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TOPIC: Milky Way
Blobrana


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RE: Milky Way
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Title: Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
Authors: Meng Su, Tracy R. Slatyer, Douglas P. Finkbeiner

Data from the Fermi-LAT reveal two large gamma-ray bubbles, extending 50 degrees above and below the Galactic centre, with a width of about 40 degrees in longitude. The gamma-ray emission associated with these bubbles has a significantly harder spectrum (dN/dE ~ E^-2) than the IC emission from electrons in the Galactic disk, or the gamma-rays produced by decay of pions from proton-ISM collisions. There is no significant spatial variation in the spectrum or gamma-ray intensity within the bubbles, or between the north and south bubbles. The bubbles are spatially correlated with the hard-spectrum microwave excess known as the WMAP haze; the edges of the bubbles also line up with features in the ROSAT X-ray maps at 1.5-2 keV. We argue that these Galactic gamma-ray bubbles were most likely created by some large episode of energy injection in the Galactic centre, such as past accretion events onto the central massive black hole, or a nuclear starburst in the last ~10 Myr. Dark matter annihilation/decay seems unlikely to generate all the features of the bubbles and the associated signals in WMAP and ROSAT; the bubbles must be understood in order to use measurements of the diffuse gamma-ray emission in the inner Galaxy as a probe of dark matter physics. Study of the origin and evolution of the bubbles also has the potential to improve our understanding of recent energetic events in the inner Galaxy and the high-latitude cosmic ray population.

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Blobrana


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NASA'S Fermi Telescope Discovers Giant Structure In Our Galaxy

NASA's Fermi Gamma-ray Space Telescope has unveiled a previously unseen structure centred in the Milky Way. The feature spans 50,000 light-years and may be the remnant of an eruption from a supersized black hole at the centre of our galaxy.
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Blobrana


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Astronomers Find Giant, Previously Unseen Structure in our Galaxy

NASA's Fermi Gamma-ray Space Telescope has unveiled a previously unseen structure centred in the Milky Way -- a finding likened in terms of scale to the discovery of a new continent on Earth. The feature, which spans 50,000 light-years, may be the remnant of an eruption from a supersized black hole at the center of our galaxy.

"What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center. We don't fully understand their nature or origin" - Doug Finkbeiner, an astronomer at the Harvard-Smithsonian Centre for Astrophysics (CfA) in Cambridge, Mass., who first recognised the feature. "

At more than 100 degrees across, the structure spans more than half of the sky, from the constellation Virgo to the constellation Grus. It may be millions of years old.
A paper on the findings will appear in an upcoming issue of The Astrophysical Journal.

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Blobrana


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Title: The Fermi Haze: A Gamma-Ray Counterpart to the Microwave Haze
Authors: Gregory Dobler (KITP/UCSB, Harvard/CfA), Douglas P. Finkbeiner (Harvard/CfA), Ilias Cholis (NYU), Tracy R. Slatyer (Harvard/CfA), Neal Weiner (NYU)
(Version v2)

The Fermi Gamma-Ray Space Telescope reveals a diffuse inverse Compton signal in the inner Galaxy with a similar spatial morphology to the microwave haze observed by WMAP, supporting the synchrotron interpretation of the microwave signal. Using spatial templates, we regress out pi0 gammas, as well as IC and bremsstrahlung components associated with known soft-synchrotron counterparts. We find a significant gamma-ray excess towards the Galactic centre with a spectrum that is significantly harder than other sky components and is most consistent with IC from a hard population of electrons. The morphology and spectrum are consistent with it being the IC counterpart to the electrons which generate the microwave haze seen at WMAP frequencies. In addition, the implied electron spectrum is hard; electrons accelerated in supernova shocks in the disk which then diffuse a few kpc to the haze region would have a softer spectrum. We describe the full sky Fermi maps used in this analysis and make them available for download.

