Subscribe free to our newsletters via your
. 24/7 Space News .

Quasars Quash Star Formation In Active Galactic Nuclei
by Anita Heward
London, UK (SPX) Apr 09, 2008

Multicolour SDSS optical images of NGC5806 and NGC5750, nearby spiral galaxies with active nuclei similar to those being studied by Westoby and his collaborators. Image 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 at the RAS National Astronomy Meeting in Belfast.

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.


Related Links
Stellar Chemistry, The Universe And All Within It

Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks DiggDigg RedditReddit GoogleGoogle

Memory Foam Mattress Review
Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

Witnessing The Formation Of Distant Galaxies
London, UK (SPX) Apr 09, 2008
UK astronomers have produced the most sensitive infrared map of the distant Universe ever undertaken. Combining data over a period of three years, they have produced an image containing over 100,000 galaxies over an area four times the size of the full Moon. Some of the first results from this project will be presented by Dr Sebastien Foucaud from the University of Nottingham ... read more

NASA Sets Sights On Lunar Dust Exploration Mission

The 2008 Great Moonbuggy Race

UMaine Engineering Team To Test Inflatable Habitats For NASA Moon Mission

Workers Ready Course For NASA's 15th Annual Great Moonbuggy Race

NASA Spacecraft Images Mars Moon In Color And In 3D

Spirit Advances Toward Midwinter

Visting Mars, Again And Again

Mars Rover Opportunity Completes Dental Checkup At Victoria Crater's Duck Bay

NASA starts new science Web site

NASA officials report Goddard 'incident'

Hall of fame inducts NASA technologies

First Korean astronaut edges towards space station

Three Rocketeers For Shenzhou

China's space development can pose military threat: Japan

Brazil To Deepen Space Cooperation With China

China Approves Second-Phase Lunar Probe Program

The ESA opens a new space laboratory

First Korean astronaut docks with space station

Astronauts Relish New Asian Space Food As Expedition 17 Docks

New Station Crew Prepares For Launch Tuesday

Vietnam delays launch of first satellite

Successful Qualification Firing Test For Zefiro 23

Zenit Rocket To Orbit Israeli Satellite In Late April

German military satellite launched by Russia: report

New Laser Technology Could Find First Earth-like Planets

Scientists Discover 10 New Planets Outside Solar System

Googling Alien Life

Searching For Earth

Newly Discovered Superinsulators Promise To Transform Materials Research, Electronics Design

Chemists work on bamboo fabric development

TDRS-1 Satellite Reaches 25 Years Of Age

Saab Signs GIRAFFE AMB Multi Mission Radar Contract

The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement