- ID:
- ivo://CDS.VizieR/J/A+A/574/A127
- Title:
- Photodissociation with mechanical heating
- Short Name:
- J/A+A/574/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CO observations in active galactic nuclei and starbursts reveal high kinetic temperatures. Those environments are thought to be very turbulent due to dynamic phenomena, such as outflows and high supernova rates. We investigate the effect of mechanical heating on atomic fine-structure and molecular lines and on their ratios. We try to use those ratios as a diagnostic to constrain the amount of mechanical heating in an object and also study its significance on estimating the H_2_ mass. Equilibrium photodissociation models (PDRs hereafter) were used to compute the thermal and chemical balance for the clouds. The equilibria were solved for numerically using the optimized version of the Leiden PDR-XDR code. Large velocity-gradient calculations were done as post-processing on the output of the PDR models using RADEX. High-J CO line ratios are very sensitive to mechanical heating ({GAMMA}mech hereafter). Emission becomes at least one order of magnitude brighter in clouds with n~10^5^cm^-3^ and a star formation rate of 1M_{sun}/yr (corresponding to {GAMMA}mech=2x10^-19^erg/cm^3^/s). The Emission of low-J CO lines is not as sensitive to {GAMMA}mech, but they do become brighter in response to {GAMMA}mech. Generally, for all of the lines we considered, {GAMMA}mech increases excitation temperatures and decreases the optical depth at the line centre. Hence line ratios are also effected, strongly in some cases. Ratios involving HCN are a good diagnostic for {GAMMA}mech , where the HCN(1-0)/CO(1-0) increases from 0.06 to 0.25, and the HCN(1-0)/HCO^+^ (1-0) increase from 0.15 to 0.5 for amounts of {GAMMA}mech that are equivalent to 5% of the surface heating rate. Both ratios increase to more than 1 for higher {GAMMA}mech , as opposed to being much less than unity in pure PDRs. The first major conclusion is that low-J to high-J intensity ratios will yield a good estimate of the mechanical heating rate (as opposed to only low-J ratios). The second one is that the mechanical heating rate should be taken into account when determining AV or, equivalently, NH, and consequently the cloud mass. Ignoring {GAMMA}mech will also lead to large errors in density and radiation field estimates.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/628/A110
- Title:
- Photometry of submm cores in Vela C
- Short Name:
- J/A+A/628/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a study of the population of compact submm cores in Vela C, one of the molecular clouds making up the Vela Molecular Ridge, a nearby (~700pc) star forming region in the Galactic plane. A large scale map of dust emission at 345GHz was obtained with LABOCA at the APEX telescope. Core retrieval and photometry were performed with the algorithms CuTEx and CLUMPFIND. Table 1 lists the sources retrieved by CuTEx. Table 2 lists the sources retrieved by CLUMPFIND.
- ID:
- ivo://CDS.VizieR/J/ApJ/665/369
- Title:
- Photopolarimetry of Southern Coalsack stars
- Short Name:
- J/ApJ/665/369
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new multicolor photopolarimetry of stars behind the Southern Coalsack. Analyzed together with multiband polarization data from the literature, probing the Chamaeleon I, Musca, rho Opiuchus, R CrA, and Taurus clouds, we show that the wavelength of maximum polarization ({lambda}_max_) is linearly correlated with the radiation environment of the grains. Using far-infrared emission data, we show that the large scatter seen in previous studies of {lambda}_max_ as a function of Av is primarily due to line-of-sight effects causing some Av measurements to not be a good tracer of the extinction (radiation field strength) seen by the grains being probed.
