arXiv subjects

F. Louvet

Publications and source records attributed to F. Louvet.

At least 37 records · Page 2Linked to original sources

arXiv2022

ALMA-IMF IV -- A comparative study of the main hot cores in W43-MM1: detection, temperature and molecular composition

W43-MM1 is a young region, very rich in terms of high-mass star formation. We aim to systematically identify the massive cores which contain a hot core and compare their molecular composition. We used ALMA high-spatial resolution (2500 au) data of W43-MM1 to identify line-rich protostellar cores and make a comparative study of their temperature and molecular composition. The identification of hot cores is based on both the spatial distribution of the complex organic molecules and the contribution of molecular lines relative to the continuum intensity. We rely on the analysis of CH3CN and CH3CCH to estimate the temperatures of the selected cores. Finally, we rescale the spectra of the different hot cores based on their CH3OCHO line intensities to directly compare the detections and line intensities of the other species. W43-MM1 turns out to be a region rich in massive hot cores with at least 1 less massive and 7 massive hot cores. The excitation temperature of CH3CN is of the same order for all of them (120-160 K). There is a factor of up to 30 difference in the intensity of the complex organic molecules (COMs) lines. However the molecular emission of the hot cores appears to be the same within a factor 2-3. This points towards both a similar chemical composition and excitation of most of the COMs over these massive cores, which span about an order of magnitude in core mass. In contrast, CH3CCH emission is found to preferentially trace more the envelope, with a temperature ranging from 50 K to 90 K. Core 1, the most massive hot core of W43-MM1, shows a richer line spectrum than the other cores. In core 2, the emission of O-bearing molecules does not peak at the dust continuum core center; the blue and red shifted emission correspond to the outflow lobes, suggesting a formation via the sublimation of the ice mantles through shocks or UV irradiation on the walls of the cavity.

astro-ph.GA↗

arXiv2022

ALMA-IMF III -- Investigating the origin of stellar masses: Top-heavy core mass function in the W43-MM2&MM3 mini-starburst

The ALMA-IMF Large Program observed the W43-MM2-MM3 ridge, whose 1.3mm and 3mm ALMA 12m array continuum images reach a 2500au spatial resolution. We used both the best-sensitivity and the line-free ALMA-IMF images, reduced the noise with the multi-resolution segmentation technique MnGSeg, and derived the most complete and most robust core catalog possible. Using two different extraction software packages, getsf and GExt2D, we identified 200 compact sources, whose 100 common sources have on average fluxes consistent to within 30%. We filtered sources with non-negligible free-free contamination and corrected fluxes from line contamination, resulting in a W43-MM2-MM3 catalog of 205 getsf cores. With a median deconvolved FWHM size of 3400au, core masses range from 0.1Msun to 70Msun and the getsf catalog is 90% complete down to 0.8Msun. The high-mass end of the core mass function (CMF) of W43-MM2-MM3 is top-heavy compared to the canonical IMF. Fitting the cumulative CMF with a single power law of the form N(>logM)\propto M^a, we measured a=-0.95\pm0.04, compared to the canonical a=-1.35 Salpeter IMF slope. The slope of the CMF is robust with respect to map processing, extraction software package, and reasonable variations in the assumptions taken to estimate core masses. We explore several assumptions on how cores transfer their mass to stars and sub-fragment to predict the IMF resulting from the W43-MM2-MM3 CMF. In stark contrast to the commonly accepted paradigm, our result argues against the universality of the CMF shape. More robust functions of the star-formation efficiency and core sub-fragmentation are required to better predict the resulting IMF, here suggested to remain top-heavy at the end of the star-formation phase. If confirmed, the IMFs emerging from starburst events could inherit their top-heavy shape from their parental CMFs, challenging the IMF universality.

astro-ph.GA↗

arXiv2021

ALMA-IMF I -- Investigating the origin of stellar masses: Introduction to the Large Program and first results

