New Herschel maps and catalogues reveal Stellar Nurseries across the Galactic Plane

Herschel’s view of the Eagle Nebula. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project Herschel’s view of the Galactic Plane. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project

ESA’s Herschel mission releases today a series of unprecedented maps of star-forming hubs in the plane of our Milky Way galaxy. This is accompanied by a set of catalogues of hundreds of thousands of compact sources that span all phases leading to the birth of stars in our Galaxy. These maps and catalogues will be valuable resources for astronomers for planning follow-up studies of particularly interesting regions in the Galactic Plane.

Herschel’s view of the Eagle Nebula. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project

During its 4 years of operations (2009-2013), the Herschel space observatory scanned the sky at far-infrared and sub-mm wavelengths. Observations in this portion of the electromagnetic spectrum are sensitive to some of the coldest objects in the Universe, including cosmic dust, a minor but crucial component of the interstellar material from which stars are born. The Herschel infrared Galactic Plane Survey (Hi-GAL) is the largest of all observing programmes carried out with Herschel, in terms of both observing time – over 900 hours of total observations – and sky coverage – ~800 sq degs, or 2% of the entire sky. Its aim was to map the entire disc of the Milky Way, where most of its stars form and reside, in 5 of Herschel’s wavelength channels: 70, 160, 250, 350 and 500 μm.
Over the past 2 years, the Hi-GAL team has processed the data to obtain a series of calibrated maps of extraordinary quality and resolution. With a dynamical range of at least 2 orders of magnitude, these maps reveal the emission by diffuse material as well as huge filamentary structures and individual, point-like sources scattered across the images.

The RCW 120 bubble seen by ESA’s Herschel space observatory. It lies about 4300 light-years away. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project

The images provide an unprecedented view of the Galactic Plane, ranging from diffuse interstellar material to denser filamentary structures of gas and dust that fragment into clumps where star formation sets in. They include pre-stellar clumps, protostars in various evolutionary stages and compact cores on the verge of turning into stars, as well as fully-fledged stars and the bubbles carved by their highly energetic radiation.
Today, the team releases the first part of this data set, consisting of 70 maps which investigate the different phases of star formation in our Galaxy.

The centre of our Galaxy, the Milky Way, about 25 000 light-years away, as seen seen by ESA’s Herschel space observatory. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project

The observations have been made available through the ESA Herschel Science Archive, including raw data as well as data products generated by systematic pipeline processing. The data has regularly been reprocessed to gradually higher quality and fidelity products. The maps cover the inner part of the Milky Way, towards the Galactic Centre as seen from the Sun, with Galactic longitudes between +68° and -70°. A second release, the remaining part of the survey, is foreseen for end of 2016.

The result is a set of 5 catalogues, one for each of the surveyed wavelengths, listing the source position, flux, size, signal-to-noise ratio and other parameters related to their emission. The largest catalogue is the one compiled from the 160-μm maps, with over 300 000 sources.

The War and Peace Nebula, also known as NGC 6357 (left), and the Cat’s Paw Nebula, also known as NGC 6334 (right), seen by ESA’s Herschel space observatory. Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL Project

“The Hi-GAL maps and catalogues provide a complete census of stellar nurseries in the inner Galaxy,” says Göran Pilbratt, Herschel Project Scientist at ESA.
“These will be an extremely useful resource for studies of star formation across the Milky Way, helping astronomers to delve into the Galactic Plane and also to identify targets for follow-up observations with other facilities.”
http://sci.esa.int/herschel/57755-new-herschel-maps-and-catalogues-reveal-stellar-nurseries-across-the-galactic-plane/