- ID:
- ivo://CDS.VizieR/J/ApJ/800/7
- Title:
- Physical conditions of high redshift DLAs
- Short Name:
- J/ApJ/800/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new method is used to measure the physical conditions of the gas in damped Ly{alpha} systems (DLAs). Using high-resolution absorption spectra of a sample of 80 DLAs, we are able to measure the ratio of the upper and lower fine-structure levels of the ground state of C^+^ and Si^+^. These ratios are determined solely by the physical conditions of the gas. We explore the allowed physical parameter space using a Monte Carlo Markov chain method to constrain simultaneously the temperature, neutral hydrogen density, and electron density of each DLA. The results indicate that at least 5% of all DLAs have the bulk of their gas in a dense, cold phase with typical densities of ~100/cm3 and temperatures below 500K. We further find that the typical pressure of DLAs in our sample is log(P/k_B_)=3.4(K/cm3), which is comparable to the pressure of the local interstellar medium (ISM), and that the components containing the bulk of the neutral gas can be quite small with absorption sizes as small as a few parsecs. We show that the majority of the systems are consistent with having densities significantly higher than expected for a purely canonical warm neutral medium, indicating that significant quantities of dense gas (i.e., n_H_>0.1/cm3) are required to match observations. Finally, we identify eight systems with positive detections of Si II*. These systems have pressures (P/k_B_) in excess of 20000K/cm3, which suggest that these systems tag a highly turbulent ISM in young, star-forming galaxies.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A86
- Title:
- PILS-Cygnus. observations of CygX-N30
- Short Name:
- J/A+A/655/A86
- Date:
- 10 Mar 2022 07:33:06
- Publisher:
- CDS
- Description:
- Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominant process in the release of these COMs from the icy grains -- where they predominately form -- to the gas phase is still an open question. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range. We used 32 GHz Submillimeter Array (SMA) observations with continuous frequency coverage from 329 to 361GHz at an angular resolution of ~1'' to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency range was used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution of the different species. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We find that the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blue- shifted H_2_CO and CS emission. Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axis through the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources where COMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH_2_DOH is derived, leading to a D/H ratio of <0.1%. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sources along with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of the continuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N- bearing species on the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than the other component of the system. The low D/H ratio likely reflects a pre- stellar phase where the COMs formed on the ices at warm temperatures (~30K), where the deuterium fractionation would have been inefficient. The observations and results presented here demonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.
- ID:
- ivo://CDS.VizieR/J/A+A/620/A24
- Title:
- Pipe nebula optical-depth, column-density maps
- Short Name:
- J/A+A/620/A24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Multi-wavelength observations in the sub-mm regime provide information on the distribution of both the dust column density and the effective dust temperature in molecular clouds. In this study, we created high-resolution and high-dynamic-range maps of the Pipe nebula region and explored the value of dust-temperature measurements in particular towards the dense cores embedded in the cloud. The maps are based on data from the Herschel and Planck satellites, and calibrated with a near-infrared extinction map based on 2MASS observations. We have considered a sample of previously defined cores and found that the majority of core regions contain at least one local temperature minimum. Moreover, we observed an anti-correlation between column density and temperature. The slope of this anti-correlation is dependent on the region boundaries and can be used as a metric to distinguish dense from diffuse areas in the cloud if systematic effects are addressed appropriately. Employing dust-temperature data thus allows us to draw conclusions on the thermodynamically dominant processes in this sample of cores: external heating by the interstellar radiation field and shielding by the surrounding medium. In addition, we have taken a first step towards a physically motivated core definition by recognising that the column-density-temperature anti-correlation is sensitive to the core boundaries. Dust-temperature maps therefore clearly contain valuable information about the physical state of the observed medium.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A116
- Title:
- PKS 1830-211 OH and HI spectra
- Short Name:
- J/A+A/648/A116
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The Large Survey Project (LSP) "MeerKAT Absorption Line Survey" (MALS) is a blind HI 21-cm and OH 18-cm absorption line survey in the L- and UHF-bands, with the primary goal to better determine the occurrence of atomic and molecular gas in the circumgalactic and inter-galactic medium, and its redshift evolution. Here we present the first results using the UHF-band, obtained towards the strongly lensed radio source PKS 1830-211, detecting absorption produced by the lensing galaxy. With merely 90 mins of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known HI 21-cm and OH 18-cm main lines at z=0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, in each 6km/s wide channel). For the first time we report the detection at z=0.89 of OH satellite lines, so far not detected at z>0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720MHz lines are conjugate. The total OH 1720MHz emission line luminosity is 6100L_{sun}_. This is the most luminous known 1720MHz maser line. It is also among the highest luminosities for the OH-main lines megamasers. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time, on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20yrs ago, and find no variation, in spite of the high signal-to-noise ratios. We interpret the absorption spectra with the help of a lens galaxy model, derived from an N-body hydro-dynamical simulation, with a morphology similar to its optical HST image. The resulting absorption lines depend mainly on the background continuum, and the radial distribution of the gas surface density, for each atomic /molecular species.We show that it is possible to reproduce the observations assuming a realistic spiral galaxy disk, without invoking any central gas outflows. There are, however, distinct and faint high-velocity features in the ALMA millimeter absorption spectra, that most likely originate from high-velocity clouds or tidal features. These clouds may contribute to broaden the Hi and OH spectra.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A65
