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SUMMARY:The Metallicity Dependence of PAH Emission in Galaxies. II. Insigh
 ts from JWST/ NIRCam Imaging of the Smallest Dust Grains in M101
DTSTART:20260504T123000Z
DTEND:20260504T124500Z
DTSTAMP:20260509T051800Z
UID:indico-event-1813@indico.dfa.unipd.it
DESCRIPTION:Speakers: Gaia Edes Esposto (INAF - Università degli Studi di
  Padova)\n\nWe explore the physical origins of the observed deficit of pol
 ycyclic aromatic hydrocarbons (PAHs) at subsolar metallicity using JWST/NI
 RCam imaging of the nearby galaxy M101\, covering regions from solar metal
 licity (Z⊙) down to 0.4 Z⊙. These maps are used to trace the radial ev
 olution of the shortest-wavelength PAH feature at 3.3 μm\, which is emitt
 ed preferentially by the smallest PAHs (<100 carbon atoms). The fractional
  contribution of PAH 3.3 μm to the total PAH luminosity (ΣPAH) increases
  by 3× as metallicity declines\, rising from ∼1% to ∼3% over the obse
 rved range\, consistent with prior predictions from the inhibited grain gr
 owth model based on Spitzer spectroscopy. We explore model refinements inc
 luding photon effects and alternative size evolution prescriptions and fin
 d that a modest amount of small grain photodestruction remains possible\, 
 provided the grain size cutoff does not exceed ∼55 carbon atoms. The bes
 t-fit models predict 3.3 μm/ΣPAH will rise to ∼5.6%─7.7% at 10% Z⊙
 . Surprisingly\, even as ΣPAH drops significantly relative to the total i
 nfrared luminosity (TIR) as metallicity declines\, 3.3 μm/TIR alone rises
 \, potentially indicating the mass fraction of the smallest PAH grains inc
 reases as the total dust content in galaxies drops. The current model cann
 ot fully reproduce this trend even if the unusually strong effects of chan
 ging radiation field hardness on 3.3 μm/TIR are included. This may be evi
 dence that the smallest PAHs are uniquely robust against destruction and i
 nhibited growth effects. These results highlight the pivotal role that sho
 rt-wavelength PAH emission can play in studies of low-metallicity and high
 -redshift galaxies.\n\n\nhttps://indico.dfa.unipd.it/event/1813/
LOCATION:Aula Rosino (Dipartimento di Fisica e Astronomia - Edificio ex-Ri
 zzato)
URL:https://indico.dfa.unipd.it/event/1813/
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