H II GALAXIES VERSUS PHOTOIONIZATION MODELS FOR EVOLVING STARBURSTS

摘要: We have constructed a grid of models representing an H II region produced by evolving starburst embedded in gas cloud the same metallicity. The were with spectral energy distribution from stellar evolutionary synthesis code as input for photoionization that computes emission-line strengths and equivalent widths. Stellar evolution was assumed to proceed according Maeder. radiation -eld computed using Kurucz model atmospheres, supple- mented expanding non-LTE atmospheres Schmutz et al. phases strong winds, making signi-cant improvement over previous works classical static, plane-parallel atmospheres. Models interiors being still phase continuous improvement, our population reNect state art 1995. used analyze sample 100 galaxies which both Hb widths (O III) j4363 line intensities available (the latter allowing direct determination oxygen abundances based on measured electron temperatures). Because these selection criteria, results study are restricted metal-poor objects metallicities less than about one-half solar. confrontation observations is presented six diagnostic diagrams involving hydro- gen lines. Our approach many respects much more constraining studies regions ionized starbursts. found standard (instantaneous burst star formation Salpeter initial mass function upper cuto† reproduces observational constraints pro- M _ ) vided nebular emission lines extremely well if e†ects taken into account. unique consistent essentially all metal- licity range D0.025 D0.25 In contrast, Salpeter-type Z . truncated at 50 not observations: they violate observed mean e†ective temperature ionizing cluster declines 50,000 40,000 K during time when enough be measurable. W ithin framework models, abundance where comparisons made observations, there no signi-- cant evidence variation metallicity, other one generated metallicity-dependent atmospheric models. A very narrow ionization parameters required reproduce ratios. This should set limits dynamical giant regions. -nd large fraction having I) j6300/Hb ratios larger 0.02. Even lowest considered do produce An approximate esti- mate mechanical released winds supernovae later leads suggestion ratioEin contrast studiedEis cantly a†ected shocks. small spread free necessary properties poor allows us propose new indicator age: j5007 width quite robust can up ages traditional high signal-to-noise spectra. also prove useful low spectra star-forming higher redshift, because value j5007/Hb starbursts younger 5 Myr.