Mapping of interstellar clouds with infrared light scattered from dust:
  TMC-1N
  Mapping of near-infrared (NIR) scattered light is a recent method for the
study of interstellar clouds, complementing other, more commonly used methods,
like dust emission and extinction. Our goal is to study the usability of this
method on larger scale, and compare the properties of a filament using NIR
scattering and other methods. We also study the radiation field and differences
in grain emissivity between diffuse and dense areas. We have used scattered J,
H, and K band surface brightness WFCAM-observations to map filament TMC-1N in
Taurus, covering an area of 1dx1d corresponding to ~(2.44 pc)^2. We have
converted the data into optical depth and compared the results with NIR
extinction and Herschel observations of submm dust emission. We see the
filament in scattered light in all three NIR bands. We note that our WFCAM
observations in TMC-1N show notably lower intensity than previous results in
Corona Australis using the same method. We show that 3D radiative transfer
simulations predict similar scattered surface brightness levels as seen in the
observations. However, changing the assumptions about the background can change
the results of simulations notably. We derive emissivity by using optical depth
in the J band as an independent tracer of column density. We obtain opacity
sigma(250um) values 1.7-2.4x10^-25 cm^2/H, depending on assumptions of the
extinction curve, which can change the results by over 40%. These values are
twice as high as obtained for diffuse areas, at the lower limit of earlier
results for denser areas. We show that NIR scattering can be a valuable tool in
making high resolution maps. We conclude, however, that NIR scattering
observations can be complicated, as the data can show relatively low-level
artefacts. This suggests caution when planning and interpreting the
observations.
