[ASA] ANITA online lecture, Friday 3pm (AEST) 26th July

Darren Croton dcroton at astro.swin.edu.au
Wed Jul 24 13:02:10 AEST 2013

Dear ANITA and ASA members.

This Friday at 3pm (AEST) ANITA will hold its first online lecture. All are welcome to join! The target audience will range from undergrad to postdoc, however anyone interested is sure to get something out of it.


The lecture will be held through Google Hangouts on Air. 

You'll first need a Google account (e.g. gmail). Log in to it.
If you've never done a Google Hangout before you'll need to install a plugin for your browser. See https://www.google.com/tools/dlpage/hangoutplugin
On Google+ search for "Anita Chapter" and head to our page.
Alternatively, go directly to our Chapter page here: https://plus.google.com/u/0/104967001091880466806/posts
You'll see a post for the Hangout on Air at around 3pm - hit play and enjoy!

Some hints for a better experience:

You can breakout the small video window on the Google+ page by opening it in YouTube. This gives you a much bigger view.
Post any comments/questions under the video in the comments box on the Google+ or YouTube page.
I don't believe that comments are updated in real time; you may need to reload the page to see the latest.

I'll be broadcasting video and slides. There'll be time for questions throughout and at the end. If you have a question please post it as a comment and prefix it with "QUESTION: ..." so it stands out. I'll then try to answer it as best i can.

All lectures will be hosted on our ANITA YouTube page for later viewing. In the coming weeks we'll set up the appropriate links from the ANITA homepage etc.

Finally, this is a bit of an experiment! Our trial ran fairly smoothly, but please bear with us. Any feedback on your experience will help make future lectures more valuable for all.

Thanks, and see you on Friday!


Title: Damn you little h!
Speaker: Darren Croton, Swinburne University
Date: 3pm (AEST) Friday 26th July
Abstract: The Hubble constant, H_0, or its dimensionless equivalent, “little h”, is a fundamental cosmological property that is now known to an accuracy better than a few percent. Despite its cosmological nature, little h commonly appears in the measured properties of individual galaxies. This can pose unique challenges for users of such data, particularly with survey data. 

In this talk I show:

how little h arises in the measurement of galaxies, 
how to compare like-properties from different datasets that have assumed different little h cosmologies, and 
how to fairly compare theoretical data with observed data, where little h can manifest in vastly different ways.

This last point is particularly important when observations are used to calibrate galaxy formation models, as calibrating with the wrong (or no) little h can lead to disastrous results when the model is later converted to the correct h cosmology. 

I'll argue that in this modern age little h is an anachronism, being one of least uncertain parameters in astrophysics, and propose that observers and theorists instead treat this uncertainty like any other. 

I'll conclude with a “cheat sheet” of nine points that should be followed when dealing with little h in data analysis.


Darren Croton
Associate Professor & QEII Research Fellow 
Centre for Astrophysics & Supercomputing
Swinburne University of Technology
PO Box 218, Hawthorn, VIC 3122, Australia
Phone: 61-3-9214-5537; Fax: 61-3-9214-8797

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