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We present a novel technique for the decomposition of line-of-sight (LOS) stellar polarization as a function of distance, aimed at reconstructing 3D plane-of-sky magnetic structures in the interstellar medium. The method is based on the assumption that the observed polarization arises from discrete, thin dust layers located at varying distances along the LOS. Using a simple and intuitive frequentist framework, our method identifies structural changes in the distance-sorted cumulative Mahalanobis distance between Stokes parameters (qandu) to detect the locations of dust layers and estimates their associated physical properties (parallax and Stokes parameters) necessary for constructing 3D maps. We benchmarked the method using mock datasets representative of high-Galactic-latitude regions, incorporating realistic parallax uncertainties fromGaiaand expected polarization measurements from the upcoming PASIPHAEsurvey. Our tests show that the method reliably recovers the distances and polarization properties of dust clouds when the polarization signal exceeds 0.1%, and the effective fraction of background stars is greater than 10% in our tested samples with ∼345 stars. The effect of background star fraction on the performance becomes less critical with increasing amplitude of the polarization source field from the dust cloud. We applied our method to existing polarization data from two illustrative sight lines - one at intermediate-high Galactic latitude and one near the Galactic plane - with known tomographic solutions, finding excellent agreement with the literature and demonstrating its accuracy across both regions. We compare the performance of our method with that of the Bayesian method BISP-1. While both methods effectively recover dust cloud properties, our approach is prior-free and computationally more efficient in determining the optimal number of clouds along the LOS. These advantages make our method more flexible and broadly applicable for multilayer dust cloud reconstruction for the upcoming era of large-scale stellar polarization surveys.
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A compendium of distances to molecular clouds in the Star Formation Handbook
Accurate distances to local molecular clouds are critical for understanding the star and planet formation process, yet distance measurements are often obtained inhomogeneously on a cloud-by-cloud basis. We have recently developed a method that combines stellar photometric data with Gaia DR2 parallax measurements in a Bayesian framework to infer the distances of nearby dust clouds to a typical accuracy of ∼5%. After refining the technique to target lower latitudes and incorporating deep optical data from DECam in the southern Galactic plane, we have derived a catalog of distances to molecular clouds in Reipurth (2008, Star Formation Handbook, Vols. I and II) which contains a large fraction of the molecular material in the solar neighborhood. Comparison with distances derived from maser parallax measurements towards the same clouds shows our method produces consistent distances with ≲10% scatter for clouds across our entire distance spectrum (150 pc−2.5 kpc). We hope this catalog of homogeneous distances will serve as a baseline for future work.
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- PAR ID:
- 10189725
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 633
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A51
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Context. Filamentary structures in nearby molecular clouds have been found to exhibit a characteristic width of 0.1 pc, as observed in dust emission. Understanding the origin of this universal width has become a topic of central importance in the study of molecular cloud structure and the early stages of star formation. Aims. We investigate how the recovered widths of filaments depend on the distance from the observer by using previously published results from the Herschel Gould Belt Survey. Methods. We obtained updated estimates on the distances to nearby molecular clouds observed with Herschel by using recent results based on 3D dust extinction mapping and Gaia . We examined the widths of filaments from individual clouds separately, as opposed to treating them as a single population. We used these per-cloud filament widths to search for signs of variation amongst the clouds of the previously published study. Results. We find a significant dependence of the mean per-cloud filament width with distance. The distribution of mean filament widths for nearby clouds is incompatible with that of farther away clouds. The mean per-cloud widths scale with distance approximately as 4−5 times the beam size. We examine the effects of resolution by performing a convergence study of a filament profile in the Herschel image of the Taurus Molecular Cloud. We find that resolution can severely affect the shapes of radial profiles over the observed range of distances. Conclusions. We conclude that the data are inconsistent with 0.1 pc being the universal characteristic width of filaments.more » « less
