%0 Generic %1 kewley2015ionizing %A Kewley, Lisa J. %A Zahid, H. Jabran %A Geller, Margaret J. %A Dopita, Michael A. %A Hwang, Ho Seong %A Fabricant, Dan %D 2015 %K emission galaxy gas high-z lines metallicity %T A rise in the ionizing photons in star-forming galaxies over the past 5 billion years %U http://arxiv.org/abs/1507.07932 %X We investigate the change in ionizing photons in galaxies between 0.2<z<0.6 using the F2 field of the SHELS complete galaxy redshift survey. We show, for the first time, that while the OIII/Hb and OIII/OII ratios rise, the NII/H-alpha and SII/H-alpha ratios fall significantly over the 0.2<z<0.35 redshift range for stellar masses between 9.2<log(M/Msun)<10.6. The OIII/H-beta and OIII/OII ratios continue to rise across the full 0.2<z<0.6 redshift range for stellar masses between 9.8<log(M/Msun)<10.0. We conclusively rule out AGN contamination, a changing ISM pressure, and a change in the hardness of the EUV radiation field as the cause of the change in the line ratios between 0.2<z<0.35. We find that the ionization parameter rises significantly with redshift (by 0.1 to 0.25 dex depending on the stellar mass of the sample). We show that the ionization parameter is strongly correlated with the fraction of young-to-old stars, as traced by the H-beta equivalent width. We discuss the implications of this result on higher redshift studies, and we consider the implications on the use of standard optical metallicity diagnostics at high redshift.

@misc{kewley2015ionizing, abstract = {We investigate the change in ionizing photons in galaxies between 0.2<z<0.6 using the F2 field of the SHELS complete galaxy redshift survey. We show, for the first time, that while the [OIII]/Hb and [OIII]/[OII] ratios rise, the [NII]/H-alpha and [SII]/H-alpha ratios fall significantly over the 0.2<z<0.35 redshift range for stellar masses between 9.2<log(M/Msun)<10.6. The [OIII]/H-beta and [OIII]/[OII] ratios continue to rise across the full 0.2<z<0.6 redshift range for stellar masses between 9.8<log(M/Msun)<10.0. We conclusively rule out AGN contamination, a changing ISM pressure, and a change in the hardness of the EUV radiation field as the cause of the change in the line ratios between 0.2<z<0.35. We find that the ionization parameter rises significantly with redshift (by 0.1 to 0.25 dex depending on the stellar mass of the sample). We show that the ionization parameter is strongly correlated with the fraction of young-to-old stars, as traced by the H-beta equivalent width. We discuss the implications of this result on higher redshift studies, and we consider the implications on the use of standard optical metallicity diagnostics at high redshift.}, added-at = {2015-07-30T06:50:58.000+0200}, author = {Kewley, Lisa J. and Zahid, H. Jabran and Geller, Margaret J. and Dopita, Michael A. and Hwang, Ho Seong and Fabricant, Dan}, biburl = {https://www.bibsonomy.org/bibtex/21309b3865dde7d9ed9a9a21510d49ef8/miki}, description = {[1507.07932] A rise in the ionizing photons in star-forming galaxies over the past 5 billion years}, interhash = {7f66d91e78ec17ac45dc7bc942d80fb0}, intrahash = {1309b3865dde7d9ed9a9a21510d49ef8}, keywords = {emission galaxy gas high-z lines metallicity}, note = {cite arxiv:1507.07932Comment: 6 pages, 4 figures, accepted for publication in ApJL}, timestamp = {2015-07-30T06:50:58.000+0200}, title = {A rise in the ionizing photons in star-forming galaxies over the past 5 billion years}, url = {http://arxiv.org/abs/1507.07932}, year = 2015 }