Project duration: 1 year
PI: Alaina Henry; http://www.alainahenry.com
Project Abstract:
Nearby analogs to reioinization-epoch galaxies can provide important clues about astrophysics that is difficult to quantify at high-redshifts. In particular, the z~0.2-0.3 "Green Pea" galaxies are commonly found to leak hydrogen-ionizing Lyman Continuum (LyC) photons-- a condition that must be shared by z>6 galaxies. In order to understand this ionizing output, we must constrain two components: (1) the intrinsic production of ionizing photons from galaxies like those that reionized the IGM, and (2) the fraction of these photons that can escape the galaxies. The focus of this project is the former issue.
I have obtained 21 high signal-to-noise spectra of Green Pea galaxies, using the ESI spectrograph at Keck Observatory. An example, highlighting an interesting part of the spectrum for one object, is shown below (right). Since the spectra are very deep, we detect high-ionization lines like ArIV and He II, which are only rarely seen in spectra of more typical sensitivity. The ionization potentials of these lines are high, meaning that an abundant source of high-energy photons is required to match the observations. The left panel of the figure below compares the ionization potential of many of the lines that we detect to spectra from model stellar populations. For the proposed project, we would measure the lines in these spectra, and carry out photoionization modeling (e.g. with Cloudy). In this way, we will learn which ionizing spectra can produce the line ratios that we observe, and which ionizing spectra can be ruled out.
