Starship Asterisk*

by **geckzilla** » Fri Apr 29, 2016 7:11 pm

starsurfer wrote:
geckzilla wrote:
starsurfer wrote:I've found the ESO archive quite straightforward and easy to use and found lots of great quality data!
It's fine if you already know what you're looking for. Otherwise, it's terrible. With the HLA I can just browse thumbnails and pick up something that looks intriguing. You can see the target name in ESO's archive, but you have to look each one up, and usually they are like... IRAS012938-987.32 which is both useful and incredibly unhelpful at the same time.
It's true that it is only effective when you know what you want to look up. If you're interested, do you want a list of planetary nebulae I could PM you?

Do you have that kind of list that can just be uploaded to the form?

by **starsurfer** » Fri Apr 29, 2016 6:03 pm

geckzilla wrote:
starsurfer wrote:I've found the ESO archive quite straightforward and easy to use and found lots of great quality data!
It's fine if you already know what you're looking for. Otherwise, it's terrible. With the HLA I can just browse thumbnails and pick up something that looks intriguing. You can see the target name in ESO's archive, but you have to look each one up, and usually they are like... IRAS012938-987.32 which is both useful and incredibly unhelpful at the same time.

It's true that it is only effective when you know what you want to look up. If you're interested, do you want a list of planetary nebulae I could PM you?

by **geckzilla** » Thu Apr 28, 2016 6:29 pm

starsurfer wrote:I've found the ESO archive quite straightforward and easy to use and found lots of great quality data!

It's fine if you already know what you're looking for. Otherwise, it's terrible. With the HLA I can just browse thumbnails and pick up something that looks intriguing. You can see the target name in ESO's archive, but you have to look each one up, and usually they are like... IRAS012938-987.32 which is both useful and incredibly unhelpful at the same time.

by **starsurfer** » Thu Apr 28, 2016 1:39 pm

geckzilla wrote:I'm right here, you know! You can speak to me directly instead of in third person.

I never got the hang of ESO's archive. The interface is, imo, inferior to the Hubble Legacy Archive, at least as far as simple browsing goes. There are no thumbnails so when you're not sure what you're looking for it's pretty painful to deal with. I did some mass downloading and then would find maybe 1 or 2 nice things in there after some exhaustive searching.

Oops I'm sorry, I forgot that both of you are the same person!

Also I've not been sleeping well lately.

I've found the ESO archive quite straightforward and easy to use and found lots of great quality data!

by **rstevenson** » Thu Apr 28, 2016 12:02 pm

star struk wrote:spiral galaxy appearing next to ngc 6872 needs to be studied further

I'm sure that can be arranged. Payment is accepted via PayPal or electronic bank transfer.

Rob

by **star struk** » Thu Apr 28, 2016 11:37 am

spiral galaxy appearing next to ngc 6872 needs to be studied further

by **geckzilla** » Thu Apr 28, 2016 2:46 am

Ann wrote:far infrared (814 nm) and either yellow-green (555 nm) or orange (616 nm) light. Okay, maybe I got those figures a few nanometers wrong, but basically Hubble doesn't photograph most of its targets in ultraviolet light.

F814W is a broad, near infrared filter, and when you said 616 you were probably referring to F606W. ...Close enough with that last one. We'll see far infrared with JWST, assuming all goes as planned.

by **Ann** » Wed Apr 27, 2016 11:38 pm

geckzilla wrote:So I poked around a bit more with the GALEX data because it's fun and I wondered if my eyes were deceiving me or if it was perhaps some kind of quirk of the detector, but I noticed this faintly visible connection between NGC 6872 and its neighboring elliptical NGC 6876. I looked for any other study by other observatories and there was a notable connection between the two seen by astronomers using data from XMM-Newton. So it's not far-fetched to suppose that this faint connection is also observed by GALEX. Here's a pic.
GALEX_NGC6872-NGC6876.jpg

Fascinating picture, Geck. I love the GALEX images, and I'm really sorry that GALEX is now defunct, and that there is no other telescope photographing galaxies in ultraviolet light. Well, the Hubble does sometimes, but it mostly photographs its targets in far infrared (814 nm) and either yellow-green (555 nm) or orange (616 nm) light. Okay, maybe I got those figures a few nanometers wrong, but basically Hubble doesn't photograph most of its targets in ultraviolet light.

