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1. ATLASGAL clumps with IRAS flux and MALT90 data
ID:
ivo://CDS.VizieR/J/ApJ/824/29
Title:
ATLASGAL clumps with IRAS flux and MALT90 data
Short Name:
J/ApJ/824/29
Date:
21 Oct 2021
Publisher:
CDS
Description:
In a survey of 65 galaxies, Gao & Solomon (2004ApJS..152...63G) found a tight linear relation between the infrared luminosity (L_IR_, a proxy for the star formation rate) and the HCN(1-0) luminosity (L_HCN_). Wu et al. (2005ApJ...635L.173W) found that this relation extends from these galaxies to the much less luminous Galactic molecular high-mass star-forming clumps (~1pc scales), and posited that there exists a characteristic ratio L_IR_/L_HCN_ for high-mass star-forming clumps. The Gao-Solomon relation for galaxies could then be explained as a summation of large numbers of high-mass star-forming clumps, resulting in the same L_IR_/L_HCN_ ratio for galaxies. We test this explanation and other possible origins of the Gao-Solomon relation using high-density tracers (including HCN(1-0), N_2_H^+^(1-0), HCO^+^(1-0), HNC(1-0), HC_3_N(10-9), and C_2_H(1-0)) for ~300 Galactic clumps from the Millimetre Astronomy Legacy Team 90GHz (MALT90) survey. The MALT90 data show that the Gao-Solomon relation in galaxies cannot be satisfactorily explained by the blending of large numbers of high-mass clumps in the telescope beam. Not only do the clumps have a large scatter in the L_IR_/L_HCN_ ratio, but also far too many high-mass clumps are required to account for the Galactic IR and HCN luminosities. We suggest that the scatter in the L_IR_/L_HCN_ ratio converges to the scatter of the Gao-Solomon relation at some size-scale >~1kpc. We suggest that the Gao-Solomon relation could instead result from of a universal large-scale star formation efficiency, initial mass function, core mass function, and clump mass function.
2. Atlas of Galactic Neutral Hydrogen
ID:
ivo://CDS.VizieR/VIII/54
Title:
Atlas of Galactic Neutral Hydrogen
Short Name:
VIII/54
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Leiden/Dwingeloo HI survey mapped the 21-cm spectral line emission over the entire sky above declinations of -30 degrees using a grid spacing of ~ 0.5 degree and a velocity sampling of ~ 1.03 km/s. The useful velocity (V_lsr) range is from -450 to +400 km/s. The Atlas presents calibrated spectra in units of brightness temperature. Using interpolation and averaging, the authors have placed their data on an evenly-spaced grid in Galactic coordinates (l,b). A detailed discussion of the instrument and calibration procedures is provided in the published Atlas. The average sensitivity level of the survey is 0.07 K (1-sigma, rms). This sensitivity level depends critically on the success of the stray-radiation correction as discussed in Hartmann et al. (1996A&AS..119..115H). In that discussion, several caveats are offered regarding the removal of stray radiation, in particular that component which might be due to reflection from the ground. Some instances have been found where there are residuals which are clearly larger than the mean accuracy quoted as representative of the Leiden/Dwingeloo survey. Users of the data are reminded that the stray-radiation correction was applied conservatively, ensuring that no overestimate was calculated and removed, thereby yielding spurious negative intensities. A specific example of remaining spurious emission is evident towards the North Galactic Pole, a direction notoriously difficult to observe. All spectra taken towards b=+90 degrees should, of course, be identical, no matter the longitude or the orientation of the telescope with respect to the ground or to the meridian. Because the sky was sampled in 5x5 degree boxes, a spectrum was recorded at b=+90 degrees for every Nx5 degrees (N=0..72) in longitude. The spectra in the final dataset were interpolated between these measured spectra to yield a 0.5x0.5 degree grid. So, only every 10th spectrum at this extreme latitude corresponds to an observed spectrum. Comparing all spectra at b=+90 reveals differences which are larger than expected. The origin of this discrepancy is currently unknown. There is also an instrumental effect which reveals itself as correlated noise, showing a pattern which alternates sign at adjacent channels when the very lowest levels of intensity are examined. This effect is due to an offset in the DAS autocorrelator used as the backend in the Leiden/Dwingeloo survey. The presence of this artifact becomes noticeable only after averaging 50 or more spectra. Although a Hanning convolution of the data would eliminate this effect, it would also degrade the velocity resolution; as the correlated noise is noticeable only at very low levels (about 