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suivant: Session ASHRA-SF2A-SAIt monter: Session ASGaia-PNCG précédent: Session ASGaia-PNCG

Poster contributions

The catalogue of Radial Velocity standard stars for the RVS : status and progress
L. Chemin, C. Soubiran, F. Crifo, G. Jasniewicz, L. Veltz, D. Hestroffer, D. Katz, A. Siebert, S. Udry
(Laboratoire d'Astrophysique de Bordeaux)
A new full-sky catalogue of Radial Velocity standard stars is being built for the determination of the Radial Velocity Zero Point (RVZP) of the RVS. After a careful selection of 1420 candidates matching well defined criteria, we are now observing all of them to verify that they are stable enough over several years to be qualified as reference stars. We present the status of this long-term observing programme on three spectrographs : SOPHIE, NARVAL and CORALIE, complemented by the ELODIE archive. Because each instrument has its own zero-point, we observe intensively IAU RV standards and asteroids to homogenize the radial velocity measurements. We can already estimate that $\sim$10% of the candidates have to be rejected because of variations larger than the requested level of 300 m/s.

SED fitting of nearby galaxies in the Herschel Reference Survey
Laure Ciesla, Alessandro Boselli, Véronique Buat, Luca Cortese
(Laboratoire d'Astrophysique de Marseille)
The Herschel Reference Survey is a guaranteed time Herschel (infrared ESA space observatory) key project and will be a benchmark study of dust in the nearby universe (Boselli et al. 2010a). We use Herschel images of a statistically complete sample of 323 galaxies at 250, 360, 520 $\sim$m. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the centre of the Virgo Cluster). We plan to use the Survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass and environment, (ii) the connexion between the dust content and composition and the other phases of the interstellar medium, and (iii) the origin and evolution of dust in galaxies. We also use the available multi-frequency data to carry out an analysis of the statistical properties of the sample. The first step of this work is to perform optical, near-infrared and far-infrared photometry of the selected galaxies (data are given by SDSS, Spitzer and Herschel telescopes). For other wavelengths (ultra-violet, radio), we use data from the NASA database NED. Yet, we have computed UV to radio continuum spectral energy distributions of 51 nearby galaxies recently observed with SPIRE (Spectral and Photometric Imaging REceiver) onboard Herschel (Boselli et al. 2010b). We fit the data using Draine & Li (2007) models of dust emission implemented in the code CIGALE (Code Investigating GALaxy Emission, Noll et al. 2009). CIGALE enables us to determine the best fit model and, thanks to a Bayesian analysis, estimate several physical parameters such as dust mass, dust temperatures, the fraction of PAH composing the dust, for all the galaxies of the sample. The results of Draine & Li (2007) are compared to those obtained using other models or SED templates such as Siebenmorgen & Krügel (2007), Dale & Helou (2002), Chary & Elbaz (2001), and combinations of modified black bodies, in order to compare them. The goal of this study is to provide galaxy parameters and SEDs templates for all morphological types in any environment.

LIRGs at intermediate redshift
Studying Luminous InfraRed Galaxies (LIRGs) is particularly important in the growing-up of the stellar mass from z=1 to z=0, and to determine physical properties of these objects at the redshift 0.7. LIRGs are now identified to play a major role in galaxy evolution from z=1 to 0. The global star formation rate (SFR) at z $\sim$ 0.7 is mainly produced by LIRGs. We perform a multiwavelengths study of a LIRGs sample in the Extended Chandra Deep Field South at z=0.7, selected at 24 $\mu$m by MIPS onboard Spitzer Space Telesco pe and detected in 17 filters. Data go from the near ultraviolet to the mid-infrared. This multiwavelengths dataset allows us to bring strong constraints on the spectral energy distributions (SEDs) of galaxies, and thus to efficiently derive physical parameters as the SFR, the total infrared luminosity, attenuation parameters and star formation history. We distinguish a sub-sample of galaxies detected at 70 $\mu$m which we compare to the rest of the sample to investigate the relative importance of this wavelength on the determination of the physical parameters. An important part of this work is the elaboration of a mock catalogue which allows us to have a reliability criteria for the derived parameters. We study LIRGs by means of a SED-fitting code CIGALE. At first, this code creates synthetic spectra from the Maraston (2005) stellar population models.The stellar population spectra are being attenuated by using a synthetic Calzetti-based attenuation law before the addition of the dust emission as given by the infrared SED library of Dale&Helou (2002). The originality of CIGALE is that it allows us to perform consistent fits of the dust-affected ultaviolet-to-infrared wavelength range. This technique appears to be a very powerful tool in the case where we can have access to a dataset well-sampled over a large range of wavelengths. We are able to derive a star formation history and to estimate the fraction of infrared luminosity reprocessed by an active galactic nucleus. We study the dust temperatures of our galaxies detected at 70 $\mu$m and find them colder than predicted by models. We also study the relation between the SFR and the stellar mass and do not find a tight correlation between both, but a flat distribution and a large scatter which is interpreted in terms of variations of star formation history.

