Stacy Kim

Stacy Kim


Areas of specialism

near-field cosmology; dark matter; computational astrophysics


Research interests


Keith Horne, G. De Rosa, B. M. Peterson, A. J. Barth, J. Ely, M. M. Fausnaugh, G. A. Kriss, L. Pei, M. C. Bentz, E. M. Cackett, R. Edelson, M. Eracleous, M. R. Goad, C. J. Grier, J. Kaastra, C. S. Kochanek, Y. Krongold, S. Mathur, H. Netzer, D. Proga, N. Tejos, M. Vestergaard, C. Villforth, S. M. Adams, M. D. Anderson, P. Arevalo, T. G. Beatty, V. N. Bennert, A. Bigley, S. Bisogni, G. A. Borman, T. A. Boroson, M. C. Bottorff, W. N. Brandt, A. A. Breeveld, M. Brotherton, J. E. Brown, J. S. Brown, G. Canalizo, M. T. Carini, K. I. Clubb, J. M. Comerford, E. M. Corsini, D. M. Crenshaw, S. Croft, K. V. Croxall, E. Dalla Bonta, A. J. Deason, M. Dehghanian, A. De Lorenzo-Caceres, K. D. Denney, M. Dietrich, C. Done, N. V. Efimova, P. A. Evans, G. J. Ferland, A. V. Filippenko, K. Flatland, O. D. Fox, E. Gardner, E. L. Gates, N. Gehrels, S. Geier, J. M. Gelbord, L. Gonzalez, V. Gorjian, J. E. Greene, D. Grupe, A. Gupta, P. B. Hall, C. B. Henderson, S. Hicks, E. Holmbeck, T. W. -S. Holoien, T. Hutchison, M. Im, J. J. Jensen, C. A. Johnson, M. D. Joner, J. Jones, S. Kaspi, P. L. Kelly, J. A. Kennea, M. Kim, S. Kim, S. C. Kim, A. King, S. A. Klimanov, K. T. Korista, M. W. Lau, J. C. Lee, D. C. Leonard, Miao Li, P. Lira, C. Lochhaas, Zhiyuan Ma, F. MacInnis, M. A. Malkan, E. R. Manne-Nicholas, J. C. Mauerhan, R. McGurk, I. M. McHardy, C. Montuori, L. Morelli, A. Mosquera, D. Mudd, F. Muller-Sanchez, S. V. Nazarov, R. P. Norris, J. A. Nousek, M. L. Nguyen, P. Ochner, D. N. Okhmat, A. Pancoast, I. Papadakis, J. R. Parks, M. T. Penny, A. Pizzella, R. W. Pogge, R. Poleski, J. -U. Pott, S. E. Rafter, H. -W. Rix, J. Runnoe, D. A. Saylor, J. S. Schimoia, K. Schnuelle, B. Scott, S. G. Sergeev, B. J. Shappee, I. Shivvers, M. Siegel, G. V. Simonian, A. Siviero, A. Skielboe, G. Somers, M. Spencer, D. Starkey, D. J. Stevens, H. -I. Sung, J. Tayar, T. Treu, C. S. Turner, P. Uttley, J. Van Saders, L. Vican, S. Villanueva, Y. Weiss, J. -H. Woo, H. Yan, S. Young, H. Yuk, W. Zheng, W. Zhu, Y. Zu (2021)Space Telescope and Optical Reverberation Mapping Project. IX. Velocity-Delay Maps for Broad Emission Lines in NGC 5548, In: The Astrophysical journal907(2)76 Iop Publishing Ltd

In this contribution, we achieve the primary goal of the active galactic nucleus (AGN) STORM campaign by recovering velocity-delay maps for the prominent broad emission lines (Ly alpha, C IV, He II, and H beta) in the spectrum of NGC 5548. These are the most detailed velocity-delay maps ever obtained for an AGN, providing unprecedented information on the geometry, ionization structure, and kinematics of the broad-line region. Virial envelopes enclosing the emission-line responses show that the reverberating gas is bound to the black hole. A stratified ionization structure is evident. The He ii response inside 5-10 lt-day has a broad single-peaked velocity profile. The Ly alpha, C IV, and H beta responses extend from inside 2 to outside 20 lt-day, with double peaks at 2500 km s(-1) in the 10-20 lt-day delay range. An incomplete ellipse in the velocity-delay plane is evident in H beta. We interpret the maps in terms of a Keplerian disk with a well-defined outer rim at R = 20 lt-day. The far-side response is weaker than that from the near side. The line-center delay tau = (R/c)(1 - sin i) approximate to 5 days gives the inclination i approximate to 45 degrees. The inferred black hole mass is (BH) 7 x 10(7) M-circle dot. In addition to reverberations, the fit residuals confirm that emission-line fluxes are depressed during the "BLR Holiday" identified in previous work. Moreover, a helical "Barber-Pole" pattern, with stripes moving from red to blue across the C IV and Ly alpha line profiles, suggests azimuthal structure rotating with a 2 yr period that may represent precession or orbital motion of inner-disk structures casting shadows on the emission-line region farther out.

P. R. Williams, A. Pancoast, T. Treu, B. J. Brewer, B. M. Peterson, A. J. Barth, M. A. Malkan, G. De Rosa, Keith Horne, G. A. Kriss, N. Arav, M. C. Bentz, E. M. Cackett, E. Dalla Bonta, M. Dehghanian, C. Done, G. J. Ferland, C. J. Grier, J. Kaastra, E. Kara, C. S. Kochanek, S. Mathur, M. Mehdipour, R. W. Pogge, D. Proga, M. Vestergaard, T. Waters, S. M. Adams, M. D. Anderson, P. Arevalo, T. G. Beatty, V. N. Bennert, A. Bigley, S. Bisogni, G. A. Borman, T. A. Boroson, M. C. Bottorff, W. N. Brandt, A. A. Breeveld, M. Brotherton, J. E. Brown, J. S. Brown, G. Canalizo, M. T. Carini, K. I. Clubb, J. M. Comerford, E. M. Corsini, D. M. Crenshaw, S. Croft, K. V. Croxall, A. J. Deason, A. De Lorenzo-Caceres, K. D. Denney, M. Dietrich, R. Edelson, N. V. Efimova, J. Ely, P. A. Evans, M. M. Fausnaugh, A. V. Filippenko, K. Flatland, O. D. Fox, E. Gardner, E. L. Gates, N. Gehrels, S. Geier, J. M. Gelbord, L. Gonzalez, V. Gorjian, J. E. Greene, D. Grupe, A. Gupta, P. B. Hall, C. B. Henderson, S. Hicks, E. Holmbeck, T. W. -S. Holoien, T. Hutchison, M. Im, J. J. Jensen, C. A. Johnson, M. D. Joner, J. Jones, S. Kaspi, P. L. Kelly, J. A. Kennea, M. Kim, S. Kim, S. C. Kim, A. King, S. A. Klimanov, C. Knigge, Y. Krongold, M. W. Lau, J. C. Lee, D. C. Leonard, Miao Li, P. Lira, C. Lochhaas, Zhiyuan Ma, F. MacInnis, E. R. Manne-Nicholas, J. C. Mauerhan, R. McGurk, I. M. McHardy, C. Montuori, L. Morelli, A. Mosquera, D. Mudd, F. Muller-Sanchez, S. V. Nazarov, R. P. Norris, J. A. Nousek, M. L. Nguyen, P. Ochner, D. N. Okhmat, I. Papadakis, J. R. Parks, L. Pei, M. T. Penny, A. Pizzella, R. Poleski, J. -U. Pott, S. E. Rafter, H. -W. Rix, J. Runnoe, D. A. Saylor, J. S. Schimoia, B. Scott, S. G. Sergeev, B. J. Shappee, I. Shivvers, M. Siegel, G. V. Simonian, A. Siviero, A. Skielboe, G. Somers, M. Spencer, D. Starkey, D. J. Stevens, H. -I. Sung, J. Tayar, N. Tejos, C. S. Turner, P. Uttley, J. Van Saders, S. A. Vaughan, L. Vican, S. Villanueva, C. Villforth, Y. Weiss, J. -H. Woo, H. Yan, S. Young, H. Yuk, W. Zheng, W. Zhu, Y. Zu (2020)Space Telescope and Optical Reverberation Mapping Project. XII. Broad-line Region Modeling of NGC 5548, In: The Astrophysical journal902(1)74 Iop Publishing Ltd

