Star formation powers optical line emission from the CGM
Abstract
Using integral field spectroscopy, we explore the disk-halo interface, or the inner circumgalactic medium (CGM), of individual galaxies by constructing and analyzing emission-line maps for a large sample (72) of normal, low-redshift galaxies spanning three orders of magnitude in stellar mass and four orders in star formation rate (SFR). We find a steep turnover occurring at ( 1 to 2 ) R e in the Hα, [O II], and [O III] line emission radial profiles. Beyond this radius, the slope of the line emission radial profiles becomes shallower as the SFR of the central galaxy decreases, which might reflect the strength of the feedback processes. The line emission fluxes at a large radius [ ( 5 to 10 ) R e or ∼ ( 0.1 to 0.25 ) r vir ] correlate with the galaxy’s SFR but not with its stellar mass. These findings suggest that ionizing photons escaping from star-forming regions in the central galaxy account for the observed emission-line fluxes from the inner CGM, with escape fractions inferred from the [O III] and [O II] ratio. Different state-of-the-art theoretical models do not agree on the predicted dependence of cool gas on the SFR of the central galaxies, highlighting the importance of CGM emission line measurements to distinguish between different subgrid models for star formation and feedback processes.
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Authors: Huanian Zhang, Lizhi Xie, Zhijie Qu, Dennis Zaritsky, Luis C. Ho, Min Bao, Fabio Fontanot, Michaela Hirschmann, Chenxu Liu, Gabriella De Lucia, Enci Wang, Haoyan Zheng
Institutions: Peking University, University of Arizona, Huazhong University of Science and Technology, Tsinghua University, Nanjing University, University of Science and Technology of China, University of Milano-Bicocca, Tianjin Normal University, Yunnan University, Nanjing Normal University, National Institute for Astrophysics, Institute for Fundamental Physics of the Universe, Kavli Institute for Theoretical Sciences, Dongfeng Motor (China)