by ems57fcva » Fri Nov 09, 2012 5:19 am
Ann wrote:ems57fcva wrote:As best I can tell, the small galaxy at the bottom of the photo IS the intruder galaxy. There is a bridge running between the cores of the two galaxies! It comes out of the central code at 6:00, sweeps up past the 2:00 position (where what I think is a tidal tail is being mistaken for the intruder), continues above Arp 188 and then dives down in front of Arp 188 towards a point to the right of the smaller galaxy. Then it turns like a "J" and heads into the core of the smaller galaxy.
My guess is that the smaller galaxy swept past Arp 188 going just above it to form a bridge between the galaxies. It then got swung around and down towards its current position. The tidal effects create the big tidal tail and a smaller one whose remnants at 2:00 are being mistaken for the intruder. The bridge then got stretched out and twisted around by the path the smaller galaxy took, but if you look for it, the full bridge is still there. In this case, the galaxies did not interact all that strongly and are now separating with their identities intact. The bridge is disintegrating as the galaxies continue to separate.
These bridges are something that I keep finding in cases of colliding galaxies, but I have never seen them modeled. There is something fundamental that we don't understand about interacting galaxies IMO.
Personally I doubt that the small disk galaxy has anything to do with Arp 188. I believe, instead, that the disk galaxy near the bottom of the picture is a background object. It is very well-formed and bright, and its disk has symmetric dust lanes and star formation. Its appearance makes it resemble our large galactic neighbour, the Andromeda galaxy. Such well-formed and symmetric galaxies are almost always big, but if this galaxy is so close to Arp 188 that it has collided with it, then it must be small indeed. I find that extremely unlikely. Instead, I think that it is a big spiral galaxy that is many millions of light-years further away from us than Arp 188.
Also, if this galaxy had actually collided with a galaxy that was as big as itself or even bigger, then its symmetric shape would be completely ruined. This galaxy is simply much, much too well-formed to have had a recent close encounter with a galaxy larger than itself.
Indeed, when you take a close look at the "tail" that seems to emanate from the center of this spiral galaxy, it becomes obvious that the tail instead emanates from the small round galaxy at its lower right. The "tail" is in fact two long star streams emerging from opposite sides of the small galaxy.
But Arp 188 does indeed have a tail pointing downwards. Follow the tail down, and you'll come to a small round shape at the upper right of the small bright spiral galaxy. This small round object could indeed be a dwarf galaxy, a so-called dwarf spheroidal, that is interacting with Arp 188. This object and Arp 188 actually resemble
the Andromeda galaxy and its dwarf spheroidal companion NGC 205.
Ann
Ann - You are mostly right. I was fooled by the star stream coming out of the background galaxy and getting mixed in with the tidal tail for the small galaxy that you mentioned. However, I now interpret that small galaxy as being the remains of the intruder, which has lost a lot of its material to the larger galaxy and the connecting bridge. Interpreting the overall picture gets a bit difficult for me now: The bridge and the secondary tidal tail are mixed together in this case. I am guessing that the intruder came in from below and behind, passed about the core of Arp188 and then swung down and ended up as the small galaxy that we are talking about. A lot of its original material ended up in the bridge, and is forming a new satellite galaxy that is being mistaken for the actual intruder. Close to the start of the bridge, a secondary tidal tail is also present, making the bridge look bigger than it really is. The extended period of interaction and its originally being much bigger would be how that small galaxy ended up creating the Tadpole Galaxy's tail.
The smaller galaxy is also worthy of comment. It has a small satellite galaxy just to its right, and what appears to be a star stream defining a closed path that goes from the core, through the satellite galaxy and the curves around behind the "parent" galaxy and back to the core.
[quote="Ann"][quote="ems57fcva"]As best I can tell, the small galaxy at the bottom of the photo [b]IS[/b] the intruder galaxy. [i]There is a bridge running between the cores of the two galaxies![/i] It comes out of the central code at 6:00, sweeps up past the 2:00 position (where what I think is a tidal tail is being mistaken for the intruder), continues above Arp 188 and then dives down in front of Arp 188 towards a point to the right of the smaller galaxy. Then it turns like a "J" and heads into the core of the smaller galaxy.
My guess is that the smaller galaxy swept past Arp 188 going just above it to form a bridge between the galaxies. It then got swung around and down towards its current position. The tidal effects create the big tidal tail and a smaller one whose remnants at 2:00 are being mistaken for the intruder. The bridge then got stretched out and twisted around by the path the smaller galaxy took, but if you look for it, the full bridge is still there. In this case, the galaxies did not interact all that strongly and are now separating with their identities intact. The bridge is disintegrating as the galaxies continue to separate.
These bridges are something that I keep finding in cases of colliding galaxies, but I have never seen them modeled. There is something fundamental that we don't understand about interacting galaxies IMO.[/quote]
Personally I doubt that the small disk galaxy has anything to do with Arp 188. I believe, instead, that the disk galaxy near the bottom of the picture is a background object. It is very well-formed and bright, and its disk has symmetric dust lanes and star formation. Its appearance makes it resemble our large galactic neighbour, the Andromeda galaxy. Such well-formed and symmetric galaxies are almost always big, but if this galaxy is so close to Arp 188 that it has collided with it, then it must be small indeed. I find that extremely unlikely. Instead, I think that it is a big spiral galaxy that is many millions of light-years further away from us than Arp 188.
Also, if this galaxy had actually collided with a galaxy that was as big as itself or even bigger, then its symmetric shape would be completely ruined. This galaxy is simply much, much too well-formed to have had a recent close encounter with a galaxy larger than itself.
Indeed, when you take a close look at the "tail" that seems to emanate from the center of this spiral galaxy, it becomes obvious that the tail instead emanates from the small round galaxy at its lower right. The "tail" is in fact two long star streams emerging from opposite sides of the small galaxy.
But Arp 188 does indeed have a tail pointing downwards. Follow the tail down, and you'll come to a small round shape at the upper right of the small bright spiral galaxy. This small round object could indeed be a dwarf galaxy, a so-called dwarf spheroidal, that is interacting with Arp 188. This object and Arp 188 actually resemble [url=http://apod.nasa.gov/apod/image/0809/m110_cfht_c800.jpg]the Andromeda galaxy and its dwarf spheroidal companion NGC 205[/url].
Ann[/quote]
Ann - You are mostly right. I was fooled by the star stream coming out of the background galaxy and getting mixed in with the tidal tail for the small galaxy that you mentioned. However, I now interpret that small galaxy as being the remains of the intruder, which has lost a lot of its material to the larger galaxy and the connecting bridge. Interpreting the overall picture gets a bit difficult for me now: The bridge and the secondary tidal tail are mixed together in this case. I am guessing that the intruder came in from below and behind, passed about the core of Arp188 and then swung down and ended up as the small galaxy that we are talking about. A lot of its original material ended up in the bridge, and is forming a new satellite galaxy that is being mistaken for the actual intruder. Close to the start of the bridge, a secondary tidal tail is also present, making the bridge look bigger than it really is. The extended period of interaction and its originally being much bigger would be how that small galaxy ended up creating the Tadpole Galaxy's tail.
The smaller galaxy is also worthy of comment. It has a small satellite galaxy just to its right, and what appears to be a star stream defining a closed path that goes from the core, through the satellite galaxy and the curves around behind the "parent" galaxy and back to the core.