Extended Star Formation in Luminous Infrared Galaxies at z ∼ 1 in the SMILES Field

Luminous infrared galaxies (LIRGs) and ultraluminous infrared galaxies (ULIRGs) in the local Universe are highly centrally concentrated in the mid-infrared (MIR) and substantially more likely than non-(U)LIRGs to be involved in mergers. At higher redshifts, images of radio emission, cold dust, and molecular gas have suggested that (U)LIRGs at cosmic noon and even earlier may be relatively less concentrated than their z ∼ 0 counterparts. Prior to the launch of the James Webb Space Telescope (JWST), quantifying the extent of obscured star formation in (U)LIRGs at z ∼ 1 was not possible due to the low spatial resolution of previous instruments in the MIR. With JWST’s Mid-Infrared Instrument (MIRI), it is now possible. We use MIRI imaging to identify a sample of 24 LIRGs at 0.5 ≤ z ≤ 1.22 in the Systematic Mid-Infrared Legacy Extragalactic Survey and find that they are generally less centrally concentrated than their z ∼ 0 counterparts. Compared to high-mass star-forming galaxies that are not LIRGs, we find little evidence that LIRGs are more likely to be morphologically disturbed at rest-frame UV, optical, and near-infrared wavelengths at z ∼ 1. This also differs from the local counterparts where strong disturbances and major mergers are closely associated with LIRGs. These results support suggestions that smaller disturbances and perhaps even internal processes can trigger the collapse of gas clouds outside of galactic cores and cause very high levels of extended star formation at z ≳ 1.