Tuesday, June 24, 2014

3D map shows dusty structure of the Milky Way

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.


NAM 2014 press office landlines: +44 (0) 02392 845176, +44 (0)2392 845177, +44 (0)2392 845178

Robert Massey

Royal Astronomical Society

Mob: +44 (0)794 124 8035

Anita Heward

Royal Astronomical Society

Mob: +44 (0)7756 034 243

Keith Smith

Royal Astronomical Society


Prof Janet Drew


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


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


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
The map can be explored interactively on the IPHAS website (http://www.iphas.org/extinction/)


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.


The RAS National Astronomy Meeting (NAM 2014) will bring together more than 600 astronomers, space scientists and solar physicists for a conference running from 23 to 26 June in Portsmouth. NAM 2014, the largest regular professional astronomy event in the UK, will be held in conjunction with the UK Solar Physics (UKSP), Magnetosphere Ionosphere Solar-Terrestrial physics (MIST) and UK Cosmology (UKCosmo) meetings. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and the University of Portsmouth. Meeting arrangements and a full and up to date schedule of the scientific programme can be found on the official website at http://www.nam2014.org and via Twitter @RASNAM2014

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