The Milky Way Mapper dust carton provides observational constraints on the distance-resolved velocity field of the Galaxy at ~ 100 pc resolution to probe the nature of gas flows in the Milky Way on both small (e.g. molecular cloud) and large (e.g. spiral arm) scales.  To achieve this, the dust carton will target a sample of bright, nearby, midplane (|z| < 200 pc) giants that, when combined with the more distant and/or heavily reddened sample from Galactic Genesis, produces a minimum of 10 stars per (100 pc) volume (a “voxel”) within 5 kpc of the Sun. 

Map of the diffuse interstellar bands from APOGEE and SDSS optical data.
The strength of DIB absorption seen in optical wavelengths from SDSS background galaxies and quasars (Lan et al. 2015) and in infrared wavelengths with APOGEE (Zasowski et al. 2015). MWM’s Dust program will increase the resolution of this map, especially in the midplane and add an additional dimension of molecular velocities.
Credit: T.W. Lan, G. Zasowksi, B. Ménard, SDSS AND 2MASS/UMASS/IPAC-CALTECH/NASA/NSF

The minimum of 10 stars per voxel translates to ~ 100 pc spatial resolution. This target density is necessary since 100 pc is roughly the size of both large molecular cloud complexes and of supernovae-driven bubbles in the ISM. Resolving this small-scale structure is thus necessary to achieve the carton’s key science goals (e.g. the molecular cloud lifecycle, the effect of shocks on the extinction curve).

Spectra of red giants across the Galaxy will yield dust information by providing 1) intrinsic colors for the observed stars and 2) access to the diffuse interstellar bands in the infrared.


Dust Cartons in Targeting Generation v0.5.3

In v0.5.3, there is a single dust carton: mwm_dust_core. To select the targets, nearby giants are identified using the following criteria. The astrometry is from Gaia DR2 . The J, H, and K photometry are from 2MASS. The 4.5 micron magnitudes are taken from, in order of preference, GLIMPSE or AllWISE.

  • mwm_dust_core
    • Parallax error/error < 0.2
    • distance < 5 kpc where distance=1/parallax
    • |z| < 0.2 kpc
    • MK < 2.6 where AK=0.918 (H-4.5)
    • (J-K)0 > 0.5 where E(J-K)=1.5 AK
    • H < 11.2
    • Galactic Genesis quality flags on the 2MASS photometry:
      • 2MASS gal_contam == 0
      • 2MASS cc_flg == 0
      • 0 < 2MASS rd_flag <= 3
      • 2MASS ph_qual flag is A or B

Next, the Galaxy within 5 kpc and with |z| < 0.2 kpc is divided into regions of 100 pc3 and the number of Galactic Genesis targets in the database that fall into each region are counted. If there are fewer than 10 stars in a given region, then additional stars (up to a total of 10) from the nearby giant selection above are included. It is these additional stars that comprise the mwm_dust_core carton.


The magnitude limit of H < 11.2 mag was chosen so that all the additional dust cartons could be observed in a single bright-time exposure.

  • bright_1x1
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