- ID:
- ivo://CDS.VizieR/J/A+A/619/A166
- Title:
- SEDIGISM, kinematics of ATLASGAL filaments
- Short Name:
- J/A+A/619/A166
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Analyzing the kinematics of filamentary molecular clouds is a crucial step toward 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 analyze the kinematics of these targets and to determine their physical properties at a resolution of 30-arcsec and 0.25km/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{prop.to}{sigma}_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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- ID:
- ivo://CDS.VizieR/J/A+A/551/A34
- Title:
- SED information for CrA members
- Short Name:
- J/A+A/551/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CrA region and the Coronet cluster form a nearby (138pc), young (1-2Myr) star-forming region that hosts a moderate population of Class I, II, and III objects. We study the structure of the cluster and the properties of the protostars and protoplanetary disks in the region. We present Herschel PACS photometry at 100 and 160um, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members within the cloud with high sensitivity and high dynamic range.
- ID:
- ivo://CDS.VizieR/J/ApJS/220/11
- Title:
- SEDs of Spitzer YSOs in the Gould Belt
- Short Name:
- J/ApJS/220/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78Myr for Class 0+I YSOs and 0.26-0.50Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13-0.26Myr (Class 0) and 0.27-0.52Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A36
- Title:
- Self-absorption in RCW 120
- Short Name:
- J/A+A/659/A36
- Date:
- 02 Mar 2022 07:09:25
- Publisher:
- CDS
- Description:
- Revealing the 3D dynamics of HII region bubbles and their associated molecular clouds and HI envelopes is important for developing an understanding of the longstanding problem as to how stellar feedback affects the density structure and kinematics of the different phases of the interstellar medium. We employed observations of the HII region RCW 120 in the [CII] 158um line, observed within the Stratospheric Observatory for Infrared Astronomy (SOFIA) legacy program FEEDBACK, and in the ^12^CO and ^13^CO (3-2) lines, obtained with the Atacama Pathfinder Experiment (APEX) to derive the physical properties of the gas in the photodissociation region (PDR) and in the molecular cloud. We used high angular resolution HI data from the Southern Galactic Plane Survey to quantify the physical properties of the cold atomic gas through HI self-absorption. The high spectral resolution of the heterodyne observations turns out to be essential in order to analyze the physical conditions, geometry, and overall structure of the sources. Two types of radiative transfer models were used to fit the observed [CII] and CO spectra. A line profile analysis with the 1D non-LTE radiative transfer code SimLine proves that the CO emission cannot stem from a spherically symmetric molecular cloud configuration. With a two-layer multicomponent model, we then quantified the amount of warm background and cold foreground gas. To fully exploit the spectral-spatial information in the CO spectra, a Gaussian mixture model was introduced that allows for grouping spectra into clusters with similar properties. The CO emission arises mostly from a limb-brightened, warm molecular ring, or more specifically a torus when extrapolated in 3D. There is a deficit of CO emission along the line-of-sight toward the center of the HII region which indicates that the HII region is associated with a flattened molecular cloud. Self-absorption in the CO line may hide signatures of infalling and expanding molecular gas. The [CII] emission arises from an expanding [CII] bubble and from the PDRs in the ring/torus. A significant part of [CII] emission is absorbed in a cool (~60-100K), low-density (<500cm^-3^) atomic foreground layer with a thickness of a few parsec. We propose that the RCW 120 HII region formed in a flattened, filamentary, or sheet-like, molecular cloud and is now bursting out of its parental cloud. The compressed surrounding molecular layer formed a torus around the spherically expanding HII bubble. This scenario can possibly be generalized for other HII bubbles and would explain the observed "flat" structure of molecular clouds associated with HII bubbles. We suggest that the [CII] absorption observed in many star-forming regions is at least partly caused by low-density, cool, HI-envelopes surrounding the molecular clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/517/A21
- Title:
- Sensitivity analysis list of chemical reactions
- Short Name:
- J/A+A/517/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Because of new telescopes that will dramatically improve our knowledge of the interstellar medium, chemical models will have to be used to simulate the chemistry of many regions with diverse properties. To make these models more robust, it is important to understand their sensitivity to a variety of parameters. In this article, we report a study of the sensitivity of a chemical model of a cold dense core, with homogeneous and time-independent physical conditions, to variations in the following parameters: initial chemical inventory, gas temperature and density, cosmic-ray ionization rate, chemical reaction rate coefficients, and elemental abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A62
- Title:
- Serpens filament emission lines datacubes
- Short Name:
