Tuesday, September 16, 2014

Gemini Frontier Field: First Data Now Available

Figure 1. Part of MACS J0416-2403 seen by GSAOI. The average angular resolution is about 80 milliarcseconds, the full field-of-view of the data released is nearly twice as large as shown here. 

Figure 2. Comparison of the Ks-band (2.2 micron) image taken with GSAOI (left) and the H-band (1.6 micron) image as observed with HST/WFC3. While not as deep as HST data, the new GeMS/GSAOI dataset offers twice the resolution on the distant universe

The first data from the Gemini Frontier Fields are now available for astronomers. This dataset features wide-field adaptive optics images of a strong lensing galaxy cluster obtained with the GeMS adaptive optics system and GSAOI on the Gemini South telescope. 

Massive clusters of galaxies provide astronomers with a unique view of the very distant Universe behind them as well as revealing their galaxies themselves. The deep gravitational potential of clusters distorts and amplifies the background galaxies - an effect known as strong gravitational lensing. In this way, galaxies that are otherwise unobservable with existing telescopes, are acquirable. This circumstance allows astronomers to study these distant galaxies in great detail, shedding light on how the very young universe looked, and pushing the frontiers of our knowledge. 

In the course of the Frontier Fields campaign, the Hubble Space Telescope (HST) observed six galaxy clusters, selected for their strong lensing effects. Deep optical and near-infrared images are already included in the HST dataset, augmented by additional X-ray and far-infrared observations with the Chandra and Spitzer space telescopes, respectively. However, one limitation of the HST data is its sensitivity cut-off at wavelengths longer than 1.7 microns. 

A Director's Discretionary Time program at Gemini has helped to fill the gap at 2.2 microns (Ks-band), utilizing Gemini's advanced multi-conjugated adaptive optics system, GeMS with the Gemini South Adaptive Optics Imager (GSAOI). Staff astronomer Rodrigo Carrasco led the observations, and the first of three targets visible from Gemini South in Chile is MACS J0416.1-2403, which is available now. Observations of the galaxy cluster Abell 2744 have started recently, and Abell 370 is slated for observation at Gemini South over the next year. 

GeMS/GSAOI delivers near diffraction-limited images in the near infrared (0.9-2.5 microns), over a field nearly as large as HST's Wide Field Camera 3 (WFC3). Using five artificial laser guide stars, and up to three natural guide stars, GeMS/GSAOI can correct for atmospheric turbulence at an unprecedented level, making it the most powerful wide-field adaptive optics system currently available to astronomers. This system is also the only multi-conjugated adaptive optics system currently operational at an 8-meter-class telescope. "We have achieved an angular resolution of 70-100 milliarcseconds with these data, which is a factor of two better than HST/WFC3, even though we did not go as deep as HST. These are truly spectacular data!" says Mischa Schirmer, a staff astronomer at Gemini who led the data processing effort. 

The fully calibrated and co-added images of MACS J0416.1-2403 are now available to the scientific community in order to maximize scientific return. 

The associated paper is available from http://arxiv.org/abs/1409.1820.