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Planck
 
February 13, 2012


PLANCK ALL-SKY IMAGES SHOW COLD GAS AND STRANGE HAZE

  The mysterious Galactic Haze seen by Planck Credit: ESA/Planck Collaboration   The mysterious Galactic Haze seen by Planck

This all-sky image shows the spatial distribution over the whole sky of the galactic haze at 30 and 44 GHz, extracted from the Planck observations. In addition to this component, other foreground components such as charged particles accelerated radially, known as synchrotron radiation, thermal dust, spinning dust, and extragalactic point sources contribute to the total emission detected by Planck at these frequencies. The prominent empty band across the plane of the galaxy corresponds to the mask that has been used in the analysis of the data to exclude regions with strong foreground contamination due to the galaxy's diffuse emission. The mask also includes strong point-like sources located over the whole sky.

The galactic haze is the infinity-like symbol seen around the galactic center, and its spectrum is similar to that of synchrotron emission, a type of non-thermal radiation generated by charged particles. However, compared to the synchrotron emission seen elsewhere in the Milky Way, the galactic haze has a "harder" spectrum, meaning that its emission does not decline as rapidly with increasing frequency. Diffuse synchrotron emission in the galaxy is interpreted as radiation from highly energetic electrons that have been accelerated in shocks created by supernova explosions.

Several explanations have been proposed for the unusual shape of the haze's spectrum, including enhanced supernova rates, galactic winds and even annihilation of dark-matter particles. Thus far, none of them have been confirmed and the issue remains open.
 
 

New images from the Planck mission show previously undiscovered islands of star formation and a mysterious haze of microwave emissions in our Milky Way galaxy. The views give scientists new treasures to mine and take them closer to understanding the secrets of our galaxy.

Planck is a European Space Agency mission with significant NASA participation.

"The images reveal two exciting aspects of the galaxy in which we live," said Planck scientist Krzysztof M. Gorski from NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Warsaw University Observatory in Poland. "They show a haze around the center of the galaxy, and cold gas where we never saw it before."

The new images show the entire sky, dominated by the murky band of our Milky Way galaxy. One of them shows the unexplained haze of microwave light previously hinted at in measurements by NASA's Wilkinson Microwave Anisotropy Probe (WMAP).

  Galactic Haze seen by Planck and Galactic 'bubbles' seen by Fermi Credit: ESA/Planck Collaboration (microwave); NASA/DOE/Fermi LAT/D. Finkbeiner et al. (gamma rays)   Galactic Haze seen by Planck and Galactic 'bubbles' seen by Fermi

This all-sky image shows the distribution of the galactic haze seen by ESA's Planck mission at microwave frequencies superimposed over the high-energy sky, as seen by NASA's Fermi Gamma-ray Space Telescope.

The Planck data (shown here in red and yellow) correspond to the haze emission at frequencies of 30 and 44 GHz, extending from and around the galactic center.

The Fermi data (shown here in blue) correspond to observations performed at energies between 10 and 100 gigaelectronvolt and reveal two bubble-shaped, gamma-ray emitting structures extending from the galactic center.

Synchrotron emission, a type of non-thermal radiation generated by charged particles, associated with the galactic haze seen by Planck, exhibits distinctly different characteristics from the synchrotron emission seen elsewhere in the Milky Way. Diffuse synchrotron emission in the galaxy is interpreted as radiation from highly energetic electrons that have been accelerated in shocks created by supernova explosions. Compared to this well-studied emission, the galactic haze has a "harder" spectrum, meaning that its emission does not decline as rapidly with increasing frequency.

Several explanations have been proposed for this unusual behavior, including enhanced supernova rates, galactic winds and even annihilation of dark-matter particles. Thus far, none of them have been confirmed and the issue remains open.
 
 

"The haze comes from the region surrounding the center of our galaxy and looks like a form of light energy produced when electrons accelerate through magnetic fields," said Davide Pietrobon, another JPL Planck scientist.