NGC 6872 looks so striking in the GALEX image you posted, and so different from the other galaxies in the group. Even so I must insist that NGC 6872 is a moderately red spiral galaxy, which is obvious from its large bulge and yellowish bright inner arms. I checked the B-V index of NGC 6876, the large elliptical neighbor of NGC 6872, and NGC 6876 isn't that much redder than elongated NGC 6872: its B-V is 1.03 versus 0.92 for NGC 6872. That is not a negligible difference, but it isn't huge. And yet, in ultraviolet light they look so totally different.

NGC 6872 is clearly "fluffy" with its extremely long outstretched arms. It is perhaps not surprising that there should be a bridge of material between (in particular) the fluffiest arm of NGC 6872 and the (likely very massive) elliptical galaxy NGC 6876. But if it isn't surprising, it is sure fascinating to see it.

Thanks for finding and posting that image, Geck!

Ann

by **geckzilla** » Wed Apr 27, 2016 10:34 pm

So I poked around a bit more with the GALEX data because it's fun and I wondered if my eyes were deceiving me or if it was perhaps some kind of quirk of the detector, but I noticed this faintly visible connection between NGC 6872 and its neighboring elliptical NGC 6876. I looked for any other study by other observatories and there was a notable connection between the two seen by astronomers using data from XMM-Newton. So it's not far-fetched to suppose that this faint connection is also observed by GALEX. Here's a pic.

: Possible bridge between NGC6872 and NGC6876

by **geckzilla** » Wed Apr 27, 2016 9:57 am

I'm right here, you know! You can speak to me directly instead of in third person.

I never got the hang of ESO's archive. The interface is, imo, inferior to the Hubble Legacy Archive, at least as far as simple browsing goes. There are no thumbnails so when you're not sure what you're looking for it's pretty painful to deal with. I did some mass downloading and then would find maybe 1 or 2 nice things in there after some exhaustive searching.

by **starsurfer** » Wed Apr 27, 2016 9:37 am

I'd really like it if Judy Schmidt processed some of the many PN there are data for in the ESO archive. Her processing and aesthetic sensibilities are well balanced and really good for lack of words.

by **geckzilla** » Wed Apr 27, 2016 7:42 am

Here we go, an ESO+GALEX assembly. Only used the NUV filter. The extra-blue galaxy is now extra-extra-blue.

by **geckzilla** » Tue Apr 26, 2016 11:47 pm

qskeptic@bigpond.com wrote:No need for dark matter and energy. Somebody better do the maths and let me know.

Just pop my Nobel Prize in the mail

Seriously? Your theory is awful and finishing it like this is like putting a little rotten cherry on top of it.

by **qskeptic@bigpond.com** » Tue Apr 26, 2016 11:45 pm

Hi,

The explanation that galaxies are formed mostly by gravity that we can't account for is a bit rich.

So an alternative explanation is that the galaxy is driven by something else. The galaxy is riding an eddy in space/time left over from the big bang. The eddy is a lower energy area that permits the condensation of matter which accumulates and obeys normal gravitational laws but is part of a rotational mass that is held in place by the eddy.

Consider a vortex which can be driven by a paddle from the centre; then consider a vortex which is driven by rotating the container; the effect is the same ie. a vortex but the energy distribution across the vortex is reversed.

No need for dark matter and energy. Somebody better do the maths and let me know.

Just pop my Nobel Prize in the mail

Cheers, BB

by **geckzilla** » Tue Apr 26, 2016 11:41 pm

The density definitely plays a role. It's something like rolling a marble through a stack of feathers. One does wonder if that compact dwarf always had those arms to it, though. It could have started out as a spheroid. If you'd seen the whole thing play out maybe you'd say the dwarf was perturbed, after all.

by **Ann** » Tue Apr 26, 2016 11:37 pm

Tszabeau wrote:It's seems surprising, to me, that the smaller galaxy is not as distorted as the larger one.

My amateur guess is that the small galaxy is less distorted than the larger one because the small galaxy is compact and pretty much devoid of gas.

