LARgE Survey – II. The dark matter haloes and the progenitors and descendants of ultramassive passive galaxies at cosmic noon

Abstract

We use a 27.6 deg 2 survey to measure the clustering of gzK s -selected quiescent galaxies at z ∼ 1.6, focusing on ultra-massive quiescent galaxies. We find that z ∼ 1.6 Ultra-Massive Passively Evolving Galaxies (UMPEGs), which have K s (AB) < 19.75 (stellar masses of M > ∼ 10 11.4 M and mean <M > = 10 11.5 M ), cluster more strongly than any other known galaxy population at high redshift. Comparing their correlation length, r 0 = 29.77 ± 2.75 h −1 Mpc, with the clustering of dark matter halos in the Millennium XXL N-body simulation suggests that these z ∼ 1.6 UMPEGs reside in dark matter halos of mass M h ∼ 10 14.1 h −1 M . Such very massive z ∼ 1.6 halos are associated with the ancestors of z ∼ 0 massive galaxy clusters such as the Virgo and Coma clusters. Given their extreme stellar masses and lack of companions with comparable mass, we surmise that these UMPEGs could be the already-quenched central massive galaxies of their (proto)clusters. We conclude that with only a modest amount of further growth in their stellar mass, z ∼ 1.6 UMPEGs could be the progenitors of some of the massive central galaxies of present-day massive galaxy clusters observed to be already very massive and quiescent near the peak epoch of the cosmic star formation.

LARgE survey – III. Environments of ultra-massive passive galaxies at cosmic noon: BCG progenitors growing through mergers

“…(v) Were the estimated merger rate continue to z∼0, then a typical UMPEG, with M UMPEG ∼ 10 11.6 M at z∼1.6 would grow to M ∼ 10 12.0 through mergers with such relatively massive companions. This projected z∼0 mass is consistent with the masses of present-day massive cluster BCGs lending further support to the idea (raised by Cheema et al 2020) that UMPEGs are the direct, already-quiescent and massive progenitors of the central galaxies of some of the present-day massive galaxy clusters such as Virgo and Coma.…”

“…Our mass growth calculation is crude as it assumes a constant merger rate (whereas -at least for lower-mass galaxies -merger rates decrease with time; e.g., Patton et al 2002;Bridge et al 2010) and, moreover, does not account for accretion of low-mass satellites or for possible re-ignition of star formation in the UMPEGs. However, this rough calculation does yield a projected z∼0 UMPEG mass that is consistent with the masses of massive cluster BCGs at z∼0 and thereby with the idea, first suggested on the basis of clustering measurements in Cheema et al (2020), that our z∼1.6 UMPEGs are the direct progenitors of some of the central BCGs of massive present-day galaxy clusters.…”

“…Of course, mergers that build UMPEGs might also be wet (i.e., gas-rich and resulting in additional star-formation), but we have no immediate way of observationally linking our UMPEGs to such wet merger progenitors with the present data. We note that our UMPEGs cluster extremely strongly (see Cheema et al 2020) -much more strongly that do potential high-z massive wet merger candidates such as submillimetre galaxies (SMGs, e.g., Blain et al 2004;Hickox et al 2012;Wilkinson et al 2017) or Dust Obscured Galaxies (DOGs, e.g., Brodwin et al 2008;Toba et al 2017). It therefore seems that UMPEGs are associated with more massive, rarer dark matter halos than is typical of high-z starbursts.…”

An ALMA survey of the SCUBA-2 Cosmology Legacy Survey UKIDSS/UDS field: halo masses for submillimetre galaxies

“…For comparison, we also show observational estimates of the SHMR for gzK-selected quiescent galaxies at z ∼ 1.6 from Cheema et al (2020), that as we mentioned above, could be immediate descendants of our SMG population. We see that the SHMR for the SMGs are broadly consistent with the maximum SHMR inferred for these quiescent galaxies, supporting the presence of a peak in the SHMR in haloes of mass log 10 (M halo [M ]) ∼ 12.5, characteristic of SMGs.…”

“…For comparison, we show a number of empirical model predictions for central galaxies at z = 2 fromMoster et al (2010) andMoster, Naab & White (2013) with dotted and dot-dashed lines, respectively, and a dashed line with the shaded region showing models using the abundance matching fromBehroozi, Conroy & Wechsler (2010), where the shaded region shows the 1σ uncertainties. Observational results for z ∼ 1.6 massive gzK s -selected quiescent galaxies(Cheema et al 2020) are shown by the diamond points. The models show that SMGs, with halo masses log 10 (M halo [M ]) ∼ 12.5-12.8 are expected to maximal stellar mass-halo mass ratios and thus represent the peak efficiency of star formation at their redshifts.…”