Future Technology for TMT WFOS

Our group is carrying out research and development works toward an integral field unit (IFU) for the optical imaging spectrograph WFOS which is one of the instruments for TMT.

What is integral field spectroscopy?

There are two representative observation methods, imaging and spectroscopy. We can obtain an image (two spatial dimensions) with an imaging method (left panel of the above figure). In the case of spectroscopy, we observe the light thorough a narrow slit, so we can obtain only one spatial dimension. However we can get one additional wavelength dimension (right panel of the above figure). With these two methods, we obtain two-dimensional data (two spatial, or one spatial and one wavelength dimensions).

On the other hand, by using integral field spectroscopy, we can obtain three-dimensional data simultaneously. Simultaneity is very important because we can get homogeneous data which is not affected by whether condition change. For example, we can obtain three-dimensional data thorough many imaging observations with different filters. However, in such case, we cannot get homogenous data because each observation is carried out at different time and affected by whether condition change. In addition, such observations take long time.

Once we obtain three-dimensional data, we can extract various information such as monochromatic images or velocity fields from it. Because of this benefit, the integral field spectroscopy is the most suitable method for detailed studies of extended objects like galaxies.

A detection area of the detector such as CCD is two-dimensional plane, so the key point is how to obtain 3-dimensional information with 2-dimensional detector. An integral field unit (IFU) plays crucial role in this trick. Although there are some types of IFU, an image slicer IFU most efficiently use detection area of the detector. This means that we can obtain more information in one exposure.

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