VizieR Online Data Catalog: Hydra I cluster study with H I emission (Reynolds+, 2022)

The environment in which a galaxy resides has a large effect on its observed properties. This is clearly demonstrated by the morphology-density relation (e.g. Oemler 1974ApJ...194....1O ; Dressler 1980ApJ...236..351D), in which the fraction of late-type galaxies decreases (and early-type galaxies increase) with increasing galaxy number density (i.e. moving from galaxies located in the field to the centre of clusters). The environments with the highest galaxy number and intergalactic medium (IGM) densities are galaxy clusters, containing hundreds to thousands of galaxies. Here we investigate the star formation connected to the neutral atomic hydrogen (H I) gas content of galaxies, as H I provides a potential reservoir for future star formation through its conversion to molecular gas, H2 (e.g. Leroy et al. 2008AJ....136.2782L).

In this study, we use the Widefield ASKAP L-band (radio around 21 cm H I for our case) Legacy All-sky Blind Survey (WALLABY, Koribalski et al. 2020Ap&SS.365..118K) on ASKAP aiming to cover three-quarters of the sky up to δ = +30 deg and detect H I emission in 500000 galaxies in which ~ 5000 will be spatially resolved. ASKAP provide 30 deg² instantaneous field-of-view footprint on the sky with high flux sensitivity. Thanks to it, we are focusing on gas removal and star formation in the Hydra I cluster using wide-field, high spatial resolution WALLABY observations that cover 60 deg², going out to ~5*R_vir from the cluster centre, by comparing the H I to optical disc diameter ratio and star formation rate (SFR) of cluster and infall galaxies with a control sample of field galaxies. We adopt optical velocities (cz) in the heliocentric reference frame, the AB magnitude convention and we assume a flat Γ cold dark matter cosmology with H0 = 67.7 km/s/Mpc (i.e see Introduction section).

Throughout these observations (Reynolds et al. 2021MNRAS.505.1891R) and data reductions (ASKAP/WALLABY process) (i.e section 2 Data), we produce H I spectral line cube with spectral resolution of 4 km/s. Further, we apply the Source Finding Application 2 (SoFiA 2, Serra et al. 2015MNRAS.448.1922S; Westmeier et al. 2021MNRAS.506.3962W) to detect sources of H I emission across a redshift range of cz ~500-25000 km/s. As Hydra I has a systemic velocity of cz ~3780 km/s, we select a subsample of the H I detections below cz < 7000 km/s detections for which the H I mass sensitivity will be similar to cluster members. After several quality cuts (i.e section 2.1 WALLABY observations and sample selection), our sample contains 129 individual galaxies with detected H I emission and systemic velocities cz < 7000 km/s. While for galaxies with not considered H I emission, we use the 6dF Galaxy Survey (6dFGS, Jones et al. 2009MNRAS.399..683J, Cat. VII/259) to identify galaxies within the Hydra field footprint and with systemic velocities cz < 7000 km/s leading us to a second galaxy group of 142 galaxies.

Next, out of this two galaxy samples, we classify galaxies within the Hydra field footprint as cluster, infall, or field galaxies based on their location on a phase space diagram of the Hydra I cluster (i.e see figure 2 of the section 2.1 WALLABY observations and sample selection). Finally, we compute physical properties such gas/stellar masses, angular light diameters and total SFR with the help of optical photometric images from PanSTARRS g/r bands, UV and IR photometric images from GALEX and WISE (see its dedicated subsections in the section 2 Data). Our results are synthesized in the tablea1.dat for H I WALLABY detections and in the tablea2.dat for H I not WALLABY detections cases respectively.

(2 data files).