- ID:
- ivo://CDS.VizieR/J/A+A/643/A48
- Title:
- Linking ice and gas. Serpens SVS4
- Short Name:
- J/A+A/643/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interaction between dust, ice, and gas during the formation of stars produces complex organic molecules. While observations indicate that several species are formed on ice-covered dust grains and are released into the gas phase, the exact chemical interplay between solid and gas phases and their relative importance remain unclear. Our goal is to study the interplay between dust, ice, and gas in regions of low-mass star formation through ice- and gas- mapping and by directly measuring gas-to-ice ratios. This provides constraints on the routes that lead to the chemical complexity that is observed in solid and gas phases. We present observations of gas-phase methanol (CH_3_OH) and carbon monoxide (^13^CO and C^18^O) at 1.3mm towards ten low-mass young protostars in the Serpens SVS4 cluster from the SubMillimeter Array (SMA) and the Atacama Pathfinder EXperiment (APEX) telescope. We used archival data from the Very Large Telescope (VLT) to derive abundances of ice H_2_O, CO, and CH_3_OH towards the same region. Finally, we constructed gas-ice maps of SVS4 and directly measured CO and CH_3_OH gas-to-ice ratios. The SVS4 cluster is characterised by a global temperature of 15+/-5K. At this temperature, the chemical behaviours of CH_3_OH and CO are anti-correlated: larger variations are observed for CH_3_OH gas than for CH_3_OH ice, whereas the opposite is seen for CO. The gas-to-ice ratios (N_gas_/N_ice_) range from 1-6 for CO and 1.4x10^-4^-3.7x10^-3^for CH_3_OH. The CO gas-maps trace an extended gaseous component that is not sensitive to the effect of freeze-out. Because of temperature variations and dust heating around 20K, the frozen CO is efficiently desorbed. The CH_3_OH gas-maps, in contrast, probe regions where methanol is predominantly formed and present in ices and is released into the gas phase through non-thermal desorption mechanisms. Combining gas- and ice-mapping techniques, we measure gas-to-ice ratios of CO and CH_3_OH in the SVS4 cluster. The CH_3_OH gas-to-ice ratio agrees with values that were previously reported for embedded Class 0/I low-mass protostars. We find that there is no straightforward correlation between CO and CH_3_OH gas with their ice counterparts in the cluster. This is likely related to the complex morphology of SVS4: the Class 0 protostar SMM4 and its envelope lie in the vicinity, and the outflow associated with SMM4 intersects the cluster. This study serves as a pathfinder for future observations with ALMA and the James Webb Space Telescope (JWST) that will provide high-sensitivity gas-ice maps of molecules more complex than methanol. Such comparative maps will be essential to constrain the chemical routes that regulate the chemical complexity in star-forming regions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/160/66
- Title:
- LITTLE THINGS catalog of HI holes in 41 galaxies
- Short Name:
- J/AJ/160/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of holes and shells in the neutral atomic hydrogen (HI) of 41 gas-rich dwarf galaxies in LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey). We analyzed their properties as part of an investigation into the relation between star formation and structures and kinematics in the HI of small galaxies. We confirmed 306 holes between 38pc (our resolution limit) and 2.3kpc, with expansion velocities up to 30km/s. The global star formation rates (SFRs) measured by H{alpha} and far-UV (FUV) emission are consistent with those estimated from the energy required to create the cataloged holes in our sample. Although we found no obvious correlation between global star forming regions (SFRs) and the HI surface and volume porosities of our sample, two of the four galaxies with the lowest porosity and the two galaxies with the highest porosity have no recent star formation as measured by H{alpha} and FUV emission.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A62
- Title:
- 4 LMC SFRs velocity profile maps
- Short Name:
- J/A+A/621/A62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of our study is to investigate the physical properties of the star-forming interstellar medium (ISM) in the Large Magellanic Cloud (LMC) by separating the origin of the emission lines spatially and spectrally. The LMC provides a unique local template to bridge studies in the Galaxy and high redshift galaxies because of its low metallicity and proximity, enabling us to study the detailed physics of the ISM in spatially resolved individual star-forming regions. Following Okada et al. (2015A&A...580A..54O), we investigate different phases of the ISM traced by carbon-bearing species in four star-forming regions in the LMC, and model the physical properties using the KOSMA-{tau} PDR model. We mapped 3-13 arcmin^2^ areas in 30 Dor, N158, N160, and N159 along the molecular ridge of the LMC in [C II] 158 {mu}m with GREAT on board SOFIA. We also observed the same area with CO(2-1) to (6-5), ^13^CO(2-1) and (3-2), [C I] ^3^P_1_-^3^P_0_ and ^3^P_2_-^3^P_1_ with APEX. For selected positions in N159 and 30 Dor, we observed [O I] 145 {mu}m and [O I] 63 {mu}m with upGREAT. All spectra are velocity resolved. In all four star-forming regions, the line profiles of CO, ^13^CO, and [C I] emission are similar, being reproduced by a combination of Gaussian profiles defined by CO(3-2), whereas [C II] typically shows wider line profiles or an additional velocity component. At several positions in N159 and 30 Dor, we observed the velocity-resolved [O I] 145 and 63 {mu}m lines for the first time. At some positions, the [O I] line profiles match those of CO, at other positions they are more similar to the [C II] profiles. We interpret the different line profiles of CO, [C II] and [O I] as contributions from spatially separated clouds and/or clouds in different physical phases, which give different line ratios depending on their physical properties. We modeled the emission from the CO, [C I], [C II], and [O I] lines and the far-infrared continuum emission using the latest KOSMA-{tau} PDR model, which treats the dust-related physics consistently and computes the dust continuum SED together with the line emission of the chemical species. We find that the line and continuum emissions are not well-reproduced by a single clump ensemble. Toward the CO peak at N159 W, we propose a scenario that the CO, [C II], and [O I] 63 {mu}m emission are weaker than expected because of mutual shielding among clumps.
