title: 3D map of the dust distribution in the Milky Way
creator: Rezaeikhoshbakht, Sara
subject: 520
subject: 520 Astronomy and allied sciences
description: In this thesis, I present a new non-parametric model for inferring the three-dimensional  (3D) distribution of dust density in the Milky Way. Our approach uses the extinction  measured towards stars at different locations in the Galaxy at known distances. Each  extinction measurement is proportional to the integrated dust density along its line  of sight (l.o.s). Making simple assumptions about the spatial correlation of the dust  density, we infer the most probable 3D distribution of dust across the entire observed  region, including along sight lines which were not observed. This is possible because our  model employs a Gaussian process to connect all l.o.s. The result is a smooth, 3D map  of the dust density, which is the local property of the interstellar medium (ISM) rather  than an integrated quantity. Owing to our smoothness constraint and its isotropy, the  method provides one of the first maps without “fingers of God” artefact.  I then present the first continuous map of the dust distribution in the Galactic  disk out to 7 kpc within 100 pc of the Galactic midplane, using red giant stars from  SDSS APOGEE DR14. The resulting map traces some features of the local Galactic  spiral arms, even though the model contains no prior suggestion of spiral arms, nor any  underlying model for the Galactic structure. This is the first time that such evident arm  structures have been captured by a dust density map in the Milky Way. Our resulting  map also traces some of the known giant molecular clouds in the Galaxy and puts some  constraints on their distances, some of which were hitherto relatively uncertain.  I also demonstrate a map of the 3D distribution of dust in the Orion complex. Orion  is the closest site of high-mass star formation, making it an excellent laboratory for  studying the ISM and star formation. We use data from the Gaia-TGAS catalogue  combined with photometry from 2MASS and WISE to get the distances and extinctions  of individual stars in the vicinity of the Orion complex. We find that the distance and  depth of the cloud are compatible with other recent works, which show that the method  can be applied to local molecular clouds to map their 3D dust distribution. We also use  data from the recent second Gaia data release (GDR2) to update the map that shows  complex dust clouds in the Orion region.  I finally show a 3D map of hydrogen density in the local ISM. The hydrogen equivalent  column densities were obtained from the Exploring the X-ray Transient and variable Sky  project (EXTRAS), which provides equivalent NH values from X-ray spectral fits of  observations within the XMM-Newton Data Release. A cross-correlation between the  EXTRAS catalogue and the first Gaia Data Release was performed in order to obtain  accurate parallax and distance measurements. The resulting map shows small-scale  density structures which can not be modelled using analytic density profiles.
date: 2018
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/25664/1/thesis.pdf
identifier: DOI:10.11588/heidok.00025664
identifier: urn:nbn:de:bsz:16-heidok-256646
identifier:   Rezaeikhoshbakht, Sara  (2018) 3D map of the dust distribution in the Milky Way.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/25664/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng