Pinning The Tails On Galaxy Clusters


When it comes to understanding how galaxies behave both inside and outside of galaxy clusters, it would seem that we still have quite a lot to learn. Tom Scott from the Instituto de Astrofisica de Andalucia in Granada, Spain, and a group of international astronomers have been busy with the Expanded Very Large Array (EVLA) of the National Radio Astronomy Observatory (NRAO) in the USA, checking out an assortment of galaxies associated with galaxy cluster Abell 1367. What they have found is unexpectedly long one-sided gaseous tails in two sets of galaxies… the longest of their type ever observed.

Located in the constellation of Leo and about 300 million light years away, galaxies CGCG 097-026 and FGC1287 are displaying gaseous tail structures that may rearrange thinking on how stripping of materials behaves. Current thinking has hot gases trapped within the galaxy cluster’s gravitational field – with incoming galaxies being depleted of their cold hydrogen gases when captured by the gravitational influence. Through this impact, galaxies added to the cluster generally tend to lose their star-forming abilities and begin to quickly age. Astronomers assume this is why less aggressive galaxy structures tend to be found in lower density environments. However, thanks to Scott’s research, astronomers might be able to assume that galaxies can be robbed of their gases before entering a clustered environment.

“When we looked at the data, we were amazed to see these tail structures” says Tom Scott. “The projected lengths of the gaseous tails are 9 to 10 times that of the size of the parent galaxies, i.e., 520,000 and 815,000 light years respectively. In both cases the amount of cold hydrogen gas in the tails is approximately the same as that remaining in the galaxy’s disk. In other words, these galaxies have already left behind half of their fuel for star formation before entering the sphere of influence of the cluster.”

As stated, the commonly accepted theory for gaseous tail structures is interaction with the hot, gaseous medium located within the cluster’s influence – a process known as ram-pressure stripping. But this case is different. Galaxies CGCG 097-026 and FGC1287 aren’t being perturbed by the nearby cluster just yet… But they are still displaying long tails of material.

“We considered the various physical processes proposed by theorists in the past to describe gas removal from galaxies, but no one seems to be able to explain our observations” says Luca Cortese, researcher at ESO-Garching, Germany, and co-author of this work. “Whereas in the case of CGCG97-026, the gravitational interaction between the various members of the group could explain what we see, FGC1287 is completely different from any case we have seen before.”

Right now, ram-pressure stripping isn’t the answer – and gravitational interactions don’t seem to fit the picture, either. It’s leaving scientists at a loss to explain these long tails and lack of stellar disturbance.

“Although the mechanism responsible for this extraordinary gas tail remains to be determined, our discovery highlights how much there still is to learn about environmental effects in galaxy groups” says team member Elias Brinks, a scientist at the University of Hertfordshire. “This discovery might open a new chapter in our understanding of environmental effects on galaxy evolution.”

Original Story Source: Royal Astronomical Society News Release. For Further Reading: Two long tails in the outskirts of Abell 1367.

6 Replies to “Pinning The Tails On Galaxy Clusters”

  1. This popped into my mind, knowing nothing of the field:

    IIRC cluster formation happens in the DM dominated filaments from primordial fluctuations. Wouldn’t DM set up a ram pressure on those unlucky galaxies caught in a filament? Not as efficient as an EM interacting particle ram, but some.

    1. OK… So recently within the space of a few days we have discovered black holes 100’s or 1,000’s of times more dense/massive than theory had generally predicted. Now this article showing our undertstanding of the intracluster gas of galaxies may need serious tweeking.

      I do understand you are a DM proponent and do not blame you for trying to make your hyposthesis fit the data as this is part of the sceintific process. Howerver, I do think you could be a little more open to questioning your own assumptions.

      Remember it’s fun to learn new things and there’s no penalty for being wrong in science other than revising and expanding ones current knowledge and understanding.

      I look forward to more of our friendly exchanges on DM versus other possible theories (and by the way I do not necessarily accept DM or MOND and am personally eyeing a third choice – like quantum vacuum polarisation and the fact that charge fields of protons and photons may be misunderstood when it comes to the equillibrium between AGN core and intracluster gassses and halo’s of galaxies and interacting galaxy clusters).

      All the best,


      1. If you don’t mind for those not having so much time to check your references, if you could advise on how those links explain visible gas features mentioned in the article.

        Also, the paper is quite nice (It has nice picts :))

        And also it has quite plausible explanation that the gas was stripped by the high speed galaxy intruder near FGC1287 (real crime strory there).

      2. Hi Martin,

        My links and references show a possible alternative mechanism for intracluster gas distribution – in  reply to Torbjorn’s speculaton of DM being involved in the galaxy structuures mentioned in the above article..

        I am not sure which paper you are referencing when you make claims of a plausible explanation???  Did we read the same article above? Where is there any mention of a plausible explanation? Please provide the excerpt or links.

      3. Hi Wezley,

        Please excuse my ignorance and laziness, as I presume your references propose alternative mechanism, but I think it might be beyond my comprehension to relate them in particular to those visible features. So just asking – always like to learn something new and keep open-minded 🙂

        And paper which I refer to is the one provided by the link when one clicks on “For Further Reading:” at the bottom of the article.

      4. quoting Martin post above//
        And also it has quite plausible explanation that the gas was stripped by the high speed galaxy intruder near FGC1287 (real crime strory there//

        I got an entirely different interpretation reading the paper…
        What i understood is that the high speed galaxy intruder you mentioned (LSBC.D571-03) showed NO signs of any interaction and the researchers identify this hypothesis as ‘speculation’ until further observations.
        In terms of explaining the alternate mechanism of Quantum Vacuum Polarization, to be honest, I am not really qualified and am still digesting the information- but the first link I provided has a discussion forum where more ‘laymen’ discussion can be found.
        And no offence taken- I enjoy reading and learning new things and do not pretend to be any authority on such complex subjects.

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