A Search for Spatially Resolved Infrared Ro-Vibrational Molecular
  Hydrogen Emission from the Disks of Young Stars
  We present results from a survey searching for spatially resolved
near-infrared line emission from molecular hydrogen gas in the circumstellar
environments of nine young stars: AA Tau, AB Aur, DoAr 21, GG Tau, GM Aur, LkCa
15, LkH$\alpha$ 264, UY Aur, and V773 Tau. Prior high-resolution spectra of
these stars showed the presence of ro-vibrational H$_2$ line emission at
2.12$\mu$m with characteristics more typical of gas located in proto-planetary
disks rather than outflows. In this study, we spatially resolve the H$_2$
emission in the eight stars where it is detected. LkCa 15 is the only target
that exhibits no appreciable H$_2$ despite a prior detection. We find an
anti-correlation between H$_2$ and X-ray luminosities, likely indicating that
the X-ray ionization process is not the dominant H$_2$ excitation mechanism in
these systems. AA Tau, UY Aur, and V773 Tau show discrete knots of H$_2$, as
typically associated with shocks in outflowing gas. UY Aur and V773 Tau exhibit
spatially resolved velocity structures, while the other systems have spectrally
unresolved emission consistent with systemic velocities. V773 Tau exhibits a
complex line morphology indicating the presence of multiple excitation
mechanisms, including red and blue-shifted bipolar knots of shock-excited
outflowing gas. AB Aur, GM Aur, and LkH$\alpha$ 264 have centralized, yet
spatially resolved H$_2$ emission consistent with a disk origin. The H$_2$
images of AB Aur reveal spiral structures within the disk, matching those
observed in ALMA CO maps. This survey reveals new insights into the structure
and excitation of warm gas in the circumstellar environments of these young
stars.
