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ALMACAL V: absorption-selected galaxies with evidence for excited ISMs

Klitsch, A; Zwaan, MA; Péroux, C; Smail, I; Oteo, I; Popping, G; Swinbank, AM; Ivison, RJ; Biggs, AD

ALMACAL V: absorption-selected galaxies with evidence for excited ISMs Thumbnail


A Klitsch

MA Zwaan

C Péroux

I Oteo

G Popping

RJ Ivison

AD Biggs


Gas-rich galaxies are selected efficiently via quasar absorption lines. Recently, a new perspective on such absorption-selected systems has opened up by studying the molecular gas content of absorber host galaxies using ALMA CO emission line observations. Here, we present an analysis of multiple CO transitions (L CO ∼ 109 K km s−1) in two z ∼ 0.5 galaxies associated with one Ly α absorber towards J0238+1636. The CO spectral line energy distributions (CO SLEDs) of these galaxies appear distinct from that of typical star-forming galaxies at similar redshifts and is comparable with that of luminous infrared galaxies or active galactic nucleus (AGN). Indeed, these galaxies are associated with optically identified AGN activity. We infer that the CO line ratios and the αCO conversion factor differ from the Galactic values. Our findings suggest that at least a fraction of absorption-selected systems shows interstellar medium conditions deviating from those of normal star-forming galaxies. For a robust molecular gas mass calculation, it is therefore important to construct the CO SLED. Absorption line selection identifies systems with widely distributed gas, which may preferentially select interacting galaxies, which in turn will have more excited CO SLEDs than isolated galaxies. Furthermore, we raise the question whether quasar absorbers preferentially trace galaxy overdensities.

Journal Article Type Article
Acceptance Date Sep 24, 2018
Online Publication Date Oct 9, 2018
Publication Date Oct 9, 2018
Deposit Date Dec 6, 2018
Publicly Available Date Dec 6, 2018
Journal Monthly Notices of the Royal Astronomical Society: Letters
Electronic ISSN 1745-3933
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 482
Issue 1
Pages L65-L69
Public URL


Published Journal Article (1.3 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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