The implications of the surprising existence of a large, massive CO disk in a distant protocluster

Dannerbauer, H, Lehnert, M D, Emonts, B, Ziegler, B, De Breuck, C, Hatch, N, Kodama, T, Koyama, Y, Kurk, J, Matiz, T, Miley, G, Narayanan, D, Norris, R, Overzier, R, Röttgering, H J A, Sargent, M, Seymour, N, Tanaka, M, Valtchanov, I and Wylezalek, D (2017) The implications of the surprising existence of a large, massive CO disk in a distant protocluster. Astronomy and Astrophysics. ISSN 0004-6361

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It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 hours of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, Mmol = 2.0 ± 0.2 × 10^11 M⊙, extended, ∼40 kpc, CO(1-0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at zCO = 2.1478, is a clumpy, massive disk galaxy, M∗ ∼ 5 × 10^11 M⊙, which lies 250 kpc in projection from MRC 1138−262 and is a known Hα emitter, HAE229. HAE229 has a molecular gas fraction of ∼30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies.
HAE229 is the first CO(1-0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z > 0.4 that are detected in low-order CO transitions with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and FWHM are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results uggest that environment does not impact the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk,
suggests that environmentally-specific processes such as ram pressure stripping are not operating efficiently in (proto)clusters. We discuss why this might be so.

Item Type: Article
Schools and Departments: School of Mathematical and Physical Sciences > Physics and Astronomy
Research Centres and Groups: Astronomy Centre
Subjects: Q Science > QB Astronomy
Depositing User: Catrina Hey
Date Deposited: 17 Nov 2017 15:05
Last Modified: 21 Feb 2018 12:45

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