Braving the Storm I: Quantifying Disk-wide Ionized Outflows in the Large Magellanic Cloud with ULLYSES
arxiv(2024)
摘要
The Large Magellanic Cloud (LMC) is home to many HII regions, which may lead
to significant outflows. We examine the LMC's multiphase gas (T∼10^4-5
K) in HI, SII, SiIV, and CIV using 110 stellar sight lines observed with the
HST's Ultraviolet Legacy Library of Young Stars as Essential Standards
(ULLYSES) program. We develop a continuum fitting algorithm based on the
concept of Gaussian Process regression and identify reliable LMC interstellar
absorption lines over v_ helio=175-375 km s^-1. Our analyses show
disk-wide, warm, ionized outflows in SiIV and CIV across the LMC with bulk
velocities of |v_ out, bulk|∼20-60 km s^-1, which indicates that
most of the outflowing mass is gravitationally bound. The outflows' column
densities correlate with the LMC's star formation rate surface densities
(Σ_ SFR), and the outflows in star-forming regions with higher
Σ_ SFR tend to be more ionized. Considering the ionized outflows
from both sides of the LMC as traced by CIV, we conservatively estimate a total
outflow rate of Ṁ_ out≳ 0.03 M_⊙ yr^-1 and a
mass loading factor of η≳ 0.2. We compare the LMC's outflows with
those detected in starburst galaxies, and find a universal scaling relation of
|v_ out, bulk|∝Σ_ SFR^0.22 over a range of
star-forming conditions (Σ_ SFR∼10^-2-10^2 M_⊙
yr^-1 kpc^-2). Lastly, we find that the outflows are co-rotating
with the LMC's young stellar disk and the velocity field does not seem to be
significantly impacted by external forces; we thus speculate on the existence
of a bow shock leading the LMC, which may have shielded the outflows from ram
pressure as the LMC orbits the Milky Way.
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