Comments on: GALEX Spies a Ghost — And It's Alive!

By: Jon Hanford

Jon Hanford — Sun, 02 Nov 2008 17:49:33 +0000

In the 2004 paper mentioned above, the authors found that the mass of the external HI ring was on the order of 38 million solar masses and slightly inclined to the plane of rotation of NGC 404. What I find curious is that if vigorous star & cluster formation is evident in far-UV observations presumably from this HI disk, why are no hydrogen-alpha (H-a) regions observed as would be expected when hi-energy radiation from these young objects should profusely produce H-a star forming regions?

By: Jon Hanford

Jon Hanford — Sat, 01 Nov 2008 19:42:23 +0000

The paper is available at arXiv:astro-ph/0403467. Sorry for the broken link.

By: Jon Hanford

Jon Hanford — Sat, 01 Nov 2008 19:37:08 +0000

I believe the paper to which you are referring to in regards to NGC 404's HI excess is 'High-Resolution Observations of the Galaxy NGC 404: A Dwarf S0 with Abundant Interstellar Gas' by MS del Rio et al published in the Astrophysical Journal in 2004 (http://tinyurl.com/5lmhaz). In this paper, pg 10 has a remarkable side by side view of comparably sized fields around NGC 404 (both containing Mirach, BTW) one from the Palomar Sky Survey and the other from the VLA radio telescope. The radio view is eerily similar to the GALEX UV view! In the paper, the authors propose several explanations for this ring of neutral hydrogen, one being that simply no stars formed from it! (Clearly a moot point now with the GALEX observation). Also mentioned is the possibility of NGC 404 disrupting a nearby gas-rich dwarf galaxy. But clearly the jury is still out on this peculiar finding in a galaxy long thought to have given up the ghost.:)

By: DrNecropolis

DrNecropolis — Fri, 31 Oct 2008 21:00:38 +0000

Amazing, it's almost like stars hiding in plain sight! Sometimes it's not where you look but how you look! (hmmm, that almost sounds conceited doesn't it?)