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Large and Long Programs (LLPs)

August 14, 2014

Large and Long Programs (LLPs) enable high-impact science programs and Gemini, allowing observations that require significantly more time than a partner typically approves for a single program or long-term status. LLPs may extend from two to six semesters, and they are expected to promote collaborations from across the parnership’s communities.

The first LLPs began observations in the 2014B semester:

 

 

GN-2014B-LP-1 COL-OSSOS: COLours for the Outer Solar System Object Survey
Principal Investigator: W. Fraser (NRC Herzberg Astronomy and Astrophysics)

The surfaces of trans-Neptunian objects (TNOs) have for a long time been poorly understood. Other than the large objects which exhibit signatures of various ices, astronomers have been able to discern very little about the compositional makeup of most TNOs. In recent years, some concrete knowledge about the distribution of surface colours of small TNOs has come to light. It is now generally accepted that small TNOs fall into at least three classes of object based on their surface colours and albedo. TNO surface type is also highly correlated with dynamical class, with certain types of TNO only being found in certain regions of the outer Solar System. For example, the so-called cold classical objects are both uniquely red and dynamically cold, while more dynamically excited objects such as the Plutinos - of which Pluto is a member - exhibit a bimodal distribution of surface colours from almost entirely neutral reflectors to some of the reddest objects in the Solar System. This colour-dynamical correlation presents the intriguing idea that the surfaces of TNOs contain information on more than composition, but as well hold the key to understanding the dynamical processes that lead to the giant planets violently dispersing the protoplanetesimal disk and populating the Kuiper Belt region. It is around this idea that the COL-OSSOS survey is designed. Using nearly 400 hours GMOS and NIRI observations on Gemini-North, over the next 4 years this program will observe optical and NIR Colours of all targets in the Outer Solar System Origins Survey (OSSOS) brighter than r’=23.5. The focus of the survey is completeness and consistency, with the same SNR=25 being reached in all bands, for all targets brighter than our depth limit.

This survey will, for the first time, provide a combined compositional-dynamical test to answer key questions about the Outer Solar System’s cosmogony. For example, was Neptune’s motion from its primordial formation location to its current locale violent and ‘jumpy’, or smooth? By mapping the fraction of objects with cold-classical like surface colours throughout the Trans-Neptunian region, we will be able to determine how much of the belt was populated by dynamical scattering, a signature of violent motion, versus sweep-up, a signature of smooth motion as Neptune passed through and dispersed the protoplanetesimal disk. As another example, we will be able to determine if the primordial disk was compositionally homogenous, or heterogeneously structured with many ice lines throughout its extent. The surfaces of TNOs must reflect that structure; a heterogeneous disk will result in a clumpy colour distribution with many unique types, while a homogeneous disk will result in a smooth distribution of colours with only a few distinct types. The legacy of COL-OSSOS is a large TNO dynamical and colour database of roughly 140 TNOs with fully understood observational biases from discovery to compositional characterization.

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GN-2014B-LP-2 Rapid Spectroscopy of Elusive Transients and Young Supernovae
Principal Investigator: M. Kasliwal (Carnegie)

The intermediate Palomar Transient Factory (iPTF) is systematically exploring the optical transient sky. We focus on short timescales to optimize the survey discovery rate of very young supernovae and rare ephemeral transients. Building on the PTF legacy, our new iPTF software pipeline is geared towards automated alerts for follow-up within hours of discovery. Rapid response spectroscopy of iPTF transients will unveil (i) progenitors of supernovae: shock cooling, companion, circumstellar material properties, (ii) origin of recently discovered but poorly understood new classes of gap transients, and (iii) redshifts of relativistic afterglows discovered in seventy square degree searches or even independent of a high energy trigger. These unique physical insights into the nature of the explosion cannot be gained from late-time observations. Hence, we will undertake a dedicated iPTF-Gemini program for rapid spectroscopy. The rapid Gemini data will be complemented with panchromatic observations: radio with JVLA and CARMA, UV/X-ray with the Swift satellite and long-term optical/near-IR studies with Palomar/Magellan/Keck.

Figure 1. Gemini Observatory’s queue observing mode and quick response to Target Of Opportunity (ToO) triggers facilitates the early observation of young supernova.

Figure 2. The iPTF team.

