The Galactic neutral hydrogen (H i ) sky at high Galactic latitudes is suffused with linear structure. Particularly prominent in narrow spectral intervals, these linear H i features are well aligned ...with the plane-of-sky magnetic field orientation as measured with optical starlight polarization and polarized thermal dust emission. We analyze the coherence of the orientation of these features with respect to line-of-sight velocity, and propose a new metric to quantify this H i coherence. We show that H i coherence is linearly correlated with the polarization fraction of 353 GHz dust emission. H i coherence constitutes a novel method for measuring the degree of magnetic field tangling along the line of sight in the diffuse interstellar medium. We propose applications of this property for H i -based models of the polarized dust emission in diffuse regions, and for studies of frequency decorrelation in the polarized dust foreground to the cosmic microwave background (CMB).
We present observations of a new group of structures in the diffuse Galactic interstellar medium (ISM): slender, linear H I features we dub "fibers" that extend for many degrees at high Galactic ...latitude. To characterize and measure the extent and strength of these fibers, we present the Rolling Hough Transform, a new machine vision method for parameterizing the coherent linearity of structures in the image plane. With this powerful new tool we show that the fibers are oriented along the interstellar magnetic field as probed by starlight polarization. We find that these low column density (N sub(H I) Asymptotically = to 5 x 10 super(18) cm super(-2)) fiber features are most likely a component of the local cavity wall, about 100 pc away. The H I data we use to demonstrate this alignment at high latitude are from the Galactic Arecibo L-Band Feed Array H I (GALFA-H I) Survey and the Parkes Galactic All Sky Survey. We find better alignment in the higher resolution GALFA-H I data, where the fibers are more visually evident. This trend continues in our investigation of magnetically aligned linear features in the Riegel-Crutcher H I cold cloud, detected in the Southern Galactic Plane Survey. We propose an application of the RHT for estimating the field strength in such a cloud, based on the Chandrasekhar-Fermi method. We conclude that data-driven, quantitative studies of ISM morphology can be very powerful predictors of underlying physical quantities.
Recent analyses of 21 cm neutral hydrogen (H i) emission have demonstrated that H i gas is organized into linear filamentary structures that are preferentially aligned with the local magnetic field, ...and that the coherence of these structures in velocity space traces line-of-sight magnetic field tangling. On this basis, we introduce a paradigm for modeling the properties of magnetized, dusty regions of the interstellar medium (ISM), using the orientation of H i structure at different velocities to map "magnetically coherent" regions of space. We construct three-dimensional (position-position-velocity) Stokes parameter maps using H i4PI full-sky spectroscopic H i data. We compare these maps, integrated over the velocity dimension, to Planck maps of the polarized dust emission at 353 GHz. Without any free parameters governing the relation between H i intensity and dust emission, we find that our Q and U maps are highly correlated (r > 0.75) with the 353 GHz Q and U maps of polarized dust emission observed by Planck and reproduce many of its large-scale features. The E/B ratio of the dust emission maps agrees well with the H i-derived maps at large angular scales ( 120), supporting the interpretation that this asymmetry arises from the coupling of linear density structures to the Galactic magnetic field. We demonstrate that our 3D Stokes parameter maps constrain the 3D structure of the Galactic ISM and the orientation of the interstellar magnetic field.
Abstract
Neutral hydrogen (H
I
) emission exhibits complex morphology that encodes rich information about the physics of the interstellar medium. We apply the scattering transform (ST) to ...characterize the H
I
emission structure via a set of compact and interpretable coefficients, and find a connection between the H
I
emission morphology and H
I
cold neutral medium (CNM) phase content. Where H
I
absorption measurements are unavailable, the H
I
phase structure is typically estimated from the emission via spectral line decomposition. Here, we present a new probe of the CNM content using measures that are solely derived from H
I
emission spatial information. We apply the ST to GALFA-H
I
data at high Galactic latitudes (
b
>
30
°
), and compare the resulting coefficients to CNM fraction measurements derived from archival H
I
emission and absorption spectra. We quantify the correlation between the ST coefficients and the measured CNM fraction (
f
CNM
), finding that the H
I
emission morphology encodes substantial
f
CNM
-correlating information and that ST-based metrics for small-scale linearity are particularly predictive of
f
CNM
. This is further corroborated by the enhancement of the
I
857
/
N
HI
ratio with larger ST measures of small-scale linearity. These results are consistent with the picture of regions with higher CNM content being more populated by small-scale filamentary H
I
structures. Our work illustrates a physical connection between the H
I
morphology and phase content, and suggests that future phase decomposition methods can be improved by making use of both H
I
spectral and spatial information.
