- ID:
- ivo://CDS.VizieR/J/A+A/602/A37
- Title:
- Millimeter RRL in ATLASGAL-selected massive clumps
- Short Name:
- J/A+A/602/A37
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of millimeter wavelength radio recombination lines (mm-RRLs) are used to search for HII regions in an unbiased way that is complementary to many of the more traditional methods previously used (e.g., radio continuum, far-infrared colors, maser emission). The mm-RRLs can be used to derive physical properties of HII regions and to provide velocity information of ionized gas. We carried out targeted mm-RRL observations (39<= principal quantum number (n) <=65 and {Delta}n = 1, 2, 3, and 4, named Hn{alpha}, Hn{beta}, Hn{gamma}, and Hn{delta}) using the IRAM 30m and Mopra 22m telescopes. In total, we observed 976 compact dust clumps selected from a catalog of ~10000 sources identified by the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL). The sample was selected to ensure a representative mix of star-forming and quiescent clumps such that a variety of different evolutionary stages is represented. Approximately half of the clumps are mid-infrared quiet while the other half are mid-infrared bright. We detected Hn{alpha} mm-RRL emission toward 178 clumps; Hn{beta}, Hn{gamma}, and Hn{delta} were also detected toward 65, 23, and 22 clumps, respectively. This is the largest sample of mm-RRLs detections published to date. Comparing the positions of these clumps with radio continuum surveys we identified compact radio counterparts for 134 clumps, confirming their association with known HII regions. The nature of the other 44 detections is unclear, but 8 detections are thought to be potentially new HII regions while the mm-RRL emission from the others may be due to contamination from nearby evolved HII regions. Broad linewidths are seen toward nine clumps (linewidth>40km/s) revealing significant turbulent motions within the ionized gas; in the past, such wide linewidths were found toward very compact and dense HII regions. We find that the systemic velocity of the associated dense molecular gas, traced by H^13^CO^+^(1-0), is consistent with the mm-RRL velocities and confirms them as embedded HII regions. We also find that the linewidth of the H^13^CO^+^(1-0) emission is significantly wider than those without mm-RRL detection, indicating a physical connection between the embedded H II region and their natal environments. We also find a correlation between the integrated fluxes of the mm-RRLs and the 6cm continuum flux densities of their radio counterparts (the correlation coefficient, {rho}, is 0.70). By calculating the electron densities we find that the mm-RRL emission is associated with HII regions with n_e_<10^5^cm^3^ and HII region diameter >0.03pc. We detected mm-RRLs toward 178 clumps and identified eight new HII region candidates. The broad mm-RRL from nine clumps may indicate that they arise in very young hyper-compact HII regions. The mm-RRLs trace the radio continuum sources detected by high-resolution observations and their line parameters show associations with the embedded radio sources and their parental molecular clumps.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/553/A115
- Title:
- Millimetric and far-IR maps of IRDC 18310-4
- Short Name:
- J/A+A/553/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of their short evolutionary time-scales, the earliest stages of high-mass star formation prior to the existence of any embedded heating source have barely been characterized until today. We study the fragmentation and dynamical properties of a massive starless gas clump at the onset of high-mass star formation. Based on Herschel continuum data we identify a massive gas clump that remains far-infrared dark up to 100um wavelengths. The fragmentation and dynamical properties are investigated by means of Plateau de Bure Interferometer and Nobeyama 45m single-dish spectral line and continuum observations.