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GN-2014B-LP-3 / GS-2014B-LP-4 Where Accretion Meets Feedback: A Galaxy Redshift Survey in HST/COS Quasar Fields
Principal Investigator: J. Werk (University of California, Santa Cruz)

We will perform a new GMOS galaxy redshift survey at z = 0.1 - 0.7 in the fields of 18 QSOs that have been observed with Hubble's Cosmic Origins Spectrograph. With thousands of new galaxy redshifts (a 50x gain over present surveys) we will fill the existing map of circumgalactic medium (CGM) gas out to 3Rvir to address the extent of metal transport and recycling, and the mechanisms of galaxy quenching in halos and large-scale environments, and the 2D structure of the CGM. This program will provide a uniquely rich dataset with a substantial legacy value.

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Figure 3.

GS-2014B-LP-1 The GOGREEN Survey of dense galaxy environments at 1<z<1.5
Principal Investigator: M. Balogh (University of Waterloo)

Clusters of galaxies are among the most massive structures in the Universe, with up to 1000 trillion times the mass of the Sun in stars, gas and dark matter. Such clusters play a central role in studies of cosmology, galaxy and structure formation, as well as plasma physics and supermassive black hole growth, and for the determination of the nature of dark matter. Their enormous gravitational potentials allow them to act as cosmic "calorimeters", maintaining an observable record of all the energy inputs and outputs associated with galaxy formation over the history of the Universe. They host the most massive galaxies, which are among the first luminous objects to form. Clusters are also the ideal places to study rare and extraordinary perturbations to galaxy evolution, such as hydrodynamic stripping of gas, tidal stripping of matter, and high-speed gravitational encounters. Much of what we have learned about galaxy evolution is thanks to years of research on these systems.

The Gemini Observations of Galaxies in Rich Early ENvironments (GOGREEN) Survey will take advantage of upgraded detectors, which will make Gemini's GMOS spectrographs the best in the world for studying distant galaxy clusters. The survey will obtain multi-object spectroscopy of 21 clusters in the redshift range 1<z<1.5, representing the Universe when it was a third of its present age. The targets are selected to span a wide range of masses, representing the range of building blocks from which today's clusters were built. The sample of over 1000 spectroscopically confirmed members will reach unprecedented stellar masses at this redshift, providing the first look at environmental effects on galaxy evolution at a time when galaxies were growing in a fundamentally different way from today. With up to 15 hours of total integration time on the faintest galaxies, the spectra will allow us to measure the dynamics of different galaxy populations, their stellar populations, and to obtain a robust measurement of the abundance of low-mass, quiescent galaxies. By combining GOGREEN with our existing data on the lower-redshift descendants of these clusters, we will measure the evolution of satellite galaxy dynamics and stellar populations over the last 9.3Gyr of cosmic time. This will provide new leverage to theoretical models, importantly testing them at an epoch where there are currently almost no constraints.

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Figure 4. Distribution of targets on the sky.

GS-2014B-LP-2 Probing the dark halo of the Milky Way with GeMS/GSAOI
Principal Investigator: Tobias Fritz (University of Virginia)

The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a testbed for the study of the processes of galaxy formation in general. This is because the constituents of the Local Group span a wide range of parameters such as star formation efficiency, dark matter halo size, and environment. These parameters can be turned into tests of the pressing questions governing both cold dark matter theory and galaxy formation studies, such as the distribution of matter on small scales, and even the impact of reionization. A better estimate of the total Milky Way halo mass is important for many of these questions. Due to the mass anisotropy degeneracy it is not well determined from radial velocities. Current constraints on the shape of the halo are surprising: it is oblate, but misaligned by 90 degrees with the Disk. Proper motions are required in addition to the (generally known) radial velocities to test such halo models. Turning to the baryonic sector, while accretion evidently plays a role in galaxy formation, as attested to by the existence of tidal debris streams, it is not yet excluded that some halo components formed in situ. To disentangle this process in detail, orbits are necessary.

In this program we use GeMS/GSAOI to obtain proper motions, which are missing phase space components, for a variety of tracers in the Milky Way halo, in order to constrain its shape and total mass, as well as the orbital histories of the tracers. We will employ background galaxies as a reference frame to obtain absolute motions. This pioneering study will also produce an astrometric calibration suitable for other uses of GeMS/GSAOI. Using 143 h distributed over three years we will obtain proper motions for a set of dwarf galaxies, globular clusters, and M-giants in the Sagittarius stream, distributed between 20 and 100 kpc in the halo of our Galaxy (see Figure 4 for the target distribution over the sky).

