- ID:
- ivo://CDS.VizieR/J/A+A/597/A98
- Title:
- Faraday tomography of foreground towards IC342
- Short Name:
- J/A+A/597/A98
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields pervade the interstellar medium (ISM), but are difficult to detect and characterize. The new generation of low-frequency radio telescopes, such as the Low Frequency Array (LOFAR: a Square Kilometre Array-low pathfinder), provides advancements in our capability of probing Galactic magnetism through low-frequency polarimetry. Maps of diffuse polarized radio emission and the associated Faraday rotation can be used to infer properties of, and trace structure in, the magnetic fields in the ISM. However, to date very little of the sky has been probed at high angular and Faraday depth resolution. We observed a 5 by 5 degree region centred on the nearby galaxy IC 342 (l=138.2, b=+10.6) using the LOFAR High Band Antennas in the frequency range 115-178MHz. We imaged this region at 4.5x3.8arcmin^2^ resolution and performed Faraday tomography to detect foreground Galactic polarized synchrotron emission separated by Faraday depth (different amounts of Faraday rotation). Our Faraday depth cube shows rich polarized structure, with up to 30K of polarized emission at 150MHz. We clearly detect two polarized features that extend over most of the field but are clearly separated in Faraday depth. Simulations of the behaviour of the depolarization of Faraday-thick structures at such low frequencies show that such structures would be too strongly depolarized to explain the observations. These structures are therefore rejected as the source of the observed polarized features. Only Faraday thin structures will not be strongly depolarized at low frequencies; producing such structures requires localized variations in the ratio of synchrotron emissivity to Faraday depth per unit distance. Such variations can arise from several physical phenomena, such as a transition between regions of ionized and (mostly) neutral gas. We conclude that the observed polarized emission is Faraday thin, and propose that the emission originates from two mostly neutral clouds in the local ISM. Using maps of the local ISM to estimate distances to these clouds, we have modelled the Faraday rotation for this line of sight and estimated that the strength of the line of sight component of magnetic field of the local ISM for this direction varies between -0.86 and +0.12uG (where positive is towards the Earth). We propose that this may be a useful method for mapping magnetic fields within the local ISM in all directions towards nearby neutral clouds.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/418/131
- Title:
- Far-infrared loops in the 2nd Galactic Quadrant
- Short Name:
- J/A+A/418/131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an investigation of the large structure of the diffuse interstellar medium in the 2nd Galactic Quadrant (90{deg}<=l<=180{deg}). 145 loops were identified on IRAS based on far-infrared maps. Our catalogue lists their basic physical properties. The distribution clearly suggests that there is an efficient process that can generate loop-like features at high galactic latitudes. Distances are provided for 30 loops. We also give an observational estimate on the volume filling factor of the hot gas in the Local Arm, 4.6%<=f_2nd_<6.4%.
- ID:
- ivo://CDS.VizieR/J/ApJ/714/1256
- Title:
- Far-IR star formation rate indicators
- Short Name:
- J/ApJ/714/1256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spitzer data at 24, 70, and 160um and ground-based H{alpha} images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160um. We compare recently published recipes for SFR measures using combinations of the 24um and observed H{alpha} luminosities with those using 24um luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70um and 160um luminosity are found for L(70)>~1.4x10^42^erg/s and L(160)>~2x10^42^erg/s, corresponding to SFR>~0.1-0.3M_{sun}_/yr, and calibrations of SFRs based on L(70) and L(160) are proposed. Below those two luminosity limits, the relation between SFR and 70um (160um) luminosity is nonlinear and SFR calibrations become problematic. A more important limitation is the dispersion of the data around the mean trend, which increases for increasing wavelength.
