- ID:
- ivo://CDS.VizieR/J/A+A/633/A118
- Title:
- 3mm-band study of L183 and L1544
- Short Name:
- J/A+A/633/A118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pre-stellar cores (PSCs) are units of star formation. Besides representing early stages of the dynamical evolution leading to the formation of stars and planets, PSCs also provide a substrate for incipient chemical complexity in the interstellar space. Our aim is to understand the influence of external conditions on the chemical composition of PSCs. For this purpose, we compared molecular column densities in two typical PSCs, L183 and L1544, which are embedded in different environments. A single-pointing survey of L183 at {lambda}=3mm was conducted using the IRAM 30-m single-dish antenna. This led to the detection of more than 100 emission lines from 46 molecular species. The molecular column densities and excitation temperatures derived from these lines were compared to the corresponding parameters in L1544. The data for L1544 were obtained from literature or publicly available surveys, and they were analysed using the same procedure as adopted for L183. An astrochemical model, previously developed for the interpretation of organic molecule emissions towards the methanol peak of L1544, was used to interpret the combined data. Our analysis reveals clear chemical differences between the two PSCs. While L1544 is richer in carbon-bearing species, in particular carbon chains, oxygen-containing species are generally more abundant in L183. The results are well-reproduced by our chemical model. The observed chemical differentiation between the two PSCs is caused by the different environmental conditions: the core of L183 is deeply buried in the surrounding cloud, whereas L1544 lies close to the edge of the Taurus Molecular Cloud. The obscuration of L183 from the interstellar radiation field (ISRF) allows the carbon atoms to be locked in carbon monoxide, which ultimately leads to a large abundance of O-bearing species. In contrast, L1544, being more affected by the ISRF, can keep a fraction of carbon in atomic form, which is needed for the production of carbon chains.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/447/609
- Title:
- 1.2mm continuum observations in rho Oph cloud
- Short Name:
- J/A+A/447/609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a wide field survey for dust sources at 1.2-millimetres in the rho Ophiuchi molecular cloud, covering more than 1 square degree in an unbiased fashion. We detect a number of previously unknown sources, ranging from extended cores over compact, starless cores to envelopes surrounding young stellar objects of Class 0, Class I, and Class II type. We analyse the mass distribution, spatial distribution and the potential equilibrium of the cores.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/2222
- Title:
- 1.1mm dust continuum emission along Gal. plane
- Short Name:
- J/MNRAS/473/2222
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Sensitive, imaging observations of the {lambda}1.1mm dust continuum emission from a 1deg^2^ area collected with the AzTEC bolometer camera on the Large Millimeter Telescope are presented. A catalogue of 1545 compact sources is constructed based on a Wiener-optimization filter. These sources are linked to larger clump structures identified in the Bolocam Galactic Plane Survey. Hydrogen column densities are calculated for all sources and mass and mean volume densities are derived for the subset of sources for which kinematic distances can be assigned. The AzTEC sources are localized, high-density peaks within the massive clumps of molecular clouds and comprise 5-15 per cent of the clump mass. We examine the role of the gravitational instability in generating these fragments by comparing the mass of embedded AzTEC sources to the Jeans mass of the parent BGPS object. For sources with distances less than 6kpc the fragment masses are comparable to the clump Jeans mass, despite having isothermal Mach numbers between 1.6 and 7.2. AzTEC sources linked to ultra compact HII regions have mass surface densities greater than the critical value implied by the mass-size relationship of infrared dark clouds with high-mass star formation, while AzTEC sources associated with Class II methanol masers have mass surface densities greater than 0.7gcm^-2^ that approaches the proposed threshold required to form massive stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/411/1367
- Title:
- 12mm line survey towards W28 SNR
- Short Name:
- J/MNRAS/411/1367
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 12mm Mopra observations of dense molecular gas towards the W28 supernova remnant (SNR) field. The focus is on the dense molecular gas towards the TeV gamma-ray sources detected by the HESS telescopes, which likely trace the cosmic rays from W28 and possibly other sources in the region. Using the NH_3_ inversion transitions we reveal several dense cores inside the molecular clouds,
- ID:
- ivo://CDS.VizieR/J/A+A/499/149
- Title:
- 1.2mm maps of southern Infrared Dark Clouds
- Short Name:
- J/A+A/499/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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) likely represent the birth sites massive stars. Therefore, this class of objects gets increasing attention, and their analysis offers the opportunity to tackle the above mentioned questions. 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 set up a program to study the gas and dust of southern infrared dark clouds. The present paper aims at characterizing the continuum properties of this sample of IRDCs. We cross-correlated 1.2 mm continuum data from SIMBA@SEST with Spitzer/GLIMPSE images to establish the connection between emission sources at millimeter wavelengths a nd the IRDCs we see at 8{mu}m in absorption against the bright PAH background. Analysing the dust emission and extinction leads to a determination of 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. The morphology of the 1.2mm 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 1150M_{sun}_ (emission data) and from 300 to 1750M_{sun}_ (extinction data). We derived peak column densities between 0.9 and 4.6x10^22^cm^-2^ (emission data) and 2.1 and 5.4x10^22^cm^-2^ (extinction data). We demonstrate that the extinction method fails for very high extinction values (and column densities) beyond A_V_ values of roughly 75mag according to the Weingartner & Draine (2001ApJ...548..296W) extinction relation R_V_=5.5 model B (around 200mag when following the common Mathis (1990ARA&A..28...37M) extinction calibration). By taking the spatial resolution effects into account and restoring the column densities derived from the dust emission back to a linear resolution of 0.01pc, peak column densities of 3.0x10^23^cm^-2^ are obtained, much higher than typic al values for low-mass cores. The derived column densities, taking into account the spatial resolution effects, are beyond the column density threshold of 3.0x10^23^cm^-2^ required by theoretical considerations for massive star formation. We conclude that the values for column densities derived for the selected IRDC sample make these objects excellent candidates for objects in the earliest stages of massive star formation.
