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

Abstract

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<SUP>-1</SUP>) 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}<SUB>CO</SUB>,{CO}}({k}<SUB>CO</SUB>(2-1)})≤slant 1.9× {10}<SUP>2</SUP> μK<SUP>2</SUP> (Mpc h <SUP>-1</SUP>)<SUP>3</SUP>. 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}<SUB>CO</SUB>,{CO}}({k}<SUB>CO</SUB>(2-1)}) inferred from these LFs, which we attribute primarily to large uncertainties in the normalization Φ<SUB>*</SUB> and knee L <SUB>*</SUB> 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}<SUB>CO</SUB>}> =0.55+/- 0.02 μK, which we estimate represents 68%-80% of the total CO surface brightness at this frequency.