Data for Cosmic CO and [CII] Backgrounds and the Fueling of Star Formation over 12 Gyr

Data for Cosmic CO and [CII] Backgrounds and the Fueling of Star Formation over 12 Gyr

We provide empirical tomographic measurements of the cosmic CO and [CII] line backgrounds 
arising from the aggregate emission of galaxies and potentially diffuse gas in large-scale structure.
Previously, only the most luminous galaxies were detected in these lines, revealing just the tip of
the iceberg. Using the intensity mapping method, we measure the total background integrated
over the entire line-emitting populations and report the cosmic mean. These measurements are
based on detections of line excesses above the cosmic infrared background (CIB) continuum—at
7σ significance for CO and 3σ for [CII]—using CIB–galaxy correlations over 0 < z < 4.2, originally
measured in Chiang et al. (2025, ApJ, 992, 1, 65). We use these redshift-dependent, multi-band
correlation amplitudes to isolate the line contributions, which are released here.

The [CII] background corresponds to the 158 µm fine-structure line. The CO background includes
the nine rotational transitions from J = 1–0 to 9–8, beginning at 115.27 GHz with equal spacing in
frequency. Two sets of line posteriors are provided:

1. Comoving luminosity density
   "rho_CO_CII--dense_z_fiducial.ecsv" gives the fiducial full-model posterior, sampled in dense
   redshift bins over 0 < z < 10.
   "rho_CO_CII--8_z_bins.ecsv" gives refits with independent line amplitudes in 8 redshift bins
   within the range probed by the data (0 < z < 4.2), with all other nuisance parameters fixed to
   their global best-fit values. 
   Both files are in units of L_sun/Mpc^3.

2. Monopole
   "Tb_cosmic_CO_CII.ecsv" provides brightness temperatures in microkelvin (µK).
   "I_nu_cosmic_CO_CII.ecsv" provides intensities in Jy/sr.
   The two are equivalent. Both are derived from the full-model posterior, sampled densely over
   0 < z < 10 and tabulated across observed frequency in GHz. Best-fit values correspond to
   posterior medians, with lower and upper bounds indicating the 68% credible interval.

This data release serves as an empirical baseline for future line intensity mapping efforts and
forecasts, and as a reference for comparison with galaxy surveys in astrophysical studies.