The Distant Galaxy In Red And Infrared Light

Color Image of Redshift in Red and Near Infrared Light
The center of the Abell 370 cluster field seen in red optical (I + Z) and infrared (J+K') light. The arrow shows the position of the z=6.56 galaxy. Numerous arcs show gravitational lensing of faint galaxies behind the cluster by the mass of the many galaxies in the cluster's core. The horizontal streaks are due to stars just outside the field of the picture. The image combines 8 hours of infrared exposures on the Subaru 8.3-m telescope with 7 hours exposure in red optical light on the Keck I 10-m telescope, both on Mauna Kea.  The galaxy  can be seen, though very faintly, at these wavelengths.


These enlarged images show the distant galaxy in bright Lyman alpha emission (left panel) and at optical (R) wavelengths (right panel). The galaxy is undetectable in an 8-hour long R exposure with the Keck I 10-m telescope, but is readily seen in the 5.8-hour exposure through a 118 Å wide narrowband filter (central wavelength 9152 Å) containing hydrogen Lyman alpha emission from star formation. The insets show the narrowband image with a normalized continuum (Z) subtracted, to show emission, and with the neighboring galaxy completely removed (left panel), and the same region viewed with Hubble Space Telescope's WFPC2 camera in a 1.6 hour exposure through the F675W filter. The galaxy cannot be seen at any wavelengths below the emission line.


The spectrum of the Lyman alpha emitter from a 4-hr exposure made with the LRIS spectrograph on the Keck I 10m telescope. The emission line is at 9187 Angstrom. The solid line near the axis shows the median continuum flux above the line, and gives a break strength consistent with the broadband measurements. The solid line above the emission shows the 50 percent width of the narrowband filter, whose profile is shown overlaid on the fluxed nightsky spectrum, plotted at 1 percent strength above the object spectrum. Enlarged plots of the object's emission line and 1 percent of the nightsky background spectra are shown in the inset, where the asymmetry of the line profile, which is produced by the absorption in the intergalactic gas, can be clearly seen.

Esther M. Hu