Our knowledge of galaxy formation and evolution has incredibly progressed through multi-wavelength observational constraints of the interstellar medium (ISM) of galaxies at all cosmic epochs. However, little is known about the physical properties of the more diffuse and lower surface brightness reservoir of gas and dust that extends beyond ISM scales and fills dark matter haloes of galaxies up to their virial radii, the circumgalactic medium (CGM). New theoretical studies increasingly stress the relevance of the latter for understanding the feedback and feeding mechanisms that shape galaxies across cosmic times, whose cumulative effects leave clear imprints into the CGM. Recent studies are showing that a - so far unconstrained - fraction of the CGM mass may reside in the cold ( T < 10 4 K) molecular and atomic phase, especially in high-redshift dense environments. These gas phases, together with the warmer ionised phase, can be studied in galaxies from z ∼ 0 to z ∼ 10 through bright far-infrared and sub-millimeter emission lines such as [C ii] 158 µm, [O iii] 88 µm, [C I] 609 µm, [C i] 370 µm, and the rotational transitions of CO. Imaging such hidden cold CGM can lead to a breakthrough in galaxy evolution studies but requires a new facility with the specifications of the proposed Atacama Large Aperture Submillimeter Telescope (AtLAST). In this paper, we use theoretical and empirical arguments to motivate future ambitious CGM observations with AtLAST and describe the technical requirements needed for the telescope and its instrumentation to perform such science.
Keywords: Galaxies; ISM; Submillimeter galaxies; circumgalactic medium; evolution; intergalactic medium; radio lines.
The paper aims to demonstrate the need for a new large aperture (50 m), single-antenna telescope receiving sub-millimeter and millimeter (hereafter sub-mm) 1 wave-length light from a high elevation site in the Atacama desert in Chile, named the Atacama Large Aperture Sub-millimeter Telescope (AtLAST). Here, we particularly focus on the science case of the so-called circumgalactic medium (CGM). This gaseous component exists beyond the scale of the matter that lies between stars in a galaxy (the interstellar medium, ISM) but still within the gravitationally bounded region of a galaxy. Our understanding of galaxies has so far been based on observations that focus on the ISM, but theory shows that observing the CGM may help us solve crucial open questions in the field of galaxy formation and evolution. Indeed, the properties of the CGM carry the vital imprints of the physical mechanisms that shape galaxies, specifically the powerful winds driven by newly formed stars and by supermassive black holes, and the incoming gas flows from the large-scale structure of the Universe that provide galaxies with their fuel to form stars. Despite its crucial role, little is known about the CGM, particularly its cold and dense gas content, because none of the current sub-mm telescopes enables such observations. We illustrate that exploring the hidden cold CGM components is an urgent task in the coming decades and evaluate how feasible this science case is, based on our current knowledge. We suggest a set of telescope parameters and instrumentation for AtLAST to achieve such key science goals of probing the cold CGM. Finally, we discuss expected synergies with current and future telescopes.
Copyright: © 2024 Lee M et al.