Oral Presentation

Bridging optical and far-infrared emission-line diagrams of galaxies from local to z > 6

Author(s): Yuma Sugahara (NAOJ/Waseda), Akio K. Inoue (Waseda), Yoshinobu Fudamoto (NAOJ/Waseda), Takuya Hashimoto (Tsukuba), Satoshi Yamanaka (Toba-shosen), Yuichi Harikane (ICRR)

Presenter: Yuma Sugahara (NAOJ / Waseda University)

We will present results of photoionization modeling of galaxies at local to z > 6 to bridge the BPT ([OIII]/Hb-[NII]/Ha) and FIR ([OIII]88/SFR-[CII]158/SFR) emission-line diagrams. These two diagrams illustrate the redshift evolution of ISM properties, but these are independently used for optical and FIR studies. Our aim is to bridge the diagrams using simple photoionization models constructed with Cloudy. First, we found that some galaxies at z > 6, observed with ALMA, exhibit high [OIII]88/SFR ratios, requiring low hydrogen density (n < 30 cm^-3) and high ionization parameters (log U > -2.0) to our photoionization models. We will propose three scenarios to explain the high [OIII]88/SFR: 1. underestimated SFR, 2. bursty/increasing star-formation history, and 3. [OIII]88 contribution from diffuse ionized gas. Second, by modeling galaxies at z~0 and 2, our photoionization models predict that galaxy distributions from z~0 to >6 continuously changes their locations on the BPT and FIR diagrams. Upcoming JWST observations will test these ISM properties and distributions on the BPT diagram at z > 6 predicted by our photoionization modeling.