Tycho SN 1572: A Naked Ia Supernova Remnant without Associated Ambient
  Molecular Cloud
  The historical supernova remnant (SNR) Tycho SN 1572 originates from the
explosion of a normal Type Ia supernova which is believed to have originated
from a carbon-oxygen white dwarf in a binary system. We analyze the 21cm
continuum, HI and 12CO-line data from the Canadian Galactic Plane Survey in the
direction of SN 1572 and surrounding region. We construct HI absorption spectra
to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no
molecular cloud interaction, which argues against previous claims that a
molecular cloud is interacting with the SNR. This new result does not support a
recent claim that dust, newly detected by AKARI, originates from such a
SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5
- 3.0 kpc based on a nonlinear rotational curve model. Very-high-energy
Gamma-ray emission from the remnant has been detected by the VERITAS telescope,
so our result shows that its origin should not be an SNR-cloud interaction.
Both radio and X-ray observations support that SN 1572 is an isolated Type Ia
SNR.
