- ID:
- ivo://CDS.VizieR/J/MNRAS/510/6085
- Title:
- Magnetic field of Taurus/B211
- Short Name:
- J/MNRAS/510/6085
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Optical and infrared polarization mapping and recent Planck observations of the filamentary cloud L1495 in Taurus show that the large-scale magnetic field is approximately perpendicular to the long axis of the cloud. We use the HAWC+ polarimeter on SOFIA to probe the complex magnetic field in the B211 part of the cloud. Our results reveal a dispersion of polarization angles of 36{deg}, about five times that measured on a larger scale by Planck. Applying the Davis-Chandrasekhar-Fermi (DCF) method with velocity information obtained from IRAM 30m C^18^O(1-0) observations, we find two distinct sub-regions with magnetic field strengths differing by more than a factor 3. The quieter sub-region is magnetically critical and sub-Alfvenic; the field is comparable to the average field measured in molecular clumps based on Zeeman observations. The more chaotic, super-Alfvenic sub-region shows at least three velocity components, indicating interaction among multiple substructures. Its field is much less than the average Zeeman field in molecular clumps, suggesting that the DCF value of the field there may be an underestimate. Numerical simulation of filamentary cloud formation shows that filamentary substructures can strongly perturb the magnetic field. DCF and true field values in the simulation are compared. Pre-stellar cores are observed in B211 and are seen in our simulation. The appendices give a derivation of the standard DCF method that allows for a dispersion in polarization angles that is not small, present an alternate derivation of the structure function version of the DCF method, and treat fragmentation of filaments.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/385/1014
- Title:
- Magnetic field structure in W51A
- Short Name:
- J/A+A/385/1014
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 850{mu}m imaging polarimetry of the W51A massive star forming region performed with SCUBA on the James Clerk Maxwell Telescope (JCMT) situated close to the summit of Mauna Kea, Hawaii, on the night 6 October 2000. Positions, fluxes and polarimetry of the data points shown in Fig. 1 of the paper are reported in the file table2.dat. The positional offsets are given relative to W51d (19:23:39.0, +14:31:08, J2000). All fluxes (including the Stokes Q and U parameters) are given in units of Jy/beam. The position angles give the direction of the E-vector.
383. MALT90 pilot survey
- ID:
- ivo://CDS.VizieR/J/ApJS/197/25
- Title:
- MALT90 pilot survey
- Short Name:
- J/ApJS/197/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a pilot survey conducted with the Mopra 22m radio telescope in preparation for the Millimeter Astronomy Legacy Team Survey at 90GHz (MALT90). We identified 182 candidate dense molecular clumps using six different selection criteria and mapped each source simultaneously in 16 different lines near 90GHz. We present a summary of the data and describe how the results of the pilot survey shaped the design of the larger MALT90 survey. We motivate our selection of target sources for the main survey based on the pilot detection rates and demonstrate the value of mapping in multiple lines simultaneously at high spectral resolution.
- ID:
- ivo://CDS.VizieR/J/A+A/487/993
- Title:
- MAMBO Mapping of c2d Clouds and Cores
- Short Name:
- J/A+A/487/993
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present maps from our MAMBO 1.2mm wavelength dust emission survey of nearby (<500pc) dense starless and star-forming cores. This data was collected to study evolutionary trends among the dense cores and the associated young stellar objects. This survey was specifically designed to complement Spitzer Space Telescope imaging of these regions. The maps are unusually sensitive and rich in structure.
- ID:
- ivo://CDS.VizieR/J/A+A/626/A28
- Title:
- M8 and Her 36 C_2_H and c-C_3_H_2_ data
- Short Name:
- J/A+A/626/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydrocarbons are ubiquitous in the interstellar medium, but their formation is still not well understood, depending on the physical environment they are found in. Messier 8 (M8) is host to one of the brightest Hii regions and photodissociation regions (PDRs) in our galaxy. With the observed C_2_H and c-C_3_H_2_ data toward M8, we aim at obtaining their densities and abundances and to shed some light on their formation mechanism. Using the Atacama Pathfinder Experiment (APEX) 12m, and the Institut de Radioastronomie Millimetrique (IRAM) 30m telescopes, we performed a line survey toward Herschel 36 (Her 36), which is the main ionizing stellar system in M8, and an imaging survey within 1.3x1.3pc around Her 36 of various transitions of C_2_H and C_3_H_2_. We used both Local Thermodynamic Equilibrium (LTE) and non-LTE methods to determine the physical conditions of the emitting gas along with the column densities and abundances of the observed species, which we compared with (updated) gas phase photochemical PDR models. In order to examine the role of polycyclic aromatic hydrocarbons (PAHs) in the formation of small hydrocarbons and to investigate their association with the Hii region, the PDR and the molecular cloud, we compared archival Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) 8{mu}m and the Spectral and Photometric Imaging Receiver (SPIRE) 250{mu}m continuum images with the C_2_H emission maps. We observed a total of three rotational transitions of C_2_H with their hyperfine structure components and four rotational transitions of C_3_H_2_ with ortho and para symmetries toward the HII region and the PDR of M8. Fragmentation of PAHs seems less likely to contribute to the formation of small hydrocarbons as the 8 m emission does not follow the distribution of C_2_H emission, which is more associated with the molecular cloud toward the north-west of Her 36. From the quantitative analysis, we obtained abundances of 10^-8 ^and 10^-9^ for C_2_H and c-C_3_H_2_ respectively, and volume densities of the hydrocarbon emitting gas in the range n(H_2_)~5x10^4^-5x10^6^cm^-3^. The observed column densities of C_2_H and c-C_3_H_2_ are reproduced reasonably well by our PDR models. This supports the idea that in high-UV flux PDRs, gas phase chemistry is sufficient to explain hydrocarbon abundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/724/1389
- Title:
- Mapping the diffuse UV sky with GALEX
- Short Name:
- J/ApJ/724/1389
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a map of the diffuse ultraviolet cosmic background in two wavelength bands (FUV: 1530{AA} and NUV: 2310{AA}) over almost 75% of the sky using archival data from the Galaxy Evolution Explorer (GALEX) mission. Most of the diffuse flux is due to dust-scattered starlight and follows a cosecant law with slopes of 545 photons/cm^2^/s/sr/{AA} and 433 photons/cm^2^/s/sr/{AA} in the FUV and NUV bands, respectively. There is a strong correlation with the 100um Infrared Astronomy Satellite (IRAS) flux with an average UV/IR ratio of 300 photons/cm^2^/s/sr/{AA}/(MJy/sr) in the FUV band and that of 220 photons/cm^2^/s/sr/{AA}/(MJy/sr) in the NUV band but with significant variations over the sky. In addition to the large-scale distribution of the diffuse light, we note a number of individual features including bright spots around the hot stars Spica and Achernar.
