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Using spectroscopic data from the Deep Extragalactic Evolutionary Probe Groth Strip Survey (DGSS), we analyze the gas-phase oxygen abundances in the warm ionized medium for 64 emission-line field galaxies in the redshift range 0.26 < z < 0.82. These galaxies comprise a small subset selected from among 693 objects in the DGSS. They are chosen for chemical analysis by virtue of having the strongest emission lines. Oxygen abundances relative to hydrogen are in the range 8.4 < 12 + log(O/H) < 9.0 with typical internal plus systematic measurement uncertainties of 0.17 dex. The 64 DGSS galaxies collectively exhibit an increase in metallicity with B-band luminosity, i.e., an L-Z relation like that seen among local galaxies. Using the DGSS sample and local galaxy samples for comparison, we searched for a "second parameter" that might explain some of the dispersion seen in the L-Z relation. Parameters such as galaxy color, emission-line equivalent width, and effective radius were explored but found to be uncorrelated with residuals from the mean L-Z relation. Subsets of DGSS galaxies binned by redshift also exhibit L-Z correlations with slopes and zero points that evolve smoothly with redshift. DGSS galaxies in the highest redshift bin (z = 0.6-0.82) are brighter, on average, by ~1 mag at fixed metallicity than those in the lowest DGSS redshift bin (z = 0.26-0.40) and by up to ~2.4 mag compared to local (z < 0.1) emission-line field galaxies. Alternatively, DGSS galaxies in the highest redshift bin (z = 0.6-0.82) are, on average, 40% (0.15 dex) more metal-poor at fixed luminosity than local (z < 0.1) emission-line field galaxies. For 0.6 < z < 0.8 galaxies, the offset from the local L-Z relation is greatest for objects at the low-luminosity (MB > -19) end of the sample and is vanishingly small for objects at the high-luminosity end of the sample (MB ~ -22). We compare these data to simple single-zone, exponential-infall PEGASE2 models, which follow the chemical and luminous evolution of galaxies from formation to z = 0. A narrow range of model parameters can qualitatively produce the slope of the L-Z relation and the observed evolution of slope and zero point with redshift when at least two of the following are true: (1) low-mass galaxies have lower effective chemical yields than massive galaxies, (2) low-mass galaxies assemble on longer timescales than massive galaxies, and (3) low-mass galaxies begin the assembly process at a later epoch than massive galaxies. The single-zone models do a reasonable job of reproducing the observed evolution for the low-luminosity galaxies (MB ~ -19) in our sample but fail to predict the relative lack of evolution in the L-Z plane observed for the most luminous galaxies (MB ~ -22). More realistic multizone models will be required to explain the chemoluminous evolution of large galaxies.

The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion-limited infrared survey of $\frac{2}{3}$ of the inner Galactic disk with a pixel resolution of [?]12 using the Infrared Array Camera at 3.6, 4.5, 5.8, and 8.0 um. The survey will cover Galactic latitudes |b| [?] 1deg and longitudes |l| = 10deg-65deg (both sides of the Galactic center). The survey area contains the outer ends of the Galactic bar, the Galactic molecular ring, and the inner spiral arms. The GLIMPSE team will process these data to produce a point-source catalog, a point-source data archive, and a set of mosaicked images. We summarize our observing strategy, give details of our data products, and summarize some of the principal science questions that will be addressed using GLIMPSE data. Up-to-date documentation, survey progress, and information on complementary data sets are available on the GLIMPSE Web site.

The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility(SIRTF) Legacy Science Program, will be a fully sampled, confusion-limited infrared survey of 2/3 of the inner Galactic disk with a pixel resolution of ?1.?2 using the Infrared Array Camera at 3.6, 4.5, 5.8, and 8.0 ?m. The survey will cover Galactic latitudes |b|?1° and longitudes |l| = 10°-65° (both sides of the Galactic center). The survey area contains the outer ends of the Galactic bar, the Galactic molecular ring, and the inner spiral arms. The GLIMPSE team will process these data to produce a point-source catalog, a point-source data archive, and a set of mosaicked images. We summarize our observing strategy, give details of our data products, and summarize some of the principal science questions that will be addressed using GLIMPSE data. Up-to-date documentation, survey progress, and information on complementary data sets are available on the GLIMPSE Web site.

