PHYSICAL PROPERTIES OF COMPLEX C HALO CLOUDS

Abstract

Observations from the Galactic Arecibo L-band Feed Array H i (GALFA-H I) Survey of the tail of Complex C are presented and the halo clouds associated with this complex are cataloged. The properties of the Complex C clouds are compared to clouds cataloged at the tail of the Magellanic Stream to provide insight into the origin and destruction mechanism of Complex C. Magellanic Stream and Complex C clouds show similarities in their mass distributions (slope = −0.7 and −0.6 log(N (log(mass))) / log(mass), respectively) and have a common line width of 20–30 km s−1 (indicative of a warm component), which may indicate a common origin and/or physical process breaking down the clouds. The clouds cataloged at the tail of Complex C extend over a mass range of 101.1–104.8 M, sizes of 101.2–102.6 pc, and have a median volume density and pressure of 0.065 cm−3 and (P/k) = 580 K cm−3. We do not see a prominent two-phase structure in Complex C, possibly due to its low metallicity and inefficient cooling compared to other halo clouds. Assuming that the Complex C clouds are in pressure equilibrium with a hot halo medium, we find a median halo density of 5.8 × 10−4 cm−3, which given a constant distance of 10 kpc is at a z-height of ∼3 kpc. Using the same argument for the Stream results in a median halo density of 8.4×10−5(60 kpc/d) cm−3. These densities are consistent with previous observational constraints and cosmological simulations. We also assess the derived cloud and halo properties with three-dimensional grid simulations of halo