Context. The star formation process requires the dust and gas present in the Milky Way to self-assemble into dense reservoirs of neutral material where the new generation of stars will emerge. ...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. Aims. A better understanding of the star formation process in the Galaxy can be obtained by studying several regions. This allows increasing the sample of objects (clumps, cores, and stars) for further statistical works and deeper follow-up studies. Here, we studied the G345.5+1.5 region, which is located slightly above the Galactic plane, to understand its star formation properties. Methods. We combined Large Apex BOlometer CAmera (LABOCA) and 12CO(4−3) transition line (NANTEN2) observations complemented with the Hi-GAL and Spitzer-GLIMPSE surveys to study the star formation toward this region. We used the Clumpfind algorithm to extract the clumps from the 870 μm and 12CO(4−3) data. Radio emission at 36 cm was used to estimate the number of H II regions and to remove the contamination from the free–free emission at 870 μm. We employed color–color diagrams and spectral energy distribution (SED) 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 (SFE) and star formation rate (SFR) of the region and used the Schmidt–Kennicutt diagram to compare its ability to form stars with other regions of the Galactic plane. Results. Of the 13 radio sources that we found using the MGPS-2 catalog, 7 are found to be associated with H II regions corresponding to late-B or early-O stars. We found 45 870 μm clumps with diameters between 0.4 and 1.2 pc and masses between 43 M⊙ and 3923 M⊙, and 107 12CO clumps with diameters between 0.4 and 1.3 pc and masses between 28 M⊙ and 9433 M⊙. More than 50% of the clumps are protostellar and bounded and are able to host (massive) star formation. High SFR and SFR density (ΣSFR) values are associated with the region, with an SFE of a few percent. Conclusions. 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.
We report a centimetre-wave (cm-wave, 5–31 GHz) excess over free–free emission in planetary nebulae (PNe). Accurate 31- and 250-GHz measurements show that the 31-GHz flux densities in our sample are ...systematically higher than the level of optically thin free–free continuum extrapolated from 250-GHz. The 31-GHz excess is observed, within one standard deviation, in all 18 PNe with reliable 31- and 250-GHz data, and is significant in nine PNe. The only exception is the peculiar object M2-9, whose radio spectrum is that of an optically thick stellar wind. On average the fraction of non-free–free emission represents 51 per cent of the total flux density at 31 GHz, with a scatter of 11 per cent. The average 31–250 GHz spectral index of our sample is 〈α25031〉=−0.43 ± 0.03 (in flux density, with a scatter of 0.14). The 31–250 GHz drop is reminiscent of the anomalous foreground observed in the diffuse interstellar medium (ISM) by cosmic microwave background (CMB) anisotropy experiments. The 5–31 GHz spectral indices are consistent with both flat spectra and spinning dust emissivities, given the 10 per cent calibration uncertainty of the comparison 5-GHz data. However, a detailed study of the objects with the largest cm-excess, including the low-frequency data available in the literature, shows that present spinning dust models alone cannot explain the cm-wave excess in PNe. Although we have no definitive interpretation of our data, the least implausible explanation involves a synchrotron component absorbed by a cold nebular screen. We give flux densities for 37 objects at 31 GHz, and for 26 objects at 250 GHz.
ABSTRACT We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the z = 3.042 gravitationally lensed submillimeter galaxy HATLAS ...J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to ∼15 km. We present continuum imaging at 151, 236, and 290 GHz at unprecedented angular resolutions as fine as 23 mas, corresponding to an unmagnified spatial scale of ∼180 pc at z = 3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ∼1 5. We also present imaging of CO J = 10 − 9, J = 8 − 7, and J = 5 − 4 and ) line emission. The CO emission, at an angular resolution of ∼170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of line emission, using only the shortest baselines, provides the most resolved detection to date of thermal emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.