"We're puzzled though, because this haze is brighter at shorter wavelengths than similar light emitted elsewhere in the galaxy," added Gorski.

Several explanations have been proposed for this unusual behaviour.

"Theories include higher numbers of supernovae, galactic winds and even the annihilation of dark-matter particles," said Greg Dobler, a Planck collaborator from the University of California in Santa Barbara, Calif. Dark matter makes up about a quarter of our universe, but scientists don't know exactly what it is.

The second all-sky image is the first map to show carbon monoxide over the whole sky. Cold clouds with forming stars are predominantly made of hydrogen molecules, difficult to detect because they do not readily emit radiation. Carbon monoxide forms under similar conditions, and though it is rarer, the gas emits more light. Astronomers can use carbon monoxide to identify the clouds of hydrogen where stars are born.

  All-sky image of molecular gas and three molecular cloud complexes seen by Planck Credit: ESA/Planck Collaboration   All-sky image of molecular gas and three molecular cloud complexes seen by Planck

This all-sky image shows the distribution of carbon monoxide (CO), a molecule used by astronomers to trace molecular clouds across the sky, as seen by Planck.

Molecular clouds, the dense and compact regions throughout the Milky Way where gas and dust clump together, represent one of the sources of foreground emission seen by Planck. The vast majority of gas in these clouds consists of molecular hydrogen, and it is in these cold regions that stars are born. Since cold molecular hydrogen does not easily radiate, astronomers trace these cosmic cribs across the sky by targeting other molecules, which are present there in very low abundance but radiate quite efficiently. The most important of these tracers is CO, which emits a number of rotational emission lines in the frequency range probed by Planck's High Frequency Instrument.

Emission lines affect a very limited range of frequencies compared to the broad range to which each of Planck's detectors is sensitive, and are usually observed using spectrometers. But some CO lines are so bright, they actually dominate the total amount of light collected by certain detectors on Planck when they are pointed towards a molecular cloud.

This is the first all-sky map of CO ever compiled. The largest CO surveys thus far have concentrated on mapping the full extent of the Galactic Plane, where most clouds are concentrated, leaving large areas of the sky unobserved.
 
 

Surveys of carbon monoxide undertaken with radio telescopes on the ground are time-consuming, so they are limited to portions of the sky where clouds of molecules are already known or expected to exist. Planck scans the whole sky, allowing astronomers to detect the gas where they weren't expecting to find it.

Planck's primary goal is to observe the Cosmic Microwave Background, the relic radiation from the Big Bang, and to extract its encoded information about what our universe is made of, and the origin of its structure.

This relic radiation can only be reached once all sources of foreground emission, such as the galactic haze and the carbon monoxide signals, have been identified and removed.

"The lengthy and delicate task of foreground removal provides us with prime datasets that are shedding new light on hot topics in galactic and extragalactic astronomy alike," said Jan Tauber, Planck project scientist at the European Space Agency.

Planck's first findings on the Big Bang's relic radiation are expected to be released in 2013. The new results are being presented this week at an international astronomy conference in Bologna, Italy.

NASA's Planck Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for both of Planck's science instruments. European, Canadian and U.S. Planck scientists will work together to analyze the Planck data.

JPL is managed for NASA by the California Institute of Technology in Pasadena.

More information on Planck is online at http://www.nasa.gov/planck and http://www.esa.int/planck.

The NASA Planck data archive is at http://irsa.ipac.caltech.edu/Missions/planck.html.

Planck is a European Space Agency mission, with significant participation from NASA. NASA's Planck Project Office is based at JPL. JPL contributed mission-enabling technology for both of Planck's science instruments. European, Canadian, and U.S. Planck scientists will work together to analyze the Planck data. JPL is managed for NASA by the California Institute of Technology in Pasadena.

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

Markus Bauer +31 71 565 6799
European Space Agency
markus.bauer@esa.int

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