Ionization state of inter-stellar medium in galaxies: evolution, SFR–M*–Z dependence, and ionizing photon escape

• DOI: 10.1093/mnras/stu902
• Publication Date: 2014-06-10T03:19:32Z
• Authors: Kimihiko Nakajima; Masami Ouchi
• Keywords: Stellar mass

We present a systematic study for ionization state of inter-stellar medium in galaxies at z=0-3 with ~140,000 SDSS and 108 intermediate to high redshift from the literature, using an ionization-parameter sensitive line ratio [OIII]5007/[OII]3727 photoionization models. confirm that z=2-3 show [OIII]/[OII] significantly higher than typical star-forming galaxy by factor >~10, models reveal these high-z have parameter log(qion/cm s^{-1})~7.6-9.0, ~4-10 local galaxies. For any redshift, we identify correlation between global properties star-formation rate (SFR), stellar mass (M_star), metallicity (Z). extend fundamental relation (FMR) develop (FIR), four-dimensional parameter, SFR, M_star, Z. The up z~3 follow FIR defined galaxies, contrast FMR whose possible evolution z~2 3 is reported. find z~2-3 appears, if one omits differences, does not exist average solution high-ionization parameter. Interestingly, all two Lyman-continuum emitting (LyC leakers) ratio, indicating positive ionizing photon escape fraction (fesc), which successfully explained our Because ratios especially Ly-alpha emitters (LAEs), are comparable to, or than, those LyC leakers, candidates objects. (abridged)