Claire Bolda, “How Did Galaxies in the Early Universe Grow?”
Mentor: Dawn Erb, Physics
Poster #46

Whereas nearby galaxies primarily grow by merging with other galaxies, cosmological simulations predict that galaxies in the distant, early universe predominantly obtained fuel for new star formation by accreting gas from their environments. Galaxy growth can be observed due to star formation within a galaxy, which produces Lyman-α (Lyα) photons that illuminate extended halos of hydrogen gas surrounding galaxies called Lyα halos and indicate the kinematic structure of these halos. Here we present observations of the Lyα halos surrounding a galaxy pair within a large-scale structure of galaxies in the early universe using the Keck Cosmic Web Imager (KCWI), an integral field spectrograph on the Keck II Telescope. The Lyα emission spectral profiles throughout these galaxies‘ Lyα halos exhibit signs that gas is flowing into this galaxy pair, which is rarely observed among galaxies in the early universe, thereby rendering them excellent tools to study galaxy growth during this era. In order to confirm whether this galaxy pair is actively accreting gas, we measured the spatially varying peak flux ratio and peak separation of the double-peaked Lyα profiles throughout the galaxy pair’s Lyα halos. Additionally, we fit these Lyα profiles against a Monte Carlo Radiative Transfer model which assumes that gas mostly flows outward from a galaxy near the center of its Lyα halo and then gradually switches to flowing in towards the galaxy near the outer regions of its Lyα halo. According to our spectral measurements and radiative transfer models, this galaxy pair is actively growing, possibly due to a merger between them or due to the accretion of gas from the nearby large-scale structure of galaxies. We propose that more galaxies with the same special spectroscopic signature in various environments should be targeted for observations in order to better understand how galaxies in the early universe formed.