Producing synthetic maps of dust polarization using a velocity channel gradient technique

Lu, Zekun; Lazarían, A.; Pogosyan, D.

doi:10.1093/mnras/staa1570

Cited by 28 publications

(17 citation statements)

References 53 publications

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“…Most recently, a different class of models has been developed in which H I velocity channel maps are treated as "layers" of emission along the line of sight (Clark & Hensley 2019;Lu et al 2020;Hu et al 2020). These approaches utilize morphological information and the column density to successfully reconstruct properties of the polarized dust emission that are related to the 3D structure of the ISM magnetic field.…”

Section: Comparison Of the Number Of Clouds Per Sight Line With Previmentioning

confidence: 99%

“…Innovative, data-driven approaches are being developed to characterize the ISM properties (Clark et al 2015;Clark 2018;Philcox et al 2018;González-Casanova & Lazarian 2019;Zhang et al 2019). Recent studies try to construct realistic realizations of dust foregrounds using 3D dust maps (Martínez-Solaeche et al 2018) or H I data (Ghosh et al 2017;Clark & Hensley 2019;Lu et al 2020;Adak et al 2020;Hu et al 2020).…”

Section: Introductionmentioning

confidence: 99%

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Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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Characterizing the structure of the Galactic interstellar medium (ISM) in three dimensions is of high importance for accurate modeling of dust emission as a foreground to the cosmic microwave background (CMB). At high Galactic latitude, where the total dust content is low, accurate maps of the 3D structure of the ISM are lacking. We develop a method to quantify the complexity of the distribution of dust along the line of sight with the use of H I line emission. The method relies on a Gaussian decomposition of the H I spectra to disentangle the emission from overlapping components in velocity. We use this information to create maps of the number of clouds along the line of sight. We apply the method to (a) the high Galactic latitude sky and (b) the region targeted by the BICEP/Keck experiment. In the north Galactic cap we find on average three clouds per 0.2 square degree pixel, while in the south the number falls to 2.5. The statistics of the number of clouds are affected by intermediate-velocity clouds (IVCs), primarily in the north. IVCs produce detectable features in the dust emission measured by Planck. We investigate the complexity of H I spectra in the BICEP/Keck region and find evidence for the existence of multiple components along the line of sight. The data (doi: 10.7910/DVN/8DA5LH) and software are made publicly available and can be used to inform CMB foreground modeling and 3D dust mapping.Unified Astronomy Thesaurus concepts: Interstellar medium (847); Neutral hydrogen clouds (1099); Interstellar atomic gas (833)

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Section: Comparison Of the Number Of Clouds Per Sight Line With Previmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Panopoulou

Lenz

2020

ApJ

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“…Compared with dust polarization, the VGT, used in this work, exhibits several advantages in tracing magnetic fields. Firstly, it employs the spectroscopic data to measure the molecular cloud's local magnetic fields so that it gets rids of the contamination from the foreground (Lazarian & Yuen 2018a;Hu et al 2020a;Lu et al 2020). Using spectroscopic data and VGT, one can achieve a higher resolution of the resulting magnetic field map.…”

Section: Measuring Mean Magnetic Field Strengthmentioning

confidence: 99%

Revealing Gravitational Collapse in Serpens G3-G6 Molecular Cloud using Velocity Gradients

Hu,

Lazarian,

Stanimirovic

2021

Preprint

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The relative role of turbulence, magnetic fields, self-gravity in star formation is a subject of intensive debate. We present IRAM 30m telescope observations of the 13 CO (1-0) emission in the Serpens G3-G6 molecular cloud and apply to the data a set of statistical methods. Those include the probability density functions (PDFs) of column density and the Velocity Gradients Technique (VGT). We combine our data with the Planck 353 GHz polarized dust emission observations, Hershel H 2 column density. We suggest that the Serpens G3-G6 south clump is undergoing a gravitational collapse. Our analysis reveals that the gravitational collapse happens at volume density n HI ≥ 10 3 cm −3 . We estimate the plane-of-the-sky magnetic field strength of approximately 120 µG using the traditional Davis-Chandrasekhar-Fermi method and 100 µG using a new technique proposed in Lazarian et al. (2020). We find the Serpens G3-G6 south clump's total magnetic field energy significantly surpasses kinetic energy and gravitational energy. We conclude that the gravitational collapse could be successfully triggered in a supersonic and sub-Alfvénic cloud.

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“…In this scenario, the peak of the Gaussian fitting function returns the local magnetic field directions. This procedure is termed block-averaging in Yuen & Lazarian (2017a) and has been the core of the gradient technique despite other procedures or improvements are introduced (e.g., Lu et al 2020, Ho & Lazarian 2020. Aside from some special situations, e.g., regions of the gravitational collapse (see, e.g., Yuen & Lazarian 2017b;Hu et al 2019c), velocity gradient directions after block averaging are statistically perpendicular to the local block-averaged magnetic 17 For large M A cases the fitting should be a von-Mise function.…”

Section: Improving Magnetic Field Tracing With Velocity Channel Mapsmentioning

confidence: 99%

“…field directions. The block-averaging criterion has been extended by Lu et al (2020) under theoretical considerations such that it should be a special Lorentzian-sinusoidal function that fits the gradient orientation histogram. The success of the VGT is further confirmed by the numerous application examples available in different astrophysical environments (See e.g.…”

Section: Improving Magnetic Field Tracing With Velocity Channel Mapsmentioning

confidence: 99%

Technique for separating velocity and density contributions in spectroscopic data and its application to studying turbulence and magnetic fields

Yuen,

Ho,

Lazarian

2020

Preprint

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Based on the theoretical description of Position-Position-Velocity (PPV) statistics in Lazarian & Pogosyan (2000), we introduce a new technique called the Velocity Decomposition Algorithm (VDA) in separating the contribution of turbulent velocity from density fluctuations. Using MHD turbulence simulations, we demonstrate its promise in recovering the velocity caustics in various physical conditions and, in conjunction with the Velocity Gradient Technique (VGT), its prospects in accurately tracing the magnetic field based on pure velocity fluctuations. Employing the theoretical framework developed in Lazarian & Pogosyan (2004), we find that for localized clouds, the velocity fluctuations are most prominent at the wing part of the spectral line, and they dominate the density fluctuations. The same velocity dominance applies to extended HI regions with galactic rotations. Our numerical experiment demonstrates that velocity channels arising from the cold phase of atomic hydrogen (HI) are still strongly affected by the velocity caustics in small scales. We apply the VDA to the HI GALFA-DR2 data corresponding to the high-velocity cloud HVC186+19-114 and high latitude galactic diffuse HI data. Our study confirms the crucial role of velocity caustics in forming linear structures observed within PPV cubes. We discuss the implications of the VDA for both magnetic field studies and predicting polarized galactic emission that acts as the foreground for the Cosmic Microwave Background (CMB) studies. Besides, we address the controversy related to the nature of the filaments in HI channel maps and explain the importance of velocity caustics in the formation of structures in PPV data cubes. The VDA method will allow astronomers to obtain velocity caustics from almost every piece of spectroscopic PPV data and allows direct investigation of the turbulent velocity field in observations.

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Producing synthetic maps of dust polarization using a velocity channel gradient technique

Cited by 28 publications

References 53 publications

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Maps of the Number of H i Clouds along the Line of Sight at High Galactic Latitude

Revealing Gravitational Collapse in Serpens G3-G6 Molecular Cloud using Velocity Gradients

Technique for separating velocity and density contributions in spectroscopic data and its application to studying turbulence and magnetic fields

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