Using high-resolution data from the Galactic Arecibo L-Band Feed Array HI (GALFA-Hi) survey, we show that linear structure in Galactic neutral hydrogen (Hi) correlates with the magnetic field ...orientation implied by Planck 353 GHz polarized dust emission. The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. At high Galactic latitudes, where the Planck data are noise dominated, the Hi data provide an independent constraint on the Galactic magnetic field orientation, and hence the local dust polarization angle. We detect strong cross-correlations between template maps constructed from estimates of dust intensity combined with either Hi-derived angles, starlight polarization angles, or Planck 353 GHz angles. The Hi data thus provide a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination.
If a single line of sight (LOS) intercepts multiple dust clouds with different spectral energy distributions and magnetic field orientations, then the frequency scaling of each of the Stokes
Q
and
U
...parameters of the thermal dust emission may be different, a phenomenon we refer to as LOS frequency decorrelation. We present first evidence for LOS frequency decorrelation in
Planck
data using independent measurements of neutral-hydrogen (H
I
) emission to probe the 3D structure of the magnetized interstellar medium (ISM). We use H
I
-based measurements of the number of clouds per LOS and the magnetic field orientation in each cloud to select two sets of sightlines: (i) a target sample of pixels that are likely to exhibit LOS frequency decorrelation and (ii) a control sample of pixels that lack complex LOS structure. We test the null hypothesis that LOS frequency decorrelation is not detectable in
Planck
353 and 217 GHz polarization data at high Galactic latitudes. We reject the null hypothesis at high significance based on data that show that the combined effect of polarization angle variation with frequency and depolarization are detected in the target sample. This detection is robust against the choice of cosmic microwave background (CMB) map and map-making pipeline. The observed change in polarization angle due to LOS frequency decorrelation is detectable above the
Planck
noise level. The probability that the detected effect is due to noise alone ranges from 5 × 10
−2
to 4 × 10
−7
, depending on the CMB subtraction algorithm and treatment of residual systematic errors; correcting for residual systematic errors consistently increases the significance of the effect. Within the target sample, the LOS decorrelation effect is stronger for sightlines with more misaligned magnetic fields, as expected. With our sample, we estimate that an intrinsic variation of ~15% in the ratio of 353 to 217 GHz polarized emission between clouds is sufficient to reproduce the measured effect. Our finding underlines the importance of ongoing studies to map the three-dimensional structure of the magnetized and dusty ISM that could ultimately help component separation methods to account for frequency decorrelation effects in CMB polarization studies.
We investigate the physical properties of structures seen in channel map observations of 21 cm neutral hydrogen (H i) emission. H i intensity maps display prominent linear structures that are well ...aligned with the ambient magnetic field in the diffuse interstellar medium (ISM). Some literature hold that these structures are "velocity caustics," fluctuations imprinted by the turbulent velocity field, and are not three-dimensional density structures in the ISM. We test this hypothesis by stacking probes of the density field-broadband far-infrared (FIR) emission and the integrated H i column density ( )-at the locations of linear H i intensity structures. We find that the H i intensity features are real density structures and not velocity caustics. We generalize the investigation to all small-scale structure in H i channel maps and analyze this correlation as a function of velocity channel width, finding no measurable contribution from velocity caustics to the H i channel map emission. Further, we find that small-scale H i channel map structures have elevated FIR/ , implying that this emission originates from a colder, denser phase of the ISM than the surrounding material. The data are consistent with a multiphase diffuse ISM in which small-scale structures in narrow H i channel maps are preferentially cold neutral medium (CNM) that is anisotropically distributed and aligned with the local magnetic field. The shallow spatial power spectrum (SPS) of narrow H i channels is often attributed to velocity caustics. We conjecture instead that the small-scale structure and narrow line widths typical of CNM explain the observed relationship between the SPS and channel width.
