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Trancho G.,Giant Magellan Telescope Organization | Miller B.W.,Gemini Observatory | Schweizer F.,Carnegie Observatories | Burdett D.P.,University of Adelaide | Palamara D.,Monash University
Astrophysical Journal | Year: 2014

We present the results of combining Hubble Space Telescope optical photometry with ground-based Ks -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIKs GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ∼1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies. © 2014. The American Astronomical Society. All rights reserved.

Davari R.,University of California at Riverside | Davari R.,Carnegie Institution for Science | Ho L.C.,Carnegie Institution for Science | Ho L.C.,Peking University | And 2 more authors.
Astrophysical Journal | Year: 2014

Massive quiescent galaxies at z 2 are apparently much more compact than galaxies of comparable mass today. How robust are these size measurements? We perform comprehensive simulations to determine possible biases and uncertainties in fitting single-component light distributions to real galaxies. In particular, we examine the robustness of the measurements of the luminosity, size, and other structural parameters. We devise simulations with increasing realism to systematically disentangle effects due to the technique (specifically using GALFIT) and the intrinsic structures of the galaxies. By accurately capturing the detailed substructures of nearby elliptical galaxies and then rescaling their sizes and signal-to-noise to mimic galaxies at different redshifts, we confirm that the massive quiescent galaxies at z 2 are significantly more compact intrinsically than their local counterparts. Their observed compactness is not a result of missing faint outer light due to systematic errors in modeling. In fact, we find that fitting multi-component galaxies with a single Sérsic profile, the procedure most commonly adopted in the literature, biases the inferred sizes higher by up to 10%-20%, which accentuates the amount of size evolution required. If the sky estimation has been done robustly and the model for the point-spread function is fairly accurate, GALFIT can retrieve the properties of single-component galaxies over a wide range of signal-to-noise ratios without introducing any systematic errors. © 2014. The American Astronomical Society. All rights reserved.

Glaese R.M.,Moog | Sheehan M.,Giant Magellan Telescope Organization
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The Giant Magellan Telescope (GMT) is a planned large terrestrial telescope with a segmented primary mirror with a 24.5 meter overall diameter. Like most terrestrial telescopes, the GMT resides within an enclosure designed to protect the telescope from the elements and to reduce the effects of wind on the optical performance of the telescope. Wind impingement on the telescope causes static deformation and vibration in the telescope structure that affects the alignment and image jitter performance of the telescope. Actively controlled primary mirror segments and a secondary mirror can correct for the static and low frequency portions of the wind effects, but typically the actuators do not have the bandwidth to address higher frequency components of the wind environment. Preliminary analyses on the GMT indicate that the image jitter associated with wind effects meets budgeted allowances but without much margin. Preliminary models show that the bulk of the residual jitter arises from excitation of a small number of modes in the 9 to 12 Hz range. Therefore, as a risk mitigation effort to increase the margin on the wind induced jitter, passive and active vibration mitigation approaches have been examined for the GMT, which will be the focus of this paper. Using a finite element model of the GMT along with wind loading load cases, several passive and active vibration mitigation approaches were analyzed. These approaches include passive approaches such as tuned mass dampers targeting the worst offending modes, and constrained layer damping targeting all of the modes within the troublesome frequency range. Active approaches evaluated include two active damping approaches, one using several reaction mass actuators and the other using active strut type actuators. The results of the study show that although all approaches are successful in reducing the jitter, the active damping approach using reaction mass actuators offers the lightest weight, least implementation impact, and most adaptability of any of the approaches. © 2012 SPIE.

News Article | November 12, 2015

The Giant Magellan Telescope, an international project designed to take astronomy into the next decade, will begin operations in 2021 and provide images 10 times clearer than the Hubble space telescope, organizers said. "The Giant Magellan Telescope will revolutionize our view and understanding of the universe, and allow us to see and study objects whose light has been traveling for over 13 billion years to reach us," said Taft Armandroff, the head of the consortium behind the project, at a groundbreaking ceremony attended by Chilean President Michelle Bachelet. The $500 million telescope is being built in the Atacama Desert in northern Chile, whose exceptionally clear skies have already drawn some of the world's most powerful telescopes and leading stargazers. It combines seven enormous mirrors, each 8.4 meters (27.5 feet) wide, to create a single telescope 25 meters in diameter. "Astronomy is a long-term science. We will continue down the path of surprises the universe sets out for us," Bachelet said at the ceremony at the Las Campanas Observatory. The telescope will help scientists answer fundamental questions about the cosmos by studying planets outside our solar system, watching galaxies and stars form, and collecting evidence on the existence of dark matter and dark energy, said the Giant Magellan Telescope Organization. It will allow them to see galaxies whose light has been traveling toward Earth since shortly after the Big Bang—13.8 billion years, said the 11-member consortium. Finding Earth-like planets orbiting nearby stars is a major aim, it said.

