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Dr Denis Erkal


Lecturer of Astrophysics
+44 (0)1483 686990
12 BC 03

Academic and research departments

Astrophysics Research Group.

Biography

Areas of specialism

Galactic archaeology; Near field cosmology

Research

Research interests

My publications

Publications

Koposov Sergey E, Walker Matthew G, Belokurov Vasily, Casey Andrew R, Geringer-Sameth Alex, Mackey Dougal, Da Costa Gary, Erkal Denis, Jethwa Prashin, Mateo Mario, Olszewski Edward W, Bailey III John I (2018) Snake in the Clouds: A new nearby dwarf galaxy in the Magellanic bridge,Monthly Notices of the Royal Astronomical Society Oxford University Press
We report the discovery of a nearby dwarf galaxy in the constellation of Hydrus,
between the Large and the Small Magellanic Clouds. Hydrus 1 is a mildy elliptical
ultra-faint system with luminosity MV from the Sun and 24 kpc from the LMC. From spectroscopy of measure a velocity dispersion of 2.7±0.5 km s?1 and find tentative evidence for a radial
velocity gradient consistent with 3 km s?1
rotation. Hydrus 1?s velocity dispersion indicates
that the system is dark matter dominated, but its dynamical mass-to-light ratio
M/L=66+29
?20 is significantly smaller than typical for ultra-faint dwarfs at similar luminosity.
The kinematics and spatial position of Hydrus 1 make it a very plausible member
of the family of satellites brought into the Milky Way by the Magellanic Clouds.
While Hydrus 1?s proximity and well-measured kinematics make it a promising target
for dark matter annihilation searches, we find no evidence for significant gamma-ray
emission from Hydrus 1. The new dwarf is a metal-poor galaxy with a mean metallicity
[Fe/H]=?2.5 and [Fe/H] standard deviation of 0.4 dex, similar to other systems of
similar luminosity. Alpha-abundances of Hyi 1 members indicate that star-formation
was extended, lasting between 0.1 and 1 Gyr, with self-enrichment dominated by SN
Ia. The dwarf also hosts a highly carbon-enhanced extremely metal-poor star with
[Fe/H]
Erkal Denis, Li T S, Koposov S E, Belokurov V, Balbinot E, Bechtol K, Buncher B, Drlica-Wagner A, Kuehn K, Marshall J L, Martínez-Vázquez C E, Pace A B, Shipp N, Simon J D, Stringer K M, Vivas A K, Wechsler R H, Yanny B, Abdalla F B, Allam S, Annis J, Avila S, Bertin E, Brooks D, Buckley-Geer E, Burke D L, Rosell A Carnero, Kind M Carrasco, Carretero J, D?Andrea C B, da Costa L N, Davis C, De Vicente J, Doel P, Eifler T F, Evrard A E, Flaugher B, Frieman J, García-Bellido J, Gaztanaga E, Gerdes D W, Gruen D, Gruendl R A, Gschwend J, Gutierrez G, Hartley W G, Hollowood D L, Honscheid K, James D J, Krause E, Maia M A G, March M, Menanteau F, Miquel R, Ogando R L C, Plazas A A, Sanchez E, Santiago B, Scarpine V, Schindler R, Sevilla-Noarbe I, Smith M, Smith R C, Soares-Santos M, Sobreira F, Suchyta E, Swanson M E C, Tarle G, Tucker D L, Walker A R (2018) Modelling the Tucana III stream - a close passage with the LMC,Monthly Notices of the Royal Astronomical Society 481 (3) pp. 3148-3159 Oxford University Press (OUP)
We present results of the first dynamical stream fits to the recently discovered Tucana III stream. These fits assume a fixed Milky Way potential and give proper motion predictions, which can be tested with the upcoming Gaia Data Release 2. These fits reveal that Tucana III is on an eccentric orbit around the Milky Way and, more interestingly, that Tucana III passed within 15 kpc of the Large Magellanic Cloud (LMC) approximately 75 Myr ago. Given this close passage, we fit the Tucana III stream in the combined presence of the Milky Way and the LMC. We find that the predicted proper motions depend on the assumed mass of the LMC and that the LMC can induce a substantial proper motion perpendicular to the stream track. A detection of this misalignment will directly probe the extent of the LMC?s influence on our Galaxy, and has implications for nearly all methods which attempt to constraint the Milky Way potential. Such a measurement will be possible with the upcoming Gaia DR2, allowing for a measurement of the LMC?s mass.
