%0 Generic %1 steidel2014strong %A Steidel, C. C. %A Rudie, G. C. %A Strom, A. L. %A Pettini, M. %A Reddy, N. A. %A Shapley, A. E. %A Trainor, R. F. %A Erb, D. K. %A Turner, M. L. %A Konidaris, N. P. %A Kulas, K. R. %A Mace, G. %A Matthews, K. %A McLean, I. S. %D 2014 %K lbg line nebular spectra %T Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE %U http://arxiv.org/abs/1405.5473 %X We present initial results of a large near-IR spectroscopic survey covering the 15 fields of the Keck Baryonic Structure Survey (KBSS) using the recently-commissioned MOSFIRE instrument on the Keck 1 10m telescope. We focus on 179 galaxies with redshifts 2.0 < z < 2.6, most of which have high-quality MOSFIRE spectra in both H and K-band atmospheric windows, allowing sensitive measurements of OIII4960,5008, H-beta, NII6585, and H-alpha emission lines. We show unambiguously that the locus of z~2.3 galaxies in the "BPT" nebular diagnostic diagram exhibits an almost entirely disjoint, yet similarly tight, relationship between the line ratios NII/Halpha and OIII/Hbeta as compared to local galaxies. We argue that the offset of the z~2.3 BPT locus relative to that at z~0 is caused primarily by higher excitation (driven by both higher ionization parameter and harder stellar ionizing radiation field) than applies to most local galaxies. Also unlike nearby counterparts, a z~2.3 galaxy's position along the BPT locus is surprisingly insensitive to gas-phase O/H. The observed emission line ratios are most easily reproduced by models in which the stellar ionizing radiation field has Teff=50000-60000 K, gas-phase O/H in the range 0.2 < Z/Zsun < 1.0, and gas-phase N/O close to solar. Such high sustained Teff are not easily produced by standard population synthesis models, but are expected if massive binaries and/or rapid stellar rotation are important for the evolution of main sequence O-stars in typical high-redshift galaxies. We assess the applicability of commonly-used strong line indices for estimating gas-phase metallicities of high redshift galaxies, as well as their likely systematic biases. The empirical correlation between M* and inferred metallicity (the "MZR") at z~2.3 is as tight as for local galaxy samples, but is offset to lower metallicity (at all M*) by ~0.35 dex (abridged)

@misc{steidel2014strong, abstract = {We present initial results of a large near-IR spectroscopic survey covering the 15 fields of the Keck Baryonic Structure Survey (KBSS) using the recently-commissioned MOSFIRE instrument on the Keck 1 10m telescope. We focus on 179 galaxies with redshifts 2.0 < z < 2.6, most of which have high-quality MOSFIRE spectra in both H and K-band atmospheric windows, allowing sensitive measurements of [OIII]4960,5008, H-beta, [NII]6585, and H-alpha emission lines. We show unambiguously that the locus of z~2.3 galaxies in the "BPT" nebular diagnostic diagram exhibits an almost entirely disjoint, yet similarly tight, relationship between the line ratios [NII]/Halpha and [OIII]/Hbeta as compared to local galaxies. We argue that the offset of the z~2.3 BPT locus relative to that at z~0 is caused primarily by higher excitation (driven by both higher ionization parameter and harder stellar ionizing radiation field) than applies to most local galaxies. Also unlike nearby counterparts, a z~2.3 galaxy's position along the BPT locus is surprisingly insensitive to gas-phase O/H. The observed emission line ratios are most easily reproduced by models in which the stellar ionizing radiation field has Teff=50000-60000 K, gas-phase O/H in the range 0.2 < Z/Zsun < 1.0, and gas-phase N/O close to solar. Such high sustained Teff are not easily produced by standard population synthesis models, but are expected if massive binaries and/or rapid stellar rotation are important for the evolution of main sequence O-stars in typical high-redshift galaxies. We assess the applicability of commonly-used strong line indices for estimating gas-phase metallicities of high redshift galaxies, as well as their likely systematic biases. The empirical correlation between M* and inferred metallicity (the "MZR") at z~2.3 is as tight as for local galaxy samples, but is offset to lower metallicity (at all M*) by ~0.35 dex (abridged)}, added-at = {2014-05-22T09:57:35.000+0200}, author = {Steidel, C. C. and Rudie, G. C. and Strom, A. L. and Pettini, M. and Reddy, N. A. and Shapley, A. E. and Trainor, R. F. and Erb, D. K. and Turner, M. L. and Konidaris, N. P. and Kulas, K. R. and Mace, G. and Matthews, K. and McLean, I. S.}, biburl = {https://www.bibsonomy.org/bibtex/22ded6ac60a5605d08d58f52867200440/miki}, description = {[1405.5473] Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE}, interhash = {1b7dfd08c08e5b77054bdd68511e4d72}, intrahash = {2ded6ac60a5605d08d58f52867200440}, keywords = {lbg line nebular spectra}, note = {cite arxiv:1405.5473Comment: 38 pages, 25 figures. Submitted to the Astrophysical Journal. Version with full-resolution figures available at http://www.astro.caltech.edu/~ccs/mos_bpt_submit.pdf}, timestamp = {2014-05-22T09:57:35.000+0200}, title = {Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE}, url = {http://arxiv.org/abs/1405.5473}, year = 2014 }