摘要：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-zcandidate structures has been found usingPlanck’s all-sky submillimetre maps, and a sub-set of 234 have been followed up withHerschel-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 byPlanckandHerschel, and to find out whether they constitute the progenitors of present-day, massive galaxy clusters. Thus, we targeted the eight brightestHerschel-SPIRE sources in the centre of thePlanckpeak PLCK G073.4−57.5 using ALMA at 1.3 mm, and complemented these observations with multi-wavelength data fromSpitzer-IRAC, CFHT-WIRCam in theJandKsbands, and JCMT’s SCUBA-2 instrument. We detected a total of 18 millimetre galaxies brighter than 0.3 mJy within the 2.4 arcmin2ALMA 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 8σstacking detection of the ALMA sources in the SCUBA-2 map at 850μm. 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 aroundz ≃ 1.5 and 2.4. The two groups show two “red sequences”, that is similar near-IR [3.6] − [4.5] colours and differentJ − Kscolours. 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 thez ≃ 1.5 group has total SFR = 840−100+120M⊙yr−1and ℳ = 5.8−2.4+1.7× 1011M⊙, and that thez ≃ 2.4 group has SFR = 1020−170+310M⊙yr−1and ℳ = 4.2−2.1+1.5× 1011M⊙, 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 atz = 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.
关键词：enlarge-scale structure of Universesubmillimeter: galaxiesradio continuum: galaxiesradio lines: galaxiesgalaxies: star formation
