Current research:

Star Formation in high redshift quasars

Star formation in galaxies and AGN are thought to be linked, though how is still debated. The trouble is the AGN is so bright, in the optical the light form the galaxy is dominated by the AGN and it is very hard to extract any information about the star formation. The light form the AGN and star formation is absorbed by dust and re-emitted in the infrared. In the far-infrared, this re-emitted light will be mainly from the cooler star formation.

I am using FIR data from Herschel to studying the star formation in quasars, optically selected from the SDSS DR9 BOSS survey. Stripe 82 is covered by both the BOSS survey and Herschel imaging surveys HeLMS and HeRS, providing us with a large sample of quasars. We are stacking the images, in different combinations (i.e. redshift, luminosity, metallicity) and studying the stars formation as a function of these average properties of the quasars.  


Origin and distribution of Intracluster light
I am also working on a project studying a N-body simulation of a Fornax-like galaxy cluster to look at the intra-cluster light (ICL) from stars within the intra cluster medium. which we are assuming have been removed from the cluster members as they fall into the cluster potential. We are looking at the origin (disc or halo), radial distribution, and ages of these stars. When observed, methods such as planetary nebulae and supernovae 1aare often used to estimate the number of stars in the inter cluster medium. However these methods use a specific type/age of star. And to get a good estimate you need to have an underlying understanding of the stellar population. 

We have found that the stars in the ICL are older than previously assumed. Therefore the methods used to observe the ICL need to be adjusted to take into account this different in the stellar population.

Previous Research 

For my Ph.D thesis, I worked on the large scale environment of Quasars and AGN with respect to galaxy clusters and star forming galaxies.

I looked at AGN formation and fuelling, from the perspective of the environment around the AGN or quasar. There are various methods proposed, such as major mergers (e.g., Kauffmann2000, Hopkins2008), minor mergers (e.g., Ostriker1975, Hernquist1995), galaxy harassment (e.g., Lake1998, Lake1999), etc. I believe different formation mechanisms will dominant in different environments (and likely at different redshifts). It is also very likely different mechanisms will produce different luminosity AGN. For example, major mergers are the most likely method to create luminous quasars (e.g., Kauffman2000).
For a more detail introduction to AGN, please see the attached pdf, which is the introduction from my thesis.

 One of the main results from my thesis is the existence of an strong overdensity of AGN with strong to ultra-strong emission from UV FeII Harris2013. All of the quasars are within the redshift range 1.11 < z < 1.65 and are all within 2 sq. deg of sky. In this region, there is a possible over dense of quasars.

In previous literature, there are five notable quasars with ultra-strong UV FeII emission (e.g., Weymann1991, Graham1996, Vestergaard2001, Bruhweiler2008).
In this region, there are eight with ultra-strong and eight with strong UV FeII emitting quasars. This work suggests galaxies in overdense regions may have an enhanced star formation history. 

AGN_introduction.pdf AGN_introduction.pdf
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Type : pdf
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