A5077147673- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Star Formation Studies
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Cosmology and Gravitation Theories
- History and Developments in Astronomy
- Scientific Research and Discoveries
- Dark Matter and Cosmic Phenomena
- Fluid Dynamics Simulations and Interactions
- Adaptive optics and wavefront sensing
- Meteorological Phenomena and Simulations
- Remote Sensing in Agriculture
- Computational Physics and Python Applications
- Geophysics and Gravity Measurements
- Maritime and Coastal Archaeology
- Radio Astronomy Observations and Technology
- Iterative Learning Control Systems
- Calibration and Measurement Techniques
- Photonic Crystals and Applications
- Climate variability and models
University College London
2016-2025
National Astronomical Observatory of Japan
2022-2025
University College Lahore
2023
University of Nottingham
2013
Swinburne University of Technology
2001-2009
Carnegie Observatories
2005-2009
University of Central Lancashire
2006
Tohoku University
1999-2001
Czech Academy of Sciences, Astronomical Institute
1999
Ibaraki University
1998
The disk galaxy simulated using our chemodynamic formation code, GCD+, is shown to have a thick-disk component. This evidenced by the velocity dispersion versus age relation for solar neighborhood stars, which clearly shows an abrupt increase in at look-back time of approximately 8 Gyr, and excellent agreement with observation. These stars are formed from gas that accreted during chaotic period hierarchical clustering high redshift. scenario be consistent observations both Milky Way...
ABSTRACT A key event in the history of Milky Way is formation bar. This affects subsequent structural and dynamical evolution entire Galaxy. When bar formed, gas was likely rapidly funnelled to centre Galaxy settling a star-forming nuclear disc. The can then be dated by considering age distribution oldest stars formed stellar In this highly obscured crowded region, reliable tracers are limited, but bright, high-amplitude Mira variables make useful indicators as they follow period–age...
We use a cosmological chemodynamical simulation to study how the group environment impacts star formation (SF) properties of disk galaxies. The simulated has total mass M ~ 8 × 1012 M☉ and X-ray luminosity LX 1041 erg s−1. Our suggests that ram pressure is not sufficient in this remove cold gas from Vrot 150 km s−1 galaxy. However, majority hot galaxy stripped over timescale approximately 1 Gyr. Since cooling hot-gas component provides source for new gas, stripping effectively cuts off...
We have developed a new galactic chemodynamical evolution code, called gcd+, for studies of galaxy formation and evolution.This code is based on our original three-dimensional tree N-body/smoothed particle hydrodynamics which includes self-gravity, hydrodynamics, radiative cooling, star formation, supernova feedback metal enrichment.gcd+ Type II (SNe II) Ia Ia) supernovae model, taking into account the lifetime progenitor stars chemical enrichment from intermediate-mass stars.We apply gcd+...
Within a cosmological hydrodynamical simulation, we form disc galaxy with sub- components which can be assigned to thin stellar disc, thick disk, and low mass halo via chemical decomposition. The populations so selected are distinct in their ages, kinematics, metallicities. Thin stars young (<6.6 Gyr), possess velocity dispersion ({\sigma}U,V,W = 41, 31, 25 km/s), high [Fe/H], [O/Fe]. old (6.6<age<9.8 Gyrs), lag the by \sim21 km/s, higher 49, 44, 35 relatively [Fe/H] component comprises less...
We examine radial and vertical metallicity gradients using a suite of disk galaxy simulations, supplemented with two classic chemical evolution approaches. determine the rate change gradient reconcile differences between extant models observations within `inside-out' growth paradigm. A sample 25 disks is used, consisting 19 from our RaDES (Ramses Disk Environment Study) sample, realised adaptive mesh refinement code RAMSES. Four are selected MUGS (McMaster Unbiased Galaxy Simulations)...
Spiral density wave theory attempts to describe the spiral pattern in galaxies terms of a long-lived structure with constant speed order avoid winding dilemma. The is consequently rigidly rotating, feature. We run N-body simulations giant disc galaxy consisting pure stellar and static dark matter halo, find that arms are transient features whose speeds decrease radius such way almost equal rotation curve galaxy. trace particle motion around arms. show particles from behind front arm drawn...
Investigations of the origin and evolution Milky Way disk have long relied on chemical kinematic identification its components to reconstruct our Galactic past. Difficulties in determining precise stellar ages restricted most studies small samples, normally confined solar neighbourhood. Here we break this impasse with help asteroseismic inference perform a chronology throughout age Galaxy. We chemically dissect population using sample red giant stars spanning out 2~kpc annulus observed by...
The stellar disk of the Milky Way shows complex spatial and abundance structure that is central to understanding key physical mechanisms responsible for shaping our Galaxy. In this study, we use six very high resolution cosmological zoom simulations Way-sized haloes study prevalence formation chemically distinct disc components. We find develop a clearly bimodal distribution in $[\rm \alpha/Fe]$ -- Fe/H]$ plane. two main pathways creating dichotomy which operate different regions galaxies:...
We analyse a set of cosmological magneto-hydrodynamic simulations the formation Milky Way-mass galaxies identified to have prominent radially anisotropic stellar halo component similar so-called "Gaia Sausage" found in Gaia data. examine effects progenitor Sausage (the Gaia-Enceladus-Sausage, GES) on major galactic components analogous Galactic thick disc and inner halo. find that GES merger is likely been gas-rich contribute 10-50$\%$ gas merger-induced centrally concentrated starburst...
