Herschel Maps Display Stellar Nurseries Throughout Galactic Plane


The Herschel mission of the ESA released a series of maps containing hubs where stars are created within the Milky Way galaxy, along with catalogues containing hundreds of thousands of compact sources that extend through all phases from birth to death of stars within our Galaxy.

From 2009 to 2013, the Herschel mission observed and scanned the sky using far-infrared and sub-millimetre wavelengths. The electromagnetic spectrum picks up on some of the coldest objects throughout the Universe, such as cosmic dust. The Herschel infrared Galactic Plan Survey (or Hi-GAL) is the largest observation program being completed by Herschel: including almost 40 days of observation as well as two percent of the sky. The goal of the project was to map the entire Milky Way disc to get a better understanding of star formation.

eagle nebula
Herschel’s glimspe of the Galactic Plane. Image Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL

The Hi-GAL team has been processing data since 2013 in order to build a calibrated map with quality and resolution that has not been seen before. The dynamic range contains at least two orders of magnitude and the maps showcase emission by diffuse material. Filamentary structures are shown throughout the photographs, offering a groundbreaking view of the Galactic Plane. These images show interstellar material, filamentary structures containing gas and dust that begin the formation of stars, pre-stellar clumps, protostars in a range of evolutionary stages and a handful of other very interesting information.

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

This month, the team released the first part of data which contained 70 maps. Sergio Molinari from IAPS/INAF, Principal Investigator for the Hi-GAL Project says these maps are stunning aesthetically but also represent a rich amount of data that will allow astronomers to further study the different phases of star formation throughout our Galaxy.

RCW 120 Bubble
The RCW 120 bubble that lies around 4300 light-years away, seen by Herschel’s observatory. Image Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL

These new maps have been available on the ESA Herschel Science Archive since the beginning of the latest research, as the observation team agreed to waive their proprietary period right. There, both the raw data and generated data that is being reprocessed to higher quality can be seen. The current released material shows an additional step in the data processing. Maps are accompanied by catalogues within each of the five bands, allowing the community to study a wide range of subjects. Maps display the inner Milky Way and move towards the Galactic Centre from the viewpoint of the Sun. There are plans of a second release of data containing the rest of the survey, which should be made public by the end of 2016.

milky way
The centre of the Milky Way around 25 000 light-years away as viewed by the Herschel’s observatory. Image Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL

Molinari explains a special technique was developed in order to extract each individual source for the maps. This helped to maximize contrast and amplify the large masses of objects while keeping the background intact. The largest catalogue thus far contains 300,000 sources. Goran Pilbratt, ESA Herschel Project Scientist says the Hi-GAL maps and catalogues offer a complete census of all stellar nurseries within the inner Galaxy that will prove to be useful resources for studies of star formation throughout the Milky Way. This will help astronomers to dig deeper into the Galactic Plane and identify areas where follow-up research may be requested. This will help facilities to work together to pinpoint exact locations they want to put their focus in.

war peace nebula
The War and Peace Nebula – NGC 6357 (left), and the Cat’s Paw Nebula – NGC 6334 (right). Image Credit: ESA/Herschel/PACS, SPIRE/Hi-GAL

The complete information about this study are published in the Astronomy & Astrophysics journal.