Category Archives: Herschel

Press Release: Herschel shows galaxies had cool beginnings

Beginnings and Endings for Herschel this week:

Recently we heard the news that the Herschel Observatory has run out of Helium, required to cool the telescope

To celebrate the success of Herschel we post here a copy of the article featuring on the UK Herschel site herscheltelescope.org.uk, as a press release for Symeonidis et al. 2013 (MNRAS, 431, 2317), which was published on May 1, 2013.

Herschel shows galaxies had cool beginnings

Observations from the Herschel Space Observatory have shown that galaxies in the early Universe were cooler than those we see around us today. This indicates that early galaxies were more bloated, containing more dust, distributed over larger regions.

Around a thousand galaxies were studied, chosen because they are very distant and forming stars at very high rates. Because they are so distant, the galaxies are seen as they were when the Universe was much younger, with those studied here spanning a range of cosmic times between 1 and 10 billion years ago – a significant portion of its fourteen billion year history

Most of these galaxies are seen when the Universe was about half its current age, a period during which galaxies tended to be much more “active” than those we see around us today, with some forming stars hundreds or even thousands of times faster than our Milky Way. Although rare, such “starburst galaxies” have produced as much energy over the course of cosmic history as all the other galaxies combined. This makes them crucial for studying the history of star formation in the Universe.

Stars form from massive clouds of gas and dust, and these early galaxies have large quantities of both. Most of the dust in these galaxies is cold by human standards, at temperatures of around −240 Celsius, and so can only be seen at far-infrared wavelengths. Using Herschel’s cameras, astronomers are able to study the properties of the dust and deduce the average conditions within each galaxy.

“These galaxies are all but invisible to optical telescopes, but Herschel sees the far-infrared glow from their dust,” says Dr Myrto Symeonidis, who led and carried out the research at UCL and is currently based at the University of Sussex. “With so many galaxies in the Herschel images, we can start to look at how galaxies have changed over the history of the Universe.”

The newly formed stars in these galaxies heat up the dust, so galaxies which form stars more rapidly are expected to have higher dust temperatures overall.  But the surprise for astronomers was that the galaxies in the younger Universe appeared cooler than those seen today. “There are two explanations for this surprising result,” explains Dr Symeonidis. “Either the earlier starburst galaxies were much larger than we thought, or they contain greater quantities of dust than predicted. In either case, they are different from those we see around us today.”

These results used images and data from Herschel’s two cameras, PACS and SPIRE. By studying seemingly blank regions of sky for long periods of time, these revolutionary instruments picked out the light from thousands of galaxies in the early Universe.

“Previous assumptions have generally assumed that these early starburst galaxies were similar to those in the local Universe,” commented Prof Seb Oliver, University of Sussex, who leads “HerMES”, one of the Herschel surveys used in this study. “What we’ve shown here is that this wasn’t always the case, we need to look more carefully at the conditions in these early galaxies”.

“This work brought together some of the best data collected over Herschel’s four year lifetime, showcasing the immense advances we can make in understanding how stars form and under what conditions”, points out Dr Dieter Lutz, from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who leads the “PEP” survey.

“Herschel’s cameras have provided unrivalled views of the early Universe, allowing us to study the distant past in unprecedented detail,” says Prof Matt Griffin, of Cardiff University, the lead scientist of the international team which designed, built and operated the SPIRE instrument on board Herschel. “We’ve only scratched the surface of the immense Herschel data archive, and there is undoubtedly much, much more to come”, he concludes.

These results are published in the 1st May 2013 edition of the journal Monthly Notices of the Royal Astronomical Society: Symeonidis et al (2013) MNRAS 431, 2317

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One of the regions of sky studied by Herschel, seen towards the constellation of Ursa Major and containing hundreds of distant starburst galaxies. This patch is around the size of the full Moon as seen from Earth. Image credit: ESA/Herschel/SPIRE/HerMES
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The galaxy Messier 82, the closest example of a “starburst galaxy”, seen by NASA’s Spitzer satellite. Image credit: NASA/JPL-Caltech High-res: http://www.spitzer.caltech.edu/uploaded_files/images/0008/6785/ssc2006-09a1.jpg
The galaxy Messier 82, the closest example of a “starburst galaxy”, seen by NASA’s Spitzer satellite. Image credit: NASA/JPL-Caltech
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Teenage Galaxies

Hello, I am Dr Myrto Symeonidis a postdoctoral researcher at UCL’s Mullard Space Science Laboratory (MSSL), and this week I will be telling you about some of my research here at MSSL on galaxies “in their teenage years”: some of the youngest, dustiest and most energetic, galaxies in the Universe.