Abstract Recent measurements of Galactic polarized dust emission have found a nonzero TB signal, a correlation between the total intensity and the B -mode polarization component. We present evidence ...that this parity-odd signal is driven by the relative geometry of the magnetic field and the filamentary interstellar medium in projection. Using neutral hydrogen morphology and Planck polarization data, we find that the angle between intensity structures and the plane-of-sky magnetic field orientation is predictive of the signs of Galactic TB and EB . Our results suggest that magnetically misaligned filamentary dust structures introduce nonzero TB and EB correlations in the dust polarization, and that the intrinsic dust EB can be predicted from measurements of dust TB and TE over the same sky mask. We predict correlations between TE , TB , EB , and EE / BB , and confirm our predictions using synthetic dust polarization maps from magnetohydrodynamic simulations. We introduce and measure a scale-dependent effective magnetic misalignment angle, ψ ℓ dust ∼ 5 ° for 100 ≲ ℓ ≲ 500, and predict a positive intrinsic dust EB with amplitude D ℓ EB ≲ 2.5 μ K CMB 2 for the same multipole range at 353 GHz over our sky mask. Both the sign and amplitude of the Galactic EB signal can change with the sky area considered. Our results imply that searches for parity violation in the cosmic microwave background must account for the nonzero Galactic EB and TB signals, necessitating revision of existing analyses of the evidence for cosmic birefringence.
Abstract
We present evidence for scale-independent misalignment of interstellar dust filaments and magnetic fields. We estimate the misalignment by comparing millimeter-wave dust-polarization ...measurements from Planck with filamentary structures identified in neutral-hydrogen (H
i
) measurements from H
i
4PI. We find that the misalignment angle displays a scale independence (harmonic coherence) for features larger than the H
i
4PI beamwidth (16.′2). We additionally find a spatial coherence on angular scales of
(
1
°
)
. We present several misalignment estimators formed from the auto- and cross-spectra of dust-polarization and H
i
-based maps, and we also introduce a map-space estimator. Applied to large regions of the high-Galactic-latitude sky, we find a global misalignment angle of ∼2°, which is robust to a variety of masking choices. By dividing the sky into small regions, we show that the misalignment angle correlates with the parity-violating
TB
cross-spectrum measured in the Planck dust maps. The misalignment paradigm also predicts a dust
EB
signal, which is of relevance in the search for cosmic birefringence but as yet undetected; the measurements of
EB
are noisier than those of
TB
, and our correlations of
EB
with misalignment angle are found to be weaker and less robust to masking choices. We also introduce an H
i
-based dust-polarization template constructed from the Hessian matrix of the H
i
intensity, which is found to correlate more strongly than previous templates with Planck dust
B
modes.
Despite years of research and hundreds of reports on tumour markers in oncology, the number of markers that have emerged as clinically useful is pitifully small. Often initially reported studies of a ...marker show great promise, but subsequent studies on the same or related markers yield inconsistent conclusions or stand in direct contradiction to the promising results. It is imperative that we attempt to understand the reasons that multiple studies of the same marker lead to differing conclusions. A variety of methodological problems have been cited to explain these discrepancies. Unfortunately, many tumour marker studies have not been reported in a rigorous fashion, and published articles often lack sufficient information to allow adequate assessment of the quality of the study or the generalisability of the study results. The development of guidelines for the reporting of tumour marker studies was a major recommendation of the US National Cancer Institute and the European Organisation for Research and Treatment of Cancer (NCI-EORTC) First International Meeting on Cancer Diagnostics in 2000. Similar to the successful CONSORT initiative for randomised trials and the STARD statement for diagnostic studies, we suggest guidelines to provide relevant information about the study design, preplanned hypotheses, patient and specimen characteristics, assay methods, and statistical analysis methods. In addition, the guidelines suggest helpful presentations of data and important elements to include in discussions. The goal of these guidelines is to encourage transparent and complete reporting so that the relevant information will be available to others to help them to judge the usefulness of the data and understand the context in which the conclusions apply.
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