Detection of the Milky Way spiral arms in dust from 3D mapping

Abstract

Large stellar surveys are sensitive to interstellar dust through the effects of reddening. Using extinctions measured from photometry and spectroscopy, together with three-dimensional (3D) positions of individual stars, it is possible to construct a three-dimensional dust map. We 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 clump and giant stars from SDSS APOGEE DR14. We use a non-parametric method based on Gaussian Processes to map the dust density, which is the local property of the ISM rather than an integrated quantity. This method models the dust correlation between points in 3D space and can capture arbitrary variations, unconstrained by a pre-specified functional form. This produces a continuous map without line-of-sight artefacts. Our 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.

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

“…The ability to reconstruct the 3D distribution of matter in the Galactic interstellar medium (ISM) is important for astrophysics and cosmology. 3D maps inform us about nearby Galactic spiral structure (e.g., Rezaei et al 2018, and references therein), dust evolution (e.g., Schlafly et al 2017), star-forming regions (e.g., Zucker et al 2019), and the ISM magnetic field (e.g., Van Eck et al 2017). Such maps are also necessary for accurately modeling polarized dust emission (e.g., Martínez-Solaeche et al 2018), which acts as a dominant foreground contaminating the polarization of the cosmic microwave background (CMB; e.g., Planck Collaboration et al 2016).…”

Applying Noether’s Theorem to Matter in the Milky Way: Evidence for External Perturbations and Non-steady-state Effects from Gaia Data Release 2

“…Thus to test the extent to which the angular momentum L z serves as an integral of motion, we can study whether the stellar mass distribution is axially symmetric. Of course the Galaxy possesses features that break axial symmetry, such as spiral arms Reid et al 2019) or dust (Rezaei Kh. et al 2018), so that to test axial symmetry we select regions so as to minimize such effects.…”

“…et al 2018), so that to test axial symmetry we select regions so as to minimize such effects. For example, we avoid the immediate Galactic mid-plane (z = 0) region, choosing stars at vertical heights z with 0.2 ≤ |z| ≤ 3 kpc, noting that the the dust has a vertical scale height H d of 94 ± 22 pc at the Sun's location (Drimmel & Spergel 2001) 1 -and the latest three-dimensional dust map considers |z| < 100 pc (Rezaei Kh. et al 2018).…”

Charting nearby dust clouds using Gaia data only (Corrigendum)

“…Hereby the term "parallax" may refer to both astrometric parallaxes, that is to say distance estimates derived from the angular displacement of stars due to the observers displacement, as well as photometric parallaxes, that is distances derived from spectra using stellar models. -In the column labeled " Kh et al (2018b)," we misclassified the method of Rezaei Kh et al (2018) as a 2D method. The method takes correlations in three dimensions into account similarly to Lallement et al (2018), Sale & Magorrian (2018), and our own method.…”

“…For the reconstruction of Sale & Magorrian (2018) the concept of voxel resolution is not readily applicable; Sale & Magorrian (2018) use 140 inducing points spanning a region for which one could evaluate the posterior mean at any point. The resolution for Green et al (2018) andRezaei Kh et al (2018) is different in radial/angular direction, we report only radial resolution for Rezaei Kh et al (2018) and both for Green et al (2018). The fourth row provides the number of used data points.…”