Jethwa P, Torrealba G, Navarrete C, Carballo-Bello J.A., de Boer Thomas, Erkal Denis, Koposov S.E., Duffau S, Geisler D, Catelan M, Belokurov V (2018) Discovery of a thin stellar stream in the SLAMS survey,Monthly Notices of the Royal Astronomical Society 480 (4) pp. 5342-5351 Oxford University Press
We report the discovery of a thin stellar stream - which we name the Jet stream - cross-
ing the constellations of Hydra and Pyxis. The discovery was made in data from the
SLAMS survey, which comprises deep g and r imaging for a 650 square degree region
above the Galactic disc performed by the CTIO Blanco + DECam. SLAMS photomet-
ric catalogues have been made publicly available. The stream is approximately 0.18
degrees wide and 10 degrees long, though it is truncated by the survey footprint. Its
colour-magnitude diagram is consistent with an old, metal-poor stellar population at
a heliocentric distance of approximately 29 kpc. We corroborate this measurement by
identifying a spatially coincident overdensity of likely blue horizontal branch stars at
the same distance. There is no obvious candidate for a surviving stream progenitor.
Belokurov V, Erkal Denis, Evans NW, Koposov SE, Deason AJ (2018) Co-formation of the disc and the stellar halo,Monthly Notices of the Royal Astronomical Society 478 (1) pp. 611-619 Oxford University Press
Using a large sample of Main Sequence stars with 7-D measurements supplied by Gaia and
SDSS, we study the kinematic properties of the local (within halo. We demonstrate that the halo?s velocity ellipsoid evolves strongly with metallicity.
At the low [Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction
compared to the tangential one) is mildly radial with 0.2 for stars with [Fe/H]> ?1.7 we measure extreme values of ² range considered, i.e. ?3 20 ) we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of
dwarf satellites. Instead, we argue, the stellar debris in the inner halo were deposited in a
major accretion event by a satellite with Mvir > 1010M™ around the epoch of the Galactic
disc formation, i.e. between 8 and 11 Gyr ago. The radical halo anisotropy is the result of the
dramatic radialisation of the massive progenitor?s orbit, amplified by the action of the growing
disc.
Erkal Denis, Boubert Douglas, Gualandris Alessia, Evans N. Wyn, Antonini Fabio (2018) A hypervelocity star with a Magellanic origin,Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
Using proper motion measurements from Gaia DR2, we probe the origin of 26 previously known hypervelocity stars (HVSs) around the Milky Way. We find that a significant fraction of these stars have a high probability of originating close to the Milky Way centre, but there is one obvious outlier. HVS3 is highly likely to be coming almost from the centre of the Large Magellanic Cloud (LMC). During its closest approach, 21.1 +6.1 ?4.6 Myr ago, it had a relative velocity of 870 +69 ?66 kms ?1 with respect to the LMC. This large kick velocity is only consistent with the Hills mechanism, requiring a massive black hole at the centre of the LMC. This provides strong direct evidence that the LMC itself harbours a massive black hole of at least 4×10 3 ?10 4 M ™ .
Li T. S., Simon J. D., Kuehn K., Pace A. B., Erkal D., Bechtol K., Yanny B., Drlica-Wagner A., Marshall J. L., Lidman C., Balbinot E., Carollo D., Jenkins S., Martínez-Vázquez C. E., Shipp N., Stringer K. M., Vivas A. K., Walker A. R., Wechsler R. H., Abdalla F. B., Allam S., Annis J., Avila S., Bertin E., Brooks D., Buckley-Geer E., Burke D. L., Rosell A. Carnero, Kind M. Carrasco, Carretero J., Cunha C. E., D?Andrea C. B., Costa L. N. da, Davis C., Vicente J. De, Doel P., Eifler T. F., Evrard A. E., Flaugher B., Frieman J., García-Bellido J., Gaztanaga E., Gerdes D. W., Gruen D., Gruendl R. A., Gschwend J., Gutierrez G., Hartley W. G., Hollowood D. L., Honscheid K., James D. J., Krause E., Maia M. A. G., March M., Menanteau F., Miquel R., Plazas A. A., Sanchez E., Santiago B., Scarpine V., Schindler R., Schubnell M., Sevilla-Noarbe I., Smith M., Smith R. C., Soares-Santos M., Sobreira F., Suchyta E., Swanson M. E. C., Tarle G., Tucker D. L. (2018) The First Tidally Disrupted Ultra-faint Dwarf Galaxy?: A Spectroscopic Analysis of the Tucana III Stream,The Astrophysical Journal 866 (1) IOP Publishing / The American Astronomical Society
