  We have analyzed the thermal and turbulent properties of the Low-Latitude
Intermediate-Velocity Arch 1 (LLIV1). This was accomplished using archival H I
emission and absorption data from two 21,cm line surveys: GHIGLS at
$9.^\prime$4 resolution and DHIGLS at $1^\prime$ resolution. The spectral
decomposition code $\tt{ROHSA}$ was used to model the column density of
different thermal phases and also to analyze an absorption measurement against
the radio source 4C~+66.09. From the latter we found spin temperature
$T_{\mathrm{s}} \sim 75$K, cold gas mass fraction $f\sim0.5$, and turbulent
sonic Mach number $M_t\sim3.4$. Similar to the absorption line modeling against
4C~+66.09, our best emission line decomposition model has no unstable gas
across the whole field of view, suggesting that the thermal condensation and
phase transition are not on-going but rather have reached an equilibrium state.
The cold phase of LLIV1 appears as a collection of elongated filaments that
forms a closed structure within the field decomposed. These substructures
follow the orientation of the overall large scale cloud, along the diagonal of
the GHIGLS field from north-west to south-east (in Galactic coordinates). The
angular power spectrum of the cold phase is slightly shallower than that of the
warm phase, quantifying that the cold phases have relatively more structure on
small scales. Our spatially resolved map of the cold gas mass fraction in LLIV1
from DHIGLS reveals significant variations spanning the possible range of $f$,
with mean and standard deviation 0.33 and 0.19, respectively.

Astrophysics of Galaxies