Pressemitteilung

Newly Discovered Quasar Is Most Distant Known Object in the Universe

10. September 1987

A newly discovered quasar (eso8712) has been found to have a record redshift [1] of 4.11 and is therefore the hitherto most distant known object in the Universe.

This value of the redshift indicates that the quasar is receeding with 93 % of the speed of light and that we observe it as it was when the age of the Universe was only about one-tenth of its present age. Detailed spectra of the quasar have been obtained at the ESO La Silla observatory which will permit the investigation of matter in the young Universe, at an earlier time than ever before possible.

This object, now designated Q0000-26, is seen as a star-like object of magnitude 17.5 near the border between the southern constellations of Sculptor and Cetus. It emerged as a bright candidate for a record redshift quasar during a programme by Cyril Hazard (University of Pittsburgh and Institute of Astronomy, Cambridge), Richard McMahon and Mike Irwin (Institute of Astronomy, Cambridge) to search for high-redshift quasars. Candidate objects were selected on the basis of an objective prism survey carried out with the UK 1.2 m Schmidt telescope at Siding Spring in New South Wales, Australia.

The high redshift was then confirmed and measured by John Webb (Leiden Observatory, The Netherlands) together with Bob Carswell and Helen Parnell (Institute of Astronomy, Cambridge) during an observing run in mid-August 1987 at the 3.9 m Anglo-Australian telescope, also at Siding Spring Mountain.

The astronomers became aware of the record redshift when they noted that a strong emission line of hydrogen, known as Lyman-alpha, was seen in the red region of the spectrum of Q0000-26, at a wavelength near 620 nanometres. During a subsequent observing run at the ESO La Silla observatory, John Webb was able to obtain very detailed spectra of this quasar. A preliminary analysis of these data has now shown that this quasar is of very particular interest and will yield invaluable information about the conditions in the Universe when it was much younger than now.

The La Silla observations were made on August 30 - September 1 with the ESO 3.6 m telescope, equipped with a powerful spectrograph (CASPEC). In order to see as many and as fine spectral details as possible, the spectral resolution was unusually high for an object of this magnitude (about 0.06 nm) and the total integration time during the two nights was in excess of 12 hours. The recorded spectrum covered the 480 - 660 nm spectral region and, in addition to the Lyman-alpha line, also showed lines of double and triple ionized carbon. The Lyman-beta and Lyman-gamma lines also fall in this spectral region.

Although the definitive data reduction is still in progress, several results have already emerged which are causing great excitement among astrophysicists. First, Q0000-26 is one of the intrinsically brightest objects in the Universe (as shown by its great distance and apparent magnitude). In particular, Q0000-26 is brighter than any other of the few quasars which have been detected so far at redshifts around 4.0.

A very large number of narrow absorption lines are seen in the spectrum. They originate when the quasar light passes through condensations of matter between the quasar and us. By measuring the redshift of these lines, the spatial distribution of the intervening matter can be determined. Additionally, the absorption line strengths and shapes supply more detailed physical information about the individual clouds.

Several absorption lines in the spectrum of Q0000-26 have the same redshift 4.13, that is even larger than the redshift of the quasar itself. They are believed to be caused by matter near the quasar, now falling towards it. Other absorption lines at slightly smaller redshifts now for the first time allow us to probe in detail the matter in the Universe beyond a distance corresponding to redshift 4.

It is most interesting that the spectrum also reveals strong absorption lines from a cloud with redshift 3.39. They probably originate when the quasar light passes through a disc of an intervening galaxy - herewith confirming the presence of galaxies at this very large distance and at the corresponding early time.

More information about this exciting discovery will become available in some weeks' time, when the reduction of the observations will be more complete.

Endnoten

[1] In astronomy, the redshift denotes the shift of lines in the spectrum of a receding object towards longer wavelengths. The lines in the visible part of spectrum are shifted towards the red. The redshifts of galaxies and quasars are approximately proportional to their velocities and also to their distances.

Kontaktinformationen

Richard West
ESO
Garching, Germany
Tel: +49 89 3200 6276
E-Mail: rwest@eso.org

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