A distant quasar house

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In my last post I spent a lot of time explaining what a quasar is. Which is handy as Goto et al. have just detected the host galaxy of the most distant quasar currently known (its a vast 12.8 billion light years away from us which means we’re seeing back to a time when the Universe was 16 times younger than it is today).

Quick recap – remember that a quasar is an AGN orientated such that its light completely outshines the light from the galaxy hosting it. “Well”, you’re probably thinking, “if that’s true, how is it possible to see the host at all then?” The answer’s simple – it can’t be seen, not directly. Its (very faint) light makes up a tiny part of the total received by us though. If the quasar’s (massive) contribution could be completely removed, then the galaxy would appear.

This tricky measurement is exactly what Goto et al. did using a newly upgraded camera on the Subaru telescope in Hawaii. The image below is from their paper (copyright Tomotsugu Goto, University of Hawaii). On the left is the original image of the most-distant-quasar CFHQSJ2329-0301 (yes, that really is its name); the blob in the middle is their model of the quasar light coming from the central black hole region. The final image on the right is what’s left after subtracting the model – i.e. the host galaxy. Incidentally, 4 arcseconds (“) are equivalent to 22 kpc or 72,000 light years at the distance of this object.


The detected host turns out to be as large as our own Milky Way which is interesting as it means that it, and its associated supermassive, quasar creating, black hole must have formed rapidly to be the size they are at this early epoch of the Universe. Studying this system, and others like it, will help to understand the complicated mechanisms of galaxy formation.

ResearchBlogging.org Tomotsugu Goto, Yousuke Utsumi, Hisanori Furusawa, Satoshi Miyazaki, & Yutaka Komiyama (2009). A QSO host galaxy and its Lyalpha emission at z=6.43 Accepted for publication in MNRAS arXiv: 0908.4079v1

2 Comments on “A distant quasar house”

  1. That’s an interesting technique, haven’t heard of that before. Are there any test cases with objects where we know what they should look like (i.e., some verification 🙂 )?

    I imagine you could so this with a distant type Ia supernova if you had a model of the supernova and before and after pictures taken with the same camera…?

    • Emma says:

      Quasars look like stars in images (hence their other name – ‘quasi-stellar objects’) so creating a model for their light, as in this technique, involves looking at the shapes of stars in the same image I think.

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