We present a spectroscopic study of the tidal tails and core of the Milky Way satellite Tucana III, collectively referred to as the Tucana III stream, using the 2dF+AAOmega spectrograph on the Anglo-Australian Telescope and the IMACS spectrograph on the Magellan Baade Telescope. In addition to recovering the brightest nine previously known member stars in the Tucana III core, we identify 22 members in the tidal tails. We observe strong evidence for a velocity gradient of 8.0 ± 0.4 km/s-1 deg-1 over at least 3° on the sky. Based on the continuity in velocity, we confirm that the Tucana III tails are real tidal extensions of Tucana III. The large velocity gradient of the stream implies that Tucana III is likely on a radial orbit. We successfully obtain metallicities for four members in the core and 12 members in the tails. We find that members close to the ends of the stream tend to be more metal-poor than members in the core, indicating a possible metallicity gradient between the center of the progenitor halo and its edge. The spread in metallicity suggests that the progenitor of the Tucana III stream is likely a dwarf galaxy rather than a star cluster. Furthermore, we find that with the precise photometry of the Dark Energy Survey data, there is a discernible color offset between metal-rich disk stars and metal-poor stream members. This metallicity-dependent color offers a more efficient method to recognize metal-poor targets and will increase the selection efficiency of stream members for future spectroscopic follow-up programs on stellar streams.
Belokurov Vasily A., Erkal Denis (2018) Clouds in Arms,Monthly Notices of the Royal Astronomical Society Letters Oxford University Press
We use astrometry and broad-band photometry from Data Release 2 of the ESA?s Gaia mission
to map out low surface-brightness features in the stellar density distribution around the
Large and Small Magellanic Clouds. The LMC appears to have grown two thin and long stellar
streams in its Northern and Southern regions, highly reminiscent of spiral arms. We use
computer simulations of the Magellanic Clouds? in-fall to demonstrate that these arms were
likely pulled out of the LMC?s disc due to the combined influence of the SMC?s most recent
fly-by and the tidal field of the Milky Way.
Boubert D, Belokurov V, Erkal Denis, Iorio G (2018) A Magellanic origin for the Virgo substructure,Monthly Notices of the Royal Astronomical Society sty3014 Oxford University Press (
The Milky Way halo has been mapped out in recent work using a sample of RR Lyrae stars drawn from a cross-match of Gaia with 2MASS. We investigate the significant residual in this map which we constrain to lie at Galactocentric radii 12
Read J. I., Erkal D. (2019) Abundance matching with the mean star formation rate: there is no missing satellites problem in the Milky Way above M2009M™,Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
We introduce a novel abundance matching technique that produces a more accurate estimate of the pre-infall halo mass, M200, for satellite galaxies. To achieve this, we abundance match with the mean star formation rate, averaged over the time when a galaxy was forming stars, èSFRé, instead of the stellar mass, M?. Using data from the Sloan Digital Sky Survey, the GAMA survey and the Bolshoi simulation, we obtain a statistical èSFRé?M200 relation in ›CDM. We then compare the pre-infall halo mass, Mabund200, derived from this relation with the pre-infall dynamical mass, Mdyn200, for 21 nearby dSph and dIrr galaxies, finding a good agreement between the two. As a first application, we use our new èSFRé?M200 relation to empirically measure the cumulative mass function of a volume-complete sample of bright Milky Way satellites within 280 kpc of the Galactic centre. Comparing this with a suite of cosmological 'zoom' simulations of Milky Way-mass halos that account for subhalo depletion by the Milky Way disc, we find no missing satellites problem above M2009M™ in the Milky Way. We discuss how this empirical method can be applied to a larger sample of nearby spiral galaxies.
