Abstract
Abstract Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by energetic photons emitted from the first galaxies. The [C ii] 158 μm fine-structure line is typically one of the brightest emission lines of star-forming galaxies and thus a promising tracer of the global EoR star formation activity. However, [C ii] intensity maps at 6 ≲ z ≲ 8 are contaminated by interloping CO rotational line emission (3 ≤ J upp ≤ 6) from lower-redshift galaxies. Here we present a strategy to remove the foreground contamination in upcoming [C ii] intensity mapping experiments, guided by a model of CO emission from foreground galaxies. The model is based on empirical measurements of the mean and scatter of the total infrared luminosities of galaxies at z < 3 and with stellar masses M * > 10 8 M ⊙ selected in the K-band from the COSMOS/UltraVISTA survey, which can be converted to CO line strengths. For a mock field of the Tomographic Ionized-carbon Mapping Experiment, we find that masking out the “voxels” (spectral–spatial elements) containing foreground galaxies identified using an optimized CO flux threshold results in a z-dependent criterion m K AB ≲ 22 (or M * ≳ 10 9 M ⊙ ) at z < 1 and makes a [C ii]/COtot power ratio of ≳10 at k = 0.1 h/Mpc achievable, at the cost of a moderate ≲8% loss of total survey volume.
Highlights
The formation of stars in the first generations of galaxies is closely associated with the epoch of reionization (EoR) occurring at 6 z 10, during which Lyman continuum photons ionized the mostly neutral intergalactic medium (IGM) after recombination (z ∼ 1100)
The results presented in this work are performed on the COSMOS field (Scoville et al 2007) by combining a catalog derived using the imaging described in Laigle et al (2016) but processed by the Muzzin et al (2013a) pipeline, with maps spanning the full far-infrared/sub-millimeter (FIR/sub-mm) spectral range of the thermal spectral energy distribution (SED) from interstellar dust
The constant versus evolving stellar-mass cut approaches are explicitly compared in Figure 8, where we show the predicted CO(4–3) power at k = 0.1 h/Mpc for the two different masking strategies, and for the two different LIR–LC¢O prescriptions considered in this work, namely CW13 and G14
Summary
The formation of stars in the first generations of galaxies is closely associated with the epoch of reionization (EoR) occurring at 6 z 10, during which Lyman continuum photons ionized the mostly neutral intergalactic medium (IGM) after recombination (z ∼ 1100). Advances in surveys of individual high-redshift galaxies at both near-infrared (e.g., Ellis et al 2013; Bouwens et al 2015; Oesch et al 2015; Livermore et al 2017) and millimeter/sub-millimeter wavelengths (e.g., Capak et al 2015; Carilli et al 2016), together with constraints on the global ionization history from the cosmic microwave background (Planck Collaboration et al 2016b) and a variety of spectroscopic diagnostics of the evolving IGM neutrality (see Robertson et al 2015 for a compilation), have greatly deepened our understanding of the reionization era over the past few years None of these observables directly probes the entire ionizing photon budget responsible for reionization—even for a typical “ultradeep” survey with the most powerful telescopes like the JWST, limitations on the sensitivity may result in missing up to 50% of the total star formation inside galaxies at z > 8, given the steep faint-end slope of the galaxy luminosity function implied. The variance on large scales carries information about the total line emission from all galaxies, integrated over the full luminosity function, including all faint sources (Visbal & Loeb 2010; Visbal et al 2011)
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