D11 Galaxies: Integral Field Spectroscopy

Topic

The centerpiece of this model is the world's largest integral-field spectrograph, installed on an eight-meter telescope and capable of capturing tens of thousands of simultaneous spectra across its entire field of view.

The integral-field technique employed by this spectrograph subdivides the light from every point in the field into numerous modules; each module reformats its portion of the field into slits that feed parallel spectrometers, ensuring that every spatial pixel in the final image is associated with its own complete spectrum.

Having a complete spectrum for every pixel makes it possible to measure—in a single observation—both the kinematics of an entire galaxy (such as radial velocities and velocity dispersion) and its chemical composition across its entire extent.

The most remarkable feature of this instrument is that it converts every point in the sky into a spectrum rather than merely photographing it, thereby producing a three-dimensional data cube instead of a simple image; when combined with adaptive optics over a narrower field, its resolution rivals that of a space telescope, despite the observations being conducted from the ground.

This same instrument has discovered faint gas filaments connecting galaxies to their surrounding medium, mapped dark matter in various clusters via strong gravitational lensing, and detected supernovae in distant galaxies without having been aimed directly at them. Thus, from the integral-field spectrograph that opens this account to the serendipitously detected supernovae that conclude it—encompassing the integral-field technique and the three-dimensional data cube along the way—integral-field spectroscopy enables a single instrument, while observing a specific point in the sky, to yield not only a galaxy's kinematics and chemical makeup but also discoveries that were never even the target of the observation.

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