arXiv subjects

L. Bronfman

Publications and source records attributed to L. Bronfman.

At least 55 records · Page 3Linked to original sources

arXiv2020

SEDIGISM-ATLASGAL: Dense Gas Fraction and Star Formation Efficiency Across the Galactic Disk

By combining two surveys covering a large fraction of the molecular material in the Galactic disk we investigate the role the spiral arms play in the star formation process. We have matched clumps identified by ATLASGAL with their parental GMCs as identified by SEDIGISM, and use these giant molecular cloud (GMC) masses, the bolometric luminosities, and integrated clump masses obtained in a concurrent paper to estimate the dense gas fractions (DGF$_{\rm gmc}=\sum M_{\rm clump}/M_{\rm gmc}$) and the instantaneous star forming efficiencies (i.e., SFE$_{\rm gmc} = \sum L_{\rm clump}/M_{\rm gmc}$). We find that the molecular material associated with ATLASGAL clumps is concentrated in the spiral arms ($\sim$60% found within $\pm$10 km s$^{-1}$ of an arm). We have searched for variations in the values of these physical parameters with respect to their proximity to the spiral arms, but find no evidence for any enhancement that might be attributable to the spiral arms. The combined results from a number of similar studies based on different surveys indicate that, while spiral-arm location plays a role in cloud formation and HI to H$_2$ conversion, the subsequent star formation processes appear to depend more on local environment effects. This leads us to conclude that the enhanced star formation activity seen towards the spiral arms is the result of source crowding rather than the consequence of a any physical process.

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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.

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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.

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arXiv2019

Revealing The CO X-factor In Dark Molecular Gas through Sensitive ALMA Absorption Observations

Carbon-bearing molecules, particularly CO, have been widely used as tracers of molecular gas in the interstellar medium (ISM). In this work, we aim to study the properties of molecules in diffuse, cold environments, where CO tends to be under-abundant and/or sub-thermally excited. We performed one of the most sensitive (down to $\mathrm{τ_{rms}^{CO} \sim 0.002}$ and $\mathrm{τ_{rms}^{HCO^+} \sim 0.0008}$) sub-millimeter molecular absorption line observations towards 13 continuum sources with the ALMA. CO absorption was detected in diffuse ISM down to $\mathrm{A_v< 0.32\,mag}$ and \hcop was down to $\mathrm{A_v < 0.2\,mag}$, where atomic gas and dark molecular gas (DMG) starts to dominate. Multiple transitions measured in absorption toward 3C454.3 allow for a direct determination of excitation temperatures $\mathrm{T_{ex}}$ of 4.1\,K and 2.7\,K, for CO and for \hcop, respectively, which are close to the cosmic microwave background (CMB) and provide explanation for their being undercounted in emission surveys. A stronger linear correlation was found between $\mathrm{N_{HCO^+}}$ and $\mathrm{N_{H_2}}$ (Pearson correlation coefficient P $\sim$ 0.93) than that of $\mathrm{N_{CO}}$ and $\mathrm{N_{H_2}}$ (P $\sim$ 0.33), suggesting \hcop\ being a better tracer of H$_2$ than CO in diffuse gas. The derived CO-to-\h2 conversion factor (the CO X-factor) of (14 $\pm$ 3) $\times$ 10$^{20}$ cm$^{-2}$ (K \kms)$^{-1}$ is approximately 6 times larger than the average value found in the Milky Way.

