arXiv subjects

R. Cesaroni

Publications and source records attributed to R. Cesaroni.

At least 91 records · Page 5Linked to original sources

arXiv2012

Different evolutionary stages in massive star formation. Centimeter continuum and H2O maser emission with ATCA

We present ATCA observations of the H2O maser line and radio continuum at 18.0GHz and 22.8GHz, toward a sample of 192 massive star forming regions containing several clumps already imaged at 1.2mm. The main aim of this study is to investigate the water maser and centimeter continuum emission (likely tracing thermal free-free emission) in sources at different evolutionary stages, using the evolutionary classifications proposed by Palla et al (1991) and Molinari et al (2008). We used the recently comissioned CABB backend at ATCA obtaining images with 20arcsec resolution in the 1.3cm continuum and H2O maser emission, in all targets. For the evolutionary analysis of the sources we used the millimeter continuum emission from Beltran et al (2006) and the infrared emission from the MSX Point Source Catalogue. We detect centimeter continuum emission in 88% of the observed fields with a typical rms noise level of 0.45mJy/beam. Most of the fields show a single radio continuum source, while in 20% of them we identify multiple components. A total of 214 centimeter continuum sources have been identified, likely tracing optically thin HII regions, with physical parameters typical of both extended and compact HII regions. Water maser emission was detected in 41% of the regions, resulting in a total of 85 distinct components. The low angular (20arcsec) and spectral (14km/s) resolutions do not allow a proper analysis of the water maser emission, but suffice to investigate its association with the continuum sources. We have also studied the detection rate of HII regions in the two types of IRAS sources defined by Palla et (1991) on the basis of the IRAS colours: High and Low. No significant differences are found, with large detection rates (>90%) for both High and Low sources. We classify the millimeter and infrared sources in our fields in three evolutionary stages following the scheme presented by ...

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arXiv2012

High CO depletion in southern infrared-dark clouds

Infrared-dark high-mass clumps are among the most promising objects to study the initial conditions of the formation process of high-mass stars and rich stellar clusters. In this work, we have observed the (3-2) rotational transition of C18O with the APEX telescope, and the (1,1) and (2,2) inversion transitions of NH3 with the Australia Telescope Compact Array in 21 infrared-dark clouds already mapped in the 1.2 mm continuum, with the aim of measuring basic chemical and physical parameters such as the CO depletion factor (fD), the gas kinetic temperature and the gas mass. In particular, the C18O (3-2) line allows us to derive fD in gas at densities higher than that traced by the (1-0) and (2-1) lines, typically used in previous works. We have detected NH3 and C18O in all targets. The clumps possess mass, H2 column and surface densities consistent with being potentially the birthplace of high-mass stars. We have measured fD in between 5 and 78, with a mean value of 32 and a median of 29. These values are, to our knowledge, larger than the typical CO depletion factors measured towards infrared-dark clouds and high-mass dense cores, and are comparable to or larger than the values measured in low-mass pre-stellar cores close to the onset of the gravitational collapse. This result suggests that the earliest phases of the high-mass star and stellar cluster formation process are characterised by fD larger than in low-mass pre-stellar cores. Thirteen out of 21 clumps are undetected in the 24 μm Spitzer images, and have slightly lower kinetic temperatures, masses and H2 column densities with respect to the eight Spitzer-bright sources. This could indicate that the Spitzer-dark clumps are either less evolved or are going to form less massive objects.

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arXiv2012

Massive star-formation toward G28.87+0.07 (IRAS 18411-0338) investigated by means of maser kinematics and radio to infrared, continuum observations

We used the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN) to perform phase-referenced VLBI observations of the three most powerful maser transitions associated with the high-mass star-forming region G28.87+0.07: the 22.2 GHz H$_{2}$O, 6.7 GHz CH$_{3}$OH, and 1.665 GHz OH lines. We also performed VLA observations of the radio continuum emission at 1.3 and 3.6 cm and Subaru observations of the continuum emission at 24.5 $μ$m. Two centimeter continuum sources are detected and one of them (named "HMC") is compact and placed at the center of the observed distribution of H$_{2}$O, CH$_{3}$OH and OH masers. The bipolar distribution of line-of-sight (l.o.s) velocities and the pattern of the proper motions suggest that the water masers are driven by a (proto)stellar jet interacting with the dense circumstellar gas. The same jet could both excite the centimeter continuum source named "HMC" (interpreted as free-free emission from shocked gas) and power the molecular outflow observed at larger scales -- although one cannot exclude that the free-free continuum is rather originating from a hypercompact \ion{H}{2} region. At 24.5 $μ$m, we identify two objects separated along the north-south direction, whose absolute positions agree with those of the two VLA continuum sources. We establish that $\sim$90% of the luminosity of the region ($\sim$\times10^{5} L_\sun$) is coming from the radio source "HMC", which confirms the existence of an embedded massive young stellar object (MYSO) exciting the masers and possibly still undergoing heavy accretion from the surrounding envelope.