Erkal D, Belokurov V, Laporte C F P, Koposov S E, Li T S, Grillmair C J, Kallivayalil N, Price-Whelan A M, Evans N W, Hawkins K, Hendel D, Mateu C, Navarro J F, Pino A del, Slater C T, Sohn S T (2019) The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream,Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
In a companion paper by Koposov et al., RR Lyrae from Gaia Data Release 2 are used to demonstrate that stars in the Orphan stream have velocity vectors significantly misaligned with the stream track, suggesting that it has received a large gravitational perturbation from a satellite of the Milky Way. We argue that such a mismatch cannot arise due to any realistic static Milky Way potential and then explore the perturbative effects of the Large Magellanic Cloud (LMC). We find that the LMC can produce precisely the observed motion-track mismatch and we therefore use the Orphan stream to measure the mass of the Cloud. We simultaneously fit the Milky Way and LMC potentials and infer that a total LMC mass of 1.38+0.27?0.24×1011M™ is required to bend the Orphan Stream, showing for the first time that the LMC has a large and measurable effect on structures orbiting the Milky Way. This has far-reaching consequences for any technique which assumes that tracers are orbiting a static Milky Way. Furthermore, we measure the Milky Way mass within 50 kpc to be 3.80+0.14?0.11×1011M™`. Finally, we use these results to predict that, due to the reflex motion of the Milky Way in response to the LMC, the outskirts of the Milky Way?s stellar halo should exhibit a bulk, upwards motion.
Li T S, Koposov S E, Zucker D B, Lewis G F, Kuehn K, Simpson J D, Ji A P, Shipp N, Mao Y-Y, Geha M, Pace A B, Mackey A D, Allam S, Tucker D L, Da Costa G S, Erkal Denis, Simon J D, Mould J R, Martell S L, Wan Z, De Silva G M, Bechtol K, Balbinot E, Belokurov V, Bland-Hawthorn J, Casey A R, Cullinane L, Drlica-Wagner A, Sharma S, Vivas A K, Wechsler R H, Yanny B (2019) The Southern Stellar Stream Spectroscopic Survey (Su): Overview, Target Selection, Data Reduction, Validation, and Early Science,Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
We introduce the Southern Stellar Stream Spectroscopy Survey (Su), an on-going program to map the kinematics and chemistry of stellar streams in the Southern Hemisphere. The initial focus of Su has been spectroscopic observations of recently identified streams within the footprint of the Dark Energy Survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9-m Anglo-Australian Telescope?s 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far Su has mapped 9 DES streams and 3 streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the Su program, describing the scientific motivation for the survey, target selection, observation strategy, data reduction and survey validation. Finally, we describe early science results on stellar streams and Milky Way halo stars drawn from the survey. Updates on Su, including future public data releases, can be found at http://s5collab.github.io.
Koposov Sergey E, Boubert Douglas, Li Ting S, Erkal Denis, Da Costa Gary S, Zucker Daniel B, Ji Alexander P, Kuehn Kyler, Lewis Geraint F, Mackey Dougal, Simpson Jeffrey D, Shipp Nora, Wan Zhen, Belokurov Vasily, Bland-Hawthorn Joss, Martell Sarah L, Nordlander Thomas, Pace Andrew B, De Silva Gayandhi M, Wang Mei-Yu (2020) Discovery of a nearby 1700 km/s star ejected from the Milky Way by Sgr A*,Monthly Notices of the Royal Astronomical Society 491 (2) pp. 2465-2480 Oxford University Press
We present the serendipitous discovery of the fastest main-sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a ?1 without any signature of velocity variability. The current 3D velocity of the star in the Galactic frame is 1755 ± 50 kms?1`. When integrated backwards in time, the orbit of the star points unambiguously to the Galactic Centre, implying that S5-HVS1 was kicked away from Sgr A* with a velocity of ?1 and travelled for 4.8 Myr to its current location. This is so far the only HVS confidently associated with the Galactic Centre. S5-HVS1 is also the first hyper-velocity star to provide constraints on the geometry and kinematics of the Galaxy, such as the Solar motion Vy,™ = 246.1 ± 5.3 kms?1 or position R0 = 8.12 ± 0.23 kpc. The ejection trajectory and transit time of S5-HVS1 coincide with the orbital plane and age of the annular disc of young stars at the Galactic Centre, and thus may be linked to its formation. With the S5-HVS1 ejection velocity being almost twice the velocity of other hyper-velocity stars previously associated with the Galactic Centre, we question whether they have been generated by the same mechanism or whether the ejection velocity distribution has been constant over time.
