2019ApJ...887...37U

We present a power spectrum analysis of the ALMA Spectroscopic Survey Large Program (ASPECS LP) data from 84 to 115 GHz. These data predominantly probe small-scale fluctuations (k = 10-100 h Mpc^–1) in the aggregate CO emission in galaxies at 1<= z <= 4. We place an integral constraint on CO luminosity functions (LFs) in this redshift range via a direct measurement of their second moments in the three-dimensional (3D) autopower spectrum, finding a total CO shot-noise power P_CO,CO(k_CO(2–1))≤ 1.9×10²µK² (Mpc h^–1)³. This upper limit (3σ) is consistent with the observed ASPECS CO LFs in Decarli et al. but rules out a large space in the range of P_CO,CO(k_CO(2–1)) inferred from these LFs, which we attribute primarily to large uncertainties in the normalization Φ_* and knee L_* of the Schechter-form CO LFs at z > 2. Also, through power spectrum analyses of ASPECS LP data with 415 positions from galaxies with available optical spectroscopic redshifts, we find that contributions to the observed mean CO intensity and shot-noise power of MUSE galaxies are largely accounted for by ASPECS blind detections. Finally, we sum the fluxes from individual blind CO detections to yield a lower limit on the mean CO surface brightness at 99 GHz of <T_CO>=0.55±0.02µK, which we estimate represents 68%-80% of the total CO surface brightness at this frequency.