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arXiv2019

Cyanoacetylene in the outflow/hot molecular core G331.512-0.103

Using APEX-1 and APEX-2 observations, we have detected and studied the rotational lines of the HC$_3$N molecule (cyanoacetylene) in the powerful outflow/hot molecular core G331.512-0.103. We identified thirty-one rotational lines at $J$ levels between 24 and 39; seventeen of them in the ground vibrational state $v$=0 (9 lines corresponding to the main C isotopologue and 8 lines corresponding to the $^{13}$C isotopologues), and fourteen in the lowest vibrationally excited state $v_7$=1. Using LTE-based population diagrams for the beam-diluted $v$=0 transitions, we determined $T_{\rm exc}$=85$\pm$4 K and $N$(HC$_3$N)=(6.9$\pm$0.8)$\times$10$^{14}$ cm$^{-2}$, while for the beam-diluted $v_7$=1 transitions we obtained $T_{\rm exc}$=89$\pm$10 K and $N$(HC$_3$N)=2$\pm$1$\times$10$^{15}$ cm$^{-2}$. Non-LTE calculations using H$_2$ collision rates indicate that the HC$_3$N emission is in good agreement with LTE-based results. From the non-LTE method we estimated $T_{\rm kin}$ $\simeq$90~K, $n$(H$_2$)$\simeq$2$\times$10$^7$~cm$^{-3}$ for a central core of 6 arcsec in size. A vibrational temperature in the range from 130~K to 145~K was also determined, values which are very likely lower limits. Our results suggest that rotational transitions are thermalized, while IR radiative pumping processes are probably more efficient than collisions in exciting the molecule to the vibrationally excited state $v_7$=1. Abundance ratios derived under LTE conditions for the $^{13}$C isotopologues suggest that the main formation pathway of HC$_3$N is ${\rm C}_2{\rm H}_2 + {\rm CN} \rightarrow {\rm HC}_3{\rm N} + {\rm H}$.

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arXiv2019

SCOPE: SCUBA-2 Continuum Observations of Pre-protostellar Evolution - Survey Description and Compact Source Catalogue

We present the first release of the data and compact-source catalogue for the JCMT Large Program SCUBA-2 Continuum Observations of Pre-protostellar Evolution (SCOPE). SCOPE consists of 850-um continuum observations of 1235 Planck Galactic Cold Clumps (PGCCs) made with the Submillimetre Common-User Bolometer Array 2 on the James Clerk Maxwell Telescope. These data are at an angular resolution of 14.4 arcsec, significantly improving upon the 353-GHz resolution of Planck at 5 arcmin, and allowing for a catalogue of 3528 compact sources in 558 PGCCs. We find that the detected PGCCs have significant sub-structure, with 61 per cent of detected PGCCs having 3 or more compact sources, with filamentary structure also prevalent within the sample. A detection rate of 45 per cent is found across the survey, which is 95 per cent complete to Planck column densities of $N_{H_{2}}$ $>$ 5 $\times$ 10$^{21}$ cm$^{-2}$. By positionally associating the SCOPE compact sources with YSOs, the star formation efficiency, as measured by the ratio of luminosity to mass, in nearby clouds is found to be similar to that in the more distant Galactic Plane, with the column density distributions also indistinguishable from each other.

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arXiv2019

Multiwavelength study of the G345.5+1.5 region

Star-forming regions are usually studied in the context of Galactic surveys, but dedicated observations are sometimes needed when the study reaches beyond the survey area. Here, we studied the G345.5+1.5 region, which is located slightly above the Galactic plane, to understand its star formation properties. We combined the LABOCA and $^{12}$CO(4$-$3) transition line observations complemented with the Hi-GAL and $\it{Spitzer}$-GLIMPSE surveys to study the star formation toward this region. We used the Clumpfind algorithm to extract the clumps from the 870$μ$m and $^{12}$CO(4$-$3) data. Radio emission at 36cm was used to estimate the number of HII regions and to remove the contamination from the free-free emission at 870$μ$m. We employed color-color diagrams and spectral energy distribution slopes to distinguish between prestellar and protostellar clumps. We studied the boundedness of the clumps through the virial parameter. Finally, we estimated the star formation efficiency and star formation rate of the region and used the Schmidt-Kennicutt diagram to compare its ability to form stars. Of the 13 radio sources that we found using the MGPS-2 catalog, 7 are found to be associated with HII regions corresponding to late-B or early-O stars. We found 45 870$μ$m clumps, and 107 $^{12}$CO clumps. More than 50\% of the clumps are protostellar and bounded and are able to host star formation. High SFR and SFR density values are associated with the region, with an SFE of a few percent. With submillimeter, CO transition, and short-wavelength infrared observations, our study reveals a population of massive stars, protostellar and bound starless clumps, toward G345.5+1.5. This region is therefore actively forming stars, and its location in the starburst quadrant of the Schmidt-Kennicutt diagram is comparable to other star-forming regions found within the Galactic plane.

