POLAR-II: modeling star formation history of galaxies on the 21-cm signal from Epoch of Reionization

Abstract

Galaxies may suffer some starburst and quenched periods in their history due to e.g. galaxy mergers and feedback. However, semi-numerical simulations of the Epoch of Reionization (EoR) typically do not accurately model the effects of the star formation history (SFH) of galaxies. Keeping the same total ionizing photon budget from galaxies, we investigate how the ionization and heating of the Intergalactic Medium (IGM), as well as the associated 21-cm signal during the EoR, depends on the variations in the modeling of the SFH of galaxies. We adopt the Jiutian-300 N-body dark matter simulation and the semi-analytic model L-Galaxies 2020 to model galaxy formation. Using the galaxy catalog from L-Galaxies 2020 as input, we post-process the Jiutian-300 density field with the one-dimensional radiative transfer code Grizzly to model the reionization process and the 21-cm signal. We find that the ionized regions produced by galaxies with a SFH derived from L-Galaxies 2020 are slightly larger and warmer than the ones obtained with a constant SFR. For a fixed stellar mass, galaxies produce smaller ionized regions with increasing stellar mass weighted stellar age $τ_{\rm age}$. This results in a different topology and timing of the IGM ionization and heating obtained from Grizzly. The SFH of galaxies is highly dependent on $τ_{\rm age}$ and redshift. Different models of the galactic SFH affect the gas heating and ionizing processes during the EoR, and as a consequence also the 21-cm global signal and power spectrum.

Figures (9)

• Figure 1: Average stellar mass normalized integrated SED, $\langle {\rm iSED} \rangle$, of stellar sources (red), XRB (magenta), hot-ISM (cyan) and all source types combined (black) at $z=11.9$ (solid), 10.07 (dashed), 7.88 (dash-dotted) and 6.99 (dotted) obtained from the LG20 simulation. These results are the mean values of all galaxies with $>10^{4}\,\rm M_{\odot}$. The slight differences ($<10\%$) observed in $\langle {\rm iSED} \rangle$ at various redshifts are due to the evolution of galactic properties such as metallicity and stellar age.
• Figure 2: Average SFR history of galaxies with $M_{\star} \sim 10^{7}\,\rm M_{\odot}$ and stellar age $\tau_{\rm age}=0.02\,\rm Gyr$ (cyan), $0.04\,\rm Gyr$ (magenta), $0.06\,\rm Gyr$ (blue), $0.1\,\rm Gyr$ (red), $0.2\,\rm Gyr$ (yellow) and $0.4\,\rm Gyr$ (green) at $z=11.9$, 10.94, 10.07, 8.91, 7.88, 6.99 and 5.96 from left to right and top to bottom. The x-axis $t_{b}$ is the time of galaxies traced back from $z$ to higher redshift.
• Figure 3: Average specific SFR (i.e. SFR per unit stellar mass) history of galaxies with stellar age $\tau_{\rm age}=0.02\,\rm Gyr$ (cyan) and $0.2\,\rm Gyr$ (yellow) for galaxies with $M_{\star} \sim 10^{6}\,\rm M_{\odot}$ (dashed), $10^{7}\,\rm M_{\odot}$ (solid) and $10^{8}\,\rm M_{\odot}$ (dotted). The results are at $z=6.99$.
• Figure 4: Distributions of stellar age $\tau_{\rm age}$ versus stellar mass $M_{\star}$ of galaxies at $z=11.9$, 10.94, 10.07, 8.91, 7.88, 6.99 and 5.96, from left to right and top to bottom. The solid lines are the mean $\tau_{\rm age}$ of galaxies within the same $M_{\star}$ bins, which are shown together for all redshifts in the bottom-right plot.
• Figure 5: 1-D profiles of ionization fraction $x_{\rm HII}$ (left), gas temperature $T_{\rm k}$ (middle) and 21-cm signal $T_{\rm 21cm}$ (right) as functions of the physical distance $R$ from a galaxy with $M_{\ast} = 10^7\,\rm M_{\odot}$ at $z=10.07$. The colors refer to galaxies with $\tau_{\rm age} = 0.02\,\rm Gyr$ (cyan), $0.1\,\rm Gyr$ (red) and $0.2\,\rm Gyr$ (yellow). The solid lines are the results obtained by adopting the SFH from LG20 ($\rm SFH\_LG20$), while the dotted lines refer to a constant SFR throughout the SFH ($\rm SFH\_const$). The surrounding IGM is assumed to be uniform with mean density of the Universe at $z=10.07$.