Compact substructure is expected to arise in a starless core as mass becomes concentrated in the central region likely to form a protostar. Additionally, multiple peaks may form if fragmentation occurs. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are >15 '' from the nearest Spitzer young stellar object. Only one of these has strong evidence for being truly starless after considering ancillary data, e.g., from Herschel and X-ray telescopes. An additional extended emission structure has tentative evidence for starlessness. The number of our detections is consistent with estimates from a combination of synthetic observations of numerical simulations and analytical arguments. This result suggests that a similar ALMA study in the Chamaeleon. I cloud, which detected no compact substructure in starless cores, may be due to the peculiar evolutionary state of cores in that cloud.

We sort 4683 molecular clouds between 10 degrees < l < 65 degrees from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 mu m sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH II. regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (alpha similar to 0.7) with >75% of clumps with known distance being gravitationally bound (alpha < 2). These samples show a statistically significant increase in the median clump mass of Delta M similar to 170-370 M-circle dot from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at (M) over dot similar to 200-440 M-circle dot Myr(-1) for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii). a variation in the ratio of starless to protostellar clump lifetime that scales as similar to M-0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase. lifetime of massive (M > 10(3) M-circle dot) starless clumps to be 0.37 +/- 0.08 Myr (M/10(3) M-circle dot)(-1); the majority (M < 450 M-circle dot) have phase. lifetimes longer than their average freefall time.

We present a catalog of all CO (J = 4-3 through J = 13-12), [ C I], and [ N II] lines available from extragalactic spectra from the Herschel SPIRE Fourier Transform Spectrometer (FTS) archive combined with observations of the low-J CO lines from the literature and from the Arizona Radio Observatory. This work examines the relationships between L-FIR, L'(CO), and L-CO/L-CO,L-1-0. We also present a new method for estimating probability distribution functions from marginal signal-to-noise ratio Herschel FTS spectra, which takes into account the instrumental "ringing" and the resulting highly correlated nature of the spectra. The slopes of log(L-FIR) versus log (L'(CO)) are linear for all mid- to high-J CO lines and slightly sublinear if restricted to (ultra) luminous infrared galaxies ((U) LIRGs). The mid-to high-J CO luminosity relative to CO J - 1-0 increases with increasing L-FIR, indicating higher excitement of the molecular gas, although these ratios do not exceed similar to 180. For a given bin in L-FIR, the luminosities relative to CO J = 1-0 remain relatively flat from J = 6-5 through J = 13-12, across three orders of magnitude of L-FIR. A single component theoretical photodissociation region (PDR) model cannot match these flat SLED shapes, although combinations of PDR models with mechanical heating added qualitatively match the shapes, indicating the need for further comprehensive modeling of the excitation processes of warm molecular gas in nearby galaxies.

Aims. The aim of this work is to constrain properties of the disk around the archetype FU Orionis object, FU Ori, with as good as similar to 25 au resolution. Methods. We resolved FU Ori at 29-37 GHz using the Karl G. Jansky Very Large Array (JVLA) in the A-array configuration, which provided the highest possible angular resolution to date at this frequency band (similar to 0 ''.07). We also performed complementary JVLA 8-10 GHz observations, Submillimeter Array (SMA) 224 GHz and 272 GHz observations, and compared these with archival Atacama Large Millimeter Array (ALMA) 346 GHz observations to obtain the spectral energy distributions (SEDs). Results. Our 8-10 GHz observations do not find evidence for the presence of thermal radio jets, and constrain the radio jet/wind flux to at least 90 times lower than the expected value from the previously reported bolometric luminosity-radio luminosity correlation. The emission at frequencies higher than 29 GHz may be dominated by the two spatially unresolved sources, which are located immediately around FU Ori and its companion FU Ori S, respectively. Their deconvolved radii at 33 GHz are only a few au, which is two orders of magnitude smaller in linear scale than the gaseous disk revealed by the previous Subaru-HiCIAO 1.6 mu m coronagraphic polarization imaging observations. We are struck by the fact that these two spatially compact sources contribute to over 50% of the observed fluxes at 224 GHz, 272 GHz, and 346 GHz. The 8-346 GHz SEDs of FU Ori and FU Ori S cannot be fit by constant spectral indices (over frequency), although we cannot rule out that it is due to the time variability of their (sub)millimeter fluxes. Conclusions. The more sophisticated models for SEDs considering the details of the observed spectral indices in the millimeter bands suggest that the >29 GHz emission is contributed by a combination of free-free emission from ionized gas and thermal emission from optically thick and optically thin dust components. We hypothesize that dust in the innermost parts of the disks (less than or similar to 0.1 au) has been sublimated, and thus the disks are no longer well shielded against the ionizing photons. The estimated overall gas and dust mass based on SED modeling, can be as high as a fraction of a solar mass, which is adequate for developing disk gravitational instability. Our present explanation for the observational data is that the massive inflow of gas and dust due to disk gravitational instability or interaction with a companion/intruder, was piled up at the few-au scale due to the development of a deadzone with negligible ionization. The piled up material subsequently triggered the thermal instability and the magnetorotational instability when the ionization fraction in the inner sub-au scale region exceeded a threshold value, leading to the high protostellar accretion rate.