The ALMA-IMF Large Program imaged a total noncontiguous area of 53pc2, covering 15 extreme, nearby protoclusters of the Milky Way. They were selected to span relevant early protocluster evolutionary stages. Our 1.3mm and 3mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of 0.2 and 0.6Msun, respectively, with a matched spatial resolution of 2000au. We also detect lines that probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores. We classify ALMA-IMF protoclusters as Young, Intermediate, or Evolved based on the amount of dense gas in the cloud that has potentially been impacted by HII regions. The ALMA-IMF catalog contains 700 cores that span a mass range of 0.15-250Msun at a typical size of 2100au. We show that this core sample has no significant distance bias and can be used to build core mass functions at similar physical scales. Significant gas motions, which we highlight here in the G353.41 region, are traced down to core scales and can be used to look for inflowing gas streamers and to quantify the impact of the possible associated core mass growth on the shape of the CMF with time. Our first analysis does not reveal any significant evolution of the matter concentration from clouds to cores or from the youngest to more evolved protoclusters, indicating that cloud dynamical evolution and stellar feedback have for the moment only had a slight effect on the structure of high-density gas in our sample. Furthermore, the first-look analysis of the line richness toward bright cores indicates that the survey encompasses several tens of hot cores, of which we highlight the most massive in the G351.77 cloud. Their homogeneous characterization can be used to constrain the emerging molecular complexity in protostars of high to intermediate masses.

astro-ph.GA↗

arXiv2021

HII regions and high-mass starless clump candidates II. Fragmentation and induced star formation at ~0.025 pc scale: An ALMA continuum study

The ionization feedback from HII regions modifies the properties of high-mass starless clumps (HMSCs, of several hundred to a few thousand solar masses with a size of ~0.1-1 pc), such as temperature and turbulence, on the clump scale. The question of whether the presence of HII regions modifies the core-scale fragmentation and star formation in HMSCs remains to be explored. We aim to investigate the difference of 0.025 pc-scale fragmentation between candidate HMSCs that are strongly impacted by HII regions and less disturbed ones. We also search for evidence of mass shaping and induced star formation in the impacted HMSCs. Using the ALMA 1.3 mm continuum with a resolution of ~1.3", we imaged eight candidate HMSCs, including four impacted by HII regions and another four situated in the quiet environment. The less-impacted HMSCs are selected on the basis of their similar mass and distance compared to the impacted ones to avoid any possible bias linked to these parameters. A total of 51 cores were detected in eight clumps, with three to nine cores for each clump. Within our limited sample, we did not find a clear difference in the ~0.025 pc-scale fragmentation between impacted and non-impacted HMSCs, even though HII regions seem to affect the spatial distribution of the fragmented cores. Both types of HMSCs present a thermal fragmentation with two-level hierarchical features at the clump thermal Jeans length ${λ_{J, clump}^{th}}$ and 0.3${λ_{J, clump}^{th}}$. The ALMA emission morphology of the impacted HMSCs AGAL010.214-00.306 and AGAL018.931-00.029 sheds light on the capacities of HII regions to shape gas and dust in their surroundings and possibly to trigger star formation at ~0.025 pc-scale in HMSCs. Future ALMA surveys covering a large number of impacted HMSCs with high turbulence are needed to confirm the trend of fragmentation indicated in this study.

