How much of the circumgalactic medium around nearby galaxies is rotating? Quasar sightline observations reveal that the Doppler shift of low-ionization-state gas shares the sign expected from gas rotation in the disk plane. The projected velocities are lower than predicted for gas on circular orbits in a thin disk, suggesting that this cool gas will spiral towards the galactic disk. This result raises important questions about the kinematics of the warm-hot circumgalactic medium which must be rapidly cooling given its temperature near the peak of the radiative cooling curve. If this warm-hot phase is also corotating with the galactic disks, then it would seem likely that both phases of corotating gas are dynamically related. A number of HST/COS programs have established the prevalence of substantial column densities of O+5 ions in the halos of star-forming galaxies. These OVI absorbers are widely believed to trace the warm-hot phase, although alternative scenarios where the gas is photoionized instead of collisionally ionized imply different conditions. Several known examples of corotating OVI absorbers exist; yet a recent analysis of a small sample of galaxy - quasar pairs did not detect net corotation. We propose new Cosmic Origins Spectrograph observations of eight quasars paired with galaxies for which we have measured rotation curves. We will combine these results with ground-based rotation curves for 15 galaxies having OVI detections in their existing COS spectra. If most of the OVI systems turn out to be corotating, then 23 pairs will be sufficient to obtain a statistically significant result.
- Pub Date:
- June 2019