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High-resolution Spectroscopic Imaging of CO in a z = 4.05 Proto-cluster

Hodge, J. A. and Carilli, C. L. and Walter, F. and Daddi, E. and Riechers, D. (2013) High-resolution Spectroscopic Imaging of CO in a z = 4.05 Proto-cluster. Astrophysical Journal, 776 (1). Art. No. 22. ISSN 0004-637X. doi:10.1088/0004-637X/776/1/22.

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We present a study of the formation of clustered, massive galaxies at large look-back times via spectroscopic imaging of CO in the unique GN20 proto-cluster at z = 4.05. Existing observations show that this is a dense concentration of gas-rich, very active star forming galaxies, including multiple bright submillimeter galaxies (SMGs). Using deep, high-resolution Karl G. Jansky Very Large Array CO(2-1) observations, we image the molecular gas with a resolution of ~1 kpc just 1.6 Gyr after the big bang. The SMGs GN20.2a and GN20.2b have deconvolved sizes of ~5 kpc × 3 kpc and ~8 kpc × 5 kpc (Gaussian FWHM) in CO(2-1), respectively, and we measure gas surface densities up to ~12,700/1700 × (sin i) (α_(CO)/0.8) M_☉ pc^(–2) for GN20.2a/GN20.2b in the highest-resolution maps. Dynamical mass estimates allow us to constrain the CO-to-H_2 conversion factor to α_(CO) = 1.7 ± 0.8 M_☉ (K km s^(–1) pc^2)^(–1) for GN20.2a and α_(CO) = 1.1^(1.5)_(1.1) M_☉ (K km s^(–1) pc^2)^(–1) for GN20.2b. We measure significant offsets (0."5-1") between the CO and optical emission, indicating either dust obscuration on scales of tens of kiloparsecs or that the emission originates from distinct galaxies. CO spectral line energy distributions imply physical conditions comparable to other SMGs and reveal further evidence that GN20.2a and GN20.2b are in different merging stages. We carry out a targeted search for CO emission from the 14 known B-band Lyman break galaxies (LBGs) in the field, tentatively detecting CO in a previously undetected LBG and placing 3σ upper limits on the CO luminosities of those that may lie within our bandpass. A blind search for emission-line sources down to a 5σ limiting CO luminosity of L'_(CO(2-1)) = 8 x 10^9 K km s^(–1) pc^2 and covering Δz = 0.0273 (~20 comoving Mpc) produces no other strong contenders associated with the proto-cluster.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Hodge, J. A.0000-0001-6586-8845
Carilli, C. L.0000-0001-6647-3861
Walter, F.0000-0003-4793-7880
Daddi, E.0000-0002-3331-9590
Riechers, D.0000-0001-9585-1462
Additional Information:© 2013 American Astronomical Society. Received 2012 September 11; accepted 2013 July 16; published 2013 September 23. The authors thank Roberto Decarli, Qinghua Tan, and Lindley Lentati for assistance with various aspects of the data reduction/analysis, and we thank Christian Henkel for his work on the LVG code. C.C. thanks the Kavli institute of Cosmology for their hospitality. E.D. acknowledges support from grants ERC–StG UPGAL 240039 and ANR-08-JCJC-0008. D.R. acknowledges funding from NASA through a Spitzer Space Telescope grant. The National Radio Astronomy Observatory is a facility of the National Science Foundation under cooperative agreement by Associated Universities, Inc.
Funding AgencyGrant Number
European Research Council (ERC)240039
Agence Nationale pour la Recherche (ANR)ANR-08-JCJC-0008
Subject Keywords:galaxies: evolution; galaxies: formation; galaxies: high-redshift; galaxies: ISM; galaxies: star formation
Issue or Number:1
Record Number:CaltechAUTHORS:20131101-150551495
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Official Citation:High-resolution Spectroscopic Imaging of CO in a z = 4.05 Proto-cluster J. A. Hodge et al. 2013 ApJ 776 22
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42203
Deposited By: Ruth Sustaita
Deposited On:01 Nov 2013 22:26
Last Modified:10 Nov 2021 16:19

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