Greenland Cosmology Program

PI Institute/Department Email
Lubin, Philip
U of California, Santa Barbara, Physics Department
Funding Agency
DK\Research/Higher Ed\U. Copenhagen
Program Manager Funding Agency Email
Mercer, Dr. Jennifer
NSF, Office of Polar Programs
Space Physics
Science Summary

The millimeter wavelength sky is critical for understanding cosmological foregrounds in order to remove the galactic signature from the cosmological signature. This is especially important in searching for the gravity wave signature from the proposed inflationary era from polarization in the Cosmic Microwave Background (CMB). It is also much more interesting in its own right, than was anticipated even a few years ago, particularly with the recent Planck results. Our galaxy has two primary and very different emission mechanisms, namely synchrotron emission from high energy Cosmic Rays that dominates below 100 GHz and dust emission from heated interstellar dust grains that dominates above 100 GHz. It is critical that we have a series of very sensitive maps from 10-100 GHz to understand the synchrotron component of our galaxy to combine with the Planck high frequency dust maps from 100-900 GHz. The current WMAP and Planck maps at 23, 30, 40 and 70 GHz are insufficient, especially in polarization which neither satellite was specifically designed to measure and for which there is both insufficient sensitivity and serious systematic concerns. There are two major goals for the longer term effort in Greenland. One is to study the galactic foregrounds by making over about 50% of the sky AND to feed these maps and understanding into the deep cosmological maps we will make from Greenland at 30, 40 and eventually at 80 GHz to search for evidence of gravitational waves from the early universe. In order to do the latter (search for gravitational waves) researchers must do the former (characterize the galactic foregrounds) as so poignantly been shown by the recent Planck release. Greenland is one of the best observing sites and allow coverage of the northern hemisphere, which is less contaminated by the galaxy and is complimentary to southern hemisphere measurements at higher frequencies that study dust contaminated frequencies. A critical factor that is new is that the Planck data has recently shown that the higher frequency (about 100 GHz) polarization measurements are heavily contaminated by a much more complex dust emission than we had anticipated and at a higher level than anticipated. Since the atmosphere is quite absorptive above 100 GHz and essentially opaque above 300 GHz, with only a few observing frequency windows, in order to fully characterize the dust emission space based systems are needed. On the other hand the lower frequencies below 100 GHz are essentially completely open to observation from the ground with an exception being thr 60 GHz oxygen cluster but otherwise we can observe down to the ionospheric cutoff at 30 MHz. This will allow researchers to make much more detailed measurements of the galactic contamination from ground based measurements. Additionally the advantage of going into space compared to ground is only about a factor of 2 in system noise for the critical bands while at higher frequencies ground observations are much less sensitive than space both due to the increased opacity of the atmosphere and the decreased flux from the CMB at higher frequencies. These two effects give a strong science case to push to lower frequencies and to use the high altitude site in Greenland (Summit site) as an observing site. Another critical factor that favors observing at lower frequencies is that the technology we will use to make these measurements uses detectors that are extremely linear compared to the bolometers used at higher frequencies and thus atmospheric perturbations from water vapor fluctuations and pressure waves will be largely cancelled out to a much higher degree than bolometer based measurements allowing us to get polarization information on larger angular scales that is critical to understanding inflation and to measuring the ionization fraction of the universe (Tau). In the longer term we will want to duplicate the same system we build in Greenland in the Southern hemisphere to get complete sky coverage, possibly in Antarctica. This experiment will consist of a series of replicated telescopes using molds and technology the researchers have recently developed that allows for a staged approach with both short term results and long term observations. This data will be of use to not only the field of cosmology but to those who study galactic processes , high energy cosmic rays, galactic magnetic fields and even studies of the neutrino mass. This program has broad scientific implications and will place Denmark at the forefront of a critical area of cosmology.

Logistics Summary

With funding from Denmark’s University of Copenhagen, the project team will study the galactic foregrounds of the Milky Way from a ground-based sensing site at Summit Station. They will use data and understanding from these activities to create deep cosmological maps with which to search for evidence of gravitational waves from the early universe. The team’s primary activities involve deployment and operation of a 2.2m microwave telescope and supporting lab structure to carry out project activities, which will span two seasons, 2016 and 2017. In 2016, one field team member will make a site visit to Summit in August to help researchers plan for future visits. In 2017, no researchers will travel to Greenland. In 2018, plans currently are for two researchers to deploy the 2.2m microwave telescope and supporting infrastructure with two goals. First, they will map the polarized emission from the Milky Way at 10 GHz as a contaminant for Cosmic Microwave Background (CMB) polarization studies of the signature of Inflation. Second, they will assess Summit Station’s suitability and their observational techniques for measuring this CMB polarization signature at higher frequencies. An ancillary goal is to use the telescope to demonstrate the use of new infrared instruments for atmospheric monitoring. Findings from this initial study will inform future potential work by this group and the wider CMB radiation community.

In 2016, CPS will provide Air National Guard (ANG) coordination for one passenger and cargo, and Summit Station user days. NSF will recoup the costs of CPS support directly from the sponsoring institute. The PI will make all other arrangements, including KISS user days, and pay for them through the grant.

Season Field Site Date In Date Out #People
Greenland - Summit
Greenland - Summit