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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. (2018) Low star formation efficiency in typical galaxies at z = 5-6. . (Unpublished) http://resolver.caltech.edu/CaltechAUTHORS:20190521-144707894

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Abstract

We report the detection of CO(2-1) line emission from a Lyman Break Galaxy at z ∼ 5.7 with the VLA. The CO line luminosity implies a massive molecular gas reservoir of (1.3±0.3)(α_(CO)/4.5M⊙ (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 ∼3 times lower SFR, perhaps implying a high α_(CO) conversion factor, as typically found in low metallicity galaxies. Using ALMA, we find faint [NII] 205μm emission relative to [CII] in all but the most IR-luminous "normal" galaxies at z = 5−6 for a sample including both CO targets, suggesting more intense or harder radiation fields in the ionized gas relative to lower redshift. These radiation properties indicate low metallicity may be common in typical ∼10^(10)M⊙ galaxies at z = 5−6, consistent with our CO measurements. Our sample shows evidence for high dust temperatures, and a young starburst producing high radiation intensity and hardness even with substantial dust obscuration. While a fraction of Main Sequence star formation in the first billion years may take place in conditions not dissimilar to lower redshift, lower metallicity may affect the remainder of the population.


Item Type:Report or Paper (Discussion Paper)
Related URLs:
URLURL TypeDescription
http://arxiv.org/abs/1812.00006arXivDiscussion Paper
ORCID:
AuthorORCID
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:We thank Chelsea Sharon and Avani Gowardhan for useful discussion. R.P. and D.R. acknowledge support from the National Science Foundation under grant number 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 ESO (representing its member states), NSF (USA) and NINS (Japan), together with 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 ESO, AUI/NRAO and NAOJ.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
NSFAST-1614213
National Radio Astronomy ObservatorySOSPA3-008
Associated Universities, Inc.UNSPECIFIED
Record Number:CaltechAUTHORS:20190521-144707894
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20190521-144707894
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95651
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:21 May 2019 21:57
Last Modified:21 May 2019 21:57

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