- ID:
- ivo://CDS.VizieR/J/A+A/636/A2
- Title:
- HII regions detected in absorption
- Short Name:
- J/A+A/636/A2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Cosmic rays (CRs) and the Galactic magnetic field (GMF) are fundamental actors in many processes in the Milky Way. The observed interaction product of these actors is Galactic synchrotron emission integrated over the line of sight (LOS). A comparison to simulations can be made with this tracer using existing GMF models and CR density models. This probes the GMF strength and morphology and the CR density. Our aim is to provide insight into the Galactic CR density and the distribution and morphology of the GMF strength by exploring and explaining the differences between the simulations and observations of synchrotron intensity. At low radio frequencies HII regions become opaque due to free-free absorption. Using these HII regions we can measure the synchrotron intensity over a part of the LOS through the Galaxy. The measured intensity per unit path length, that is, the emissivity, for HII regions at different distances, allows us to probe the variation in synchrotron emission not only across the sky but also in the third dimension of distance. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using a number of existing GMF models in conjunction with the Galactic CR modeling code GALPROP, we can simulate these synchrotron emissivities. We present an updated catalog, compiled from the literature, of low-frequency absorption measurements of HII regions, their distances, and electron temperatures. We report a simulated emissivity that shows a compatible trend for HII regions that are near the observer. However, we observe a systematically increasing synchrotron emissivity for HII regions that are far from the observer, which is not compatible with the values simulated by the GMF models and GALPROP. Current GMF models plus a GALPROP generated CR density model cannot explain low-frequency absorption measurements. One possibility is that distances to all HII regions catalogued at the kinematic "far" distance are erroneously determined, although this is unlikely since it ignores all evidence for far distances in the literature. However, a detection bias due to the nature of this tracer requires us to keep in mind that certain sources may be missed in an observation. The other possibilities are an enhanced emissivity in the outer Galaxy or a diminished emissivity in the inner Galaxy.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/578/A93
- Title:
- IC 342 multi-frequency radio polarization study
- Short Name:
- J/A+A/578/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields play an important role in the formation and stabilization of spiral structures in galaxies, but the interaction between interstellar gas and magnetic fields has not yet been understood. In particular, the phenomenon of "magnetic arms" located between material arms is a mystery. The strength and structure of interstellar magnetic fields and their relation to spiral arms in gas and dust are investigated in the nearby and almost face-on spiral galaxy IC 342.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A72
- Title:
- Intermediate-mass T Tau stars spectra
- Short Name:
- J/A+A/622/A72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The origin of the fossil magnetic fields detected in 5 to 10% of intermediate-mass main sequence stars is still highly debated. We want to bring observational constraints to a large population of intermediate-mass pre-main sequence (PMS) stars in order to test the theory that convective-dynamo fields generated during the PMS phases of stellar evolution can occasionally relax into fossil fields on the main sequence. Using distance estimations, photometric measurements, and spectropolarimetric data from HARPSpol and ESPaDOnS of 38 intermediate-mass PMS stars, we determined fundamental stellar parameters (T_eff_, L and vsini) and measured surface magnetic field characteristics (including detection limits for non-detections, and longitudinal fields and basic topologies for positive detections). Using PMS evolutionary models, we determined the mass, radius, and internal structure of these stars. We compared different PMS models to check that our determinations were not model- dependant. We then compared the magnetic characteristics of our sample accounting for their stellar parameters and internal structures. Results: We detect magnetic fields in about half of our sample. About 90% of the magnetic stars have outer convective envelopes larger than ~25% of the stellar radii, and heavier than ~2% of the stellar mass. Going to higher mass, we find that the magnetic incidence in intermediate-mass stars drops very quickly, within a time-scale of the order of few times 0.1Myr. Finally, we propose that intermediate-mass T Tauri stars with large convective envelopes, close to the fully convective limit, have complex fields and that their dipole component strengths may decrease as the sizes of their convective envelopes decrease, similar to lower-mass T Tauri stars.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A154
- Title:
- IRAS 15398-3359 polarization maps
- Short Name:
- J/A+A/631/A154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Magnetic fields can significantly affect the star formation process. The theory of the magnetically driven collapse in a uniform field predicts that the contraction initially happens along the field lines. When the gravitational pull grows strong enough, the magnetic field lines pinch inwards, giving rise to a characteristic hourglass shape. We investigate the magnetic field structure of a young Class 0 object, IRAS 15398-3359, embedded in the Lupus I cloud. Previous observations at large scales have suggested that this source evolved in an highly magnetised environment. This object thus appears to be an ideal candidate to study the magnetically driven core collapse in the low-mass regime. We performed polarisation observations of IRAS 15398-3359 at 214um using the SOFIA telescope, thus tracing the linearly polarised thermal emission of cold dust. Our data unveil a significant bend of the magnetic field lines from the gravitational pull. The magnetic field appears ordered and aligned with the large-scale B-field of the cloud and with the outflow direction. We estimate a magnetic field strength of B=78uG, which is expected to be accurate within a factor of two. The measured mass-to-flux parameter is {lambda}=0.95, indicating that the core is in a transcritical regime.
