A galactic rose highlights Hubble's 21st anniversary

Apr 20, 2011
This image of a pair of interacting galaxies called Arp 273 was released to celebrate the 21st anniversary of the launch of the NASA/ESA Hubble Space Telescope. The distorted shape of the larger of the two galaxies shows signs of tidal interactions with the smaller of the two. It is thought that the smaller galaxy has actually passed through the larger one. Credit: NASA, ESA and the Hubble Heritage Team (STScI/AURA)

(PhysOrg.com) -- In celebration of the 21st anniversary of the Hubble Space Telescope’s deployment into space, astronomers pointed Hubble at an especially photogenic group of interacting galaxies called Arp 273.

This image, taken by the NASA/ESA , shows a group of called Arp 273. The larger of the spiral galaxies, known as UGC 1810, has a disc that is tidally distorted into a rose-like shape by the gravitational pull of the companion galaxy below it, known as UGC 1813. The swathe of blue jewels across the top is the combined light from clusters of intensely bright and hot young blue stars. These massive stars glow fiercely in ultraviolet light.

The smaller, nearly edge-on companion shows distinct signs of intense star formation at its nucleus, perhaps triggered by the encounter with the companion galaxy.

A series of uncommon spiral patterns in the large galaxy are a telltale sign of interaction. The large, outer arm appears partially as a ring, a feature that is seen when interacting galaxies actually pass through one another. This suggests that the smaller companion actually dived deeply, but off-centre, through UGC 1810. The inner set of spiral arms is highly warped out of the plane, with one of the arms going behind the bulge and coming back out the other side. How these two spiral patterns connect is still not precisely known.

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This video shows a phenomenon known as gravitational lensing, which is used by astronomers to study very distant and very faint galaxies. Credit: NASA, ESA & L. Calçada

A possible mini-spiral may be visible in the spiral arms of UGC 1810 to the upper right. It is noticeable how the outermost spiral arm changes character as it passes this third galaxy, from smooth with lots of old stars (reddish in colour) on one side, to clumpy and extremely blue on the other. The fairly regular spacing of the blue star-forming knots fits with what is seen in the of other galaxies and can be predicted from the known instabilities in the gas contained within the arm.

The larger galaxy in the UGC 1810-UGC 1813 pair has a mass that is about five times that of the smaller galaxy. In unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric structure in the main spiral. Also in such encounters, the starburst activity typically begins earlier in the minor galaxy than in the major galaxy. These effects could be due to the fact that the smaller galaxies have consumed less of the gas present in their nucleus, from which new stars are born.

Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. The image shows a tenuous tidal bridge of material between the two that are separated by tens of thousands of light-years from each other.

The interaction was imaged on 17 December 2010, with Hubble's Wide Field Camera 3 (WFC3).

This Hubble image is a composite of data taken with three separate filters on WFC3 that allow a broad range of wavelengths covering the ultraviolet, blue, and red portions of the spectrum.

Explore further: Does the galactic spiral lead the rotation of a galaxy?

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ubavontuba
2.3 / 5 (3) Apr 20, 2011
Wow. Thanks Hubble team. That's beautiful.

I noticed another small spiral in the gap of the lower arm in the main galaxy. Is this a background galaxy, or another swirl in the larger galaxy?

And what's the blue feature to the left of the main galaxy? It appears organized. Is it a hot star formation in the main galaxy, or a distant background galaxy? The pixels around it look strangely smudged.

Also, what's the brilliant blue feature in the lower left corner? Upon magnification, it doesn't look like it has much organization. Is it a spin-off?

All in all, the universe certainly is a pretty thing, isn't it?
omatumr
2 / 5 (2) Apr 20, 2011
The Hubble Space Telescope is the crowning achievement of NASA's space program.


Congratulations!
yyz
3.4 / 5 (5) Apr 20, 2011
@uba,I was working on a post on these objects earlier. I note that there is little published work on Arp 273; no refs (or redshifts) could be found for these minor systems near UGC 1810-13. But to answer your questions:

"I noticed another small spiral in the gap of the lower arm in the main galaxy. Is this a background galaxy, or another swirl in the larger galaxy?"

This is likely a background object, seeing as it appears visibly reddened and its HII regions-clusters appear unresolved; possibly a barred spiral in the distant background.

"...what's the blue feature to the left of the main galaxy? It appears organized"

It would appear to be a lenticular dwarf galaxy seen highly inclined to our LOS and undergoing a starburst phase. The visible blue clusters in it appear similar in size to those in Arp 273 and it looks to have a stellar nuclear cluster at or near its center. The fuzziness around it may be a population of less luminous older, redder disk stars.

con't

yyz
3.4 / 5 (5) Apr 20, 2011
con't

"...what's the brilliant blue feature in the lower left corner?"

