Astrophysics Data Facility

Multiwavelength Milky Way

This web site is intended to be both educational and useful to the scientific community. We are developing additional astronomy educational resources, some related to this one, which might interest you.

Seven of the nine images below are low-resolution versions of the corresponding image in the Multiwavelength Milky Way poster.

For an expanded view of any feature, click on the region of interest. Two levels of increased detail are available. The images are the same as used in the poster, except the radio continuum images and an improved optical image are included here. Also the, number of individual colors used is limited here. The images are also available on 35-mm slides and in printable form, in case you would like to make a viewgraph.

**NEW: Multiwavelength ALL-SKY Images are now available as a 35-mm slide set.**

    Radio (0.4 GHz) 

    Atomic Hydrogen 

NEW Radio (2.7 GHz) 

 Molecular Hydrogen 

           Infrared 

      Near Infrared 

            Optical 

              X-Ray 

          Gamma Ray 

        Finder

The Images

The Milky Way Galaxy is generally considered an Sbc-type galaxy. It has a central bulge of stars and spiral arms of gas and stars in a disk. We view the Milky Way essentially edge-on from our perspective near the plane of the disk and 28,000 light years from the Galactic center. In recent decades, Galactic astronomy has benefitted from a tremendous broadening of coverage of the electromagnetic spectrum by ground-based and spaced-based instruments. Presented above are images of the sky near the Galactic plane in spectral lines and continuum bands spanning a frequency range of more than 14 orders of magnitude. The images are derived from several space and ground-based surveys, many of which are available through the Astrophysics Data Facility and the Astronomical Data Center of the Space Science Data Operations Office at NASA Goddard Space Flight Center.

Each image represents a 360° false color view of the Milky Way within 10° of the plane; the images are in Galactic coordinates with the direction of the Galactic center in the center of each. For scale, the vertical dimension of each image is forty times the angular diameter of the full moon on the sky; the areas shown represent about one-sixth of the entire sky. The image in the finder chart is derived from the IRAS 100 micron map with COBE DIRBE 3.5 micron contours overlaid.

Original Data Files

For users interested in quantitative examination of the maps, the actual data files corresponding to most of the images are available for retrieval by anonymous ftp. These were derived from the surveys cited below and in most cases were transformed and interpolated to lie on regular grids in Galactic coordinates, with sampling appropriate to the resolution.

The files are not known to contain errors, but the user is advised to check any scientific results against the data from the original sources. The user is also referred to the original references for descriptions of backgrounds, sensitivities, resolutions, and other considerations relevant to the interpretation of the data.

The files are compressed and in FITS image format, a binary format commonly used in astronomy. The infrared, near-infrared, and X-ray images contain three planes, one for each band represented in the corresponding image in the poster. The optical image is divided into four parts, by Galactic quadrant, because it is very large. Descriptions of the FITS standard and links to software for reading and displaying FITS images are available from the FITS Support Office at NASA/GSFC.

Notes on the production of the individual maps are included in the headers of the files.

Digital versions of several of the original surveys may be accessed, and images of selected fields constructed, online via the SkyView service. The complete data for some of the surveys are available via the World Wide Web; links are listed in the relevant sections.

Poster Version

Seven of these images (all but the Radio Continuum map) are available on a colorful poster by request. The poster measures approximately 55 cm x 80 cm and is printed on heavy paper stock. Click here to see a low-resolution picture of the poster (166 kbytes).

Slide Set

The images are also available as a set of ten 35-mm slides, for a nominal fee. The set consists of full-resolution versions of the individual astronomical images shown above, including the finder diagram, plus a composite of all the images. Contact the Coordinated Request User Support Office (request@nssdca.gsfc.nasa.gov) to order the set.

Viewgraph

If you would like to make a viewgraph for an educational or scientific presentation, an image showing the Milky Way at 8 wavelengths is available in the following formats:

Postscript [10 MB]
JPEG [1 MB]

Radio Continuum (408 MHz)

Intensity of radio continuum emission from hot, ionized gas in the Milky Way, from surveys with ground-based radio telescopes (Jodrell Bank MkI and MkIA, Bonn 100 meter, and Parkes 64 meter). At this frequency, most of the emission is from the scattering of free electrons in interstellar plasmas. Near some discrete sources, such as the supernova remnant Cas A near 110 degrees longitude, a significant fraction of the emission also comes from electrons accelerated in strong magnetic fields. The emission from Cas A is so intense that the diffraction pattern of the support legs for the radio receiver on the telescope is visible as a 'cross' shape.

