We have modeled a large sample of infrared starburst galaxies using both the PEGASE v2.0 and STARBURST99 codes to generate the spectral energy distribution (SED) of the young star clusters. PEGASE utilizes the Padova group tracks, while STARBURST99 uses the Geneva group tracks, allowing comparison between the two. We used our MAPPINGS III code to compute photoionization models that include a self-consistent treatment of dust physics and chemical depletion. We use the standard optical diagnostic diagrams as indicators of the hardness of the EUV radiation Ðeld in these galaxies. These diagnostic diagrams are most sensitive to the spectral index of the ionizing radiation Ðeld in the 1È4 ryd region. We Ðnd that warm infrared starburst galaxies contain a relatively hard EUV Ðeld in this region. The PEGASE ionizing stellar continuum is harder in the 1È4 ryd range than that of STARBURST99. As the spectrum in this regime is dominated by emission from Wolf-Rayet (W-R) stars, this discrepancy is most likely due to the di †erences in stellar atmosphere models used for the W-R stars. The PEGASE models use the Clegg & Middlemass planetary nebula nuclei (PNN) atmosphere models for the W-R stars, whereas the STARBURST99 models use the Schmutz, Leitherer, & Gruenwald W-R atmosphere models. We believe that the Schmutz et al. atmospheres are more applicable to the starburst galaxies in our sample ; however, they do not produce the hard EUV Ðeld in the 1È4 ryd region required by our observations. The inclusion of continuum metal blanketing in the models may be one solution. Supernova remnant (SNR) shock modeling shows that the contribution by mechanical energy from SNRs to the photoionization models is >20%. The models presented here are used to derive a new theoretical classiÐcation scheme for starbursts and active galactic nucleus (AGN) galaxies based on the optical diagnostic diagrams.

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We have used a combination of stellar population synthesis and photoionization models to develop a set of ionization parameter and abundance diagnostics based only on the use of the strong optical emission lines. These models are applicable to both extragalactic H II regions and star-forming galaxies. We show that, because our techniques solve explicitly for both the ionization parameter and the chemical abundance, the diagnostics presented here are an improvement on earlier techniques based on strong emission-line ratios.Our techniques are applicable at all metallicities. In particular, for metallicities above half solar, the ratio [N II]/[O II] provides a very reliable diagnostic since it is ionization parameter independant and does not have a local maximum. This ratio has not been used historically because of worries about reddening corrections. However, we show that the use of classical reddening curves is quite sufficient to allow this [N II]/[O II] diagnostic to be used with confidence as a reliable abundance indicator.As we had previously shown, the commonly-used abundance diagnostic R 23 depends strongly on the ionization parameter, while the commonly-used ionization parameter diagnostic [O III]/[O II] depends strongly on abundance. The iterative method of solution presented here allows both of these parameters to be obtained without recourse to the use of temperature-sensitive line ratios involving faint emission lines.We compare three commonly-used abundance diagnostic techniques and show that individually, they contain systematic and random errors. This is a problem affecting many abundance diagnostics and the errors generally have not been properly studied or understood due to the lack of a reliable comparison abundance, except for very low metallicities, where the [O III] λ4363 auroral line is used. Here, we show that the average of these techniques provides a fairly reliable comparison abundance indicator against which to test new diagnostic methods.The cause of the systematic effects are discussed, and we present a new 'optimal' abundance diagnostic method based on the use of line ratios involving [N II],

We present a new library of fully-radiative shock models calculated with the MAPPINGS III shock and photoionization code. The library consists of grids of models with shock velocities in the range v=100-1000 km/s and magnetic parameters B/sqrt(n) of 10^-4 - 10 muG cm^(3/2) for five different atomic abundance sets, and for a pre-shock density of 1.0 cm^(-3). Additionally, Solar abundance model grids have been calculated for densities of 0.01, 0.1, 10, 100, and 1000 cm^(-3) with the same range in v and B/sqrt(n). Each model includes components of both the radiative shock and its photoionized precursor, ionized by the EUV and soft X-ray radiation generated in the radiative gas. We present the details of the ionization structure, the column densities, and the luminosities of the shock and its precursor. Emission line ratio predictions are separately given for the shock and its precursor as well as for the composite shock+precursor structure to facilitate comparison with observations in cases where the shock and its precursor are not resolved. Emission line ratio grids for shock and shock+precursor are presented on standard line ratio diagnostic diagrams, and we compare these grids to observations of radio galaxies and a sample of AGN and star forming galaxies from the Sloan Digital Sky Survey. This library is available online, along with a suite of tools to enable the analysis of the shocks and the easy creation of emission line ratio diagnostic diagrams. These models represent a significant increase in parameter space coverage over previously available models, and therefore provide a unique tool in the diagnosis of emission by shocks.Comment: 39 pages, 34 figures, accepted for publication in ApJS, April 200

We have developed a technique to systematically discover and study high-redshift supernovae that can be used to measure the cosmological parameters. We report here results based on the initial seven of more than 28 supernovae discovered to date in the high-redshift supernova search of the Supernova Cosmology Project. We Ðnd an observational dispersion in peak magnitudes of this disperp MB \ 0.27 ; sion narrows to after "" correcting ÏÏ the magnitudes using the light-curve "" widthp MB,corr \ 0.19 luminosity ÏÏ relation found for nearby (z ¹ 0.1) Type Ia supernovae from the Cala n/Tololo survey (Hamuy et al.). Comparing light-curve widthÈcorrected magnitudes as a function of redshift of our distant (z \ 0.35È0.46) supernovae to those of nearby Type Ia supernovae yields a global measurement of the mass density, for a " \ 0 cosmology. For a spatially Ñat universe (i.e., not correspond to a unique value of the deceleration parameterWe present analyses and checks q 0 . for statistical and systematic errors and also show that our results do not depend on the speciÐcs of the width-luminosity correction. The results for are inconsistent with "-dominated, low-) " -versus-) M density, Ñat cosmologies that have been proposed to reconcile the ages of globular cluster stars with higher Hubble constant values.