H$\alpha$ Imaging spectroscopy of Balmer-dominated shocks in Tycho's
  supernova remnant
  We present Fabry-P\'erot interferometric observations of the narrow H$\alpha$
component in the shock front of the historical supernova remnant Tycho (SN
1572). Using GH$\alpha$FaS (Galaxy H$\alpha$ Fabry-P\'erot Spectrometer) on the
William Herschel Telescope, we observed a great portion of the shock front in
the northeastern (NE) region of the remnant. The angular resolution of
$\sim$1$^{\prime\prime}$ and spectral resolving power of R$\sim$21 000 together
with the large field-of-view (3.4$^{\prime}$ $\times$ 3.4$^{\prime}$) of the
instrument allow us to measure the narrow H$\alpha$-line width in 73 bins
across individual parts of the shock simultaneously and thereby study the
indicators of several shock precursors in a large variety of shock front
conditions. Compared to previous studies, the detailed spatial resolution of
the filament also allows us to mitigate possible artificial broadening of the
line from unresolved differential motion and projection. Covering one quarter
of the remnant's shell, we confirm the broadening of the narrow H$\alpha$ line
beyond its intrinsic width of $\sim$20 km/s and report it to extend over most
of the filament, not only the previously investigated dense 'knot g'.
Similarly, we confirm and find additional strong evidence for wide-spread
intermediate-line ($\sim$150 km/s) emission. Our Bayesian analysis approach
allows us to quantify the evidence for this intermediate component as well as a
possible split in the narrow line. Suprathermal narrow line widths point toward
an additional heating mechanism in the form of a cosmic-ray precursor, while
the intermediate component, previously only qualitatively reported as a small
non-Gaussian contribution to the narrow component, reveals a broad-neutral
precursor.