: Click to view full size image

NGC 205 (Messier 110). Photo: Wikisky.

NGC 1512 and 1510.
Photo: NASA/JPL-Caltech.

Take a look at dwarf galaxy NGC 205 at left, sitting right next to the big galactic bully, the Andromeda Galaxy. There isn't a lot of gas in NGC 205, and it isn't particularly distorted.

At right is a Spitzer Space Telescope infrared image of the galactic pair NGC 1512 and 1510. NGC 1512, the big bully, also has all the gas and dust, which looks red in the Spitzer image. The dust-less dwarf companion is all cyan. The ultraviolet GALEX image of the pair looks like this.

: Click to view full size image

M31 and M32. Photo: Sid Leach.

My point is that compact, gas-poor dwarf galaxies next to big bullies don't get distorted so easily. That is probably because any "appendage" they stick out is likely to be swallowed by the galactic giant right next to it. An extreme example is M32, another prominent satellite galaxy of M31, which has been whittled down to the core by the tremendous tidal forces of its huge neighbor. M32 has been reduced to an ultra-compact dwarf galaxy, likely because M31 has stolen all its gas and "outer fluff".

Ann

by **geckzilla** » Tue Apr 26, 2016 11:23 pm

NGC3314 wrote:Those outer features are pretty blue. They're blazingly bright in the UV. There was a GALEX press release, but the only graphic they had (AFAICT) was an optical-UV comparison that didn't make this visually clear. So here's the GALEX UV color image (yellow=near-UV, 2400 A, blue=far-UV at 1500 A). One paper analyzing these results named this system the Condor.

I had to look up that press release. Is this it? I have my doubts the GALEX and Spitzer data is even included in the main part of the galaxy. It looks like it's only surrounding it at the edges.
https://www.nasa.gov/mission_pages/gale ... 30110.html

by **geckzilla** » Tue Apr 26, 2016 11:11 pm

Ann wrote: A fascinating difference between the combined minimally processed image and the finished processed image is that the combined minimally processed image is generally darker. The brightness of the core of NGC 6872 stands out, while the bulge is somewhat faint.

Yeah, I always start with very dark images so I don't lose details in the brighter parts. The dynamic range of a galaxy is always compressed in a way that downplays the brightness of the brighter parts and the utter dimness of the dimmest parts is completely lost. Astro imagers are always fighting against the noise in even the best data because it competes with those dim signals. It's a largely futile battle. You can see how smooth the data looked before I took a virtual sledge hammer to it.

by **Ann** » Tue Apr 26, 2016 10:51 pm

geckzilla wrote:
Ann wrote:But you know me, I can't stop talking color. Sigh.
I expected this, so I came up with some thoughts to add before the APOD went up. Yes, the blue channel was quite bright in the arms and much more details can be seen. So much so that I put some of the B filter into the green channel to make it easier to see. Blue on its own likes to be very dark ... it may be an idiosyncrasy of human vision.

An interesting way to look at astro images to get a better feel for how they are is to view each filter alone in grayscale. Not just interesting, actually. Essential. Maybe astronomers take it for granted that they have such easy access to data in its raw form. Anyway. It reduces the bias your brain's interpretation of color introduces. Here are some minimally processed, north-up frames of what the individual filters captured. When you look at the B filter you will notice so much more detail in the galaxy's outer reaches.
http://www.geckzilla.com/astro/NGC6872_ESO_R.jpg
http://www.geckzilla.com/astro/NGC6872_ESO_V.jpg
http://www.geckzilla.com/astro/NGC6872_ESO_B.jpg

If you combine those three, it looks like this. See how hard the arms are to see? Looking at just the B filter you know they're there, though. I could say I actually made them less blue with my image just to make them easier to see.
http://www.geckzilla.com/astro/NGC6872_ESO_RVB.jpg

Maybe you'll like them, maybe not.

Thanks, Geck, very interesting. A fascinating difference between the combined minimally processed image and the finished processed image is that the combined minimally processed image is generally darker. The brightness of the core of NGC 6872 stands out, while the bulge is somewhat faint. The inner parts of IC 4970 look interestingly bright too, although their brightness have been enhanced by their rather edge-on perspective. There is a hint of a faintly bluish ring inside the featureless arms of IC 4970.