Infrared Radiation

For most people, the word “astronomy” brings to mind beautiful, colourful images of galaxies taken by the Hubble Space Telescope. Those images are usually showing you what galaxies look like in the optical part of the  electromagnetic spectrum. However, few people realise that what we can “see” with our own eyes is only a very small part of the picture.

EM Spectrum from http://en.wikipedia.org/wiki/Electromagnetic_spectrum

In fact, more than half of the total light produced by all galaxies in the Universe since the beginning of time emerges as infrared radiation, invisible to the human eye. The reason is dust.

Cosmic dust is somewhat of a misnomer; unlike the dust that you find in your home which has many constituents, cosmic dust is a conglomeration of tiny grains of rock-like material typically of carbon and silicon. It is prevalent in all galaxies and readily absorbs ultraviolet and visible light, subsequently re-radiating it in the infrared. Discovering the dust-obscured side of the Universe was one of the major scientific breakthroughs of the last century, enabling us to make immense progress in our understanding of the cosmos.

Star Formation or Supermassive Black holes?

Since the start of my career in astronomy I have been very keen to make sense of the role of dust in galaxy formation and evolution. One reason is that the dust content of a galaxy is intricately linked to its ability to make new stars, what astronomers refer to as the ‘star-formation rate’. The most dusty galaxies appear to make the most stars, which means that, on a cosmic scale, dust-rich galaxies are the main contributors to the total  cosmic energy budget. The other main way in which galaxies release energy into the cosmos are through Active Galactic Nuclei (AGN). This is a mundane name for an awesome phenomenon: AGN are supermassive black holes (many billions of times the mass of the Sun) that reside in the centres of galaxies and devour all infalling matter. In the process of consuming matter, AGN release copious amounts of energy. To understand the energy content of the Universe we therefore need to disentangle the contributions from star formation and AGN.

Measuring star-formation rates in galaxies that host AGN is a challenging feat because in many cases the AGN is luminous enough to completely drown the stellar emission from its host. To make things even more challenging, dusty galaxies were far more common in the early Universe, and thus identifying and studying them requires cutting-edge observational facilities to look back in time.

Herschel and the Rosetta Nebula from http://spaceinimages.esa.int/Images/2010/04/Herschel_and_Rosette_Nebula

The Herschel Space Observatory 

We are now fortunate to be living in the most data-rich era that infrared astronomy has ever seen, thanks to the Herschel Space Observatory, one of ESA’s most ambitious missions. Herschel is the largest space telescopes ever launched and is the only facility to date and for the foreseeable future that can span the part of the electromagnetic spectrum in which most of the Universe’s radiation from galaxies emerges.

MSSL has had a major role in the Herschel mission since its conception, with particular involvement in designing and building Herschel’s Spectral and Photometric Imaging receiver (SPIRE). Seeing the planing, building and eventual scientific results from space missions is one of things that makes MSSL such an exciting place to work.

The mechanical and thermal engineering group at MSSL assembled and tested the whole SPIRE structure, additionally providing key components such as thermal straps, detector boxes, mirror mounts and filter holders. Moreover, since Herschel’s successful launch in 2009, the MSSL astronomy group has been heavily involved in the exploitation of Herschel data with a strong focus on measuring the physical attributes of the primary energy production mechanisms in dust-rich galaxies, determining how these mechanisms interact and charting the changes in their characteristics back to when the Universe was less than a quarter of its current age.

With the advent of Herschel, we have been able to exploit the far-infrared part of the electromagnetic spectrum, where the energetic balance between AGN and star-formation tilts towards the latter. Taking advantage of Herschel data in a recent project that was led by the MSSL Herschel team, we were able to measure the star-formation rates of the galaxies which host the most powerful AGN at the time when the Universe was less than half its current age.

We discovered that although the host galaxies of AGN experience intense star-formation, if the AGN becomes powerful enough it seems that it is able to slow down and eventually terminate the star-formation, placing the whole galaxy in a rapid course towards old age.

An artistic impression of an AGN from here http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=5033

Although we still have a long way to go with respect to solving the mysteries of the cosmos, thanks to Herschel we are now step closer to understanding how galaxies evolve, from young ,dusty and active into old age.

 

 

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