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trinitree88
2008-Dec-02, 12:55 AM
The January issue of Astronomy magazine has a nice perspective on page 20 of a rare celestial alignment...unlike the Jupiter/moon/Venus one tonight which has it's own admirers.
A small spiral galaxy finds itself silhouetted against the luminous backdrop of a much larger second galaxy....about the size of the Milky Way. Silhouetted this way, the small galaxy reveals dust tendrils trailing far away from the small galaxy's outer edges....at least a half galaxy radius.
The tendrils are not tenuous, but dense, and filter out most of the light from the stars in the large galaxy...(this is known as "column density", or extinction coefficient in Beer's Law)...and astronomers have never seen this before...(Benne Holwerda, Space Telescope Science Institute, codiscoverer).
Their surprise is the extent of the dust structures, (normal baryonic matter, not requiring bizarre properties of dark matter), in otherwise a "normal " galaxy. Nice job here:http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2646v1.pdf
check out p 21 on the link for a quick picture of the galaxies....the dust/gas mix extends 6 half-light radii...nice.
pete

ngc3314
2008-Dec-02, 02:33 PM
Thanks :)

The 160,000 volunteer scientists at Galaxy Zoo have now found another 1300 examples of galaxy backlighting, so eventually we can get some statistical results on how often such extended dust is present (among other things that at last some of us find interesting).

trinitree88
2008-Dec-04, 12:58 AM
Thanks :)

The 160,000 volunteer scientists at Galaxy Zoo have now found another 1300 examples of galaxy backlighting, so eventually we can get some statistical results on how often such extended dust is present (among other things that at last some of us find interesting).

ngc3314. Interesting. I'd expect a good deal of the missing dark matter is about to show up as baryonic matter in the extended tendrils. The UV survey done recently showed up about half of it(missing dark matter), as hot ionized gas in galactic halos. Now, cooler gas and dust contributions can be quantified in the additional 1300 backlit galaxies. Along with supernovae making ~ 10 times as much dust as previously thought, we ought to be pretty close.
This may effect the recalibration of dim supernova1a standard candles in such a way as to infer their low luminosity not being due to accelerated space-time, but merely their presence in a dusty tendril....an investigation that will have people waiting with baited breath for the results. They are already being revised for an oversight on polarization studies that should have been done to ascertain viewing angle,(part of my talk at Harvard at the Olney Science Center, Spring 1994, AAPT Meeting, GRB's, A Halo of Neutron Stars at 400 Kiloparsecs? When I finished the last transparency, and started the Q&A session, an incredulous student asserted..."If what you say about asymmetry is true, that calls into question the validity of using type 1a supernovae as standard candles in the distance scale of the universe, doesn't it? Yes, that's true, I replied.)
If they'd had tomatoes, they would have thrown them at me....

It is conceivable that the missing dark matter, and the mysterious dark energy will both fall prey to the 1300 backlit galactic survey. That'd be a very Merry Christmas.

Kudos to Benny Holwerda & company...I look forward to the 1300 survey, and the possible resolution to one of the most perplexing problems in astrophysics.

pete

Spaceman Spiff
2008-Dec-04, 04:13 PM
I think there is a misconception here on the part of trinitree. The findings of GALEX (warm UV gas) and various x-ray observations of galaxies and galaxy clusters have found a large fraction of the reservoir(s) of missing baryonic matter -- missing from the point of view of what is predicted by big bang nucleosynthesis and the observed fluctuations in the cosmic background radiation compared to what is stored in "optically luminous" stars and gas within galaxies.

I may be mistaken, but I don't think these findings are making a serious dent in the "dark matter" budget. But maybe ngc3314 (a co-author on the above linked paper (http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2646v1.pdf)) can comment on this.

They are interesting nonetheless from the point of view of understanding the full nature of galaxies as well as knowing where most of the baryons ended up.

ngc3314
2008-Dec-04, 04:48 PM
What Spaceman Spiff said. The intergalactic gas observations (which are epochal and groundbreaking, and for which I've been a willing cheerleader) fill in some of the baryonic matter which was thought to remain undetected based on big-bang nucleosynthetic arguments, and don't begin to sneak into the total mass density required by dynamics. The dust is only a minor player by mass (typically 1/200 of the mass in gas in galaxies like this), although it has a much larger role in star formation because it allows gas clumps to cool and collapse rapidly in temperature regimes where cooling by gas processes (collisional excitation, for example) is comparatively inefficient.

Spaceman Spiff
2008-Dec-04, 05:47 PM
What Spaceman Spiff said. The intergalactic gas observations (which are epochal and groundbreaking, and for which I've been a willing cheerleader) fill in some of the baryonic matter which was thought to remain undetected based on big-bang nucleosynthetic arguments, and don't begin to sneak into the total mass density required by dynamics. The dust is only a minor player by mass (typically 1/200 of the mass in gas in galaxies like this), although it has a much larger role in star formation because it allows gas clumps to cool and collapse rapidly in temperature regimes where cooling by gas processes (collisional excitation, for example) is comparatively inefficient.

