation method and numerous tests that we have carried out to investigate the reliability of our results. The average r-band disc scalelength is 3.79 kpc, with an rms dispersion of 2.05 kpc, and this is a typical value irrespective of passband and galaxy morphology, concentration and asymmetry. The derived scalelengths presented here are representative for a typical galaxy mass of 1010.8±0.54 M⊙, and the rms dispersion is larger for more massive galaxies. Separating the derived scalelengths for different galaxy masses, the r-band scalelength is 1.52 ± 0.65 kpc for galaxies with total stellar mass 109-1010 M⊙ and 5.73 ± 1.94 kpc for galaxies with total stellar mass between 1011 and 1012 M⊙. Distributions and typical trends of scalelengths have also been derived in all the other SDSS bands with linear relations that indicate the relation that connect scalelengths in one passband to another. Such transformations could be used to test the results of forthcoming cosmological simulations of galaxy formation and evolution of the Hubble sequence. © 2010 The Authors. Journal compilation © 2010 RAS.

Groves B.A.,Leiden University | Allen M.G.,Observatoire de Strasbourg
New Astronomy | Year: 2010

We present a new software tool to enable astronomers to easily compare observations of emission-line ratios with those determined by photoionization and shock models, ITERA, the IDL Tool for Emission-line Ratio Analysis. This tool can plot ratios of emission lines predicted by models and allows for comparison of observed line ratios against grids of these models selected from model libraries associated with the tool. We provide details of the libraries of standard photoionization and shock models available with ITERA, and, in addition, present three example emission-line ratio diagrams covering a range of wavelengths to demonstrate the capabilities of ITERA. ITERA, and associated libraries, is available from http://www.brentgroves.net/itera.html. © 2010 Elsevier B.V. All rights reserved.

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