377 research outputs found
Opening remarks (Emsellem)
No full textI will provide a few introductory words about the European Southern Observatory (ESO), one of the sponsors of the present conference, taking this opportunity to provide important factual items pertaining to the recently established Australia-ESO partnership, and its already evident positive impact (observing programmes, collaborations, etc). I will advertise further the existing opportunities, which go well beyond Paranal/La Silla observing time, and will give a perspective for the future. I will end up on a final note of encouragement for a prompt engagement from all to contribute (now) to this unique adventure.
This presentation will be delivered in close coordination with astronomer Fred Watson from the Department of Industry, Innovation and Science (DIIS)
Star Formation Feedback on the ISM Properties
No full textWe observed nearby (D < 10 Mpc) galaxies (Henize 2-10, IC 10, IC 342, M 83, NGC 253 and NGC 6946) in the rotational lines of carbon monoxide CO and in the fine-structure transitions of atomic carbon [CI] with the Caltech Submillimeter Observatory (CSO). Using our new data, those from the literature and the LVG and PDR models, we derived the physical properties of the warm and dense molecular gas (kinetic temperature, UV radiation field, gas density...) in each nucleus. We predicted lines intensities for the ^(12)CO(5-4), ^(12)CO(7-6) and ^(12)CO(8-7) lines which are, even now, still difficult or impossible to detect from the ground but will become available in few years with ALMA and HIFI or PACS, on board the Herschel satellite. Studying the ISM of nearby galaxies, we provide a first step in the understanding of the ISM processes in more distant galaxies
Optical emission lines in the most massive galaxies: Morphology, kinematics, and ionisation properties
No full textIn order to better characterise the upper end of the galaxy stellar mass range, the MUSE Most Massive Galaxies (M3G) Survey targeted the most massive galaxies (M > 1012 M⊙) found in the densest known clusters of galaxies at z ∼ 0.046. The sample is composed of 25 early-type galaxies: 14 brightest cluster galaxies (BCGs), of which 3 are in the densest region of the Shapley super cluster (SSC), and 11 massive satellites in the SSC. In the present work we use MUSE data to derive the spatial distribution and kinematics of the gas and discuss its ionisation mechanism and origin in the optical wavelength range. We fit the continuum of the spectra using an extensive library of single stellar population models and model the emission lines employing up to three Gaussian functions. In the M3G sample, ionised gas was detected in five BCGs, of which one is in the densest region of the SSC, and six massive satellites in the SSC. Among these objects, [O
Formation and evolution of the low-mass galaxies, from the local to the intermediate redshift universe
No full textLes galaxies de faible masse constituent la population de galaxies la plus nombreuse à tous les âges de l'Univers, et sont légitimement considérées dans un contexte cosmologique comme les "éléments fondamentaux" de la croissance des galaxies. Dans l'Univers local, les galaxies de faible masse se trouvent principalement dans des amas de galaxies où elles se forment à partir de processus complexes de formation in-situ et d'événements d' accrétion. Cependant, les détails de la formation des galaxies de faible masse et de leurs processus d'évolution, ainsi que leurs rôles exacts dans la formation des galaxies plus massives sont encore très peu contraints. Ceci est dû en particulier aux difficultés technologiques associées à leur observation. Après une introduction sur les connaissances actuelles des galaxies de faible masse, je présente l'étude d'un échantillon de huit galaxies compactes dans l'amas de la Vierge. À l'aide de leur cinématique et de propriétés telles que l'âge et la métallicité de leur population stellaire estimées avec les données du spectrographe intégral de champ (IFS) GMOS/Gemini, je démontre que les propriétés des populations stellaires évoluent de manière continue avec la taille des galaxies, leurs masses, ainsi qu'avec leurs environnements, et ceci à la fois pour les galaxies de faible et de grande masse. Cela suggère que l'ensemble des processus physiques qui contrôlent les caractéristiques des galaxies sont similaires quelle que soit la masse des galaxies, mais en revanche, leurs influences individuelles varient doucement suivant la taille et la masse des galaxies. J'estime ensuite les histoires de formation stellaire de ces huit galaxies compactes ainsi que celles d'un échantillon de 20 galaxies de faible masse, et présente une étude de leur dépandence par rapport à l'environnement et la masse des galaxies. Ainsi, grâce à cette étude, je mets en avant à la fois le rôle important de l'environnement mais également celui des galaxies les plus massives dans le contrôle de la formation et de l'évolution des galaxies de faible masse. Mais les processus d'évolution des galaxies sont complexes et les galaxies de l'Univers local sont seulement leurs produits finaux, ce qui