We present geometric and dynamical modeling of the broad line region (BLR) for the multi-wavelength reverberation mapping campaign focused on NGC 5548 in 2014. The data set includes photometric and spectroscopic monitoring in the optical and ultraviolet, covering the H beta, Civ, and Ly alpha broad emission lines. We find an extended disk-like H beta BLR with a mixture of near-circular and outflowing gas trajectories, while the Civand Ly alpha BLRs are much less extended and resemble shell-like structures. There is clear radial structure in the BLR, with Civand Ly alpha emission arising at smaller radii than the H beta emission. Using the three lines, we make three independent black hole mass measurements, all of which are consistent. Combining these results gives a joint inference of log(10) (M-BH/M-circle dot) = 7.64(-0.18)(+0.21). We examine the effect of using the V band instead of the UV continuum light curve on the results and find a size difference that is consistent with the measured UV-optical time lag, but the other structural and kinematic parameters remain unchanged, suggesting that theVband is a suitable proxy for the ionizing continuum when exploring the BLR structure and kinematics. Finally, we compare the H beta results to similar models of data obtained in 2008 when the active galactic nucleus was at a lower luminosity state. We find that the size of the emitting region increased during this time period, but the geometry and black hole mass remained unchanged, which confirms that the BLR kinematics suitably gauge the gravitational field of the central black hole.

Zhichao Carton Zeng, Annika H. G. Peter, Xiaolong Du, Andrew Benson, Stacy Kim, Fangzhou Jiang, Francis-Yan Cyr-Racine, Mark Vogelsberger (2022)Core-collapse, evaporation, and tidal effects: the life story of a self-interacting dark matter subhalo, In: Monthly notices of the Royal Astronomical Society513(4)4845pp. 4845-4868 Oxford Univ Press

Self-interacting dark matter (SIDM) cosmologies admit an enormous diversity of dark matter (DM) halo density profiles, from low-density cores to high-density core-collapsed cusps. The possibility of the growth of high central density in low-mass haloes, accelerated if haloes are subhaloes of larger systems, has intriguing consequences for small-halo searches with substructure lensing. However, following the evolution of less than or similar to 10(8) M-circle dot subhaloes in lens-mass systems (similar to 10(13) M-circle dot) is computationally expensive with traditional N-body simulations. In this work, we develop a new hybrid semi-analytical + N-body method to study the evolution of SIDM subhaloes with high fidelity, from core formation to core-collapse, in staged simulations. Our method works best for small subhaloes (less than or similar to 1/1000 host mass), for which the error caused by dynamical friction is minimal. We are able to capture the evaporation of subhalo particles by interactions with host halo particles, an effect that has not yet been fully explored in the context of subhalo core-collapse. We find three main processes drive subhalo evolution: subhalo internal heat outflow, host-subhalo evaporation, and tidal effects. The subhalo central density grows only when the heat outflow outweighs the energy gain from evaporation and tidal heating. Thus, evaporation delays or even disrupts subhalo core-collapse. We map out the parameter space for subhaloes to core-collapse, finding that it is nearly impossible to drive core-collapse in subhaloes in SIDM models with constant cross-sections. Any discovery of ultracompact dark substructures with future substructure lensing observations favours additional degrees of freedom, such as velocity-dependence, in the cross-section.

Amandine Doliva-Dolinsky, Nicolas F. Martin, Zhen Yuan, Alessandro Savino, Daniel R. Weisz, Annette M. N. Ferguson, Rodrigo A. Ibata, Stacy Y. Kim, Geraint F. Lewis, Alan W. McConnachie, Guillaume F. Thomas (2023)The PAndAS View of the Andromeda Satellite System. IV. Global Properties, In: The Astrophysical journal952(1)72 IOP Publishing Ltd

We build a statistical framework to infer the global properties of the satellite system of the Andromeda galaxy (M31) from the properties of individual dwarf galaxies located in the Pan-Andromeda Archaelogical Survey (PAndAS) and the previously determined completeness of the survey. Using forward modeling, we infer the slope of the luminosity function of the satellite system, the slope of its spatial density distribution, and the size-luminosity relation followed by the dwarf galaxies. We find that the slope of the luminosity function is beta = -1.5 +/- 0.1. Combined with the spatial density profile, it implies that, when accounting for survey incompleteness, M31 hosts 92(-26)(+19) dwarf galaxies with M-V < -5.5 and a sky-projected distance from M31 between 30 and 300 kpc. We conclude that many faint or distant dwarf galaxies remain to be discovered around Andromeda, especially outside the PAndAS footprint. Finally, we use our model to test if the higher number of satellites situated in the hemisphere facing the Milky Way could be explained simply by the detection limits of dwarf galaxy searches. We rule this out at >99.9% confidence and conclude that this anisotropy is an intrinsic feature of the M31 satellite system. The statistical framework we present here is a powerful tool to robustly constrain the properties of a satellite system and compare those across hosts, especially considering the upcoming start of the Euclid or Rubin large photometric surveys that are expected to uncover a large number of dwarf galaxies in the Local Volume.