Shipp N., Li T. S., Pace A. B., Erkal D., Drlica-Wagner A., Yanny B., Belokurov V., Wester W., Koposov S. E., Kuehn K., Lewis G. F., Simpson J. D., Wan Z., Zucker D. B., Martell S. L., Wang M. Y. (2019) Proper Motions of Stellar Streams Discovered in the Dark Energy Survey,The Astrophysical Journal 885 (3) The American Astronomical Society
We cross-match high-precision astrometric data from Gaia DR2 with accurate multi-band photometry
from the Dark Energy Survey (DES) DR1 to confidently measure proper motions for nine stellar
streams in the DES footprint: Aliqa Uma, ATLAS, Chenab, Elqui, Indus, Jhelum, Phoenix, Tucana
III, and Turranburra. We determine low-confidence proper motion measurements for four additional
stellar streams: Ravi, Wambelong, Willka Yaku, and Turbio. We find evidence for a misalignment
between stream tracks and the systemic proper motion of streams that may suggest a systematic
gravitational in
uence from the Large Magellanic Cloud. These proper motions, when combined with
radial velocity measurements, will allow for detailed orbit modeling which can be used to constrain
properties of the LMC and its on nearby streams, as well as global properties of the Milky Way's
gravitational potential.
Mau S., Cerny W., Pace A.B, Choi Y., Drlica-Wagner A., Santana-Silver L., Riley A.H, Erkal Denis, Stringfellow S., Adamow M., Carlin J.L, Gruendal R.A, Hernandez-Lang D., Kuropatkin N., Li T.S, Martinez-Vasquez C.E, Morganson E., Mutlu-Pakdil B., Neilsen E.H, Nidever D.L, Olsen K.A.G, Sand D.J, Tollerud E.J, Tucker D.L, Yanny B., Zenteno A., Allam S., Barkhouse W.A, Bechtol K., Bell E.F, Balaji P., Crnojevic D., Esteves J., Ferguson P.S, Gallart C., Hughes A.K, James D.J, Jethwa P., Johnson L.C, Kuehn K., Majewski S., Mao Y-Y., Massana P., McNanna M., Monachesi A., Nadler E.O, Noel Noelia, Palmese A., Paz-Chinchon F., Pieres A., Sanchez J., Shipp N., Simon J.D, Soares-Santos M., Tavangar K., van der Marel R.P, Vivas A.K, Walker A.R, Wechsler R.H (2020) Two Ultra-Faint Milky Way Stellar Systems Discovered in Early Data from the DECam Local Volume Exploration
Survey
,
Astrophysical Journal American Astronomical Society
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local
Volume Exploration survey (DELVE). The ýrst system, Centaurus I (DELVE J1238
de Boer T.J.L, Erkal Denis, Gieles M. (2020) A closer look at the spur, blob, wiggle, and gaps in GD-1,Monthly Notices of the Royal Astronomical Society Royal Astronomical Society
The GD-1 stream is one of the longest and coldest stellar streams discovered to date, and one of the best objects for constraining the dark matter properties of the Milky Way. Using data from Gaia DR2 we study the proper motions, distance, morphology and density of the streamto uncover small scale perturbations. The proper motion cleaned data shows a clear distance gradient across the stream, ranging from 7 to 12 kpc. However, unlike earlier studies thatfound a continuous gradient, we uncover a distance minimum atÆ1H-50 deg, after which the distance increases again. We can reliably trace the stream between -85
Belokurov Vasily A, Erkal Denis (2020) Limit on the LMC mass from a census of its satellites,Monthly Notices of the Royal Astronomical Society 495 (3) pp. 2554-2563 Oxford University Press (OUP)
