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. Copyright: ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/Sloan Digital Sky Survey/ L. Cortese (Swinburne University)
Collage of galaxies included in the Herschel Reference Survey, the
largest census of cosmic dust in the local Universe. The galaxies are
presented in false-colour to highlight different dust temperatures, with
blue and red representing colder and warmer regions respectively. The
collage is presented with dust-rich, spiral and irregular galaxies in
the top left, and giant, dust-poor elliptical galaxies in the
bottom-right. The images were composed from PACS and SPIRE observations
at 100, 160 and 250 microns. Copyright ESA/Herschel/HRS-SAG2 and HeViCS Key Programmes/L. Cortese (Swinburne University)
.
Collage of galaxies included in the Herschel Reference Survey as seen
at visible wavelengths in images obtained by the Sloan Digital Sky
Survey. The colour distribution highlights different stellar ages, with
red and blue indicating older and younger stars, respectively. Copyright: 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.
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.
For example, a galaxy forming stars at a faster rate should have more
massive, hot stars in it, and thus the dust in the galaxy should also be
warmer. In turn, that means that more of the light emitted by the dust
should come out at shorter wavelengths.
However, the data show greater variations than expected from one galaxy
to another based on their star formation rates alone, implying that
other properties, such as its chemical enrichment, also play an
important role.
By allowing astronomers to investigate these correlations and
dependences, the survey provides a much-needed local benchmark for
quantifying the role played by dust in galaxy evolution throughout the
history of the Universe.
The data will complement observations being made by other telescopes,
such as the ground-based Atacama Large Millimeter Array in Chile, which
will allow astronomers to look at dust in galaxies to the very edge of
the observable Universe.
More information:
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3954
Email: markus.bauer@esa.int
Luca Cortese
Swinburne University of Technology, Australia
Email: lcortese@swin.edu.su
Göran Pilbratt
ESA Herschel Project Scientist
Tel: +31 71 565 3621
Email: gpilbratt@rssd.esa.int
Source: ESA/Herschel