S. Y. Kim, Neal J. Turner (2020)X-Ray Ionization of Planet-opened Gaps in Protostellar Disks, In: The Astrophysical journal889(2)159 Iop Publishing Ltd

Young planets with masses approaching Jupiter's have tides strong enough to clear gaps around their orbits in the protostellar disk. Gas flow through the gaps regulates the planets' further growth and governs the disk's evolution. Magnetic forces may drive that flow if the gas is sufficiently ionized to couple to the fields. We compute the ionizing effects of the X-rays from the central young star, using Monte Carlo radiative transfer calculations to find the spectrum of Compton-scattered photons reaching the planet's vicinity. The scattered X-rays ionize the gas at rates similar to or greater than the interstellar cosmic-ray rate near planets with the masses of Saturn and of Jupiter, located at 5 au and at 10 au, in disks with the interstellar mass fraction of sub-micron dust and with the dust depleted by a factor 100. Solving a gas-grain recombination reaction network yields charged particle populations whose ability to carry currents is sufficient to partly couple the magnetic fields to the gas around the planet. Most cases can undergo Hall-shear instability, and some can launch magnetocentrifugal winds. However, the material on the planet's orbit has diffusivities so large in all the cases we examine that magnetorotational turbulence is prevented and the non-ideal terms govern the magnetic field's evolution. Thus the flow of gas in the gaps opened by young giant planets depends crucially on the finite conductivity.

Nora Shipp, Nondh Panithanpaisal, Lina Necib, Robyn Sanderson, Denis Erkal, Ting S. Li, Isaiah B. Santistevan, Andrew Wetzel, Lara R. Cullinane, Alexander P. Ji, Sergey E. Koposov, Kyler Kuehn, Geraint F. Lewis, Andrew B. Pace, Daniel B. Zucker, Joss Bland-Hawthorn, Emily C. Cunningham, Stacy Y. Kim, Sophia Lilleengen, Sanjib Sharma, Jorge Moreno, (2023)Streams on FIRE: Populations of Detectable Stellar Streams in the Milky Way and FIRE, In: The Astrophysical journal949(2)44 IOP Publishing Ltd

We present the first detailed comparison of populations of dwarf galaxy stellar streams in cosmological simulations and the Milky Way. In particular, we compare streams identified around 13 Milky Way analogs in the FIRE-2 simulations to streams observed by the Southern Stellar Stream Spectroscopic Survey (S (5)). For an accurate comparison, we produce mock Dark Energy Survey (DES) observations of the FIRE streams and estimate the detectability of their tidal tails and progenitors. The number and stellar mass distributions of detectable stellar streams is consistent between observations and simulations. However, there are discrepancies in the distributions of pericenters and apocenters, with the detectable FIRE streams, on average, forming at larger pericenters (out to >110 kpc) and surviving only at larger apocenters (greater than or similar to 40 kpc) than those observed in the Milky Way. We find that the population of high-stellar-mass dwarf galaxy streams in the Milky Way is incomplete. Interestingly, a large fraction of the FIRE streams would only be detected as intact satellites in DES-like observations, since their tidal tails have too low surface brightness to be detectable. We thus predict a population of yet-undetected tidal tails around Milky Way satellites, as well as a population of fully undetected low-surface-brightness stellar streams, and estimate their detectability with the Rubin Observatory. Finally, we discuss the causes and implications of the discrepancies between the stream populations in FIRE and the Milky Way, and explore future avenues for tests of satellite disruption in cosmological simulations.

