A Foreground Masking Strategy for [C ii] Intensity Mapping Experiments Using Galaxies Selected by Stellar Mass and Redshift

Abstract

Intensity mapping provides a unique means to probe the epoch of reionization (EoR), when the neutral intergalactic medium was ionized by the energetic photons emitted from the first galaxies. The [C II] 158µm 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 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 (TIME), 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 AB K 22 (or M * 10 9 M ) at z < 1 and makes a [C II]/CO tot power ratio of 10 at k = 0.1 h/Mpc achievable, at the cost of a moderate 8% loss of total survey volume.

The ALMA Spectroscopic Survey in the HUDF: Constraining Cumulative CO Emission at 1 ≲ z ≲ 4 with Power Spectrum Analysis of ASPECS LP Data from 84 to 115 GHz

“…Table 1 summarizes the ASPECS survey parameters adopted for the power spectrum analysis, and their mappings to physical dimensions in real-and k-space. In Figure 2, we indicate the location of k and k ⊥ values for ASPECS relative to the predicted total CO(2-1) power-including both clustering and shot noise contributions-at z = 1 from Sun et al (2018). The ranges of transverse and line-of-sight k modes have important implications to be considered when computing the power spectrum.…”

“…These physical scales are important, however, for extracting information about large-scale clustering. Based on models (e.g., Sun et al 2018;Pullen et al 2013) for the total CO power spectrum at the redshift range relevant to this study, we expect any power from galaxy clustering between dark matter halos, P clust CO,CO (k, z), to dominate the total CO power spectrum, P tot CO,CO (k, z), up to k 1 h Mpc −1 compared to contributions from smallscale clustering of galaxies that share a common host dark matter halo or shot noise power, P shot CO,CO (cf. Figure 2).…”

Constraining the evolution of [C ii] intensity through the end stages of reionization

“…The most dominant interloper lines arise from the CO (3-2) and (4-3) emission from z ∼ 0 − 2, with an additional component coming from the cosmic infrared background (CIB). Efficient removal techniques (cleaning/masking) have been developed to mitigate line foregrounds (e.g., Breysse et al 2015;Cheng et al 2016;Visbal & Loeb 2010;Lidz & Taylor 2016;Sun et al 2018). At lower redshifts, the main contaminants are expected to be Galactic and extragalactic thermal dust emissions and their associated instrument response.…”

User’s guide to extracting cosmological information from line-intensity maps

“…We refer the reader interested in foreground and line-interloper removal strategies to, e.g., Refs. [79,[84][85][86][87][88][89]. We also assume a Gaussian covariance without mode coupling.…”