Lyman-break galaxies arestar-forminggalaxies at highredshift that are selected using the differing appearance of the galaxy in severalimaging filters due to the position of theLyman limit. The technique has primarily been used to select galaxies at redshifts ofz = 3–4 usingultraviolet andoptical filters, but progress inultraviolet astronomy and ininfrared astronomy has allowed the use of this technique at lower[1] and higher redshifts using ultraviolet and near-infrared filters.
The Lyman-break galaxy selection technique relies upon the fact that radiation at higher energies than theLyman limit at 912 Å is almost completely absorbed by neutral gas aroundstar-forming regions of galaxies. In therest frame of the emitting galaxy, the emittedspectrum is bright at wavelengths longer than 912 Å, but very dim or imperceptible at shorter wavelengths. This is known as a "dropout", or "break", and can be used to find the position of the Lyman limit. Light with a wavelength shorter than 912 Å is in the far-ultraviolet range, and is blocked by Earth's atmosphere, but for very distant galaxies, the wavelengths of light arestretched considerably because of theexpansion of the universe. For a galaxy at redshiftz = 3, the Lyman break will appear to be at wavelengths of about 3600 Å, which is long enough to be detected by ground- or space-basedtelescopes.
Candidate galaxies around redshiftz = 3 can then be selected by looking for galaxies which appear in optical images (which are sensitive to wavelengths greater than 3600 Å), but do not appear in ultraviolet images (which are sensitive to light at wavelengths shorter than 3600 Å). The technique may be adapted to look for galaxies at other redshifts by choosing different sets of filters; the method works as long as images may be taken through at least one filter above and below the wavelength of the redshifted Lyman limit. In order to confirm the redshift estimated by the color selection, follow-upspectroscopy is performed. Although spectroscopic measurements are necessary to obtain a high-precision redshift, spectroscopy is typically much more time-consuming than imaging, so the selection of candidate galaxies via the Lyman-break technique greatly improves the efficiency of high-redshift galaxy surveys.[2][3]
The issue of their far-infrared emission is still central to the study of Lyman-break galaxies to better understand their evolution and to estimate their total star-formation rate. So far, only a small sample has been detected in far-infrared. Most of the individual results rely upon information that is gathered from lensed Lyman-break galaxies or from the rest-frame ultraviolet, or from a few objects detected by theHerschel Space Observatory[1] or using the stacking technique[4] that allows researchers to obtain averaged values for individually undetected Lyman-break galaxies.
But, recently, the stacking techniques on about22000 galaxies allowed, for the first time, to collect some statistical information on the dust properties of LBGs.[5]
In February 2022, astronomers reported the discovery of two Lyman break galaxies, namedHD1 andHD2, atz ~ 12–13, based upon studies that used the Lyman technique.[6][7] Also noteGLASS-z12, a distant galaxy that was discovered by theJames Webb Space Telescope in July 2022, andJADES-GS-z14-0, a Lyman-break galaxy atz ~ 14.32, which was also found by the JWST.