Thanks again. It is interesting to see what data you have been working with.

Ann

by **NGC3314** » Tue Apr 26, 2016 10:02 pm

Those outer features are pretty blue. They're blazingly bright in the UV. There was a GALEX press release, but the only graphic they had (AFAICT) was an optical-UV comparison that didn't make this visually clear. So here's the GALEX UV color image (yellow=near-UV, 2400 A, blue=far-UV at 1500 A). One paper analyzing these results named this system the Condor.

by **geckzilla** » Tue Apr 26, 2016 8:29 pm

Ann wrote:But you know me, I can't stop talking color. Sigh.

I expected this, so I came up with some thoughts to add before the APOD went up. Yes, the blue channel was quite bright in the arms and much more details can be seen. So much so that I put some of the B filter into the green channel to make it easier to see. Blue on its own likes to be very dark ... it may be an idiosyncrasy of human vision.

An interesting way to look at astro images to get a better feel for how they are is to view each filter alone in grayscale. Not just interesting, actually. Essential. Maybe astronomers take it for granted that they have such easy access to data in its raw form. Anyway. It reduces the bias your brain's interpretation of color introduces. Here are some minimally processed, north-up frames of what the individual filters captured. When you look at the B filter you will notice so much more detail in the galaxy's outer reaches.
http://www.geckzilla.com/astro/NGC6872_ESO_R.jpg
http://www.geckzilla.com/astro/NGC6872_ESO_V.jpg
http://www.geckzilla.com/astro/NGC6872_ESO_B.jpg

If you combine those three, it looks like this. See how hard the arms are to see? Looking at just the B filter you know they're there, though. I could say I actually made them less blue with my image just to make them easier to see.
http://www.geckzilla.com/astro/NGC6872_ESO_RVB.jpg

Maybe you'll like them, maybe not.

by **Chris Peterson** » Tue Apr 26, 2016 8:24 pm

ems57fcva wrote:I continue to wonder why these bridges form. They are not tidal in origin and do not appear in the current galaxy collision models.

I'm curious why you say that. Long tidal tails and bridges are extremely common in numerical galaxy collision simulations. What we see in this image looks a lot like many simulations I've seen.

by **Tekija** » Tue Apr 26, 2016 8:11 pm

Cosmic rack?

by **ems57fcva** » Tue Apr 26, 2016 5:52 pm

The interesting part of this picture for me is the bridge of blue star starting at IC 4970 and initially running downwards and to the left before curving around NGC 6872. I take this (and the disruption of NGC 6872's spiral arms) to indicate that IC 4970 has already made its closest pass to NGC 6872, passing below it from the point of view of this photo. As it did so, and bridge of gas and dust formed running between their cores, like I have seen for many other galaxy encounters. The bridge has become twisted, stretched, and stagnant. Without a flow of new gas into/through it, it has condensed into nebulae and clusters, and that is why it is blue.

I continue to wonder why these bridges form. They are not tidal in origin and do not appear in the current galaxy collision models. I strongly suspect that they are due to dark matter and its properties. Indeed, this may be related to how dark and normal matter are disconnected in the Bullet Cluster. Perhaps the dark matter halos are colliding and forming an plane of added density with then contracts into a line and pulls matter into itself from the galaxies.

by **Tszabeau** » Tue Apr 26, 2016 4:45 pm

Fred the Cat wrote:
Tszabeau wrote:It's seems surprising, to me, that the smaller galaxy is not as distorted as the larger one.
https://arxiv.org/pdf/astro-ph/0701291v1

"We have used simulations to investigate the evolution of gas and
stars in such a close encounter, examine the influence of the dark
matter halo and of the geometry of the collision on the characteristics
of the tidal tails and place constraints on the dynamical
history of the observed system."

That doesn't speak to the disruption of IC 4970 but N-body simulations appear to suggest the geometry of the interaction and dark matter halos could have colluded to play their part as Art nefariously pointed out.

Oops! I referenced the wrong comment with my previous reply. Sorry 'bout that Fred.

Starship Asterisk*

APOD: NGC 6872: A Stretched Spiral Galaxy (2016 Apr 26)

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