We present a four-step group-finding algorithm for the Gas in Galaxy Groups (G3) initiative, a spin-off of the
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Abstract z ∼ 0 REsolved Spectroscopy Of a Local VolumE (RESOLVE) and Environmental COntext (ECO) surveys. In preparation for future comparisons to intermediate redshift (e.g., the LADUMA survey), we design the group finder to adapt to incomplete, shallow, or nonuniform data. We use mock catalogs to optimize the group finder’s performance. Compared to friends-of-friends (with false-pair splitting), the G3 algorithm offers improved completeness and halo-mass recovery with minimal loss of purity. Combining it with the volume-limited Hi census data for RESOLVE and ECO, we examine the Hi content of galaxy groups as a function of group halo mass. Group-integrated Hi massM H I,grprises monotonically over halo massesM halo∼ 1011–1014.5M ⊙, pivoting in slope atM halo∼ 1011.4M ⊙, the gas-richness threshold scale. We present the first measurement of the scatter in this relation, which has a median of ∼0.3 dex and is asymmetric toward lowerM H I,grp. We discuss interesting tensions with theoretical predictions and prior measurements of theM H I,grp–M halorelation. In an appendix, we release RESOLVE DR4 and ECO DR3, including updates to survey redshifts, photometry, and group catalogs, as well as a major expansion of the ECO Hi inventory with value-added data products. -
Abstract In the local universe, OH megamasers (OHMs) are detected almost exclusively in infrared-luminous galaxies, with a prevalence that increases with IR luminosity, suggesting that they trace gas-rich galaxy mergers. Given the proximity of the rest frequencies of OH and the hyperfine transition of neutral atomic hydrogen (H
i ), radio surveys to probe the cosmic evolution of Hi in galaxies also offer exciting prospects for exploiting OHMs to probe the cosmic history of gas-rich mergers. Using observations for the Looking At the Distant Universe with the MeerKAT Array (LADUMA) deep Hi survey, we report the first untargeted detection of an OHM atz > 0.5, LADUMA J033046.20−275518.1 (nicknamed “Nkalakatha”). The host system, WISEA J033046.26−275518.3, is an infrared-luminous radio galaxy whose optical redshiftz ≈ 0.52 confirms the MeerKAT emission-line detection as OH at a redshiftz OH= 0.5225 ± 0.0001 rather than Hi at lower redshift. The detected spectral line has 18.4σ peak significance, a width of 459 ± 59 km s−1, and an integrated luminosity of (6.31 ± 0.18 [statistical] ± 0.31 [systematic]) × 103L ⊙, placing it among the most luminous OHMs known. The galaxy’s far-infrared luminosityL FIR= (1.576 ±0.013) × 1012L ⊙marks it as an ultraluminous infrared galaxy; its ratio of OH and infrared luminosities is similar to those for lower-redshift OHMs. A comparison between optical and OH redshifts offers a slight indication of an OH outflow. This detection represents the first step toward a systematic exploitation of OHMs as a tracer of galaxy growth at high redshifts. -
HI line observations of nearby galaxies often reveal the presence of extraplanar and/or kinematically anomalous gas that deviates from the general circular flow. In this work, we study the dependence of kinematically anomalous HI gas in galaxies taken from the SIMBA cosmological simulation on galaxy properties such as HI mass fraction, specific star formation rate, and local environmental density. To identify kinematically anomalous gas, we use a simple yet effective decomposition method to separate it from regularly rotating gas in the galactic disc; this method is well-suited for application to observational data sets but has been validated here using the simulation. We find that at fixed atomic gas mass fraction, the anomalous gas fraction increases with the specific star formation rate. We also find that the anomalous gas fraction does not have a significant dependence on a galaxy’s environment. Our decomposition method has the potential to yield useful insights from future HI surveys.more » « less