Walsh J.R.,European Southern Observatory | Jacoby G.H.,Giant Magellan Telescope Organization | Peletier R.F.,NOVA Kapteyn Astronomical Institute | Walton N.A.,University of Cambridge
Astronomy and Astrophysics | Year: 2012

Context. Planetary nebulae in the nearest large elliptical galaxy provide light element abundances difficult or impossible to measure by other means in a stellar system very different from the galaxies in the Local Group. Aims. The light element abundance pattern from many planetary nebulae (PNe) at a range of radial distances was measured from optical spectroscopy in the elliptical galaxy NGC 5128, which hosts the radio source Centaurus A. The PN abundances, in particular for oxygen, and the PN progenitor properties are related to the galaxy stellar properties. Methods. PNe in NGC 5128 covering the upper 4 mag of the luminosity function were selected from a catalogue. VLT FORS1 multi-slit spectra in blue and red ranges were obtained over three fields at 3, 9 and 15′ projected radii (4, 8 and 17 kpc, for an adopted distance of 3.8 Mpc) and spectra were extracted for 51 PNe. Accurate electron temperature and density diagnostics are usually required for abundance determination, but were not available for most of the PNe. Cloudy photoionization models were run to match the spectra by a spherical, constant density nebula ionized by a black body central star. He, N, O and Ne abundances with respect to H were determined and, for brighter PN, S and Ar; central star luminosities and temperatures are also derived. Results. Emission line ratios for the 51 PNe are entirely typical of PN such as in the Milky Way. The temperature sensitive [O III]4363 Å line was weakly detected in 10 PNe, both [O II] and [O III] lines were detected in 30 PNe, and only the bright [O III]5007 Å line was detected in 7 PN. For 40 PNe with Cloudy models, from the upper 2 mag of the [O III] luminosity function, the most reliably estimated element, oxygen, has a mean 12 + log(O/H) of 8.52 with a narrow distribution. No obvious radial gradient is apparent in O/H over a range 2-20 kpc. Comparison of the PN abundances with the stellar population, from the spectra of the integrated stellar light on the multi-slits and existing photometric studies, suggests an average metallicity of [Fe/H] =-0.4 and [O/Fe] = 0.25. Conclusions. The masses of the PN central stars in NGC 5128 deduced from model tracks imply an epoch of formation even more recent than found for the minority young population from colour magnitude studies. The PN may belong to the young tail of a recent, minor, star formation episode or derive from other evolutionary channels, perhaps involving binary stars. © 2012 ESO.

Acton D.S.,Ball Corporation | Bouchez A.,Giant Magellan Telescope Organization
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The Giant Magellan Telescope (GMT) is a 25.4 m diameter ground-based segmented Gregorian telescope, composed of 7 8.4 meter diameter primary mirror segments, and 7 1 meter diameter adaptive secondary mirror segments. Co-phasing of the integrated optical system will be partially achieved by making real-time measurements of the wavefront of an off-axis guide star. However, slowly varying aberrations due to thermal and gravitational effects, as well as wind buffeting, will make it difficult to maintain alignment using real-time optical measurements alone. Consequently, we are proposing internal metrology systems to maintain the relative alignment of the optical elements. In this paper we describe a differential capacitive edge sensing system to maintain the relative alignment of the adaptive secondary mirror reference bodies. We also propose an interferometric system for sensing of the relative displacements of primary mirror segments. © 2012 SPIE.

