3D maps of interstellar dust in the Local Arm: using $Gaia$, 2MASS and APOGEE-DR14 (1804.06060v1)

Abstract: Gaia data and stellar surveys open the way to the construction of detailed 3D maps of the Galactic interstellar (IS) dust based on the synthesis of star distances and extinctions. Reliable extinction measurements require very accurate photometric calibrations. We show the first step of an iterative process linking 3D dust maps and photometric calibrations and improving them simultaneously. Our previous 3D map of nearby IS dust was used to select low reddening SDSS/APOGEE-DR14 red giants, and this database served for an empirical effective temperature- and metallicity-dependent photometric calibration in the Gaia G and 2MASS Ks bands. This calibration has been combined with Gaia G-band empirical extinction coefficients recently published, G, J and Ks photometry and APOGEE atmospheric parameters to derive the extinction of a large fraction of the survey targets. Distances were estimated independently using isochrones and the magnitude-independent extinction K(J-Ks). This new dataset has been merged with the one used for the earlier version of dust map. A new Bayesian inversion of distance-extinction pairs has been performed to produce an updated 3D map. We present several properties of the new map. Its comparison with 2D dust emission reveals that all large dust shells seen in emission at mid- and high-latitude are closer than 300pc. The updated distribution constrains the well debated, X-ray bright North Polar Spur to originate beyond 800 pc. We use the Orion region to illustrate additional details and distant clouds. On the large scale the map reveals a complex structure of the Local Arm. 2 to 3 kpc-long chains of clouds appear in planes tilted by 15 deg with respect to the Galactic plane. A series of cavities oriented along a l=60-240deg axis crosses the Arm. (http://stilism.obspm.fr)

• The paper improves 3D mapping of interstellar dust in the Local Arm by integrating Gaia distances with 2MASS and APOGEE-DR14 photometric calibrations.
• It extends the dust mapping to 2 kpc in the Galactic plane and reveals intricate cloud chains tilted about 15° from the plane.
• The refined maps enhance stellar calibration techniques and provide a robust framework for future Galactic ISM studies using upcoming Gaia data.

Analysis of 3D Maps of Interstellar Dust Using $Gaia$, 2MASS, and APOGEE-DR14 Data

The manuscript offers a detailed examination of the construction and refinement of three-dimensional (3D) interstellar dust maps within the Local Arm of the Galaxy. By integrating data from various surveys, namely $Gaia$, 2MASS, and APOGEE-DR14, the authors aim to achieve a substantial improvement in both the accuracy and extent of the Galactic interstellar dust mapping.

Methodology and Data Utilization

The authors employ an overview of $Gaia$-based distance data combined with extinctions measured from extensive stellar surveys to develop 3D Galactic IS dust maps. The challenge is achieving precise extinction measurements, which are contingent on rigorous photometric calibrations. The methodology introduced is iterative, where photometric calibrations and 3D dust maps are refined concurrently. This iterative process could be pivotal in enhancing the fidelity of Galactic models.

In the detailed process, previously constructed 3D maps of nearby interstellar dust were utilized to identify low reddening SDSS/APOGEE-DR14 red giants. These stars facilitated the calibration process that is temperature and metallicity-dependent within the $Gaia$ G and 2MASS K$_{s}$ photometric bands. This calibration was then employed in conjunction with recently published $Gaia$ G-band empirical extinction coefficients to derive extinctions for a significant fraction of survey targets. Distances, estimated independently using isochronal fitting and magnitude-independent extinction coefficients (K$_{J-K}$), were then merged with previous datasets to create an updated, more refined 3D dust map via a Bayesian inversion method.

Key Findings

1. Extension and Detail in Dust Maps: The created 3D maps extend up to 2 kpc in the Galactic plane and 300 pc vertically from the plane, incorporating large dust shells and providing robust constraints on complex structures like the X-ray bright North Polar Spur. Such findings support the hypothesis that these structures originate farther than 800 pc from the Sun, a noteworthy clarification in Galactic modeling.
2. Complex Local Arm Structure: The map reveals intricate details of the Local Arm's structure, featuring chains of clouds spanning 2 to 3 kpc, oriented in planes tilted about 15 degrees in respect to the Galactic plane. This suggests that the Local Arm is not a simple structure but rather consists of multiple interconnected cloud chains and cavities, embodying a complex and dynamic interstellar medium (ISM).
3. Map Synergy and Stellar Calibration Enhancement: The synergy between improved 3D dust mapping and stellar photometric calibrations underscores the potential for these maps to serve as prior models for further specific target calibrations or extinction studies. As maps build on these calibrations, they can supply more data for generating even more detailed and extensive maps, benefiting future releases of $Gaia$ data and complementing stellar science.

Implications and Future Directions

The creation of these dust maps holds substantial implications for the paper of the Galactic ISM. Practically, they can be pivotal in corrections required for stellar observations that account for reddening and facilitate more accurate studies of Galactic objects. Theoretically, these maps offer a more nuanced understanding of the ISM's structure and distribution.

The research sets the stage for future developments as $Gaia$ data continues to provide more precise astrometric information. Future efforts will likely harness this synergy to iterate and expand these mappings, further enhancing our understanding of the spatial distribution of interstellar objects and feeding into the broader dialogue on Galactic modeling and the ISM structures.

As the modes of data synthesis improve and incorporate even more extensive datasets like future $Gaia$ releases or new ground-based surveys, the endeavor undertaken in this paper projects a trajectory towards increasingly accurate and comprehensive models of the Galaxy's interstellar environment. Such advancements will continue to augment our comprehension of fundamental Galactic processes and their broader cosmological contexts.