Balmer-dominated shocks in Tycho's SNR: omnipresence of CRs
  We present wide-field, spatially and highly resolved spectroscopic
observations of Balmer filaments in the northeastern rim of Tycho's supernova
remnant in order to investigate the signal of cosmic-ray (CR) acceleration. The
spectra of Balmer-dominated shocks (BDSs) have characteristic narrow (FWHM
$\sim$ 10 kms$^{-1}$) and broad (FWHM $\sim$ 1000 kms$^{-1}$) H$\alpha$
components. CRs affect the H$\alpha$-line parameters: heating the cold neutrals
in the interstellar medium results in broadening of the narrow H$\alpha$-line
width beyond 20 kms$^{-1}$, but also in reduction of the broad H$\alpha$-line
width due to energy being removed from the protons in the post-shock region.
For the first time we show that the width of the narrow H$\alpha$ line, much
larger than 20 kms$^{-1}$, is not a resolution or geometric effect nor a
spurious result of a neglected intermediate (FWHM $\sim$ 100 kms$^{-1}$)
component resulting from hydrogen atoms undergoing charge exchange with warm
protons in the broad-neutral precursor. Moreover, we show that a narrow line
width $\gg$ 20 kms$^{-1}$ extends across the entire NE rim, implying CR
acceleration is ubiquitous, and making it possible to relate its strength to
locally varying shock conditions. Finally, we find several locations along the
rim, where spectra are significantly better explained (based on Bayesian
evidence) by inclusion of the intermediate component, with a width of 180
kms$^{-1}$ on average.