ne donne que peu de contraintes sur l' évolution des galaxies au début de l'histoire de l'Univers. Je montre alors à l'aide d'observations de la galaxie NGC3115 obtenues avec l'IFS MUSE/VLT, que les cartes de cinématique et de populations stellaires de galaxies couvrant une grande surface et ayant une grande résolution spatiale sont des éléments clés pour révéler l'histoire d'assemblage de la masse des galaxies, et donc leur formation et leur évolution au cours de toute l'histoire de l'Univers. Pour mieux contraindre la formation des galaxies de faible masse, j'utilise donc les observations profondes de l'instrument MUSE/VLT dans le champ de Hubble (HDFS) pour étudier un échantillon de dix galaxies à des décalages spectraux intermédiaires. J' estime pour la première fois la cinématique stellaire de galaxies situées entre z ~ 0.2 - 0.7 et montre que le degré de rotation et de dispersion de vitesse stellaire est en accord avec les précédentes études portant sur la cinématique de leur gaz. De telles informations, confrontées aux modèles d'évolution de galaxies aideront ainsi à mieux comprendre la croissance en masse des galaxies ainsi que l'origine des galaxies de faible masse de l'Univers local.Low-mass galaxies form the most numerous galaxy population in the Universe at all cosmic times, and are legitimately considered as the "building-blocks" of galaxy formation in a cosmological context. In the local Universe, low-mass galaxies are preferentially found in galaxy clusters where they form through a complex chain of in-situ formation and accretion events. However, the detailed formation and evolution processes of low-mass galaxies, and their exact roles in the formation of more massive galaxies are still poorly constrained, in particular due to challenging observations. After setting the scene with an introduction on our current understanding of low-mass galaxies, I present the study of a sample of eight compact low-mass galaxies in the Virgo cluster. I derive their stellar kinematics as well as the age and metallicity of their stellar content from GMOS/Gemini Integral Field Spectrograph (IFS) data, and demonstrate that the stellar population properties evolve smoothly with galaxy size, mass and environment over the full range of galaxy mass. This suggests that a similar set of physical processes is at play on both low- and high-mass galaxies, but the relative efficiency of each of these processes in shaping galaxies varies smoothly from the low- to the high-mass ends. I then derive their star formation histories as well as those of a sample of 20 more extended typical low-mass galaxies, and present a study of their dependencies on the environment and the mass of their host galaxy. As a result, I underline through this work that the environment as well as the most massive galaxies play an important role in controlling the formation and evolution of low-mass galaxies. But local galaxies only represent the end products of a complex evolution path, leaving ambiguity about the early evolution of galaxies. However, I then show with the help of IFS observations of the nearby galaxy NGC3115 obtained with MUSE/VLT, that two-dimensional maps of the kinematics and stellar populations of galaxies, with large spatial coverage and high spatial resolution, are keys to unveil their whole mass assembly history, and thus their formation and evolution through all cosmic times. Thus, to better constrain the evolution of low-mass galaxies, I use deep MUSE/VLT observations in the Hubble Deep Field South to study low-mass galaxies at intermediate redshift. I derive for the first time the spatially resolved stellar kinematics of a sample of ten galaxies at a redshift between z ~ 0.2 - 0.7, and show that the stellar rotation amplitude and velocity dispersion are in agreement with previous studies of their gas kinematics. Such information put into the light of current galaxy evolution models will help to better understand the growth of stellar mass in galaxies and the origins of today low-mass galaxies
Galex-derived residual star formation history of elliptical galaxies
No full textBright early-type galaxies are still forming stars at low-level residual star formation (RSF) mode. The GALEX UV satellite has detected excessive UV flux in > 30% of our volume-limited sample of ∼10 galaxies. The RSF galaxy fraction is higher among the dynamically low-mass sample (RSF-σ relation). We postulate that this is a result of a "critical" MBH - σ relation that regulates residual star formation activities in early type galaxies. Implications are discussed
Unravelling giant molecular clouds
No full textGiant molecular clouds (GMCs) provide the fuel for star formation and bear various feedbacks. Thus, they are key to our understanding of galaxy evolution and the baryon cycle. In this thesis, I study the cold molecular gas content in the nearby universe, including three megamaser-host galaxies, one early-type galaxy, and the central molecular zone (CMZ) of the Milky Way (MW). The spatial scales probed by the analyses range from kpc-scale gas discs (i.e. the environment GMCs reside in) to sub-pc clumps within GMCs.