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ABSTRACT The Eos cloud, recently discovered in the far ultraviolet via H$$_2$$ fluorescence, is one of the nearest known dark molecular clouds to the Sun, with a distance spanning from $${\sim} 94\rm{\!-\!}136$$ pc. However, with a mass ($${\sim} 5.5\times 10^3$$ M$$_\odot$$) just under $$40\,$$ per cent that of star forming clouds like Taurus and evidence for net molecular dissociation, its evolutionary and star forming status is uncertain. We use Gaia data to investigate whether there is evidence for a young stellar population that may have formed from the Eos cloud. Comparing isochrones and pre-main sequence evolutionary models there is no clear young stellar population in the region. While there are a small number of $${<} 10$$ Myr stars, that population is statistically indistinguishable from those in similar search volumes at other Galactic latitudes. We also find no unusual spatial or kinematic clustering toward the Eos cloud over distances $$70\!-\!150$$ pc. Overall, we conclude that the Eos cloud has most likely not undergone any recent substantial star formation and further study of the dynamics of the cloud is required to determine whether it will do so in the future.more » « less
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Kinematic distance determinations are complicated by a kinematic distance ambiguity (KDA) within the Solar orbit. For an axisymmetric Galactic rotation model, two distances, a "near" and "far" distance, have the same radial velocity. Formaldehyde (H2CO) absorption measurements have been used to resolve the KDA toward Galactic HII regions. This method relies on the detection of H2CO absorption against the broadband radio continuum emission from HII regions. H2CO absorption at velocities between the HII region velocity and the maximum velocity along the line of sight (the tangent point velocity) implies that the HII region lies at the far kinematic distance whereas a lack of absorption implies that it lies at the near kinematic distance. The reliability of KDA resolutions using H2CO is unclear, however, as disagreements between distances derived using H2CO absorption and those derived using other methods are common. Here we use new H2CO and radio recombination line data from the Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) to test whether H2CO absorption measurements can accurately resolve the KDA for 44 Galactic HII regions that have known distances from maser parallax measurements. For each of the 44 HII regions we determine whether the parallax distance is consistent with either the near or the far kinematic distance. We find that the Galactic distribution of H2CO is too sparse to reliably determine whether an HII region is at its near kinematic distance. The H2CO method also incorrectly resolves the KDA for 80% of HII regions that it places at the far kinematic distance; in such cases H2CO absorption may be caused by other sources of radio continuum emission (possibly the CMB, diffuse free-free, or synchrotron). Our results indicate that the H2CO method is unsuitable to resolve the KDA toward Galactic HII regions.more » « less
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Abstract We dendrogram the Leike et al. 3D dust map, leveraging its ∼1 pc spatial resolution to produce a uniform catalog of molecular clouds in the solar neighborhood. Using accurate distances, we measure the properties of 65 clouds in true 3D space, eliminating much of the uncertainty in mass, size, and density. Clouds in the catalog contain a total of 1.1 × 105M☉, span distances of 116−440 pc, and include a dozen well-studied clouds in the literature. In addition to deriving cloud properties in 3D volume density space, we create 2D dust extinction maps from the 3D data by projecting the 3D clouds onto a 2D “Sky” view. We measure the properties of the 2D clouds separately from the 3D clouds. We compare the scaling relation between the masses and sizes of clouds following Larson. We find that our 2D projected mass–size relation,M∝r2.1, agrees with Larson's Third Relation, but our 3D derived properties lead to a scaling relation of about one order larger:M∝r2.9. Validating predictions from theory and numerical simulations, our results indicate that the mass–size relation is sensitive to whether column or volume density is used to define clouds, since mass scales with area in 2D (M∝r2) and with volume in 3D (M∝r3). Our results imply a roughly constant column and volume density in 2D and 3D, respectively, for molecular clouds, as would be expected for clouds where the lower density, larger volume-filling gas dominates the cloud mass budget.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1051/0004-6361/201936145
