HEIC: Merging Galaxies Break Radio Silence

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bystander
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HEIC: Merging Galaxies Break Radio Silence

Post by bystander » Fri May 29, 2015 4:45 am

Merging Galaxies Break Radio Silence
ESA Hubble Science Release | 2015 May 28
[img3="Illustration of galaxy with jets from a supermassive black hole
Credit: ESA/Hubble, L. Calçada (ESO)
"]http://cdn.spacetelescope.org/archives/ ... c1511a.jpg[/img3][img3="Galaxies with relativistic jets
Credit: NASA, ESA, M. Chiaberge (STScI)
"]http://cdn.spacetelescope.org/archives/ ... c1511b.jpg[/img3][hr][/hr]
In the most extensive survey of its kind ever conducted, a team of scientists have found an unambiguous link between the presence of supermassive black holes that power high-speed, radio-signal-emitting jets and the merger history of their host galaxies. Almost all of the galaxies hosting these jets were found to be merging with another galaxy, or to have done so recently. The results lend significant weight to the case for jets being the result of merging black holes and will be presented in the Astrophysical Journal.

A team of astronomers using the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) have conducted a large survey to investigate the relationship between galaxies that have undergone mergers and the activity of the supermassive black holes at their cores.

The team studied a large selection of galaxies with extremely luminous centres — known as active galactic nuclei (AGNs) — thought to be the result of large quantities of heated matter circling around and being consumed by a supermassive black hole. Whilst most galaxies are thought to host a supermassive black hole, only a small percentage of them are this luminous and fewer still go one step further and form what are known as relativistic jets. The two high-speed jets of plasma move almost with the speed of light and stream out in opposite directions at right angles to the disc of matter surrounding the black hole, extending thousands of light-years into space. The hot material within the jets is also the origin of radio waves.

It is these jets that Marco Chiaberge from the Space Telescope Science Institute, USA (also affiliated with Johns Hopkins University, USA and INAF-IRA, Italy) and his team hoped to confirm were the result of galactic mergers.

The team inspected five categories of galaxies for visible signs of recent or ongoing mergers — two types of galaxies with jets, two types of galaxies that had luminous cores but no jets, and a set of regular inactive galaxies. ...

Radio Loud AGNs are Mergers - Marco Chiaberge, Roberto Gilli, Jennifer Lotz, Colin Norman
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Re: HEIC: Merging Galaxies Break Radio Silence

Post by Ann » Fri May 29, 2015 7:00 pm

heic1511 — Science Release wrote:

Almost all of the galaxies hosting these jets were found to be merging with another galaxy, or to have done so recently.


The press release is illustrated with an artist's illustration of a galaxy based on the appearance of Centaurus A, NGC 5128. We know that NGC 5128 is a merger product, and the jet is clearly caused by the same merger history.

But what about the most famous and prototypical of nearby active galaxies with jets, M87? Of course I realize that a galaxy as large as M87 must have undergone several merger events during its lifetime, but it is far from obvious to me that M87 has recently merged with anything.

Admittedly, I found this page, which states that
[M87] likely formed from a recent merger between two other galaxies.
Am I the only one who is surprised by this? What about the rest of you? Have you known or suspected that M87 is the product of a recent merger?

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Re: HEIC: Merging Galaxies Break Radio Silence

Post by geckzilla » Sat May 30, 2015 12:31 am

It is a little surprising, yes. And no, I probably wouldn't have thought that up on my own. After hearing about this I don't have a problem accepting that it could have gone through a recent merger, though.

At some point a galaxy gets so big it can merge with smaller ones and not result in a hugely evident change. Think about a spiral merger and why they are frequently so impressive. A spiral galaxy is typically much smaller galaxy, so the chance that it meets another galaxy that is equivalent enough in mass to jumble up the stars is much better. Not that they can't acquire a dwarf here and there without much more than a faint star stream to look at, but what about a humongous galaxy? It'll take another massive galaxy to jumble things up. A smaller spiral might incorporate with little tumult, hence why we often see faint shells rather than totally wonky ellipticals. Maybe jets are really good evidence for recent merging.
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