- J/A+A/620/A62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Serpens filament, as one of the nearest infrared dark clouds, is regarded as a pristine filament at a very early evolutionary stage of star formation. In order to study its molecular content and dynamical state, we mapped this filament in seven species including C^18^O, HCO^+^, HNC, HCN, N_2_H^+^, CS, and CH_3_OH. Among them, HCO^+^, HNC, HCN, and CS show self-absorption, while C^18^O is most sensitive to the filamentary structure. A kinematic analysis demonstrates that this filament forms a velocity-coherent (trans-)sonic structure, a large part of which is one of the most quiescent regions in the Serpens cloud. Widespread C^18^O depletion is found throughout the Serpens filament. Based on the Herschel dust-derived H_2_ column density map, the line mass of the filament is 36-41~M_{sun}_/pc, and its full width at half maximum width is 0.17+/-0.01pc, while its length is ~1.6pc. The inner radial column density profile of this filament can be well fitted with a Plummer profile with an exponent of 2.2+/-0.1, a scale radius of 0.018+/-0.003pc and a central density of (4.0+/-0.8)x10^4^cm^-3^. The Serpens filament appears to be slightly supercritical. The widespread blue-skewed HNC and CS line profiles and HCN hyperfine line anomalies across this filament indicate radial infall in parts of the Serpens filament. C^18^O velocity gradients also indicate accretion flows along the filament. The velocity and density structures suggest that such accretion flows are likely due to a longitudinal collapse parallel to the filament's long axis. Both the radial infall rate and the longitudinal accretion rate along the Serpens filament are lower than all previously reported values in other filaments. This indicates that the Serpens filament lies at an early evolutionary stage when collapse has just begun, or that thermal and non-thermal support are effective in providing support against gravity.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A6
- Title:
- SgrB2 ALMA continuum and spectral index
- Short Name:
- J/A+A/604/A6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The two hot molecular cores SgrB2(M) and SgrB2(N), which are located at the center of the giant molecular cloud complex Sagittarius B2, have been the targets of numerous spectral line surveys, revealing a rich and complex chemistry. We seek to characterize the physical and chemical structure of the two high-mass star-forming sites SgrB2(M) and SgrB2(N) using high-angular resolution observations at millimeter wavelengths, reaching spatial scales of about 4000au. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to perform an unbiased spectral line survey of both regions in the ALMA band 6 with a frequency coverage from 211GHz to 275GHz. The achieved angular resolution is 0.4-arcsec, which probes spatial scales of about 4000au, i.e., able to resolve different cores and fragments. In order to determine the continuum emission in these line-rich sources, we used a new statistical method, STATCONT, which has been applied successfully to this and other ALMA datasets and to synthetic observations. We detect 27 continuum sources in SgrB2(M) and 20 sources in SgrB2(N). We study the continuum emission variation across the ALMA band 6 (i.e., spectral index) and compare the ALMA 1.3mm continuum emission with previous SMA 345GHz and VLA 40GHz observations to study the nature of the sources detected. The brightest sources are dominated by (partially optically thick) dust emission, while there is an important degree of contamination from ionized gas free-free emission in weaker sources. While the total mass in SgrB2(M) is distributed in many fragments, most of the mass in SgrB2(N) arises from a single object, with filamentary-like structures converging toward the center. There seems to be a lack of low-mass dense cores in both regions. We determine H2 volume densities for the cores of about 10^7^-10^9^cm^-3^ (or 10^5^-10^7^M_{sun}_/pc^3^), i.e., one to two orders of magnitude higher than the stellar densities of super star clusters. We perform a statistical study of the chemical content of the identified sources. In general, SgrB2(N) is chemically richer than SgrB2(M). The chemically richest sources have about 100 lines per GHz and the fraction of luminosity contained in spectral lines at millimeter wavelengths with respect to the total luminosity is about 20%-40%. There seems to be a correlation between the chemical richness and the mass of the fragments, where more massive clumps are more chemically rich. Both SgrB2(N) and SgrB2(M) harbor a cluster of hot molecular cores. We compare the continuum images with predictions from a detailed 3D radiative transfer model that reproduces the structure of SgrB2 from 45pc down to 100au. This ALMA dataset, together with other ongoing observational projects in the range 5GHz to 200GHz, better constrain the 3D structure of SgrB2 and allow us to understand its physical and chemical structure.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A32
- Title:
- Sgr B2 Herschel/SPIRE-FTS and IRAM 30m maps
- Short Name:
- J/A+A/649/A32