J Taprogge, A Jungclaus, H Grawe, S Nishimura, P Doornenbal, G Lorusso, GS Simpson, P-A Soederstroem, T Sumikama, ZY Xu, H Baba, F Browne, N Fukuda, R Gernhaeuser, G Gey, N Inabe, T Isobe, HS Jung, D Kameda, GD Kim, Y-K Kim, I Kojouharov, T Kubo, N Kurz, YK Kwon, Z Li, H Sakurai, H Schaffner, K Steiger, H Suzuki, H Takeda, Z Vajta, H Watanabe, J Wu, A Yagi, K Yoshinaga, G Benzoni, S Boenig, KY Chae, L Coraggio, A Covello, J-M Daugas, F Drouet, A Gadea, A Gargano, S Ilieva, FG Kondev, T Kroell, GJ Lane, A Montaner-Piza, K Moschner, D Mucher, F Naqvi, M Niikura, H Nishibata, A Odahara, R Orlandi, Z Patel, Z Podolyak, A Wendt (2015)beta decay of Cd-129 and excited states in In-129, In: PHYSICAL REVIEW C91(5)ARTN 0pp. ?-? AMER PHYSICAL SOC
A. Revel, O. Sorlin, F.M Marques, Y. Kondo, J. Kahlbow, T. Nakamura, N.A Orr, F. Nowacki, Jeffrey Tostevin, C.X Yuan, N.L Achouri, H. Al Falou, L. Atar, T. Aumann, H. Baba, K. Boretzky, C. Caesar, D. Calvet, H. Chae, N. Chiga, A. Corsi, H.L Crawford, F. Delaunay, A. Delbart, Q. Deshayes, Z. Dombradi, C.A Douma, Z. Elekes, P. Fallon, I. Gasparic, J.M Gheller, J. Gibelin, A. Gillibert, M.N Harakeh, W. He, A. Hirayama, C.R Hoffman, M. Holl, A. Horvat, A. Horvath, J.W Hwang, T. Isobe, N. Kalantar-Nayestanaki, S. Kawase, S. Kim, K. Kisamori, T. Kobayashi, D. Korper, S. Koyama, I. Kuti, V. Lapoux, S. Lindberg, S. Masuoka, J. Mayer, K. Miki, T. Murakami, M. Najafi, K. Nakano, N. Nakatsuka, T. Nilsson, A. Obertelli, F. de Oliviera Santos, H. Otsu, T. Ozaki, V. Panin, S. Paschalis, D. Rossi, A.T Saito, T. Saito, M. Sasano, H. Sato, Y. Satou, H. Scheit, F. Schindler, P. Schrock, M. Shikata, Y. Shimizu, H. Simon, D. Sohler, L. Stuhl, S. Takeuchi, M. Tanaka, M. Thoennsen, H. Tornqvist, Y. Togano, T. Tomai, J. Tscheuschner, J. Tsubota, T. Uesaka, Z. Yang, M. Yasuda, K. Yoneda (2020)Extending the Southern Shore of the Island of Inversion to 28F, In: Physical Review Letters124(15) American Physical Society

Detailed spectroscopy of the neutron-unbound nucleus 28 F has been performed for the first time following proton/neutron removal from 29 Ne / 29 F beams at energies around 230 MeV / nucleon . The invariant-mass spectra were reconstructed for both the 27 F ( * ) + n and 26 F ( * ) + 2 n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the 28 F ground state, with S n ( 28 F ) = − 199 ( 6 )     keV , while analysis of the 2 n decay channel allowed a considerably improved S n ( 27 F ) = 1620 ( 60 )     keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of 28 F . Importantly, in the case of the ground state, the reconstructed 27 F + n momentum distribution following neutron removal from 29 F indicates that it arises mainly from the 1 p 3 / 2 neutron intruder configuration. This demonstrates that the island of inversion around N = 20 includes 28 F , and most probably 29 F , and suggests that 28 O is not doubly magic.

N Kobayashi, T Nakamura, Y Kondo, JA Tostevin, N Aoi, H Baba, R Barthelemy, MA Famiano, N Fukuda, N Inabe, M Ishihara, R Kanungo, S Kim, T Kubo, GS Lee, HS Lee, M Matsushita, T Motobayashi, T Ohnishi, NA Orr, H Otsu, T Sako, H Sakurai, Y Satou, T Sumikama, H Takeda, S Takeuchi, R Tanaka, Y Togano, K Yoneda (2016)One-neutron removal from Ne29: Defining the lower limits of the island of inversion, In: Physical Review C: Nuclear Physics93014613 American Physical Society

