Morphology of spitzer 24 μm detected galaxies in the UDF: The links between star formation and galaxy morphology

We have studied the morphologies of infrared-luminous galaxies at 0.3 ≤ z < 1.4 in the HST Ultra Deep Field (UDF) by calculating concentration and asymmetry indices and comparing the results with similar calculations for: (1) galaxies at similar redshift that are less infrared-active, and (2) local luminous infrared galaxies [LIRGs; L_IR(8-1000 μm)> 10 ¹¹ L_⊙]. We find that the high-redshift samples are dominated by galaxies with concentrations similar to local late-type disk galaxies; however, they are significantly more asymmetric than most local galaxies but are similar in both regards to local LIRGs. On average, the high-redshift infrared-active galaxies are slightly more asymmetric than the less active ones, although they do include a significantly higher portion of highly asymmetric (merging?) systems and a lower portion of more concentrated, symmetric ones. The morphological similarity of infrared-active and typical infrared-inactive galaxies at high redshift suggests that they may be from the same parent population, but are in different stages of an episodic star formation process. The similarity between high redshift and local LIRGs suggests that a certain level of asymmetry is generally associated with LIRG-level activity.