4-8 July 2016
Kramer Law building
Africa/Johannesburg timezone
The Proceedings of SAIP2016 published on 24 December 2017
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Finding the needle in Galaxy Evolution: HI Stacking

Presented by Ms. Julia HEALY on 6 Jul 2016 from 16:10 to 18:00
Type: Poster Presentation
Track: Track D1 - Astrophysics
Board #: D1.320


Neutral atomic hydrogen (HI) is the raw fuel from which the star-forming molecular gas forms and is therefore an important tracer of galaxy evolution. Due to the intrinsic faintness of the HI emission line (observed at rest at 21cm), galaxies beyond a few hundred megaparsecs are difficult to observe directly with current radio telescopes. However, in the next year, MeerKAT and other SKA pathfinder telescopes will begin operating and enable deeper, large surveys (e.g. LADUMA) of neutral gas in galaxies. HI Stacking is an observational technique that will be highly exploited to learn about the HI content of galaxies that are not directly detected. Stacking involves combing the HI spectra of all the galaxies in a distant sample, thereby generating a high signal-to-noise measure of their total HI content. We have developed a Python-based software package that is capable of carrying out this HI stacking procedure for a set of given input HI galaxy spectra. We have applied our software to studying the non-detected HI spectra of galaxies in the Nancay Interstellar Baryons Legacy Extragalactic Survey (NIBLES). In doing so, we aim to extend by two orders of magnitude the stellar mass range probed by local Universe stacking experiments. Our future goal is for our package to be used to stack HI spectra from the LADUMA survey which aims to study the HI galaxy properties of galaxies over more than two thirds the age of the universe.






Dr Sarah Blyth (sarblyth@ast.uct.ac.za), Dept of Astronomy, University of Cape Town






Location: Kramer Law building
Address: UCT Middle Campus Cape Town

Primary authors



  • Dr. Sarah BLYTH Dept of Astronomy, University of Cape Town
  • Dr. Ed ELSON University of Cape Town + South African Astronomical Observatory