Astronomers Release Gargantuan Survey of Milky Way’s Galactic Plane

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The second data release of the Dark Energy Camera Plane Survey (DECaPS2), which took two years to complete and produced more than 10 terabytes of data from 21,400 individual exposures, contains a staggering 3.32 billion celestial objects. The DECaPS2 data were gathered by the Dark Energy Camera (DECam) instrument on the Víctor M. Blanco 4-m Telescope at NSF’s Cerro Tololo Inter-American Observatory in Chile.

This image is a small extract of the DECaPS2 survey of the Milky Way. Image credit: DECaPS2 / DOE / FNAL / DECam / CTIO / NOIRLab / NSF / AURA / M. Zamani & D. de Martin, NSF’s NOIRLab.

This image is a small extract of the DECaPS2 survey of the Milky Way. Image credit: DECaPS2 / DOE / FNAL / DECam / CTIO / NOIRLab / NSF / AURA / M. Zamani & D. de Martin, NSF’s NOIRLab.

DECaPS2 is a survey of the plane of the Milky Way as seen from the southern sky taken at optical and near-infrared wavelengths.

The first trove of data from DECaPS was released in 2017, and with the addition of the new data release, the survey now covers 6.5% of the night sky and spans a staggering 130 degrees in length.

While it might sound modest, this equates to 13,000 times the angular area of the full Moon.

“Most of the stars and dust in the Milky Way are located in its disk, in which the spiral arms lie,” explained Andrew Saydjari, a graduate student at Harvard University and an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.

“While this profusion of stars and dust makes for beautiful images, it also makes the Galactic plane challenging to observe.”

“Another challenge arises from the sheer number of stars, which can overlap and make it difficult to disentangle individual stars from their neighbors.”

“Despite the challenges, we delved into the Galactic plane to gain a better understanding of our Milky Way.”

“By observing at near-infrared wavelengths, we were able to peer past much of the light-absorbing dust.”

The astronomers also used an innovative data-processing approach, which allowed them to better predict the background behind each star.

This helped to mitigate the effects of nebulae and crowded star fields on such large astronomical images, ensuring that the final catalog of processed data is more accurate.

“One of the main reasons for the success of DECaPS2 is that we simply pointed at a region with an extraordinarily high density of stars and were careful about identifying sources that appear nearly on top of each other,” Saydjari said.

“Doing so allowed us to produce the largest such catalog ever from a single camera, in terms of the number of objects observed.”

“When combined with images from Pan-STARRS 1, DECaPS2 completes a 360-degree panoramic view of the Milky Way’s disk and additionally reaches much fainter stars,” said Dr. Edward Schlafly, an astronomer at the Space Telescope Science Institute.

“With this new survey, we can map the three-dimensional structure of the Milky Way’s stars and dust in unprecedented detail.”

“Since my work on the Sloan Digital Sky Survey two decades ago, I have been looking for a way to make better measurements on top of complex backgrounds,” said Professor Douglas Finkbeiner, an astronomer at the Harvard & Smithsonian’s Center for Astrophysics.

“This work has achieved that and more!”

The results were published in the Astrophysical Journal Supplement.

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Andrew K. Saydjari et al. 2023. The Dark Energy Camera Plane Survey 2 (DECaPS2): More Sky, Less Bias, and Better Uncertainties. ApJS 264, 28; doi: 10.3847/1538-4365/aca594

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