Astronomers made an important contribution to knowledge about the universe when they discovered a galaxy with a redshift of 380 percent, placing it among the most distant observable objects from Earth, including quasars.
Prior to 1985, the most distant objects in the universe that were visible from Earth were quasars.
Because astronomers were able to see farther out into the universe, they began to discover objects with larger and larger redshifts. In April of 1988, astronomy graduate student Kenneth Carter Chambers reported the discovery of an elongated object with a redshift of 227 percent (2.27). The elongated image ruled the object out as a quasar, which is more compact, like a star. In August of 1988, Simon Lilly
Since 1960, astronomers have used radio-wave emission from distant sources to pinpoint distant galaxies. Techniques involving the use of multiple radio telescopes, or arrays, improve resolution by offering a larger combined collecting area. An array known as the Very Large Array
To limit the search for the most suitable sources of the spectrum Lilly had obtained, a specialized technique was employed. Candidates were selected from the Palomar Sky Survey of radio sources. Radio-emitting sources were selected that had spectra considered ultrasteep. Ultrasteep radio sources are both powerful and distant. Various explanations have been advanced regarding such spectra, such as hot regions caused by gaseous jets of material interacting with magnetic fields of the galaxy. Fifty radio sources were selected, and wavelengths of 0.20, 0.06, and 0.02 meters were studied with comparisons made to known quasar radio sources for calibration purposes.
The discovery of the object, which was named 4C41.17, was made in March of 1988 (announced in August of 1988) at the 4-meter telescope at Kitt Peak National Observatory in Tucson, Arizona, by the team of Chambers, George Miley, and Willem Johannes van Breugel. The scientists measured the redshift by identifying two emission lines, the brightest one centered at 583.2 nanometers and the fainter one at 743.2 nanometers. The wavelengths agreed with the known Lyman alpha and five-times-ionized carbon lines when shifted toward the red by 380 percent of the original values. The actual lines observed in the yellow and red wavelengths would have originated in the ultraviolet. To improve the overall quality of the image, Chambers and his colleagues used the telescope with an enhanced red-sensitive CCD scanned across the image in an incremental fashion. The image obtained was a composite of many separate scans. This served two purposes: It improved the contrast, and it eliminated distortion surrounding the image.
The astronomers had to obtain much of the imaging in infrared wavelengths because of the high redshifts. At these wavelengths, details may be revealed—such as the gaseous components from stars—that are not always discernible at others. For the infrared survey, the astronomers used the 3.5-meter United Kingdom telescope in Hawaii. The background sky is ordinarily brighter at the 2.2-micron wavelength observed than the distant source. Therefore, to improve the image sharpness, the astronomers took multiple images over the source galaxy, with a total exposure time of 171 minutes.
Spectroscopy
The optical and infrared emission from 4C41.17 is aligned with the radio axis of the galaxy. Researchers believe this can be explained as resulting from star formation caused by the radio source. The extended source of emission radiation shows spectra identified from stars and is, therefore, probably a distant stellar system. The star formation may have been caused by the radio source compressing the protogalactic clouds. Similarities among the ionized gas, the optical/infrared radiation, and the radio source suggest an interactive mechanism.
From studies of an ideal galactic model, the astronomers concluded that the stars would have formed in less than 100 million years, making 4C41.17 no more than 300 million years old. This would be a very young galaxy when compared with galactic systems visible from Earth’s solar system, including the Milky Way galaxy. The galaxy apparently has a very luminous halo out to 100 kiloparsecs, which appears as ionized gas dominated by the Lyman alpha line. The ionization may be caused by hot young stars or may be induced by the radio source; perhaps it is even the effect of nuclear emissions.
Astronomers infer the distances to objects such as 4C41.17 by comparing the objects’ observed redshifts to values assumed from Hubble’s law
The techniques employed by the research team of using Lyman alpha spectral line identification and radio emission from this galaxy allowed detection out to a redshift of 6.0; at distances greater than this, the spectral lines would no longer be observed optically. Extension of this technique to very faint samples may increase the numbers of known high-redshift galaxies and serve as a method of probing the early universe.
The 4C41.17 research team also made a significant discovery of an alignment effect between the optical and infrared radiation from the galaxy extending along the radio source. The radio source may induce star formation and may be responsible for this alignment that could occur early in the history of a galaxy. The ultraviolet spectrum (wavelengths from 10 to 100 nanometers) is dominated with starlight, demonstrating that the rate of star formation probably was higher in the past. Most of the radiation emitted by a star consists of invisible wavelengths, including ultraviolet, but the atmosphere of Earth filters out nearly all of these wavelengths before they reach the surface. Lilly has suggested that the visible component of radiation is caused by newly formed blue stars, and the infrared light may be caused by red stars that are from one to two billion years old.
The discovery of a mature galaxy far out in the visible universe and therefore early in time, perhaps soon after the big bang event, presents some problems for present cosmological theories. Some cosmologists believe that galaxies formed around dense concentrations of invisible particles may compose 90 percent of the material in the universe, called cold dark matter. Models for this theory require millions of years for star systems to form in galaxies, but 4C41.17 probably required much less time than that.
Additional research will likely provide insights into the relationships between quasars and early protogalaxies such as 4C41.17. Finding a galaxy at such a great distance was unexpected because, previously, only quasars were known to reside that far away. Quasars were evidently much more abundant in the early universe and have either evolved into galactic systems since then or have disappeared altogether since that epoch.
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Chambers, K. C., G. K. Miley, and W. J. M. van Breugel. “4C41.17: A Radio Galaxy at the Redshift of 3.8.” Astrophysical Journal 363 (November, 1990): 21-39. Reports on the discovery, the observational techniques used, and conclusions drawn from the data. Figures show clearly the emission lines detected with evidence for the correct identification using redshifts. -
Ferris, Timothy. Galaxies. 1982. Reprint. New York: Harrison House, 1987. Excellent introduction to the subject presents a clearly written, beautifully illustrated discussion of astronomy and cosmology. Easily accessible to lay readers. Includes many photographs of galaxies and star clusters. -
_______. The Red Limit: The Search for the Edge of the Universe. Rev. ed. New York: Harper Perennial, 2002. Well-presented volume discusses the history of the major discoveries in astronomy, paying particular attention to the individuals involved. Provides a comprehensible, accurate discussion of astronomy written in an engaging style for readers who have no familiarity with modern cosmological ideas. Includes extensive glossary, selected bibliography, and index. -
Hodge, Paul W., comp. The Universe of Galaxies. New York: W. H. Freeman, 1984. Collection of excellent articles previously published in Scientific American covers topics such as dark matter, superclusters, tidal effects between galaxies, and quasars as probes of the past. -
Pasachoff, Jay M. Astronomy: From the Earth to the Universe. 6th ed. Monterey, Calif.: Brooks/Cole, 2002. Excellent text includes an outstanding chapter on galaxies with many photographs of galaxies and clusters of galaxies. Discusses how 4C41.17 was located.
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