Cosmological simulations and galaxy formation: prospects for HST/WFC3
S. Peirani, R. M. Crockett, S. Geen, S. S. Khochfar, S. Kaviraj & J. Silk
The star formation history of nearby early-type galaxies is investigated via numerical modelling. Idealized hydrodynamical N-body simulations with a star formation prescription are used to study the minor merger process between a giant galaxy (host) and a less massive spiral galaxy (satellite). We find that the evolution of the star formation rate is extended over several dynamical times and shows peaks which correspond to pericentre passages of the satellite. The newly formed stars are mainly located in the central part of the satellite remnant while the older stars of the initial disc are deposited at larger radii in shell-like structures. Synthetic 2D images in J, H, NUV, H$\beta$ and V bands, using the characteristic filters of the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope, reveal that residual star formation induced by gas-rich minor mergers can be clearly observed during and after the final plunge, especially in the near-ultraviolet band, for interacting systems at (z <= 0.023) over moderate numbers of orbits.

The Herschel view of HII regions in M33 (HERM33ES)
S. Verley, M. Relaño, C. Kramer, E. M. Xilouris, M. Boquien, D. Calzetti, F. Combes, C. Buchbender, J. Braine, G. Quintana-Lacaci, F. S. Tabatabaei, S. Lord, F. Israel, G. Stacey, P. van der Werf
(Universidad de Granada - LERMA ObsPM)
Using the high resolution and sensitivity of the Herschel PACS and SPIRE photometric data, we study the compact emission in the Local Group spiral galaxy M33 to investigate the nature of the compact SPIRE emission sources. We extracted a catalogue of sources at 250um in order to investigate the nature of this compact emission. For the 159 compact sources selected at 250um, we find a very strong Pearson correlation coefficient with the MIPS 24um emission and a rather strong correlation with the Halpha emission, although with more scatter. The very strong link between the 250um compact emission and the 24um and Halpha emissions, by recovering the star formation rate from standard recipes for HII regions, allows us to provide star formation rate calibrations based on the 250um compact emission alone. Taking advantage of the unprecedented Herschel resolution at these wavelengths, we also focus on a more precise study of some striking Halpha shells in the northern part of the galaxy. The morphological study of the Halpha shells shows a displacement between far-ultraviolet, Halpha, and the SPIRE bands. The different locations of the Halpha and far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to a dynamical age of a few Myr for the Halpha shells and the associated cool dust.

The XMM large scale structure survey
Nicolas CLERC, Marguerite PIERRE, Jon WILLIS and the XMM-LSS collaboration
(CEA/Service d'astrophysique)
The XMM-LSS is the largest deep galaxy cluster survey to date. Extensive coverage exists from X-ray to radio wavelengths over the 11 deg2 area. The survey enables the detection of clusters (M$\sim$10$^{14}$ Mo) well above z$>$1, taking into account the well-modelled selection function. We provide the current census of the XMM-LSS clusters and focus on the characterization and identification of high redshift (z$>$1.2) X-ray clusters.

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suivant: Session ASHRA-SF2A-SAIt monter: Session ASGaia-PNCG précédent: Session ASGaia-PNCG
Samuel Boissier 2010-06-16