Optical and ultraviolet spectroscopy obtained with the Hubble Space Telescope Faint Object Spectrograph at three locations in the central H II complex of the amorphous starburst galaxy NGC 5253 confirms an apparent area of enhanced nitrogen abundance seen in ground-based studies. At two positions, N appears enhanced by a factor of 3 [log (N/O) = -0.85] compared to a third location 50 pc away where the measured N abundance is typical of metal-poor galaxies [log (N/O) = -1.30]. No other elemental species shows spatial abundance fluctuations, including C as measured from the C III] ll1907, 1909 A emission lines. Extinction to the emission-line regions is quite low (AV = 0.25), and we rule out reddening uncertainties as the cause of the apparent N enhancement. Comparison of the observed ionic fractions to predictions of photoionization models shows that ionization uncertainties cannot be responsible for the anomalously high N/O ratio. These findings require the existence of a N production mechanism that is decoupled from C and O production. Although the high N/He enrichment ratio is consistent with that expected from non-Type I planetary nebulae (PNs), the localized nature of the enrichment, the large number of PNs (150-500), and the long timescales (109 yr) required make this explanation highly unlikely. Given the proximity of the N overabundance to a very young, heavily obscured star cluster, we attribute the N excess to recent "pollution" from massive stars. Plausible N enrichment scenarios involve O star winds, He-deficient W-R star winds, and/or ejection events from luminous blue variables. If the N enrichment is due to localized pollution from the winds of W-R stars observed in the burst, then an accompanying He enrichment of 40% ought to be observed, but we are able to rule out He enhancements at the 2 s level at both locations showing N enhancement. We propose that if the N-rich wind or ejecta is incorporated into self-gravitating clumps of molecular gas, and if the 106 yr old clusters of massive stars in starburst galaxies are precursors of globular clusters, then N-overabundant halo and globular cluster stars in the Galaxy may owe their chemical peculiarity to similar N-enrichment episodes early in the history of the Milky Way.

We measure the H II-region oxygen and nitrogen abundances for 14 star-forming emission-line galaxies (ELGs) at intermediate redshifts (0.11-1.4, similar to local spiral galaxies. These chemical properties are inconsistent with unevolved objects undergoing a first burst of star formation. Comparison with local galaxies showing similar chemical properties suggests that these intermediate-z objects contain substantial old stellar populations that were responsible for the bulk of the heavy elements presently seen in the ionized gas. Four of the 14 galaxies exhibit small half-light radii and narrow emission-line profiles (compact narrow emission-line galaxies [CNELGs]; Koo et al. 1995) consistent with small dynamical masses despite their large optical luminosities and high levels of chemical enrichment. We find that the four CNELGs are indistinguishable from the 10 other emission-line galaxies (ELGs) in the sample on the basis of their metallicity and luminosity alone. Because of their morphological similarity to H II and spheroidal galaxies, CNELGs have been proposed as the starburst progenitors of today's spheroidal galaxies. Our assessment of the stellar chemical abundances in nearby spheroidal galaxies reveals that the majority of the CNELGs are presently ~4 mag brighter and ~0.5 dex more metal rich than the bulk of the stars in well-known metal-poor dwarf spheroidal galaxies such as NGC 205 and NGC 185. Two of the four CNELGs exhibit oxygen abundances higher than the planetary nebula oxygen abundances in NGC 205, making an evolution between these two CNELGs and metal-poor dwarf spheroidal galaxies highly improbable. However, the data are consistent with the hypothesis that more luminous and metal-rich spheroidal galaxies like NGC 3605 may become the evolutionary endpoints of some CNELGs after 1-3 mag of fading. We suggest that the z=0.1-0.4 ELGs, and perhaps some of the CNELGs, are the precursors to today's spiral galaxies during an episode of vigorous bulge star formation ~5 Gyr ago.

Using Hubble Space Telescope ultraviolet and ground-based optical spectroscopy, we measure the C/O and N/O ratios of three metal-poor galaxies with similar metallicity but differing N/O. These observations, in conjunction with photoionization models, indicate that the C/O ratios estimated from C III] l1909 and [O III] l5007 lines are consistent with those measured from C II] l2326 and [O II] l3727 lines. Although inherently more uncertain than C++/O++ due to poorly known ionization correction factors, we develop the use of the C+/O+ ratio as a reasonable substitute diagnostic of the carbon abundance in H II regions. The C II] l2326 multiplet is typically quite weak, but its proximity to the [O II] ll3726, 3729 lines makes these transitions a potential tool for measuring the carbon abundance in high-redshift emission-line objects. The derived chemical properties are consistent with a statistically significant correlation between N and C abundances in metal-poor extragalactic H II regions, in the sense that systems with the largest N/O ratios also have the highest C/O ratios. This result is unexpected if the dispersion in N/O among galaxies of similar metallicity is caused by localized, temporary chemical enrichments from massive stars. The presence of a correlation suggests, instead, that the majority of N and C production is coupled, as expected from chemical evolution models where C is produced predominantly by low-mass stars and N is produced predominantly by intermediate-mass stars. The C/N ratio is, then, fixed by the initial mass function. Since the occurrence of localized chemical "pollution" in star-forming galaxies appears to be low, the relative overabundance of N in some galaxies compared to others at similar metallicity is most plausibly interpreted as an indicator of the global, secular chemical enrichment history. As such, the N/O and perhaps the C/O ratios can be used as a "clock" to estimate the time since the last major episode of star formation.