HIStoryNU “The HI Story of the Nearby Universe”

People involved:
Thijs van der Hulst (PI)
Davide Punzo (visualisation and visual analytics)
Nadine Giese (source finding and characterisation, effect of environment on 3D source structure )
Kelley Hess (HI in galaxy groups)
Manolis Papastergis (HI velocity function, Too Big to Fail problem in galaxies)


As Apertif will deliver data cubes with ~100 detectable objects every day it is imperative to have detection, characterisation and visualisation tools at hand to quickly examine and characterise the data. These are being put in place to serve the general use of Apertif survey data and will be used to examine the properties of all detections in relation to many oqther aspects of the host galaxies, the most important being the general environment and placement of the objects with respect to the Cosmic Web, the backbone of Large Scale Structure and galaxy evolution.

As this goal is very general and requires completion of large parts of the shallow and medium deep surveys, the initial focus will be on studying selected groups in the nearby universe, of varying density and galaxy population. In groups the main processes affecting the gas reservoirs of galaxies are interactions and ram pressure, but the balance of these will depend on the group properties, in particular the group mass. A representative selection of nearby groups will be selected from the early survey area to begin to explore these gas accretion and gas removal processes in relation to the group mass and location within the Cosmic Web.

The initial survey will deliver a small, but not insignificant number of targeted galaxies which are well resolved and subject to IFU surveys such as MaNGA and WEAVE. These will be studied in detail combination with the optical spectroscopy to determine the properties of their ISM, their kinematics, structure and mass distribution. These galaxies will also provide more detailed information on the gas removal and gas accretion processes mentioned before.

The surveys will detect many small galaxies (i.e. galaxies with HI masses below 10^8 solar masses. These are objects that can be used to study the so called “too big to fail” problem, i.e. the discrepancy between the number density and kinematics of dwarf galaxies predicted by Lambda CDM theory and the observed number density and kinematics of dwarf galaxies. HI observations will trace the rotation to large enough radii to properly assess their dark matter content beyond the central regions.
Design: Kuenst.    Development: Dripl.    © 2021 ASTRON