This is so cool. A lot of questions come to mind, and the discussion on page 12 of your paper is teasingly brief. No doubt -- the findings of these observations will impact a lot of what we know about galaxies. Great find!

ngc3314
2008-Dec-04, 06:50 PM
Let me just whet y'all's appetites with a few more examples, mostly found in the SDSS courtesy of the Galaxy Zoo participants:

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=38.99292188&dec=1.25745426&scale=0.39612&width=200&height=200&opt=&query=

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=119.55999&dec=42.26864&scale=0.3961&width=200&height=200&opt=&query=

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=126.0713979&dec=30.48582956&scale=0.39612&width=200&height=200&opt=&query=

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=132.15565572&dec=14.48677568&scale=0.39612&width=200&height=200&opt=&query=

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=149.72928958&dec=47.73522645&scale=0.39612&width=200&height=200&opt=&query=


http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=153.2139&dec=4.79448&scale=0.3961&width=200&height=200&opt=&query=

http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=159.26547&dec=20.43643&scale=0.3961&width=200&height=200&opt=&query=

Over the years about 7 such pairs have been observed with HST - there's a gallery here (http://www.galaxyzooforum.org/index.php?topic=272494.msg184423#msg184423). (I forgot UGC 3995 in that list, which has one image available but not a PR version available for easy linking).

parejkoj
2008-Dec-04, 08:09 PM
No time to read the paper right now, but are any of the objects from the paper in stripe 82, thus having deeper stacks available?

trinitree88
2008-Dec-04, 08:43 PM
I think there is a misconception here on the part of trinitree. The findings of GALEX (warm UV gas) and various x-ray observations of galaxies and galaxy clusters have found a large fraction of the reservoir(s) of missing baryonic matter -- missing from the point of view of what is predicted by big bang nucleosynthesis and the observed fluctuations in the cosmic background radiation compared to what is stored in "optically luminous" stars and gas within galaxies.

I may be mistaken, but I don't think these findings are making a serious dent in the "dark matter" budget. But maybe ngc3314 (a co-author on the above linked paper (http://arxiv.org/PS_cache/arxiv/pdf/0810/0810.2646v1.pdf)) can comment on this.

They are interesting nonetheless from the point of view of understanding the full nature of galaxies as well as knowing where most of the baryons ended up.

Spaceman Spiff. I think what Spaceman Spiff said here is correct also...trinitree88 was laboring under a misconception on the magnitude of the hot gas found, and stands corrected therein.. Thanks. pete

ngc3314
2008-Dec-04, 10:39 PM
No time to read the paper right now, but are any of the objects from the paper in stripe 82, thus having deeper stacks available?

The paper is only on a single object which showed up serendipitously in HST images (all the annoying foreground stars are in the halo of NGC 253!). But some of the objects from the Galaxy Zoo catalog are indeed in stripe 82, and we've been licking our chops at the release of the stacked images - that saves us a lot of extra imaging work to get useful results. Just looking ahead to how much of the sky will look like that and deeper from Pan-STARRS and LSST.

parejkoj
2008-Dec-05, 02:02 AM
Mmmmm... LSST.

Zeljko was here today and gave our colloquium on it. I'm pretty familiar with the project, but I'm always amazed with the comparison images with SDSS. Particularly the simulated final stacks (the example was from MUSYC), though that won't be until ~2020. r~27 just boggles the mind! Only problem is how to get spectra of things at that limit. Keck isn't big enough!

matt.o
2008-Dec-05, 03:14 AM
Mmmmm... LSST.

r~27 just boggles the mind! Only problem is how to get spectra of things at that limit. Keck isn't big enough!

GMT, E-ELT etc. etc.!

parejkoj
2008-Dec-05, 06:05 AM
Yeah, but it's hard to fund both LSST and GMT/TMT. The cost per project is roughly the same, and the impact factor for LSST is much higher (in terms of the number of things it will do and the number of people who will benefit from the data).

Gigabyte
2009-Mar-18, 06:41 PM
After gazing at the multitudes of galaxies that show vast amounts of dust outside the visible portion, things seem most interesting.

http://imgsrc.hubblesite.org/hu/db/images/hs-2008-16-ap-web.jpg

I downloaded the large file of that, very very interesting.

rommel543
2009-Mar-18, 07:35 PM
Spaceman Spiff. I think what Spaceman Spiff said here is correct also...trinitree88 was laboring under a misconception on the magnitude of the hot gas found, and stands corrected therein.. Thanks. pete


I made the same assumptions here (http://www.bautforum.com/space-astronomy-questions-answers/85486-more-matter-matter-fact.html).

Amber Robot
2009-Mar-18, 07:38 PM
Thanks :)

The 160,000 volunteer scientists at Galaxy Zoo have now found another 1300 examples of galaxy backlighting, so eventually we can get some statistical results on how often such extended dust is present (among other things that at last some of us find interesting).

Based on what was seen in this case, can you convert the optical depth in dust to a column density of hydrogen? Should these tendrils that extend far out be observable in H I ?

transreality
2009-Mar-18, 11:34 PM
The dust is only a minor player by mass (typically 1/200 of the mass in gas in galaxies like this), although it has a much larger role in star formation because it allows gas clumps to cool and collapse

In many of these images the distant galaxies have poorly defined spiral arms, the galaxies look more like flat disks. Is this because in this early epoch this clumping is still in a primitive state, or is it a resolution effect?

Gigabyte
2009-Jul-01, 03:13 PM
Nobody knows.

Cougar
2009-Jul-02, 01:21 PM
Let me just whet y'all's appetites with a few more examples...
http://casjobs.sdss.org/ImgCutoutDR7/getjpeg.aspx?ra=119.55999&dec=42.26864&scale=0.3961&width=200&height=200&opt=&query=

How do we know these smaller galaxies aren't being ejected from the cores of the larger galaxy, with their redshift difference being due to the younger galaxy's particles being new to this universe?

Ha ha. Just a little astronomy humor there. :o

Gigabyte
2009-Jul-02, 02:58 PM
Post moved to ATM.

heh heh

Gigabyte
2009-Aug-10, 02:38 AM
I love discoveries like these.