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Register a new userMetal Abundances of KISS Galaxies. II. Nebular Abundances of Twelve Low-Luminosity Emission-Line Galaxies
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J. Melbourne
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We present follow-up spectra of 39 emission-line galaxies (ELGs) from the KPNO International Spectroscopic Survey (KISS). Many targets were selected as potentially low metallicity systems based on their absolute B magnitudes and the metallicity-luminosity relation. The spectra, obtained with the Lick 3-m telescope, cover the full optical region from [O II]3726,29 to beyond [S IIl6717,31 and include measurement of [O IIIl4363 in twelve objects. The spectra are presented and tables of the strong line ratios are given. For twelve high signal-to-noise ratio spectra, we determine abundance ratios of oxygen, nitrogen, neon, sulfur and argon. We find these galaxies to be metal deficient with three systems approaching O/H of 1/25th solar. We compare the abundance results from the temperature-based T_e method to the results from the strong-line p_3 method of Pilyguin (2000).
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We present high S/N spectroscopy of 15 emission-line galaxies (ELGs) cataloged in the KPNO International Spectroscopic Survey (KISS), selected for their possession of high equivalent width [O III] lines. The primary goal of this study was to attempt to derive direct-method ($T_e$) abundances for use in constraining the upper-metallicity branch of the $R_{23}$ relation. The spectra cover the full optical region from [O II]{lambda}{lambda}3726,3729 to [S III]{lambda}{lambda}9069,9531 and include the measurement of [O III]{lambda}4363 in 13 objects. From these spectra, we determine abundance ratios of helium, nitrogen, oxygen, neon, sulfur, and argon. We find these galaxies to predominantly possess oxygen abundances in the range of 8.0 $lesssim$ 12+log(O/H) $lesssim$ 8.3. We present a comparison of direct-method abundances with empirical SEL techniques, revealing several discrepancies. We also present a comparison of direct-method oxygen abundance calculations using electron temperatures determined from emission lines of O$^{++}$ and S$^{++}$, finding a small systematic shift to lower $T_e$ (~1184 K) and higher metallicity (~0.14 dex) for sulfur-derived $T_e$ compared to oxygen-derived $T_e$. Finally, we explore in some detail the different spectral activity types of targets in our sample, including regular star-forming galaxies, those with suspected AGN contamination, and a local pair of low-metallicity, high-luminosity compact objects.
We derive metal abundance estimates for a large sample of starbursting emission-line galaxies (ELGs). Our sample is drawn from the KPNO International Spectroscopic Survey (KISS) which has discovered over 2000 ELG candidates to date. Follow-up optical spectra have been obtained for ~900 of these objects. A three step process is used to obtain metal abundances for these galaxies. We first calculate accurate nebular abundances for 12 galaxies whose spectra cover the full optical region from [OII]3726,29 to beyond [SII]6717,31 and include detection of [OIII]4363. Using secondary metallicity indicators R_23 and p_3, we calculate metallicities for an additional 59 galaxies with spectra that cover a similar wavelength range but lack [OIII]4363. The results are used to calibrate relations between metallicity and two readily observed emission-line ratios, which allow us to estimate coarse metallicities for 519 galaxies in total. The uncertainty in these latter abundance estimates is 0.16 dex. From the large, homogeneously observed sample of star-forming galaxies we identify low metallicity candidates for future study and investigate the metallicity-luminosity relation. We find a linear metallicity-luminosity relation of the following form: 12 + log(O/H) = 4.059 - 0.240 M_B, with an RMS scatter of 0.252. This result implies that the slope of the metallicity- luminosity relation is steeper than when dwarf galaxies are considered alone, and may be evidence that the relationship is not linear over the full luminosity range of the sample.
We present updated metallicity relations for the spectral database of star-forming galaxies (SFGs) found in the KPNO International Spectroscopic Survey (KISS). New spectral observations of emission-line galaxies (ELGs) obtained from a variety of telescope facilities provide oxygen abundance information. A nearly four-fold increase in the number of KISS objects with robust metallicities relative to our previous analysis provides for an empirical abundance calibration to compute self-consistent metallicity estimates for all SFGs in the sample with adequate spectral data. In addition, a sophisticated spectral energy distribution (SED) fitting routine has provided robust calculations of stellar mass. With these new and/or improved galaxy characteristics, we have developed luminosity-metallicity ($L$-$Z$) relations, mass-metallicity ($M_{*}$-$Z$) relations, and the so-called Fundamental Metallicity Relation (FMR) for over 1,450 galaxies from the KISS sample. This KISS $M_{*}$-$Z$ relation is presented for the first time and demonstrates markedly lower scatter than the KISS $L$-$Z$ relation. We find that our relations agree reasonably well with previous publications, modulo modest offsets due to differences in the SEL metallicity calibrations used. We illustrate an important bias present in previous $L$-$Z$ and $M_{*}$-$Z$ studies involving direct-method ($T_{e}$) abundances that may result in systematically lower slopes in these relations. Our KISS FMR shows consistency with those found in the literature, albeit with a larger scatter. This is likely a consequence of the KISS sample being biased toward galaxies with high levels of activity.
We explore the galaxian luminosity-metallicity (L-Z) relationship in both the optical and the near-IR using a combination of optical photometric and spectroscopic observations from the KPNO International Spectroscopic Survey (KISS) and near-infrared photometry from the Two-micron All Sky Survey (2MASS). We supplement the 2MASS data with our own NIR photometry for a small number of lower-luminosity ELGs that are under-represented in the 2MASS database. Our B-band L-Z relationship includes 765 star-forming KISS galaxies with coarse abundance estimates from our follow-up spectra, while the correlation with KISS and 2MASS yields a total of 420 galaxies in our J-band L-Z relationship. We explore the effect that changing the correlation between the strong-line abundance diagnostic R_23 and metallicity has on the derived L-Z relation. We find that the slope of the L-Z relationship decreases as the wavelength of the luminosity bandpass increases. We interpret this as being, at least in part, an effect of internal absorption in the host galaxy. Furthermore, the dispersion in the L-Z relation decreases for the NIR bands, suggesting that variations in internal absorption contribute significantly to the observed scatter. We propose that our NIR L-Z relations are more fundamental than the B-band relation, since they are largely free of absorption effects and the NIR luminosities are more directly related to the stellar mass of the galaxy than are the optical luminosities.
The validity of oxygen and nitrogen abundances derived from the global emission-line spectra of galaxies via the P-method has been investigated using a collection of published spectra of individual HII regions in irregular and spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that global emission-line spectra can reliably indicate the chemical properties of galaxies has been confirmed. It has been shown that the comparison of the global spectrum of a galaxy with a collection of spectra of individual HII regions can be used to distinguish high and low metallicity objects and to estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen abundances in samples of UV-selected and normal nearby galaxies have been determined. It has been found that the UV-selected galaxies occupy the same area in the N/O -- O/H diagram as individual HII regions in nearby galaxies. Finally, we show that intermediate-redshift galaxies systematically deviate from the metallicity -- luminosity trend of local galaxies.
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