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The IRAS Galaxy Atlas (IGA) 

Final Report 

NASA/Goddard Contract NAS5-32642 

PI: Thomas A. Prince, Caltech 
December 15, 1999 


After its launch in 1983, IRAS conducted the first all-sky 
survey of infrared emission, and fundamentally changed our view 
of many astrophysical phenomena including star formation, 
Galactic structure, and galaxy evolution. IRAS remains the only 
full-sky infrared sky-survey obtained to date and thus 
represents a unique data set for astronomical research. 

Shortly after the IRAS mission, an atlas of the entire sky 
was produced, having a resolution of about 5 minutes of arc 
(about 1/1 2th of a degree). This atlas was produced using 
straightforward image processing algorithms. In the late 1980’s 
it was realized that more sophisticated algorithms could extract 
considerably better spatial resolution from the data, as fine as 1 
minute of arc (1 /60th of a degree), allowing resolution of 
features 25 times smaller in terms of angular area. These 
algorithms were based on maximum entropy and. maximum 
correlation techniques, and were computationally much more 
intensive than the algorithms used to produce the original IRAS 
sky atlas. One widely used algorithm was the HIRES algorithm 
[ 1 ). 

The computational demands of the advanced image 
processing algorithms prevented their widespread applications to 
the IRAS data and also the production of a new IRAS sky atlas 
with greatly improved angular resolution. Recognizing this fact, 
in 1993 we proposed a project to NASA having the goal of 
producing a new infrared map of our Galaxy. In particular, we 
proposed to reprocess the IRAS data taken in the early 1980’s 
using modern image processing algorithms and the large Intel 
parallel computers of the Center for Advanced Computing 
Research (at that time called the Caltech Concurrent 
Supercomputing Facilities - CCSF). The rationale was simple: 
what took approximately 100 days on a typical workstation would 
take less than a day on the multi-processor parallel computers, 
thus making a high-resolution infrared atlas of the Galaxy 
feasible. 



The first attempt to process a large (6 degree x 6 degree)' 
field with the higher resolution was a technical success but an 
aesthetic failure. While we clearly demonstrated high resolution, 
high efficiency and high throughput using parallel computers, the 
resulting image of a molecular cloud complex in the constellation 
of Ophiuchus did not look particularly good. Although the HIRES 
image processing algorithm had worked well on small-size fields, 
the large Ophiuchus image showed numerous distracting large- 
scale artifacts, in particular prominent “stripes” due to changes 
in the gain and background of the IRAS detectors from orbit to 
orbit. To solve this problem, Caltech graduate student Yu Cao 
developed a new image processing algorithm considerably more 
robust in suppressing artifacts such as stripes [2]. Using the 
new algorithm we proceeded with the production of an atlas at 
60 and 100 microns which included an band 5 degrees on both 
sides of the Galactic plane, as well as the Orion, Ophiuchus, and 
Taurus-Auriga molecular clouds. We then applied the algorithm 
to the full 60 and 100 micron IRAS Galactic plane data set to 
construct a comprehensive atlas of images of the Galaxy. 

The IRAS Galaxy Atlas (IGA) has been a collaboration 
between the Center for Advanced Computing Research (CACR) 
and the NASA/JPL Infrared Processing and Analysis Center 
(IPAC). Drs. Sue Terebey and Chas Beichman of IPAC were key 
contributors to the project. The IRAS Galaxy Atlas (IGA) was 
completed and was delivered to IPAC for distribution to the 
entire astronomical community [3,4]. The Infrared Science 
Archive (IRSA) has continuing responsibility for archiving, 
maintaining, and distributing the IGA to the astronomical 
community and the atlas can be accessed at [4]. 

With its considerably higher spatial resolution the IGA images 
have been used in conjunction with high-resolution radio surveys 
to undertake broad-band multi-wavelength studies of star 
forming regions containing young stars and supernova remnants. 
We anticipate significant additional science from the IRAS Galaxy 
atlas for years to come. Examples of science undertaken by 
members of the IGA project are described in [5, 6, 7, 8]. 

A modest amount of additional work was performed to 
investigate possible improvements to the image processing 
algorithms. Results of one of these investigations is discussed 
in [9]. In addition, studies of the so-called “pixon algorithm” 


were also undertaken as a comparison to the HIRES algorithm 
used in the production of the IGA. 

[1] Aumann, H.H., Fowler, J.W., & Melnyk, M., Astronomical 
Journal, 99, 1674 (1990). 

[2] Cao, Y., Prince, T.A., Terebey, S., & Beichman, C.A., 
“ Parallelization and Algorithmic Enhancements of High-Resolution 
IRAS image Construction", Pub. of the Astronomical Society of 
the Pacific, 108 , 535 (1996). 

[3] Cao, Y., Terebey, S., Prince, T.A., & Beichman, C.A., “The High 
Resolution IRAS Galaxy Atlas” Ap.J.Suppl., Ill, 387 (1997). 

[4] http://irsa.ipac.caltech.edu 

[5] Wallyn, P., Mahoney, W.A., Corbel, S., Cao, Y., Durouchoux, P., 
and Vilhu, O., “Millimeter and Infrared Observations of SGR 1806- 
20”, Astrophy. & Sp. Sci., 231 , 89 (1995). 

[6] Meyer MH, et. al., “A Massive Cometary Cloud Associated with 
1C 1805 \ Ap.J., 464 , LI 75 (1996). 

[7] Noriega Crespa, A., Van Buren, D., Cao, Y., and Dgani R., “A 
Parsec-Size Bow Shock Around Betelgeuse”, A.J., 114, 837 
(1997). 

[8] Heyer, M.H. and Terebey, S., “The Anatomy of the Perseus 
Spiral Arm: (CO)-C-12 and IRAS Imaging of the W3-W4-W5 Cloud 
Complex ”, Ap.J., 508, 721 (1998). 

[9] Cao, Y., Eggermont, P.P.B., and Terebey, S., “Cross-Burg 
Entropy Maximization and its Application to Ringing Suppression 
in Image Reconstruction”, IEEE Trans. Image Proccess., 8, 286 
(1999).