COLD ACCRETION IN EARLY GALAXY FORMATION AND ITS ${\rm Ly}\alpha $ SIGNATURES

Abstract

Lyα emission has played an important role in detecting high-redshift galaxies, including recently distant ones at redshifts > z 7. It may also contain important information concerning the origin of these galaxies. Here, we investigate the formation of a typical L * galaxy and its observational signatures at the earliest stage by combining a cosmological hydrodynamic simulation with three-dimensional radiative transfer (RT) calculations using the newly improved ART 2 code. Our cosmological simulation uses the Aquila initial condition, which zooms in on a Milky-Way-like halo with high resolutions, and our RT couples multi-wavelength continuum, Lyα line, and ionization of hydrogen. We find that the modeled galaxy starts to form at redshift z ∼ 24 through the efficient accretion of cold gas, which produces a strong Lyα line with a luminosity ofã 1 as early as z ∼ 14. The Lyα emission appears to trace the cold, dense gas. The lines exhibit asymmetric, single-peak profiles, and are shifted to the blue wing, a characteristic feature of gas inflow. Moreover, the contribution to the total Lyα luminosity from excitation cooling increases with redshift and becomes dominant at z  6. We predict that L * galaxies such as the modeled one may be detected at z  8 by the James Webb Space Telescopeand Atacama Large Millimeter Array with a reasonable integration time. Beyond redshift 12, however, the Lyα line may only be observable by spectroscopic surveys. Our results suggest that the Lyα line is one of the most powerful tools to detect the first generation of galaxies and decipher their formation mechanism.

A CLOSE COMPARISON BETWEEN OBSERVED AND MODELED LyαLINES FORz∼ 2.2 LyαEMITTERS

“…Furthermore, gravitational cooling can reproduce not only the observed enhanced Lyα blue bump flux (e.g., Dijkstra et al 2006), but also the spatially extended Lyα source (Rosdahl & Blaizot 2012), i.e., diffuse Lyα haloes which are common features around galaxies (Steidel et al 2011;Matsuda et al 2012;Hayes et al 2013;Momose et al 2014). We note here that there exists a large uncertainty in modeling the Lyα emission from gravitational cooling due to its difficulty and assumed observation sensitivity (cf., Faucher-Giguère et al 2010;Goerdt et al 2010;Rosdahl & Blaizot 2012;Yajima et al 2012Yajima et al , 2015. Our results as well as observational results quoted above can be useful for future modeling.…”

FOREVER22: galaxy formation in protocluster regions

“…Using the code, we reproduced successfully observational properties of high-redshift galaxies (Yajima et al 2012b(Yajima et al , 2013(Yajima et al , 2014(Yajima et al , 2015aArata et al 2019Arata et al , 2020). We will model the observational properties of member galaxies of PCs in the next papers.…”

Formation of the first galaxies in the aftermath of the first supernovae

“…Thus, Pop III stars make an important contribution to the observable UV fluxes from the first galaxies. As for the Lyα emission, there are uncertainties due to the resonant scattering nature and the IGM transmission (Laursen et al 2011(Laursen et al , 2019Yajima et al 2012Yajima et al , 2014Yajima et al , 2015. In Fig.…”