Featured Research

from universities, journals, and other organizations

Quasars Quash Star Formation In Active Galactic Nuclei

Date:
April 9, 2008
Source:
Royal Astronomical Society
Summary:
An ambitious study of active and inactive galaxies has given new insights into the complex interaction between super-massive black holes at the heart of Active Galactic Nuclei (AGN) and star formation in the surrounding galaxy. Astronomers studied the properties of light from 360,000 galaxies in the local Universe to understand the relationship between accreting black holes, the birth of stars in galaxy centres and the evolution of the galaxies as a whole.

Multicolour SDSS optical images of NGC5806 and NGC5750, nearby spiral galaxies with active nuclei similar to those being studied by Westoby and his collaborators.
Credit: The Sloan Digital Sky Survey

An ambitious study of active and inactive galaxies has given new insights into the complex interaction between super-massive black holes at the heart of Active Galactic Nuclei (AGN) and star formation in the surrounding galaxy. Results will be presented in a talk by Paul Westoby on 4th April at the RAS National Astronomy Meeting in Belfast.

Related Articles


Along with colleagues, Carole Mundell and Ivan Baldry from the Astrophysics Research Institute of Liverpool John Moores University, Westoby studied the properties of light from 360,000 galaxies in the local Universe to understand the relationship between accreting black holes, the birth of stars in galaxy centres and the evolution of the galaxies as a whole.

The study finds that gas ejected during the quasar stage of AGN snuffs out star formation, leaving the host galaxies to evolve passively. The study also reveals a strong link between galaxy mergers and the formation of super-massive black holes in AGN, but shows that if the environment becomes too crowded with galaxies, then the likelihood of firing up a supermassive black hole becomes suppressed.

Scientists believe that all AGN go through a quasar phase, where the radiation emitted from the growing accretion disc around the central black hole becomes so bright that it outshines its entire host galaxy. Today, most massive galaxies are thought to contain a dormant super-massive black hole at their heart, a legacy of this earlier phase of powerful quasar activity, but for reasons unknown, some of these local black holes have been reignited.

The Liverpool team concentrated on these local AGN, which can be studied in more detail than their more distant quasar cousins, and, by comparing the properties of a large number of galaxies, the team addressed a key question – do galaxies that host AGN represent an adolescent or transition phase of galaxy evolution?

“The starlight from the host galaxy can tell us much about how the galaxy has evolved,” said Westoby. “Galaxies can be grouped into two simple colour families: the blue sequence, which are young, hotbeds of star-formation and the red sequence, which are massive, cool and passively evolving.” Westoby continued “Scientists have thought for some time that AGN host galaxies might be a stepping stone between the two families and therefore represent a critical point in the lifetime of a galaxy, but our study has been able to rule this out.”

Instead the AGNs identified by the team lay in galaxies that showed a clear overlap with red sequence galaxies. This suggests that the star-forming days for AGN host galaxies have a distinct cut-off point and that the post-quasar local AGNs are no longer generating new stars. This conclusion is reinforced by the team’s findings that the majority of local AGNs are linked with “classical bulges”, round balls of stars formed during violent mergers of gas-rich galaxies early on in the Universe’s history, rather than “pseudo bulges”, disc-only galaxies that have not undergone a major merger since their formation. This implies that the formation of the super-massive black hole that drives the AGN is linked to the evolution of the bulge, rather than the galaxy as a whole.

Finally, the team identified an intriguing population of galaxies that have an active population of young stars together with an actively accreting black hole, so-called composite galaxies. These masquerade as a transition population, and lie in the region predicted for galaxies experiencing AGN feedback – the process by which material ejected by the AGN has a direct impact on the evolution of the surrounding galaxy. However, Westoby and colleagues find feedback an unlikely explanation for the observed properties of these galaxies and suggest that feedback may only be important during the quasar phase and not in weaker, nearby AGN.


Story Source:

The above story is based on materials provided by Royal Astronomical Society. Note: Materials may be edited for content and length.


Cite This Page:

Royal Astronomical Society. "Quasars Quash Star Formation In Active Galactic Nuclei." ScienceDaily. ScienceDaily, 9 April 2008. <www.sciencedaily.com/releases/2008/04/080404200325.htm>.
Royal Astronomical Society. (2008, April 9). Quasars Quash Star Formation In Active Galactic Nuclei. ScienceDaily. Retrieved October 31, 2014 from www.sciencedaily.com/releases/2008/04/080404200325.htm
Royal Astronomical Society. "Quasars Quash Star Formation In Active Galactic Nuclei." ScienceDaily. www.sciencedaily.com/releases/2008/04/080404200325.htm (accessed October 31, 2014).

Share This



More Space & Time News

Friday, October 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: Antares Liftoff Explosion

Raw: Antares Liftoff Explosion

AP (Oct. 29, 2014) Observers near Wallops Island recorded what they thought would be a routine rocket launch Tuesday night. What they recorded was a major rocket explosion shortly after lift off. (Oct 29) Video provided by AP
Powered by NewsLook.com
Raw: Russian Cargo Ship Docks at Space Station

Raw: Russian Cargo Ship Docks at Space Station

AP (Oct. 29, 2014) Just hours after an American cargo run to the International Space Station ended in flames, a Russian supply ship has arrived at the station with a load of fresh supplies. (Oct. 29) Video provided by AP
Powered by NewsLook.com
Journalist Captures Moment of Antares Rocket Explosion

Journalist Captures Moment of Antares Rocket Explosion

Reuters - US Online Video (Oct. 29, 2014) A space education journalist is among those who witness and record the explosion of an unmanned Antares rocket seconds after its launch. Rough Cut (no reporter narration) Video provided by Reuters
Powered by NewsLook.com
Rocket Explosion Under Investigation

Rocket Explosion Under Investigation

AP (Oct. 28, 2014) NASA and Orbital Sciences officials say they are investigating the explosion of an unmanned commercial supply rocket bound for the International Space Station. It blew up moments after liftoff Tuesday evening over the launch site in Virginia. (Oct. 28) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins