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Diffuse Interstellar Bands in the galaxy AM 1353-272 B at 160 Mpc: a leap forward in mapping the extragalactic organic interstellar matter

» Tuesday 24 March 2015

In 1922, Mary Lea Heger, a PhD student at the Lick Observatory, identified some faint absorption features of unknown origin in the spectra of stars. Soon after, astronomers realized that they were created in the material between stars, the so-called Interstellar Medium and as such, they named them "diffuse interstellar bands" (DIBs). Almost one century after their discovery, astronomers know more than 400 of these bands. However, they have not yet identified what causes them. The best candidates are some kind of large carbon-based molecules and as such, these bands could be the footprint of the largest reservoir of organic matter in galaxies. This is, however, a extremely faint footprint, and therefore difficult to spot. Maps for some of the bands exits only for some areas of the Milky Way and only in galaxies of the Local Group has been possible to spot this footprint at several locations within the galaxy.

Using data of the new instrument MUSE at the VLT, a team of astronomers led by Ana Monreal-Ibero, at GEPI, and Peter Weilbacher at Leibniz-Institut für Astrophysik Potsdam has just detected one of the mysterious features over a large extent of the member with highest extinction in an interacting system nicknamed "The Dentist’s Chair". The galaxy, at 160 Mpc, is at a distance more than 2 orders of magnitude larger than any other galaxy with detection of these features at several locations. With this discovery, the team demonstrate that mapping of this footprint in distant galaxies is possible. Thanks to the combination of high sensitivity instruments and large telescopes, astronomers will be able to answer one day the question: At what stage in the evolution of galaxies and in which favourable conditions have emerged in organic species still mysterious?

The left panel presents a colour image for AM1353-272 using filters V (blue channel), R (green channel), and I (red channel), reconstructed from the MUSE cube. The right panel contains a zoom of the area associated to AM 1353-272 B, the galaxy studied by this team. On top of the image, the figure shows the regions of the galaxy where the DIB was detected. Each tile has been coloured differently using a palette that follows the blue-to-red (approaching-to-receding) velocity distribution within the galaxy. On top of these, the detected DIBs are shown. Note their faintness. The combination of a extremely efficient spectrograph and a telescope of large aperture as well as the detection of stronger features tracing the Interstellar Medium made possible their detection.

In the Canary Islands, the days of good weather, one can see the neighbouring islands. However, those days with "calima", where the wind brings the sand from the Sahara, that is more difficult. The interstellar medium has also its own "calima": it is the dust. It absorbs the light of the stars making them more difficult to observe, as the "calima" when one looks towards a neighbouring island. This phenomenon is called extinction. The figure shows the relation between the strength of the DIB and this extinction (and therefore, the dust) for several galaxies. This team of researchers has found that the DIBs in the galaxy AM 1353-272 B follow a similar relation with the dust as the one that we found for the two large spirals in the Local Group: The Milky Way and Andromeda.

Link to the scientific publication: