2025/02/25 by Jianwei Lyu, Xuejuan Yang, Lyu, Jianwei +11 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Gamma-ray bursts and supernovae
paper · pdf · doi:10.48550/arxiv.2502.18464
openalex publication_date 2025/02/25 · openalex created_date 2025/10/16 · openalex updated_date 2026/07/28
Utilizing deep NIRCam/WFSS data from JWST's FRESCO program, we spectroscopically survey the 3.3 μm aromatic and 3.4 μm aliphatic C--H stretching emission bands of polycyclic aromatic hydrocarbon (PAH) molecules in galaxies at redshifts z∼0.2--0.5. Unlike pre-JWST studies, largely limited to infrared (IR)-bright galaxies (L\rm IR\gtrsim1011~L_\odot) at z\lesssim0.1, we probe 200 galaxies down to L\rm IR∼108.5--1010~L_\odot well beyond the local Universe. The 3.3 μm emission is detected at ≥3-σ in 88 out of 187 galaxies, correlating tightly with galaxy IR luminosity and star formation rate (SFR) and confirming the 3.3 μm PAH as a viable SFR tracer. Despite a large scatter, the 3.3 μm-to-IR luminosity ratio (L3.3/L\rm IR) exhibits a strong metallicity dependence with a drop of L3.3/L\rm IR by a factor of \gtrsim10 at 12+log(O/H)∼8.4--8.5 towards lower metallicities. The 3.4 μm emission is detected in 37 out of 159 galaxies, with the 3.4 μm-to-3.3 μm luminosity ratio (L3.4/L3.3) spanning from ∼0.05 to ∼0.58 (median ∼0.19), corresponding to PAH aliphatic fractions of ∼0.78%--8.3% (median ∼2.9%) in terms of fractional carbon atoms in aliphatic units. While L3.4/L3.3 does not depend significantly on redshift, stellar mass, metallicity, or galaxy morphology, it does decrease with various SFR tracers, suggesting that ultraviolet photons in active star-forming regions may strip aliphatic sidegroups from PAH molecules. Our study showcases the unique power of JWST's NIRCam/WFSS to systematically map PAH aromatic and aliphatic content in statistically significant, less-biased galaxy samples, providing critical insights into PAH chemistry and its connection to galaxy properties.