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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.

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arXiv2018

SEDIGISM: The kinematics of ATLASGAL filaments

Analysing the kinematics of filamentary molecular clouds is a crucial step towards understanding their role in the star formation process. Therefore, we study the kinematics of 283 filament candidates in the inner Galaxy, that were previously identified in the ATLASGAL dust continuum data. The $^{13}$CO(2 - 1) and C$^{18}$O(2 - 1) data of the SEDIGISM survey (Structure, Excitation, and Dynamics of the Inner Galactic Inter Stellar Medium) allows us to analyse the kinematics of these targets and to determine their physical properties at a resolution of 30 arcsec and 0.25 km/s. To do so, we developed an automated algorithm to identify all velocity components along the line-of-sight correlated with the ATLASGAL dust emission, and derive size, mass, and kinematic properties for all velocity components. We find two-third of the filament candidates are coherent structures in position-position-velocity space. The remaining candidates appear to be the result of a superposition of two or three filamentary structures along the line-of-sight. At the resolution of the data, on average the filaments are in agreement with Plummer-like radial density profiles with a power-law exponent of p = 1.5 +- 0.5, indicating that they are typically embedded in a molecular cloud and do not have a well-defined outer radius. Also, we find a correlation between the observed mass per unit length and the velocity dispersion of the filament of $m \sim σ_v^2$. We show that this relation can be explained by a virial balance between self-gravity and pressure. Another possible explanation could be radial collapse of the filament, where we can exclude infall motions close to the free-fall velocity.

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arXiv2018

Digital compensation of the side-band-rejection ratio in a fully analog 2SB sub-millimeter receiver

In observational radio astronomy, sideband-separating receivers are preferred, particularly under high atmospheric noise, which is usually the case in the sub-millimeter range. However, obtaining a good rejection ratio between the two sidebands is difficult since, unavoidably, imbalances in the different analog components appear. We describe a method to correct these imbalances without making any change in the analog part of the sideband-separating receiver, specifically, keeping the intermediate-frequency hybrid in place. This opens the possibility of implementing the method in any existing receiver. We have built hardware to demonstrate the validity of the method and tested it on a fully analog receiver operating between 600 and 720GHz. We have tested the stability of calibration and performance vs time and after full resets of the receiver. We have performed an error analysis to compare the digital compensation in two configurations of analog receivers, with and without intermediate frequency (IF) hybrid. An average compensated sideband rejection ratio of 46dB is obtained. Degradation of the compensated sideband rejection ratio on time and after several resets of the receiver is minimal. A receiver with an IF hybrid is more robust to systematic errors. Moreover, we have shown that the intrinsic random errors in calibration have the same impact for configuration without IF hybrid and for a configuration with IF hybrid with analog rejection ratio better than 10dB. Compensated rejection ratios above 40dB are obtained even in the presence of high analog rejection. The method is robust allowing its use under normal operational conditions at any telescope. We also demonstrate that a full analog receiver is more robust against systematic errors. Finally, the error bars associated to the compensated rejection ratio are almost independent of whether IF hybrid is present or not.

