Friday, December 21, 2012

Life as an Observer

The Keck Telescopes on Mauna Kea
Courtesy W. M. Keck Observatory
One of the best aspects of being an astronomer is actually using a telescope and collecting data. Tonight, I have the opportunity to use one of the best telescopes in the world along with an exciting new instrument. Fellow CANDELS team member Mark Dickinson and I are observing on one of the Keck telescopes atop Mauna Kea on the Big Island of Hawaii. Mauna Kea is one of the best observing sites on the planet because the peak of the mountain where the telescopes are located sits above a substantial portion of the atmosphere. Because of this, the atmosphere has less of an effect on the images of astronomical objects than it would from an observatory at sea level. While the Keck telescopes themselves are at the summit of the 14,000 foot mountain, observers work from a remote observing facility located in Waimea. Being at this lower altitude makes it much easier to work and all of the instruments can be controlled remotely. 

The instrument that we are using is called MOSFIRE (Multi-Object Spectrometer for InfraRed Exploration) and is very new. It is a top of the line instrument that allows us to obtain sensitive, high resolution near-infrared spectroscopy of many objects at the same time. Most spectrographs in the near-infrared observe one object at a time. There are now several available that can observe many objects at once but they are often difficult to use for very faint galaxies. MOSFIRE is still brand new but so far has been working well. CANDELS team member Jonathan Trump recently published a paper on some first results! 

Mark Dickinson and I observing in the Keck I Remote Observing
Control Room
We spent the last several days carefully selecting targets to observe in two of the CANDELS fields, GOODS-S and COSMOS. Our primary targets of interest are distant luminous infrared galaxies detected by the Herschel Space Observatory at z~2. At this redshift, many of the interesting optical emission lines (such as the Hydrogen line known as H-alpha) are shifted into the near infrared. We can use these various lines to measure precisely how far away the galaxies are, whether or not an AGN might be present, how important that AGN is to the energy output of the galaxy, how much star formation is taking place in the galaxy, as well as many other things.

In addition to these targets, we are also observing AGN selected in other ways, such as through X-ray detections or from the shape of their SED in the near-infrared. If there is any space left we are also looking at other types of galaxies at these high redshifts to see if we can detect lines

Once our target selection was complete, we waited anxiously to see what the weather would do. The forecast called for clear skies but starting last night the summit of Mauna Kea became foggy. We awoke this morning (morning for an observing astronomer is really about 2 PM) to find that the fog had not cleared and some clouds had rolled in. We were really starting to get nervous! However, we proceeded as planned and began our afternoon setup. Around sunset, things were really looking dicey and it started to snow! Luckily for us that didn't last too long and the road to the summit remained clear for the night crew to head up and check things out. After a couple of hours, the fog cleared and the humidity dropped to a level low enough to open. We had a good time learning how to operate this new instrument and at 9:30 PM we started our first exposure on a set of galaxies in GOODS-S!

Video from a webcam at CFHT (the Canada-France-Hawaii Telescope) on Mauna Kea showing the clouds roll in Wednesday night and ice starting to form on the camera itself. Video courtesy of CFHT Observatory

Over the course of the night clouds have come and gone but the weather has steadily been improving. Right now we are observing galaxies in COSMOS and things are looking good. We are anxious to analyze our data and see how many of our galaxies have been detected. With any luck, we will soon be writing a blog post about our results! 

This is our last blog post before the holidays but we look forward to discussing more CANDELS science in January. Happy Holidays! 

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