A5032906309- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Astrophysics and Star Formation Studies
- Scottish History and National Identity
- Irish and British Studies
- Scientific Research and Discoveries
- Cosmology and Gravitation Theories
- Astrophysical Phenomena and Observations
- Historical Studies of British Isles
- Dark Matter and Cosmic Phenomena
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Adaptive optics and wavefront sensing
- Quantum chaos and dynamical systems
- Geophysics and Gravity Measurements
- Quantum Mechanics and Non-Hermitian Physics
- Australian History and Society
- Nonlinear Waves and Solitons
- Relativity and Gravitational Theory
- Statistical Mechanics and Entropy
- Statistical and numerical algorithms
- Neural Networks and Applications
University of Cambridge
2015-2024
Field Museum of Natural History
2021
Institute of Astronomy
2003-2019
Flatiron Health (United States)
2018
Flatiron Institute
2018
Andrew Faulkner Associates
2018
Bridge University
2005-2006
Diocese of Brooklyn
2006
Center for Theoretical Physics
1998-2003
University of Oxford
1997-2002
The Sloan Extension for Galactic Understanding and Exploration (SEGUE) Survey obtained ≈240,000 moderate-resolution (R ∼ 1800) spectra from 3900 Å to 9000 of fainter Milky Way stars (14.0 < g 20.3) a wide variety spectral types, both main-sequence evolved objects, with the goal studying kinematics populations our Galaxy its halo. are clustered in 212 regions spaced over three quarters sky. Radial velocity accuracies at 18, degrading 20. For signal-to-noise ratio >10 per resolution element,...
We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u, g, r, i, z photometry to study Milky Way halo substructure in the area around north Galactic cap. A simple color cut (g - r < 0.4) reveals tidal stream of Sagittarius dwarf spheroidal galaxy, as well a number other stellar structures field. Two branches (A and B) are clearly visible an RGB composite image created from three magnitude slices, there is also evidence for still more distant wrap behind branch. comparison these data...
This paper describes the Fifth Data Release (DR5) of Sloan Digital Sky Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and represents completion SDSS-I project (whose successor, SDSS-II will continue mid-2008). It five-band photometric for 217 million objects selected over 8000 square degrees, 1,048,960 spectra galaxies, quasars, stars from 5713 degrees that imaging data. These numbers represent a roughly 20% increment those Fourth Release; previous releases are...
We have used data from the Sloan Digital Sky Survey (SDSS) Data Release 5 to explore overall structure and substructure of stellar halo Milky Way using about 4 million color-selected main sequence turn-off stars. fit oblate triaxial broken power-law models data, found a `best-fit' oblateness 0.5~100pc, after accounting for (known) contribution Poisson uncertainties. The fractional RMS deviation actual distribution any smooth, parameterized model is >~40%: hence, highly structured....
Abstract The Gaia Sausage is the major accretion event that built stellar halo of Milky Way galaxy. Here, we provide dynamical and chemical evidence for a second substantial episode, distinct from Sausage. Sequoia Event provided bulk high-energy retrograde stars in halo, as well recently discovered globular cluster FSR 1758. There are up to six further clusters, including ω Centauri, many substructures Myeong et al., associated with progenitor dwarf galaxy, named Sequoia. mass galaxy ∼5 × 10...
Superintegrable Hamiltonians in three degrees of freedom possess more than functionally independent globally defined and single-valued integrals motion. Some familiar examples, such as the Kepler problem harmonic oscillator, have been known since time Laplace. Here, a classification theorem is given for superintegrable potentials with invariants that are quadratic polynomials canonical momenta. Such systems must separable solutions to Hamilton-Jacobi equation one coordinate system. There 11...
In this Letter, we announce the discovery of a new dwarf satellite Milky Way, located in constellation Canes Venatici. It was found as stellar overdensity north Galactic cap using Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The satellite's color-magnitude diagram shows well-defined red giant branch well horizontal branch. As judged from tip branch, it lies at distance ~220 kpc. Based on SDSS data, estimate an absolute magnitude MV ~ -7.9, central surface brightness μ0, V 28 mag...