- ID:
- ivo://CDS.VizieR/J/MNRAS/483/299
- Title:
- Local Bubble & Gould Belt polarization
- Short Name:
- J/MNRAS/483/299
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We create and analyse the largest up-to-date all-sky compilation of the interstellar optical polarization data supplemented by the reddening data This compilation includes 13 data sources with optical interstellar linear polarization for 3871 Gaia DR2 and Hipparcos stars within 500pc, which do not exhibit a considerable intrinsic polarization. These data are analysed together with five 3D maps and models of the reddening E(B-V). We consider variations of the polarization degree P, position angle theta, and polarization efficiency P/E(B-V) with Galactic coordinates, distance R, and dereddened colour. P shows a maximum at the Gould Belt mid-plane. P/R drops in the Local Bubble by several times defining a boundary of the Bubble at P=0.1 per cent. All the data sources of the reddening, except Lallement et al., show a drop of P/E(B-V) in the Bubble. The spatial- and colour-dependent variations of P and E(B-V) outside the Bubble compensate each other, resulting in a nearly constant P/E(B-V). A giant envelope of aligned dust dominates at middle and high latitudes outside the Bubble. The Markkanen's cloud, the North Polar Spur, and some other filaments are parts of this envelope.
- ID:
- ivo://CDS.VizieR/J/ApJ/840/115
- Title:
- Local interstellar spectra of cosmic-ray species
- Short Name:
- J/ApJ/840/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Local interstellar spectra (LIS) for protons, helium, and antiprotons are built using the most recent experimental results combined with state-of-the-art models for propagation in the Galaxy and heliosphere. Two propagation packages, GALPROP and HelMod, are combined to provide a single framework that is run to reproduce direct measurements of cosmic-ray (CR) species at different modulation levels and at both polarities of the solar magnetic field. To do so in a self-consistent way, an iterative procedure was developed, where the GALPROP LIS output is fed into HelMod, providing modulated spectra for specific time periods of selected experiments to compare with the data; the HelMod parameter optimization is performed at this stage and looped back to adjust the LIS using the new GALPROP run. The parameters were tuned with the maximum likelihood procedure using an extensive data set of proton spectra from 1997 to 2015. The proposed LIS accommodate both the low-energy interstellar CR spectra measured by Voyager 1 and the high-energy observations by BESS, Pamela, AMS-01, and AMS-02 made from the balloons and near-Earth payloads; it also accounts for Ulysses counting rate features measured out of the ecliptic plane. The found solution is in a good agreement with proton, helium, and antiproton data by AMS-02, BESS, and PAMELA in the whole energy range.
- ID:
- ivo://CDS.VizieR/J/A+A/591/A134
- Title:
- LOFAR census of non-recycled pulsars
- Short Name:
- J/A+A/591/A134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results from a LOFAR census of non-recycled pulsars. The census includes almost all such pulsars known (194 sources) at declinations Dec>8{deg} and Galactic latitudes |Gb|>3{deg}, regardless of their expected flux densities and scattering times. Each pulsar was observed for >=20minutes in the contiguous frequency range of 110-188MHz. Full-Stokes data were recorded. We present the dispersion measures, flux densities, and calibrated total intensity profiles for the 158 pulsars detected in the sample. The median uncertainty in census dispersion measures (1.5x10^-3^pc/cm^3^) is ten times smaller, on average, than in the ATNF pulsar catalogue. We combined census flux densities with those in the literature and fitted the resulting broadband spectra with single or broken power-law functions. For 48 census pulsars such fits are being published for the first time. Typically, the choice between single and broken power-laws, as well as the location of the spectral break, were highly influenced by the spectral coverage of the available flux density measurements. In particular, the inclusion of measurements below 100MHz appears essential for investigating the low-frequency turnover in the spectra for most of the census pulsars. For several pulsars, we compared the spectral indices from different works and found the typical spread of values to be within 0.5-1.5, suggesting a prevailing underestimation of spectral index errors in the literature. The census observations yielded some unexpected individual source results, as we describe in the paper. Lastly, we will provide this unique sample of wide-band, low-frequency pulse profiles via the European Pulsar Network Database.
