Correlation between star formation activity and electron density of ionized gas at z = 2.5

Rhythm Shimakawa, Tadayuki Kodama, Charles C. Steidel, Ken ichi Tadaki, Ichi Tanaka, Allison L. Strom, Masao Hayashi, Yusei Koyama, Tomoko L. Suzuki, Moegi Yamamoto

Research output: Contribution to journalArticlepeer-review

42 Citations (Scopus)


In the redshift interval of 2 < z < 3, the physical conditions of the interstellar medium (ISM) in star-forming galaxies are likely to be different from those in the local Universe because of lower gaseous metallicities, higher gas fractions, and higher star formation activities. In fact, observations suggest that higher electron densities, higher ionization parameters, and harder UV radiation fields are common. In this paper, based on the spectra of H α-selected starforming galaxies at z = 2.5 taken with Multi-Object Spectrometer for InfraRed Exploration on Keck-1 telescope, we measure electron densities (ne) using the oxygen line ratio ([O II] λλ3726,3729), and investigate the relationships between the electron density of ionized gas and other physical properties. As a result, we find that the specific star formation rate (sSFR) and the surface density of SFR (ΣSFR) are correlated with the electron density at z =2.5 for the first time. The ΣSFR-ne relation is likely to be linked to the star formation law in HII regions (where star formation activity is regulated by interstellar pressure). Moreover, we discuss the mode of star formation in those galaxies. The correlation between sSFR and ΣSFR suggests that highly star-forming galaxies (with high sSFR) tend to be characterized by higher surface densities of star formation (ΣSFR) and thus higher ne values as well.

Original languageEnglish
Pages (from-to)1284-1289
Number of pages6
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 2015 May 1
Externally publishedYes


  • Galaxies: ISM
  • Galaxies: formation
  • Galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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