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The UV bump is a broad absorption feature centered at 2175{\AA} that is seenin the attenuation/extinction curve of some galaxies, but its origin is notwell known. Here, we use a sample of 86 star-forming galaxies at z=1.7-2.7 withdeep rest-frame UV spectroscopy from the MUSE HUDF Survey to study theconnection between the strength of the observed UV 2175{\AA} bump and theSpitzer/MIPS 24 micron photometry, which at the redshift range of our sampleprobes mid-IR polycyclic aromatic hydrocarbon (PAH) emission at ~6-8 micron.The sample has robust spectroscopic redshifts and consists of typicalmain-sequence galaxies with a wide range in stellar mass (log(Mstar/Msun) ~8.5-10.7) and star formation rates (SFRs; SFR ~ 1-100 Msun/yr). Galaxies withMIPS detections have strong UV bumps, except for those with mass-weighted agesyounger than ~150 Myr. We find that the UV bump amplitude does not change withSFR at fixed stellar mass but increases with mass at fixed SFR. The UV bumpamplitude and the PAH strength (defined as mid-IR emission normalized by SFR)are highly correlated and both also correlate strongly with stellar mass. Weinterpret these correlations as the result of the mass-metallicityrelationship, such that at low metallicities PAH emission is weak due to alower abundance of PAH molecules. The weak or complete absence of the 2175{\AA}bump feature on top of the underlying smooth attenuation curve at lowmass/metallicities is then expected if the PAH carriers are the main source ofthe additional UV absorption.

The UV 2175{\AA} Attenuation Bump and its Correlation with PAH Emission at z~2