We study the orbits of dwarf galaxies in the combined presence of the Milky Way and Large Magellanic Cloud (LMC) and find six dwarfs that were likely accreted with the LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, and Ret 2), in addition to the Small Magellanic Cloud (SMC), representing strong evidence of dwarf galaxy group infall. This procedure depends on the gravitational pull of the LMC, allowing us to place a lower bound on the Cloud?s mass of MLMCÃ1.24×1011M™ if we assume that these are LMC satellites. This mass estimate is validated by applying the technique to a cosmological zoom-in simulation of a Milky Way-like galaxy with an LMC analogue where we find that while this lower bound may be overestimated, it will improve in the future with smaller observational errors. We apply this technique to dwarf galaxies lacking radial velocities and find that Eri 3 has a broad range of radial velocities for which it has a significant chance (Ã0.4) of having been bound to the Cloud. We study the non-Magellanic classical satellites and find that Fornax has an appreciable probability of being an LMC satellite if the LMC is sufficiently massive (`11M™`). In addition, we explore how the orbits of Milky Way satellites change in the presence of the LMC and find a significant change for several objects. Finally, we find that the dwarf galaxies likely to be LMC satellites are slightly smaller than Milky Way satellites at a fixed luminosity, possibly due to the different tidal environments they have experienced.
De Leo Michele, Carrera Ricardo, Noel Noelia E.D, Read Justin I., Erkal Denis, Gallart Carme (2020) Revealing the tidal scars of the Small Magellanic Cloud,Monthly Notices of the Royal Astronomical Society 495 (1) pp. 98-113 Oxford University Press (OUP)
Due to their close proximity, the Large and Small Magellanic Clouds (LMC/SMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for
Gregory Alexandra L., Collins Michelle L. M., Erkal Denis, Tollerud Erik, Delorme Maxime, Hill Lewis, Sand David J., Strader Jay, Willman Beth (2020) Uncovering the Orbit of the Hercules Dwarf Galaxy,Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP)
We present new chemo{kinematics of the Hercules dwarf galaxy based on Keck II{
DEIMOS spectroscopy. Our 21 conýrmed members, including 9 newly con-
ýrmed members, have a systemic velocity of vHerc = 46:4 ý 1:3 kms
Boubert D., Erkal D., Gualandris A. (2020) Deflection of the hypervelocity stars by the pull of the
Large Magellanic Cloud on the Milky Way
,
Monthly Notices of the Royal Astronomical Society Oxford University Press
Stars slingshotted by the supermassive black hole at the Galactic centre escape from
the Milky Way so quickly that their trajectories are almost straight lines. Previous
works have shown how these `hypervelocity stars' (stars moving faster than the local
Galactic escape speed) are subsequently de
ected by the gravitational field of the Milky
Way and the Large Magellanic Cloud (LMC), but have neglected to account for the reflex motion of the Milky Way in response to the y-by of the LMC. A consequence
of this motion is that the hypervelocity stars we see in the outskirts of the Milky Way today were ejected from where the Milky Way centre was hundreds of millions of years
ago. This change in perspective causes large apparent de
ections of several degrees in
the trajectories of the hypervelocity stars. We quantify these deflections by simulating the ejection of hypervelocity stars from an isolated Milky Way (with a spherical or flattened dark matter halo), from a fixed-in-place Milky Way with a passing LMC,
and from a Milky Way which responds to the passage of the LMC, finding that LMC passage causes larger de
ections than can be caused by a
attened Galactic dark matter halo in ýCDM. The 10 ýas yr
Sedda Manuel Arca, Gualandris Alessia, Do Tuan, Feldmeier-Krause Anja, Neumayer Nadine, Erkal Denis (2020) On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster,Astrophysical Journal Letters IOP Publishing
We explore the origin of a population of stars recently detected in the inner parsec of the Milky
Way Nuclear Cluster (NC), which exhibit sub-solar metallicity and a higher rotation compared to
the dominant population. Using state-of-the-art N-body simulations, we model the infall of massive
stellar systems into the Galactic center, both of Galactic and extra-galactic origin. We show that
the newly discovered population can either be the remnant of a massive star cluster formed a few
kpc away from the Galactic center (Galactic scenario) or be accreted from a dwarf galaxy originally
located at 10-100 kpc (extragalactic scenario) and that reached the Galactic center 3