A comparison of Galactic electron density models using PyGEDM
  Galactic electron density distribution models are crucial tools for
estimating the impact of the ionised interstellar medium on the impulsive
signals from radio pulsars and fast radio bursts. The two prevailing Galactic
electron density models are YMW16 (Yao et al., 2017) and NE2001 (Cordes &
Lazio, 2002). Here, we introduce a software package PyGEDM which provides a
unified application programming interface (API) for these models and the YT20
(Yamasaki & Totani, 2020) model of the Galactic halo. We use PyGEDM to compute
all-sky maps of Galactic dispersion measure (DM) for YMW16 and NE2001, and
compare the large-scale differences between the two. In general, YMW16 predicts
higher DM values toward the Galactic anticentre. YMW16 predicts higher DMs at
low Galactic latitudes, but NE2001 predicts higher DMs in most other
directions. We identify lines of sight for which the models are most
discrepant, using pulsars with independent distance measurements. YMW16
performs better on average than NE2001, but both models show significant
outliers. We suggest that future campaigns to determine pulsar distances should
focus on targets where the models show large discrepancies, so future models
can use those measurements to better estimate distances along those line of
sight. We also suggest that the Galactic halo should be considered as a
component in future GEDMs, to avoid overestimating the Galactic DM contribution
for extragalactic sources such as FRBs.