Reference:
Haslam, C. G. T., Salter, C. J., Stoffel, H., & Wi lson, W. E. 1982, Astron. Astrophys. Suppl. Ser., 47, 1

Frequency: 408 MHz

Intensities: 10-4250 K

Angular resolution: 51'

Atomic Hydrogen

Column density of atomic hydrogen, derived on the assumption of optically thin emission, from radio surveys of the 21-cm spectral line of hydrogen. On a large scale the 21-cm emission traces the "warm" interstellar medium, which is organized into diffuse clouds of gas and dust that have sizes of up to hundreds of light years. Most of the image is based on the Leiden-Dwingeloo Survey of Galactic Neutral Hydrogen, made available by the authors in advance of publication. This survey was conducted over a period of 4 years using the Dwingeloo 25-m radio telescope, operated by the Netherlands Foundation for Research in Astronomy. The data were corrected for sidelobe contamination in collaboration with the University of Bonn.

References:
Burton, W. B. 1985, Astron. Astrophys. Suppl. Ser., 62, 365
Hartmann, Dap, & Burton, W. B., "Atlas of Galactic Neutral Hydrogen," Cambridge Univ. Press, (1997, book and CD-ROM)
Kerr, F. J., et al. 1986, Astron. Astrophys. Suppl. Ser.

Frequency: 1.4 GHz

Column densities: 10 x 10²⁰ -230 x 10²⁰ cm^-2

Angular resolution: 45-60'

Radio Continuum (2.4-2.7 GHz)

Intensity of radio continuum emission from hot, ionized gas and high-energy electrons in the Milky Way, from surveys with both the Bonn 100 meter, and Parkes 64 meter radio telescopes. Unlike the other views of our Galaxy presented here, these data extend to latitudes of only 5° from the Galactic midplane. The majority of the bright emission seen in the image is from hot, ionised regions, or is produced by energetic electrons moving in magnetic fields. The higher resolution of this image, relative to the 408 MHz picture above, shows Galactic objects in more detail. Note that the bright "ridge" of Galactic radio emission, appearing prominently in the 408 MHz image, has been subtracted here in order to show Galactic features and objects more clearly.

References:
Duncan, A. R., Stewart, R. T., Haynes, R. F., & Jones, K. L. 1995, Mon. Not. Roy. Astr. Soc., 277, 36
Fuerst, E., Reich, W., Reich, P., & Reif, K. 1990, Astron. Astrophys. Suppl. Ser., 85, 691
Reich, W., Fuerst, E., Reich, P., & Reif, K. 1990, Astron. Astrophys. Suppl. Ser., 85, 633

Online data access:
Survey data from the Max-Planck-Institut fuer Radioastronomie

Frequency: 2.4-2.7 GHz

Intensities: 0-430 K

Angular resolution: 10.4'

Molecular Hydrogen

Column density of molecular hydrogen inferred from the intensity of the J = 1-0 spectral line of carbon monoxide, a standard tracer of the cold, dense parts of the interstellar medium. Such gas is concentrated in the spiral arms in discrete "molecular clouds" and most molecular clouds are sites of star formation. The molecular gas is predominantly H₂, but H₂ is difficult to detect directly at interstellar conditions and CO, the second most abundant interstellar molecule, is observed as a surrogate. The column densities were derived on the assumption of a constant proportionality between the column density of H₂ and the intensity of the CO emission. Black areas in the image indicate regions not yet surveyed for CO.

References:
Dame, T. M., et al. 1987, Astrophysical Journal, 322, 706
Digel, S. W., & Dame, T. M. 1995, unpublished update

Online data access:
CO data from ADC archives

Frequency: 115 GHz

Column densities: 12 x 10²⁰ -285 x 10²⁰ cm^-2

Angular resolution: 30'

Infrared

Composite mid and far-infrared intensity observed by the Infrared Astronomical Satellite (IRAS) in 12, 60, and 100 micron wavelength bands. The images are encoded in the blue, green, and red color ranges, respectively. Most of the emission is thermal, from interstellar dust warmed by absorbed starlight, including that in star-forming regions embedded in interstellar clouds. The image here is a mosaic of IRAS Sky Survey Atlas plates; emission from interplanetary dust in the solar system, the "zodiacal emission," was modeled and subtracted in the production of the Atlas at the Infrared Processing and Analysis Center (IPAC). The black, wedge-shaped areas indicate gaps in the IRAS survey.

Reference:
Wheelock, S. L., et al. 1994, IRAS Sky Survey Atlas Explanatory Supplement, JPL Publication 94-11 (Pasadena: JPL) Order: CASI HC A08/MF A02

Online data access:
IRAS pages at IPAC
ADF/IRAS interface to all released IRAS data products

Frequencies: 3.0 x 10³-25 x 10³ GHz

Intensities: 0.25-100 (12 microns), 1.5-750 (60 microns), 12-750 MJy sr^-1 (100 microns)

Angular resolution: 5'

Near Infrared

Composite near-infrared intensity observed by the Diffuse Infrared Background Experiment (DIRBE) instrument on the Cosmic Background Explorer (COBE) in the 1.25, 2.2, and 3.5 micron wavelength bands. The images are encoded in the blue, green, and red color ranges, respectively. Most of the emission at these wavelengths is from cool, low-mass K stars in the disk and bulge of the Milky Way. Interstellar dust does not strongly obscure emission at these wavelengths; the maps trace emission all the way through the Galaxy, although absorption in the 1.25 micron band is evident in the general direction of the Galactic center.

