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The ALMA Spectroscopic Survey in the HUDF: the Molecular Gas Content of Galaxies and Tensions with IllustrisTNG and the Santa Cruz SAM

Popping, Gergö; Pillepich, Annalisa; Somerville, Rachel S.; Decarli, Roberto; Walter, Fabian; Aravena, Manuel; Carilli, Chris; Cox, Pierre; Nelson, Dylan; Riechers, Dominik; Weiss, Axel; Boogaard, Leindert; Bouwens, Richard; Contini, Thierry; Cortes, Paulo C.; Cunha, Elisabete da; Daddi, Emanuele; Díaz-Santos, Tanio; Diemer, Benedikt; González-López, Jorge; Hernquist, Lars; Ivison, Rob; Fèvre, Olivier Le; Marinacci, Federico; Rix, Hans-Walter; Swinbank, Mark; Vogelsberger, Mark; Werf, Paul van der; Wagg, Jeff; Yung, L.Y. Aaron

The ALMA Spectroscopic Survey in the HUDF: the Molecular Gas Content of Galaxies and Tensions with IllustrisTNG and the Santa Cruz SAM Thumbnail


Gergö Popping

Annalisa Pillepich

Rachel S. Somerville

Roberto Decarli

Fabian Walter

Manuel Aravena

Chris Carilli

Pierre Cox

Dylan Nelson

Dominik Riechers

Axel Weiss

Leindert Boogaard

Richard Bouwens

Thierry Contini

Paulo C. Cortes

Elisabete da Cunha

Emanuele Daddi

Tanio Díaz-Santos

Benedikt Diemer

Jorge González-López

Lars Hernquist

Rob Ivison

Olivier Le Fèvre

Federico Marinacci

Hans-Walter Rix

Mark Vogelsberger

Paul van der Werf

Jeff Wagg

L.Y. Aaron Yung


The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) provides new constraints for galaxy formation models on the molecular gas properties of galaxies. We compare results from ASPECS to predictions from two cosmological galaxy formation models: the IllustrisTNG hydrodynamical simulations and the Santa Cruz semianalytic model (SC SAM). We explore several recipes to model the H2 content of galaxies, finding them to be consistent with one another, and take into account the sensitivity limits and survey area of ASPECS. For a canonical CO-to-H2 conversion factor of αCO = 3.6 Me/(K km s−1 pc2 ) the results of our work include: (1) the H2 mass of z > 1 galaxies predicted by the models as a function of their stellar mass is a factor of 2–3 lower than observed; (2) the models do not reproduce the number of H2-rich (M M H2 > ´3 1010 ) galaxies observed by ASPECS; (3) the H2 cosmic density evolution predicted by IllustrisTNG (the SC SAM) is in tension (in tension but with less disagreement than IllustrisTNG) with the observed cosmic density, even after accounting for the ASPECS selection function and field-to-field variance effects. The tension between models and observations at z > 1 can be alleviated by adopting a CO-to-H2 conversion factor in the range αCO = 2.0–0.8 Me/(K km s−1 pc2 ). Additional work on constraining the CO-to-H2 conversion factor and CO excitation conditions of galaxies through observations and theory will be necessary to more robustly test the success of galaxy formation models.

Journal Article Type Article
Acceptance Date Jun 21, 2019
Online Publication Date Nov 30, 2019
Publication Date Sep 10, 2019
Deposit Date Oct 8, 2019
Publicly Available Date Oct 8, 2019
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 882
Issue 2
Public URL


Published Journal Article (6.3 Mb)

Copyright Statement
© 2019. The American Astronomical Society. All rights reserved.

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