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Title: HIGH-RESOLUTION SPECTROSCOPIC IMAGING OF CO IN A z = 4.05 PROTO-CLUSTER

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{sub CO}/0.8) M{sub ☉} pc{sup –2} for GN20.2a/GN20.2b in the highest-resolution maps. Dynamical mass estimates allow us to constrain the CO-to-H{sub 2} conversion factor to α{sub CO} = 1.7 ± 0.8 M{sub ☉} (K km s{sup –1} pc{sup 2}){sup –1} for GN20.2a and α{sub CO}= 1.1±{sup 1.5}{sub 1.1} M{sub ☉} (K km s{sup –1} pc{sup 2}){sup –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 themore » 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{sup ′}{sub CO(2-1)} = 8 x 10{sup 9} K km s{sup –1} pc{sup 2} and covering Δz = 0.0273 (∼20 comoving Mpc) produces no other strong contenders associated with the proto-cluster.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4]
  1. Max-Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  2. National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801-0387 (United States)
  3. CEA, Laboratoire AIM-CNRS, Université Paris Diderot, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette (France)
  4. Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
Publication Date:
OSTI Identifier:
22270900
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; CONCENTRATION RATIO; COSMIC DUST; EMISSION; ENERGY SPECTRA; GALAXIES; GALAXY CLUSTERS; HYDROGEN; LUMINOSITY; LYMAN LINES; RED SHIFT; RESOLUTION; STARS