ESA Herschel Survey: Completion largest census of dust in local galaxies

Collage of galaxies in the Herschel Reference Survey at infrared /submillimetre wavelengths by Herschel (left) and at visible wavelengths from the Sloan Digital Sky Survey (SDSS, right).

The Herschel image is coloured with blue representing cold dust and red representing warm dust; the SDSS image shows young stars in blue and old stars in red. 

Together, the observations plot young, dust-rich spiral/irregular galaxies in the top left, with giant dust-poor elliptical galaxies in the bottom right.

ESA /Herschel /HRS-SAG2 and HeViCS Key Programmes /Sloan Digital Sky Survey / L. Cortese (Swinburne University)

The largest census of dust in local galaxies has been completed using data from ESA’s Herschel space observatory, providing a huge legacy to the scientific community.

Cosmic dust grains are a minor but fundamental ingredient in the recipe of gas and dust for creating stars and planets but despite its importance, there is an incomplete picture of the dust properties in galaxies beyond our own Milky Way.

Key questions include how the dust varies with the type of galaxy, and how it might affect our understanding of how galaxies evolve.

Before concluding its observations in April 2013, Herschel provided the largest survey of cosmic dust, spanning a wide range of nearby galaxies located 50–80 million light-years from Earth.

The catalogue contains 323 galaxies with varying star formation activity and different chemical compositions, observed by Herschel’s instruments across far-infrared and submillimetre wavelengths.

A sample of these galaxies is displayed in a collage, arranged from dust-rich in the top left to dust-poor in the bottom right.

The dust-rich galaxies are typically spiral or irregular, whereas the dust-poor ones are usually elliptical.

Blue and red colours represent cooler and warmer regions of dust, respectively.

Dust is gently heated across a range of temperatures by the combined light of all of the stars in each galaxy, with the warmest dust being concentrated in regions where stars are being born.

For comparison, the galaxies are also shown in visible light images obtained by the Sloan Digital Sky Survey SDSS.

Here, blue corresponds to young stars – hot, massive stars that burn through their fuel very quickly and are therefore short-lived.

Conversely, red stars are older population – they are less massive and cooler, and therefore live for longer.

The Herschel observations allow astronomers to determine how much light is emitted by the dust as a function of wavelength, providing a means to study the physical properties of the dust.