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arXiv2018

Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM

Observations of interstellar dust are often used as a proxy for total gas column density $N_\mathrm{H}$. By comparing $\textit{Planck}$ thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et al. 2018), with accurate (opacity-corrected) HI column densities and newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth $τ_{353}$, reddening $E(B{-}V)$ and the total proton column density $N_\mathrm{H}$ in the range (1$-$30)$\times$10$^{20}$cm$^{-2}$, along sightlines with no molecular gas detections in emission. We derive an $N_\mathrm{H}$/$E(B{-}V)$ ratio of (9.4$\pm$1.6)$\times$10$^{21}$cm$^{-2}$mag$^{-1}$ for purely atomic sightlines at $|b|$$>$5$^{\circ}$, which is 60$\%$ higher than the canonical value of Bohlin et al. (1978). We report a $\sim$40$\%$ increase in opacity $σ_{353}$=$τ_{353}$/$N_\mathrm{H}$, when moving from the low column density ($N_\mathrm{H}$$<$5$\times$10$^{20}$cm$^{-2}$) to moderate column density ($N_\mathrm{H}$$>$5$\times$10$^{20}$cm$^{-2}$) regime, and suggest that this rise is due to the evolution of dust grains in the atomic ISM. Failure to account for HI opacity can cause an additional apparent rise in $σ_{353}$, of the order of a further $\sim$20$\%$. We estimate molecular hydrogen column densities $N_{\mathrm{H}_{2}}$ from our derived linear relations, and hence derive the OH/H$_2$ abundance ratio of $X_\mathrm{OH}$$\sim$1$\times$10$^{-7}$ for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with $N_{\mathrm{H}_{2}}$ in the range $N_{\mathrm{H}_{2}}$$\sim$(0.1$-$10)$\times$10$^{21}$cm$^{-2}$. This suggests that OH may be used as a reliable proxy for H$_2$ in this range, which includes sightlines with both CO-dark and CO-bright gas.

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arXiv2018

A FPGA-based Fast Converging Digital Adaptive Filter for Real-time RFI Mitigation on Ground Based Radio Telescopes

Radio Frequency Interference (RFI) is a growing concern in the radio astronomy community. Single-dish telescopes are particularly susceptible to RFI. Several methods have been developed to cope with RF-polluted environments, based on flagging, excision, and real-time blanking, among others. All these methods produce some degree of data loss or require assumptions to be made on the astronomical signal. We report the development of a real-time, digital adaptive filter implemented on a Field Programmable Gate Array (FPGA) capable of processing 4096 spectral channels in a 1 GHz of instantaneous bandwidth. The filter is able to cancel a broad range of interference signals and quickly adapt to changes on the RFI source, minimizing the data loss without any assumption on the astronomical or interfering signal properties. The speed of convergence (for a decrease to a 1%) was measured to be 208.1 us for a broadband noise-like RFI signal and 125.5 us for a multiple-carrier RFI signal recorded at the FAST radio telescope.

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arXiv2018

The search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS): I. Indication for a centrifugal barrier in the environment of a single high-mass envelope

The formation of the most massive O-type stars is poorly understood. We present a case study of a young massive clump from the ATLASGAL survey, G328.2551-0.5321. It exhibits a bolometric luminosity of 1.3$\times$10$^4$ L$_{\odot}$ corresponding to a current protostellar mass of $\sim$11 and 16 M$_{\odot}$. We analyze high angular-resolution observations with ALMA at $\sim$0.17" corresponding a physical scale of $\sim$400 au in dust continuum and molecular lines. The dust continuum emission reveals a single high-mass protostellar envelope and shows evidence for a marginally resolved continuum source. We detect a rotational line of CH$_3$OH within its $v_{\rm t}$=1 torsionally excited state revealing two bright peaks of emission spatially offset from the dust continuum peak, and exhibiting a distinct velocity component $\pm$4.5 km s$^{-1}$ offset compared to the source $v_{\rm lsr}$. Local thermodynamic equilibrium analysis suggests N(CH$_3$OH)=1.2$-$2$\times$10$^{19}$ cm$^{-2}$, and kinetic temperatures of 160$-$200 K at the position of these peaks. Their velocity shifts correspond well to the expected Keplerian velocity around a central object with 15M$_{\odot}$ consistent with the mass estimate based on the source's bolometric luminosity. We propose a picture where the CH$_3$OH emission peaks trace the accretion shocks around the centrifugal barrier, pinpointing the interaction region between the collapsing envelope and an accretion disk. Because the HC$_3$N $v_{\rm 7}$=1e ($J$=38-37) line shows compact emission, and a velocity pattern consistent with models of Keplerian rotation, we suggest that this could be a new tracer for compact accretion disks around high-mass protostars. The estimated physical properties of the accretion disk suggest a specific angular momentum several times larger than typically observed towards low-mass protostars.