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GS-2014B-LP-3 Followup of newly discovered Near-Earth objects from the NEOWISE survey
Principal Investigator: J. Masiero (JPL)

Our program's goal is to acquire followup observations of asteroids and comets that pass close to the Earth, which have been newly discovered by the NEOWISE survey. NEOWISE is an Earth-orbiting infrared survey telescope that is constantly scanning the sky 90 degrees from the Sun. Measurements in infrared light allow us not only to find new small bodies of the Solar system, but also constrain their diameters, an important physical parameter for understanding the potential danger they pose to Earth. With ground-based followup at visible wavelengths we can also determine how reflective asteroids are, giving us an idea of their composition, and study the gas and dust properties of comets.

NEOWISE can only observe newly discovered objects for about one day, which is enough to identify asteroids and comets but not constrain their orbits. Followup data are critical to ensuring the orbits of these objects are accurately measured, and thus they can be tracked until their next pass by the Earth. The Gemini South telescope allows our team to ensure that the faintest new discoveries in the Southern Hemisphere are not lost, and that their physical properties are well understood.

Figure 5. The NEOWISE team as seen in the infrared (L-to-R: Carrie Nugent, Rachel Stevenson, Tommy Grav, Joe Masiero, John Dailey, Amy Mainzer, James Bauer, Sarah Sonnett).

Figure 6. Sequence of four Gemini images of near-Earth asteroid 2014 EN45 (circled). This object was discovered by the NEOWISE survey on 6 March 2014 and imaged by GMOS-S on 13 March 2014, which provided critical astrometry needed to confirm the asteroid's orbit. 2014 EN45 is ~800 meters in diameter and is as dark as a piece of coal.

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GS-2014B-LP-5 Spectroscopic Confirmation and AO imaging Follow-Up of Dark Energy Survey Strong Lensing Systems and Spectra for Photometric Redshift Calibration
Principal Investigator: E. Buckley-Geer  (Fermi National Accelerator Laboratory)

Over five observing seasons, which started in August 2013, the Dark Energy Survey (DES) will carry out a wide field survey of 5000 deg2 over the Southern Galactic Cap in the 5 filters grizY and a 30 deg2 supernova survey spread over 10 fields. Among the millions of astronomical objects that will be imaged by DES are rare instances of "strong lensing" systems, where the effects of general relativity, Einstein's theory of gravity, are demonstrated in a visually striking fashion. When a foreground "lens" object is by chance very closely aligned, along the line of sight, on the sky with a much more distant background "source" object, the light from the source may be significantly deflected as it passes by the lens, due to the gravitational field produced by the lensing object's mass. When the distant source is fuzzy single distant background galaxy the this strong lensing effect leads to big distortions in it's appearance: it may be transformed into a long bright arc, maybe into multiple blue knots or, in the rarest cases, into a so-called Einstein ring. On the other hand if the source is a quasar (a quasar is a compact region in the center of a massive galaxy, that surrounds its central supermassive black hole) then it will be transformed into multiple stellar-like objects.

Figure 7. Examples of lensing objects.

Figure 8. Team photo.

This wide variety in appearance of strongly lensed images is a consequence of the complexities of the lensing mass, which can range from an individual galaxy to a rich cluster of many galaxies, together with the much more massive dark matter halos in which the (luminous) galaxies reside. Studies of strong lensing systems can thus reveal to us properties of the distribution of dark matter that accompanies galaxies and galaxy clusters. Moreover strong lensing can provide yet another way to study dark energy. For example, cosmological parameters, including dark energy, will affect the abundance and frequency of strong lensing systems and hence influence how many such systems we'll find in DES. The lensed quasars are particularly useful for determining the Hubble constant which governs the rate of expansion of the universe. We expect to find many new lenses quasars in DES.

In order to use these strong lenses for constraining dark matter and dark energy we need to know how far away they are and we do this by measuring their redshifts. We observe the object and obtain a spectrum of it's light and look for features such as absorption lines and emission lines. These features can be compared with known features in the spectrum of various chemical compounds found on earth. If the same features are seen in an observed spectrum from a distant source but occurring at shifted wavelengths then the redshift can be calculated. Each lensing system typically contains multiple images of the source object so we will use the GMOS instrument in its multi-object mode to efficiently obtain many spectra simultaneously.

In addition to the primary lensing targets, we are also piggybacking observations of about another 50 galaxy targets per field, for a total of about 3000 galaxy redshifts over the course of our full program. This sample will be used to improve the measurement of the redshift distribution of faint DES galaxies, by providing a galaxy sample distributed over many fields spread across the DES footprint, as opposed to our present situation of relying on a small number of fields for this purpose. Better knowledge of the galaxy redshift distribution will in particular be used to help improve the determination of dark energy cosmological parameters by DES.

The team consists of 29 scientists from the USA, Australia, Brazil, the United Kingdom, Switzerland, Japan and Taiwan.

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