- ID:
- ivo://CDS.VizieR/J/A+A/635/A75
- Title:
- LOFAR census of non-recycled pulsars sample
- Short Name:
- J/A+A/635/A75
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results from the low-frequency (40-78MHz) extension of the first pulsar census of non-recycled pulsars carried out with the LOw-Frequency ARray (LOFAR). We used the low-band antennas of the LOFAR core stations to observe 87 pulsars out of 158 that had been previously detected using high-band antennas. We present flux densities and flux-calibrated profiles for the 43 pulsars we detected. Of this sample, 17 have not, to our knowledge, previously been detected at such low frequencies. Here we recalculate the spectral indices using the new low-frequency flux density measurements from the LOFAR census and discuss the prospects of studying pulsars at very low frequencies using current and upcoming facilities, such as the New Extension in Nancay Upgrading LOFAR (NenuFAR).
- ID:
- ivo://CDS.VizieR/J/A+A/583/A137
- Title:
- LOFAR-HBA 3C196 field RM cubes
- Short Name:
- J/A+A/583/A137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) in the 3C196 field, one of the primary fields of the LOFAR-Epoch of Reionization key science project. We have used the high band antennas (HBA) of LOFAR to image this region and Rotation Measure (RM) synthesis to unravel the distribution of polarized structures in Faraday depth. The brightness temperature of the detected Galactic emission is 5-15K in polarized intensity and covers the range from -3 to +8 rad/m^2^ in Faraday depth. The most interesting morphological feature is a strikingly straight filament at a Faraday depth of +0.5 rad/m^2^ running from north to south, right through the centre of the field and parallel to the Galactic plane. There is also an interesting system of linear depolarization canals conspicuous in an image showing the peaks of Faraday spectra. We used the Westerbork Synthesis Radio Telescope (WSRT) at 350MHz to image the same region. For the first time, we see some common morphology in the RM cubes made at 150 and 350MHz. There is no indication of diffuse emission in total intensity in the interferometric data, in line with results at higher frequencies and previous LOFAR observations. Based on our results, we determined physical parameters of the ISM and proposed a simple model that may explain the observed distribution of the intervening magneto-ionic medium. The mean line-of-sight magnetic field component is determined to be 0.3-/+0.1uG and its spatial variation across the 3C196 field is 0.1uG. The filamentary structure is probably an ionized filament in the ISM, located somewhere within the Local Bubble. This filamentary structure shows an excess in thermal electron density (n_e_*B_||_>6.2cm^-3^uG) compared to its surroundings.
- ID:
- ivo://CDS.VizieR/J/AJ/152/36
- Title:
- Low-mass star-forming cores observed with SHARC-II
- Short Name:
- J/AJ/152/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of low-mass dense cores observed with the SHARC-II instrument at 350{mu}m. Our observations have an effective angular resolution of 10'', approximately 2.5 times higher than observations at the same wavelength obtained with the Herschel Space Observatory, albeit with lower sensitivity, especially to extended emission. The catalog includes 81 maps covering a total of 164 detected sources. For each detected source, we tabulate basic source properties including position, peak intensity, flux density in fixed apertures, and radius. We examine the uncertainties in the pointing model applied to all SHARC-II data and conservatively find that the model corrections are good to within ~3'', approximately 1/3 of the SHARC-II beam. We examine the differences between two array scan modes and find that the instrument calibration, beam size, and beam shape are similar between the two modes. We also show that the same flux densities are measured when sources are observed in the two different modes, indicating that there are no systematic effects introduced into our catalog by utilizing two different scan patterns during the course of taking observations. We find a detection rate of 95% for protostellar cores but only 45% for starless cores, and demonstrate the existence of a SHARC-II detection bias against all but the most massive and compact starless cores. Finally, we discuss the improvements in protostellar classification enabled by these 350{mu}m observations.
- ID:
- ivo://CDS.VizieR/J/PASJ/65/119
- Title:
- Low-resolution NIR spectra of zodiacal light
- Short Name:
- J/PASJ/65/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog contains the 278 low-resolution (R~20) near-infrared (1.8-5.3micron) spectra of diffuse sky covering a wide range of galactic and ecliptic latitudes with the Infrared Camera (IRC) on board AKARI before the exhaustion of liquid-helium (from September 2006 to May 2007). Advanced reduction methods specialized for the slit spectroscopy of diffuse sky spectra are developed for constructing this spectral catalog. Filter wheel of the IRC instrument has dark position to measure the dark current, and uncertainty due to dark current subtraction is estimated to be <3nW/m2/sr at 2micron (Tsumura & Wada, 2011PASJ...63..755T). Point sources brighter than mK(Vega)=19 were detected on the slit and masked for deriving the diffuse spectrum. It was confirmed that the brightness due to unresolved galactic stars under this detection limit is negligible (<0.5% of the sky brightness at 2.2 micron) by a Milky Way star count model (TRILEGAL; Girardi et al., 2005A&A...436..895G). Cumulative brightness contributed by unresolved galaxies can be estimated by the deep galaxy counts, being <4nW/m2/sr at K band in the case of limiting magnitude of mK=19 (Keenan et al., 2010ApJ...723...40K).