- ID:
- ivo://CDS.VizieR/J/ApJ/641/389
- Title:
- Millimetric observations of IRDC cores
- Short Name:
- J/ApJ/641/389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Infrared dark clouds (IRDCs) are dense molecular clouds seen as extinction features against the bright mid-infrared Galactic background. Millimeter continuum maps toward 38 IRDCs reveal extended cold dust emission to be associated with each of the IRDCs. IRDCs range in morphology from filamentary to compact and have masses of 120 to 16000M_{sun}_, with a median mass of 940M_{sun}_. Each IRDC contains at least one compact (0.5pc) dust core and most show multiple cores. We find 140 cold millimeter cores unassociated with MSX 8{mu}m emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/734/51
- Title:
- Mineralogical compositions of dust grains
- Short Name:
- J/ApJ/734/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mineralogical studies of silicate features emitted by dust grains in protoplanetary disks and solar system bodies can shed light on the progress of planet formation. The significant fraction of crystalline material in comets, chondritic meteorites, and interplanetary dust particles indicates a modification of the almost completely amorphous interstellar medium dust from which they formed. The production of crystalline silicates, thus, must happen in protoplanetary disks, where dust evolves to build planets and planetesimals. Different scenarios have been proposed, but it is still unclear how and when this happens. This paper presents dust grain mineralogy (composition, crystallinity, and grain size distribution) of a complete sample of protoplanetary disks in the young Serpens cluster. These results are compared to those in the young Taurus region and to sources that have retained their protoplanetary disks in the older Upper Scorpius and {eta} Chamaeleontis stellar clusters, using the same analysis technique for all samples. This comparison allows an investigation of the grain mineralogy evolution with time for a total sample of 139 disks. The mean cluster age and disk fraction are used as indicators of the evolutionary stage of the different populations. Our results show that the disks in the different regions have similar distributions of mean grain sizes and crystallinity fractions (~10%-20%) despite the spread in mean ages. Furthermore, there is no evidence of preferential grain sizes for any given disk geometry nor for the mean cluster crystallinity fraction to increase with mean age in the 1-8Myr range. The main implication is that a modest level of crystallinity is established in the disk surface early on (<=1Myr), reaching an equilibrium that is independent of what may be happening in the disk midplane. These results are discussed in the context of planet formation, in comparison with mineralogical results from small bodies in our own solar system.
- ID:
- ivo://CDS.VizieR/J/ApJ/676/427
- Title:
- MIPS and IRAC data on ChaII PMS stars
- Short Name:
- J/ApJ/676/427
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and NIR data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population in an area of ~1.75deg^2^ and study the spatial distribution and properties of the cloud members and candidate pre-main-sequence (PMS) objects and their circumstellar matter. Our census is complete down to the substellar regime (M~0.03M_{sun}).
- ID:
- ivo://CDS.VizieR/J/ApJ/671/470
- Title:
- MIPS survey of YSOs in Vela Molecular Ridge-D
- Short Name:
- J/ApJ/671/470
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new, unbiased Spitzer MIPS imaging survey (~1.8deg^2^) of the young stellar content of the Vela Molecular Ridge-D (VMR-D) is presented. The survey is complete down to 5 and 250mJy at 24 and 70{mu}m, respectively. A total of 849 sources are detected at 24{mu}m, and 52 of them also have a 70{mu}m counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the millimeter contours. About half of the 24{mu}m sources are located inside the region delimited by the ^12^CO(1-0) contours, corresponding to only one-third of the full area mapped with MIPS. Therefore, the 24{mu}m source density increases by about 100% moving from outside to inside the CO contours. For the 70{mu}m sources, the corresponding density increase is a factor of 4. About 400 sources of these have a 2MASS counterpart, and we have used this to construct a Ks versus Ks-[24] diagram and to identify the protostellar population inside the cloud.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/231
- Title:
- MISFITS survey: HCO+ obs. of Spitzer YSOs
- Short Name:
- J/ApJ/806/231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an HCO^+^ J=3->2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO^+^ J=3->2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I + Flat SED sample). Using the criteria from van Kempen et al. (2009, J/A+A/498/167), we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54Myr. We find significant correlations of HCO^+^ integrated intensity with {alpha} and T_bol_ but not with L_bol_. The detection fraction increases smoothly as a function of {alpha} and L_bol_, while decreasing smoothly with T_bol_. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with A_V_>8mag. Class 0+I and Flat SED YSOs that are not detected in HCO^+^ have, on average, a factor of ~2 higher T_bol_ and a factor of ~5 lower L_bol_than YSOs with HCO^+^ detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with T_bol_<~600K and L_bol_>~1L_{sun}_. The contamination percentage is >90% at A_V_<4mag and decreases as A_V_ increases.
- 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.
- 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.