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Blobrana


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NASA's Fermi Finds Giant, Previously Unseen Structure In Our Galaxy

NASA will hold a media teleconference at 2:30 p.m. EST on Tuesday, Nov. 9, to discuss a new discovery by the Fermi Gamma-ray Space Telescope. Gamma rays are the highest-energy form of light. The soon-to-be published findings include the discovery of enormous but previously unrecognised "gamma-ray bubbles" centred in the Milky Way.
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Blobrana


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Arches cluster
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Title: Disks in the Arches cluster -- survival in a starburst environment
Authors: Andrea Stolte, Mark Morris, Andrea Ghez, Tuan Do, Jessica Lu, Shelley Wright, Christopher Ballard, Elizabeth Mills, Keith Matthews

Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic centre reveal a significant population of near-infrared excess sources. We combine the L'-band excess observations with K'-band proper motions, to confirm cluster membership of excess sources in a starburst cluster for the first time. The robust removal of field contamination provides a reliable disk fraction down to our completeness limit of H=19 mag, or about 5 Msun at the distance of the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable proper motion measurements, all of which are proper motion members of the Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources reveals strong CO bandhead emission, which we interpret as the signature of dense circumstellar disks. The detection of strong disk emission from the Arches stars is surprising in view of the high mass of the B-type main sequence host stars of the disks and the intense starburst environment. We find a disk fraction of 6 ±2% among B-type stars in the Arches cluster. A radial increase in the disk fraction from 3 to 10% suggests rapid disk destruction in the immediate vicinity of numerous O-type stars in the cluster core. A comparison between the Arches and other high- and low-mass star-forming regions provides strong indication that disk depletion is significantly more rapid in compact starburst clusters than in moderate star-forming environments.

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Blobrana


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U.B.C. astronomer probes 'archaeology' of Milky Way

New Canadian-led research that uses NASA's Hubble telescope to examine the age of elderly stars is shedding new light on how the Milky Way was "put together."
The study is being conducted by a team of 13 researchers in Canada, the United States and Australia to learn when exactly the centre of our galaxy developed compared to the rest of the Milky Way.
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Blobrana


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Bursting 'bubbles' the origin of galactic gas clouds

Their study explains the origin of these clouds for the first time.
Swinburne University PhD student Alyson Ford (now at the University of Michigan) and her supervisors; Dr Naomi McClure-Griffiths (CSIRO Astronomy and Space Science) and Felix Lockman (US National Radio Astronomy Observatory), have made the first detailed observations of 'halo' gas clouds in our Galaxy.
Just as Earth has an atmosphere, the main starry disk of our Galaxy is surrounded by a thinner halo of stars, gas and 'dark matter'.
The halo clouds skim the surface of our Galaxy, sitting 400 to 10 000 light-years outside the Galactic disk. They are big: an average-sized cloud contains hydrogen gas 700 times the mass of the Sun and is about 200 light-years across.
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Blobrana


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H II regions
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Astronomers Discover New Star-Forming Regions in Milky Way

Astronomers studying the Milky Way have discovered a large number of previously unknown regions where massive stars are being formed. Their discovery, made with the help of NASA's Spitzer Space Telescope, provides important new information about the structure of our home galaxy and promises to yield new clues about its composition.
The star-forming regions the astronomers sought, called H II regions, are sites where hydrogen atoms are stripped of their electrons by intense radiation from massive, young stars. To find these regions, hidden from visible-light detection by the Milky Way's gas and dust, the researchers used infrared and radio telescopes.
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Blobrana


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Astronomers using NASA's Spitzer Space Telescope say they have discovered a number of previously unknown regions where massive stars are forming.
The astronomers said the star-forming areas, called "H II regions," are sites where hydrogen atoms are stripped of their electrons by intense radiation from massive, young stars. To find the regions, which are hidden from visible-light detection by the Milky Way's gas and dust, the researchers said they used infrared and radio telescopes.
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