Friday, October 25, 2013

The Universe Explored by Herschel

The Herschel Space Observatory
Image credit: ESA (Image by AOES Medialab);
Background: HST, NASA/ ESA/ STScI
After nearly four years of operation, on April 29, 2013 the Herschel Space Observatory finished its mission. However, this was not the end of its job. The wealth of data from Herschel is still being analyzed and new results are being discovered. A conference, "The Universe Explored by Herschel," was held in the Netherlands from Oct 15-18 to discuss exciting results that have been made with Herschel.

Herschel is a space telescope that was launched on May 14, 2009. Its mirror is 3.5m which makes it the largest space telescope launched so far. It observed the sky in the infrared. Why do astronomers care about infrared? Infrared allows astronomers to detect dust emission that is caused by objects embedded in the dust, observe low temperature objects like some planets, and study high redshift galaxies. Herschel could observe the wavelength range of 60-670 microns in the infrared. This range covers a part of the infrared bump of dust emission in galaxies and many important infrared spectral lines that play a role in determining gas properties in the interstellar medium. CANDELS also has 85-670 micron deep imaging data taken with Herschel in the GOODS-S, GOODS-N, COSMOS, and UDS fields. With these data sets, we can detect the dust emission in distant galaxies.

During the conference, I mainly attended the sessions related to galaxy formation and evolution. Infrared galaxies were common in the early universe and they dominated the star formation history. We discussed how infrared galaxies were formed and evolved -- how much dust these galaxies have, what is the dust temperature, how many stars they made at a given period (star formation rates), why some of them have intense star formation compared with typical star-forming galaxies, how they stop making stars, what kind of shapes they have, what mechanisms heat the dust, etc. 

View of a canal in Leiden. Image Credit: H. Inami
From the CANDELS team, Jeyhan Kartaltepe displayed a poster (shown below) presenting interesting results on the morphology of galaxies detected with Herschel. In particular, she explored the role that galaxy mergers play in high redshift ultraluminous infrared galaxies. David Rosario discussed the connection between active galactic nuclei and star formation using the Herschel data. I presented infrared luminosity functions built with our own Herschel data, and star formation rate comparisons based on the infrared luminosity and the optical/near-infrared spectral energy distribution fitting, which Janine Pforr has been working on. Without Herschel, it would have been difficult to answer these questions accurately. Although Herschel is not observing anymore and many interesting discoveries have been made, astronomers are still working hard to explore the infrared universe using its data.

Image Credit: J. Kartaltepe

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