Special Talk

• Special Talks

  Speaker: Sapna Mishra (STScI)
  Title: Studying Diffuse Gas in the Magellanic System: Insights from UV and Optical Spectroscopy
  Abstract: The Milky Way (MW) and its companions, the Large and Small Magellanic Clouds (LMC and SMC), form a dynamic system where tidal and hydrodynamic interactions drive gas exchange, shaping large-scale features such as the Magellanic Stream (MS). This MS acts as a reservoir of neutral and ionized gas, fueling the MW and influencing its long-term evolution. Yet, despite extensive research, fundamental questions remain: Does the LMC possess a circumgalactic medium (CGM) capable of shielding its gas from ram-pressure stripping by the MW? And how close does the MS approach the Sun before its gas accretes onto the MW disk? In this talk, I will present results from my recent UV and optical spectroscopic studies of Magellanic gas, focusing on two key aspects: characterizing the LMC’s CGM and constraining the distance to the MS. Using archival HST/COS spectra of 28 quasars located within 35 kpc of the LMC, we detect UV absorption lines (Si II, Si III, Si IV, and C IV) and find evidence for a multi-phase CGM around the LMC, truncated at a radius of 17 kpc—consistent with simulations of ram-pressure stripping. In parallel, by analyzing VLT/UVES spectra of five blue horizontal branch (BHB) stars at distances between 13 and 55 kpc from the Sun, we find no Ca II or Na I absorption at Stream velocities, establishing the first observational lower limit of 55 kpc for the distance to the MS. I will discuss these results in detail and explore their broader implications for our understanding of the CGM in interacting galaxies.

  Speaker: Vida Saeedzadeh (STScI)
  Title: Mapping the Circumgalactic Medium in Emission: Mass, Observability, and Kinematics from FOGGIE Simulations
  Abstract: The circumgalactic medium (CGM) plays a central role in regulating galaxy formation and evolution through gas accretion and feedback-driven outflows. Emission-line observations offer a unique opportunity to map the three-dimensional structure and kinematics of the CGM, complementing absorption-line studies. Using high-resolution Figuring Out Gas & Galaxies In Enzo (FOGGIE) simulations, we generate mock emission maps for six Milky Way–mass galaxies across multiple UV lines, including CII, CIII, CIV, OVI, SiII, SiIII, SiIV, and MgII. We investigate the mass budget of neutral hydrogen (HI) compared to ionized CGM gas, and quantify how much of this gas is detectable given the spatial resolution and sensitivity limits of current and upcoming instruments. We find that with instruments such as the Keck Cosmic Web Imager (KCWI) and the Multi Unit Spectroscopic Explorer (MUSE), less than 10% of the ionized CGM mass is observable in emission, underscoring the need for deeper sensitivity and finer resolution in future surveys. We further explore the kinematic signatures of CGM gas by constructing emissivity-weighted velocity maps. We assess the ability to distinguish inflows from outflows as a function of spectral resolution, providing guidance for interpreting future observations. Our results highlight the observational challenges and opportunities for mapping the multiphase CGM in emission and constraining the baryon cycle in galaxy halos.