Ram Pressure Stripping of the Large Magellanic Cloud’s Disk as a Probe of the Milky Way’s Circumgalactic Medium

Abstract

Recent observations have constrained the orbit and structure of the Large Magellanic Cloud (LMC), implying a well-constrained pericentric passage about the Milky Way (MW) ∼ 50 Myr ago. In this scenario, the LMC's gaseous disk has recently experienced stripping, suggesting the current extent of its HI disk directly probes the medium in which it is moving. From the observed stellar and HI distributions of the system we find evidence of a truncated gas profile along the windward "leading edge' of the LMC disk, despite a far more extended stellar component. We explore the implications of this ram pressure stripping signature, using both analytic prescriptions and full 3-dimensional hydrodynamic simulations of the LMC. Our simulations subject the system to a headwind whose velocity components correspond directly to the recent orbital history of the LMC. We vary the density of this headwind, using a variety of sampled parameters for a β-profile for a theoretical MW circumgalactic medium (CGM), comparing the resulting HI morphology directly to observations of the LMC HI and stellar components. This model can match the radial extent of the LMC's leading (windward) edge only in scenarios where the MW CGM density at pericentric passage is n p (R = 48.2 ± 5 kpc) = 1.1−.45 × 10 −4 cm −3 . The implied pericentric density proves insensitive to both the broader CGM structure and temperature profile, thus providing a model-independent constraint on the local gas density. This result imposes an important constraint on the density profile of the MW's CGM, and thus the total baryon content of the MW. From our work, assuming a β-profile valid to ∼ r vir , we infer a total diffuse CGM mass M (300 kpc) = 2.6 ± 1.4 × 10 10 M ⊙ or approximately 15% of a 10 12 M ⊙ MW's baryonic mass budget.

The environmental dependence of H i in galaxies in the eagle simulations

“…Interestingly, it is believed that the Magellanic Stream -the spectacular H I trail that the Magellanic Clouds are leaving behind as they move around the Milky Way -is produced by the mutual interactions between the clouds, and possibly amplified by the ram pressure by the Galaxy's hot halo (Besla et al 2012;Salem et al 2015). Despite the uncertainties of our analysis, our conclusions are consistent with those of Besla et al (2012) i.e.…”

Star cluster formation history along the minor axis of the Large Magellanic Cloud

“…Recently, Salem et al (2015) and Indu & Subramaniam (2015) have suggested from observations and modelling of H I spatial and velocity distributions, that the outer regions of the LMC were disturbed by ram pressure effects due to the motion of the LMC in the MW halo. Particularly, Salem et al (2015) found evidence that the LMC's gaseous disc has recently experienced ram pressure stripping, with a truncated gas profile along the windward leading edge of the LMC disc. This means that some amount of gas could travel in the opposite direction to the LMC motion, and thus could contribute with material for the cluster formation in the western-outermost part of the galaxy (see their figure 17).…”

Under pressure: quenching star formation in low-mass satellite galaxies via stripping

“…Within the Milky Way, a variety of indirect probes point towards halo gas densities of ∼ 10 −4 cm −3 for the hot (T ∼ 10 6 K) component (e.g. Weiner & Williams 1996;Stanimirović et al 2002;Fox et al 2005;Grcevich & Putman 2009;Salem et al 2015). Moreover, both observed X-ray emission and pulsar dispersion measurements in the Milky Way are consistent with a cored hot halo distribution with a density of > 10 −4 cm −3 extending to radial distances of ∼ 100 kpc (Fang, Bullock & Boylan-Kolchin 2013, see also Anderson & Bregman 2010;Gupta et al 2012;Miller & Bregman 2013Faerman, Sternberg & McKee 2016).…”

“…Lin & Lynden-Bell 1977;Besla et al 2010Besla et al , 2012Guglielmo, Lewis & Bland-Hawthorn 2014) versus ram-pressure or viscous stripping (e.g. Moore & Davis 1994;Mastropietro et al 2005;Salem et al 2015;Hammer et al 2015). Given the uncertainties associated with the orbit of the LMC and SMC and the physical origins of the stripped gas, it is difficult to make a clear accounting of the stripped fraction for the two systems (e.g.…”