- ID:
- ivo://CDS.VizieR/J/A+A/567/A116
- Title:
- Maps and datacubes of NGC 7538 IRS 1
- Short Name:
- J/A+A/567/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact HII regions, molecular outflows, and masers. In such a complex environment, interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces in the formation and evolution of high-mass star-forming clusters. Methods: We performed SMA high angular resolution observations at 880um with the compact configuration. We developed the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. To quantify the stability against gravitational collapse we developed the "mass balance" analysis that accounts for all the energetics on core scales. We detect 14 dust cores from 3.5M_{sun}_ to 37M_{sun}_ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large-scale velocity gradients in H^13^CO^+^ 4-3 and C^17^O 3-2, and magnetic field segments aligned well to the dust main axis. The velocity gradient is reproduced well by a spiral arm expanding at 9km/s with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable to the spiral-arm kinetic energy, which dominates gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. On core scales, those embedded in the central bar seem to be unstable against gravitational collapse and prone to forming high-mass stars, while those in the spiral arm have lower masses that seem to be supported by non-thermal motions and magnetic fields. The NGC 7538 IRS 1-3 cluster seems to be dominated by protostellar feedback. The dusty spiral arm appears to be formed in a snowplow fashion owing to the outflow from the MM1 core. We speculate that the external pressure from the redshifted lobe of the outflow could trigger star formation in the spiral arm cores. This scenario would form a small cluster with a few central high-mass stars, surrounded by a number of low-mass stars formed through protostellar feedback.
- ID:
- ivo://CDS.VizieR/J/MNRAS/459/2262
- Title:
- Maps of dust distribution in M31 bulge
- Short Name:
- J/MNRAS/459/2262
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We map the dust distribution in the central 180" (~680pc) region of the M31 bulge, based on HST WFC3 and ACS observations in ten bands from near-ultraviolet (2700{AA}) to near-infrared (1.5-micron). This large wavelength coverage gives us great leverage to detect not only dense dusty clumps, but also diffuse dusty molecular gas. We fit a pixel-by-pixel spectral energy distributions to construct a high-dynamic-range extinction map with unparalleled angular resolution (~0.5", i.e., ~2pc) and sensitivity (the extinction uncertainty, delta A_V_~0.05). In particular, the data allow to directly fit the fractions of starlight obscured by individual dusty clumps, and hence their radial distances in the bulge. Most of these clumps seem to be located in a thin plane, which is tilted with respect to the M31 disk and appears face-on. We convert the extinction map into a dust mass surface density map and compare it with that derived from the dust emission as observed by Herschel. The dust masses in these two maps are consistent with each other, except in the low-extinction regions, where the mass inferred from the extinction tends to be underestimated. Further, we use simulations to show that our method can be used to measure the masses of dusty clumps in Virgo cluster early-type galaxies to an accuracy within a factor of ~2.
- ID:
- ivo://CDS.VizieR/J/ApJ/689/108
- Title:
- MASIV survey. II. First four epochs
- Short Name:
- J/ApJ/689/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on the variability of 443 flat-spectrum, compact radio sources monitored using the VLA for 3 days in four epochs at ~4 month intervals at 5GHz as part of the Micro-Arcsecond Scintillation-Induced Variability (MASIV) survey. Over half of these sources exhibited 2%-10% rms variations on timescales over 2 days. We analyzed the variations by two independent methods and find that the rms variability amplitudes of the sources correlate with the emission measure in the ionized interstellar medium along their respective lines of sight. We thus link the variations with interstellar scintillation of components of these sources, with some (unknown) fraction of the total flux density contained within a compact region of angular diameter in the range 10-50{mu}as. We also find that the variations decrease for high mean flux density sources and, most importantly, for high-redshift sources. The decrease in variability is probably due either to an increase in the apparent diameter of the source or to a decrease in the flux density of the compact fraction beyond z~2.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/173
- Title:
- Masses of giant molecular clouds in Milky Way
- Short Name:
- J/ApJ/780/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using ^13^CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') ^13^CO J=1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200M_{sun}_/pc^2^, which are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin ^13^CO J=1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11^+0.12^_-0.06__. The high column density subregions comprise 0.07^+0.13^_-0.05_ of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4km/s for various flow configurations.