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present 168 arcmin^2^ spectral images of the Sgr B2 complex taken with Herschel/SPIRE-FTS. We detect ubiquitous emission from CO (up to J=12-11), H2O 2_1,1_-2_0,2_, [CI]492, 809GHz, and [NII] 205um lines. We also present maps of the SiO, N_2_H^+^, HCN, and HCO^+^ emission obtained with the IRAM30m telescope. The cloud environment dominates the emitted FIR (80%), H_2_O 752GHz (60%) mid-J CO (91%), and [CI] (93%) luminosity. The region shows very extended [NII] emission (spatially correlated with the 24 and 70um dust emission). The observed FIR luminosities imply G_0_~10^3^. The extended [CI] emission arises from a pervasive component of neutral gas with n_H_~10^3cm^-3^. The high ionization rates, produced by enhanced cosmic-ray (CR) fluxes, drive the gas heating to T_k_~40-60K. The mid-J CO emission arises from a similarly extended but more pressurized gas component (P_th_/k~10^7^K/cm^3^). Specific regions of enhanced SiO emission and high CO-to-FIR intensity ratios (>10^-3^) show mid-J CO emission compatible with shock models. A major difference compared to more quiescent star-forming clouds in the disk of our Galaxy is the extended nature of the SiO and N_2_H^+^ emission in Sgr B2. This can be explained by the presence of cloud-scale shocks, induced by cloud-cloud collisions and stellar feedback, and the much higher CR ionization rate (>10^-15^s^-1^) leading to overabundant H_3_^+^ and N_2_H^+^. Hence, Sgr B2 hosts a more extreme environment than star-forming regions in the disk of the Galaxy. As a usual template for extra- galactic comparisons, Sgr B2 shows more similarities to ultra luminous infrared galaxies such as Arp 220, including a "deficit" in the [CI]/FIR and [NII]/FIR intensity ratios, than to pure starburst galaxies such as M82. However, it is the extended cloud environment, rather than the cores, that serves as a useful template when telescopes do not resolve such extended regions in galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A10
- Title:
- Sgr B2 los molecular absorption line spectra
- Short Name:
- J/A+A/610/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The 1-50 GHz PRebiotic Interstellar MOlecular Survey (PRIMOS) contains >50 molecular absorption lines observed in clouds located in the line-of-sight to Sgr B2(N). The line-of- sight material is associated with diffuse and translucent clouds located in the Galactic Center, Bar, and spiral arms in the disk. We measure the column densities and estimate abundances, relative to H_2_, of 11 molecules and additional isotopologues observed in this material. We use absorption by optically thin transitions of c-C_3_H_2_ to estimate the molecular hydrogen columns, and argue that this method is preferable to more commonly used methods. We discuss the kinematic structure and abundance patterns of small molecules including the sulfur-bearing species CS, SO, CCS, H_2_CS, and HCS+; oxygen-bearing molecules OH, SiO, and H_2_CO; and simple hydrocarbon molecules c-C_3_H_2_, l-C_3_H, and l-C_3_H^+^. Finally, we discuss the implications of the observed chemistry for the structure of the gas and dust in the ISM. Highlighted results include the following. First, whereas gas in the disk has a molecular hydrogen fraction of 0.65, clouds on the outer edge of the Galactic Bar and in or near the Galactic Center have molecular fractions of 0.85 and >0.9, respectively. Second, we observe trends in isotope ratios with Galactocentric distance; while carbon and silicon show enhancement of the rare isotopes at low Galactocentric distances, sulfur exhibits no trend with Galactocentric distance. We also determine that the ratio of c-C_3_H_2_/c-H^13^CCCH provides a good estimate of the ^12^C/^13^C ratio, whereas H_2_CO/H_2_(^13^C)O exhibits fractionation. Third, we report the presence of l-C_3_H^+^ in diffuse clouds for the first time. Finally, we suggest that CS has an enhanced abundance within higher density clumps of material in the disk, and therefore may be diagnostic of cloud conditions. If this holds, the diffuse clouds in the Galactic disk contain multiple embedded hyperdensities in a clumpy structure, and the density profile is not a simple function of A_V_.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A80
- Title:
- Signatures of an incipient hot corino in B1b-S
- Short Name:
- J/A+A/620/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Barnard 1b core shows signatures of being at the earliest stages of low- mass star formation, with two extremely young and deeply embedded proto- stellar objects. Hence, this core is an ideal target to study the structure and chemistry of the first objects formed in the collapse of prestellar cores. We present ALMA Band 6 spectral line observations at ~0.6" of angular resolution towards Barnard 1b. We have extracted the spectra towards both protostars, and used a local thermodynamic equilibrium (LTE) model to reproduce the observed line profiles. B1b-S shows rich and complex spectra, with emission from high energy transitions of complex molecules, such as CH_3_OCOH and CH_3_CHO, including vibrational level transitions. We have tentatively detected for the first time in this source emission from NH_2_CN, NH_2_CHO, CH_3_CH_2_OH, CH_2_OHCHO, CH_3_CH_2_OCOH and both aGg' and gGg' conformers of (CH_2_OH)_2_. This is the first detection of ethyl formate (CH_3_CH_2_OCOH) towards a low-mass star forming region. On the other hand, the spectra of the FHSC candidate B1b-N are free of COMs emission. In order to fit the observed line profiles in B1b-S, we used a source model with two components: an inner hot and compact component (200K, 0.35") and an outer and colder one (60K, 0.6"). The resulting COM abundances in B1b-S range from 10^-13^ for NH_2_CN and NH_2_CHO, up to 10^-9^ for CH_3_OCOH. Our ALMA Band 6 observations reveal the presence of a compact and hot component in B1b-S, with moderate abundances of complex organics. These results indicate that a hot corino is being formed in this very young Class 0 source.
