Detail from map at 9000 light years (3 kiloparsec). The map is coloured according to how much dust lies in each direction in the northern Milky Way. The red/brown areas are dustiest directions. Credit: Sale et al/IPHAS
A team of international astronomers has created a detailed three-dimensional map of the dusty structure of the Milky Way – the star-studded bright disc of our own galaxy – as seen from Earth’s northern hemisphere. The map will be presented by Prof Janet Drew of the University of Hertfordshire at the National Astronomy Meeting (NAM) 2014 in Portsmouth on Monday 23 June.
Dust and gas, which make up the interstellar medium (ISM), fill the space between stars in galaxies. The dust in the ISM is shaped by turbulent flows that form intricate fractal structures on scales ranging from thousands of light years down to hundreds of kilometres. Rather than measuring the dust itself to create the map, the team has used observations of more than 38 million stars to estimate how much starlight has been obscured by the ISM and thus how much dust lies in our line of sight to each star. This ‘extinction’ map derives from the newly released catalogue of the Isaac Newton Telescope Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS), the first digital survey to cover the entire northern Milky Way.
"Because the Solar System is embedded in the disc of the Milky Way, our view of it is choked with dust, with the result we know less about its internal structure than we do about some external galaxies, such as M31 in Andromeda." said Drew, the Principal Investigator for the IPHAS survey. "In this Northern survey, we are mainly looking at the parts of the Galactic disc that lie outside the Sun's orbit around the Galactic Centre. This 3-D map demonstrates with greater force than existing 2-D maps that dust in the outer disc does not trace the Perseus spiral arm and other expected structures in a simple way."
The map shows how extinction builds with distance away from the Sun (typically out to 12,000 light years or more) in any part of the surveyed northern Milky Way. Detail on an angular scales 7 times finer than the angular size of the moon is captured. The fractal nature of the ISM is visible in the map, as are large-scale features, such as star-forming molecular clouds and bubbles of ionized gas around clusters of hot stars.
"We can see a number of specific features, including the Rosette Nebula and the star-forming belt in the Perseus Arm of the Milky Way," said Dr Stuart Sale, who led the team that created the map. "Our location within the Milky Way means that we can study the ISM in far greater detail than for any other galaxy. The knowledge that we gain from studying our own galaxy can subsequently be applied to others."
"IPHAS has been a major part of the Isaac Newton Telescope's programme of observation over the last decade. It is one of several ground-based surveys beginning to provide important new and very large collections of data, complementing ESA's Gaia mission as it starts its work, that are being discussed at NAM 2014. The common goal is to properly unravel the full 3-D spatial organisation of our own Galaxy" said Drew.
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SCIENCE CONTACTS
Prof Janet Drew
IPHAS Survey PI
Centre for Astrophysics Research
University of Hertfordshire
Dr Geert Barentsen
Centre for Astrophysics Research
University of Hertfordshire
Dr Stuart Sale
Rudolf Peierls Centre for Theoretical Physics
University of Oxford
IMAGES
1.
Each panel is a map coloured according to how much dust lies in each
direction in the northern Milky Way, out to a fixed distance. Maps for 3
distances (1, 2 and 3 kiloparsecs or ~3000, ~6000 and ~9000 light
years) are shown, using a colour scale that trends to red/brown for the
dustiest directions. Credit: Sale et al/IPHAS
2.
Detail from map at 9000 light years (3 kiloparsec). The map is
coloured according to how much dust lies in each direction in the
northern Milky Way. The red/brown areas are dustiest directions. Credit:
Sale et al/IPHAS
https://www.ras.org.uk/images/stories/NAM/2014/Drew_3kpc_small.jpg
FURTHER INFORMATION
A 3D extinction map of the Northern Galactic Plane based on IPHAS photometry. Sale et al, MNRAS, 2014, http://arxiv.org/abs/1406.0009
Barentsen et al, MNRAS, 2014, see www.iphas.org/data.shtml
About IPHAS
The
INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS,
www.iphas.org) was carried out at the Isaac Newton Telescope (INT).
IPHAS is a digital survey of the northern Milky Way in two optical/red
colours and narrow-band H-alpha - a filter that picks out the most
prominent line of hydrogen, the most abundant element in the Universe.
The work on this survey began in 2003 in La Palma, and only now is close
enough to completion that most of the ~45000 exposures making up the
survey have been uniformly calibrated. These data are now being made
available to the astronomical community as source catalogues that
measure the brightness of over 200 million objects (nearly all stars)
brighter than ~20th magnitude
The
INT is operated on the island of La Palma by the Isaac Newton Group in
the Spanish Observatorio del Roque de los Muchachos of the Instituto de
Astrofisica de Canarias. All IPHAS data are processed by the Cambridge
Astronomical Survey Unit, at the Institute of Astronomy in Cambridge.
The bandmerged DR2 catalogue was assembled at the Centre for
Astrophysics Research, University of Hertfordshire, supported by STFC
grant ST/J001333/1.
NOTES FOR EDITORS
The
RAS National Astronomy Meeting (NAM 2014) will bring together more than
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