Formation Of Sub-Structure In Luminous Submillimeter galaxies (FOSSILS): Evidence of Multiple Pathways to Trigger Starbursts in Luminous Submillimeter Galaxies
Ryota Ikeda, Daisuke Iono, Ken-ichi Tadaki, Maximilien Franco, Min S. Yun, Jorge A. Zavala, Yoichi Tamura, Takafumi Tsukui, Christina C. Williams, Bunyo Hatsukade, Minju M. Lee, Tomonari Michiyama, Ikki Mitsuhashi, Kouichiro Nakanishi, Caitlin M. Casey, Soh Ikarashi, Kianhong Lee, Yuichi Matsuda, Toshiki Saito, Andrea Silva, Hideki Umehata, Hidenobu Yajima
TL;DR
We analyze rest-frame optical and far-IR emission in three luminous SMGs at $3.0 \lesssim z \lesssim 4.5$, achieving ~400-500 pc resolution with JWST and ALMA. Despite similar FIR luminosities, the galaxies show heterogeneous morphologies across wavelengths: AzTEC-4 and AzTEC-8 appear disk-like in optical while AzTEC-1 is highly concentrated with Sérsic index $n=5.4$, and FIR emission is clumpy. AzTEC-4 exhibits a two-arm spiral of dust not traced by the stellar distribution, indicating multiple triggering pathways: secular disk instability (AzTEC-4), possible minor mergers (AzTEC-8), and a combination of efficient central gas fueling by a gas-rich major merger plus reformation of a cold gas disk (AzTEC-1). This demonstrates that luminous SMGs at high redshift can be triggered by multiple physical mechanisms, highlighting the complex pathways to starbursts and informing models of massive galaxy assembly.
Abstract
We present an analysis of rest-frame optical and far-infrared continuum emission in three luminous submillimeter galaxies (SMGs) at $3.0\lesssim z\lesssim4.5$. The SMGs are spatially resolved down to 400-500 pc ($\sim0.05$'') resolution by James Webb Space telescope (JWST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations. Despite similarities in their observed far-infrared properties (flux density, infrared luminosity, and effective radius), the three SMGs exhibit heterogeneous morphologies both across wavelengths and among the sources themselves. While two of them (AzTEC-4 and AzTEC-8) show a disk-like structure in optical continuum, AzTEC-1 is dominated by highly concentrated component with the Sérsic index of $n=5.4$, where its far-infrared continuum emission is clumpy and less concentrated. AzTEC-4, which is confirmed to be at $z=4.198$, shows a two-arm spiral of dust, but not in the stellar distribution. These three SMGs exemplify that multiple physical mechanisms exist in triggering starbursts in luminous SMGs at high redshift: secular instability in gas disks (AzTEC-4) in addition to possible minor mergers (AzTEC-8), and a combination of the efficient gas supply to the central core induced by a gas-rich major merger and the reformation of cold gas disk (AzTEC-1).