15 mK), well below the mean rms sensitivity of the survey itself, the original spectra have not been Hanning smoothed. Excepted are those spectra which suffered from sinc interference. These spectra were Hanning smoothed to enable the elimination of the interference spike. Dr. Lloyd Higgs has compared the HI spectra made with the DRAO 26-m telescope in support of the Canadian Galactic Plane Survey with those of the Leiden Dwingeloo Survey, and has pointed out what are evidently calibration problems in a small number of isolated LDS spectra. Either Hartmann, Burton, or Higgs could provide additional information. The Leiden/Dwingeloo HI survey is intended primarily for studies of the interstellar gas associated with our own Galaxy. There are, however, a small number of spectra in which 'contaminating' signatures from known external galaxies are present. Detections of roughly 50 such external galaxies were made; refer to table 4 of the Atlas for a list. The HI spectra from the Leiden/Dwingeloo survey are archived as 721 files. Each file is in FITS image format, and maps the 21-cm brightness temperature at a fixed Galactic longitude for an evenly-spaced rectangular grid of (Galactic latitude, velocity) points. There is one FITS file for every 0.5 degree in Galactic longitude in the "fits" subdirectory. In addition to the 721 (b,v) FITS files, there is an (l,b) FITS image named TOTAL_HI.FIT, which contains the integrated intensity map over the velocity range -450 km/s <= V_lsr <= +400 km/s. The map units are in [K.km/s] and the FITS header contains comments regarding the conversion to column densities. Included as a visual aid is the GIF image file total_hi.gif, which depicts the velocity-integrated map. The data were originally distributed on a CD-ROM enclosed with the Atlas of Galactic Neutral Hydrogen (reference given above). The CD also contains animations of velocity slices through the data cube.
3. Bell Lab. H I Survey - High Velocity Clouds
ID:
ivo://CDS.VizieR/J/ApJS/79/77
Title:
Bell Lab. H I Survey - High Velocity Clouds
Short Name:
J/ApJS/79/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
The sky north of declination -40 deg. was observed in the 21 cm line of atomic hydrogen with the FWHM = 2 deg. beam of the 20 foot horn reflector at AT&T Bell Laboratories, Crawford Hill. The survey covers a velocity range of 654 km/s centered on the Galactic standard of rest, with 5.3 km/s wide filters. This survey is distinguished by its sensitivity to low surface brightness features (antenna temperature about 50 mK) and relative freedom from sidelobe contamination. The high-velocity cloud list was extracted and catalogued automatically from the survey data.
4. Bell Laboratories H I Survey
ID:
ivo://CDS.VizieR/VIII/28
Title:
Bell Laboratories H I Survey
Short Name:
VIII/28
Date:
21 Oct 2021
Publisher:
CDS
Description:
The sky north of declination -40{deg} was observed in the 21cm line of atomic hydrogen with the FWHM=2{deg} beam of the 20 foot horn reflector at AT&T Bell Laboratories, Crawford Hill. The survey covers a velocity range of 654km/s centered on the Galactic standard of rest, with 5.3km/s wide filters. This survey is distinguished by its sensitivity to low surface brightness features (antenna temperature about 50mK) and relative freedom from sidelobe contamination. High-velocity clouds are extracted and catalogued automatically. The data are presented in declination zones in equatorial and polar coordinates, and as R.A. - velocity images.
5. BGPS. XIV. Molecular cloud clumps GBT obs.
ID:
ivo://CDS.VizieR/J/ApJ/822/59
Title:
BGPS. XIV. Molecular cloud clumps GBT obs.
Short Name:
J/ApJ/822/59
Date:
21 Oct 2021
Publisher:
CDS
Description:
We sort 4683 molecular clouds between 10{deg}<l<65{deg} from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70{mu}m sources, mid-IR color-selected YSOs, H_2_O and CH_3_OH masers, and UCHII regions. We also present a combined NH_3_-derived gas kinetic temperature and H_2_O maser catalog for 1788 clumps from our own GBT 100m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial ({alpha}~0.7) with >75% of clumps with known distance being gravitationally bound ({alpha}<2). These samples show a statistically significant increase in the median clump mass of {Delta}M~170-370M_{sun}_ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at dM/dt~200-440M_{sun}_/Myr for an average freefall 0.8Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ~M^-0.4^. By comparing to the observed number of CH_3_OH maser containing clumps, we estimate the phase lifetime of massive (M>10^3^M_{sun}_) starless clumps to be 0.37+/-0.08Myr (M/10^3^M_{sun}_)^-1^; the majority (M<450M_{sun}_) have phase lifetimes longer than their average freefall time.
