Hintze Centre for Astrophysical Surveys

Abstract:

We obtain CO(1-0) molecular gas measurements with the Australia Telescope Compact Array on a sample of 43 spectroscopically confirmed Hα emitters in the Spiderweb protocluster at z = 2.16 and investigate the relation between their star formation activities and cold gas reservoirs as a function of environment. We achieve a CO(1-0) detection rate of ¼23 ± 12% with ten dual CO(1-0) and Hα detections within our sample at 10 < log M∗/M < 11.5. In addition, we obtain upper limits for the remaining sources. In terms of total gas fractions (Fgas), we find our sample is divided into two different regimes mediated by a steep transition at log M∗/M 10.5. Galaxies below that threshold have gas fractions that in some cases are close to unity, indicating that their gas reservoir has been replenished by inflows from the cosmic web. However, objects at log M∗/M > 10.5 display significantly lower gas fractions than their lower stellar mass counterparts and are dominated (12 out of 20) by objects hosting an active galactic nucleus (AGN). Stacking results yield Fgas 0.55 for massive emitters excluding AGN, and Fgas 0.35 when examining only AGN candidates. Furthermore, depletion times of our sample show that most Hα emitters at z = 2.16 will become passive by 1 < z < 1.6, concurrently with the surge and dominance of the red sequence in the most massive clusters. Our environmental analyses suggest that galaxies residing in the outskirts of the protocluster have larger molecular-to-stellar mass ratios and lower star formation efficiencies than galaxies residing in the core. However, star formation across the protocluster structure remains consistent with the main sequence, indicating that galaxy evolution is primarily driven by the depletion of the gas reservoir towards the inner regions. We discuss the relative importance of inflow and outflow processes in regulating star formation during the early phases of cluster assembly and conclude that a combination of feedback and overconsumption may be responsible for the rapid cold gas depletion these objects endure.

Abstract:

This paper presents the first effort to Extend the Investigation of Stellar Populations In RElics (E-INSPIRE). We present a catalogue of 430 spectroscopically confirmed ultra-compact massive galaxies (UCMGs) from the Sloan Digital Sky Survey at redshifts . This increases the original INSPIRE sample eightfold, bridging the gap with the local Universe. For each object, we compute integrated stellar velocity dispersion, age, metallicity, and [Mg/Fe] through spectroscopic stellar population analysis. We infer star formation histories (SFHs), metallicity evolution histories (MEHs) and compute the Degree of Relicness (DoR) of each object. The UCMGs, covering a wide range of DoR from 0.05 to 0.88, can be divided into three groups, according to how extreme their SFH was. The first group consists of 81 extreme relics () that have formed the totality of their stellar mass by and have super-solar metallicities at all cosmic epochs. The second group () contains 293 objects also characterized by peaked SFHs but with a small percentage of later-formed stars and with a variety of MEHs. The third group (), has 56 objects that cannot be considered relics since they have extended SFHs and formed a non-negligible fraction ( per cent) of their stellar mass at . We conclude that the most efficient method of finding relics is to select UCMGs with a combination of large velocity dispersion values (as already found by INSPIRE), super-solar metallicities and high [Mg/Fe].