Background: Very neutron-rich isotopes, including Ne30-32, in the vicinity of N=20 are known to exhibit ground states dominated by fp-shell intruder configurations: the “island of inversion.” Systematics for the Ne-isotopic chain suggest that such configurations may be in strong competition with normal shell-model configurations in the ground state of Ne29. Purpose: A determination of the structure of Ne29 is thus important to delineate the extent of the island of inversion and better understand structural evolution in neutron-rich Ne isotopes. This is accomplished here through a combined investigation of nuclear and Coulomb-induced one-neutron removal reactions. Method: Cross sections for one-neutron removal on carbon and lead targets and the parallel momentum distribution of the Ne28 residues from the carbon target are measured at around 240 MeV/nucleon. The measurements are compared with reaction calculations combined with spectroscopic information from SDPF-M shell-model wave functions. Results: The deduced width of the inclusive parallel momentum distribution, 98(12) MeV/c (FWHM), suggests that the ground state of Ne29 has a spin parity of 3/2-. Detailed comparisons of the measured inclusive and partial cross sections of the two targets and the parallel momentum distribution of the carbon target with reaction calculations, combined with spectroscopic information from large-scale shell-model calculations, are all consistent with a 3/2- spin-parity assignment. Conclusions: The results indicate that Ne29 lies within the island of inversion and that the ground state of Ne29 is dominated by a Ne28(0+1)xp3/2 neutron configuration. Combined with recently measured interaction cross sections, it is concluded that Ne29 may exhibit a moderately developed halo-like distribution

N Kobayashi, T Nakamura, Y Kondo, JA Tostevin, Y Utsuno, N Aoi, H Baba, R Bartelemy, MA Famiano, N Fukuda, N Inabe, M Ishihara, R Kunungo, S Kim, T Kim, GS Kubo, HS Lee, M Lee, T Matsushita, T Motobayashi, NA Ohnishi, H Orr, T Otsu, T Otsuka, H Sako, Y Sakurai, T Satou, H Sumikama, S Takeda, R Takeuchi, Y Tanaka, K Togano, Yoneda (2014)Observation of a p-Wave One-Neutron Halo Configuration in 37Mg, In: Physical Review Letters112242501

Cross sections of 1n-removal reactions from the neutron-rich nucleus Mg37 on C and Pb targets and the parallel momentum distributions of the Mg37 residues from the C target have been measured at 240  MeV/nucleon. A combined analysis of these distinct nuclear- and Coulomb-dominated reaction data shows that the Mg37 ground state has a small 1n separation energy of 0.22+0.12−0.09  MeV and an appreciable p-wave neutron single-particle strength. These results confirm that Mg37 lies near the edge of the “island of inversion” and has a sizable p-wave neutron halo component, the heaviest such system identified to date.

Emily J. E Charles, Michelle L. M Collins, R. Michael Rich, Justin I Read, Stacy Y Kim, Rodrigo A Ibata, Nicolas F Martin, Scott C Chapman, Eduardo Balbinot, Daniel R Weisz (2023)Andromeda XXV - a dwarf galaxy with a low central dark matter density, In: Monthly Notices of the Royal Astronomical Society521(3)pp. 3527-3539 Oxford University Press

Andromeda (And) XXV has previously been reported as a dwarf spheroidal galaxy (dSph) with little-to-no dark matter. However, the uncertainties on this result were significant. In this study, we double the number of member stars and re-derive the kinematics and mass of And XXV. We find that And XXV has a systemic velocity of $\nu_\mathrm{r}=-107.7\pm1.0 \mathrm{~km s}^{-1}$ and a velocity dispersion of $\sigma_\nu=4.5\pm1.0\mathrm{~km s}^{-1}$. With this better constrained velocity dispersion, we derive a mass contained within the half-light radius of $M(r< r_\mathrm{h})=6.9^{+3.2}_{-2.8}\times10^6\mathrm{~M}_\odot$. This mass corresponds to a mass-to-light ratio of $\mathrm{[M/L]}_\mathrm{r_\mathrm{h}}=37^{+17}_{-15}\mathrm{~M}_\odot/\mathrm{L}_\odot$, demonstrating, for the first time, that And XXV has an unambiguous dark matter component. We also measure the metallicity of And XXV to be $\mathrm{[Fe/H]}=-1.9\pm0.1$$\mathrm{~}$dex, which is in agreement with previous results. Finally, we extend the analysis of And XXV to include mass modelling using GravSphere. We find that And XXV has a low central dark matter density, $\rho_\mathrm{DM}(150\mathrm{pc})= 2.7^{+1.8}_{-1.6}\times10^7\mathrm{~M}_\odot\mathrm{kpc}^{-3}$, making And XXV a clear outlier when compared to other Local Group (LG) dSphs of the similar stellar mass. In a companion paper, we will explore whether some combination of dark matter cusp-core transformations and/or tides can explain And XXV's low density.

