Line Intensity Mapping in Astrophysics
Summary
Line intensity mapping (LIM) is an observational technique that measures the integrated emission of spectral lines across large cosmological volumes without resolving individual sources. By capturing aggregate fluctuations in lines such as carbon monoxide (CO), singly ionised carbon ([C II]) and hydrogen’s Lyα transition, LIM probes the distribution of gas, star formation and large-scale structure from the nearby Universe back to cosmic dawn. This approach complements traditional galaxy surveys by accessing low-luminosity and high-redshift populations, offering a statistical census of baryons across cosmic time. Key scientific goals include tracing the build-up of molecular gas in galaxies, mapping the growth of ionised regions during the epoch of reionization, constraining models of galaxy evolution and feedback, and testing fundamental physics through measurements of the power spectrum of intensity fluctuations. Realising these ambitions requires careful mitigation of astrophysical foregrounds, instrumental systematics and line interlopers, often through a combination of masking strategies, component-separation algorithms and cross-correlation with ancillary data. Recent advances in simulations and instrument development have begun to demonstrate the feasibility of LIM as a next-generation cosmological and astrophysical probe.
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Line Intensity Mapping in Astrophysics publication trend
The graph below shows the total number of articles in line intensity mapping in astrophysics across all publications each year (not limited to Nature Index journals).
Technical terms
Line intensity mapping: Measurement of spatial fluctuations in the integrated emission of a spectral line over cosmic volumes without resolving individual emitters.
Power spectrum: Statistical representation of intensity fluctuations as a function of spatial or angular scale, used to infer clustering and large-scale structure.
Interloper: Unwanted spectral line from a different redshift that contaminates the target emission signal in a LIM survey.
Epoch of Reionization: The period in the early universe (approximately 400 million to 1 billion years after the Big Bang) when the first luminous sources ionised intergalactic hydrogen.
Dark matter halo: A gravitationally bound structure of dark matter that hosts galaxies and determines their large-scale clustering properties.
References
- CONCERTO: Extracting the power spectrum of the [CII] emission line. Astronomy & Astrophysics (2023).
- CONCERTO: High-fidelity simulation of millimeter line emissions of galaxies and [CII] intensity mapping. Astronomy & Astrophysics (2022).
- LIMFAST. II. Line Intensity Mapping as a Probe of High-redshift Galaxy Formation. The Astrophysical Journal (2023).
- COMAP Early Science. V. Constraints and Forecasts at z ∼ 3. The Astrophysical Journal (2022).
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