SPIRE images of M74 at three different wavelengths
On 24 June 2009 the SPIRE instrument recorded its first images during the in-orbit commissioning phase of the Herschel mission. These pictures, made before fine-tuning or in-orbit final calibration was performed show SPIRE images of M74 at three different wavelengths 250, 300 and 500 microns, scaled 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 telescopes produce sharper 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.
M74 (also known as NGC 628) is a face-on spiral galaxy located about 24 million light-years from Earth in the constellation Pisces. Visible light, produced mainly by the stars within the galaxy, reveals a bright nucleus and well-defined spiral arms that contain many small, bright regions where young massive stars have formed recently. The submillimetre SPIRE images trace the cold dust between the stars, and the spiral arms appear much more enhanced. They also contain many faint dots that are actually distant galaxies in the background. These galaxies also contain dust radiating at submillimetre wavelengths but are too distant for the structure in the galaxies to be resolved.