  HL Tau is a Class I-II protostar embedded in an infalling and rotating
envelope and possibly associated with a planet forming disk, and it is
co-located in a 0.1 pc molecular cloud with two nearby young stellar objects.
Our ALMA observations revealed two arc-like structures on a 1000 au scale
connected to the disk, and their kinematics could not be explained with any
conventional model of infalling and rotational motions. In this work, we
investigate the nature of these arc-like structures connected to the HL Tau
disk. We conducted new observations in the 13CO and C18O (3-2; 2-1) lines with
JCMT and IRAM 30m, and obtained the ACA data with the 7-m array. With the
single-dish, ACA, and ALMA data, we analyzed the gas motions on both 0.1 pc and
1000 au scales in the HL Tau region. We constructed new kinematical models of
an infalling and rotating envelope with the consideration of relative motion
between HL Tau and the envelope. By including the relative motion between HL
Tau and its protostellar envelope, our kinematical model can explain the
observed velocity features in the arc-like structures. The morphologies of the
arc-like structures can also be explained with an asymmetric initial density
distribution in our model envelope. In addition, our single-dish results
support that HL Tau is located at the edge of a large-scale (0.1 pc) expanding
shell driven by the wind or outflow from XZ Tau, as suggested in the
literature. The estimated expanding velocity of the shell is comparable to the
relative velocity between HL Tau and its envelope in our kinematical model.
These results hints that the large-scale expanding motion likely impacts the
protostellar envelope around HL Tau and affects its gas kinematics. We found
that the mass infalling rate from the envelope onto the HL Tau disk can be
decreased by a factor of two due to this impact by the large-scale expanding
shell.

Solar and Stellar Astrophysics;Astrophysics of Galaxies