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 −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) auto-power spectrum, finding a total CO shot noise power P CO,CO (k CO(2-1) ) ≤ 1.9 × 10 2 µK 2 (Mpc h −1 ) 3 . This upper limit (3σ) is consistent with the observed ASPECS CO LFs in Decarli et al. (2019), 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, though there are ∼ 20% contributions to the CO(2-1) mean intensity due to sources previously undetected in the blind line search. 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 ± 0.02 µK, which we estimate represents 68-80% of the total CO surface brightness at this frequency.

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Multiband Constraints on Line-luminosity Functions and the Cosmic Density of Molecular Gas

“…The ASPECS-Pilot program (Walter et al 2016;Aravena et al 2016aAravena et al , 2016bDecarli et al 2016aDecarli et al , 2016bBouwens et al 2016;Carilli et al 2016) offered a first glimpse at the molecular gas content in galaxies residing in one of the best-studied regions of the extragalactic sky, the HUDF (Beckwith et al 2006). The ASPECS-Pilot survey was then expanded into an ALMA Large Program (LP) targeting a 4.6 arcmin 2 area, with the same survey strategy (Aravena et al 2019, 2020; Boogaard et al 2019, 2020; Decarli et al 2019;González-López et al 2019Popping et al 2019Popping et al , 2020Uzgil et al 2019;Inami et al 2020;Magnelli et al 2020;Walter et al 2020). Among other results, ASPECS provided robust constraints on the low-J CO luminosity functions up to z∼4, and an estimate of the evolution of the cosmic density of molecular gas in galaxies, ρ H2 (z).…”

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Nature of the Faintest Dusty Star-forming Galaxies

“…The ASPECS large program (LP) builds on the observational strategy and results presented by the ASPECS pilot observations, extending the covered area of the HUDF to 4.6 arcmin 2 , roughly composing the Hubble eXtremely Deep Field (XDF), the region of the HUDF with the deepest near-IR (NIR) observations (Illingworth et al 2013;Koekemoer et al 2013). The first results of the ASPECS LP based on the ALMA band 3 observations are presented in a series of recent papers (Aravena et al 2019;Boogaard et al 2019;Decarli et al 2020;González-López et al 2019;Popping et al 2019;Uzgil et al 2019;H. Inami et al 2020, in preparation).…”

Probing Cosmic Reionization and Molecular Gas Growth with TIME

“…Unfortunately, the faintness of cold ISM tracers, such as rotational lines of carbon monoxide (CO), has restricted observations to only the more luminous galaxies (Tacconi et al 2013;Decarli et al 2016;Riechers et al 2019;Decarli et al 2020). A census of the bulk molecular gas, however, requires a complete CO survey down to the very faint end of the line luminosity function (see e.g., Uzgil et al 2019).…”