astro-ph.GA↗

arXiv2020

Interstellar anatomy of the TeV gamma-ray peak in the IC443 supernova remnant

Supernovae remnants (SNRs) represent a major feedback source from stars on the interstellar medium of galaxies. During the latest stage of supernovae explosions, shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy in the surroundings, and may alter star formation characteristics. Simultaneously, gamma-ray emission is generated by the interaction between the ambiant medium and the cosmic rays. We study the stellar and interstellar contents of IC443, an evolved shell type SNR at a distance of 1.9 kpc, with an estimated age of 30 kyr. We aim to measure the mass of the gas within the extended G region, which corresponds to the peak of gamma-ray emission detected by VERITAS and Fermi. We performed 10'x10' mapped observations of 12CO and 13CO J=1-0, J=2-1 and J=3-2 pure rotational lines, as well as C18O J=1-0 and J=2-1 obtained with the IRAM-30m and APEX telescopes. We first compared our data with local thermodynamic equilbrium (LTE) models. We estimated the optical depth of each line from the emission of the isotopologues 13CO and C18O. We used the population diagram and large velocity gradient (LVG) assumption to measure the column density, mass, and kinetic temperature of the gas using 12CO and 13CO lines. We used complementary data (stars, gas, and dust at multiple wavelengths) and infrared point source catalogues to search for protostar candidates. Our results emphasize how the mass associated with the ring-like structure and the cloudlet cannot be overlooked when quantifying the interaction of cosmic rays with the dense local medium. Additionally, the presence of numerous possible protostars in the region might represent a fresh source of CR, which must also be taken into account in the interpretation of gamma-ray observations in this region.

astro-ph.HE↗

arXiv2020

Mass segregation and sequential star formation in NGC 2264 revealed by Herschel

The mass segregation of stellar clusters could be primordial rather than dynamical. Despite the abundance of studies of mass segregation for stellar clusters, those for stellar progenitors are still scarce, so the question on the origin and evolution of mass segregation is still open. Our goal is to characterize the structure of the NGC 2264 molecular cloud and compare the populations of clumps and young stellar objects (YSOs) in this region whose rich YSO population has shown evidence of sequential star formation. We separated the Herschel column density map of NGC 2264 in three subregions and compared their cloud power spectra using a multiscale segmentation technique. We identified in the whole NGC 2264 cloud a population of 256 clumps with typical sizes of ~0.1 pc and masses ranging from 0.08 Msun to 53 Msun. Although clumps have been detected all over the cloud, the central subregion of NGC 2264 concentrates most of the massive, bound clumps. The local surface density and the mass segregation ratio indeed indicate a strong degree of mass segregation for the 15 most massive clumps, with a median $Σ_6$ three time that of the whole clumps population and $Λ_{MSR}$ about 8. We showed that this cluster of massive clumps is forming within a high-density cloud ridge, itself formed and probably still fed by the high concentration of gas observed on larger scales in the central subregion. The time sequence obtained from the combined study of the clump and YSO populations in NGC 2264 suggests that the star formation started in the northern subregion, that it is now actively developing at the center and will soon start in the southern subregion. Taken together, the cloud structure and the clump and YSO populations in NGC 2264 argue for a dynamical scenario of star formation.

astro-ph.GA↗

arXiv2020

Outflows, cores and magnetic field orientations in W43-MM1 as seen by ALMA

It has been proposed that the magnetic field, pervasive in the ISM, plays an important role in the process of massive star formation. To better understand its impact at the pre and protostellar stages, high-angular resolution observations of polarized dust emission toward a large sample of massive dense cores are needed. To this end, we used the Atacama Large Millimeter Array in Band 6 (1.3 mm) in full polarization mode to map the polarized emission from dust grains at a physical scale of $\sim$2700 au in the massive protocluster W43-MM1. We used these data to measure the orientation of the magnetic field at the core scale. Then, we examined the relative orientations of the core-scale magnetic field, of the protostellar outflows determined from CO molecular line emission, and of the major axis of the dense cores determined from 2D Gaussian fit in the continuum emission. We found that the orientation of the dense cores is not random with respect to the magnetic field. Instead, the dense cores are compatible with being oriented 20-50$^°$ with respect to the magnetic field. The outflows could be oriented 50-70$^°$ with respect to the magnetic field, or randomly oriented with respect to the magnetic field, similar to current results in low-mass star-forming regions. In conclusion, the observed alignment of the position angle of the cores with respect to the magnetic field lines shows that the magnetic field is well coupled with the dense material; however, the 20-50$^°$ preferential orientation contradicts the predictions of the magnetically-controlled core-collapse models. The potential correlation of the outflow directions with respect to the magnetic field suggests that, in some cases, the magnetic field is strong enough to control the angular momentum distribution from the core scale down to the inner part of the circumstellar disks where outflows are triggered.

