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Register a new userPredictions and sensitivity forecasts for reionization-era [C II] line intensity mapping
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Sebastian Dumitru
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Observations of the high-redshift Universe using the 21 cm line of neutral hydrogen and complimentary emission lines from the first galaxies promise to open a new door for our understanding of the epoch of reionization. We present predictions for the [C II] 158-micron line and H I 21 cm emission from redshifts z=6--9 using high-dynamic-range cosmological simulations combined with semi-analytical models. We find that the CONCERTO experiment should be able to detect the large scale power spectrum of [C II] emission to redshifts of up to z=8 (signal-to-noise ratio ~ 1 at k = 0.1 h/cMpc with 1500 hr of integration). A Stage II experiment similar to CCAT-p should be able to detect [C II] from even higher redshifts to high significance for similar integration times (signal-to-noise ratio of ~50 at k = 0.2 h/cMpc at z=6--9). We study the possibility of combining such future [C II] measurements with 21 cm measurements using LOFAR and SKA to measure the [C II]-21cm cross power spectra, and find that a Stage II experiment should be able to measure the cross-power spectrum for k < 1 h/cMpc to signal-to-noise ratio of better than 10. We discuss the capability of such measurements to constrain astrophysical parameters relevant to reionization and show that a measurement of the [C II]-21cm cross power spectrum helps break the degeneracy between the mass and brightness of ionizing sources.
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We combine recent simulation work on the SFR--[C II] correlation at high redshift with empirical modeling of the galaxy--halo connection (via UniverseMachine) to forecast [C II] auto power spectra from $zsim4$ to $zsim8$. We compare these to sensitivities realistically expected from various instruments expected to come on-line in the next decade. If the predictions of our model are correct, [C II] should be detectable up to $zsim6$ in this generation of surveys, but detecting [C II] past the end of reionization will require a generational leap in line-intensity survey capabilities.
Line-intensity mapping observations will find fluctuations of integrated line emission are attenuated by varying degrees at small scales due to the width of the line emission profiles. This attenuation may significantly impact estimates of astrophysical or cosmological quantities derived from measurements. We consider a theoretical treatment of the effect of line broadening on both the clustering and shot-noise components of the power spectrum of a generic line-intensity power spectrum using a halo model. We then consider possible simplifications to allow easier application in analysis, particularly in the context of inferences that require numerous, repeated, fast computations of model line-intensity signals across a large parameter space. For the CO Mapping Array Project (COMAP) and the CO(1-0) line-intensity field at $zsim3$ serving as our primary case study, we expect a $sim10%$ attenuation of the spherically averaged power spectrum on average at relevant scales of $kapprox0.2$-$0.3$ Mpc$^{-1}$, compared to $sim25%$ for the interferometric Millimetre-wave Intensity Mapping Experiment (mmIME) targeting shot noise from CO lines at $zsim1$-$5$ at scales of $kgtrsim1$ Mpc$^{-1}$. We also consider the nature and amplitude of errors introduced by simplified treatments of line broadening, and find that while an approximation using a single effective velocity scale is sufficient for spherically-averaged power spectra, a more careful treatment is necessary when considering other statistics such as higher multipoles of the anisotropic power spectrum or the voxel intensity distribution.
Line intensity mapping (LIM) is a promising observational method to probe large-scale fluctuations of line emission from distant galaxies. Data from wide-field LIM observations allow us to study the large-scale structure of the universe as well as galaxy populations and their evolution. A serious problem with LIM is contamination by foreground/background sources and various noise contributions. We develop conditional generative adversarial networks (cGANs) that extract designated signals and information from noisy maps. We train the cGANs using 30,000 mock observation maps with assuming a Gaussian noise matched to the expected noise level of NASAs SPHEREx mission. The trained cGANs successfully reconstruct H{alpha} emission from galaxies at a target redshift from observed, noisy intensity maps. Intensity peaks with heights greater than 3.5 {sigma} noise are located with 60 % precision. The one-point probability distribution and the power spectrum are accurately recovered even in the noise-dominated regime. However, the overall reconstruction performance depends on the pixel size and on the survey volume assumed for the training data. It is necessary to generate training mock data with a sufficiently large volume in order to reconstruct the intensity power spectrum at large angular scales. Our deep-learning approach can be readily applied to observational data with line confusion and with noise.
We forecast the ability of future-generation experiments to detect the fine-structure lines of the carbon and oxygen ions, [CII] and [OIII] in intensity mapping (IM) from the Epoch of Reionization ($z sim 6-8$). Combining the latest empirically derived constraints relating the luminosity of the [OIII] line to the ambient star-formation rate, and using them in conjunction with previously derived estimates for the abundance of [CII] in haloes, we predict the expected auto-correlation IM signal to be observed using next-generation facilities based on the Fred Young Submillimetre Telescope (FYST) and the balloon-borne facility, Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) over $z sim 5.3 - 7$. We describe how improvements to both the ground-based and balloon-based surveys in the future will enable a cross-correlation signal to be detected at $sim$ 10-40 $sigma$ over $z sim 5.3 - 7$. Finally, we propose a space-based mission targeting the [OIII] 88 and 52 $mu$m lines along with the [CII] 158 $mu$m line, configured to enhance the signal-to-noise ratio of cross-correlation measurements. We find that such a configuration can achieve a high-significance detection (hundreds to thousands of $sigma$) in both auto- and cross-correlation modes.
Line-intensity mapping surveys probe large-scale structure through spatial variations in molecular line emission from a population of unresolved cosmological sources. Future such surveys of carbon monoxide line emission, specifically the CO(1-0) line, face potential contamination from a disjoint population of sources emitting in a hydrogen cyanide emission line, HCN(1-0). This paper explores the potential range of the strength of HCN emission and its effect on the CO auto power spectrum, using simulations with an empirical model of the CO/HCN--halo connection. We find that effects on the observed CO power spectrum depend on modeling assumptions but are very small for our fiducial model based on our understanding of the galaxy--halo connection, with the bias in overall CO detection significance due to HCN expected to be less than 1%.
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