Matthew D A Orkney, Justin I Read, Oscar Agertz, Andrew Pontzen, Martin P Rey, Alex Goater, Ethan Taylor, Stacy Y Kim, Maxime Delorme (2022)EDGE: the puzzling ellipticity of Eridanus II’s star cluster and its implications for dark matter at the heart of an ultra-faint dwarf, In: Monthly notices of the Royal Astronomical Society515(1)pp. 185-200 Oxford University Press

ABSTRACT The Eridanus II (EriII) ‘ultra-faint’ dwarf has a large (15 pc) and low-mass (4.3 × 103 M⊙) star cluster (SC) offset from its centre by 23 ± 3 pc in projection. Its size and offset are naturally explained if EriII has a central dark matter core, but such a core may be challenging to explain in a ΛCDM cosmology. In this paper, we revisit the survival and evolution of EriII’s SC, focusing for the first time on its puzzlingly large ellipticity ($0.31^{+0.05}_{-0.06}$). We perform a suite of 960 direct N-body simulations of SCs, orbiting within a range of spherical background potentials fit to ultra-faint dwarf (UFD) galaxy simulations. We find only two scenarios that come close to explaining EriII’s SC. In the first scenario, EriII has a low-density dark matter core (of size ${\sim}70\, \text{pc}$ and density $\lesssim 2\times 10^8\, \text{M}_{\odot }\, \text{kpc}^{-3}$). In this model, the high ellipticity of EriII’s SC is set at birth, with the lack of tidal forces in the core allowing its ellipticity to remain frozen for long times. In the second scenario, EriII’s SC orbits in a partial core, with its high ellipticity owing to its imminent tidal destruction. However, this latter model struggles to reproduce the large size of EriII’s SC, and it predicts substantial tidal tails around EriII’s SC that should have already been seen in the data. This leads us to favour the cored model. We discuss potential caveats to these findings, and the implications of the cored model for galaxy formation and the nature of dark matter.

M Holl, S Lindberg, A Heinz, Y Kondo, T Nakamura, J. A Tostevin, H Wang, T Nilsson, N. L Achouri, H. Al Falou, L Atar, T Aumann, H Baba, K Boretzky, C Caesar, D Calvet, H Chae, N Chiga, A Corsi, H. L Crawford, F Delaunay, A Delbart, Q Deshayes, P. Díaz Fernández, Z Dombrádi, C. A Douma, Z Elekes, P Fallon, I Gašparić, J. -M Gheller, J Gibelin, A Gillibert, M. N Harakeh, A Hirayama, C. R Hoffman, A Horvat, Á Horváth, J. W Hwang, T Isobe, J Kahlbow, N Kalantar-Nayestanaki, S Kawase, S Kim, K Kisamori, T Kobayashi, D Körper, S Koyama, I Kuti, V Lapoux, F. M Marqués, S Masuoka, J Mayer, K Miki, T Murakami, M Najafi, K Nakano, N Nakatsuka, A Obertelli, F. de Oliveira Santos, N. A Orr, H Otsu, T Ozaki, V Panin, S Paschalis, A Revel, D Rossi, A. T Saito, T. Y Saito, M Sasano, H Sato, Y Satou, H Scheit, F Schindler, P Schrock, M Shikata, Y Shimizu, H Simon, D Sohler, O Sorlin, L Stuhl, S Takeuchi, M Tanaka, M Thoennessen, H Törnqvist, Y Togano, T Tomai, J Tscheuschner, J Tsubota, T Uesaka, Z Yang, M Yasuda, K Yoneda (2022)Border of the Island of Inversion: Unbound states in $^{29}$Ne, In: Physical Review C105034301 American Physical Society

The nucleus $^{29}$Ne is situated at the border of the island of inversion. Despite significant efforts, no bound low-lying intruder $f_{7/2}$-state, which would place $^{29}$Ne firmly inside the island of inversion, has yet been observed. Here, the first investigation of unbound states of $^{29}$Ne is reported. The states were populated in $^{30}\mathrm{Ne}(p,pn)$ and $^{30}\mathrm{Na}(p,2p)$ reactions at a beam energy of around $230$ MeV/nucleon, and analyzed in terms of their resonance properties, partial cross sections and momentum distributions. The momentum distributions are compared to calculations using the eikonal, direct reaction model, allowing $\ell$-assignments for the observed states. The lowest-lying resonance at an excitation energy of 1.48(4) MeV shows clear signs of a significant $\ell$=3-component, giving first evidence for $f_{7/2}$ single particle strength in $^{29}$Ne. The excitation energies and strengths of the observed states are compared to shell-model calculations using the sdpf-u-mix interaction

