Speaker
Description
Beyond the local Universe the vast majority of HI galaxies detected by SKA precursor/pathfinder blind HI surveys will be spatially unresolved, therefore it will be vital to squeeze as much information as possible out of the integrated profiles. Single dish observations of $z \sim 0$ galaxies already provide numerous example spectra of such unresolved sources. In this talk I will focus on HI profile asymmetries, in particular, the mitigation of observational biases and defining a baseline of HI asymmetry for unperturbed galaxies by combining numerical simulations and observations.
HI asymmetries are known to correlate with environment; thus, recent works have used isolated galaxies to define a baseline of minimum HI asymmetry, which can then be compared with galaxy populations in other environments. The AMIGA sample of isolated galaxies has the most symmetric HI profiles of any existing galaxy sample; however, the typical AMIGA galaxy still has a 13% HI mass asymmetry. Can this level of asymmetry be fully explained by internal processes and observational effects alone, or does it also require external effects, for example, the infall of pristine gas?
To address this question we have generated an ensemble of mock HI cubes using the radiative transfer code TORUS and high resolution SPH simulations of individual $L^*$ galaxies in perfect isolation. This mock dataset allows us to fully assess the role of observational effects, such as inclination, beam size, velocity resolution, SNR, and pointing offsets, and therefore to correct the AMIGA sample for these effects and derive a baseline for the level of asymmetry that a typical galaxy can develop in isolation. We have used as well a matching sample of galaxies in low density environments from Illustris TNG100 state of the art cosmological simulations. Any remaining discrepancy between the simulated and real isolated galaxies will act as a measure of the impact of residual external influence. This baseline, and the improved understanding of the observational effects, will be directly applicable to the upcoming WALLABY, LADUMA, MIGHTEE-HI, and Apertif surveys as well as existing HI surveys such as HIPASS and ALFALFA.
| Wish list question? | 9. What robust observational evidence exists for gas infall and outflow? |
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