Emission line ratios for the circumgalactic medium and the “bimodal” nature of galaxies

Huanian Zhang, Dennis Zaritsky, Jessica Werk, Peter Behroozi

Research output: Contribution to journalArticlepeer-review


We find significantly different diagnostic emission line ratios for the circumgalactic gas associated with galaxies of stellar masses above and below 1010.4 M☉ using SDSS spectroscopy. Specifically, in a sample of 17,393 galaxies, intersected by 18,535 lines of sight at projected radii between 10 and 50 kpc, we stack measured fluxes for nebular strong emission lines, [O III] λ5007, Hα and [N II] λ6583, and find that the gas surrounding the lower mass galaxies exhibits similar line ratios to those of gas ionized by star formation and that surrounding the higher mass galaxies similar to those of gas ionized by AGN or shocks. This finding highlights yet another characteristic of galaxies that is distinctly different above and below this stellar mass threshold, but one that is more closely connected to the gas accretion behavior hypothesized to be responsible for this dichotomy.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Sep 24 2018


  • Galaxies: kinematics and dynamics
  • Halos
  • Intergalactic medium
  • Structure

ASJC Scopus subject areas

  • General

Fingerprint Dive into the research topics of 'Emission line ratios for the circumgalactic medium and the “bimodal” nature of galaxies'. Together they form a unique fingerprint.

Cite this