Herve A. Dole | Searcharxiv

arXiv2019

Using ALMA to resolve the nature of the early star-forming large-scale structure PLCK G073.4-57.5

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 >2000 high-z candidate structures has been found using Planck's all-sky submm 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. In order to resolve and characterise the individual galaxies we targeted the eight brightest 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 data from IRAC, WIRCam J,K, and SCUBA-2. We detected a total of 18 millimetre galaxies brighter than 0.3 mJy in 2.4 arcmin^2. The ALMA source density is 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 NIR counterpart. The most significant (four) SCUBA-2 sources are not included in the ALMA pointings, but we find an 8sigma stacking detection of the ALMA sources in the SCUBA-2 map at 850 um. We derive photo-z, L_IR, SFR, stellar mass, T_dust, M_dust for all of the ALMA galaxies; the photo-zs identify two groups each of five sources, at z~1.5 and 2.4. The two groups show two 'red sequences' (i.e. similar NIR [3.6]-[4.5] colours and different J-K colours). The majority of the ALMA-detected galaxies are on the SFR versus stellar mass main sequence, and half of the sample is more massive than the characteristic stellar mass at the corresponding redshift. 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 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.

astro-ph.GA↗

arXiv2017

SCUBA-2 follow-up of Herschel-SPIRE observed Planck overdensities

We present SCUBA-2 follow-up of 61 candidate high-redshift Planck sources. Of these, 10 are confirmed strong gravitational lenses and comprise some of the brightest such submm sources on the observed sky, while 51 are candidate proto-cluster fields undergoing massive starburst events. With the accompanying Herschel-SPIRE observations and assuming an empirical dust temperature prior of $34^{+13}_{-9}$ K, we provide photometric redshift and far-IR luminosity estimates for 172 SCUBA-2-selected sources within these Planck overdensity fields. The redshift distribution of the sources peak between a redshift of 2 and 4, with one third of the sources having $S_{500}$/$S_{350} > 1$. For the majority of the sources, we find far-IR luminosities of approximately $10^{13}\,\mathrm{L}_\odot$, corresponding to star-formation rates of around $1000$ M$_\odot \mathrm{yr}^{-1}$. For $S_{850}>8$ mJy sources, we show that there is up to an order of magnitude increase in star-formation rate density and an increase in uncorrected number counts of $6$ for $S_{850}>8$ mJy when compared to typical cosmological survey fields. The sources detected with SCUBA-2 account for only approximately $5$ per cent of the Planck flux at 353 GHz, and thus many more fainter sources are expected in these fields.

astro-ph.GA↗