This poorly organized galaxy is most likely another dwarf (Blue Compact Dwarf or dwarf Irregular) that may indeed be a Tidal Dwarf Galaxy. Like the previous dwarf, the size of its HII regions-clusters is consistent with it being a member of the Arp 273 system. There is also a fainter, older stellar component appearing as faint 'fuzz' around the galaxy. Just to the upper right is a nondescript elliptical galaxy that offers few clues to its actual distance.

As with all galaxies mentioned here, spectroscopic redshifts will be needed to determine membership with Arp 273. There are also several other BCDs (appearing)near this system just out of the field of view. Hopefully this new data will spur someone to follow up with redshifts and kinematics for this relatively nearby system.

But this is quite a view of a newly minted ring galaxy; also quite cool to look deep into the universe beyond Arp 273.
ubavontuba
2.3 / 5 (3) Apr 21, 2011
@yyz:

Thank you for your excellent analysis.

Question: Could the fuzziness be (at least in part) dark matter?

I ask because the superimposed appearance of the upper left BCD makes it seem surprisingly opaque. That is, I intuitively expect the light from UGC 1810 and the BCD to combine to make a brighter (not dimmer) smudge.

Anyway, simply judging by the shape of UGC 1813, the superimposed appearance of the upper BCD, and the relative distance from UGC 1813 of the lower left BCD, it looks like both of these BCD galaxies may have spun off of UGC 1813. Does that sound correct?

Hopefully this new data will spur someone to follow up with redshifts and kinematics for this relatively nearby system.
Indeed. It certainly piques my curiosity.

But this is quite a view of a newly minted ring galaxy; also quite cool to look deep into the universe beyond Arp 273.
Yes. I could spend days happily exploring the high resolution images.

yyz
4 / 5 (4) Apr 21, 2011
Ah, good questions uba.

"Could the fuzziness be (at least in part) dark matter?"

Probably not DM (if DM could be detected in this way, we would have seen this effect in many other systems by now). But I do believe your comment on the apparent opacity of the system is valid. Both of these BCDs may possess large reservoirs of HI gas and dust if indeed they have been tidally stripped from UGC 1813 (so, yes to your second query; these two galaxies are likely Tidal Dwarf Galaxies as well).

Both systems also exhibit absorption features that are indicative of unprocessed gas and dust. Some of the apparent sihouletting seen in the BCD near UGC 1810 is probably due to this component absorbing background light from UGC 1810, in a manner similar to what is seen in the interacting galaxy NGC 3314a & b: http://imgsrc.hub..._jpg.jpg

con't
yyz
4 / 5 (4) Apr 21, 2011
con't

The faint,diffuse stellar(?) component of the BCD near UGC 1810 does seem somewhat disturbed. This may be a tidal feature similar to shells and fans seen in some gravitationally disturbed elliptical and lenticular galaxies.

What I found most interesting in this image is what appears to be a third galaxy projected on an arm of UGC 1810:

"A possible mini-spiral may be visible in the spiral arms of UGC 1810 to the upper right. It is noticeable how the outermost spiral arm changes character as it passes this third galaxy, from smooth with lots of old stars(reddish in colour) on one side, to clumpy and extremely blue on the other."

This smaller "galaxy" appears much like the example of NGC 3314 I linked above, right down to the absorption features sihouletted against UGC 1810. While this object is likely not a TDG, rather a smallish disk galaxy, I could find no mention of it in the literature.

So much neat stuff in this new image. Looking forward to followup studies soon(?)

ubavontuba
3 / 5 (2) Apr 21, 2011
@yyz:

Both of these BCDs may possess large reservoirs of HI gas and dust
Considering the intense blue star activity, I'd suspect they'd have to be rich in hydrogen and poor in metals. I wonder, are the lighter elements particularly prone to being stripped away from parent galaxies in these tidal interactions?

Some of the apparent sihouletting seen in the BCD near UGC 1810 is probably due to this component absorbing background light from UGC 1810, in a manner similar to what is seen in the interacting galaxy NGC 3314a & b:
Perhaps, but it certainly isn't so neatly organized as these spiral arm densities.

What I found most interesting in this image is what appears to be a third galaxy projected on an arm of UGC 1810:
Right. I wonder, will it endlessly orbit within UGC 1810, dissolve into UGC 1810, or eventually get booted out?

Cool stuff.