A Bias in Optical Observations of High Redshift Luminous Infrared Galaxies

We present evidence for the dramatically different morphology between the rest frame UV and 7μm mid-IR emission of VV114 and Arp 299, two nearby (z∼0) violently interacting infrared luminous galaxies (LIRGs). Nearly all LIRGs are interacting systems and it is currently accepted that they dominate the IR emission at z>1. Luminous IR galaxies located at z=1–2 could easily be detected as unresolved sources in deep optical/near-IR ground based surveys, as well as in upcoming 24μm surveys with the Space Infrared Telescope Facility. We demonstrate that the spatial resolution of these surveys will result in blending of the emission from unresolved interacting components. An increased scatter will thus be introduced in the observed optical to mid-IR colors of these galaxies, leading to a systematic underestimation of their dust content. Subject headings: infrared: galaxies – ultraviolet: galaxies – galaxies: individual (Arp 299, VV 114) galaxies: high-redshift – galaxies: starburst – galaxies: irregular