Multiwavelength Milkyway

In this exercise, you will be presented with background information on the topic of interest, including lecture notes. After reviewing that material, you should download and print out the PDF of the problem. Finally with the problem in front of you, open up the image tool and use it to analyse the images in order to answer the questions on the PDF. Write on the printout of the problem and bring it to class.

Components

Background

Milkyway Panel

Click for large image of multiwavelength Milky Way

Introduction

These images of the sky near the Galactic plane have been obtained 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 Space Science Data Operations Office at NASA Goddard Space Flight Center. Each image represents a 360 degree view of the Milky Way within 10 degreesof the plane. 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.

Milkyway: Radio Continuum (408 MHz)

Milkyway Radio Continuum (408MHz)

This image is extracted from the 408 MHz all-sky survey of Haslam et al. (1982). The angular resolution is 0.85 deg. This file was produced at the Astrophysics Data Facility, NASA/GSFC. Contact: S. Digel, digel@gsfc.nasa.gov.

Reference: Haslam, C. G. T., et al. 1982, A&AS, 47, 1

Milkyway: Radio (HI)

Milkyway Radio (HI)

This image is a composite of the Weaver-Williams, Leiden-Green Bank, and Maryland-Parkes H I surveys. The relative calibrations of the surveys were scaled to provide approximate agreement in their regions of overlap. The angular resolution of the image varies, but is typically 0.75-1 degrees. This image was produced at the Astrophysics Data Facility, NASA/GSFC. Contact: S. Digel, digel@gsfc.nasa.gov.

References: Burton, W. B. 1985, A&AS, 62, 365 Kerr, F. J., et al. 1986, A&AS, 66, 373 Weaver, H., & Williams, D. R. W. 1973, A&AS, 8, 1

Milkyway: Radio (CO)

Milkyway Radio (CO)

This image is derived from an updated version of the composite CO survey of Dame et al. (1987). The updated version, available in its entirety from the Astronomical Data Center, contains somewhat more spectra and has a corrected intensity scale. The angular resolution of the image is 0.5 deg (square). This image was produced at the Astrophysics Data Facility, NASA/GSFC. Contact: S. Digel, digel@gsfc.nasa.gov.

Reference: Dame, T. M., et al. 1987, ApJ, 322, 706

Milkyway: Infrared

Milkyway Infrared

This image is derived from the IRAS Sky Survey Atlas (ISSA). Three planes were created at 12, 60, and 100 micron bands. The image here is from the 100 micron band. The plates of the ISSA were reprojected into Galactic coordinates and mosaicked to derive the images. The pixel size is 5 arcmin, approximately the same as angular resolution of the ISSA. The ISSA plates are available from NASA. This image was produced at the Astrophysics Data Facility, NASA/GSFC. Contact: S. Digel, digel@gsfc.nasa.gov.

Reference: Wheelock, S. L. 1994, IRAS Sky Survey Atlas Explanatory Supplement, JPL Publication 94-11 (Pasadena: JPL)

Milkyway: Near Infrared

Milkyway Near Infrared

This image is derived from the solar elongation 90 degree maps for the DIRBE instrument on COBE satellite. Three planes were created at 1.25, 2.2, and 3.5 microns. The 3.5 micron image is shown here. The maps are reprojected from the CSC coordinates of the original file and gridded on an 0.25 deg grid. The DIRBE beam size is 0.7 deg, and the pixel size in the original files is 0.32 deg. For information about the original datasets, see the COBE home page. This image was produced at the Astrophysics Data Facility, NASA/GSFC. Contact: S. Digel, digel@gsfc.nasa.gov.

Reference: Hauser et al. 1995, COBE DIRBE Explanatory Supplement, Vers. 2.0, COBE Reference Publication 95-A (Greenbelt, MD: NASA/GSFC)

Milkyway: Optical

Milkyway Optical

Composite photomosaic of the Milky Way constructed from scanned images taken by Laustsen, Madsen, & West (1987), 'Exploring the Southern Sky' (Berlin: Springer). The following is from Laustsen et al.: "The panorama is made from eight wide-angle photographs. The camera used was a Hasselblad SWC with a 1:4.5/38 mm Biogon lens. The plate format is 60 x 60 mm, and the 56 x 56 mm, square field covers about 72 x 72 degrees. The original scale at the centre of the field is 1.5 degrees per mm, while at the edge it is about 1.2 degrees per mm. This difference in scale is due to the fact that the camera field is flat, while distances in the sky are measured along great circles on a sphere. As a result of this it is not possible to fit the eight frames together perfectly to make a continuous panorama. Only in a narrow band along the great circle of the Milky Way is this scaling effect small enough to allow a good fit.

