- 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/568/A56
- Title:
- mm continuum and line images of G0.253+0.016
- Short Name:
- J/A+A/568/A56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The massive infrared dark cloud G0.253+0.016 projected ~45pc from the Galactic centre contains ~10^5^M_{sun}_ of dense gas whilst being mostly devoid of observed star-formation tracers. Our goals are therefore to scrutinise the physical properties, dynamics and structure of this cloud with reference to its star-forming potential. We have carried out a concerted SMA and IRAM 30m study of this enigmatic cloud in dust continuum, CO isotopologues, several shock tracing molecules, as well as H_2_CO to trace the gas temperature. In addition, we include ancillary far-IR and sub-mm Herschel and SCUBA data in our analysis. We detect and characterise a total of 36 dust cores within G0.253+0.016 at 1.3mm and 1.37mm, with masses between 25 and approximately 250M_{sun}_, and find that the kinetic temperature of the gas traced by H_2_CO ratios is >320K on size-scales of ~0.15pc. Analysis of the position-velocity diagrams of our observed lines show broad linewidths and strong shock emission in the south of the cloud, indicating that G0.253+0.016 is colliding with another cloud at v_LSR_~70km/s. We confirm via an analysis of the observed dynamics in the Central Molecular Zone that it is an elongated structure, orientated with Sgr B2 closer to the Sun than Sgr A*, however our results suggest that the actual geometry may be more complex than an elliptical ring. We find that the column density Probability Distribution Function (PDF) of G0.253+0.016 derived from SMA and SCUBA dust continuum emission is log-normal with no discernible power-law tail, consistent with little star formation, and that its width can be explained in the framework of theory predicting the density structure of clouds created by supersonic, magnetised turbulence. We also present the Delta-variance spectrum of this region, a proxy for the density power spectrum of the cloud, and show it is consistent with that expected for clouds with no current star formation. Finally, we show that even after determining a scaled column density threshold for star formation by incorporating the effects of the increased turbulence in the cloud, we would still expect ten stars with masses >15M_{sun}_ to form in G0.253+0.016. If these cannot be accounted for by new radio continuum observations, then further physical aspects may be important, such as the background column density level, which would turn an absolute column density threshold for star formation into a critical over-density. We conclude that G0.253+0.016 contains high-temperatures and wide-spread shocks, displaying evidence of interaction with a nearby cloud which we identify at v_LSR_~70km/s. Our analysis of the structure of the cloud can be well-explained by theory of magnetised turbulence, and is consistent with little or no current star formation. Using G0.253+0.016 as a test-bed of the conditions required for star formation in a different physical environment to that of nearby clouds, we also conclude that there is not one column density threshold for star formation, but instead this value is dependant on the local physical conditions.
- 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/416/178
- Title:
- 1.2-mm dust clumps with luminous water masers
- Short Name:
- J/MNRAS/416/178
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a sensitive water maser search with the Australia Telescope Compact Array towards 267 1.2-mm dust clumps presented in the literature. We combine our new observations with previous water maser observations to extend our sample to 294 1.2-mm dust clumps, towards which we detect 165 distinct water maser sites towards 128 1.2-mm dust clumps. Within the fields of our observations, we additionally find four water masers with no apparent associated 1.2-mm dust continuum emission. Our overall detection rate of 44 per cent appears to vary as a function of Galactic longitude. We find that there is an excellent correspondence between the locations of the detected water masers with the peak of the target 1.2-mm dust clump sources. As expected from previous similar studies, the water masers are chiefly detected towards the bigger, brighter and more massive 1.2-mm dust clumps.
