New Insights into Emission-Line Galaxies from HST and VLT Observations

Recent research has focused on emission-line galaxies identified through the near-infrared slitless Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) WISP survey. The study, titled "Emission-line galaxies at z~1 from near-IR HST Slitless Spectroscopy: metallicities, star formation rates and redshift confirmations from VLT/FORS2 spectroscopy," was conducted by K. Boyett and 16 co-authors. The findings were published on arXiv and accepted to the Monthly Notices of the Royal Astronomical Society.

The research targeted 85 out of 138 emission line objects across four WISP fields, with redshifts ranging from 0.4 to 2. The study confirmed 95% of the initial WFC3 grism redshifts in the 38 cases where emission lines were detected in FORS2 spectroscopy. However, it was noted that for targets showing a single emission line in WFC3, up to 65% at redshifts less than 1.28 did not have the expected emission lines detected in FORS2, indicating a potential false detection rate.

The analysis revealed that the extinction of the WISP galaxies is consistent with an extinction value of 1 magnitude in H-alpha. The median stellar mass of the galaxies was found to be approximately 8.94 in logarithmic solar mass units. Notably, the emission-line-selected galaxies tended to lie above the star-forming main sequence, indicating higher specific star formation rates.

Using various emission lines, the researchers derived gas-phase metallicities, which were typically found to be sub-solar and decreasing with redshift. The study also highlighted that the WISP galaxies lie below the mass-metallicity relation observed at redshift zero, with higher star formation rates correlating with lower metallicity.

Additionally, a significant increase in the H-alpha rest-frame equivalent width was observed with redshift, suggesting that galaxies with higher equivalent widths tend to have larger ratios of [OIII]/H-beta and O32, which may indicate lower metallicity or a higher ionization parameter in these extreme emission line galaxies.

This research contributes to the understanding of galaxy formation and evolution, particularly in the context of star formation and metallicity trends in the early universe. The findings may have implications for future studies of galaxy populations and their characteristics at different cosmic epochs.

For further details, the paper can be accessed at arXiv:2404.07497.