New Interpretation for the Orientation of the LMC’s Gaseous Arms B and E Using ULLYSES ^∗

Abstract The Large Magellanic Cloud (LMC) has experienced disruption from tidal and ram-pressure forces as it travels through the halo of the Milky Way. In this project, we combine radio emission-line observations from the Galactic All Sky Survey and Galactic Australian Square Kilometre Array Pathfinder surveys with UV absorption-line observations from the Hubble Space Telescope Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program to trace the material in front of the LMC. Along our eight stellar sight lines near 30 Doradus, we observe gaseous structures likely associated with two arm-like features flowing in and around the LMC’s disk. We detect the nearside gas in neutral, low-, and medium-ionization species. The lower-ionization species likely undergo both thermal and nonthermal broadening while the moderately ionized phase is influenced by more nonthermal processes. The total integrated column density of Al iii decreases with increasing angular offset from 30 Doradus, with sight lines within Δ θ ≲ 0 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 25 containing more moderately ionized gas. We demonstrate from a Gaussian decomposition technique on the H i emission that both arms likely trace an additional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>0</mml:mn> </mml:math> in Galactic longitude toward the 30 Doradus region than previously predicted. We constrain the orientation of the arms by suggesting that they likely converge around <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:mi>l</mml:mi> <mml:mo>,</mml:mo> <mml:mi>b</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mn>280</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>5</mml:mn> <mml:mo>,</mml:mo> <mml:mo>−</mml:mo> <mml:mn>31</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>.</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>°</mml:mi> </mml:mrow> </mml:mover> <mml:mn>2</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:math> and at least partially cross in front of the LMC. Our observations are consistent with two competing origins of the arms: (1) outflowing material is swept back by tidal and ram-pressure forces or (2) tidally stripped inflows fuel the ongoing stellar activity inside the LMC. Future studies are needed to distinguish between these scenarios.