- ID:
- ivo://CDS.VizieR/J/ApJ/749/157
- Title:
- Far-UV spectra of Galactic corona sight lines
- Short Name:
- J/ApJ/749/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the properties of the transition temperature (T~10^5^K) gas in the Milky Way corona, based on the measurements of OVI, NV, CIV, SiIV, and FeIII absorption lines seen in the far-ultraviolet spectra of 58 sight lines to extragalactic targets, obtained with the Far-Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. In many sight lines the Galactic absorption profiles show multiple components, which are analyzed separately. We find that the highly ionized atoms are distributed irregularly in a layer with a scale height of about 3 kpc, which rotates along with the gas in the disk, without an obvious gradient in the rotation velocity away from the Galactic plane. Within this layer the gas has randomly oriented velocities with a dispersion of 40-60km/s. On average the integrated column densities are logN(OVI)=14.3, logN(NV)=13.5, logN(CIV)=14.2, logN(SiIV)=13.6, and logN(FeIII)=14.2, with a dispersion of just 0.2 dex in each case. In sight lines around the Galactic center and Galactic north pole, all column densities are enhanced by a factor ~2, while at intermediate latitudes in the southern sky there is a deficit in N(O VI) of about a factor of two, but no deficit for the other ions.
- ID:
- ivo://CDS.VizieR/J/A+A/606/A50
- Title:
- Fe-rich silicate analogues mass absorption coeff.
- Short Name:
- J/A+A/606/A50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To model the cold dust emission observed in the diffuse interstellar medium, in dense molecular clouds or in cold clumps that could eventually form new stars, it is mandatory to know the physical and spectroscopic properties of this dust and to understand its emission. This work is a continuation of previous studies aiming at providing astronomers with spectroscopic data of realistic cosmic dust analogues for the interpretation of observations. The aim of the present work is to extend the range of studied analogues to iron-rich silicate dust analogues. Ferromagnesium amorphous silicate dust analogues were produced by a sol-gel method with a mean composition close to Mg_1-x_Fe_x_SiO_3_ with x=0.1, 0.2, 0.3, 0.4. Part of each sample was annealed at 500{deg}C for two hours in a reducing atmosphere to modify the oxidation state of iron. We have measured the mass absorption coefficient (MAC) of these eight ferromagnesium amorphous silicate dust analogues in the spectral domain 30-1000um for grain temperature in the range 10-300K and at room temperature in the 5-40um range. The MAC of ferromagnesium samples behaves in the same way as the MAC of pure Mg-rich amorphous silicate samples. In the 30-300K range, the MAC increases with increasing grain temperature whereas in the range 10-30K, we do not see any change of the MAC. The MAC cannot be described by a single power law in {lambda}^-{beta}^. The MAC of the samples does not show any clear trend with the iron content. However the annealing process has, on average, an effect on the MAC that we explain by the evolution of the structure of the samples induced by the processing. The MAC of all the samples is much higher than the MAC calculated by dust models. The complex behavior of the MAC of amorphous silicates with wavelength and temperature is observed whatever the exact silicate composition (Mg vs. Fe amount). It is a universal characteristic of amorphous materials, and therefore of amorphous cosmic silicates, that should be taken into account in astronomical modeling. The enhanced MAC of the measured samples compared to the MAC calculated for cosmic dust model implies that dust masses are overestimated by the models.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/L2
- Title:
- First detection of HCOOH in TW Hya disk with ALMA
- Short Name:
- J/ApJ/862/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of asteroids, comets, and planets occurs in the interior of protoplanetary disks during the early phase of star formation. Consequently, the chemical composition of the disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the disk. In this Letter, we report the first detection of formic acid (HCOOH) toward the TW Hydrae protoplanetary disk. The observations of the trans-HCOOH 6_(1,6)-5(1,5)_ transition were carried out at 129GHz with Atacama Large Millimeter/Submillimeter Array (ALMA). We measured a disk-averaged gas-phase t-HCOOH column density of ~(2-4)x10^12^cm^-2^, namely as large as that of methanol. HCOOH is the first organic molecule containing two oxygen atoms detected in a protoplanetary disk, a proof that organic chemistry is very active, albeit difficult to observe, in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/4
- Title:
- First-look analysis of {rho} Oph-A at 850um
- Short Name:
- J/ApJ/859/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 850{mu}m imaging polarimetry data of the {rho} Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2) as part of our ongoing survey project, B-fields In STar forming RegiOns (BISTRO). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2pc {rho} Oph-A core; some of them can be part of a coherent magnetic field structure in the {rho} Oph region. The results are consistent with previous observations of the brightest regions of {rho} Oph-A, where the degrees of polarization are at a level of a few percent, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (>5%). A comparison with previous near-infrared polarimetric data shows that there are several magnetic field components that are consistent at near-infrared and submillimeter wavelengths. Using the Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in several subcore regions, which range from approximately 0.2 to 5mG. We also find a correlation between the magnetic field orientations projected on the sky and the core centroid velocity components.