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arXiv2011

Dissecting a hot molecular core: The case of G31.41+0.31

We made a detailed observational analysis of a well known hot molecular core lying in the high-mass star-forming region G31.41+0.31. This core is believed to contain deeply embedded massive stars and presents a velocity gradient that has been interpreted either as rotation or as expansion, depending on the authors. Our aim was to shed light on this question and possibly prepare the ground for higher resolution ALMA observations which could directly detect circumstellar disks around the embedded massive stars. Observations at sub-arcsecond resolution were performed with the Submillimeter Array in methyl cyanide, a typical hot molecular core tracer, and 12CO and 13CO, well known outflow tracers. We also obtained sensitive continuum maps at 1.3 mm. Our findings confirm the existence of a sharp velocity gradient across the core, but cannot confirm the existence of a bipolar outflow perpendicular to it. The improved angular resolution and sampling of the uv plane allow us to attain higher quality channel maps of the CH3CN lines with respect to previous studies and thus significantly improve our knowledge of the structure and kinematics of the hot molecular core. While no conclusive argument can rule out any of the two interpretations (rotation or expansion) proposed to explain the velocity gradient observed in the core, in our opinion the observational evidence collected so far indicates the rotating toroid as the most likely scenario. The outflow hypothesis appears less plausible, because the dynamical time scale is too short compared to that needed to form species such as CH3CN, and the mass loss and momentum rates estimated from our measurements appear too high.

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arXiv2011

Molecular outflows and hot molecular core in G24.78+0.08 at sub-arcsecond angular resolution

Context. This study is part of a large project to study the physics of accretion and molecular outflows towards a selected sample of high-mass star-forming regions that show evidence of infall and rotation from previous studies. Aims. We wish to make a thorough study at high-angular resolution of the structure and kinematics of the HMCs and corresponding molecular outflows in the high-mass star-forming region G24.78+0.08. Methods. We carried out SMA and IRAM PdBI observations at 1.3 and 1.4 mm, respectively, of dust and of typical high-density and molecular outflow tracers with resolutions of <1". Complementary IRAM 30-m 12CO and 13CO observations were carried out to recover the short spacing information of the molecular outflows. Results. The millimeter continuum emission towards cores G24 A1 and A2 has been resolved into 3 and 2 cores, respectively, and named A1, A1b, A1c, A2, and A2b. All these cores are aligned in a southeast-northwest direction coincident with that of the molecular outflows detected in the region, which suggests a preferential direction for star formation in this region. The masses of the cores range from 7 to 22 Msun, and the rotational temperatures from 128 to 180 K. The high-density tracers have revealed the existence of 2 velocity components towards A1, one of them peaks close to the position of the millimeter continuum peak and of the HC HII region, and is associated with the velocity gradient seen in CH3CN towards this core, while the other one peaks southwest of core A1 and is not associated with any millimeter continuum emission peak. The position-velocity plots along outflow A and the 13CO averaged blueshifted and redshifted emission indicate that this outflow is driven by core A2.

