Summary of our knowledge of UV extinction curves at low metallicity in the Large and Small Magellanic Clouds. Possibilities for UVEX to significantly advance our knowledge of UV extinction at low metallilcieis.
MD First UVEX Community Workshop 15 Mar 2023 “Have Dust – Will Study” [email protected] @[email protected] karllark@github Slides on speakdeck@karllark
• SMC shows largest variations • LMC shows strong variations influenced by “mini-starburst” • Low metallicity = clues to earlier times • Variations clues to dust grain evolution – Formation in evolved stars – ISM grain growth – Processing by harsh radiation fields • UVEX potential is large
and IR • IR: emission – Strong variation in MIR → aromatic/PAH features – Strong variation in far-IR → emissivity slopes • UV: dust abundances (via gas phase lines [depletions]) – Strong variations in implied dust grain compositions • UV: extinction (focus of this talk) – Strong variation in 2175 A feature and far-UV
compositions • Low metallicity – less chemically evolved – Connection to galaxies at all redshifts • Magellanic Clouds – Nearby – Interesting metallicities (straddling “transition” metallicity) – External – can easily study across entire galaxy
4 similar curves are found in the star forming bar of the SMC! Ha image of the SMC Gordon & Clayton (1998, ApJ, 500, 816) Gordon et al. (2003, ApJ, 594, 279) STIS
– STIS from 3 HST programs (PI: Gordon) • Picked to just get more sightlines, sample range of q_PAH, and get MR12 stars over full UV & w/ slit • Use stellar models – Pro: no observed comparisons needed – Con: Total extinction = SMC + MW foreground • Extinction for 16 sightlines – Tripling of sample
IUE → STIS → UVEX • Could easily expand the extinction sample by factors of 10 or more(!!!!) – LMC: 19 current sightlines (may add 5-10 from ULLYSES) – SMC: 16 current sightlines (none reddened enough in ULLYSES) – Other nearby/low-metallicity galaxies?: ?? sightlines • Pick reddened sightlines to O7-B3 stars [E(B-V) > 0.2] • Pick set of lightly reddened comparison stars in each galaxy – Empirically correct for foreground extinction
high/low R(V) sightlines – Spectral followup • Reflection Nebulae (MW, LMC, SMC, etc.) – Dust radiative transfer • Derive single scattering albedo and phase function • Diagnostic of dust composition (silicates versus carbonaceous grains) – Imaging for all, spectral mapping for some (1 deg slit rocks) • MW Diffuse Galactic Light (big reflection) – Same as above
• SMC shows largest variations • LMC shows strong variations influenced by “mini-starburst” • Low metallicity = clues to earlier times • Clues to dust grain evolution – Formation in evolved stars – Processing by harsh radiation fields – ISM grain growth • UVEX potential is large