2017/09/30 by A. Hoag, Austin Hoag, Maruša Bradač +25 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Gamma-ray bursts and supernovae #Grism #Photometric redshift #Photometry (optics) #Population #Redshift #Stellar population #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aaa9c2
Accepted to ApJ. This is the accepted version
openalex created_date 2017/09/25 · arxiv created 2018/02/01 · openalex publication_date 2018/02/09 · arxiv updated 2018/02/21 · openalex updated_date 2026/08/06
Abstract We present deep spectroscopic observations of a Lyman break galaxy (LBG) candidate (hereafter MACS1149-JD) at z ∼ 9.5 with the Hubble Space Telescope ( HST ) WFC3/IR grisms. The grism observations were taken at four 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 three-parameter ( z , F160W mag, and Ly α equivalent width [EW]) LBG template to the three least contaminated grism position angles using a Markov chain Monte Carlo approach. The grism data alone are best fit with a redshift of (68% confidence), in good agreement with our photometric estimate of (68% confidence). Our analysis rules out Ly α emission from MACS1149-JD above a 3 σ EW of 21 Å, 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 from a very young stellar population rather than a 4000 Å break. We find that while this can provide an explanation for the observed IRAC color, it requires a lower redshift ( z ≲ 9.1), which is less preferred by the HST imaging data. The grism data are consistent with both scenarios, indicating that the red IRAC color can still be explained by a 4000 Å break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicates that a Myr stellar population is already present in this galaxy only ∼500 Myr after the big bang.