On Galactic Density Modeling in the Presence of Dust Extinction

Abstract

Inferences about the spatial density or phase-space structure of stellar populations in the Milky Way require a precise determination of the effective survey volume. The volume observed by surveys such as Gaia or near-infrared spectroscopic surveys, which have good coverage of the Galactic midplane region, is highly complex because of the abundant small-scale structure in the three-dimensional interstellar dust extinction. We introduce a novel framework for analyzing the importance of smallscale structure in the extinction. This formalism demonstrates that the spatially-complex effect of extinction on the selection function of a pencil-beam or contiguous sky survey is equivalent to a lowpass filtering of the extinction-affected selection function with the smooth density field. We find that the angular resolution of current 3D extinction maps is sufficient for analyzing Gaia sub-samples of millions of stars. However, the current distance resolution is inadequate and needs to be improved by an order of magnitude, especially in the inner Galaxy. We also present a practical and efficient method for properly taking the effect of extinction into account in analyses of Galactic structure through an effective selection function. We illustrate its use with the selection function of red-clump stars in APOGEE using and comparing a variety of current 3D extinction maps.

Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe

“…These limits assume observations of stars at the tip of the red giant branch (for solar metallicity and 2 Gyr of age) using isochrones from Bressan et al (2012). To calculate the distance limit, we use the dust extinction prescription of Bovy et al (2016a) and limits of H=12.2 for APOGEE-2, V=14 for GALAH, and V=19 for Gaia-ESO (their faintest limit across all fields). Longer cohorts in APOGEE-2 extend correspondingly further.…”

Evidence for Spatially Correlated Gaia Parallax Errors in the Kepler Field

“…Extinction corrections (described in §3.1) are made using the three-dimensional dust map of Green et al (2015), as implemented in mwdust 3 (Bovy et al 2016). The A V extinction for the Kepler field of view is shown in Figure 1.…”

“…The resulting IRFM temperature, T eff,IRFM , is used to compute a new log g, and the bolometric flux is used via Equation 4 to compute an asteroseismic distance/parallax, astero . An extinction for each band is then computed using the three-dimensional dust map of Green et al (2015) using mwdust (Bovy et al 2016), with which we correct the JHK s photometry, yielding dust-de-extincted J 0 , H 0 , and K s, 0 . B 0 and V 0 are computed by transforming corrected g and r magnitudes, g 0 and r 0 .…”

Milky Way chemo‐dynamics in the era of Gaia

“…1, c); • The inversion in velocity dispersion relation in RAVE and SEGUE (Fig. 1, d • The flaring of mono-abundance populations (assuming similarity to mono-age populations) found by Bovy et al (2015) and predicted earlier by Minchev et al (2015), where Model 1 in the latter paper presents the same galaxy as the one used for the MCM13 chemodynamical model. MCM13 Model Ramírez et al (2013) …”