- ID:
- ivo://CDS.VizieR/J/ApJ/897/74
- Title:
- Cold & molecular clumps and YSOs within G15.684-0.29
- Short Name:
- J/ApJ/897/74
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- The bubble G15.684-0.29 has a radius of 15.7pc. Its large size indicates that it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from the HI-GAL survey. All of them satisfy the criteria for forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from the 12CO(3-2) survey, all of which are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs, and 12 transition disks (TDs) around the bubble. For those young stellar objects (YSOs) located within the bubble boundary, 6 of 7 Class I YSOs lie in the shell, 15 of 22 Class II YSOs lie inside the bubble, and 3 of 5 TDs lie inside the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is ~4Myr, which is much greater than the shell fragmentation time, ~0.82-1.74Myr. We suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect and collapse model may work here. However, we cannot rule out the possibility that the radiation-driven implosion model may work on the formation of some YSOs. As we expected, the larger bubble has a much longer dynamical age, but we failed to find a clear age gradient for YSOs around the bubble.
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Search Results
- ID:
- ivo://CDS.VizieR/VI/51
- Title:
- Collisional Excitation Rates of Formaldehyde
- Short Name:
- VI/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Earlier calculations for rotational excitation of formaldehyde H2CO collisions with He atoms are extended to include the 81 lowest rotational levels and kinetic temperatures to 300K.
- ID:
- ivo://CDS.VizieR/J/ApJ/702/1472
- Title:
- Column densities for HI, AlIII, SiIV, CIV, OVI
- Short Name:
- J/ApJ/702/1472
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Column densities for HI, AlIII, SiIV, CIV, and OVI toward 109 stars and 30 extragalactic objects have been assembled to study the extensions of these species away from the Galactic plane into the Galactic halo. HI and AlIII mostly trace the warm neutral and warm ionized medium, respectively, while SiIV, CIV, and OVI trace a combination of warm photoionized and collisionally ionized plasmas. The much larger object sample compared to previous studies allows us to consider and correct for the effects of the sample bias that has affected earlier but smaller surveys of the gas distributions. The observations are compared to the predictions of the various models for the production of the transition temperature gas in the halo.
- ID:
- ivo://CDS.VizieR/J/A+A/510/A98
- Title:
- ^12^C^18^O(3-2) map of rho Oph A
- Short Name:
- J/A+A/510/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The large submillimetre map of rho Oph A in the ^12^C^18^O(3-2) line, obtained with the APEX 12m telescope, covers 10' in RA by 5' in DE, sampled on a rectangular grid, aligned with the equatorial coordinate system and with regular 20" spacings (548 spectra). An inner ^12^C^18^O(3-2) map, extending over 200" by 200" (462 spectra) is sampled at the Nyqvist frequency.
- ID:
- ivo://CDS.VizieR/J/A+A/489/217
- Title:
- CO maps of diffuse Galactic gas towards NRAO 150
- Short Name:
- J/A+A/489/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the environment and extended structure of the host galactic gas whose molecular absorption line chemistry, we previously observed along the microscopic line of sight to the blazar/radio-continuum source NRAO 150 (aka B0355+508). We used the IRAM 30m Telescope and Plateau de Bure Interferometer to make two series of images of the host gas: i) 22.5" resolution single-dish maps of ^12^CO J=1-0 and 2-1 emission over a 220" by 220" field; ii) a hybrid (interferometer+singledish) aperture synthesis mosaic of ^12^CO J=1-0 emission at 5.8" resolution over a 90"-diameter region. At 22.5" resolution, the CO J=1-0 emission toward NRAO 150 is 30-100% brighter at some velocities than seen previously with 1' resolution, and there are some modest systematic velocity gradients over the 220" field. Of the five CO components seen in the absorption spectra, the weakest ones are absent in emission toward NRAO 150 but appear more strongly at the edges of the region mapped in emission. The overall spatial variations in the strongly emitting gas have Poisson statistics with rms fluctuations about equal to the mean emission level in the line wings and much of the line cores. The J=2-1/J=1-0 line ratios calculated pixel-by-pixel cluster around 0.7. At 6" resolution, disparity between the absorption and emission profiles of the stronger components has been largely ameliorated. The ^12^CO J=1-0 emission exhibits i) remarkably bright peaks, Tmb=12-13K, even as 4" from NRAO 150; ii) smaller relative levels of spatial fluctuation in the line cores, but a very broad range of possible intensities at every velocity; and iii) striking kinematics whereby the monotonic velocity shifts and supersonically broadened lines in 22.5" spectra are decomposed into much stronger velocity gradients and abrupt velocity reversals of intense but narrow, probably subsonic, line cores. CO components that are observed in absorption at a moderate optical depth (0.5) and are undetected in emission at 1' resolution toward NRAO 150 remain undetected at 6" resolution. This implies that they are not a previously-hidden large-scale molecular component revealed in absorption, but they do highlight the robustness of the chemistry into regions where the density and column density are too low to produce much rotational excitation, even in CO. Bright CO lines around NRAO 150 most probably reflect the variation of a chemical process, i.e. the C+-CO conversion. However, the ultimate cause of the variations of this chemical process in such a limited field of view remains uncertain.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A54
- Title:
- Combined ArTeMiS+SPIRE 350um image of NGC6334
- Short Name:
