MIGHTEE-H I: the first MeerKAT H I mass function from an untargeted interferometric survey
Monthly Notices of the Royal Astronomical Society Oxford University Press 522:4 (2023) 5308-5319
Abstract:
We present the first measurement of the H I mass function (HIMF) using data from MeerKAT, based on 276 direct detections from the MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) Survey Early Science data covering a period of approximately a billion years (0 ≤ z ≤ 0.084). This is the first HIMF measured using interferometric data over non-group or cluster field, i.e. a deep blank field. We constrain the parameters of the Schechter function that describes the HIMF with two different methods: 1/Vmax and modified maximum likelihood (MML). We find a low-mass slope α=−1.29+0.37−0.26 , ‘knee’ mass log10(M∗/M⊙)=10.07+0.24−0.24 and normalization log10(ϕ∗/Mpc−3)=−2.34+0.32−0.36 (H0 = 67.4 km s−1 Mpc−1) for 1/Vmax , and α=−1.44+0.13−0.10 , ‘knee’ mass log10(M∗/M⊙)=10.22+0.10−0.13 and normalization log10(ϕ∗/Mpc−3)=−2.52+0.19−0.14 for MML. When using 1/Vmax we find both the low-mass slope and ‘knee’ mass to be consistent within 1σ with previous studies based on single-dish surveys. The cosmological mass density of H I is found to be slightly larger than previously reported: ΩHI=5.46+0.94−0.99×10−4h−167.4 from 1/Vmax and ΩHI=6.31+0.31−0.31×10−4h−167.4 from MML but consistent within the uncertainties. We find no evidence for evolution of the HIMF over the last billion years.MIGHTEE-HI: discovery of an H I-rich galaxy group at z = 0.044 with MeerKAT
Monthly Notices of the Royal Astronomical Society Oxford University Press 506:2 (2021) 2753-2765
Abstract:
We present the serendipitous discovery of a galaxy group in the XMM-LSS field with MIGHTEE Early Science observations. 20 galaxies are detected in H I in this z ∼ 0.044 group, with a 3σ column density sensitivity of NHI=1.6×1020cm−2. This group has not been previously identified, despite residing in a well-studied extragalactic legacy field. We present spatially resolved H I total intensity and velocity maps for each of the objects which reveal environmental influence through disturbed morphologies. The group has a dynamical mass of log10(Mdyn/M⊙)=12.32, and is unusually gas-rich, with an H I-to-stellar mass ratio of log10(f∗HI)=−0.2, which is 0.7 dex greater than expected. The group’s high H I content, spatial, velocity, and identified galaxy type distributions strongly suggest that it is in the early stages of its assembly. The discovery of this galaxy group is an example of the importance of mapping spatially resolved H I in a wide range of environments, including galaxy groups. This scientific goal has been dramatically enhanced by the high sensitivity, large field-of-view, and wide instantaneous bandwidth of the MeerKAT telescope.
MIGHTEE - HI: The relation between the HI gas in galaxies and the cosmic web
Monthly Notices of the Royal Astronomical Society, Volume 513, Issue 2, pp.2168-2177
Abstract:
We study the 3D axis of rotation (3D spin) of 77 H I galaxies from the MIGHTEE-H I Early Science observations, and its relation to the filaments of the cosmic web. For this HI-selected sample, the alignment between the spin axis and the closest filament (|cos ψ|) is higher for galaxies closer to the filaments, with ⟨|cos ψ|⟩ = 0.66 ± 0.04 for galaxies <5 Mpc from their closest filament compared to ⟨|cos ψ|⟩ = 0.37 ± 0.08 for galaxies at 5 < d < 10 Mpc. We find that galaxies with a low HI-to-stellar mass ratio (log10(MHI/M⋆) < 0.11) are more aligned with their closest filaments, with ⟨|cos ψ|⟩ = 0.58 ± 0.04; whilst galaxies with (log10(MHI/M⋆) > 0.11) tend to be mis-aligned, with ⟨|cos ψ|⟩ = 0.44 ± 0.04. We find tentative evidence that the spin axis of HI-selected galaxies tend to be aligned with associated filaments (d < 10 Mpc), but this depends on the gas fractions. Galaxies that have accumulated more stellar mass compared to their gas mass tend towards stronger alignment. Our results suggest that those galaxies that have accrued high gas fraction with respect to their stellar mass may have had their spin axis alignment with the filament disrupted by a recent gas-rich merger, whereas the spin vector for those galaxies in which the neutral gas has not been strongly replenished through a recent merger tend to orientate towards alignment with the filament. We also investigate the spin transition between galaxies with a high HI content and a low HI content at a threshold of MHI≈10^9.5M⊙ found in simulations; however, we find no evidence for such a transition with the current data.