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arXiv2011

On the kinematics of massive star forming regions: the case of IRAS 17233-3606

Direct observations of accretion disks around high-mass young stellar objects would help to discriminate between different models of formation of massive stars. However, given the complexity of massive star forming regions, such studies are still limited in number. Additionally, there is still no general consensus on the molecular tracers to be used for such investigations. Because of its close distance and high luminosity, IRAS 17233-3606 is a potential good laboratory to search for traces of rotation in the inner gas around the protostar(s). Therefore, we selected the source for a detailed analysis of its molecular emission at 230 GHz with the SMA. We systematically investigated the velocity fields of transitions in the SMA spectra which are not affected by overlap with other transitions, and searched for coherent velocity gradients to compare them to the distribution of outflows in the region. Beside CO emission we also used high-angular H2 images to trace the outflow motions driven by the IRAS 17233-3606 cluster. We find linear velocity gradients in many transitions of the same molecular species and in several molecules. We report the first detection of HNCO in molecular outflows from massive YSOs. We discuss the CH3CN velocity gradient taking into account various scenarios: rotation, presence of multiple unresolved sources with different velocities, and outflow(s). Although other interpretations cannot be ruled out, we propose that the CH3CN emission might be affected by the outflows of the region. Higher angular observations are needed to discriminate between the different scenarios. The present observations, with the possible association of CH3CN with outflows in a few thousands AU around the YSOs' cluster, (i) question the choice of the tracer to probe rotating structures, and (ii) show the importance of the use of H2 images for detailed studies of kinematics.

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arXiv2010

SiO outflows in high-mass star forming regions: A potential chemical clock?

Some theoretical models propose that O-B stars form via accretion, in a similar fashion to low-mass stars. Jet-driven molecular outflows play an important role in this scenario, and their study can help to understand the process of high-mass star formation and the different evolutionary phases involved. Observations towards low-mass protostars so far favour an evolutionary picture in which jets are always associated with Class 0 objects while more evolved Class I/II objects show less evidence of powerful jets. The present study aims at checking whether an analogous picture can be found in the high-mass case. The IRAM 30-m telescope (Spain) has been used to perform single-pointing SiO(2-1) and (3-2) observations towards a sample of 57 high-mass molecular clumps in different evolutionary stages. Continuum data at different wavelengths, from mid-IR to 1.2 mm, have been gathered to build the spectral energy distributions of all the clumps and estimate their bolometric luminosities. SiO emission at high velocities, characteristic of molecular jets, is detected in 88% of our sources, a very high detection rate indicating that there is ongoing star formation activity in most of the sources of our sample. The SiO(2-1) luminosity drops with L/M, which suggests that jet activity declines as time evolves. This represents the first clear evidence of a decrease of SiO outflow luminosity with time in a homogeneous sample of high-mass molecular clumps in different evolutionary stages. The SiO(3-2) to SiO(2-1) integrated intensity ratio shows only minor changes with evolutionary state.

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arXiv2010

Methanol and water masers in IRAS 20126+4104: The distance, the disk, and the jet

IRAS 20126+4104 is one of the best candidates for a high-mass (proto)star surrounded by an accretion disk. Such a fact may be used to set constraints on theories of high-mass star formation, but requires confirmation that the mass and luminosity of IRAS 20126+4104 are indeed typical of a B0.5 star, which in turn requires an accurate estimate of the distance. We used the Very Long Baseline Array and the European VLBI Network to observe the 22.2 GHz water and 6.7 GHz methanol masers in IRAS 20126+4104 at a number of epochs suitably distributed in time. The absolute positions of the maser features were established with respect to reference quasars, which allowed us to derive absolute proper motions. From the parallax of the water masers we obtain a distance of 1.64 \pm 0.05 kpc, which is very similar to the value adopted so far in the literature (1.7 kpc) and confirms that IRAS 20126+4104 is a high-mass (proto)star. From the methanol masers we derive the component in the plane of the sky of the systemic velocity of the disk+star system (-16 km/s in right-ascension and +7.6 km/s in declination). Accurate knowledge of the distance and systemic velocity allows us to improve on the model fit to the water maser jet presented in a previous study. Finally, we identify two groups of methanol maser features, one undergoing rotation in the disk and possibly distributed along a narrow ring centered on the star, the other characterised by relative proper motions indicating that the features are moving away from the disk, perpendicular to it. We speculate that the latter group might be tracing the disk material marginally entrained by the jet.