6. Chemical properties of red MSX sources (RMSs)
ID:
ivo://CDS.VizieR/J/ApJ/833/248
Title:
Chemical properties of red MSX sources (RMSs)
Short Name:
J/ApJ/833/248
Date:
21 Oct 2021
Publisher:
CDS
Description:
Red Midcourse Space Experiment (MSX) Sources (RMSs) are regarded as excellent candidates of massive star-forming regions. In order to characterize the chemical properties of massive star formation, we made a systematic study of 87 RMSs in the southern sky, using archival data taken from the Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), the Australia Telescope Compact Array, and the Millimetre Astronomy Legacy Team Survey at 90GHz (MALT90). According to previous multiwavelength observations, our sample could be divided into two groups: massive young stellar objects and HII regions. Combined with the MALT90 data, we calculated the column densities of N_2_H^+^, C_2_H, HC_3_N, and HNC and found that they are not much different from previous studies made in other massive star-forming regions. However, their abundances are relatively low compared to infrared dark clouds (IRDCs). The abundances of N_2_H^+^ and HNC in our sample are at least 1mag lower than those found in IRDCs, indicating chemical depletions in the relatively hot gas. Besides, the fractional abundances of N_2_H^+^, C_2_H, and HC_3_N seem to decrease as a function of their Lyman continuum fluxes (N_L_), indicating that these molecules could be destroyed by UV photons when HII regions have formed inside. We also find that the C_2_H abundance decreases faster than HC_3_N with respect to N_L_. The abundance of HNC has a tight correlation with that of N_2_H^+^, indicating that it may be also preferentially formed in cold gas. We regard our RMSs as being in a relatively late evolutionary stage of massive star formation.
7. Clouds in SEDIGISM science demonstration field
ID:
ivo://CDS.VizieR/J/A+A/601/A124
Title:
Clouds in SEDIGISM science demonstration field
Short Name:
J/A+A/601/A124
Date:
21 Oct 2021
Publisher:
CDS
Description:
The origin and life-cycle of molecular clouds are still poorly constrained, despite their importance for understanding the evolution of the interstellar medium. Many large-scale surveys of the Galactic plane have been conducted recently, allowing for rapid progress in this field. Nevertheless, a sub-arcminute resolution global view of the large-scale distribution of molecular gas, from the diffuse medium to dense clouds and clumps, and of their relationship to the spiral structure, is still missing. We have carried out a systematic, homogeneous, spectroscopic survey of the inner Galactic plane, in order to complement the many continuum Galactic surveys available with crucial distance and gas-kinematic information. Our aim is to combine this data set with recent infrared to sub-millimetre surveys at similar angular resolutions. The SEDIGISM survey covers 78deg^2^ of the inner Galaxy (-60{deg}<l<+18{deg}, |b|<0.5{deg}) in the J=2-1 rotational transition of ^13^CO. This isotopologue of CO is less abundant than ^12^CO by factors up to 100. Therefore, its emission has low to moderate optical depths, and higher critical density, making it an ideal tracer of the cold, dense interstellar medium. The data have been observed with the SHFI single-pixel instrument at APEX. The observational setup covers the ^13^CO(2-1) and C^18^O(2-1) lines, plus several transitions from other molecules. The observations have been completed. Data reduction is in progress and the final data products will be made available in the near future. Here we give a detailed description of the survey and the dedicated data reduction pipeline. To illustrate the scientific potential of this survey, preliminary results based on a science demonstration field covering -20{deg}<l<-18.5{deg} are presented. Analysis of the ^13^CO(2-1) data in this field reveals compact clumps, diffuse clouds, and filamentary structures at a range of heliocentric distances. By combining our data with data in the (1-0) transition of CO isotopologues from the ThrUMMS survey, we are able to compute a 3D realization of the excitation temperature and optical depth in the interstellar medium. Ultimately, this survey will provide a detailed, global view of the inner Galactic interstellar medium at an unprecedented angular resolution of ~30".