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arXiv2018

G331.512-0.103: An Interstellar Laboratory for Molecular Synthesis I. The Ortho-to-para Ratios for CH$_3$OH and CH$_3$CN

Spectral line surveys reveal rich molecular reservoirs in G331.512-0.103, a compact radio source in the center of an energetic molecular outflow. In this first work, we analyse the physical conditions of the source by means of CH$_3$OH and CH$_3$CN. The observations were performed with the APEX telescope. Six different system configurations were defined to cover most of the band within (292-356) GHz; as a consequence we detected a forest of lines towards the central core. A total of 70 lines of $A/E$-CH$_3$OH and $A/E$-CH$_3$CN were analysed, including torsionally excited transitions of CH$_3$OH ($ν_t$=1). In a search for all the isotopologues, we identified transitions of $^{13}$CH$_3$OH. The physical conditions were derived considering collisional and radiative processes. We found common temperatures for each $A$ and $E$ symmetry of CH$_3$OH and CH$_3$CN; the derived column densities indicate an $A/E$ equilibrated ratio for both tracers. The results reveal that CH$_3$CN and CH$_3$OH trace a hot and cold component with $T_k \sim$ 141 K and $T_k \sim$ 74 K, respectively. In agreement with previous ALMA observations, the models show that the emission region is compact ($\lesssim$ 5.5 arcsec) with gas density $n$(H$_2$)=(0.7-1) $\times$ 10$^7$ cm$^{-3}$. The CH$_3$OH/CH$_3$CN abundance ratio and the evidences for pre-biotic and complex organic molecules suggest a rich and active chemistry towards G331.512-0.103.

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arXiv2018

Where is OH and Does It Trace the Dark Molecular Gas (DMG)?

Hydroxyl (OH) is expected to be abundant in diffuse interstellar molecular gas as it forms along with $H_2$ under similar conditions and within a similar extinction range. We have analyzed absorption measurements of OH at 1665 MHz and 1667 MHz toward 44 extragalactic continuum sources, together with the J=1-0 transitions of $^{12}$CO, $^{13}$CO , and C$^{18}$O, and the J=2-1 of $^{12}$CO. The excitation temperature of OH were found to follow a modified log-normal distribution, $ f(T{\rm_{ex}}) \propto \frac{1}{ \sqrt{2π}σ} \rm{exp}\left[-\frac{[ln(\textit{T}_{ex})-ln(3.4\ K)]^2}{2σ^2}\right] $, the peak of which is close to the temperature of the Galactic emission background (CMB+synchron). In fact, 90% of the OH has excitation temperature within 2 K of the Galactic background at the same location, providing a plausible explanation for the apparent difficulty to map this abundant molecule in emission. The opacities of OH were found to be small and peak around 0.01. For gas at intermediate extinctions (A$\rm_V$ $\sim$ 0.05-2 mag), the detection rate of OH with detection limit $N(\mathrm{OH})\simeq 10^{12}$ cm$^{-2}$ is approximately independent of $A\rm_V$. We conclude that OH is abundant in the diffuse molecular gas and OH absorption is a good tracer of `dark molecular gas (DMG)'. The measured fraction of DMG depends on assumed detection threshold of the CO data set. The next generation of highly sensitive low frequency radio telescopes, FAST and SKA, will make feasible the systematic inventory of diffuse molecular gas, through decomposing in velocity the molecular (e.g. OH and CH) absorption profiles toward background continuum sources with numbers exceeding what is currently available by orders of magnitude.