Alors que les galaxies évoluent, leur milieu interstellaire (MIS) s’enrichit continuellement en métaux, et cet enrichissement influence la formation d’étoiles. Les galaxies naines de faible métallicité de l’Univers Local sont les candidates idéales pour étudier l’influence de cet enrichissement en métaux sur les propriétés du MIS des galaxies et nous donne un aperçu des processus d’enrichissement et de formation stellaire dans des conditions proches de celles trouvées dans les systèmes pauvres en métaux de l’Univers primordial. Des études précédentes ont montré que le MIS des galaxies naines pose un certain nombre d’énigmes en terme d’abondance des grains, de composition de la poussière et même des processus d’émission en infrarouge lointain (FIR). Cependant, ces études étaient limitées à la poussière chaude émettant à des longueurs d’onde plus courtes que 200 micromètres et étaient effectuées sur un petit nombre de galaxies. Grâce à une sensibilité et une résolution améliorées dans les domaines FIR et submillimétriques (submm), Herschel nous donne une vue nouvelle sur les propriétés de la poussière froide dans les galaxies et nous permet d’étudier les galaxies les plus pauvres en métaux de manière systématique. Dans ce travail, je mène une étude des propriétés des poussières dans les galaxies naines et compare avec des environnements plus riches en métaux, pour aborder la question de l’impact de la métallicité sur les propriétés de la poussière. La nouveauté de ce travail réside dans le fait que les galaxies naines sont étudiées de manière systématique, nous permettant d’accéder aux, et de quantifier les propriétés générales représentatives de ces systèmes. Cette étude est conduite sur toute la gamme de longueurs d’onde infrarouge (IR)-submm, avec les nouvelles observations en FIR/submm d’Herschel, ainsi que des données Spitzer, WISE, IRAS, et 2MASS. Nous complétons ces données avec des mesures en domaine submm de télescopes au sol comme APEX ou le JCMT, pour étudier la présence et les caractéristiques de l’excès submm dans mon échantillon de galaxies. Je collecte aussi les données HI et CO pour accéder aux propriétés du gaz dans ces galaxies et étudier l’évolution du rapport en masse gaz-sur-poussière (G/D) avec la métallicité. Notre étude révèle des propriétés de poussière différentes dans les environnements de faible métallicité que celles observées dans des systèmes plus riches en métaux (par exemple, une poussière globalement plus chaude). Une émission en excès par rapport aux modèles utilisés, apparait souvent aux alentours de 500 micromètres, menant à d’importantes incertitudes sur les propriétés de la poussière, notamment sur la masse de poussière. Les excès les moins importants peuvent cependant être expliqués en utilisant une autre composition pour la poussière, avec des grains plus émissifs. Traceur idéal de l’état d’évolution chimique d’une galaxie, le G/D est en fait bien plus grand que ce que l’on pourrait attendre si l’on considère un modèle simple d’évolution chimique. Interprétée avec des modèles d’évolution chimique plus complexes, incorporant des processus de croissance des grains et/ou une formation d’étoiles épisodique, la relation entre le G/D et la métallicité, ainsi que sa dispersion, peuvent être expliquées par la grande variété d’environnements que nous considérons dans notre étude. / As galaxies evolve, their Interstellar Medium (ISM) becomes continually enriched with metals, and this metal enrichment influences the subsequent star formation. Low metallicity dwarf galaxies of the local Universe are ideal candidates to study the influence of metal enrichment on the ISM properties of galaxies and gives us insight into the enrichment process and star formation under ISM conditions that may provide clues to conditions in early universe metal-poor systems. Previous studies have shown that the ISM of dwarf galaxies poses a number of interesting puzzles in terms of the abundance of dust grains, the dust composition and even the FIR emission processes. However these studies were limited to the warmer dust emitting at wavelengths shorter than 200 microns and were done only on a small number of dwarf galaxies. Thanks to its increased sensitivity and resolution in FIR and submillimeter (submm) wavelengths, Herschel gives us a new view on the cold dust properties in galaxies and enables us to study the lowest metallicity galaxies in a systematic way. In this work, I carry out a study of the dust properties in dwarf galaxies and compare with more metal rich environments, in order to address the question of the impact of metallicity on the dust properties. The novelty of this work lays in the fact that dwarf galaxies are studied here in a systematic way, enabling us to derive and quantify the general properties that are representative of these systems. This study is conducted over the full IR-to-submm range, using new FIR/submm Herschel observations, Spitzer, WISE, IRAS and 2MASS data. We complete this set of data with longer submm measurements from ground-based facilities such as APEX and JCMT to study the presence and characteristics of the submm excess in my sample of galaxies. I also collect Hi and CO data to access the gas properties of the galaxies and study the evolution of the G/D with metallicity. Our study reveal different dust properties in low-metallicity environments than that observed in more metal-richs systems (e.g., an overall warmer dust component). An excess submm emission is often apparent near and/or beyond 500 microns rendering large uncertainties in the dust properties, even for something as fundamental as dust masses. Some of the smallest excesses can be explained by using another dust composition with more emissive grains. Ideal tracer of the chemical evolutionary stage of a galaxy, the gas-to-dust mass ratios (G/D) is found to be much higher than what is expected by simple chemical evolution models. Interpreted with more sophisticated chemical evolution models, including dust growth in the ISM and/or episodic star formation, the relation of the G/D with metallicity and its scatter can be explained by the wide variety of environments we are considering.