We present a family of robust tracer mass estimators to compute the enclosed galaxy haloes from samples discrete positional and kinematical data tracers, such as halo stars, globular clusters dwarf satellites. The may be projected positions, distances, line sight velocities or proper motions. Forms estimator tailored for Milky Way M31 are given. Monte Carlo simulations used quantify uncertainty function sample size. For Way, satellite consists 26 galaxies with line-of-sight velocities. find...
ABSTRACT For stars with unresolved companions, motions of the centre light and that mass decouple, causing a single-source astrometric model to perform poorly. We show such can be easily detected reduced χ2 statistic, or renormalized unit weight error (RUWE), provided as part Gaia DR2. convert RUWE into amplitude image centroid wobble, which, if scaled by source distance, is proportional physical separation between companions (for periods up several years). test this idea on sample known...
In a companion paper by Koposov et al., RR Lyrae from \textit{Gaia} Data Release 2 are used to demonstrate that stars in the Orphan stream have velocity vectors significantly misaligned with track, suggesting it has received large gravitational perturbation satellite of Milky Way. We argue such mismatch cannot arise due any realistic static Way potential and then explore perturbative effects Large Magellanic Cloud (LMC). find LMC can produce precisely observed motion-track we therefore use...
We introduce a new maximum-likelihood method to model the density profile of blue horizontal branch and straggler stars apply it Sloan Digital Sky Survey Data Release 8 photometric catalogue. There are large number (∼20 000) these tracers available over an impressive 14 000 deg2 in both Northern Southern Galactic hemispheres, they provide robust measurement shape Milky Way stellar halo. After masking out vicinity Virgo overdensity Sagittarius stream, data consistent with smooth, oblate halo...
Using a large sample of bright nearby stars with accurate Gaia Data Release 2 astrometry and auxiliary spectroscopy we map out the properties principle Galactic components such as "thin" "thick" discs halo. We show that in Solar neighborhood, there exists population metal-rich ([Fe/H]>-0.7) on highly eccentric orbits. By studying evolution elemental abundances, kinematics stellar ages plane azimuthal velocity v_phi metallicity [Fe/H], demonstrate this halo-like component, which dub...
Motivated by recent observations of the Sagittarius stream, we devise a rapid algorithm to generate faithful representations centroids stellar tidal streams formed in disruption progenitor an arbitrary mass potential. Our method works releasing swarms test particles at Lagrange points around satellite and subsequently evolving them combined potential host progenitor. We stress that action progenitor's gravity is crucial making look almost indistinguishable from N-body realizations, as indeed...
Abstract The Gaia Sausage is an elongated structure in velocity space discovered by Belokurov et al. using the kinematics of metal-rich halo stars. They showed that it could be created a massive dwarf galaxy (∼5 × 10 ) on strongly radial orbit merged with Milky Way at redshift z ≲ 3. This merger would also have brought globular clusters (GCs). We seek evidence for associated Globular Clusters (GCs) analyzing 91 GCs action Data Release 2 catalog, complemented Hubble Space Telescope proper...
Predicting signals in experiments to directly detect dark matter (DM) requires a form for the local DM velocity distribution. Hitherto, standard halo model (SHM), which velocities are isotropic and follow truncated Gaussian law, has performed this job. New data, however, suggest that substantial fraction of our stellar lies strongly radially anisotropic population, ``Gaia sausage.'' Inspired by recent discovery, we introduce an updated model, ${\mathrm{SHM}}^{++}$, includes ``sausage''...
We report the discovery of a Milky Way satellite in constellation Antlia. The Antlia 2 dwarf galaxy is located behind Galactic disc at latitude $b\sim 11^{\circ}$ and spans $1.26$ degrees, which corresponds to $\sim2.9$ kpc its distance 130 kpc. While similar spatial extent Large Magellanic Cloud, orders magnitude fainter $M_V=-9$ mag, making it by far lowest surface brightness system known (at $\sim31.9$ mag/arcsec$^2$), $\sim100$ times more diffuse than so-called ultra galaxies. was...