Context. Asymptotic giant branch (AGB) stars are major contributors to the chemical enrichment of the interstellar medium through nucleosynthesis and extensive mass loss. Direct measures of both ...processes can be obtained by studying their circumstellar envelopes in molecular line emission. Most of our current knowledge of circumstellar chemistry, in particular in a C-rich environment, is based on observations of the carbon star IRC +10216. Aims. We aim to obtain a more generalised understanding of the chemistry in C-rich AGB circumstellar envelopes by studying a sample of three carbon stars, IRAS 15194–5115, IRAS 15082–4808, and IRAS 07454–7112, and to observationally test the archetypal status often attributed to IRC +10216. Methods. We performed spatially resolved, unbiased spectral surveys in ALMA Band 3 (85–116 GHz). We estimated the sizes of the molecular emitting regions using azimuthally averaged radial profiles of the line brightness distributions. We derived abundance estimates, using a population diagram analysis for molecules with multiple detected lines, and using single-line analytical calculations for the others. Results. We identify a total of 132 rotational transitions from 49 molecular species. There are two main morphologies of the brightness distributions: centrally peaked (CS, SiO, SiS, HCN) and shell-like (CN, HNC, C 2 H, C 3 H, C 4 H, C 3 N, HC 5 N, c-C 3 H 2 ). The brightness distributions of HC 3 N and SiC 2 have both a central and a shell component. The qualitative behaviour of the brightness distributions of all detected molecules, in particular their relative locations with respect to the central star, is the same for all three stars, and consistent with those observed towards IRC +10216. Of the shell distributions, the cyanopolyynes peak at slightly smaller radii than the hydrocarbons, and CN and HNC show the most extended emission. The emitting regions for each species are the smallest for IRAS 07454–7112, consistent with this object having the lowest circumstellar density within our sample. We find that, within the uncertainties of the analysis, the three stars present similar abundances for most species, and also compared to IRC +10216. We find, tentatively, that SiO is more abundant in our three stars compared to IRC+10216, and that the hydrocarbons are under-abundant in IRAS 07454–7112 compared to the other stars and IRC +10216. Our estimated 12 C/ 13 C ratios match well the literature values for the three sources and our estimated silicon and sulphur isotopic ratios are very similar across the three stars and IRC +10216. Conclusions. The observed circumstellar chemistry appears very similar across our sample and compared to that of IRC +10216, both in terms of the relative location of the emitting regions and molecular abundances. This implies that, to a first approximation, the chemical models tailored to IRC +10216 are, at least, able to reproduce the observed chemistry in C-rich envelopes across roughly an order of magnitude in wind density.
Aims. Galactic chemical evolution (GCE) is important for understanding the composition of the present-day interstellar medium (ISM) and of our solar system. In this paper, we aim to track the GCE by ...using the 29Si/30Si ratios in evolved stars and tentatively relate this to presolar grain composition. Methods. We used the APEX telescope to detect thermal SiO isotopologue emission toward four oxygen-rich M-type stars. Together with the data retrieved from the Herschel science archive and from the literature, we were able to obtain the 29Si/30Si ratios for a total of 15 evolved stars inferred from their optically thin 29SiO and 30SiO emission. These stars cover a range of masses and ages, and because they do not significantly alter 29Si/30Si during their lifetimes, they provide excellent probes of the ISM metallicity (or 29Si/30Si ratio) as a function of time. Results. The 29Si/30Si ratios inferred from the thermal SiO emission tend to be lower toward low-mass oxygen-rich stars (e.g., down to about unity for W Hya), and close to an interstellar or solar value of 1.5 for the higher-mass carbon star IRC+10216 and two red supergiants. There is a tentative correlation between the 29Si/30Si ratios and the mass-loss rates of evolved stars, where we take the mass-loss rate as a proxy for the initial stellar mass or current stellar age. This is consistent with the different abundance ratios found in presolar grains. Before the formation of the Sun, the presolar grains indicate that the bulk of presolar grains already had 29Si/30Si ratios of about 1.5, which is also the ratio we found for the objects younger than the Sun, such as VY CMa and IRC+10216. However, we found that older objects (up to possibly 10 Gyr old) in our sample trace a previous, lower 29Si/30Si value of about 1. Material with this isotopic ratio is present in two subclasses of presolar grains, providing independent evidence of the lower ratio. Therefore, the 29Si/30Si ratio derived from the SiO emission of evolved stars is a useful diagnostic tool for the study of the GCE and presolar grains.
