SDSSJ150634.27+013331.6: the second compact elliptical galaxy in the NGC5846 group

We report the discovery of the second compact elliptical (cE) galaxy SDSSJ150634.27+013331.6 in the nearby NGC5846 group by the Virtual Observatory (VO) workflow . This object (M_B = -15.98 mag, R_e = 0.24 kpc) becomes the fifth cE where the spatially-resolved kinematics and stellar populations can be obtained. We used archival HST WFPC2 images to demonstrate that its light profile has a two-component structure, and integrated photometry from GALEX, SDSS, UKIDSS, and Spitzer to build the multi-wavelength SED to constraint the star formation history (SFH). We observed this galaxy with the PMAS IFU spectrograph at the Calar-Alto 3.5m telescope and obtained two-dimensional maps of its kinematics and stellar population properties using the full-spectral fitting technique. Its structural, dynamical and stellar population properties suggest that it had a massive progenitor heavily tidally stripped by NGC5846.Comment: 5 pages, 4 figure, 1 table. Accepted to MNRAS Letter

Stellar Population Constraints on the Dark Matter Content and Origin of Ultra-Compact Dwarf Galaxies

We analyse intermediate-resolution VLT FLAMES/Giraffe spectra of six ultra-compact dwarf (UCD) galaxies in the Fornax cluster. We obtained velocity dispersions and stellar population properties by full spectral fitting against PEGASE.HR models. Objects span a large range of metallicities (-0.95 to -0.23 dex), 4 of them are older than 8 Gyr. Comparison of the stellar and dynamical masses suggests that UCDs have little dark matter at best. For one object, UCD3, the Salpeter initial mass function (IMF) results in the stellar mass significantly exceeding the dynamical one, whereas for the Kroupa IMF the values coincide. Although, this object may have peculiar dynamics or/and stellar populations, the Kroupa IMF seems more realistic. We find that UCDs lie well above the metallicity-luminosity relation of early-type galaxies. The same behaviour is demonstrated by some of the massive Milky Way globular clusters, known to contain composite stellar populations. Our results support two following UCD formation scenarii: (1) tidal stripping of nucleated dwarf elliptical galaxies; (2) formation of tidal superclusters in galaxy mergers. We also discuss some of the alternative channels of the UCD formation binding them to globular clusters.Comment: accepted to MNRAS, 7 pages, 4 figures, 3 table

Reflectivity of Venus’s Dayside Disk During the 2020 Observation Campaign: Outcomes and Future Perspectives

We performed a unique Venus observation campaign to measure the disk brightness of Venus over a broad range of wavelengths in 2020 August and September. The primary goal of the campaign was to investigate the absorption properties of the unknown absorber in the clouds. The secondary goal was to extract a disk mean SO2 gas abundance, whose absorption spectral feature is entangled with that of the unknown absorber at ultraviolet wavelengths. A total of three spacecraft and six ground-based telescopes participated in this campaign, covering the 52–1700 nm wavelength range. After careful evaluation of the observational data, we focused on the data sets acquired by four facilities. We accomplished our primary goal by analyzing the reflectivity spectrum of the Venus disk over the 283–800 nm wavelengths. Considerable absorption is present in the 350–450 nm range, for which we retrieved the corresponding optical depth of the unknown absorber. The result shows the consistent wavelength dependence of the relative optical depth with that at low latitudes, during the Venus flyby by MESSENGER in 2007, which was expected because the overall disk reflectivity is dominated by low latitudes. Last, we summarize the experience that we obtained during this first campaign, which should enable us to accomplish our second goal in future campaigns

Amas stellaires galactiques et extragalactiques effets dynamiques de la galaxie hôte