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arXiv2010

Rotating toroids in G10.62-0.38, G19.61-0.23, and G29.96-0.02

Context. In recent years, we have detected clear evidence of rotation in more than 5 hot molecular cores (HMCs). Their identification is confirmed by the fact that the rotation axes are parallel to the axes of the associated bipolar outflows. We have now pursued our investigation by extending the sample to 3 known massive cores, G10.62-0.38, G19.61-0.23, and G29.96-0.02. Aims. We wish to make a thorough study of the structure and kinematics of HMCs and corresponding molecular outflows to reveal possible velocity gradients indicative of rotation of the cores. Methods. We carried out PdBI observations at 2.7 and 1.4~mm of gas and dust with angular resolutions of 2"-3", and 1"-2", respectively. To trace both rotation and expansion, we simultaneously observed CH3CN, a typical HMC tracer, and 13CO, a typical outflow tracer. Results. The CH3CN(12-11) observations have revealed the existence of clear velocity gradients in the three HMCs oriented perpendicular to the direction of the bipolar outflows. For G19 and G29 the molecular outflows have been mapped in 13CO. The gradients have been interpreted as rotating toroids. The rotation temperatures, used to derive the mass of the cores, have been obtained by means of the rotational diagram method, and lie in the range of 87-244 K. The diameters and masses of the toroids lie in the range of 4550-12600 AU, and 28-415 Msun, respectively. Given that the dynamical masses are 2 to 30 times smaller than the masses of the cores (if the inclination of the toroids with respect to the plane of the sky is not much smaller than 45 degrees), we suggest that the toroids could be accreting onto the embedded cluster. For G19 and G29, the collapse is also suggested by the redshifted absorption seen in the 13CO(2-1) line. We infer that infall onto the embedded (proto)stars must proceed with rates of 1E-2 Msun/yr, and on timescales of the order of 4E3-1E4yr...

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arXiv2010

Infall, outflow, and rotation in the G19.61-0.23 hot molecular core

Aims: The main goal of this study is to perform a sub-arcsecond resolution analysis of the high-mass star formation region G19.61-0.23, both in the continuum and molecular line emission. While the centimeter continuum images will be discussed in detail in a forthcoming paper, here we focus on the (sub)mm emission, devoting special attention to the hot molecular core. Results: Our observations resolve the HMC into three cores whose masses are on the order of 10^1-10^3 Msun. No submm core presents detectable free-free emission in the centimeter regime, but they appear to be associated with masers and thermal line emission from complex organic molecules. Towards the most massive core, SMA1, the CH3CN (18_K-17_K) lines reveal hints of rotation about the axis of a jet/outflow traced by H2O maser and H13CO+ (1--0) line emission. Inverse P-Cygni profiles of the 13CO (3--2) and C18O (3--2) lines seen towards SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining mass with an accretion rate $ge 3 ~10^{-3}$ Msun/yr. Due to the linear scales and the large values of the accretion rate, we hypothesize that we are observing an accretion flow towards a cluster in the making, rather than towards a single massive star.

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arXiv2010

The molecular environment of the Galactic star forming region G19.61-0.23

We present single-dish (sub)millimeter observations of gas and dust in the Galactic high-mass star-forming region G19.61-0.23, with the aim of studying the large-scale properties and physical conditions of the molecular gas across the region. The final aim is to compare the large-scale (about 100 pc) properties with the small-scale (about 3 pc) properties and to consider possible implications for extragalactic studies. We have mapped CO isotopologues in the J=1-0 transition using the FCRAO-14m telescope and the J=2-1 transition using the IRAM-30m telescope. We have also used data from the ATLASGAL survey and from the BU-FCRAO Galactic Ring Survey, as well as the Spitzer infrared Galactic plane surveys GLIMPSE and MIPSGAL to characterize the star-formation activity within the molecular clouds. We reveal a population of molecular clumps in the 13CO(1-0) emission. Our analysis of the 13CO suggests that the virial parameter (ratio of kinetic to gravitational energy) varies over an order of magnitude between clumps that are unbound and some that are apparently "unstable". This conclusion is independent of whether they show evidence of ongoing star formation. We find that the majority of ATLASGAL sources have MIPSGAL counterparts with luminosities in the range 10^4 - 5 10^4 Lsun and are presumably forming relatively massive stars. We compare our results with previous extragalactic studies of the nearby spiral galaxies M31 and M33; and the blue compact dwarf galaxy Henize2-10. We find that the main giant molecular cloud surrounding G19.61-0.23 has physical properties typical for Galactic GMCs and which are comparable to the GMCs in M31 and M33. However, the GMC studied here shows smaller surface densities and masses than the clouds identified in Henize2-10 and associated with super star cluster formation.

