Massive post-starburst galaxies at z > 1 are compact proto-spheroids

Abstract

We investigate the relationship between the quenching of star formation and the structural transformation of massive galaxies, using a large sample of photometrically-selected poststarburst galaxies in the UKIDSS UDS field. We find that post-starburst galaxies at highredshift (z > 1) show high Sérsic indices, significantly higher than those of active star-forming galaxies, but with a distribution that is indistinguishable from the old quiescent population. We conclude that the morphological transformation occurs before (or during) the quenching of star formation. Recently quenched galaxies are also the most compact; we find evidence that massive post-starburst galaxies (M * > 10 10.5 M ) at high redshift (z > 1) are on average smaller than comparable quiescent galaxies at the same epoch. Our findings are consistent with a scenario in which massive passive galaxies are formed from three distinct phases: (1) gas-rich dissipative collapse to very high densities, forming the proto-spheroid; (2) rapid quenching of star formation, to create the "red nugget" with post-starburst features; (3) a gradual growth in size as the population ages, perhaps as a result of minor mergers.

The clustering of X-ray AGN at 0.5 < z < 4.5: host galaxies dictate dark matter halo mass

“…This uncertainty allows for the degeneracy between fitted parameters and the photometric redshift uncertainties. Further discussion of the supercolour stellar mass uncertainties can be found in Almaini et al (2017). Based on this work, we expect our results to be robust to known sources of random and systematic errors.…”

High-velocity outflows in massive post-starburst galaxies at z > 1

“…supercolour) has been used to identify systems that are likely to have experienced a more significant starburst (see Section 2.2). With respect to their structural parameters, interestingly, we find that these Spec+PCA PSBs are significantly more compact (r e ∼ 1.2 kpc) than those defined from spectroscopy alone, and consistent with previous studies that use only photometric PCA (supercolour) classifications (Almaini et al 2017;Maltby et al 2018). This suggests that the addition of photometric-selection criteria isolates PSBs that have undergone a more significant gas-rich dissipative event, which would also result in a more significant starburst, prior to quenching.…”

“…With respect to the quenching mechanism, using the K-band structural parameters available within the UDS field (Almaini et al 2017), we find that the high-z PSBs in our spectroscopic sample are typically compact and spheroidally-dominated (effective radius r e ∼ 2.1 kpc and Sérsic index n ∼ 3.25; see Table 1), with structures similar to that of our high-z passive galaxies. This result is consistent with previous studies that use only photometrically selected PSB samples (e.g.…”

Revealing the Stellar Mass and Dust Distributions of Submillimeter Galaxies at Redshift 2

“…Since the star-forming component is even more compact than the stars for our SMGs, those seem to fade into systems that represent the smaller and denser part of the quiescent galaxies at z = 1.5. Figure 9 also plots the effective sizes and resulting surface densities of post-starburst galaxies (i.e., systems selected to represent quiescent systems with very recent episodes of major star formation) at 1 < z < 2 determined using rest-frame optical imaging by Almaini et al (2017). The post-starburst systems exhibit on average effective sizes of 1.5-2 kpc within the stellar-mass range sampled by our SMGs, in agreement with the aforementioned decrease in stellar size of SMGs before quenching.…”