Galaxy formation and evolution

Abstract:

We present the first measurements of H i galaxy scaling relations from a blind survey at z > 0.15. We perform spectral stacking of 9023 spectra of star-forming galaxies undetected in H i at 0.23 < z < 0.49, extracted from MIGHTEE-H i Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies in bins of galaxy properties (stellar mass M *, star formation rateSFR, and specific star formation rate sSFR, with sSFR ≡ M */SFR), obtaining ≳5σ detections in most cases, the strongest H i-stacking detections to date in this redshift range. With these detections, we are able to measure scaling relations in the probed redshift interval, finding evidence for a moderate evolution from the median redshift of our sample z med ∼ 0.37 to z ∼ 0. In particular, low-M * galaxies ( log 10 ( M * / M ⊙ ) ∼ 9 ) experience a strong H i depletion (∼0.5 dex in log 10 ( M H I / M ⊙ ) ), while massive galaxies ( log 10 ( M * / M ⊙ ) ∼ 11 ) keep their H i mass nearly unchanged. When looking at the star formation activity, highly star-forming galaxies evolve significantly in M H I (f H I, where f H I ≡ M H I/M *) at fixed SFR (sSFR), while at the lowest probed SFR (sSFR) the scaling relations show no evolution. These findings suggest a scenario in which low-M * galaxies have experienced a strong H i depletion during the last ∼5 Gyr, while massive galaxies have undergone a significant H i replenishment through some accretion mechanism, possibly minor mergers. Interestingly, our results are in good agreement with the predictions of the simba simulation. We conclude that this work sets novel important observational constraints on galaxy scaling relations.

Abstract:

The phase transition between galaxies and quasars is often identified with the rare population of hyper-luminous, hot dust-obscured galaxies. Galaxy formation models predict these systems to grow via mergers, that can deliver large amounts of gas toward their centers, induce intense bursts of star formation and feed their supermassive black holes. Here we report the detection of 24 galaxies emitting Lyman-α emission on projected physical scales of about 400 kpc around the hyper-luminous hot dust-obscured galaxy W0410-0913, at redshift z = 3.631, using Very Large Telescope observations. While this indicates that W0410-0913 evolves in a very dense environment, we do not find clear signs of mergers that could sustain its growth. Data suggest that if mergers occurred, as models expect, these would involve less massive satellites, with only a moderate impact on the internal interstellar medium of W0410-0913, which is sustained by a rotationally-supported fast-rotating molecular disk, as Atacama Large Millimeter Array observations suggest.