An Empirical Representation of a Physical Model for the ISM [C ii], CO, and [C i] Emission at Redshift 1 ≤ z ≤ 9

Abstract

Submillimeter emission lines produced by the interstellar medium (ISM) are strong tracers of star formation and are some of the main targets of line intensity mapping (LIM) surveys. In this work we present an empirical multiline emission model that simultaneously covers the mean, scatter, and correlations of [C ii], CO J = 1–0 to J = 5–4, and [C i] lines in the redshift range 1 ≤ z ≤ 9. We assume that the galaxy ISM line emission luminosity versus halo mass relations can be described by double power laws with redshift-dependent lognormal scatter. The model parameters are then derived by fitting to the state-of-the-art semianalytic simulation results that have successfully reproduced multiple submillimeter line observations at 0 ≤ z ≲ 6. We cross-check the line emission statistics predicted by the semianalytic simulation and our empirical model, finding that at z ≥ 1 our model reproduces the simulated line intensities with fractional error less than about 10%. The fractional difference is less than 25% for the power spectra. Grounded on physically motivated and self-consistent galaxy simulations, this computationally efficient model will be helpful in forecasting ISM emission-line statistics for upcoming LIM surveys.

COMAP Early Science. VII. Prospects for CO Intensity Mapping at Reionization

“…For a derivation of this crossscatter effect, see Appendix A. For the remainder of this work, we assume r sc = 1 following Schaan & White (2021) and Yang et al (2022).…”

“…Our final CO model, from Yang et al (2022;hereafter Yang22), provides fitting functions optimized for intensity mapping based on semianalytic models (SAMs) from Yang et al (2021). Unlike most of the above models, which rely heavily on empirical scalings, it attempts to self-consistently model the underlying physics that gives rise to CO emission.…”

COMAP Early Science. III. CO Data Processing

“…Large volumes along a given line of sight may be surveyed simultaneously with a single spectrometer at relatively low spatial resolution, and by scanning this spectrometer across the sky, a full 3D density map may be derived. Despite multiple different modeling efforts (Righi et al 2008;Visbal & Loeb 2010;Lidz et al 2011;Pullen et al 2013;Breysse et al 2014;Li et al 2016;Padmanabhan 2018;Moradinezhad Dizgah & Keating 2019;Sun et al 2019;Chung et al 2022;Moradinezhad Dizgah et al 2022;Yang et al 2022) and significant progress on the observational front (Keating et al 2016(Keating et al , 2020Riechers et al 2019;Keenan et al 2022), the overall level of the CO signal, especially in the clustering regime, is still unknown.…”

COMAP Early Science. V. Constraints and Forecasts at z ∼ 3

“…Padmanabhan (2018) also notes that f duty = 1 is somewhat better supported in observational data. The tension between these two extremes (and their implications for the ratio between the clustering and shot-noise components of the power spectrum) could be feasibly bridged by a mass-dependent f duty that falls from 1 with higher mass, as is the case for the empirical models of Yang et al (2022).…”

“…These survey designs generally focus on statistical measurements of the line emitters as a whole, including faint populations of galaxies that cannot be detected in isolation but may be inferred in aggregate. Investigating what measurements and inferences this perspective enables, previous literature has studied the potential of high-redshift LIM with carbon monoxide (CO) lines for over a decade (see, e.g., Righi et al 2008;Visbal & Loeb 2010;Lidz et al 2011;Visbal et al 2011;Pullen et al 2013;Li et al 2016;Padmanabhan 2018;Moradinezhad Dizgah & Keating 2019;Sun et al 2019;Yang et al 2021Yang et al , 2022.…”