Reference:
Hauser, M. G., Kelsall, T., Leisawitz, D., & Weiland, J. 1995, COBE Diffuse Infrared Background Experiment Explanatory Supplement, Version 2.0, COBE Ref. Pub. No. 95-A (Greenbelt, MD: NASA/GSFC)

Online data access:
COBE data from the COBE Home Page at the ADF

Frequencies: 86 x 10³-240 x 10³ GHz

Intensities: 0.5-9 (1.25 microns), 0.35-20 (2.2 microns), 0.22-4.5 MJy sr^-1 (3.5 microns)

Angular resolution: 42'

Optical

Intensity of visible light from a mosaic of wide-field photographs by Laustsen, Madsen, & West (1987). Scanned images of the original prints were kindly provided by C. Madsen (European Southern Observatory, cmadsen@eso.org). The images are copyright (1987) by ESO. Owing to the strong obscuration by interstellar dust the light is primarily from stars within a few thousand light-years of the Sun, nearby on the scale of the Milky Way, which has a diameter on the order of 100,000 light years. Nebulosity from hot, low-density gas is widespread in the image. Dark patches are due to absorbing dust clouds, which are evident in the Molecular Hydrogen and Infrared maps as emission regions. The mosaic is constructed from eight photographs. Narrow, vertical gaps are evident between some photographs, as are slight discontinuities in brightness. This image supersedes the optical image in the poster. The original image, a mosaic of Digitized Sky Survey plates, poorly depicts the large-scale features.

Reference:
Laustsen, S., Madsen, C., West, R. 1987, Exploring the Southern Sky, (Berlin: Springer-Verlag)

Online data access:
Data files (one for each quadrant of longitude) are available in FITS format by anonymous ftp

Frequency: 460 x 10³ GHz

Intensities: uncalibrated

Angular resolution: 1'

X-Ray

Composite X-ray intensity observed by the Position-Sensitive Proportional Counter (PSPC) instrument on the Röntgen Satellite (ROSAT). Images in three broad, soft X-ray bands centered at 0.25 , 0.75, and 1.5 keV are encoded in the red, green, and blue color ranges, respectively. In the Milky Way, extended soft X-ray emission is detected from hot, shocked gas. At the lower energies especially, the interstellar medium strongly absorbs X-rays, and cold clouds of interstellar gas are seen as shadows against background X-ray emission. Color variations indicate variations of absorption or of the temperatures of emitting regions. The black regions indicate gaps in the ROSAT survey.

Reference:
Snowden, S. L., et al. 1995 Astrophys. J., 454, 643

Online data access:
ROSAT All-Sky Survey at MPE
ROSAT data archives at the HEASARC

Frequency: 60-360 x 10⁶ GHz

Intensities: 0-20 (0.25 keV), 0-10 (0.75 keV), 0-10 x 10^-4 photons arcmin^-2 s^-1 (1.5 keV)

Angular resolution: 115'

Gamma Ray

Intensity of high-energy gamma-ray emission observed by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory (CGRO). The image includes all photons with energies greater than 100 MeV. At these extreme energies, most of the celestial gamma rays originate in collisions of cosmic rays with hydrogen nuclei in interstellar clouds. The bright, compact sources near Galactic longitudes 185°, 195°, and 265° indicate high-energy phenomena associated with the Crab, Geminga, and Vela pulsars, respectively.

References:
Hunter, S. D., et al. 1997, Astrophys. J., 481, 205
Thompson, D. J., et al. 1996, Astrophys. J. Suppl., 107, 227

Online data access:
EGRET instrument team's Home Page
EGRET data from the Compton Observatory SSC

Frequencies: >2.4 x 10¹³ GHz

Intensities: 4 x 10^-5 - 93 x 10^-5 photons cm^-2 s^-1 sr^-1

Angular resolution: ~120'

Finder Diagram

Major structural features of the Milky Way (red), optical H II regions (blue), radio sources (green), and OB associations (purple) are labeled in the finder chart. The image in the finder chart is derived from the IRAS 100 micron map of intensity with contours from the COBE DIRBE 3.5 micron map overlaid. The axes of the finder diagram are labelled in degrees of Galactic longitude and latitude.

Canadian Galactic Plane Survey

Multiwavelength Atlas of Galaxies

NRAO Galactic Plane Surveys at 8.35 and 14.35 GHz

Astronomical Survey Projects