I start with analysing the distribution and kinematics of the molecular gas of three megamaser galaxies: NGC 1194, NGC 3393, and NGC 5765B. I present Atacama Large Millimeter/sub-millimeter Array (ALMA) 12CO(2-1) observations with resolutions of about 100 pc. Every galaxy has an extended rotating molecular gas disc but all also have non-axisymmetric features. I explore the tentative correlation between the existence of megamasers and these features in the gas discs. I also examine the potential for using 12CO(2-1) as a dynamical tracer in these galaxies to measure the supermassive blackhole masses.
Next, I investigate resolved GMCs of the lenticular galaxy NGC 1387, exploiting high-resolution (14 pc) 12CO(2-1) observations from ALMA. I analysed the fundamental properties of 1285 individual GMCs. Unusually for an ETG, the GMCs of NGC 1387 follow scaling relations very similar to those of the MW disc, and most are virialised. A subset of GMCs have their angular momenta aligned with the large-scale galactic rotation.
Finally, in the MW CMZ, I study the gas-structure dendrogram across a large dynamical range (1–100 pc), primarily with ALMA HNCO(4-3) observations at 0.7 pc resolution. I discuss the dynamical state of the gas structures and identify galactic shear and magnetic fields as potential physical drivers of their morphologies.
Overall, this thesis has studied cold molecular gas (clouds) in special systems (megamaser hosts, the ETG, and the MW centre) with unprecedented physical resolutions. It enriches our understanding of molecular gas properties in the context of galaxy evolution
The ATLAS3D project - XXVII. Cold gas and the colours and ages of early-type galaxies
No full textWe present a study of the cold gas contents of the ATLAS3D early-type galaxies, in the context of their optical colours, near-ultraviolet colours and Hβ absorption line strengths. Early-type (elliptical and lenticular) galaxies are not as gas poor as previously thought, and at least 40 per cent of local early-type galaxies are now known to contain molecular and/or atomic gas. This cold gas offers the opportunity to study recent galaxy evolution through the processes of cold gas acquisition, consumption (star formation) and removal. Molecular and atomic gas detection rates range from 10 to 34 per cent in red sequence early-type galaxies, depending on how the red sequence is defined, and from 50 to 70 per cent in blue early-type galaxies. Notably, massive red sequence early-type galaxies (stellar masses >5 × 1010 M⊙, derived from dynamical models) are found to have H I masses up to M(H I)/M* ˜ 0.06 and H2 masses up to M(H2)/M* ˜ 0.01. Some 20 per cent of all massive early-type galaxies may have retained atomic and/or molecular gas through their transition to the red sequence. However, kinematic and metallicity signatures of external gas accretion (either from satellite galaxies or the intergalactic medium) are also common, particularly at stellar masses ≤5 × 1010 M⊙, where such signatures are found in ˜50 per cent of H2-rich early-type galaxies. Our data are thus consistent with a scenario in which fast rotator early-type galaxies are quenched former spiral galaxies which have undergone some bulge growth processes, and in addition, some of them also experience cold gas accretion which can initiate a period of modest star formation activity. We discuss implications for the interpretation of colour-magnitude diagrams
Integral-Field Spectroscopic Surveys of Nearby Early–type Galaxies
No full textAbstractI briefly review here a few past or on-going surveys of nearby ETGs via integral-field spectroscopy, focusing on their dynamical status, evolution, and stellar/gaseous content.</jats:p
- …
