Abstract
This paper outlines the science case for line-intensity mapping with a space-borne instrument targeting the sub-millimeter (microwaves) to the far-infrared (FIR) wavelength range. Our goal is to observe and characterize the large-scale structure in the Universe from present times to the high redshift Epoch of Reionization. This is essential to constrain the cosmology of our Universe and form a better understanding of various mechanisms that drive galaxy formation and evolution. The proposed frequency range would make it possible to probe important metal cooling lines such as [CII] up to very high redshift as well as a large number of rotational lines of the CO molecule. These can be used to trace molecular gas and dust evolution and constrain the buildup in both the cosmic star formation rate density and the cosmic infrared background (CIB). Moreover, surveys at the highest frequencies will detect FIR lines which are used as diagnostics of galaxies and AGN. Tomography of these lines over a wide redshift range will enable invaluable measurements of the cosmic expansion history at epochs inaccessible to other methods, competitive constraints on the parameters of the standard model of cosmology, and numerous tests of dark matter, dark energy, modified gravity and inflation. To reach these goals, large-scale structure must be mapped over a wide range in frequency to trace its time evolution and the surveyed area needs to be very large to beat cosmic variance. Only a space-borne mission can properly meet these requirements.
Highlights
1.1 The promise of line-intensity mappingLine-intensity mapping (LIM) [1] is an emerging technique to explore galaxy and structure evolution over cosmic times by collecting all incoming photons along the line of sight at a given frequency, whether they originate from within galaxies or the intergalactic medium, and measuring the spatial fluctuations in the emission
Maps of line-intensity fluctuations are uniquely advantageous over those of cosmic microwave background fluctuations or of pixelised number counts of discrete galaxy surveys. Compared to the former, line-intensity mappingLine-intensity mapping (LIM) is not limited by diffusion damping on small scales and can be measured in tomography over huge cosmological volumes, which unlike the latter, LIM is not bound to a census of discrete bright sources and can extend to very high redshifts
We find that the proposed LIM space mission probing the CII line, in a 4-year survey with its high-resolution instrument, has the potential to constrain the amplitude of local-shape bispectrum with a 1-σ uncertainty of σ ∼ 0.75), after marginalizing over the parameters of CDM cosmology
Summary
Line-intensity mapping (LIM) [1] is an emerging technique to explore galaxy and structure evolution over cosmic times by collecting all incoming photons along the line of sight at a given frequency, whether they originate from within galaxies or the intergalactic medium, and measuring the spatial fluctuations in the emission. Maps of line-intensity fluctuations are uniquely advantageous over those of cosmic microwave background fluctuations or of pixelised number counts of discrete galaxy surveys. Compared to the former, LIM is not limited by diffusion damping on small scales and can be measured in tomography over huge cosmological volumes, which unlike the latter, LIM is not bound to a census of discrete bright sources and can extend to very high redshifts.
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