- ID:
- ivo://CDS.VizieR/J/ApJS/196/12
- Title:
- First results from Mopra HCO^+^ maps
- Short Name:
- J/ApJS/196/12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Census of High- and Medium-mass Protostars (CHaMP) is the first large-scale, unbiased, uniform mapping survey at sub-parsec-scale resolution of 90GHz line emission from massive molecular clumps in the Milky Way. We present the first Mopra (ATNF) maps of the CHaMP survey region (300{deg}>l>280{deg}) in the HCO^+^J=1->0 line, which is usually thought to trace gas at densities up to 10^11^m^-3^. In this paper, we introduce the survey and its strategy, describe the observational and data reduction procedures, and give a complete catalog of moment maps of the HCO^+^J=1->0 emission from the ensemble of 303 massive molecular clumps. From these maps we also derive the physical parameters of the clumps, using standard molecular spectral-line analysis techniques.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A59
- Title:
- Fluctuations of UV background from GALEX
- Short Name:
- J/A+A/631/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The all sky survey run by the Galaxy Evolution Explorer (GALEX AIS) mapped about 85 % of the Galaxy at ultraviolet (UV) wavelengths and detected the diffuse UV background produced by the scattering of the radiation from OBA stars by interstellar dust grains. Against this background, diffuse weak structures are detected as well as the UV counterparts to nebulae and molecular clouds. To make full profit of the survey, unsupervised and semi-supervised procedures need to be implemented. The main objective of this work is to implement and analyze the results of the method developed by us for the blind detection of ISM features in the GALEX AIS. Most ISM features are detected at very low signal levels (dark filaments, globules) against the already faint UV background. We have defined an index the UV background fluctuations index (or UBF index) to identify areas of the sky where these fluctuations are detected. The algorithm is applied to the images obtained in the FUV (1344-1786{AA}) band since this is less polluted by stellar sources, facilitating the automated detection. The UBF index is shown to be sensitive to the main star forming regions within the Gould's Belt, as well as to some prominent loops like Loop I or the Eridanus and Monogem areas. The catalogue with the UBF index values is made available on-line to the community.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/57
- Title:
- Follow-up spectroscopy of Ly{alpha} 3<z<7 emitters
- Short Name:
- J/ApJ/815/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the relationship between the spectral shape of the Ly{alpha} emission and the UV morphology of the host galaxy using a sample of 304 Ly{alpha}-emitting BVi-dropouts at 3<z<7 in the Great Observatories Origins Deep Survey and Cosmic Evolution Survey fields. Using our extensive reservoir of high-quality Keck DEIMOS spectra combined with Hubble Space Telescope WFC3 data, we measure the Ly{alpha} line asymmetries for individual galaxies and compare them to axial ratios measured from observed J- and H-band (restframe UV) images. We find that the Ly{alpha} skewness exhibits a large scatter at small elongation (a/b<2), and this scatter decreases as the axial ratio increases. Comparison of this trend to radiative transfer models and various results from the literature suggests that these high-redshift Ly{alpha} emitters are not likely to be intrinsically round and symmetric disks, but they probably host galactic outflows traced by Ly{alpha} emitting clouds. The ionizing sources are centrally located, and the optical depth is a good indicator of the absorption and scattering events on the escape path of Ly{alpha} photons from the source. Our results find no evidence of evolution in Ly{alpha} asymmetry or axial ratio with look-back time.
