A Deep, High-Angular Resolution 3D Dust Map of the Southern Galactic Plane

TL;DR

This work delivers a deep, high-angular-resolution 3D dust map of the southern Galactic plane by jointly leveraging DECaPS2, VVV, 2MASS, unWISE, and Gaia DR3 data to infer distances, extinctions, and stellar types for hundreds of millions of stars. Through a Brutus-based stellar-inference pipeline coupled with a line-of-sight, pixelized dust reconstruction at 1 arcminute resolution across 51 million sightlines and 120 distance bins, the map reaches up to roughly 10 kpc and detects prominent complexes in the Sagittarius–Carina and Scutum–Centaurus regions, with total extinction up to about 12 magnitudes in V. The resulting stellar catalog (709 million high-quality stars) and the 3D dust product (mean reddening per pixel and distance bin) are publicly released and queryable via dustmaps, enabling full-disk extinction corrections when combined with Bayestar19. This map, a pathfinder for LSST and Roman-era dust mapping, demonstrates the feasibility of pushing angular resolution, depth, and sky coverage together in 3D, while acknowledging artifacts and areas for methodological improvements in future work.

Abstract

We present a deep, high-angular resolution 3D dust map of the southern Galactic plane over $239^\circ < \ell < 6^\circ$ and $|b| < 10^\circ$ built on photometry from the DECaPS2 survey, in combination with photometry from VVV, 2MASS, and unWISE and parallaxes from Gaia DR3 where available. To construct the map, we first infer the distance, extinction, and stellar types of over 700 million stars using the brutus stellar inference framework with a set of theoretical MIST stellar models. Our resultant 3D dust map has an angular resolution of $1'$, roughly an order of magnitude finer than existing 3D dust maps and comparable to the angular resolution of the Herschel 2D dust emission maps. We detect complexes at the range of distances associated with the Sagittarius-Carina and Scutum-Centaurus arms in the fourth quadrant, as well as more distant structures out to a maximum reliable distance of $d \approx$ 10 kpc from the Sun. The map is sensitive up to a maximum extinction of roughly $A_V \approx 12$ mag. We publicly release both the stellar catalog and the 3D dust map, the latter of which can easily be queried via the Python package dustmaps. When combined with the existing Bayestar19 3D dust map of the northern sky, the DECaPS 3D dust map fills in the missing piece of the Galactic plane, enabling extinction corrections over the entire disk $|b| < 10^\circ$. Our map serves as a pathfinder for the future of 3D dust mapping in the era of LSST and Roman, targeting regimes accessible with deep optical and near-infrared photometry but often inaccessible with Gaia.

Figures (20)

• Figure 1: Schematic overview of the process of turning images of the sky into a 3D map of dust. The DECaPS2 survey forms the foundation of our 3D dust map, whose photometric colors are combined with complementary photometric (VVV, 2MASS, unWISE) and astrometric surveys (Gaia) where available and fed into our stellar inference framework. We use the brutus stellar inference framework to infer the distance, extinction, and stellar type of hundreds of millions of stars. We then group stars into pixels and fit the set of distance-reddening measurements along the line of sight in each pixel to generate a 3D map of dust.
• Figure 2: Number of photometric bands per star incorporated into the stellar modeling, tabulated across all stars in the full DECaPS2 footprint. The number of photometric detections ranges from four (the minimum) to thirteen (the maximum), with an average of five bands incorporated per star.
• Figure 3: Distribution of source density on the plane of the sky for stars we model in § \ref{['subsec:perstar_inference']}, the majority of which will be used in the line-of-sight dust reconstruction. The VVV footprint (purple polygon) shows a modest increase in source density in comparison to the rest of the DECaPS2 footprint. The median source density is 70 stars per arcmin$^2$, with an interquartile range of $37-125$ stars per arcmin$^2$ .
• Figure 4: Breakdown of the number of stars detected in each photometric band (shown in blue for DECaPS2, purple for VVV, pink for 2MASS, orange for unWISE) and with an available Gaia parallax measurement (shown in yellow). For Gaia, we further subdivide the stars into all those with a Gaia parallax detection and only those with a signal-to-noise ratio on the parallax detection $>5$. The top-panel shows the breakdown of band coverage for the entire DECaPS2 footprint, while the bottom panel shows the breakdown for the subset of the DECaPS2 footprint that overlaps with the VVV footprint (see purple polygon in Figure \ref{['fig:source_density']}).
• Figure 5: Spatial distribution of stars over the full catalog. Each panel shows a projection of the stellar density in Heliocentric Galactic Cartesian coordinates. The Galactic center is marked with a $\mathbf{\plus}$ symbol and the Sun with a $\mathbf{\odot}$ symbol in the XY and XZ projections. We detect stars out to distances of $d=15$ kpc and beyond, but with an underdensity of stars near the midplane ($z=0$ pc) due to high levels of dust extinction.