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arXiv2017

The foot points of the Giant Molecular Loops in the Galactic center region

Aims: To reveal the morphology, chemical composition, kinematics and to establish the main processes prevalent in the gas at the foot points of the giant molecular loops (GMLs) in the Galactic center region Methods: Using the 22-m Mopra telescope, we mapped the M$-3.8+0.9$ molecular cloud, placed at the foot points of a giant molecular loop, in 3-mm range molecular lines. To derive the molecular hydrogen column density, we also observed the $^{13}$CO $(2-1)$ line at 1 mm using the 12-m APEX telescope. From the 3 mm observations 12 molecular species were detected, namely HCO$^+$, HCN, H$^{13}$CN, HNC, SiO, CS, CH$_3$OH, N$_2$H$^+$, SO, HNCO, OCS, and HC$_3$N. Results: Maps revealing the morphology and kinematics of the M$-3.8+0.9$ molecular cloud in different molecules are presented. We identified six main molecular complexes. We derive fractional abundances in 11 selected positions of the different molecules assuming local thermodynamical equilibrium. Conclusions: Most of the fractional abundances derived for the M$-3.8+0.9$ molecular cloud are very similar over the whole cloud. However, the fractional abundances of some molecules show significant difference with respect to those measured in the central molecular zone (CMZ). The abundances of the shock tracer SiO are very similar between the GMLs and the CMZ. The methanol emission is the most abundant specie in the GMLs. This indicates that the gas is likely affected by moderate $\sim $ 30 km s$^{-1}$ or even high velocity (50 km s$^{-1}$) shocks, consistent with the line profile observed toward one of the studied position. The origin of the shocks is likely related to the flow of the gas throughout the GMLs towards the foot points.

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arXiv2017

The diffuse molecular component in the nuclear bulge of the Milky Way

Context: The bulk of the Molecular gas in the Central Molecular Zone (CMZ) of the Galactic center region shows warm kinetic temperatures, ranging from $>20$ K in the coldest and densest regions (n$\sim 10^{4-5}$ cm$^{-3}$) up to more than 100 K for densities of about n$\sim 10^3$ cm$^{-3}$. Recently, a more diffuse, hotter ($n \sim 100$ cm$^{-3}$, $T\sim 250$ K) gas component was discovered through absorption observations of H$_3^+$. This component may be widespread in the Galactic center, and low density gas detectable in absorption may be present even outside the CMZ along sightlines crossing the extended bulge of the Galaxy. Aims: We aim to observe and characterize diffuse and low density gas using observations of 3-mm molecular transitions seen in absorption. Methods: Using the Atacama Large (sub)Millimeter Array (ALMA) we observed the absorption against the quasar J1744-312, which is located towards the Galactic bulge region at $(l,b)=(-2{^\circ}.13,-1{^\circ}.0)$, but outside the main molecular complexes. Results: ALMA observations in absorption against the J1744-312 quasar reveal a rich and complex chemistry in low density molecular and presumably diffuse clouds. We detected three velocity components, at $\sim $ 0, $-153$, and $-192$ km s$^{-1}$. The component at $\sim 0$ km s$^{-1}$ could represent gas in the Galactic disk while the velocity components at $-153$, and $-192$ km s$^{-1}$ likely originate from the Galactic bulge. We detected 12 molecules in the survey, but only 7 in the Galactic bulge gas.

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arXiv2017

Triggered massive star formation associated with the bubble HII region Sh2-39 (N5)

Aiming at studying the physical properties of Galactic IR bubbles and to explore their impact in triggering massive star formation, we perform a multiwavelength analysis of the bubble HII region Sh2-39 (N5) and its environs. To analyze the molecular gas we use CO(3-2) and HCO+(4-3) line data obtained with the ASTE telescope. To study the physical characteristics of the dust, we make use of archival data from ATLASGAL, Herschel, and MSX, while the ionized gas was studied making use of NVSS data. We use public IR point source catalogs to search for candidate YSOs in the region. To investigate the stellar cluster [BDS2003]6 we use IR spectroscopic data obtained with the ARCoIRIS spectrograph, and new available IR Ks band observations from VVVX survey. The new ASTE observations allowed the molecular gas component in the velocity range from 30 km/s to 46 km/s, associated with Sh2-39, to be studied in detail. We have identified four molecular clumps, that were likely formed by the expansion of the ionization front, and determined some of their physical and dynamical properties. Clumps having HCO+ and 870 micron counterparts show evidence of gravitational collapse. We identified several candidate YSOs across the molecular component. Their spatial distribution, as well as the fragmentation time derived for the collected layers of the molecular gas, suggest that massive star formation might have been triggered by the expansion of the nebula via the collect and collapse mechanism. The spectroscopical distance obtained for the stellar cluster [BDS2003]6, placed over one of the collapsing clumps, reveals that this cluster is physically associated with the neabula and gives more support to the triggered massive star formation scenario. A radio continuum data analysis indicates that the nebula is older and expands at lower velocity than typical Galactic IR bubbles.

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