The global star formation rates (SFR) of galaxies at fixed stellar masses increase with redshift and are known to vary with environment unto z~2. We explore here whether the changes in the star formation rates can also apply to the electron densities of the inter-stellar medium (ISM) by measuring the [OII] (3727A/3729A) ratio for cluster and field galaxies at z~2. We measure a median electron density of ne = 366+/-84 cm-3 for six galaxies (with 1-sigma scatter = 163 cm-3) in the UDS proton-cluster at z=1.62. We find that the median electron density of galaxies in the UDS photo-cluster environment is three times higher compared to the median electron density of field galaxies (ne = 113+/- 63 cm-3 and 1-sigma scatter = 79 cm-3) at comparable redshifts, stellar mass and SFR. However, we note that a sample of six photo-cluster galaxies is insufficient to reliably measure the electron density in the average porto-cluster environment at z~2. We conclude that the electron density increases with redshift in both cluster and field environments up to z~2 (ne = 30 +/- 1 cm-3 for z ~ 0 to ne =254+/- 76 cm-3 for z~1.5). We find tentative evidence (~2.6 sigma ) for a possible dependence of electron density on environment, but the results require confirmation with larger sample sizes.
@article{arxiv.2002.08353,
title = {ZFIRE: Measuring Electron Density with [OII] as a function of environment at z = 1.62},
author = {Anishya Harshan and Anshu Gupta and Kim-Vy Tran and Leo Y. Alcorn and Tiantian Yuan and Glenn G. Kacprzak and Themiya Nanayakkara and Karl Glazebrook and Lisa J. Kewley and Ivo Labb'e and Casey Papovich},
journal= {arXiv preprint arXiv:2002.08353},
year = {2020}
}
Comments
18 Pages, 6 figures, 3 tables, Accepted for publication in Astrophysical Journal