R Shearman, G Lorusso, A Boso, PATRICK HENRY REGAN, S Nishimura, Z Y Xu, A Jungclaus, Y Shimizu, G S Simpson, P-A Söderström, H Watanabe, F Browne, P Doornenbal, G Gey, H S Jung, B Meyer, T Sumikama, J Taprogge, Zs Vajta, J Wu, H Baba, G Benzoni, K Y Chae, F C L Crespi, N Fukuda, R Gernhäuser, N Inabe, T Isobe, T Kajino, D Kameda, G D Kim, STACY YEONCHI KIM, I Kajouharov, F G Kondev, T Kubo, N Kurz, Y K Kwon, G J Lane, ZHONG LI, A Montaner-Pizá, K Moschner, F Naqvi, M Niikura, H Nishibata, A Odahara, R Orlandi, Z Patel, Zsolt Podolyak, H Sakurai, H Schaffner, P Schury, S Shibagaki, K Steiger, H Suzuki, H Takeda, A Wendt, A Yagi, K Yoshinaga (2020)Determination of beta-delayed neutron emission probability limits of rhodium isotopes by gamma-ray spectroscopy, In: Journal of physics. Conference series1643(1) IOP Publishing

The decay of five neutron-heavy rhodium isotopes were studied at the Radioactive Isotope Beam Factory (RIBF) Facility at the RIKEN Nishina Center after relativistic fission of 238U beam on a thick beryllium target. Previously unknown associated gamma-ray decay energies are reported for each nuclide, and through evaluating the intensity of the 2+ → 0+ E2 transition in the even-even palladium daughter nuclei, 120,122,124Pd, from the beta-tagged gamma-ray spectra an upper or lower limit of beta-delayed neutron emission is deduced for each nuclei. A general, expected trend of increasing Pn is observed in the direction of the neutron drip line.

Martin P. Rey, Andrew Pontzen, Oscar Agertz, Matthew D. A. Orkney, Justin Read, Amelie Saintonge, Stacy Y. Kim, Payel Das (2022)EDGE: What shapes the relationship between H i and stellar observables in faint dwarf galaxies?, In: Monthly notices of the Royal Astronomical Society511(4)pp. 5672-5681 Oxford Univ Press

We show how the interplay between feedback and mass-growth histories introduces scatter in the relationship between stellar and neutral gas properties of field faint dwarf galaxies (M-*less than or similar to 10(6) M-circle dot). Across a suite of cosmological, high-resolution zoomed simulations, we find that dwarf galaxies of stellar masses 10(5)

Matthew D. A. Orkney, Justin Read, Martin P. Rey, Imran Nasim, Andrew Pontzen, Oscar Agertz, Stacy Y. Kim, Maxime Delorme, Walter Dehnen (2021)EDGE: two routes to dark matter core formation in ultra-faint dwarfs, In: Monthly notices of the Royal Astronomical Society504(3)pp. 3509-3522 Oxford Univ Press

In the standard Lambda cold dark matter paradigm, pure dark matter simulations predict dwarf galaxies should inhabit dark matter haloes with a centrally diverging density 'cusp'. This is in conflict with observations that typically favour a constant density 'core'. We investigate this 'cusp-core problem' in 'ultra-faint' dwarf galaxies simulated as part of the 'Engineering Dwarfs at Galaxy formation's Edge' project. We find, similarly to previous work, that gravitational potential fluctuations within the central region of the simulated dwarfs kinematically heat the dark matter particles, lowering the dwarfs' central dark matter density. However, these fluctuations are not exclusively caused by gas inflow/outflow, but also by impulsive heating from minor mergers. We use the genetic modification approach on one of our dwarf's initial conditions to show how a delayed assembly history leads to more late minor mergers and, correspondingly, more dark matter heating. This provides a mechanism by which even ultra-faint dwarfs (M-star < 10(5) M-circle dot), in which star formation was fully quenched at high redshift, can have their central dark matter density lowered over time. In contrast, we find that late major mergers can regenerate a central dark matter cusp, if the merging galaxy had sufficiently little star formation. The combination of these effects leads us to predict significant stochasticity in the central dark matter density slopes of the smallest dwarfs, driven by their unique star formation and mass assembly histories.

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