Mineralogy like our Milky Way in a young galaxy 11 billion light years away

: Image of the detection of the GRB 180325A. The right panel shows the appearance of the GRB in the same field (left panel) after its trigger. Left panel: Telescope: Pan-STARRS DR1 data archive, Right Panel: Telescope: NOT R-band Date: 2018-03-25.

Full Media Release in DOC format.

An international team of astronomers led by the AAO’s Tayyaba Zafar have reported the discovery of an intense dust-related feature in a galaxy 11 billion light years away. This feature is clearly seen in the Milky Way but it is rare in other galaxies, hence it is not well understood. The detection of the dust feature in the distant galaxy was made possible via using a gamma-ray burst (GRB), an exploding massive star, as a probe.

Galaxies are made by stars, gas, dust and dark matter. Although the amount of dust is not as larger as the mass in stars, gas or dark matter, it plays a key role in understanding how galaxies work. Dust drastically affects the observed properties of galaxies, as it induces light loss between the source and the observer due to scattering and absorption.

Dust is made up of micron or sub-micron grains of carbon, silicon, iron, aluminium or iron. Our Milky Way has a significant content of carbonaceous dust producing a special broad bumpy absorption feature at ultraviolet wavelengths. The presence of this feature in other galaxies seems to be relatively rare. The reason why this dust-related feature is so evident in the Milky Way but absent in the majority of the galaxies is not well understood.

Intriguingly, the broad dust absorption has been observed in few very distant galaxies using gamma-ray bursts (GRBs) as probes.

GRBs are massive stars ending their lives with powerful explosions and outshining their hosting galaxies. GRBs are excellent probes of the dust content of distant galaxies as the dust leaves a very distinct imprint on the emission from the GRB escaping the host galaxy.

The broad ultraviolet dust feature has been now detected in a GRB named GRB180325A, as reported in a new science paper accepted by the Astrophysical Journal Letters and led by AAO’s Tayyaba Zafar.

GRB180325A was detected by the Neil Gehrels Swift Observatory (NASA) on 25 March 2018

A spectrum of GRB180325A was first taken by the 2.6m Nordic Optical Telescope (NOT) at the Roque de los Muchachos Observatory, on the Canary Island of La Palma (Spain), only a few minutes after the light from the GRB arrived on Earth.

The data obtained with the NOT confirmed that the host galaxy was at a redshift of 2.25 corresponding to a lookback time of nearly 11 billion years. These data also showed that the GRB afterglow light was affected by dust with a bump absorption very similar to that found in the Milky Way.

“This is a beautiful example of how observatories in space and around the globe work together to provide new breakthroughs”, says Professor Johan Fynbo from the Niels Bohr Institute in Copenhagen, who secured the first spectra of the afterglow with the NOT.

A higher quality spectrum was later taken using the X-shooter instrument installed at the 8.2m UT2 of the Very Large Telescope (Cerro Paranal, Chile), managed by the European Southern Observatory (ESO), under the ‘Stargate’ project (PI N. Tanvir, UK). The Milky Way-type dust absorption was all in all confirmed by spectra obtained at four different times.

“Our spectra confirm an emergent picture that the presence of neutral Carbon in the interstellar medium is an indicator for the Milky Way type dust feature”, stated Kasper Heintz, who is a PhD student from the University of Iceland.

Such a similar broad ultraviolet dust feature has been recorded before in GRBs for four events but the last detection is now a decade old, from 2008.

The new data also allowed astronomers to confirm that the galaxy hosting GRB180325A is relatively small (~1/100th the mass of the Milky Way) but has a very high star-formation activity.

“Continuous observations of such distant cases will enable more findings of such rare cases and help to infer similarities and differences in dust composition the early universe from today and eventually lead to an understanding of which conditions are required to form dust similar to that of our Galaxy”, says Dr Tayyaba Zafar.

The AAO is a division of the Department of Industry, Innovation and Science.

Publication details:

T. Zafar and 28 coauthors, “The 2175 Å extinction feature in the optical afterglow spectrum of GRB 180325A at z=2.25”, 2018, Astrophysical Journal Letters (ApJL), accepted. Online: http://arxiv.org/abs/1806.00293

Science Contacts:

- Dr Tayyaba Zafar

AAO Research Astronomer

Australian Astronomical Observatory

P: +61 2 9372 4809 E: tayyaba.zafar@aao.gov.au

Media contact:

- Dr Ángel López-Sánchez

Research Astronomer and Science Communication Officer

Australian Astronomical Observatory and Macquarie University

M: +61 406 265 917 E: angel.lopez-sanchez@aao.gov.au

 

Images:

 : Image of the detection of the GRB 180325A. The right panel shows the appearance of the GRB in the same field (left panel) after its trigger. Left panel: Telescope: Pan-STARRS DR1 data archive, Right Panel: Telescope: NOT R-band Date: 2018-03-25.

Caption: Image of the detection of the GRB 180325A. The right panel shows the appearance of the GRB in the same field (left panel) after its trigger. Left panel: Telescope: Pan-STARRS DR1 data archive, Right Panel: Telescope: NOT R-band Date: 2018-03-25.

Credit: Tayyaba Zafar (AAO) et al.

This image is available at: https://www.aao.gov.au/files/press/GRB180325A_OT.jpeg

Spectra of the GRB 180325A taken with the NOT and ESO/VLT X-shooter presenting the dust bump absorption. Inset: The Milky Way dust absorption feature is shown as a reference to compare resemblance with the GRB 180325A spectra.

Caption: Spectra of the GRB 180325A taken with the NOT and ESO/VLT X-shooter presenting the dust bump absorption. Inset: The Milky Way dust absorption feature is shown as a reference to compare resemblance with the GRB 180325A spectra. 

Credit: Tayyaba Zafar (AAO) et al.

This image is available at: https://www.aao.gov.au/files/press/GRB180325A_Specepochs.jpg

Full Media Release in DOC format.

Tags: