The abundance of cold molecular gas plays a crucial role in models of galaxy evolution. While deep spectroscopic surveys of CO emission lines have been a primary tool for measuring this abundance, the difficulty of these observations has motivated alternative approaches to studying molecular gas content. One technique, line intensity mapping, seeks to constrain the average molecular gas properties of large samples of individually undetectable galaxies through the CO brightness power spectrum. Here we present constraints on the cross-power spectrum between CO intensity maps and optical galaxy catalogs. This cross-measurement allows us to check for systematic problems in CO intensity mapping data, and validate the data analysis used the auto-power spectrum measurement of the CO Power Spectrum Survey. We place a 2-sigma upper limit on the band-averaged CO-galaxy cross-power of $P_x<540$ uK Mpc$^3$/h$^3$. Our measurement favors a non-zero mean CO brightness temperature at around 90% confidence and gives an upper limit on the mean molecular gas density at z~2.6 of $7.7 \times 10^8$ Msun/Mpc$^3$. We forecast the expected cross-power spectrum by applying a number of literature prescriptions for the CO luminosity to halo mass relation to a suite of mock light cones. Under the most optimistic forecasts the cross-spectrum could be detected with only moderate extensions of the data used here, while more conservative models could be detected with a factor of 10 increase in sensitivity. Ongoing CO intensity mapping experiments will target fields allowing extensive cross correlation analysis and should reach the sensitivity required to detect the cross-spectrum signal. 

An Intensity Mapping Constraint on the CO-galaxy Cross-power Spectrum at Redshift ∼3

ABSTRACT We construct the halo mass function (HMF) from the GAMA (Galaxy And Mass Assembly) galaxy group catalogue over the mass range of 1012.7–1015.5 M⊙, and find good agreement with the expectation from Lambda cold dark matter. In comparison to previous studies, this result extends the mass range over which the HMF has now been measured over by an order of magnitude. We combine the GAMA data release (DR) 4 HMF with similar data from the Sloan Digital Sky Survey (SDSS) DR12 and REFLEX II (ROSAT-ESO Flux Limited X-ray Galaxy Cluster Survey) surveys, and fit a four-parameter Murray–Robotham–Power function, valid at $\tilde{z} \approx 0.1$, yielding a density normalization of log10 (ϕ* Mpc$^{3})= -3.96^{+0.55}_{-0.82}$, a high mass turnover of log10 (M* M$_{\odot }^{-1})=14.13^{+0.43}_{-0.40}$, a low-mass power-law slope of $\alpha =-1.68^{+0.21}_{-0.24}$, and a high-mass softening parameter of $\beta =0.63^{+0.25}_{-0.11}$. If we fold in the constraint on ΩM from the Planck 2018 cosmology, we are able to reduce these uncertainties further, but this relies on the assumption that the power-law trend can be extrapolated from 1012.7 M⊙ to zero mass. Throughout, we highlight the effort needed to improve on our HMF measurement: improved halo mass estimates that do not rely on calibration to simulations; reduced halo mass uncertainties needed to mitigate the strong Eddington bias that arises from the steepness of the HMF low-mass slope; and deeper wider area spectroscopic surveys. To our halo mass limit of 1012.7 M⊙, we are directly resolving (‘seeing’) 41 ± 5 per cent of the total mass density, i.e. ΩM,&amp;gt;12.7 = 0.128 ± 0.016, opening the door for the direct construction of three-dimensional dark matter mass maps at Mpc resolution. 

OUP accepted manuscript

An empirical measurement of the Halo Mass Function from the combination

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An empirical measurement of the Halo Mass Function from the combination of GAMA DR4, SDSS DR12, and REFLEX II data

The ﬁeld of millimetre-wave line-intensity mapping (LIM) is seeing increased experimental activity with pathﬁnder surveys already deployed or deploying in the next few years, making spectroscopic measurements of unresolved atomic and molecular line emission tracing the large-scale structure of the Universe. The next decade will also see the Rubin Observatory Legacy Survey of Space and Time (LSST) undertake a photometric galaxy survey programme of unprecedented scope, including measurements of cosmic shear exploiting weak gravitational lensing (WL) of background galaxies to map projected large-scale structure. We consider prospects for detecting angular cross power spectra between non-tomographic cosmic shear and mm-wave LIM surveys that measure emission from CO lines at 𝑧 = 0 . 5–1. We forecast that once the LSST Year 10 WL dataset is available, a future LIM experiment, conceivably deployed in the next 10–15 years, would enable such a cross-correlation detection with an overall signal-to-noise ratio of 50, although the current pathﬁnder generation of CO/[C ii] surveys are more likely to achieve a marginal 2 𝜎 detection against an earlier-stage LSST WL dataset. The signal has modest astrophysical constraining power yielding competitive constraints on cosmic molecular gas density at 𝑧 (cid:46) 1, and degeneracies between astrophysical parameters and the intrinsic alignment amplitude mean that external information on either one could allow the cross-correlation analysis to signiﬁcantly improve its constraints on the other.

Cross-correlations between mm-wave line-intensity mapping and weak lensing surveys: preliminary consideration of long-term prospects


 Cosmological N-body simulations of the dark matter component of the universe typically use initial conditions with a fixed power spectrum and random phases of the density field, leading to structure consistent with the local distribution of galaxies only in a statistical sense. It is, however, possible to infer the initial phases which lead to the configuration of galaxies and clusters that we see around us. We analyse the CSiBORG suite of 101 simulations, formed by constraining the density field within 155 Mpc/h with dark matter particle mass 4.38 × 109 M⊙, to quantify the degree to which constraints imposed on 2.65 Mpc h−1 scales reduce variance in the halo mass function and halo–halo cross-correlation function on a range of scales. This is achieved by contrasting CSiBORG with a subset of the unconstrained Quijote simulations and expectations for the ΛCDM average. Using the FOF, PHEW and HOP halofinders, we show that the CSiBORG suite beats cosmic variance at large mass scales (≳ 1014 M⊙ h−1), which are most strongly constrained by the initial conditions, and exhibits a significant halo–halo cross-correlation out to ∼30 Mpc h−1. Moreover, the effect of the constraints percolates down to lower mass objects and to scales below those on which they are imposed. Finally, we develop an algorithm to ‘twin’ haloes between realisations and show that approximately 50 per cent of haloes with mass greater than 1015 M⊙ h−1 can be identified in all realisations of the CSiBORG suite. We make the CSiBORG halo catalogues publicly available for future applications requiring knowledge of the local halo field.

A. G. Neuhold

Papers

TheHaloMod: An online calculator for the halo model