The THESAN project: predictions for multi-tracer line intensity mapping in the Epoch of Reionization

Abstract

Line intensity mapping (LIM) is rapidly emerging as a powerful technique to study galaxy formation and cosmology in the highredshift Universe. We present LIM estimates of select spectral lines originating from the interstellar medium (ISM) of galaxies and 21 cm emission from neutral hydrogen gas in the Universe using the large volume, high resolution reionization simulations. A combination of sub-resolution photo-ionization modelling for H regions and Monte Carlo radiative transfer calculations is employed to estimate the dust-attenuated spectral energy distributions (SEDs) of high-redshift galaxies (𝑧 5.5). We show that the derived photometric properties such as the ultraviolet (UV) luminosity function and the UV continuum slopes match observationally inferred values, demonstrating the accuracy of the SED modelling. We provide fits to the luminosity-star formation rate relation (𝐿-SFR) for the brightest emission lines and find that important differences exist between the derived scaling relations and the widely used low-𝑧 ones because the interstellar medium of reionization era galaxies is generally less metal-enriched than in their low redshift counterparts. We use these relations to construct line intensity maps of nebular emission lines and cross correlate with the 21 cm emission. Interestingly, the wavenumber at which the correlation switches sign (𝑘 transition ) depends heavily on the reionization model and to a lesser extent on the targeted emission line, which is consistent with the picture that 𝑘 transition probes the typical sizes of ionized regions. The derived scaling relations and intensity maps represent a timely state-of-the-art framework for forecasting and interpreting results from current and upcoming LIM experiments.

The thesan project: ionizing escape fractions of reionization-era galaxies

“…This can be attributed to changes in the stellar population as galaxies assemble and evolve. In fact, the specific star formation rate in the halo decreases with time (see Figure 1 of Kannan et al, 2021), which explains why this evolution is not apparent in the rightmost panel of Fig. 4-2 showing the intrinsic photon rate as a function of the SFR.…”

H-alpha emission in local galaxies: star formation, time variability and the diffuse ionized gas

“…Employing our spatially resolved MCRT methology with these aforementioned improvements will be key to understanding the physics of emission lines of and within galaxies both at low-and high-redshifts. In particular, we are currently working on zoom-in simulations based on the SMUGGLE-RT framework as part of the project (Kannan et al 2021a;Smith et al 2021a;Garaldi et al 2021;Kannan et al 2021b), which are ideally suited for studying the high-redshift Universe. These and similar simulations will allow us to (𝑖) better understand current and upcoming observations by being able to accurately estimate uncertainties and be aware of possible biases; and (𝑖𝑖) gain inspiration for new observational projects.…”

Precision Tests of CO and [CII] Power Spectra Models against Simulated Intensity Maps

“…It is essential to have a model that incorporates relevant ISM physics, yet is simple enough that can be efficiently used in theoretical predictions of the line signal and in generating mock intensity maps based on Nbody simulations. In this regard, sophisticated simulations of hydrodynamical galaxy formation and radiative transfer (e.g., [44,105,106]) together with observational data (e.g., cosmic infrared background anisotropies [65], and galaxy UV luminosity functions), provide guidelines for constructing such models.…”