Outside this band, it is impossible to avoid a discontinuity between neighboring fields. The original plates were enlarged by a factor of 4.2, and when the outermost parts of the fields were cut away, the resulting average scale of the full-size panorama became approximately 3 mm per degree on the sky. The angular resolution on the plates is close to one arcminute, which means that two faint stars separated by one arc- minute will just be recognizable as two separate stars. This resolution is about the same as that of the human eye. The limiting magnitude is around 11th visual magnitude...The northern Milky Way fields were photographed in September 1984 at the Roque de los Muchachos Observatory on La Palma in the Canary Islands. Exposure times were 60 minutes and the Hasselblad camera was mounted on a 60-cm telescope belonging to the Royal Swedish Academy. The telescope motion compensated for the daily rotation of the sky, so that the camera always pointed in the same direction, relative to the sky.

The southern fields were exposed at the ESO La Silla Observatory in March 1985. Here the exposure times were 90 minutes and the camera was mounted on the GPO double astrograph. The increase in exposure time was needed to reach the same limiting magnitude because the sensitivity of the photographic material used in 1985 was less than that of the material used in 1984." The image in this FITS file was derived at the Astrophysics Data Facility (ADF), NASA/GSFC (http://adf.gsfc.nasa.gov/) from scanned versions of the enlarged photographic plates, kindly provided by C. Madsen (ESO). The scanning resolution was 600 pixels per inch. At the ADF, a coordinate system was established relative to the positions of stars with Mv <= 5.0 in the Bright Star catalog (5th Revised Ed., Hoffleit & Warren 1991; ftp://adc.gsfc.nasa.gov/pub/adc/archives/catalogs/5/5050/). The pixel positions (x,y) of typically fifty stars in the range |b| < 10 deg for each photograph were measured and polynomial models for the Galactic coordinates l(x,y) and b(x,y) were fit.

A linear model, allowing only for scaling and rotation of each photograph, yielded an rms residual of 24 arcmin for the 427 stars total (|b| < 10 deg) measured on the eight photographs. The residuals were systematic and ranged up to 2 deg. The model adopted for use here, fit separately for each photograph, included all terms up to third order in x and y, for a total of 10 parameters including cross terms. The resulting coordinate distortion maps were smooth and yielded rms residuals of less than 2 arcmin for the 427 stars. The distortion maps were used to reproject the eight photographs onto uniform, rectangular grids in Galactic coordinates with 72 pixels per degree and latitude range |b| < 10 deg. After reprojection, the photographs were mosaicked and their uncalibrated intensity scales adjusted by one factor per photograph to minimize the discontinuities across boundaries. Exposure variations within photographs remain uncompensated. Owing to the reprojection to Galactic coordinates, some narrow gaps are present between photographs.

These have typical widths less than 0.3 deg and are filled a uniform gray. A line drawn on the prints at b = 0 deg was removed by interpolation; the interpolated band is 13 pixels wide.

Contact: S. Digel, digel@gsfc.nasa.gov.

Reference:

Milkyway: X-rays

Milkyway X-rays

This image is derived from the ROSAT All Sky Survey (RASS) made, with the PSPC. Three images in the three RASS bands: 0.25, 0.75, and 1.5 keV. The image shown here is from the 1.5 keV band. The maps are reprojected from the Aitoff projection of the distributed version of the RASS, on a 0.25 deg grid. The angular resolution is 1.25 deg. The original dataset is available from the ROSAT web site. This image was produced at the Astrophysics Data Facility, NASA/GSFC.

Contact: S. Digel, digel@gsfc.nasa.gov.

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

Milkyway: Gamma Rays

Milkyway Gamma Rays

This image is derived from a composite of all CGRO/EGRET data for Phases 1-3 for the energy range E > 100 MeV. The viewing periods in Phases 1-3 were combined using photons within 30 deg of the instrument axis. The effective PSF of EGRET for E > 100 MeV has a FWHM of 1.2 deg, but with a broad tail. The small- scale fluctuations in intensity are statistical. The original data for each viewing period are available from NASA. This image was produced at the Astrophysics Data Facility, NASA/GSFC.

Contact: S. Digel, digel@gsfc.nasa.gov.

Reference: Thompson, D. J. et al. 1993, ApJS, 86, 629

PDF of Assignment

Print out the following PDF file, print out and answer using the interactive tool below.

PDF of Assignment

Milkyway: Interactive Comparison

Open Interactive Comparison Tool