- ID:
- ivo://CDS.VizieR/J/ApJS/95/457
- Title:
- IRAS images of nearby dark clouds
- Short Name:
- J/ApJS/95/457
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated ~100 nearby molecular clouds using the extensive, all-sky database of IRAS. The clouds in this study cover a wide range of physical properties including visual extinction, size, mass, degree of isolation, homogeneity and morphology. IRAS 100 and 60 micrometre co-added images were used to calculate the 100 micrometre optical depth of dust in the clouds. These images of dust optical depth compare very well with ^12^CO and ^13^CO observations, and can be related to H_2_ column density. From the optical depth images we locate the edges of dark clouds and the dense cores inside them. We have identified a total of 43 "IRAS clouds" (regions with Av>2) which contain a total of 255 "IRAS cores" (regions with Av>4) and we catalog their physical properties. We find that the clouds are remarkably filamentary, and that the cores within the clouds are often distributed along the filaments. The largest cores are usually connected to other large cores by filaments. We have developed selection criteria to search the IRAS Point Source Catalog for stars that are likely to be associated with the clouds and we catalog the IRAS sources in each cloud or core. Optically visible stars associated with the clouds have been identified from the Herbig and Bell catalog. From these data we characterize the physical properties of the clouds including their star-formation efficiency.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/628/789
- Title:
- IRAS03301+3057 water masers
- Short Name:
- J/ApJ/628/789
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we present VLA observations of the NH3, CCS, and H2O maser emission at 1cm from the star-forming region B1-IRS (IRAS 03301+3057) with ~5" (=1750AU) of angular resolution. The CCS emission is distributed in three clumps around the central source. These clumps exhibit a velocity gradient from red- to blueshifted velocities toward B1-IRS, probably due to an interaction with the outflow from an embedded protostar.
- ID:
- ivo://CDS.VizieR/J/A+A/639/A61
- Title:
- IR continuum, [CII] and [OI] maps of M33
- Short Name:
- J/A+A/639/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- M33 is a gas rich spiral galaxy of the Local Group. Its vicinity allows us to study its interstellar medium (ISM) on linear scales corresponding to the sizes of individual giant molecular clouds. We investigate the relationship between the two major gas cooling lines and the total infrared (TIR) dust continuum. We mapped the emission of gas and dust in M33 using the far-infrared lines of [CII] and [OI](63um) and the total infrared continuum. The line maps were observed with the PACS spectrometer on board the Herschel Space Observatory. These maps have 50pc resolution and form a ~370pc wide stripe along its major axis covering the sites of bright HII regions, but also more quiescent arm and inter-arm regions from the southern arm at 2kpc galacto-centric distance to the south out to 5.7kpc distance to the north. Full-galaxy maps of the continuum emission at 24um from Spitzer/MIPS, and at 70um, 100um, and 160um from Herschel/PACS were combined to obtain a map of the TIR. TIR and [CII] intensities are correlated over more than two orders of magnitude. The range of TIR translates to a range of far ultraviolet (FUV) emission of G_0,obs_~2 to 200 in units of the average Galactic radiation field. The binned [CII]/TIR ratio drops with rising TIR, with large, but decreasing scatter. The contribution of the cold neutral medium to the [CII] emission, as estimated from VLA HI data, is on average only 10%. Fits of modified black bodies (MBBs) to the continuum emission were used to estimate dust mass surface densities and total gas column densities. A correction for possible foreground absorption by cold gas was applied to the [OI] data before comparing it with models of photon dominated regions (PDRs). Most of the ratios of [CII]/[OI] and ([CII]+[OI])/TIR are consistent with two model solutions. The median ratios are consistent with one solution at n~2x10^2^cm^-3^, G_0_~60, and and a second low-FUV solution at n~10^4^cm^-3^, G_0_~1.5. The bulk of the gas along the lines-of-sight is represented by a low-density, high-FUV phase with low beam filling factors ~1. A fraction of the gas may, however, be represented by the second solution.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/53
- Title:
- IR dark clouds parameters in molecular clouds
- Short Name:
- J/ApJ/897/53
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- Ever since their discovery, infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbor HM young stellar objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to readdress the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated with a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The cataloged positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319M{odot}/pc^2^, mean mass of 1062M{odot}, and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to HM young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often-used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty-five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100M{odot}.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A22
- Title:
- IRDCs cores spectra of HCN and HNC isotopologue
- Short Name:
- J/A+A/603/A22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the measurement of nitrogen fractionation in a sample of infrared-dark clouds (IRDCs) cores which are believed to be the precursors of high-mass stars and star clusters. We observed the J=1-0 transitions of HCN, H^13/^CN, HC^15/^N, HN^13/^C, and H^15/^NC towards a sample of 22 cores in four IRDCs using the IRAM 30m telescope.Assuming LTE and a temperature of 15K, the 14N/^15/^N ratios measured are consistent with the terrestrial atmosphere(TA) and protosolar nebula(PSN) values, and with the ratios measured in low-mass prestellar cores. However, the 14N/^15/^N ratios measured in cores C1, C3, F1, F2, and G2 do not agree with the results from similar studies towards the same cores using nitrogen bearing molecules with nitrile functional group(-CN) and nitrogen hydrides (-NH) although the ratio spread covers a similar range. Relatively low 14N/^15/^N ratios amongst the four-IRDCs were measured in IRDC G which are comparable to those measured in small cosmomaterials and protoplanetary disks. The low average gas density of this cloud suggests that the gas density, rather than the gas temperature, may be the dominant parameter influencing the initial nitrogen isotopic composition in young PSN.