This study aims to assess exposure to e-cigarette advertising across multiple marketing channels among U.S. youth and to examine whether racial/ethnic disparities exist in exposure to e-cigarette ...advertisements.
This is a cross-sectional study.
Cross-sectional data were drawn from a longitudinal survey of participants recruited from two nationally representative panels (NORC's AmeriSpeak® and GfK's KnowledgePanel). A total of 2043 youth aged 13–17 completed the initial 2018 survey, and 2013 youth completed the follow-up survey in 2019 (including a replenishment sample of 690 youth). Outcome variables were self-reported e-cigarette advertisement exposure in the past three months through various sources, such as television, point of sale, and online/social media. Generalized estimating equation models were used to estimate the adjusted odds ratios (AOR) of the association between racial/ethnic identity and e-cigarette advertisement exposure.
The prevalence of reported exposure to e-cigarette advertisements through any channel was 79.8% (95% CI: 77.1–82.2) in 2018 and 74.9% (95% CI: 72.5–77.1) in 2019, respectively. Point of sale was the most common source of e-cigarette advertisement exposure in both years. Non-Hispanic Black and non-Hispanic Asian youth were more likely to report exposure to e-cigarette advertisements through television (AOR = 2.07, 95% CI: 1.44–2.99 and AOR = 2.11, 95% CI: 1.17–3.82, respectively) and online/social media (AOR = 1.61; 95% CI: 1.11–2.33 and AOR = 1.99, 95% CI: 1.10–3.59, respectively) channels compared with non-Hispanic White youth.
A substantial proportion of U.S. youth reported exposure to e-cigarette advertising through a variety of marketing channels. Significant racial/ethnic disparities existed, with non-Hispanic Black and Asian youth reporting more marketing exposure than their non-Hispanic White counterparts.
Context. What are the mechanisms by which massive stars form? What are the initial conditions for these processes? It is commonly assumed that cold and dense Infrared Dark Clouds (IRDCs) represent ...the birth-sites of massive stars. Therefore, these clouds have been receiving an increasing amount of attention, and their analysis offers the opportunity to tackle the afore mentioned questions. Aims. To enlarge the sample of well-characterised IRDCs in the southern hemisphere, where ALMA will play a major role in the near future, we have developed a program to study the gas and dust of southern infrared dark clouds. The present paper attempts to characterize the continuum properties of this sample of IRDCs. Methods. We cross-correlated 1.2 mm continuum data from SIMBA bolometer array mounted on SEST telescope with Spitzer/GLIMPSE images to establish the connection between emission sources at millimeter wavelengths and the IRDCs that we observe at 8 μm in absorption against the bright PAH background. Analysing the dust emission and extinction enables us to determine the masses and column densities, which are important quantities in characterizing the initial conditions of massive star formation. We also evaluated the limitations of the emission and extinction methods. Results. The morphology of the 1.2 mm continuum emission is in all cases in close agreement with the mid-infrared extinction. The total masses of the IRDCs were found to range from 150 to 1150 $M_\odot$ (emission data) and from 300 to 1750 $M_\odot$ (extinction data). We derived peak column densities of between 0.9 and $4.6 \times 10^{22}$ cm-2 (emission data) and 2.1 and $5.4 \times 10^{22}$ cm-2 (extinction data). We demonstrate that the extinction method is unreliable at very high extinction values (and column densities) beyond AV values of roughly 75 mag according to the Weingartner & Draine (2001) extinction relation $R_{\rm V} = 5.5$ model B (around 200 mag when following the common Mathis (1990, ApJ, 548, 296) extinction calibration). By taking the spatial resolution effects into account and restoring the column densities derived from the dust emission to a linear resolution of 0.01 pc, peak column densities of 3–$19 \times 10^{23}$ cm-2 are obtained, which are much higher than typical values for low-mass cores. Conclusions. Taking into account the spatial resolution effects, the derived column densities are beyond the column density threshold of $3.0 \times 10^{23}$ cm-2 required by theoretical considerations for massive star formation. We conclude that the values of column densities derived for the selected IRDC sample imply that these objects are excellent candidates for objects in the earliest stages of massive star formation.