- 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/A+A/426/119
- Title:
- 1.2mm mapping of RCW 106 Giant Molecular Cloud
- Short Name:
- J/A+A/426/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have mapped the dust continuum emission from the molecular cloud covering a region of 28pcx94pc associated with the well-known H II region RCW 106 at 1.2mm using SIMBA on SEST. The observations, having an HPBW of 24" (0.4pc), reveal 95 clumps, of which about 50% have MSX associations and only 20% have IRAS associations. Owing to their higher sensitivity to colder dust and higher angular resolution the present observations identify new emission features and also show that most of the IRAS sources in this region consist of multiple dust emission peaks. The detected millimeter sources (MMS) include on one end the exotic MMS5 (associated with IRAS 16183-4958, one of the brightest infrared sources in our Galaxy) and the bright (and presumably cold) source MMS54, with no IRAS or MSX associations on the other end. Around 10% of the sources are associated with signposts of high mass star formation activity.
- 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/579/A101
- Title:
- 3mm molecular line survey of 8 AGN
- Short Name:
- J/A+A/579/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim for a better understanding of the imprints that the nuclear activity in galaxies leaves in the molecular gas. We used the IRAM 30m telescope to observe the frequency range ~[86-116]GHz towards the central regions of the star- burst galaxies M83, M82, and NGC253, the galaxies hosting an active galactic nucleus (AGN) M51, NGC1068, and NGC7469, and the ultra-luminous infrared galaxies (ULIRGs) Arp220 and Mrk231. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of 27 molecules and 10 isotopologues (or their upper limits in case of non-detections).
- ID:
- ivo://CDS.VizieR/J/A+A/613/A42
- Title:
- M-3.8+0.9 molecular cloud 3mm datacubes
- Short Name:
- J/A+A/613/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to reveal the morphology, chemical composition, kinematics and to establish the main processes prevalent in the gas at the footpoints of the giant molecular loops (GMLs) in the Galactic center region. Using the 22-m Mopra telescope, we mapped the M-3.8+0.9 molecular cloud, placed at the footpoints 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 1mm 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. Maps revealing the morphology and kinematics of the M-3.8+0.9 molecular cloud in different molecules are presented. We identify six main molecular complexes. We derive fractional abundances in 11 selected positions of the different molecules assuming local thermodynamical equilibrium. 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 species in the GMLs. This indicates that the gas is likely affected by moderate ~30km/s or even high velocity (50km/s) 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 footpoints.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A146
- Title:
- M33 molecular clouds and young stellar clusters
- Short Name:
- J/A+A/601/A146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the association between giant molecular clouds (GMCs) and young stellar cluster candidates (YSCCs) to shed light on the time evolution of local star formation episodes in the nearby galaxy M33. The CO (J=2-1) IRAM all-disk survey was used to identify and classify 566 GMCs with masses between 2x10^4^ and 2x10^6^M_{sun}_ across the whole star-forming disk of M33. In the same area, there are 630 YSCCs that we identified using Spitzer-24um data. Some YSCCs are embedded star-forming sites, while the majority have GALEX-UV and H{alpha} counterparts with estimated cluster masses and ages. The GMC classes correspond to different cloud evolutionary stages: inactive clouds are 32% of the total and classified clouds with embedded and exposed star formation are 16% and 52% of the total, respectively. Across the regular southern spiral arm, inactive clouds are preferentially located in the inner part of the arm, possibly suggesting a triggering of star formation as the cloud crosses the arm. The spatial correlation between YSCCs and GMCs is extremely strong, with a typical separation of 17pc. This is less than half the CO (2-1) beam size and illustrates the remarkable physical link between the two populations. GMCs and YSCCs follow the HI filaments, except in the outermost regions, where the survey finds fewer GMCs than YSCCs, which is most likely due to undetected clouds with low CO luminosity. The distribution of the non-embedded YSCC ages peaks around 5Myr, with only a few being as old as 8-10Myr. These age estimates together with the number of GMCs in the various evolutionary stages lead us to conclude that 14Myr is the typical lifetime of a GMC in M33 prior to cloud dispersal. The inactive and embedded phases are short, lasting about 4 and 2Myr, respectively. This underlines that embedded YSCCs rapidly break out from the clouds and become partially visible in H{alpha} or UV long before cloud dispersal.