8. 1.3cm line survey toward Orion KL
ID:
ivo://CDS.VizieR/J/A+A/581/A48
Title:
1.3cm line survey toward Orion KL
Short Name:
J/A+A/581/A48
Date:
18 Nov 2021 11:23:37
Publisher:
CDS
Description:
Orion KL has served as a benchmark for spectral line searches throughout the (sub)millimeter regime. The main goal is to systematically study spectral characteristics of Orion KL in the 1.3cm band. We carried out a spectral line survey (17.9GHz to 26.2GHz) with the Effelsberg-100m telescope towards Orion KL. We find 261 spectral lines, yielding an average line density of about 32 spectral features per GHz above 3 sigma. The identified lines include 164 radio recombination lines (RRLs) and 97 molecular lines. A total of 23 molecular transitions from species known to exist in Orion KL are detected for the first time in the interstellar medium. Non-metastable ^15^NH_3_ transitions are detected in Orion KL for the first time. Based on the velocity information of detected lines and the ALMA images, the spatial origins of molecular emission are constrained and discussed. A narrow feature is found in SO_2_ (8_1,7_-7_2,6_), possibly suggesting the presence of a maser line. Column densities and fractional abundances relative to H_2_ are estimated for 12 molecules with LTE methods. Rotational diagrams of non-metastable ^14^NH_3_ transitions with J=K+1 to J=K+4 yield different results; metastable ^15^NH_3_ is found to have a higher excitation temperature than non-metastable ^15^NH_3_, indicating that they may trace different regions. Elemental and isotopic abundance ratios are estimated: ^12^C/^13^C=63+/-17, ^14^N/^15^N=100+/-51, D/H=0.0083+/-0.0045. The dispersion of the He/H ratios derived from H_alpha/He_alpha_ pairs to H_delta_/He_delta_ pairs is very small, which is consistent with theoretical predictions that the departure coefficients bn factors for hydrogen and helium are nearly identical. Based on a non-LTE code neglecting excitation by the infrared radiation field and a likelihood analysis, we find that the denser regions have lower kinetic temperature, which favors an external heating of the Hot Core.
9. CO survey of molecular clouds. III. Serpens
ID:
ivo://CDS.VizieR/J/ApJS/209/39
Title:
CO survey of molecular clouds. III. Serpens
Short Name:
J/ApJS/209/39
Date:
21 Oct 2021
Publisher:
CDS
Description:
We mapped ^12^CO and ^13^CO J=2-1 emission over 1.04deg^2^ of the Serpens molecular cloud with 38" spatial and 0.3km/s spectral resolution using the Arizona Radio Observatory Heinrich Hertz Submillimeter Telescope. Our maps resolve kinematic properties for the entire Serpens cloud. We also compare our velocity moment maps with known positions of young stellar objects (YSOs) and 1.1 mm continuum emission. We find that ^12^CO is self-absorbed and ^13^CO is optically thick in the Serpens core. Outside of the Serpens core, gas appears in filamentary structures having LSR velocities which are blueshifted by up to 2km/s relative to the 8km/s systemic velocity of the Serpens cloud. We show that the known Class I, flat, and Class II YSOs in the Serpens core most likely formed at the same spatial location and have since drifted apart. The spatial and velocity structure of the ^12^CO line ratios implies that a detailed three-dimensional radiative transfer model of the cloud will be necessary for full interpretation of our spectral data. The "starless cores" region of the cloud is likely to be the next site of star formation in Serpens.
10. CO survey of molecular clouds. IV. NGC 1333
ID:
ivo://CDS.VizieR/J/ApJS/214/7
Title:
CO survey of molecular clouds. IV. NGC 1333
Short Name:
J/ApJS/214/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
We mapped the NGC 1333 section of the Perseus Molecular Cloud in the J=2-1 emission lines of ^12^CO and ^13^CO over a 50'x60' region (3.4x4.1pc at the cloud distance of 235pc), using the Arizona Radio Observatory Heinrich Hertz Submillimeter Telescope. The angular resolution is 38" (0.04pc) and velocity resolution is 0.3km/s. We compare our velocity moment maps with known positions of young stellar objects (YSOs) and (sub)millimeter dust continuum emission. The CO emission is brightest at the center of the cluster of YSOs, but is detected over the full extent of the mapped region at >=10xrms. The morphology of the CO channel maps shows a kinematically complex structure, with many elongated features extending from the YSO cluster outward by ~1pc. One notable feature appears as a narrow serpentine structure that curves and doubles back, with a total length of ~3pc. The ^13^CO velocity channel maps show evidence for many low-density cavities surrounded by partial shell-like structures, consistent with previous studies. Maps of the velocity moments show localized effects of bipolar outflows from embedded YSOs, as well as a large-scale velocity gradient around the central core of YSOs, suggestive of large-scale turbulent cloud motions determining the location of current star formation. The CO/^13^CO intensity ratios show the distribution of the CO opacity, which exhibits a complex kinematic structure. Identified YSOs are located mainly at the positions of greatest CO opacity.

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