ABSTRACT
Using APEX-1 and APEX-2 observations, we have detected and studied the rotational lines of the HC3N molecule (cyanoacetylene) in the powerful outflow/hot molecular core G331.512−0.103. We ...identified 31 rotational lines at J levels between 24 and 39; 17 of them in the ground vibrational state v = 0 (9 lines corresponding to the main C isotopologue and 8 lines corresponding to the 13C isotopologues), and 14 in the lowest vibrationally excited state v7 = 1. Using local thermodynamic equilibrium (LTE)-based population diagrams for the beam-diluted v = 0 transitions, we determined Texc = 85 ± 4 K and N(HC3N) = (6.9 ± 0.8) × 1014 cm−2, while for the beam-diluted v7 = 1 transitions we obtained Texc = 89 ± 10 K and N(HC3N) = (2 ± 1) × 1015 cm−2. Non-LTE calculations using H2 collision rates indicate that the HC3N emission is in good agreement with LTE-based results. From the non-LTE method, we estimated Tkin ≃90 K, n(H2) ≃ 2 × 107 cm−3 for a central core of 6 arcsec in size. A vibrational temperature in the range from 130 to 145 K was also determined, values which are very likely lower limits. Our results suggest that rotational transitions are thermalized, while infrared radiative pumping processes are probably more efficient than collisions in exciting the molecule to the vibrationally excited state v7 = 1. Abundance ratios derived under LTE conditions for the 13C isotopologues suggest that the main formation pathway of HC3N is C2H2 + CN → HC3N + H.
Context. Massive condensations in giant molecular clouds (GMCs) are linked to the formation of high mass stars, which are the principal source of heavy elements and UV radiation, playing an important ...role in the evolution of galaxies. Aims. We attemp to make a complete census of massive-star formation within all of GMC G345.5+1.0. This cloud is located one degree above the Galactic plane and at 1.8 kpc from the Sun, thus there is little superposition of dust along the line-of-sight, minimizing confusion effects in identifying individual clumps. Methods. We observed the 1.2 mm continuum emission across the whole GMC using the Swedish-ESO Submillimetre Telescope (SEST) Imaging Bolometer Array (SIMBA) mounted on the SEST. Observations have a spatial resolution of 0.2 pc and cover 1\hbox{$\fdg 8 \times 2 \fdg$}°̣8 × 2°̣2 in the sky with a noise of 20 mJy beam-1. Results. We identify 201 clumps with diameters between 0.2 and 0.6 pc, masses between 3.0 and 1.3 × 103 M⊙, and densities between 5 × 103 and 4 × 105 cm-3. The total mass of the clumps is 1.2 × 104 M⊙, thus the efficiency in forming these clumps, estimated as the ratio of the total clump mass to the total GMC mass, is ~0.02. The clump mass distribution for masses between 10 and 103 M⊙ is well-fitted by a power law dN/dM ∝ M − α, with a spectral mass index α of 1.7 ± 0.1. Given their mass distribution, clumps do not appear to be the direct progenitors of single stars. Comparing the 1.2 mm continuum emission with infrared images taken by the Midcourse Space Experiment (MSX) and by the Spitzer satellite, we find that at least ~20% of the clumps are forming stars, and at most ~80% are starless. Six massive-star forming regions (MSFRs) embedded in clumps and associated with IRAS point sources have mean densities of ~105 cm-3, luminosities >103 L⊙, and spectral energy distributions that can be modeled with two dust components at different mean temperatures of 28 ± 5 and 200 ± 10 K.
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