At Stars Group meeting, Lauren Anderson (Flatiron) and Denis Erkal (Surrey) both spoke about stellar streams. Anderson spoke about finding them with a new search technique that looks at proper motions for stars found in great-circle segments; this is being prepared for Gaia DR2. Erkal spoke about constraining the Milky-Way potential using only configurational aspects of streams: If a small stream segment locally don't contain the Galactic Center, there must be asphericity in the gravitational potential.
Late in the day, Yi-Kuan Chiang (JHU) showed me absolutely beautiful results cross-correlating various Milky-Way dust maps with high-redshift objects. There ought to be no correlations, at least in the low-extinction regions. But there are correlations, and it is because the dust maps are all contaminated by high-redshift dust in the extragalactic objects themselves (or objects correlated therewith). He can conclude nice things about different dust-map techniques. We discussed (inconclusively) whether his work could be turned around and used to improve Milky-Way map-making.
This has been a problem for supernova reddening too. The host galaxy can screw up the reddening estimated from the dust maps. We are only now confronting the problem.
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