Mysterious Giant Gas Ring Explained

Article Updated: 24 Dec , 2015
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From a Canada-France-Hawaii Telescope press release:

An international team unveiled the origin of the giant gas ring in the Leo group of galaxies. With the Canada-France-Hawaii Telescope, the scientists were able to detect an optical signature of the ring corresponding to star forming regions. This observation rules out the primordial nature of the gas, which is of galactic origin. Thanks to numerical simulations made at CEA, a scenario for the formation of this ring has been proposed: a violent collision between two galaxies, slightly more than one billion years ago. The results will be published in the Astrophysical Journal Letters.

In the current theories on galaxy formation, the accretion of cold primordial gas is a key-process in the early steps of galaxy growth. This primordial gas is characterized by two main features: it has never sojourned in any galaxy and it does not satisfy the conditions required to form stars. Is such an accretion process still ongoing in nearby galaxies? To answer the question, large sky surveys are undertaken attempting to detect the primordial gas.

The Leo ring, a giant ring of cold gas 650,000 light-years wide surrounding the galaxies of the Leo group, is one of the most dramatic and mysterious clouds of intergalactic gas. Since its discovery in the 80s, its origin and its nature were debated. Last year, studies of the metal abundances in the gas led to the belief that the ring was made of this famous primordial gas.

Thanks to the sensitivity of the Canada-France-Hawaii Telescope MegaCam camera, the international team observed for the first time the optical counterpart of the densest regions of the ring, in visible light instead of radio waves. Emitted by massive young stars, this light points to the fact that the ring gas is able to form stars.

A ring of gas and stars surrounding a galaxy immediately suggests another kind of ring: a so-called collisional ring, formed when two galaxies collide. Such a ring is seen in the famous Cartwheel galaxy. Would the Leo ring be a collisional ring too?

In order to secure this hypothesis, the team used numerical simulations (performed on supercomputers at CEA) to demonstrate that the ring was indeed the result of a giant collision between two galaxies more than 38 million light-years apart: at the time of the collision, the disk of gas of one of the galaxies is blown away and will eventually form a ring outside of the galaxy. The simulations allowed the identification of the two galaxies which collided: NGC 3384, one of the galaxies at the center of the Leo group, and M96, a massive spiral galaxy at the periphery of the group. They also gave the date of the collision: more than a billion years ago!

The gas in the Leo ring is definitely not primordial. The hunt for primordial gas is still open!


8 Responses

  1. Jon Hanford says:

    Yeah, their has been a lot of debate on the age of this object since it was first discovered by radio astronomers in the 1980’s. A few years back, observations by the GALEX observatory detected a few clumps of very young stars in the Leo Ring. Primordial gas proponents claimed that these were the first stars to form from gas in the ring since the Big Bang. But these new observations cast doubt on the primordial nature of this feature. The paper, “A collisional origin for the Leo ring” can be found here: http://arxiv.org/PS_cache/arxiv/pdf/1005/1005.4208v2.pdf

  2. John Mendenhall says:

    Will a ring galaxy develop?

  3. Trippy says:

    I’m confused – why is M86 annotated in the image when M96 is the galaxy discussed?

    M96 and NGC 3384 are both members of the M96 Group of Galaxies in Leo, but, M86 lies in Virgo, part of the Virgo cluster.

    Additionally, the simulation in the original press release appears to suggest M96 (M96 being a spiral, and the other galaxy involved in the collision) in the same position as the galaxy annotated M86 in this image (M86 being a Lenticular galaxy).

    Finally, M86 is at a RA 12H26M46S DEC+12°56’46” where NGC 3384 is located at RA 10H48M16.9S DEC +12°37’46” and M96 is at RA 10H46M45.7S DEC11°49’12”.

    Additionally, I get the gist that even with the MegaPrime instrument it would still be impossible to do a single exposure that included bot NGC 3384 and M86.

  4. Jon Hanford says:

    Trippy,

    They definitely made a typo with the press release. Check Fig. 1 in the paper I linked in my post for the correctly labeled image. Locations of the bottom two closeups within the ring are also shown.

  5. Aodhhan says:

    Jon…
    Great reference find. Thank you.

  6. Jon Hanford says:

    “Will a ring galaxy develop?”

    According to the current study, the density in the HI gas ring is too low allow vigorous star formation like that seen in other collisional ring galaxies, such as the Cartwheel galaxy. The authors don’t speculate on the future of the ring, but I would guess that the remaining galaxies in the system will gradually re-accrete most of the gas in the future.

    There is a short video showing the team’s computer sim of the encounter between the gas-rich ‘target’ galaxy NGC 3384 and the more massive ‘intruder’ galaxy M 96 over the past 1.2 billion years (scroll to the bottom of the CFHT press release). According to this model, most of the gas in the Leo ring once belonged to NGC 3384. While not quantitatively precise, the measured velocities of the Leo ring match pretty well with the velocities derived from the simulation (see Figure 4 of the paper).

  7. Aqua says:

    “In the current theories on galaxy formation, the accretion of cold primordial gas is a key-process in the early steps of galaxy growth. This primordial gas is characterized by two main features: it has never sojourned in any galaxy and it does not satisfy the conditions required to form stars. Is such an accretion process still ongoing in nearby galaxies? To answer the question, large sky surveys are undertaken attempting to detect the primordial gas.”

    So this is the ‘outside in’ theory… That primordial gas from the BBang, thru gravitiy, collected to form galaxies.

    Hmmm… see my post at http://www.universetoday.com/2010/07/01/graphite-whiskers-found-in-apollo-moon-rocks/ about ongoing neucleosynthesis at Sol.

    The above theory implies that those processes are due to the product of fusion created by gravity, as the primordial gas condensed…

    Instead of from the ‘inside radiating outward’ In form of mattter fountains where inter-dimensional confluences cojoin. Where a parallel universe(s) touches ours, where the speed of light is much faster or light itself in another form altogether. And when that energy enters our time/space it slows (or speeds up?) and creates matter…. fountains of it.

    Micro to macro? As atoms forming galaxies.

  8. Torbjorn Larsson OM says:

    Aqua, the point is that very simple and observable mechanisms already predict nucleosynthesis. Speculation is futile.

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