astro-ph.GA↗

arXiv2020

Observations of edge-on protoplanetary disks with ALMA I. Results from continuum data

We analyze a sample of 12 HST-selected edge-on protoplanetary disks for which the vertical extent of the emission layers can be constrained directly. We present ALMA high angular resolution continuum images (0.1arcsec) of these disks at two wavelengths, 0.89mm and 2.06mm (respectively ALMA bands 7 and 4), supplemented with archival band 6 data (1.33mm) where available. For most sources, the millimeter continuum emission is more compact than the scattered light, both in the vertical and radial directions. Six sources are resolved along their minor axis in at least one millimeter band, providing direct information on the vertical distribution of the millimeter grains. For the second largest disk of the sample, the significant difference in vertical extent between band 7 and band 4 suggests efficient size-selective vertical settling of large grains. Furthermore, the only Class I object in our sample shows evidence of flaring in the millimeter. Along the major axis, all disks are well resolved. Four of them are larger in band 7 than in band 4 in the radial direction, and three have a similar radial extent in all bands. For all disks, we also derive the millimeter brightness temperature and spectral index maps. We find that the disks are likely optically thick and that the dust emission reveals low brightness temperatures in most cases (<10K). The integrated spectral indices are similar to those of disks at lower inclination. The comparison of a generic radiative transfer disk model with our data shows that at least 3 disks are consistent with a small millimeter dust scale height, of a few au (measured at r=100au). This is in contrast with the more classical value of h_g\sim10au derived from scattered light images and from gas line measurements. These results confirm, by direct observations, that large (millimeter) grains are subject to significant vertical settling in protoplanetary disks.

astro-ph.SR↗

arXiv2020

A statistical analysis of dust polarization properties in ALMA observations of Class 0 protostellar cores

Recent observational progress has challenged the dust grain-alignment theories used to explain the polarized dust emission routinely observed in star-forming cores. In an effort to improve our understanding of the dust grain alignment mechanism(s), we have gathered a dozen ALMA maps of (sub)millimeter-wavelength polarized dust emission from Class 0 protostars, and carried out a comprehensive statistical analysis of dust polarization quantities. We analyze the statistical properties of the polarization fraction P_frac and dispersion of polarization position angles S. More specifically, we investigate the relationship between S and P_frac as well as the evolution of the product S*P_frac as a function of the column density of the gas in the protostellar envelopes. We find a significant correlation in the polarized dust emission from protostellar envelopes seen with ALMA; the power-law index differs significantly from the one observed by Planck in star-forming clouds. The product S*P_frac, which is sensitive to the dust grain alignment efficiency, is approximately constant across three orders of magnitude in envelope column density. This suggests that the grain alignment mechanism producing the bulk of the polarized dust emission in star-forming cores may not depend systematically on the local conditions such as local gas density. Ultimately, our results suggest dust alignment mechanism(s) are efficient at producing dust polarized emission in the various local conditions typical of Class 0 protostars. The grain alignment efficiency found in these objects seems to be higher than the efficiency produced by the standard RAT alignment of paramagnetic grains. Further study will be needed to understand how more efficient grain alignment via, e.g., different irradiation conditions, dust grain characteristics, or additional grain alignment mechanisms can reproduce the observations.

astro-ph.GA↗

arXiv2020

Large-scale Map of Millimeter-wavelength Hydrogen Radio Recombination Lines around a Young Massive Star Cluster