- ID:
- ivo://CDS.VizieR/J/ApJ/694/546
- Title:
- IR dust bubbles. II. YSOs model parameters
- Short Name:
- J/ApJ/694/546
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of late-O/early-B-powered, parsec-sized bubbles and associated star formation using Two Micron All Sky Survey, GLIMPSE, MIPSGAL, and MAGPIS surveys. Three bubbles were selected from the Churchwell et al. catalog (2007, Cat. J/ApJ/670/428). We confirm that the structure identified in Watson et al. (2008ApJ...681.1341W) holds in less energetic bubbles, i.e., a photodissociated region, identified by 8um emission due to polycyclic aromatic hydrocarbons surrounding hot dust, identified by 24um emission and ionized gas, and identified by 20cm continuum. We estimate the dynamical age of two bubbles by comparing bubble sizes to numerical models of Hosokawa and Inutsuka. We also identify and analyze candidate young stellar objects using spectral energy distribution (SED) fitting and identify sites of possible triggered star formation. Lastly, we identify likely ionizing sources for two sources based on SED fitting.
- ID:
- ivo://CDS.VizieR/J/ApJ/670/1115
- Title:
- IRS spectra at 38 positions in Galactic center
- Short Name:
- J/ApJ/670/1115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Spitzer IRS spectra (R~600, 10-38um) of 38 positions in the Galactic center, all at the same Galactic longitude and spanning +/-0.3{deg} in latitude. Our positions include the Arches Cluster, the Arched Filaments, regions near the Quintuplet Cluster, the "Bubble" lying along the same line of sight as the molecular cloud G0.11-0.11, and the diffuse interstellar gas along the line of sight at higher Galactic latitudes.
- ID:
- ivo://CDS.VizieR/J/A+A/392/239
- Title:
- IR survey of outflows in Orion A
- Short Name:
- J/A+A/392/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made an unbiased imaging survey of a 1.2 square degree area in the Orion A giant molecular cloud searching for molecular hydrogen emission line features seen in the v=1-0 S(1) line at a wavelength of 2.12{mu}m originating in shocks in outflows from young stellar objects. This survey provides for the first time an unbiased census of outflows over a significant portion of a giant molecular cloud, and yields a sample of outflows free from selection effects and with all objects located at roughly the same, well-known distance. In this paper, we present the data gathered in the course of the survey, provide a comprehensive list of all molecular hydrogen emission features found, and give a list of the 76 candidate outflows identified in the data set.
- ID:
- ivo://CDS.VizieR/J/ApJ/606/929
- Title:
- IR to mm observations of IRAS 18317-0757
- Short Name:
- J/ApJ/606/929
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution, multiwavelength-continuum, and molecular-line images of the massive star forming region IRAS 18317-0757. The global infrared through millimeter spectral energy distribution can be approximated by a two-temperature model (25 and 63K) with a total luminosity of approximately log(L/L_{sun}_)=5.2. Previous submillimeter imaging resolved this region into a cluster of five dust cores, one of which is associated with the ultracompact HII region G23.955+0.150, and another with a water maser. In our new 2.7mm continuum image obtained with BIMA, only the UCHII region is detected, with total flux and morphology in good agreement with the free-free emission in the VLA centimeter-wave maps. For the other four objects, the nondetections at 2.7mm and in the MSX mid-infrared bands are consistent with cool dust emission with a temperature of 13-40K and a luminosity of 1000-40000L_{sun}_. By combining single-dish and interferometric data, we have identified over two dozen virialized C^18^O cores in this region that contain ~40% of the total molecular gas mass present.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A61
- Title:
- Isolated starless cores dust temperature
- Short Name:
- J/A+A/592/A61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Constraining the temperature and density structure of dense molecular cloud cores is fundamental for understanding the initial conditions of star formation. We use Herschel observations of the thermal FIR dust emission from nearby isolated molecular cloud cores and combine them with ground-based submillimeter continuum data to derive observational constraints on their temperature and density structure. The aim of this study is to verify the validity of a ray-tracing inversion technique developed to derive the dust temperature and density structure of isolated starless cores directly from the dust emission maps and to test if the resulting temperature and density profiles are consistent with physical models. Using this ray-tracing inversion technique, we derive the dust temperature and density structure of six isolated starless cloud cores. We employ self-consistent radiative transfer modeling to the derived density profiles, treating the ISRF as the only heating source. The best-fit values of local strength of the ISRF and the extinction by the outer envelope are derived by comparing the self-consistently calculated temperature profiles with those derived by the ray-tracing method. We find that all starless cores are significantly colder inside than outside, with the core temperatures showing a strong negative correlation with peak column density. This suggests that their thermal structure is dominated by external heating from the ISRF and shielding by dusty envelopes. The temperature profiles derived with the ray-tracing inversion method can be well-reproduced with self-consistent radiative transfer models.
