Profiling filaments: comparing near-infrared extinction and
  submillimetre data in TMC-1
  Interstellar filaments are an important part of star formation. To understand
the structure of filaments, cross-section profiles are often fitted with
Plummer profiles. This profiling is often done with submm studies, such as
Herschel. It would be convenient if filament properties could also be studied
using groundbased NIR data. We compare the filament profiles obtained by NIR
extinction and submm observations to find out if reliable profiles can be
derived using NIR data. We use J-, H-, and K-band data of a filament north of
TMC-1 to derive an extinction map from colour excesses of background stars. We
compare the Plummer profiles obtained from extinction maps with Herschel dust
emission maps. We present 2 methods to estimate profiles from NIR: Plummer
profile fits to median Av of stars or directly to the Av of individual stars.
We compare the methods by simulations. In simulations extinction maps and the
new methods give correct results to within ~10-20 for modest densities. Direct
fit to data on individual stars gives more accurate results than extinction
map, and can work in higher density. In profile fits to real observations,
values of Plummer parameters are generally similar to within a factor of ~2.
Although parameter values can vary significantly, estimates of filament mass
usually remain accurate to within some tens of per cent. Our results for TMC-1
are in agreement with earlier results. High resolution NIR data give more
details, but 2MASS data can be used to estimate profiles. NIR extinction can be
used as an alternative to submm observations to profile filaments. Direct fits
of stars can also be a valuable tool. Plummer profile parameters are not always
well constrained, and caution should be taken when making fits. In the
evaluation of Plummer parameters, one can use the independence of dust emission
and NIR data and the difference in the shapes of the confidence regions.