- Title:
- Planck and Herschel images combination
- Short Name:
- J/A+A/604/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Herschel has revolutionized our ability to measure column densities (N_H_) and temperatures (T) of molecular clouds thanks to its far infrared multiwavelength coverage. However, the lack of a well defined background intensity level in the Herschel data limits the accuracy of the NH and T maps. We aim to provide a method that corrects the missing Herschel background intensity levels using the Planck model for foreground Galactic thermal dust emission. For the Herschel/PACS data, both the constant-offset as well as the spatial dependence of the missing background must be addressed. For the Herschel/SPIRE data, the constant-offset correction has already been applied to the archival data so we are primarily concerned with the spatial dependence, which is most important at 250um. We present a Fourier method that combines the publicly available Planck model on large angular scales with the Herschel images on smaller angular scales. We have applied our method to two regions spanning a range of Galactic environments: Perseus and the Galactic plane region around l=11{deg} (HiGal-11). We post-processed the combined dust continuum emission images to generate column density and temperature maps. We compared these to previously adopted constant-offset corrections. We find significant differences (>~20%) over significant (~15%) areas of the maps, at low column densities (N_H_<~10^22^cm^-2^) and relatively high temperatures (T>~20K). We have also applied our method to synthetic observations of a simulated molecular cloud to validate our method. Our method successfully corrects the Herschel images, including both the constant-offset intensity level and the scale-dependent background variations measured by Planck. Our method improves the previous constant-offset corrections, which did not account for variations in the background emission levels.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A28
- Title:
- Planck Catalogue of Galactic cold clumps (PGCC)
- Short Name:
- J/A+A/594/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the Planck Catalogue of Galactic Cold Clumps (PGCC), an all-sky catalogue of Galactic cold clump candidates detected by Planck. This catalogue is the full version of the Early Cold Core (ECC) catalogue, which was made available in 2011 with the Early Release Compact Source Catalogue (ERCSC) and which contained 915 high signal-to-noise sources. It is based on the Planck 48-month mission data that are currently being released to the astronomical community. The PGCC catalogue is an observational catalogue consisting exclusively of Galactic cold sources. The three highest Planck bands (857, 454, and 353GHz) have been combined with IRAS data at 3THz to perform a multi-frequency detection of sources colder than their local environment. After rejection of possible extragalactic contaminants, the PGCC catalogue contains 13188 Galactic sources spread across the whole sky, i.e., from the Galactic plane to high latitudes, following the spatial distribution of the main molecular cloud complexes. The median temperature of PGCC sources lies between 13 and 14.5K, depending on the quality of the flux density measurements, with a temperature ranging from 5.8 to 20K after removing the sources with the top 1% highest temperature estimates. Using seven independent methods, reliable distance estimates have been obtained for 5574 sources, which allows us to derive their physical properties such as their mass, physical size, mean density, and luminosity. The PGCC sources are located mainly in the solar neighbourhood, but also up to a distance of 10.5kpc in the direction of the Galactic centre, and range from low-mass cores to large molecular clouds. Because of this diversity and because the PGCC catalogue contains sources in very different environments, the catalogue is useful for investigating the evolution from molecular clouds to cores. Finally, it also includes 54 additional sources located in the Small and Large Magellanic Clouds.
- ID:
- ivo://CDS.VizieR/J/ApJ/864/154
- Title:
- Planck cold clump G108.37-01.06 YSO candidates
- Short Name:
- J/ApJ/864/154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Planck Galactic Cold Clumps (PGCCs) are possible representations of the initial conditions and very early stages of star formation. With the objective of understanding better the star and star cluster formation, we probe the molecular cloud associated with PGCC G108.37-01.06 (hereafter PG108.3), which can be traced in a velocity range of -57 to -51km/s. The INT Photometric H{alpha} Survey images reveal H{alpha} emission at various locations around PG108.3, and optical spectroscopy of the bright sources in those zones of H{alpha} emission discloses two massive ionizing sources with spectral type O8-O9V and B1V. Using the radio continuum, we estimate ionizing gas parameters and find the dynamical ages of HII regions associated with the massive stars in the range of 0.5-0.75Myr. Based on the stellar surface density map constructed from the deep near-infrared Canada-France-Hawaii Telescope observations, we find two prominent star clusters in PG108.3; of these, the cluster associated with H ii region S148 is moderately massive (~240M_{sun}_). A careful inspection of James Clerk Maxwell telescope ^13^CO (3-2) molecular data exhibits that the massive cluster is associated with a number of filamentary structures. Several embedded young stellar objects (YSOs) are also identified in PG108.3 along the length and junction of filaments. We find evidence of a velocity gradient along the length of the filaments. Along with kinematics of the filaments and the distribution of ionized, molecular gas and YSOs, we suggest that the cluster formation is most likely due to the longitudinal collapse of the most massive filament in PG108.3.