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arXiv2010

Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key-project that will map the inner Galactic Plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2° x 2° tiles approximately centered at l=30° and l=59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call 'cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around A_V of about 1 is exceeded for the regions in the l=59° field; a A_V value between 5 and 10 is found for the l=30° field, likely due to the relatively larger distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm-2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.

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arXiv2010

VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41

The present paper focuses on the high-mass star-forming region G23.01-0.41. Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G23.01-0.41: H2O at 22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (< 0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3 and 3.6 cm. Results: We have detected H2O, CH3OH, and OH maser emission clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW, from which emerges a massive 12CO outflow, elongated NE-SW, extended up to the pc-scale. Although the three maser species show a clearly different spatial and velocity distribution and sample distinct environments around the massive YSO, the spatial symmetry and velocity field of each maser specie can be explained in terms of expansion from a common center, which possibly denotes the position of the YSO driving the maser motion. Water masers trace both a fast shock (up to 50 km/s) closer to the YSO, powered by a wide-angle wind, and a slower (20 km/s) bipolar jet, at the base of the large-scale outflow. Since the compact free-free emission is found offset from the putative location of the YSO along a direction consistent with that of the maser jet axis, we interpret the radio continuum in terms of a thermal jet. The velocity field of methanol masers can be explained in terms of a composition of slow (4 km/s in amplitude) motions of radial expansion and rotation about an axis approximately parallel to the maser jet. Finally, the distribution of line of sight velocities of the hydroxyl masers suggests that they can trace gas less dense (n(H2) < 10^6 cm^-3) and more distant from the YSO than that traced by the water and methanol masers, which is expanding toward the observer. (Abridged)

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arXiv2010

Class I and Class II methanol masers in high-mass star forming regions

Among the tracers of the earliest phases in the massive star formation process, methanol masers have gained increasing importance. The phenomenological distinction between Class I and II methanol masers is based on their spatial association with objects such as jets, cores, and ultracompact HII regions, but is also believed to correspond to different pumping mechanisms: radiation for Class II masers, collisions for Class I masers. In this work, we have surveyed a large sample of massive star forming regions - 296 objects divided into two groups named 'High' and 'Low' according to their [25-12] and [60-12] IRAS colours - in Class I and II methanol masers. Previous studies indicate that the High sources are likely more evolved. Therefore, the sample can be used to assess the existence of a sequence for the occurrence of Class I and II methanol masers during the evolution of a massive star forming region. We observed the 6 GHz (Class II) CH3OH maser with the Effelsberg 100-m telescope, and the 44 GHz and 95 GHz (Class I) CH3OH masers with the Nobeyama 45-m telescope. We have detected: 55 sources in the Class II line (12 new detections); 27 sources in the 44 GHz Class I line (17 new detections); 11 sources in the 95 GHz Class I line (all except one are new detections). Our statistical analysis shows that the ratio between the detection rates of Class II and Class I methanol masers is basically the same in High and Low sources. Therefore, both masers are equally associated with each evolutionary phase. In contrast, all maser species have about 3 times higher detection rates in High than in Low sources. This might indicate that the phenomena that originate all masers become progressively more active with time, during the earliest evolutionary phases of a high-mass star forming region.

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arXiv2010

VLBI study of maser kinematics in high-mass SFRs. I. G16.59-0.05

The present paper focuses on the high-mass star-forming region G16.59-0.05. Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G16.59-0.05: H2O at 22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (< 0.1 mJy) VLA observations of the radio continuum emission from the star-forming region at 1.3 and 3.6 cm. Results: This is the first work to report accurate measurements of the "relative" proper motions of the 6.7 GHz CH3OH masers. The different spatial and 3-D velocity distribution clearly indicate that the 22 GHz water and 6.7 GHz methanol masers are tracing different kinematic environments. The bipolar distribution of 6.7 GHz maser l.o.s. velocities and the regular pattern of observed proper motions suggest that these masers are tracing rotation around a central mass of about 35 solar masses. The flattened spatial distribution of the 6.7 GHz masers, oriented NW-SE, suggests that they can originate in a disk/toroid rotating around the massive YSO which drives the 12CO(2-1) outflow, oriented NE-SW, observed on arcsec scale. The extended, radio continuum source observed close to the 6.7 GHz masers could be excited by a wide-angle wind emitted from the YSO associated with the methanol masers, and such a wind is proven to be sufficiently energetic to drive the NE-SW 12CO(2-1) outflow. The H2O masers distribute across a region offset about 0".5 to the NW of the CH3OH masers, in the same area where emission of high-density molecular tracers, typical of HMCs, was detected. We postulate that a distinct YSO, possibly in an earlier evolutionary phase than that exciting the methanol masers, is responsible for the excitation of the water masers and the HMC molecular lines. (Abridged)

