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The Radio Properties of BCGs
Michael Hogan
AMI Day 30/09/11

Supervised by:

Alastair Edge

In collaboration with: Julie Hlavacek-Larrondo, Andy Fabian, Keith Grainge and Natasha Hurley-Walker.



Outline

Motivation ­ Why care about BCGs? Current Work ­ Attempting to understand AGN feedback in galaxy clusters AMI ­ Where does AMI fit in? What new understanding can be gained by using AMI?
AMI LA, image from http://www.phy.cam.ac.uk/research/ap/ami.php


Brightest Cluster Galaxies: What's the Fuss?

AGN Feedback has been a hot topic over the last few years. Feedback needed to offset cooling and explain the deficit of cold, molecular gas in cluster cores. Growing acceptance that the AGN in the BCG within rapidly cooling cores is always `on', just spends a lot of time at a `quiescent' level too low to counteract cooling. Want to know the power output of the BCGs across its duty cycle and across the spectrum to better constrain the energy available for heating cluster cores.

NGC1275: Nasa Image of the Day archive: http://www.nasa.gov/multimedia/imagegallery/image_feature_1833.html


The Diagram
Her-A

M87

NGC1275

Wide variety of spectral types observed ­ FRI, FRII, CSS, GPS Often complicated by presence of a strong nuclear component ­ AMI well-suited to help characterise this.


RXCJ0439.0+0520


RXCJ1558-14 / PKS1555-140


NGC1275 / 3C84


Where AMI comes in!

Want to get the statistics of these high-frequency peaked sources. Some already observed with AMI ­ Ideally want to observe many more (~100 ­ 150) cooling clusters in this energetically important but often overlooked frequency range.

Attack the `problem' from two sides -

Lower frequency characterised clusters. Use LOFAR to characterise the very low frequency, diffuse emission. If bright at 1.4GHz then observe with AMI Campaign to observe many clusters at higher frequency with GISMO (2mm). Also target sources detected at this higher frequency

Short AMI LA observations of targets could be used as fillers in the AMI queue


What is it good for?

Want to get the 15-20GHz radio LF to determine the energy output of BCGs at this frequency. Broad bandwidth of AMI will also allow the spectral index to be determined ­ provides information on the spread of powers provided by these nuclear components Would also allow us to quantify the level of contamination of S-Z surveys from weaker, flat spectrum sources in the BCGs. Like a `pre-screening' survey ­ find the sources then can better remove them. Much better than extrapolating fluxes from 1.4GHz to ~20GHz with a constant spectral index...this clearly wont always give a good estimate! Useful for the ongoing S-Z surveys and complements the 10C blind survey ­ lower sensitivity but would be targeted to known clusters across the observable sky.


Summary
AGN feedback required to explain the deficit of cold, molecular gas in cluster cores Radio analysis of BCGs complicated by presence of nuclear core component AMI can be used to observe a statistically significant sample of these cluster cores Observations are flexible ­ operates as a background project Complements the other programs in addition to providing valuable new resource for understanding the behaviour and energetics of BCGs and how they couple their feedback to their environments.