Dust Lanes In Centaurus A

"James Goldman" wrote in message
. ca...
Here's a question for the experts:

I was just looking at the APOD and there's rather a nice picture of
NGC 5128 up with a bit of text about the mystery of why this galaxy is so
dusty, which is unusual for an eliptical. This got me to wondering: how
do they know that the dust isn't actually a dark nebula much closer to
Earth?

I don't think it is possible to rule out your hypothesis completely, but
there would have to be some odd situation.

Since Centaurus A is also a very strong infrared source (from the heated
dust) some other explanation must explain the heatingof the dust (since the
dust and galaxy would be separated and the dust being the closer of the
two). Also concider the chances of a large non-galactic dust-cloud being in
our line of sight appearing exactly like a merged galaxy?!

It is far more likely that it is a galaxy-merger, since that gives far less
open questions. Enough open questions left anyway... ;o)

Clear Skies,
Magnus


P.S. I wish I could take a look at it, but at 51N vs declination of -43
it's never above the horizon here! I wonder if Cousin Ricky has ever
considered opening a hotel for wondering astronomers? :-)

James Goldman wrote:
This got me to wondering: how do they know that the dust
isn't actually a dark nebula much closer to Earth?

Off the top of my head, I'd guess that if the dust lane and associated
nebulosity were a foreground object, then they would almost certainly be
associated with the Milky Way. In that case, they would have a radial velocity
different than that to the galaxy, NGC 5128.

If you do a search in the SIMBAD bibliographic section, you could probably find
some research on the kinematics of the galaxy and its dust lane, which pretty
convincingly make the case that they're related.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
Email: Remove "ic" from .comic above to respond

On Wed, 06 Aug 2003 17:14:51 GMT, James Goldman
wrote:

Here's a question for the experts:

I was just looking at the APOD and there's rather a nice picture of
NGC 5128 up with a bit of text about the mystery of why this galaxy is so
dusty, which is unusual for an eliptical. This got me to wondering: how
do they know that the dust isn't actually a dark nebula much closer to
Earth?

The laterst research indicates Centaurus A is a merger of two
galaxies, a spiral (seen edge-on) and an elliptical. The dust we see
is from the spiral galaxy.

Kapella

James Goldman wrote:
Here's a question for the experts:

I was just looking at the APOD and there's rather a nice picture of
NGC 5128 up with a bit of text about the mystery of why this galaxy is so
dusty, which is unusual for an eliptical. This got me to wondering: how
do they know that the dust isn't actually a dark nebula much closer to
Earth?

P.S. I wish I could take a look at it, but at 51N vs declination of -43
it's never above the horizon here! I wonder if Cousin Ricky has ever
considered opening a hotel for wondering astronomers? :-)

We'd have to be phenomenally unlucky, since the dust wraps around the
bright body of Cen A. More to the point, it's associated with ionized
gas and young stars (and for the gas it's easy to show from both
optical and radio data that it shares the redshift of the rest of Cen A).
This becomes more of an issue for isolated dust patches seen near
the outskirts of a galaxy, where, to tie it down, you'd have to look
for something like associated neutral hydrogen where a 21-cm radio
observation could give you its redshift.

There was argument for a long time over where the dust stripes seen
crossing in front of M81 come from (pretty sure now they are tidal
debris from sideswiping M82). At first some folks thought they
were flaws in the Palomar plate...

There is one cool instance of a galaxy where half of its light is chopped
out by a foreground dark nebula - this provides another example of
the law of nature which says that large southern declinations are
more interesting that high northern ones. tarting from my notebook
whichg puts it at coordinates 70, 300 in mm on the southern sky film
centered at 16h 30m, -80. Guide8 comes to the rescue - it's IC 4633
at 17 13 47.1 -77 32 11 (2000).
At least it sure looks from the blue-light photo as if the southwestern
side is obscured by part of those foreground dust lanes winding
all through the sky-survey images...

This is probably way more than you wanted to know - one of the things I
do for a living is study dust in galaxies
(http://www.astr.ua.edu/keel/research/dust.html)
so I tend to spout off...

Bill Keel

"William C. Keel" wrote:

This is probably way more than you wanted to know - one of the things I
do for a living is study dust in galaxies
(http://www.astr.ua.edu/keel/research/dust.html)
so I tend to spout off...

And s.a.a. is the right place for it.g Bill, your expertise is always
appreciated.

Mike Simmons

William C. Keel wrote:
This is probably way more than you wanted to know - one of the things I
do for a living is study dust in galaxies
(http://www.astr.ua.edu/keel/research/dust.html)
so I tend to spout off...

Not at all. It was an informative answer to my question. Thanks!