By taking advantage of the superb measurements position and velocity for an unprecedented large number stars provided in Gaia DR2, we have generated first maps rotation velocity, $V_{\rm rot}$, vertical z}$, distributions as a function Galactocentric radius, $R_{\rm gal}$, across radial range $5
The second data release from ESA's Gaia mission has revealed many ridge-like structures in the velocity distribution of Milky Way. We show that these can arise naturally winding transient spiral structure is commonly seen N-body simulations disk galaxies. construct test particle models structure, and compare resulting orbits with observed two-dimensional extended solar neighbourhood rotational velocities over 8 kpc along Sun--Galactic-centre--Galactic anti-centre line. ridges observations...
Deciphering the assembly history of Milky Way is a formidable task, which becomes possible only if one can produce high-resolution chrono-chemo-kinematical maps Galaxy. Data from large-scale astrometric and spectroscopic surveys will soon provide us with well-defined view current chemo-kinematical structure Way, but enable blurred on temporal sequence that led to present-day As demonstrated by (ongoing) exploitation data pioneering photometric missions CoRoT, Kepler, K2, asteroseismology...
We investigate models of the Milky Way disc taking into account simultaneously bar and a two-armed quasi-static spiral pattern. Away from major resonance overlaps, mean stellar radial motions in plane are essentially linear superposition isolated effects spirals. Thus, provided is strong enough, even presence arms, these predominantly affected by Galactic for large scale velocity fluctuations. This evident when comparing peculiar line-of-sight power spectrum our coupled with bar-only models....
ABSTRACT We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates 68 360 red giant and clump stars present in the 17th data release of Sloan Digital Sky Survey, APOGEE-2 high-resolution spectroscopic survey. By examining denoised age-metallicity relationship disc stars, we identify a drop metallicity with an increase [Mg/Fe] at early epoch, followed by chemical enrichment episode increasing [Fe/H]...
A suite of high-resolution N-body simulations the Magellanic Clouds–Milky Way system are presented and compared directly with newly available data from H i Parkes All-Sky Survey (HIPASS). We show that interaction between Small Clouds (SMC) Large results in both a spatial kinematical bifurcation stream leading arm. The is readily apparent HIPASS data, also tentatively identified. This provides strong support for tidal disruption origin stream. fiducial model (MCs) upon completion an extensive...
Seven cosmological hydrodynamic simulations of disk galaxy formation are analyzed to determine the alignment within dark matter halo and internal structure halo. We find that orientation outer halo, beyond ~0.1rvir, is unaffected by presence disk. In contrast, inner aligned such minor axis aligns with axis. The relative orientations these two regions uncorrelated. appears take place simultaneously through their joint evolution. lack connection between should be taken into account when...
We run N-body smoothed particle hydrodynamics (SPH) simulations of a Milky Way sized galaxy. The code takes into account hydrodynamics, self-gravity, star formation, supernova and stellar wind feedback, radiative cooling metal enrichment. simulated galaxy is barred-spiral consisting gas disc, enveloped in static dark matter halo. Similar to what found our pure simulation non-barred Grand et. al. (2012), we find that the spiral arms are transient features whose pattern speeds decrease with...
Abstract We use a high-resolution cosmological zoom simulation of Milky Way-sized halo to study the observable features in velocity and metallicity space associated with dynamical influence spiral arms. For first time, we demonstrate that arms, form disc fully environment realistic galaxy formation physics, drive large-scale systematic streaming motions. In particular, on trailing edge arms peculiar galactocentric radial azimuthal field is directed radially outward azimuthally backward,...
We apply the GC3 stream-finding method to RR Lyrae stars (RRLSs) in Catalina survey. find 2 RRLS stream candidates at >4σ confidence and another 12 >3.5σ over Galactocentric distance range 4 < D/kpc 26. Of these, only two are associated with known globular clusters (NGC 1261 Arp2). The remainder candidate 'orphan' streams, consistent idea that cluster streams most visible close dissolution. Our detections likely a lower bound on total number of dissolving globulars inner galaxy, since many...
The length and pattern speed of the Milky Way bar are still controversial. Photometric spectroscopic surveys inner Galaxy, as well gas kinematics, favour a long slowly rotating bar, with corotation around Galactocentric radius 6 kpc. On other hand, existence Hercules stream in local velocity space favours short fast 4 This follows from fact that looks like typical signature outer Lindblad resonance bar. As we showed recently, reconciling this slow would need to find yet unknown alternative...
Radial migration is defined as the change in guiding centre radius of stars and gas caused by gains or losses angular momentum that result from gravitational interaction with non-axisymmetric structure. This has been shown to have significant impact on metallicity distribution galactic discs, therefore affects interpretation Galactic archeology. We use a simulation Milky Way-sized galaxy examine effect radial star distribution. find both component show migration. The stellar gradient remains...
Gaia DR2 has provided an unprecedented wealth of information about the kinematics stars in Solar neighbourhood, and highlighted degree features Galactic disc. We confront data with a range bar spiral models both action-angle space, $R_{\mathrm{G}}-v_{\phi}$ plane. find that phase mixing induced by transient structure creates ridges arches local which are consistent data. able to produce qualitatively good match when combined variety pattern speeds, show it is non trivial decouple effects structure.
ABSTRACT We develop a Bayesian Machine Learning framework called BINGO (Bayesian INference for Galactic archaeOlogy) centred around neural network. After being trained on the Apache Point Observatory Evolution Experiment (APOGEE) and Kepler asteroseismic age data, is used to obtain precise relative stellar estimates with uncertainties APOGEE stars. carefully construct training set minimize bias apply population that similar our set. then select 17 305 stars ages from reliable kinematic...