In:
Astronomy & Astrophysics, EDP Sciences, Vol. 625 ( 2019-05), p. A96-
Abstract:
Galaxy clusters at high redshift are key targets for understanding matter assembly in the early Universe, yet they are challenging to locate. A sample of more than 2000 high- z candidate structures has been found using Planck ’s all-sky submillimetre maps, and a sub-set of 234 have been followed up with Herschel -SPIRE, which showed that the emission can be attributed to large overdensities of dusty star-forming galaxies. As a next step, we need to resolve and characterise the individual galaxies giving rise to the emission seen by Planck and Herschel , and to find out whether they constitute the progenitors of present-day, massive galaxy clusters. Thus, we targeted the eight brightest Herschel -SPIRE sources in the centre of the Planck peak PLCK G073.4−57.5 using ALMA at 1.3 mm, and complemented these observations with multi-wavelength data from Spitzer -IRAC, CFHT-WIRCam in the J and K s bands, and JCMT’s SCUBA-2 instrument. We detected a total of 18 millimetre galaxies brighter than 0.3 mJy within the 2.4 arcmin 2 ALMA pointings, corresponding to an ALMA source density 8–30 times higher than average background estimates and larger than seen in typical “proto-cluster” fields. We were able to match all but one of the ALMA sources to a near infrared (NIR) counterpart. The four most significant SCUBA-2 sources are not included in the ALMA pointings, but we find an 8 σ stacking detection of the ALMA sources in the SCUBA-2 map at 850 μ m. We derive photometric redshifts, infrared (IR) luminosities, star-formation rates (SFRs), stellar masses (ℳ), dust temperatures, and dust masses for all of the ALMA galaxies. Photometric redshifts identify two groups each of five sources, concentrated around z ≃ 1.5 and 2.4. The two groups show two “red sequences”, that is similar near-IR [3.6] − [4.5] colours and different J − K s colours. The majority of the ALMA-detected galaxies are on the SFR versus ℳ main sequence (MS), and half of the sample is more massive than the characteristic ℳ * at the corresponding redshift. We find that the z ≃ 1.5 group has total SFR = 840 −100 +120 M ⊙ yr −1 and ℳ = 5.8 −2.4 +1.7 × 10 11 M ⊙ , and that the z ≃ 2.4 group has SFR = 1020 −170 +310 M ⊙ yr −1 and ℳ = 4.2 −2.1 +1.5 × 10 11 M ⊙ , but the latter group is more scattered in stellar mass and around the MS. Serendipitous CO line detections in two of the galaxies appear to match their photometric redshifts at z = 1.54. We performed an analysis of star-formation efficiencies (SFEs) and CO- and mm-continuum-derived gas fractions of our ALMA sources, combined with a sample of 1 〈 z 〈 3 cluster and proto-cluster members, and observed trends in both quantities with respect to stellar masses and in comparison to field galaxies.
Type of Medium:
Online Resource
ISSN:
0004-6361
,
1432-0746
DOI:
10.1051/0004-6361/201833252
Language:
English
Publisher:
EDP Sciences
Publication Date:
2019
detail.hit.zdb_id:
1458466-9
SSG:
16,12
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