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arXiv2009

ATLASGAL - The APEX Telescope Large Area Survey of the Galaxy at 870 microns

(Abridged) Studying continuum emission from interstellar dust is essential to locating and characterizing the highest density regions in the interstellar medium. In particular, the early stages of massive star formation remain poorly understood. Our goal is to produce a large-scale, systematic database of massive pre- and proto-stellar clumps in the Galaxy, to understand how and under what conditions star formation takes place. A well characterized sample of star-forming sites will deliver an evolutionary sequence and a mass function of high-mass, star-forming clumps. This systematic survey at submm wavelengths also represents a preparatory work for Herschel and ALMA. The APEX telescope is ideally located to observe the inner Milky Way. The Large APEX Bolometer Camera (LABOCA) is a 295-element bolometer array observing at 870 microns, with a beam size of 19". Taking advantage of its large field of view (11.4') and excellent sensitivity, we started an unbiased survey of the Galactic Plane, with a noise level of 50-70 mJy/beam: the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). As a first step, we covered 95 sq. deg. These data reveal 6000 compact sources brighter than 0.25 Jy, as well as extended structures, many of them filamentary. About two thirds of the compact sources have no bright infrared counterpart, and some of them are likely to correspond to the precursors of (high-mass) proto-stars or proto-clusters. Other compact sources harbor hot cores, compact HII regions or young embedded clusters. Assuming a typical distance of 5 kpc, most sources are clumps smaller than 1 pc with masses from a few 10 to a few 100 M_sun. In this introductory paper, we show preliminary results from these ongoing observations, and discuss the perspectives of the survey.

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arXiv2009

Molecular outflows towards O-type young stellar objects

We have searched for massive molecular outflows in a sample of high-mass star forming regions, and we have characterised both the outflow properties and those of their associated molecular clumps. With a sample composed largely of more luminous objects than previous ones, this work complements analogous surveys performed by other authors by adding the missing highest luminosity sources. The sample under study has been selected so as to favour the earliest evolutionary phases of star formation, and is composed of very luminous objects (L_bol > 2x10^4 L_sun and up to ~10^6 L_sun), possibly containing O-type stars. Each source has been mapped in 13CO(2-1) and C18O(2-1) with the IRAM-30m telescope on Pico Veleta (Spain). The whole sample shows high-velocity wings in the 13CO(2-1) spectra, indicative of outflowing motions. In addition, we have obtained outflow maps in 9 of our 11 sources, which display well-defined blue and/or red lobes. For these sources, the outflow parameters have been derived from the line wing 13CO(2-1) emission. An estimate of the clump masses from the C18O(2-1) emission is also provided and found to be comparable to the virial masses. From a comparison between our results and those found by other authors at lower masses, it is clear that the outflow mechanical force increases with the bolometric luminosity of the clump and with the ionising photon rate of the associated HII regions, indicating that high-mass stars drive more powerful outflows. A tight correlation between outflow mass and clump mass is also found. Molecular outflows are found to be as common in massive star forming regions as in low-mass star forming regions. This, added to the detection of a few tentative large-scale rotating structures suggests that high-mass stars may generally form via accretion, as low-mass stars.

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arXiv2008

First detection of glycolaldehyde outside the Galactic Center

Glycolaldehyde is the simplest of the monosaccharide sugars and is directly linked to the origin of life. We report on the detection of glycolaldehyde (CH2OHCHO) towards the hot molecular core G31.41+0.31 through IRAM PdBI observations at 1.4, 2.1, and 2.9 mm. The CH2OHCHO emission comes from the hottest (> 300 K) and densest (>2E8 cm^-3) region closest (< 10^4 AU) to the (proto)stars. The comparison of data with gas-grain chemical models of hot cores suggests for G31.41+0.31 an age of a few 10^5 yr. We also show that only small amounts of CO need to be processed on grains in order for existing hot core gas-grain chemical models to reproduce the observed column densities of glycolaldehyde, making surface reactions the most feasible route to its formation.

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