- ID:
- ivo://CDS.VizieR/J/A+A/564/A51
- Title:
- 3mm maps of 4 transition disks
- Short Name:
- J/A+A/564/A51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transition disks are protoplanetary disks with inner depleted dust cavities and excellent candidates to investigate the dust evolution under the existence of a pressure bump. A pressure bump at the outer edge of the cavity allows dust grains from the outer regions to stop their rapid inward migration towards the star and efficiently grow to millimetre sizes. Dynamical interactions with planet(s) have been one of the most exciting theories to explain the clearing of the inner disk. We look for evidence of the presence of millimetre dust particles in transition disks by measuring their spectral index {alpha}_mm_ with new and available photometric data. We investigate the influence of the size of the dust depleted cavity on the disk integrated millimetre spectral index. We present the 3-millimetre (100GHz) photometric observations carried out with Plateau de Bure Interferometer of four transition disks: LkH{alpha} 330, UX Tau A, LRLL 31, and LRLL 67. We use available values of their fluxes at 345GHz to calculate their spectral index, as well as the spectral index for a sample of twenty transition disks. We compare the observations with two kind of models. In the first set of models, we consider coagulation and fragmentation of dust in a disk in which a cavity is formed by a massive planet located at different positions. The second set of models assumes disks with truncated inner parts at different radius and with power-law dust size distributions, where the maximum size of grains is calculated considering turbulence as the source of destructive collisions. We show that the integrated spectral index is higher for transition disks (TD) than for regular protoplanetary disks (PD) with mean values of <{alpha}_mm_^TD^>=2.70+/-0.13 and <{alpha}_mm_^PD^>=2.20+/-0.07 respectively. For transition disks, the probability that the measured spectral index is positively correlated with the cavity radius is 95%. High angular resolution imaging of transition disks is needed to distinguish between the dust trapping scenario and the truncated disk case.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/171
- Title:
- mm point sources in the extended Sgr B2 cloud
- Short Name:
- J/ApJ/853/171
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report ALMA observations with resolution ~0.5" at 3mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000au. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact HII regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses M*>~8M_{sun}_. Their spatial distribution spread over a ~12x3pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated "starburst" within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density (N(H_2_)>~2x10^23^cm^-2^), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear {Sigma}_*_-{Sigma}_gas_ relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.
- ID:
- ivo://CDS.VizieR/J/ApJS/213/13
- Title:
- 1.3mm polarization maps of star-forming cores & SFRs
- Short Name:
- J/ApJS/213/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {lambda}1.3mm Combined Array for Research in Millimeter-wave Astronomy observations of dust polarization toward 30 star-forming cores and eight star-forming regions from the TADPOL survey. We show maps of all sources, and compare the ~2.5" resolution TADPOL maps with ~20" resolution polarization maps from single-dish submillimeter telescopes. Here we do not attempt to interpret the detailed B-field morphology of each object. Rather, we use average B-field orientations to derive conclusions in a statistical sense from the ensemble of sources, bearing in mind that these average orientations can be quite uncertain. We discuss three main findings. (1) A subset of the sources have consistent magnetic field (B-field) orientations between large (~20") and small (~2.5") scales. Those same sources also tend to have higher fractional polarizations than the sources with inconsistent large-to-small-scale fields. We interpret this to mean that in at least some cases B-fields play a role in regulating the infall of material all the way down to the ~1000AU scales of protostellar envelopes. (2) Outflows appear to be randomly aligned with B-fields; although, in sources with low polarization fractions there is a hint that outflows are preferentially perpendicular to small-scale B-fields, which suggests that in these sources the fields have been wrapped up by envelope rotation. (3) Finally, even at ~2.5" resolution we see the so-called polarization hole effect, where the fractional polarization drops significantly near the total intensity peak.
- ID:
- ivo://CDS.VizieR/J/ApJ/638/293
- Title:
- 1.1mm sources in the Perseus Molecular Cloud
- Short Name:
- J/ApJ/638/293
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have completed a 1.1mm continuum survey of 7.5{deg}^2^ of the Perseus Molecular Cloud using Bolocam at the Caltech Submillimeter Observatory. This represents the largest millimeter or submillimeter continuum map of Perseus to date. Our map covers more than 30,000 31" (FWHM) resolution elements to a 1{sigma} rms of 15mJy/beam. We detect a total of 122 cores above a 5{sigma} point-source mass detection limit of 0.18M_{sun}_, assuming a dust temperature of T_D_=10K, 60 of which are new millimeter or submillimeter detections.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/L36
- Title:
- mm-wave size study of ALMA submm galaxies
- Short Name:
- J/ApJ/849/L36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined using mid-IR photometry. We determined the millimeter-wave ({lambda}_obs_=1100um) sizes of 69 Atacama Large Millimeter/submillimeter Array (ALMA)-identified SMGs, selected with >=10{sigma} confidence on ALMA images (F_1100um_=1.7-7.4mJy). We found that all of the SMGs are located above an avoidance region in the size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at z=1-3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median R_c,e_=1.6_-0.21_^+0.34^ and 1.5_-0.24_^+0.93^kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median R_c,e_=1.0_-0.20_^+0.20^kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase.
