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Low star formation efficiency in typical galaxies at z = 5-6

Pavesi, Riccardo and Riechers, Dominik A. and Faisst, Andreas L. and Stacey, Gordon J. and Capak, Peter L. (2019) Low star formation efficiency in typical galaxies at z = 5-6. Astrophysical Journal, 882 (2). Art. No. 168. ISSN 1538-4357.

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Using the Very Large Array and ALMA, we have obtained CO(2–1), [C II], and [N II] line emission and multiple dust continuum measurements in a sample of "normal" galaxies at z = 5–6. We report the highest-redshift detection of low-J CO emission from a Lyman break galaxy, at z ~ 5.7. The CO line luminosity implies a massive molecular gas reservoir of (1.3 ± 0.3)(α CO/4.5 M_⊙ (K km s^(−1) pc^2)^(−1)) × 10^(11) M_⊙, suggesting low star formation efficiency with a gas depletion timescale of order ~1 Gyr. This efficiency is much lower than traditionally observed in z ≳ 5 starbursts, indicating that star-forming conditions in main-sequence galaxies at z ~ 6 may be comparable to those of normal galaxies probed up to z ~ 3 to date but with rising gas fractions across the entire redshift range. We also obtain a deep CO upper limit for a main-sequence galaxy at z ~ 5.3 with an approximately three times lower star formation rate, perhaps implying a high α CO conversion factor, as typically found in low-metallicity galaxies. For a sample including both CO targets, we also find faint [N II] 205 μm emission relative to [C II] in all but the most IR-luminous "normal" galaxies at z = 5–6, implying more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties suggest that low metallicity may be common in typical ~10^(10) M_⊙ galaxies at z = 5–6. While a fraction of main-sequence star formation in the first billion yr may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Pavesi, Riccardo0000-0002-2263-646X
Riechers, Dominik A.0000-0001-9585-1462
Faisst, Andreas L.0000-0002-9382-9832
Capak, Peter L.0000-0003-3578-6843
Additional Information:© 2019 The American Astronomical Society. Received 2018 November 30; revised 2019 July 29; accepted 2019 August 8; published 2019 September 16. We thank Chelsea Sharon and Avani Gowardhan for useful discussion. R.P. and D.R. acknowledge support from the National Science Foundation under grant No. AST-1614213 to Cornell University. R.P. acknowledges support through award SOSPA3-008 from the NRAO. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00928.S, 2015.1.00388.S, 2012.1.00523.S, 2011.0.00064.S. ALMA is a partnership of the ESO (representing its member states), NSF (USA), and NINS (Japan), together with the NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by the ESO, AUI/NRAO, and NAOJ.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
National Radio Astronomy ObservatorySOSPA3-008
Associated Universities, Inc.UNSPECIFIED
Subject Keywords:cosmology: observations – galaxies: formation – galaxies: high-redshift – galaxies: ISM – galaxies: star formation – radio lines: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20190521-144707894
Persistent URL:
Official Citation:Riccardo Pavesi et al 2019 ApJ 882 168
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95651
Deposited By: Tony Diaz
Deposited On:21 May 2019 21:57
Last Modified:03 Oct 2019 21:15

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