Neichel B.,Gemini Observatory | D'Orgeville C.,Australian National University | Callingham J.,University of Sydney | Rigaut F.,Australian National University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

Detailed knowledge of the mesospheric sodium layer characteristics is crucial to estimate and optimize the performance of laser guide star (LGS) assisted adaptive optics (AO) systems. In this paper, we present an analysis of two sets of data on the mesospheric sodium layer. The first set comes from a laser experiment that was carried out at Cerro Tololo to monitor the abundance and altitude of the mesospheric sodium in 2001, during six runs covering a period of one year. These data are used to derive the mesospheric sodium column density, the sodium layer thickness and the temporal behaviour of the sodium layer mean altitude. The second set of data was gathered during the first year of the Gemini Multi-Conjugate Adaptive Optics (MCAO) System (GeMS) commissioning and operations. GeMS uses five LGSs to measure and compensate for atmospheric distortions. Analysis of the LGS wavefront sensor (WFS) data provides information about the sodium photon return and the spot elongation seen by the WFS. All these parameters show large variations on a yearly, nightly and hourly basis, affecting the LGS brightness, shape and mean altitude. The sodium photon return varies by a factor of 3-4 over a year, and can change by a factor of 2 over a night. In addition, the comparison of the photon returns obtained in 2001 with those measured a decade later using GeMS shows a significant difference in laser format efficiencies. We find that the temporal power spectrum of the sodium mean altitude follows a linear trend, in good agreement with the results reported by Pfrommer & Hickson. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Huang S.,Nanjing University | Huang S.,Carnegie Institution for Science | Ho L.C.,Carnegie Institution for Science | Peng C.Y.,Giant Magellan Telescope Organization | And 2 more authors.
Astrophysical Journal Letters | Year: 2013

Massive early-type galaxies (ETGs) have undergone dramatic structural evolution over the last 10 Gyr. A companion paper shows that nearby elliptical galaxies with M * ≥ 1.3 × 1011 M generically contain three photometric subcomponents: a compact inner component with effective radius Re ≲ 1 kpc, an intermediate-scale middle component with Re ≈ 2.5 kpc, and an extended outer envelope with Re ≈ 10 kpc. Here we attempt to relate these substructures with the properties of ETGs observed at higher redshifts. We find that a hypothetical structure formed from combining the inner and middle components of local ellipticals follows a strikingly tight stellar mass-size relation, one that resembles the distribution of ETGs at z ≈ 1. Outside of the central kpc, the median stellar mass surface density profiles of this composite structure agree closest with those of massive galaxies that have similar cumulative number density at 1.5 < z < 2.0 within the uncertainty. We propose that the central substructures in nearby ellipticals are the evolutionary descendants of the "red nuggets" formed under highly dissipative ("wet") conditions at high redshifts, as envisioned in the initial stages of the two-phase formation scenario recently advocated for massive galaxies. Subsequent accretion, plausibly through dissipationless ("dry") minor mergers, builds the outer regions of the galaxy identified as the outer envelope in our decomposition. The large scatter exhibited by this component on the stellar mass-size plane testifies to the stochastic nature of the accretion events. © 2013. The American Astronomical Society. All rights reserved..

Huang S.,Nanjing University | Huang S.,Carnegie Institution for Science | Ho L.C.,Carnegie Institution for Science | Peng C.Y.,Giant Magellan Telescope Organization | And 2 more authors.
Astrophysical Journal | Year: 2013

Motivated by recent developments in our understanding of the formation and evolution of massive galaxies, we explore the detailed photometric structure of a representative sample of 94 bright, nearby elliptical galaxies, using high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample spans a range of environments and stellar masses, from M * = 1010.2 to 1012.0 M . We exploit the unique capabilities of two-dimensional image decomposition to explore the possibility that local elliptical galaxies may contain photometrically distinct substructure that can shed light on their evolutionary history. Compared with the traditional one-dimensional approach, these two-dimensional models are capable of consistently recovering the surface brightness distribution and the systematic radial variation of geometric information at the same time. Contrary to conventional perception, we find that the global light distribution of the majority (≳75%) of elliptical galaxies is not well described by a single Sérsic function. Instead, we propose that local elliptical galaxies generically contain three subcomponents: a compact (Re ∼ 1 kpc) inner component with luminosity fraction f 0.1-0.15; an intermediate-scale (Re 2.5 kpc) middle component with f 0.2-0.25; and a dominant (f = 0.6), extended (Re 10 kpc) outer envelope. All subcomponents have average Sérsic indices n 1-2, significantly lower than the values typically obtained from single-component fits. The individual subcomponents follow well-defined photometric scaling relations and the stellar mass-size relation. We discuss the physical nature of the substructures and their implications for the formation of massive elliptical galaxies. © 2013. The American Astronomical Society. All rights reserved..

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