Polaris Flare CO enhancement by MHD waves

We use archival starlight polarization data and dust emission maps in order to probe the magnetic field properties and compare against the CO morphological and kinematic properties. We assess the interaction of compressible MHD wave modes with CO chemistry by comparing their characteristic timescales. The estimated magnetic field is 38-76uG.

In the CO integrated intensity map, we observe a dominant quasi-periodic intensity structure, which tends to be parallel to the magnetic field orientation and has a wavelength of one parsec approximately. The periodicity axis is ~17 degrees off from the mean magnetic field orientation and is also observed in the dust intensity map. The contrast in the CO integrated intensity map is ~2.4 times larger than the contrast of the column density map, indicating that CO formation is enhanced locally.

We suggest that a dominant slow magnetosonic mode with estimated period 2.1-3.4Myr, and propagation speed 0.30-0.45km/s, is likely to have enhanced the formation of CO, hence created the observed periodic pattern. We also suggest that, within uncertainties, a fast magnetosonic mode with period 0.48Myr and velocity 2.0km/s could have played some role in increasing the CO abundance.