Orbital pericentres and the inferred dark matter halo structure of satellite galaxies

ABSTRACT Using the phat-ELVIS suite of Milky Way-sized halo simulations, we show that subhalo orbital pericentres, rperi, correlate with their dark matter halo structural properties. Specifically, at fixed maximum circular velocity, Vmax, subhaloes with smaller rperi are more concentrated (have smaller rmax values) and have lost more mass, with larger peak circular velocities, Vpeak, prior to infall. These trends provide information that can tighten constraints on the inferred Vmax and Vpeak values for known Milky Way satellites. We illustrate this using published pericentre estimates enabled by Gaia for the nine classical Milky Way dwarf spheroidal satellites. The two densest dSph satellites (Draco and Ursa Minor) have relatively small pericentres, and this pushes their inferred rmax and Vmax values lower than they would have been without pericentre information. For Draco, we infer $V_{\rm max} = 23.5 \, \pm 3.3$ km s−1 (compared to $27.3 \, \pm 7.1$ km s−1 without pericentre information). Such a shift exacerbates the traditional Too Big to Fail problem. Draco’s peak circular velocity range prior to infall narrows from Vpeak = 21–51 km s−1 without pericentre information to Vpeak = 25–37 km s−1 with the constraint. Over the full population of classical dwarf spheroidals, we find no correlation between Vpeak and stellar mass today, indicative of a high level of stochasticity in galaxy formation at stellar masses below ∼107 M⊙. As proper motion measurements for dwarf satellites become more precise, they should enable useful priors on the expected structure and evolution of their host dark matter subhaloes.

Gravity defined precisely with quarks – squaring the circle to achieve fine description of black hole physics, and understanding the formation of key constellations

Gravity is redefined by drawing on the author’s works and inputting quark physics in a way consistent with it ; it allows to better understand black hole dynamics, black hole eruptions and some constellation patterns in the sky (the Scorpio, Ursa Minor and Ursa Major as well as Cassiopea for instance). The concept of gravitational lensing is rapidly differenciated from black hole eruptions. Some final remarks underline a possible threat for missions to the Moon.

Почитание Большой Медведицы в среде ойратов и калмыков: древнейшие представления и буддийские напластования. Часть 2

Introduction. Ursa Major is the constellation most venerated by Mongolic peoples. Goals. The article seeks to examine related beliefs traced in folklore and collected field data, reveal key mythological characteristics, and cast light upon diachronous layers in the beliefs of Kalmyks and Oirats (Western Mongols). So, the work aims at analyzing basic Kalmyk and Oirat folklore plots dealing with origins of the Great Bear in comparison to those of other Mongolic cultures; and at examining the concept of Ursa Major against the background of some calendar rites and revered mythological images with due regard of contemporary ceremonies addressed to the constellation. Materials. The paper analyzes folklore and ethnographic materials. Results. Part 1 of the article identifies main variants of mythological texts about Ursa Major (Mong. Долоон бурхан, Долоон өвгөн, Kalm. Долан бурхн, Долан одн) existing in Kalmyk and Oirat discourses, comparing the latter to myths of other Mongolic populations. It shows that basically the myths narrate about seven male characters (siblings, sworn brothers, or thieves) or an ox-man, though etymology of terms may tie the constellation (its emergence) to the archaic plot of day and night alternation as a chase of shedeer, and the solar theme at large. Part 2 further analyzes Ursa Major-related beliefs and compares the latter to some calendar rites and mythological images revered in Kalmyk and Oirat culture. The paper informs that the constellation was sometimes referred to by the Oirats as ‘Seven Maral Deer’ (Oir. Долоон марал), which implies our analysis may extend to the legend of how the heavenly hunter pursued a flock of she-deer. The Oirat oral tradition believes that both the characters of Ursa Major stories and Khukhedei Mergen the Hunter (whose chase made three she-deer turn into the three stars of Orion’s Belt therefore referred to by the Mongols as ‘Three She-Deer’, Mong. Гурван марал, Kalm. Һурвн марл) can be considered masters of the two horses tied to the ‘Golden Pole’ (i.e. Pole Star) — two stars of Ursa Minor. Oirats and Kalmyks also associate Ursa Major with thawing weather, protection of children, livestock (from wolves), and increase of its numbers, remission of sins — similar functions attributed to the White Old Man (Kalm. Цаhан аав) revered by the Oirats as the Lord of the Altai, while Kalmyks tend to view him as a protector deity of the nation, one of his manifestations being that of the Lord of the Year (Kalm. Җилин эзн). The article also analyzes contemporary Buddhist rites dealing with Ursa Major among Mongolic populations.