We estimate the mass of Milky Way (MW) within 21.1 kpc using kinematics halo globular clusters (GCs) determined by Gaia. The second Gaia data release (DR2) contained a catalogue absolute proper motions (PMs) for set Galactic GCs and satellite galaxies measured DR2 data. select from only GCs, identifying total 34 spanning $2.0 < r 21.1$ kpc, use their 3D to anisotropy over this range be $\beta = 0.46^{+0.15}_{-0.19}$, in good agreement, though slightly lower than, recent sample HST PM...
A simple model for the Milky Way halo is presented. It has a flat rotation curve in inner regions, but density falls off sharply beyond an outer edge. This truncated, (TF) possesses rich family of distribution functions which vary velocity anisotropy. The used to estimate total mass using latest data on motions satellite galaxies and globular clusters at Galactocentric radii greater than 20 kpc. comprises set 27 objects with known distances radial velocities, six also possess measured proper...
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. Its color-magnitude diagram (CMD) shows well-defined subgiant branch, main sequence, turnoff, from which estimate distance ~30 kpc projected size ~250 × 125 pc2. The CMD suggests composite population some range metallicity and/or age. Based on its extent population, argue that is previously unknown...
In this Letter, we announce the discovery of a new dwarf galaxy, Leo T, in Local Group. It was found as stellar overdensity Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude diagram T shows two well-defined features, which interpret red giant branch and sequence young, massive stars. As judged from fits to diagram, it lies at distance about 420 kpc has an intermediate-age population with metallicity [Fe/H]= -1.6, together young blue stars age 200 Myr. There is compact...
We quantify the detectability of stellar Milky Way satellites in Sloan Digital Sky Survey (SDSS) Data Release 5. show that effective search volumes for recently discovered SDSS--satellites depend strongly on their luminosity, with maximum distance, $D_{max}$, substantially smaller than halo's virial radius. Calculating accessible volume, $V_{max}$, all faint detected satellites, allows calculation luminosity function satellite galaxies, accounting quantitatively detectability. find number...
We use Sloan Digital Sky Survey Data Release 5 photometry and spectroscopy to study a tidal stream that extends over ~50° in the north Galactic cap. From analysis of path colors magnitudes its stars, is ~20 kpc away at nearest detection (the celestial equator). detect distance gradient: farther from us higher declination. The contents are made up predominantly old metal-poor population similar globular clusters M13 M92. integrated absolute magnitude stars estimated be Mr ~ -7.5. There...
We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high accuracy using a string-length method. A subset 178 with spectrally derived metallicities employed derive metallicity-period-amplitude relations, which then used find and distances for entire sample. The lie between 5 115 kpc from Galactic center. They divided into subsets 316 RRab types 91 RRc based on their period, colour metallicity....
The latest Sloan Digital Sky Survey data reveal a prominent bifurcation in the distribution of debris Sagittarius dwarf spheroidal (Sgr) beginning at right ascension roughly 190 degrees. Two branches stream (A and B) persist same heliocentric distance over least 50 degrees arc. There is also evidence for more distant structure (C) well behind A branch. This paper provides first explanation bifurcation. It caused by projection young leading (A) old trailing (B) tidal arms Sgr, whilst arm lies...
We announce the discovery of a new Milky Way satellite Segue 2 found in data Sloan Extension for Galactic Understanding and Exploration (SEGUE). followed this up with deeper imaging spectroscopy on Multiple Mirror Telescope (MMT). From this, we derive luminosity Mv=−2.5, half-light radius 34 pc systemic velocity ∼−40 km s−1. Our also provide evidence stream around at similar heliocentric velocity, SEGUE show that it is present neighbouring fields. resolve dispersion as 3.4 s−1 possible ∼7...