Quasars in Interacting Galaxies
[Top Row] This is a selection of photos from a Hubble Space Telescope survey of
11 ultra-bright quasars that existed at the peak of the universe's
star-formation era, which was 12 billion years ago. The quasars
(powered by supermassive black holes) are so compact and bright they
make a diffraction-spike pattern in the telescope's optics — an optical
artifact typically only produced by bright nearby stars. Despite their
brightness, the quasars are actually dimmed by dusty gas around them.
The infrared capability of Hubble's Wide Field Camera 3 was able to
probe deeply into the material around the quasars.
[Bottom Row] When the glare of the quasar is subtracted, researchers see evidence
for collisions between galaxies. The collisions and mergers gave birth
to the quasars by fueling the supermassive black hole at the core of
the galaxies. The new images capture the dust-clearing transitional
phase in the merger-driven quasar birth. These observations show that
the brightest quasars in the universe live in merging galaxies.
Astronomers have used the Hubble Space Telescope's infrared vision to
uncover the mysterious early formative years of quasars, the brightest
objects in the universe. Hubble's sharp images unveil chaotic galaxy
collisions that give birth to quasars by fueling their energy source: a
supermassive central black hole devouring infalling material.
"The Hubble observations are definitely telling us that the peak of
quasar activity in the early universe is driven by galaxies colliding
and then merging together," said Eilat Glikman of Middlebury College in
Vermont. "We are seeing the quasars in their teenage years, when they
are growing quickly and all messed up."
Discovered in the 1960s, a quasar (contraction of "quasi-stellar
object") pours out the light of as much as one trillion stars from a
region of space smaller than our solar system. It took more than two
decades of research to come to the conclusion that the gusher of energy
comes from supermassive black holes inside the cores of very distant
galaxies.
The lingering question has been: How do these brilliant beacons turn
on? Now Hubble has provided the best solution. "The new images capture
the transitional phase in the merger-driven black hole scenario,"
Glikman said. "The Hubble images are incredibly beautiful."
"We've been trying to understand why galaxies start feeding their
central black holes, and galaxy collisions are one leading hypothesis.
These observations show that the brightest quasars in the universe
really do live in merging galaxies," said co-investigator Kevin
Schawinski of the Swiss Federal Institute of Technology in Zurich.
Though it had been previously theorized that the mergers of two
galaxies could do the trick, the overwhelming glow of the quasar drowns
out the light of the accompanying galaxy, making the signs of mergers
difficult to see.
Glikman came up with a clever way to use Hubble's sensitivity at
near-infrared wavelengths of light to see the host galaxies. Nature
played a helping hand by producing some quasars that are heavily
shrouded in dust. The dust dims the quasar's visible light so that the
underlying galaxy can be seen.
The quasars light up because the gravitational forces of the merger
rob much of the angular momentum that keeps gas suspended in the disks
of the colliding galaxies. The gas then falls directly toward the
supermassive black hole. The accretion zone around the black hole is so
engorged with fuel it converts it into a gusher of radiation that
blazes across the universe.
Glikman looked for candidate "dust-reddened quasars" in several
ground-based infrared and radio sky surveys. Active galaxies in this
early phase of evolution are predicted to glow brightly across the
entire electromagnetic spectrum, making them detectable in radio and
near-infrared wavelengths that are not as easily obscured as other
radiation.
She then used Hubble's Wide Field Camera 3 to take a detailed look at
the best candidate targets. Glikman looked at the dust-reddened light
of 11 ultra-bright quasars that exist at the peak of the universe's
star-formation era, which was 12 billion years ago. The infrared
capability of Hubble's Wide Field Camera 3 was able to probe deep into
the birth of this quasar era.
The paper will be published in the June 18 issue of the Astrophysical Journal.
Glikman acknowledges the support of the Cottrell College Award through the Research Corporation for Science Advancement.
Contact
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Eilat Glikman
Middlebury College, Middlebury, Vermont
802-443-5980
eglikman@middlebury.edu
Source: HubbleSite