We report the first map of large-scale (10 pc in length) emission of millimeter-wavelength hydrogen recombination lines (mm-RRLs) toward the giant H II region around the W43-Main young massive star cluster (YMC). Our mm-RRL data come from the IRAM 30 m telescope and are analyzed together with radio continuum and cm-RRL data from the Karl G. Jansky Very Large Array and HCO$^{+}$ 1-0 line emission data from the IRAM 30 m. The mm-RRLs reveal an expanding wind-blown ionized gas shell with an electron density ~70-1500 cm$^{-3}$ driven by the WR/OB cluster, which produces a total Ly$α$ photon flux of 1.5 x 10$^{50}$ s$^{-1}$. This shell is interacting with the dense neutral molecular gas in the W43-Main dense cloud. Combining the high spectral and angular resolution mm-RRL and cm-RRL cubes, we derive the two-dimensional relative distributions of dynamical and pressure broadening of the ionized gas emission and find that the RRL line shapes are dominated by pressure broadening (4-55 km s$^{-1}$) near the YMC and by dynamical broadening (8-36 km s$^{-1}$) near the shell's edge. Ionized gas clumps hosting ultra-compact H II regions found at the edge of the shell suggest that large-scale ionized gas motion triggers the formation of new star generation near the periphery of the shell.

astro-ph.GA↗

arXiv2020

Episodic accretion constrained by a rich cluster of outflows

The accretion history of protostars remains widely mysterious even though it represents one of the best ways to understand the protostellar collapse that leads to the formation of stars. Molecular outflows are here used to characterize the protostellar accretion phase in W43-MM1. The W43-MM1 protocluster host a sufficient number of protostars to statistically investigate molecular outflows in a single, homogeneous region. We used the CO(2-1) and SiO(5-4) line datacubes, taken as part of an ALMA mosaic with a 2000 AU resolution, to search for protostellar outflows, evaluate the influence that the environment has on these outflows' characteristics and put constraints on outflow variability in W43-MM1. We discovered a rich cluster of 46 outflow lobes, driven by 27 protostars with masses of 1-100 Msun. The complex environment inside which these outflow lobes develop has a definite influence on their length, limiting the validity of using outflows' dynamical timescales as a proxy of the ejection timescale in clouds with high dynamics and varying conditions. We performed a detailed study of Position-Velocity (PV) diagrams of outflows that revealed clear events of episodic ejection. The time variability of W43-MM1 outflows is a general trend and is more generally observed than in nearby, low- to intermediate-mass star-forming regions. The typical timescale found between two ejecta, about 500 yr, is consistent with that found in nearby protostars. If ejection episodicity reflects variability in the accretion process, either protostellar accretion is more variable or episodicity is easier to detect in high-mass star-forming regions than in nearby clouds. The timescale found between accretion events could be resulting from disk instabilities, associated with bursts of inflowing gas arising from the dynamical environment of high-mass star-forming cores.

astro-ph.GA↗

arXiv2020

ALMA reveals a large structured disk and nested rotating outflows in DG Tau B

We present Atacama Large Millimeter Array (ALMA) Band 6 observations at 14-20 au spatial resolution of the disk and CO(2-1) outflow around the Class I protostar DG Tau B in Taurus. The disk is very large, both in dust continuum (R$_{\rm eff,95\%}$=174 au) and CO (R$_{CO}$=700 au). It shows Keplerian rotation around a 1.1$\pm$0.2 M$_{\odot}$ central star and two dust emission bumps at $r$ = 62 and 135 au. These results confirm that large structured disks can form at an early stage where residual infall is still ongoing. The redshifted CO outflow at high velocity shows a striking hollow cone morphology out to 3000 au with a shear-like velocity structure within the cone walls. These walls coincide with the scattered light cavity, and they appear to be rooted within $<$ 60 au in the disk. We confirm their global average rotation in the same sense as the disk, with a specific angular momentum $\simeq$ 65 au \kms. The mass-flux rate of 1.7-2.9 $\times$ 10$^{-7}$M$_{\odot}$ yr$^{-1}$ is 35$\pm$10 times that in the atomic jet. We also detect a wider and slower outflow component surrounding this inner conical flow, which also rotates in the same direction as the disk. Our ALMA observations therefore demonstrate that the inner cone walls, and the associated scattered light cavity, do not trace the interface with infalling material, which is shown to be confined to much wider angles ($> 70^{\circ}$). The properties of the conical walls are suggestive of the interaction between an episodic inner jet or wind with an outer disk wind, or of a massive disk wind originating from 2-5 au. However, further modeling is required to establish their origin. In either case, such massive outflow may significantly affect the disk structure and evolution.

astro-ph.SR↗

arXiv2019

Molecular analysis of a high-mass prestellar core candidate in W43-MM1

High-mass analogues of low-mass prestellar cores are searched for to constrain the models of high-mass star formation. Several high-mass cores, at various evolutionary stages, have been recently identified towards the massive star-forming region W43-MM1 and amongst them a high-mass prestellar core candidate. We aim to characterise the chemistry in this high-mass prestellar core candidate, referred to as W43-MM1 core #6, and its environment. Using ALMA high-spatial resolution data of W43-MM1, we have studied the molecular content of core #6 and a neighbouring high-mass protostellar core, referred to as #3, which is similar in size and mass to core #6. We first subtracted the continuum emission using a method based on the density distribution of the intensities on each pixel. Then, from the distribution of detected molecules, we identified the molecules centred on the prestellar core candidate (core #6) and those associated to shocks related to outflows and filament formation. Then we constrained the column densities and temperatures of the molecules detected towards the two cores. While core #3 appears to contain a hot core with a temperature of about 190 K, core #6 seems to have a lower temperature in the range from 20 K to 90 K from a rotational diagram analysis. We have considered different source sizes for core #6 and the comparison of the abundances of the detected molecules towards the core with various interstellar sources shows that it is compatible with a core of size 1000 au with $T = 20-90$ K or a core of size 500 au with $T \sim 80$ K. Core #6 of W43-MM1 remains one of the best high-mass prestellar core candidates even if we cannot exclude that it is at the very beginning of the protostellar phase of high-mass star formation.

astro-ph.GA↗

arXiv2018

Lack of high-mass prestellar cores in the starless MDCs of NGC6334

Two families of models compete to explain the formation of high-mass stars. The quasi-static models predict the existence of high-mass pre-stellar cores sustained by a high degree of turbulence while competitive accretion models predict that high-mass proto-stellar cores evolve from low/intermediate mass proto-stellar cores in dynamic environments. We present ALMA (1.4 mm continuum emission and $^{12}$CO emission line) and MOPRA (HCO$^{+}$, H$^{13}$CO$^{+}$ and N$_2$H$^+$ molecular line emissions) observations of a sample of 9 starless massive dense cores (MDCs) discovered in a recent Herschel/HOBYS study that have masses and sizes ($\sim$110 M$_\odot$ and $r\sim$0.1 pc, respectively) similar to the initial conditions used in the quasi-static models. The MOPRA molecular line features show that 3 of the starless MDCs are subvirialized with $α_{\rm vir}\sim$0.35, and 4 MDCs show sign of collapse. Our ALMA observations, on the other hand, show very little fragmentation within the MDCs whereas the observations resolve the Jeans length ($λ_{\rm Jeans}\sim$0.03 pc) and are sensitive to the Jeans mass (M$_{\rm Jeans}\sim$0.65 M$_\odot$) in the 9 starless MDCs. Only two of the starless MDCs host compact continuum sources, whose fluxes correspond to $<3$ M$_\odot$ fragments. Therefore the mass reservoir of the MDCs has not yet been accreted onto compact objects, and most of the emission is filtered out by the interferometer. These observations do not support the quasi-static models for high-mass star formation since no high-mass pre-stellar core is found in NGC6334. The competitive accretion models, on the other hand, predict a level of fragmentation much higher than what we observe.