The subject of the thesis is the structure and dynamics of open and globular clusters in the Galaxy, as well as extragalactic star cluster systems. The aim is to better understand the processes controlling the evolution of stellar clusters, in particular when one takes into account tidal effects which disturb the spatial structure of individual star clusters and the overall distribution of the objects around their host galaxy. For resolved clusters, the detection of tidal tails requires multi-band, wide-field observations. Nearby open clusters were studied on digitized Schmidt plates. Once selected the probable cluster members in the colour-magnitude diagrams, a wavelet transform was used to reveal the shape of the clusters. The tidal extensions detected have been compared to the results of numerical simulations (Bulge attraction and Disk shocking). For the study of more distant objects, deeper images obtained from large format CCDs were needed. They allowed us to discover tidal tails around several binary but also isolated star clusters in the Large Magellanic Cloud. Finally, we have started to extend this work to the study of star cluster systems beyond the Local Group. In particular, we observed the Fornax cluster of galaxies and the compact group HCG 90 in order to detect wanderer globular clusters, ejected into the intergalactic space by strong dynamical phenomena occurring between galaxies. These new observations will be compared to numerical simulations of star cluster systems within groups of galaxies. This will bring interesting clues on the formation and evolution galaxies, as well as give new insights in the origin of various stellar populations.Cette thèse s’intéresse à la structure et à la dynamique des amas ouverts et globulaires de la Galaxie, avec une extension aux systèmes d’amas stellaires extragalactiques. Il s’agit de mieux comprendre les processus qui régissent l’évolution des amas stellaires, en particulier en tenant compte des effets produits sur ceux-ci par le potentiel de leur galaxie hôte, c’est-à-dire les effets de marées. La détection de ces phénomènes, qui modifient la structure spatiale individuelle des amas stellaires et les propriétés d’un système d’amas dans son ensemble, requiert notamment des observations photométriques multi-bandes et à grand champ. Des amas ouverts proches ont été étudiés sur des paires de plaques de Schmidt digitalisées. Après sélection des membres probables des amas dans les diagrammes couleur-magnitude obtenus, une transformée en ondelettes a permis d’étudier la structure spatiale des amas. Des extensions attribuées aux effets de marée – par comparaison à des simulations de l’attraction du Bulbe et du choc discal – ont été décelées dans chacun d’eux. Pour l’étude d’objets plus lointains, il fallait compléter les données existantes par des observations photométriques profondes avec des mosaïques de CCDs. Nous avons ainsi pu déceler des queues de marée autour de plusieurs amas stellaires binaires du Grand Nuage de Magellan. Enfin, nous avons étendu ce travail à l’étude de systèmes d’amas stellaires en dehors du Groupe Local, en observant l’amas Fornax et des groupes compacts de galaxie notamment pour y détecter des amas stellaires « vagabonds », éjectés dans le milieu intergalactique. Ces observations, comparées à des simulations de systèmes d’amas d’étoiles peuvent apporter des contraintes sur les scénarios de formation et d’évolution des galaxies, en même temps qu’éclairer l’origine des diverses populations stellaires

Star formation in isolated AMIGA galaxies: dynamical influence of bars

International audienceContext: Star formation depends strongly on both the local environment of galaxies and the internal dynamics of the interstellar medium. To disentangle the two effects, we obtained, in the framework of the AMIGA project, Halpha and Gunn r photometric data for more than 200 spiral galaxies lying in very low-density regions of the local Universe. Aims: We characterise the Halpha emission, tracing current star formation, of the 45 largest and least inclined galaxies observed for which we estimate the torques between the gas and the bulk of the optical matter. We subsequently study the Halpha morphological aspect of these isolated spiral galaxies. Methods: Using Fourier analysis, we focus on the modes of the spiral arms and also on the strength of the bars, computing the torques between the gas and newly formed stars (Halpha), and the bulk of the optical matter (Gunn r). Results: We interpret the various bar/spiral morphologies observed in terms of the secular evolution experienced by galaxies in isolation. We also classify the different spatial distributions of star forming regions in barred galaxies. The observed frequency of particular patterns brings constraints on the lifetime of the various evolution phases. We propose an evolutive sequence accounting for the transitions between the different phases we observed. Conclusions: Isolated galaxies do not appear to be preferentially barred or unbarred. Fitting the Halpha distributions using numerical simulations yields constraints on the star formation law, which is likely to differ from a genuine Schmidt law. In particular, it is probable that the relative velocity of the gas in the bar also needs to be taken into account

Star formation in isolated AMIGA galaxies: dynamical influence of bars

International audienceContext: Star formation depends strongly on both the local environment of galaxies and the internal dynamics of the interstellar medium. To disentangle the two effects, we obtained, in the framework of the AMIGA project, Halpha and Gunn r photometric data for more than 200 spiral galaxies lying in very low-density regions of the local Universe. Aims: We characterise the Halpha emission, tracing current star formation, of the 45 largest and least inclined galaxies observed for which we estimate the torques between the gas and the bulk of the optical matter. We subsequently study the Halpha morphological aspect of these isolated spiral galaxies. Methods: Using Fourier analysis, we focus on the modes of the spiral arms and also on the strength of the bars, computing the torques between the gas and newly formed stars (Halpha), and the bulk of the optical matter (Gunn r). Results: We interpret the various bar/spiral morphologies observed in terms of the secular evolution experienced by galaxies in isolation. We also classify the different spatial distributions of star forming regions in barred galaxies. The observed frequency of particular patterns brings constraints on the lifetime of the various evolution phases. We propose an evolutive sequence accounting for the transitions between the different phases we observed. Conclusions: Isolated galaxies do not appear to be preferentially barred or unbarred. Fitting the Halpha distributions using numerical simulations yields constraints on the star formation law, which is likely to differ from a genuine Schmidt law. In particular, it is probable that the relative velocity of the gas in the bar also needs to be taken into account