ACT/PIRE Workshop in Umhlanga, 27-29 January

In January, Bruce and I headed to Umhlanga, Durban to attend a conference hosted by our cosmology colleagues at UKZN. The conference was an opportunity for people from the ACT collaboration to present their latest work and future plans. It was well attended with participants from graduate students to senior researchers, from instrumentation specialists to cosmologists and representatives from Canada, Chile, the U.S.A., the U.K. and of course, South Africa.

A plot from Sehgal et al. (2010) illustrating how the likelihood contours (of σ8 vs. w) of WMAP data alone (blue) are improved when ACT data is included (red) when there is good knowledge of the underlying cluster physics.

The 6-metre Atacama Cosmology Telescope (ACT) in Chile uses the Sunyaev-Zel’dovich effect to detect clusters of galaxies from the CMB. The conference kicked off with a few talks about how such clusters are detected and the importance and use of follow up observations using optical and x-ray data. The implications of the recent measurement of σ8 by both ACT and the SPT (South Pole Telescope) were discussed and it was noted that it could be used to constrain cosmological parameters, especially the neutrino mass. We also heard about how brightest cluster galaxies can be used to test galaxy evolution models, how star forming galaxies have been found in clusters (over-turning old views of cluster galaxies always being “red and dead”) and how gravitational lensing can be used to calibrate the relationship between cluster mass and SZ observables.

Dusty galaxies (sub-mm galaxies) were largely the topic of discussion on day two of the conference. Here the importance of multi-wavelength observations was highlighted again both for understanding the population of sub-mm galaxies and also for decontaminating the ACT channels of these point sources. The difficult (and still unsolved) problem of including baryons in dark matter simulations, specifically in light of SZ clusters, was addressed and the role of AGN feedback and star formation was discussed. I also found out that the kinetic Sunyaev-Zel’dovich effect, although small, could be used to map out the velocity and mass fields of clusters and we can use it to measure bulk flows and possibly test models of cosmology and inflation.

On our last day, Bruce talked about the constraints on dark energy and curvature from the CMB and other probes and pointed out that cosmic distance-duality could be used to test exotic models such as axion-photon mixing. Next David Spergel lead a discussion about “new directions” in which he raised several important unanswered questions. We heard a number of instrumentation presentations including: science with MeerKAT, detailing the recently accepted MeerKAT science proposals; CACTUS, an ultra-deep ACT survey; MUSTANG2, a new receiver on the GBT and the current status of SALT. Talks about ACTPol, the upcoming polarisation sensitive receiver on ACT, were responded to with some excitement from the community, which lead into our final discussion on observing strategies for future surveys and cluster cosmology.

David Spergel discusses new directions in cluster cosmology.

Overall, the conference was a productive and enjoyable one. With the small group, it was possible to get to know everyone and perhaps start future collaborations. I personally enjoyed meeting scientists from other countries and introducing them to a few “South Africanisms”. Huge thanks to Kavilan Moodley, Caroline Zunckel and Matt Hilton for doing such a fantastic job in organising the conference.

For more information, visit these sites:

ACT website:

UKZN website:

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