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arXiv · 1207.2795

Deep observations of CO line emission from star-forming galaxies in a cluster candidate at z=1.5

M. Aravena·C. L. Carilli·M. Salvato·M. Tanaka·L. Lentati·E. Schinnerer·F. Walter·D. Riechers·V. Smolcic·P. Capak·H. Aussel·F. Bertoldi·S. C. Chapman·D. Farrah·A. Finoguenov·E. Le Floc'h·D. Lutz·G. Magdis·S. Oliver·L. Riguccini·S. Berta·B. Magnelli·F. Pozzi
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Abstract

We report results from a deep Jansky Very Large Array (JVLA) search for CO 1-0 line emission from galaxies in a candidate galaxy cluster at z~1.55 in the COSMOS field. We target 4 galaxies with optical spectroscopic redshifts in the range z=1.47-1.59. Two of these 4 galaxies, ID51613 and ID51813, are nominally detected in CO line emission at the 3-4 sigma level. We find CO luminosities of 2.4x10^10 K km/s pc^2 and 1.3x10^10 K km/s pc^2, respectively. Taking advantage from the clustering and 2-GHz bandwidth of the JVLA, we perform a search for emission lines in the proximity of optical sources within the field of view of our observations. We limit our search to galaxies with K<23.5 (AB) and z_phot=1.2-1.8. We find 2 bright optical galaxies to be associated with significant emission line peaks (>4 sigma) in the data cube, which we identify with the CO line emission. To test the reliability of the line peaks found, we performed a parallel search for line peaks using a Bayesian inference method. Monte Carlo simulations show that such associations are statistically significant, with probabilities of chance association of 3.5% and 10.7% for ID 51207 and ID 51380, respectively. Modeling of their optical/IR SEDs indicates that the CO detected galaxies and candidates have stellar masses and SFRs in the range (0.3-1.1)x10^11 M_sun and 60-160 M_sun/yr, with SFEs comparable to that found in other star-forming galaxies at similar redshifts. By comparing the space density of CO emitters derived from our observations with the space density derived from previous CO detections at z~1.5, and with semi-analytic predictions for the CO luminosity function, we suggest that the latter tend to underestimate the number of CO galaxies detected at high-redshift. Finally, we argue about the benefits of future blind CO searches in clustered fields with upcoming submm/radio facilities.

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M. Aravena, C. L. Carilli, M. Salvato, M. Tanaka, L. Lentati, E. Schinnerer, F. Walter, D. Riechers, V. Smolcic, P. Capak, H. Aussel, F. Bertoldi, S. C. Chapman, D. Farrah, A. Finoguenov, E. Le Floc'h, D. Lutz, G. Magdis, S. Oliver, L. Riguccini, S. Berta, B. Magnelli, F. Pozzi. 2012-07-11. Deep observations of CO line emission from star-forming galaxies in a cluster candidate at z=1.5. https://doi.org/10.1111/j.1365-2966.2012.21697.x

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