Herschel images promise bright future

These observations show that Herschel's instruments are working beyond expectations. They promise a mission of rich discoveries for waiting astronomers.

SPIRE surprises with power

On 24 June, Herschel's Spectral and Photometric Imaging Receiver (SPIRE) was trained on two galaxies for its first look at the Universe. The galaxies showed up prominently, providing astronomers with their best images yet at these wavelengths, and revealing other, more distant galaxies in the background of the images.

The pictures below show galaxies M66 and M74 at a wavelength of 250 microns, longer than any previous infrared space observatory, but still the shortest SPIRE wavelength.

The images reveal dust in clouds where star formation is active. The nucleus and spiral arms of these galaxies show up clearly. Significantly, the frames are also filled with many other galaxies, all so distant that they show up only as point sources. There are also some extended structures visible. These are possibly due to clouds of dust in our own galaxy. Credit: ESA and the SPIRE Consortium




M66 (also known as NGC 3627) is a barred spiral galaxy located about 36 million light years away in the constellation Leo. The bar is made of stars, gas, and dust. The infrared SPIRE image shows warm dust, revealing that most of the dust is located in the centre of the galaxy and near the ends of the bar. Dust is also found in the spiral arms. This arrangement is caused by the forces that the bar exerts on other objects within the galaxy. Many more distant galaxies appear as blobs in the field of view. Credit: Herschel image: ESA and the SPIRE Consortium, Spitzer image: NASA/Spitzer SINGS




M74 (also known as NGC 628) is a face-on spiral galaxy located about 24 million light years from Earth in the constellation Pisces. The infrared SPIRE images trace the cold dust between the stars, clearly showing the galaxy's spiral structure. They also contain many faint dots that are actually distant galaxies. These galaxies contain dust that radiates at infrared wavelengths, but because they are much further away, we cannot see the structure in the galaxies. Credit: Herschel image: ESA and the SPIRE Consortium, Spitzer image: NASA / Spitzer SINGS




SPIRE images of galaxy M74 at three different infrared wavelengths. These wavelengths are the equivalent of blue, green and red colours in the visible spectrum. The images have been processed to bring out the extended structure of the galaxy and to show more detail in the background sky. The image quality is best at 250 microns because all telescopes produce their sharpest images at their shortest wavelengths. By combining the three images, astronomers can measure the properties of the emitting dust and identify the nature of the many distant galaxies that also appear in the pictures. Credit: ESA and the SPIRE Consortium

SPIRE is designed to look at star formation in our own Galaxy and in nearby galaxies. It will also search for star-forming galaxies in the very distant Universe. Because these galaxies are so far away, their light has taken a very long time to reach us, so by detecting them we are looking into the past and learning how and when galaxies like our own were formed.

Herschel's primary mirror is 3.5 m in diameter, nearly four times larger than any previous infrared space telescope. These images prove that Herschel enables a giant leap forward in our ability to study celestial objects at far infrared wavelengths.

NASA's Spitzer Space Telescope primarily observes infrared wavelengths shorter than Herschel does, so the two telescopes complement each other.

These observations were all made on the first day that SPIRE was used. They clearly show that the main scientific studies planned with the instrument are going to work extremely well.

Water-hunter HIFI scores at first try

Scientists used Herschel's Heterodyne Instrument for the Far-Infrared (HIFI) on 22 June to look for warm molecular gas heated by newborn massive stars in the DR21 star-forming region in Cygnus.

Deeply hidden in the giant molecular cloud, DR21, newly formed massive stars are wreaking havoc on their stellar nursery. In this colour-coded Spitzer image of the DR 21 star-forming region, the green reveals the emission from large molecules set aglow by the newly formed stars. The large bubbles and striated clouds are caused by the complex interaction of the newly formed massive stars and their environment. To the right we see a magnified image of the active region.

HIFI will study this interaction in detail. The blue and red boxes show the area that HIFI has already surveyed for ionized carbon, a key ingredient of the molecular cloud material. The broad line at the position of the newly formed star (in red) reveals the presence of a powerful wind ripping the cloud apart. In contrast, the offset position (in blue) shows emission from quiescent material, which has not yet been disturbed by this star. The yellow stripe indicates the region studied in lines of water (right) and carbon monoxide (left) by HIFI. The large width of the carbon monoxide profile and the complex water line indicate that this material is part of a massive outflow from the newly formed star. Credits: ESA and the HIFI Consortium

HIFI provided excellent data in two different observing modes, returning information on the composition of the region with unprecedented accuracy and resolution. It works by ‘zooming in' on specific wavelengths, revealing different spectral ‘lines' that represent the fingerprints of atoms and molecules and even the physical conditions of the object observed. This makes it a powerful tool to study the role of gas and dust in the formation of stars and planets and the evolution of galaxies.

Using HIFI, scientists observed ionised carbon, carbon monoxide, and water in DR21. These different molecular lines contribute to a more complete understanding of what is happening deep in space.

The high quality of these first observations promises great new insights into the process of star formation.

PACS stares into the Cat's Eye

The first observation with the Photodetector Array Camera and Spectrometer (PACS) instrument was carried out on 23 June.

The first target was the dying star known as the Cat's Eye Nebula. Discovered by William Herschel in 1786, this nebula consists of a complex shell of gas thrown off by a dying star. Dying stars create spectacular nebulae, enriching the interstellar medium with heavy chemical elements. But how does an initially spherical star produce such a complex nebula? To solve this question we need to look at the processes close to the star, where the matter is ejected.

The panel below shows an overlay of individual spectra of the nitrogen line, all taken simultaneously with the PACS spectrometer, on the dust continuum as observed with the PACS photometer. The width of these spectral lines can be used to determine the speed of the gas. These very first data are of unprecedented sensitivity, accurately tracing the physical conditions in cold and warm gas. The next step is to supplement these first results with data from other atomic species to build up a picture of how the gaseous and dusty structures are shaped further out. Credits: ESA and the PACS Consortium

With the PACS spectrometer it is possible for the first time to take images in spectral lines and see how the wind from the star shapes the nebula in three dimensions. The PACS spectrometer was used to look into the Cat's Eye. This mode records the composition and condition of celestial objects at precisely defined wavelengths.

PACS observed the nebula in two spectral lines from ionised nitrogen and oxygen. For better orientation, the PACS photometer obtained a small map of the Cat's Eye Nebula in the 70 micron band, revealing the structure of a dust ring with an opening on one side.

Following these images, Herschel is now in the performance verification phase, where the instruments will be further tested and calibrated. This phase will last until the end of November, after which the mission will begin its routine science phase. These images demonstrate that there is a lot of science to look forward to.

Source: European Space Agency
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