- ID:
- ivo://CDS.VizieR/J/ApJ/836/199
- Title:
- IRDC G028.23-00.19 NIR polarimetry analysis
- Short Name:
- J/ApJ/836/199
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The importance of the magnetic (B) field in the formation of infrared dark clouds (IRDCs) and massive stars is an ongoing topic of investigation. We studied the plane-of-sky B field for one IRDC, G028.23-00.19, to understand the interaction between the field and the cloud. We used near-IR background starlight polarimetry to probe the B field and performed several observational tests to assess the field importance. The polarimetric data, taken with the Mimir instrument, consisted of H-band and K-band observations, totaling 17160 stellar measurements. We traced the plane-of-sky B-field morphology with respect to the sky-projected cloud elongation. We also found the relationship between the estimated B-field strength and gas volume density, and we computed estimates of the normalized mass-to-magnetic flux ratio. The B-field orientation with respect to the cloud did not show a preferred alignment, but it did exhibit a large-scale pattern. The plane-of-sky B-field strengths ranged from 10 to 165{mu}G, and the B-field strength dependence on density followed a power law with an index consistent with 2/3. The mass-to-magnetic flux ratio also increased as a function of density. The relative orientations and relationship between the B field and density imply that the B field was not dynamically important in the formation of the IRDC. The increase in mass-to-flux ratio as a function of density, though, indicates a dynamically important B field. Therefore, it is unclear whether the B field influenced the formation of G28.23. However, it is likely that the presence of the IRDC changed the local B-field morphology.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/112
- Title:
- IR polarization data in the BN region
- Short Name:
- J/ApJ/741/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New visible and K-band polarization measurements of stars surrounding molecular clouds in Orion A and stars in the Becklin-Neugebauer (BN) vicinity are presented. Our results confirm that magnetic fields located inside the Orion A molecular clouds and in their close neighborhood are spatially connected. On and around the BN object, we measured the angular offsets between the K-band polarization data and available submillimeter (submm) data. We find high values of the polarization degree, P_K_, and of the optical depth, {tau}_K_, close to an angular offset position of 90{deg} whereas lower values of P_K_ and {tau}_K_ are observed for smaller angular offsets. We interpret these results as evidence for the presence of various magnetic field components toward lines of sight in the vicinity of BN. On a larger scale, we measured the distribution of angular offsets between available H-band polarization data and the same submm data set. Here we find an increase of <P_H_> with angular offset, which we interpret as a rotation of the magnetic field by <~60{deg}. This trend generalizes previous results on small scales toward and around lines of sight to BN and is consistent with a twist of the magnetic field on a larger scale toward OMC-1. A comparison of our results with several other studies suggests that a two-component magnetic field, perhaps helical, could be wrapping the OMC-1 filament.
- ID:
- ivo://gov.nasa.gsfc.nssdc/SPMS-00560
- Title:
- ISEE-1 Energetic Ion Mass Spectrometer Data
- Short Name:
- ISEE Ion Data
- Date:
- 27 Apr 2006 17:05:46
- Publisher:
- NASA
- Description:
- Ion data from the Plasma Composition Experiment on ISEE-1 consist of a combination of (a) velocity moments for the four principal magnetospheric ion species H+, He++, He+, and O+, calculated in two different ways (using two different sets of assumptions) and covering the 0.01-0.1 and 0.1-16 keV/e energy ranges, (b) energy-angle spectra for the same four ions plus O++, covering the 0.01-17.9 keV/e range, and (c) mass spectra (<1 amu/e to about 150 amu/e) for four energy ranges, all derived once per each complete energy-mass scan cycle of the instrument, or once each 1- to 20-minute interval, depending on mode of operation, as well as (d) "total ion" moments, derived once per energy scan and assuming total count rate is due to H+ ions (0.1-16 keV).
- ID:
- ivo://CDS.VizieR/J/A+A/420/507
- Title:
- Isolated massive white dwarfs catalog
- Short Name:
- J/A+A/420/507
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalogue of 112 massive isolated white dwarfs, both magnetic and nonmagnetic, with masses M>0.8M_{sun}_. Mass determinations and other parameters of white dwarfs were compiled from the available literature.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/39
- Title:
- Jet properties of {gamma}-ray-loud 3FGL AGNs
- Short Name:
- J/ApJS/235/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on broadband spectral energy distributions (SEDs), we estimate the jet physical parameters of 1392 {gamma}-ray-loud active galactic nuclei (AGNs), the largest sample so far. The (SED) jet power and magnetization parameter are derived for these AGNs. Out of these sources, the accretion disk luminosity of 232 sources and (extended) kinetic jet powers of 159 sources are compiled from archived papers. We find the following. (1) Flat-spectrum radio quasars (FSRQs) and BL Lacs are well separated by {Gamma}=-0.127logL_{gamma}_+8.18 in the {gamma}-ray luminosity versus photon index plane with a success rate of 88.6%. (2) Most FSRQs present a (SED) jet power larger than the accretion power, which suggests that the relativistic jet-launching mechanism is dominated by the Blandford-Znajek process. This result confirms previous findings. (3) There is a significant anticorrelation between jet magnetization and a ratio of the (SED) jet power to the (extended) kinetic jet power, which, for the first time, provides supporting evidence for the jet energy transportation theory: a high- magnetization jet may more easily transport energy to a large scale than a low-magnetization jet.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/215
- Title:
- JVLA rotation measures of Smith cloud bckg sources
- Short Name:
- J/ApJ/871/215
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Smith Cloud is a high-velocity cloud with an orbit suggesting it has made at least one passage through the Milky Way disk. A magnetic field found around this cloud has been thought to provide extra stability as it passes through the Galactic halo. We use the Karl G. Jansky Very Large Array to measure Faraday rotation measures (RMs) toward 1105 extragalactic background point sources behind and next to the Smith Cloud to constrain the detailed geometry and strength of its magnetic field. The RM pattern across the cloud gives the detailed morphology of the magnetic field structure, which indicates a field draped over the ionized gas and compressed at the head of the cloud. We constrain the peak line-of-sight magnetic field strength to >~+5{mu}G and create a model of the magnetic field to demonstrate that a draped configuration can qualitatively explain the morphology of the observed RMs.
