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Published December 10, 2016 | Published
Journal Article Open

The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Search for [CII] Line and Dust Emission in 6 < z < 8 galaxies


We present a search for [C II] line and dust continuum emission from optical dropout galaxies at z > 6 using ASPECS, our Atacama Large Millimeter submillimeter Array Spectroscopic Survey in the Hubble Ultra-deep Field (UDF). Our observations, which cover the frequency range of 212–272 GHz, encompass approximately the range of 6 < z < 8 for [C II] line emission and reach a limiting luminosity of L_([C II]) ~ (1.6–2.5) × 10^8 L⊙. We identify 14 [C II] line emitting candidates in this redshift range with significances >4.5σ, two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60% of our candidates are expected to be spurious. For one of our blindly selected [C II] line candidates, we tentatively detect the CO(6-5) line in our parallel 3 mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all [C II] candidates results in a tentative detection with S_(1.2 mm) = 14 ± 5 μJy. This implies a dust-obscured star-formation rate (SFR) of (3 ± 1) M⊙ yr^(-1). We find that the two highest-SFR objects have candidate [C II] lines with luminosities that are consistent with the low-redshift L_([C II]) versus SFR relation. The other candidates have significantly higher [C II] luminosities than expected from their UV-based SFR. At the current sensitivity, it is unclear whether the majority of these sources are intrinsically bright [C II] emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for [C II] emitters at 6 < z < 8 that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.

Additional Information

© 2016 The American Astronomical Society. Received 2016 May 6; revised 2016 July 22; accepted 2016 August 3; published 2016 December 8. We thank the anonymous referee for positive feedback and useful comments. M.A. acknowledges partial support from FONDECYT through grant 1140099. F.W., I.R.S., and R.J.I. acknowledge support through ERC grants COSMIC-DAWN, DUSTYGAL, and COSMICISM, respectively. F.E.B. and L.I. acknowledge Conicyt grants Basal-CATA PFB-06/2007 and Anilo ACT1417. F.E.B. also acknowledges support from FONDECYT Regular 1141218 (FEB), and the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. E.d.C. gratefully acknowledges the Australian Research Council as the recipient of a Future Fellowship (project FT150100079). D.R. acknowledges support from the National Science Foundation under grant number AST-1614213 to Cornell University. I.R.S. also acknowledges support from STFC (ST/L00075X/1) and a Royal Society/Wolfson Merit award. Support for R.D. and B.M. was provided by the DFG priority program 1573 "The physics of the interstellar medium." A.K. and F.B. acknowledge support by the Collaborative Research Council 956, sub-project A1, funded by the Deutsche Forschungsgemeinschaft (DFG). P.I. acknowledges Conicyt grants Basal-CATA PFB-06/2007 and Anillo ACT1417. R.J.A. was supported by FONDECYT grant number 1151408. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00146.S and ADS/JAO.ALMA#2013.1.00718.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. The 3mm-part of ALMA project had been supported by the German ARC.

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August 19, 2023
August 19, 2023