astro-ph.GA↗

arXiv2018

Detection of a high-mass prestellar core candidate in W43-MM1

Aims. To constrain the physical processes that lead to the birth of high-mass stars it is mandatory to study the very first stages of their formation. We search for high-mass analogs of low-mass prestellar cores in W43-MM1. Methods. We conducted a 1.3 mm ALMA mosaic of the complete W43-MM1 cloud, which has revealed numerous cores with ~ 2000 au FWHM sizes. We investigated the nature of cores located at the tip of the main filament, where the clustering is minimum. We used the continuum emission to measure the core masses and the $^{13}$CS(5-4) line emission to estimate their turbulence level. We also investigated the prestellar or protostellar nature of these cores by searching for outflow signatures traced by CO(2-1) and SiO(5-4) line emission, and for molecular complexity typical of embedded hot cores. Results. Two high-mass cores of ~ 1300 au diameter and ~ $60~M_\odot$ mass are observed to be turbulent but gravitationally bound. One drives outflows and is associated with a hot core. The other core, W43-MM1\#6, does not yet reveal any star formation activity and thus is an excellent high-mass prestellar core candidate.

astro-ph.GA↗

arXiv2018

A catalogue of dense cores and young stellar objects in the Lupus complex based on Herschel Gould Belt Survey observations

The Herschel Gould Belt Survey key project mapped the bulk of nearby star-forming molecular clouds in five far-infrared bands with the aim of compiling complete census of prestellar cores and young, embedded protostars. In this paper, we present the catalogue of the dense cores and YSOs/protostars extracted from the Herschel maps of the Lupus I, III, and IV molecular clouds. The physical properties of the detected objects were derived by fitting their spectral energy distributions. A total of 532 dense cores, out of which 103 are presumably prestellar in nature, and 38 YSOs/protostars have been detected in the three clouds. Almost all the prestellar cores are associated with filaments against only about one third of the unbound cores and YSOs/protostars. Prestellar core candidates are found even in filaments that are on average thermally sub-critical and over a background column density lower than that measured in other star forming regions so far. The core mass function of the prestellar cores peaks between 0.2 and 0.3 solar masses and it is compatible with the log-normal shape found in other regions. Herschel data reveal several, previously undetected, protostars and new candidates of Class 0 and Class II with transitional disks. We estimate the evolutionary status of the YSOs/protostars using two independent indicators: the $α$ index and the fitting of the spectral energy distribution from near- to far-infrared wavelengths. For 70% of the objects, the evolutionary stages derived with the two methods are in agreement. Lupus is confirmed to be a very low-mass star-forming region, both in terms of the prestellar condensations and of the diffuse medium. Noticeably, in the Lupus clouds we have found star formation activity associated with interstellar medium at low column density, usually quiescent in other (more massive) star forming regions.

astro-ph.GA↗

arXiv2018

The unexpectedly large proportion of high-mass star-forming cores in a Galactic mini-starburst

Understanding the processes that determine the stellar Initial Mass Function (IMF) is a critical unsolved problem, with profound implications for many areas of astrophysics. In molecular clouds, stars are formed in cores, gas condensations which are sufficiently dense that gravitational collapse converts a large fraction of their mass into a star or small clutch of stars. In nearby star-formation regions, the core mass function (CMF) is strikingly similar to the IMF, suggesting that the shape of the IMF may simply be inherited from the CMF. Here we present 1.3 mm observations, obtained with ALMA, the world's largest interferometer, of the active star-formation region W43-MM1, which may be more representative of the Galactic-disk regions where most stars form. The unprecedented resolution of these observations reveals, for the first time, a statistically robust CMF at high masses, with a slope that is markedly shallower than the IMF. This seriously challenges our understanding of the origin of the IMF.

astro-ph.GA↗

arXiv2017

The earliest phases of high-mass star formation, as seen in NGC 6334 by \emph{Herschel}

To constrain models of high-mass star formation, the Herschel/HOBYS KP aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC6334, one of the best-studied HOBYS molecular cloud complexes. We used Herschel PACS and SPIRE 70-500mu images of the NGC6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1 pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their SEDs. A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75Msun for MDCs in NGC6334. MDCs have temperatures of 9.5-40K, masses of 75-1000Msun, and densities of 10^5-10^8cm-3. Their mid-IR emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70mu emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1-7x10^4yr and at most 3x10^5yr respectively, suggest a dynamical scenario of high-mass star formation. The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC6334, favoring a scenario presented here, which simultaneously forms clouds and high-mass protostars.

astro-ph.GA↗