Interstellar medium abundances in the Pegasus dwarf irregular galaxy

Evan D. Skillman, Dominik J. Bomans, Henry A. Kobulnicky

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59 Scopus citations


We report Hα imaging and optical spectrophotometry of a faint H II region in the Pegasus dwarf irregular galaxy, a low-luminosity, possible Local Group member. We find that the emission-line spectrum is consistent with excitation by a single star with a temperature of less than 35,000 K, in agreement with Aparicio & Gallart (1995). Although we cannot measure the electron temperature of the ionized gas directly, we can infer a narrow range in electron temperature by comparing the emission-line spectrum with photoionization models. Then we derive a relatively low oxygen abundance of approximately 10% of the solar value, in accordance with the well-known metallicity-luminosity relationship for dwarf irregular galaxies. We also find an N/O ratio of 6%, which is higher than the typical value of 3% found in more actively star-forming dwarf irregular galaxies. By comparing this high N/O ratio with the recent star formation history of the Pegasus dwarf irregular derived by Aparicio & Gallart, we hypothesize that this may be evidence of delayed N production.

Original languageEnglish (US)
Pages (from-to)205-216
Number of pages12
JournalAstrophysical Journal
Issue number1 PART I
StatePublished - 1997


  • Galaxies: ISM
  • Galaxies: abundances
  • Galaxies: individual (Pegasus DIG DDO 216)
  • Galaxies: irregular
  • Local group


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