%0 Generic %1 hoag2017grism %A Hoag, Austin %A Bradač, Maruša %A Brammer, Gabriel B. %A Huang, Kuang-Han %A Treu, Tommaso %A Mason, Charlotte A. %A Castellano, Marco %A Di Criscienzo, Marcella %A Jones, Tucker %A Kelly, Patrick %A Pentericci, Laura %A Ryan, Russell %A Schmidt, Kasper B. %A Trenti, Michele %D 2017 %K LBG high-z %T HST Grism Observations of a Gravitationally Lensed Redshift 10 Galaxy %U http://arxiv.org/abs/1709.03992 %X We present deep spectroscopic observations of a Lyman-break galaxy candidate (hereafter MACS1149-JD) at $z\sim10$ with the Hubble Space Telescope (HST) WFC3/IR grisms. The grism observations were taken at 4 distinct position angles, totaling 34 orbits with the G141 grism, although only 19 of the orbits are relatively uncontaminated along the trace of MACS1149-JD. We fit a 3-parameter ($z$, F160W mag, and rest-frame Lyman-alpha equivalent width) Lyman-break galaxy template to the three least contaminated grism position angles using an MCMC approach. The grism data alone are best fit with a redshift of $z_grism=9.53^+0.39_-0.60$ ($68\%$ confidence), in good agreement with our photometric estimate of $z_phot=9.51^+0.06_-0.12$ ($68\%$ confidence). Our analysis rules out Lyman-alpha emission from MACS1149-JD above a $3\sigma$ rest-frame equivalent width of 21 \AA, consistent with a highly neutral IGM. We explore a scenario where the red Spitzer/IRAC $3.6 - 4.5$ color of the galaxy previously pointed out in the literature is due to strong rest-frame optical emission lines rather than a 4000 \AA break. We find that this can provide an explanation for the observed IRAC photometry, but only with a probability of 0.05. Instead, the grism data add credence to the scenario that the red IRAC color is best explained by a 4000 \AA break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicates that a $340^+29_-35\, Myr$ stellar population is already present in this galaxy only $\sim500\,Myr$ after the Big Bang.

@misc{hoag2017grism, abstract = {We present deep spectroscopic observations of a Lyman-break galaxy candidate (hereafter MACS1149-JD) at $z\sim10$ with the Hubble Space Telescope (HST) WFC3/IR grisms. The grism observations were taken at 4 distinct position angles, totaling 34 orbits with the G141 grism, although only 19 of the orbits are relatively uncontaminated along the trace of MACS1149-JD. We fit a 3-parameter ($z$, F160W mag, and rest-frame Lyman-alpha equivalent width) Lyman-break galaxy template to the three least contaminated grism position angles using an MCMC approach. The grism data alone are best fit with a redshift of $z_{\mathrm{grism}}=9.53^{+0.39}_{-0.60}$ ($68\%$ confidence), in good agreement with our photometric estimate of $z_{\mathrm{phot}}=9.51^{+0.06}_{-0.12}$ ($68\%$ confidence). Our analysis rules out Lyman-alpha emission from MACS1149-JD above a $3\sigma$ rest-frame equivalent width of 21 \AA{}, consistent with a highly neutral IGM. We explore a scenario where the red Spitzer/IRAC $[3.6] - [4.5]$ color of the galaxy previously pointed out in the literature is due to strong rest-frame optical emission lines rather than a 4000 \AA{} break. We find that this can provide an explanation for the observed IRAC photometry, but only with a probability of 0.05. Instead, the grism data add credence to the scenario that the red IRAC color is best explained by a 4000 \AA{} break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicates that a $340^{+29}_{-35}\, \mathrm{Myr}$ stellar population is already present in this galaxy only $\sim500\,\mathrm{Myr}$ after the Big Bang.}, added-at = {2017-09-14T09:23:21.000+0200}, author = {Hoag, Austin and Bradač, Maruša and Brammer, Gabriel B. and Huang, Kuang-Han and Treu, Tommaso and Mason, Charlotte A. and Castellano, Marco and Di Criscienzo, Marcella and Jones, Tucker and Kelly, Patrick and Pentericci, Laura and Ryan, Russell and Schmidt, Kasper B. and Trenti, Michele}, biburl = {https://www.bibsonomy.org/bibtex/2585c2c9b5ae6ecdc820f2ea3788ad301/miki}, description = {[1709.03992] HST Grism Observations of a Gravitationally Lensed Redshift 10 Galaxy}, interhash = {d7474428d91ba67d2d1ba32544f756c0}, intrahash = {585c2c9b5ae6ecdc820f2ea3788ad301}, keywords = {LBG high-z}, note = {cite arxiv:1709.03992Comment: Submitted to ApJ}, timestamp = {2017-09-14T09:23:21.000+0200}, title = {HST Grism Observations of a Gravitationally Lensed Redshift 10 Galaxy}, url = {http://arxiv.org/abs/1709.03992}, year = 2017 }