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Deep Sky Observer's Companion – the online database

 

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A collisional origin for the Leo ring

In the 1980s, astronomers discovered a giant ring of cold gas in Leo, surrounding the galaxies of the Leo group. The ring is some 650,000 light years across, and is one of the most dramatic and mysterious clouds of intergalactic gas. Since its discovery its origin and nature were debated.

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.

Last year, studies of the metal abundances in the gas of the Leo ring led to the belief that it was made of this famous primordial gas.

Thanks to the sensitivity of the Canada-France-Hawaii Telescope MegaCam camera, an international team of astronomers 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 centre 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!

(Michel-Dansac, L. et. al. (2010) A collisional origin for the Leo ring. ApJL, 717, L143, 2010.)

CFHT news release

Recent news

top story: A charming planetary nebula in eastern Triangulum Australe. — A charming planetary nebula in eastern Triangulum Australe.

March newsletter of the ASSA Deep-Sky Section, featuring 47 Tuc on the cover. — "Nightfall" (2015 April) is the current newsletter of the Deep-Sky Observing Section of the Astronomical Society of Southern Africa.

A globular cluster in the realm of the galaxies — A rare gem - a bright globular cluster in the realm of the galaxies.

The Dark Emu rises, in pursuit of the Magellanic Clouds — The beautiful complex of dark nebulosity along the southern Milky Way appears like an ancient monster, its serpentine neck reaching out as if to gobble up the Magellanic Clouds.

Massive star forming region in the Small Magellanic Cloud — Dale Liebenberg images NGC 346, a gigantic star forming region in the SMC.

Flocculent Galaxy in Southern Leo — Dale Liebenberg images the spiral galaxy NGC 3521 in southern Leo.

Ancient open cluster in Lyra — Anthony Ayiomamitis images the old open cluster NGC 6791.

Golden Coin Galaxy — Dale Liebenberg images the Golden Coin, NGC 4945 in Centaurus.

NGC 2467 in Puppis — Dale Liebenberg images NGC 2467 in Puppis.

Last but not least - Messier 103 — Anthony Ayiomamitis images Messier 103 in Cassiopeia.

The Arkenstone of Thrain — Dale Liebenberg images Messier 22, the "Arkenstone of Thrain" according to Burnham.

ConCards available — A handy set of beginner's star charts, "Constellation Cards" are now available for free download.

Deep sky celebrations — Three deep sky observers of yore have birthdays this week: William Herschel (1738), the Fourth Earl of Rosse, and Stephane Javelle.

Necklace Nebula featured on APOD — The recently-discovered planetary nebula nicknamed the Necklace Nebula, recently featured on APOD.

Methuselah Nebula featured on APOD — The old bipolar planetary nebula MWP1, a.k.a. Methuselah Nebula, is today's APOD.

New deepsky book from CUP — Deep sky author Wolfgang Steinicke's latest book, "Observing and Cataloguing Nebulae and Star Clusters: From Herschel to Dreyer's New General Catalogue", has just been published by Cambridge University Press.

NGC 1365 in infrared (ESO VLT) — The bright barred spiral galaxy NGC 1365 in Fornax has been imaged in the infrared with the ESO VLT telescope.

New HST image of eta Carinae Nebula — New observations, combined with images made in 2005, show beautiful detail in part of the extensive eta Carinae Nebula.

First planetary in open cluster found — A team of astronomers from Australia, the UK, the USA and France have discovered the first planetary nebula known to be associated with a galactic open cluster.

NGC 300 in Sculptor imaged at ESO — The bright spiral galaxy NGC 300 has been imaged with the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile.

Superwind galaxy NGC 4666 — A remarkable galaxy with very vigorous star formation has been newly imaged on the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile.

News archives

All earlier news items can be browsed in the archives.

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Everything on DOCdb.net is © 2004-2010 by Auke Slotegraaf, unless stated otherwise or if you can prove you have divine permission to use it. Before using material published here, please consult the Creative Commons Attribution-Non-Commercial-Share Alike 2.5 License. Some material on DOCdb is copyright the individual authors. If in doubt, don't reproduce. And that goes for having children, too. Please note that the recommended browser for DOCdb is Firefox 3.x. You may also get good results with K-Meleon. Good luck if you're using IE. A successful experience with other browsers, including Opera and Safari, may vary.