- J/A+A/592/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of ~0.1pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation. In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350microns. We used the large-format bolometer camera ArTeMiS on the APEX telescope and combined the high-resolution ArTeMiS data at 350microns with Herschel/HOBYS data at 70-500microns to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8" or <0.07pc at d~1.7kpc. Our study confirms that this filament is a very dense, massive linear structure with a line mass ranging from ~500M_{sun}_/pc to ~2000M_{sun}_/pc over nearly 10pc. It also demonstrates for the first time that its inner width remains as narrow as W~0.15+/-0.05pc all along the filament length, within a factor of <2 of the characteristic 0.1pc value found with Herschel for lower-mass filaments in the Gould Belt. While it is not completely clear whether the NGC 6334 filament will form massive stars in the future, it is two to three orders of magnitude denser than the majority of filaments observed in Gould Belt clouds, and has a very similar inner width. This points to a common physical mechanism for setting the filament width and suggests that some important structural properties of nearby clouds also hold in high-mass star-forming regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/867/165
- Title:
- CO molecular clumps in Henize 2-10 dwarf galaxy
- Short Name:
- J/ApJ/867/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Atacama Large Millimeter/Submillimeter Array CO(3-2) observations at 0.3" resolution of He 2-10, a starburst dwarf galaxy and possible high-z galaxy analog. The warm dense gas traced by CO(3-2) is found in clumpy filaments that are kinematically and spatially distinct. The filaments have no preferred orientation or direction; this may indicate that the galaxy is not evolving into a disk galaxy. Filaments appear to be feeding the active starburst; the velocity field in one filament suggests acceleration onto an embedded star cluster. The relative strengths of CO(3-2) and radio continuum vary strongly on decaparsec scales in the starburst. There is no CO(3-2) clump coincident with the nonthermal radio source that has been suggested to be an AGN, nor unusual kinematics. The kinematics of the molecular gas show significant activity that is apparently unrelated to the current starburst. The longest filament, east of the starburst, has a pronounced shear of FWHM ~40km/s across its ~50pc width over its entire ~0.5kpc length. The cause of the shear is not clear. This filament is close in projection to a "dynamically distinct" CO feature previously seen in CO(1-0). The most complex region and the most highly disturbed gas velocities are in a region 200pc south of the starburst. The CO(3-2) emission there reveals a molecular outflow, of line width FWZI~120-140km/s, requiring an energy >~10^53^erg/s. There is at present no candidate for the driving source of this outflow.
- ID:
- ivo://CDS.VizieR/J/ApJ/722/395
- Title:
- Compact H I clouds from the GALFA-H I survey
- Short Name:
- J/ApJ/722/395
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Galactic Arecibo L-band Feed Array H I (GALFA-H I) survey is mapping the entire Arecibo sky at 21 cm, over a velocity range of -700 to +700 km/s (LSR), at a velocity resolution of 0.18 km/s, and a spatial resolution of 3.5 arcmin. The unprecedented resolution and sensitivity of the GALFA-H I survey have resulted in the detection of numerous isolated, very compact H I clouds at low Galactic velocities, which are distinctly separated from the H I disk emission. In the limited area of ~4600 deg^2^ surveyed so far, we have detected 96 such compact clouds. The detected clouds are cold with a median T_k,max_ (the kinetic temperature in the case in which there is no non-thermal broadening) of 300 K. Moreover, these clouds are quite compact and faint, with median values of 5 arcmin in angular size, 0.75 K in peak brightness temperature, and 5x10^18^/cm2 in H I column density. Most of the clouds deviate from Galactic rotation at the 20-30 km/s level, and a significant fraction show evidence for a multiphase medium and velocity gradients. No counterparts for these clouds were found in other wave bands. From the modeling of spatial and velocity distributions of the whole compact cloud population, we find that the bulk of the compact clouds are related to the Galactic disk, and their distances are likely to be in the range of 0.1 to a few kpc. We discuss various possible scenarios for the formation and maintenance of this cloud population and its significance for Galactic interstellar medium studies.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/476
- Title:
- Complete spectrum of ethyl cyanide
- Short Name:
- J/ApJ/714/476
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is a general consensus that many of the unidentified features in astrophysical spectra are due to low lying excited vibrational and torsional states of a few molecules -commonly referred to as the astrophysical weeds. This is a challenging spectroscopic problem not only because there are many such states, but also because these states are often highly perturbed and difficult to analyze. We have previously described an alternative approach based on experimental, intensity-calibrated spectra taken at many temperatures. In this paper, we describe the procedures and results obtained with this approach for ethyl cyanide, strategies for archiving and disseminating these results, and the prospects for using these results to reduce the confusion limit in the powerful new observatories that are coming online.
- ID:
- ivo://CDS.VizieR/J/ApJ/782/75
- Title:
- Complete spectrum of methanol
- Short Name:
- J/ApJ/782/75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The complete spectrum of methanol (CH_3_OH) has been characterized over a range of astrophysically significant temperatures in the 560.4-654.0GHz spectral region. Absolute intensity calibration and analysis of 166 experimental spectra recorded over a slow 248-398K temperature ramp provide a means for the simulation of the complete spectrum of methanol as a function of temperature. These results include contributions from v_t_=3 and other higher states that are difficult to model via quantum mechanical (QM) techniques. They also contain contributions from the ^13^C isotopologue in terrestrial abundance. In contrast to our earlier work on semi-rigid species, such as ethyl cyanide and vinyl cyanide, significant intensity differences between these experimental values and those calculated by QM methods were found for many of the lines. Analysis of these differences shows the difficulty of the calculation of dipole matrix elements in the context of the internal rotation of the methanol molecule. These results are used to both provide catalogs in the usual line frequency, linestrength, and lower state energy format, as well as in a frequency point-by-point catalog that is particularly well suited for the characterization of blended lines.