J-factor estimation of Draco, Sculptor, and Ursa Minor dwarf spheroidal galaxies with the member/foreground mixture model

ABSTRACT Dwarf spheroidal galaxies (dSphs) are promising targets of indirect detection experiments searching for dark matter (DM) at present Universe. Towards robust prediction for the amount of signal flux originating in DM annihilation inside dSphs, a precise determination of DM distributions as well as J-factors of the dSphs is particularly important. In this work, we estimate those of Draco, Sculptor, and Ursa Minor dSphs by an improved statistical method in which both foreground stars and dSph member stars are simultaneously taken into account. We define the likelihood function of the method as the so-called conditional one to remove sampling bias of observed stellar data. This improved method enables us to estimate DM distributions and J-factors of the dSphs directly from observed stellar data contaminated by foreground stars without imposing stringent membership criteria on the measured quantities.

Neutron-capture elements in dwarf galaxies

Context. We present a large homogeneous set of stellar parameters and abundances across a broad range of metallicities, involving 13 classical dwarf spheroidal (dSph) and ultra-faint dSph (UFD) galaxies. In total, this study includes 380 stars in Fornax, Sagittarius, Sculptor, Sextans, Carina, Ursa Minor, Draco, Reticulum II, Bootes I, Ursa Major II, Leo I, Segue I, and Triangulum II. This sample represents the largest, homogeneous, high-resolution study of dSph galaxies to date. Aims. With our homogeneously derived catalog, we are able to search for similar and deviating trends across different galaxies. We investigate the mass dependence of the individual systems on the production of α-elements, but also try to shed light on the long-standing puzzle of the dominant production site of r-process elements. Methods. We used data from the Keck observatory archive and the ESO reduced archive to reanalyze stars from these 13 classical dSph and UFD galaxies. We automatized the step of obtaining stellar parameters, but ran a full spectrum synthesis (1D, local thermal equilibrium) to derive all abundances except for iron to which we applied nonlocal thermodynamic equilibrium corrections where possible. Results. The homogenized set of abundances yielded the unique possibility of deriving a relation between the onset of type Ia supernovae and the stellar mass of the galaxy. Furthermore, we derived a formula to estimate the evolution of α-elements. This reveals a universal relation of these systems across a large range in mass. Finally, we show that between stellar masses of 2.1 × 107 M⊙ and 2.9 × 105 M⊙, there is no dependence of the production of heavy r-process elements on the stellar mass of the galaxy. Conclusions. Placing all abundances consistently on the same scale is crucial to answering questions about the chemical history of galaxies. By homogeneously analyzing Ba and Eu in the 13 systems, we have traced the onset of the s-process and found it to increase with metallicity as a function of the galaxy’s stellar mass. Moreover, the r-process material correlates with the α-elements indicating some coproduction of these, which in turn would point toward rare core-collapse supernovae rather than binary neutron star mergers as a host for the r-process at low [Fe/H] in the investigated dSph systems.

Multiple chemodynamic stellar populations of the Ursa Minor dwarf spheroidal galaxy

ABSTRACT We present a Bayesian method to identify multiple (chemodynamic) stellar populations in dwarf spheroidal galaxies (dSphs) using velocity, metallicity, and positional stellar data without the assumption of spherical symmetry. We apply this method to a new Keck/Deep Imaging Multi-Object Spectrograph (DEIMOS) spectroscopic survey of the Ursa Minor (UMi) dSph. We identify 892 likely members, making this the largest UMi sample with line-of-sight velocity and metallicity measurements. Our Bayesian method detects two distinct chemodynamic populations with high significance (in logarithmic Bayes factor, ln B ∼ 33). The metal-rich ([Fe/H] = −2.05 ± 0.03) population is kinematically colder (radial velocity dispersion of $\sigma _v=4.9_{-1.0}^{+0.8} \, \mathrm{km} \, \mathrm{s}^{-1}$) and more centrally concentrated than the metal-poor ($[{\rm Fe/H}]=-2.29_{-0.06}^{+0.05}$) and kinematically hotter population ($\sigma _v =11.5_{-0.8}^{+0.9}\, \mathrm{km} \, \mathrm{s}^{-1}$). Furthermore, we apply the same analysis to an independent Multiple Mirror Telescope (MMT)/Hectochelle data set and confirm the existence of two chemodynamic populations in UMi. In both data sets, the metal-rich population is significantly flattened (ϵ = 0.75 ± 0.03) and the metal-poor population is closer to spherical ($\epsilon =0.33_{-0.09}^{+0.12}$). Despite the presence of two populations, we are able to robustly estimate the slope of the dynamical mass profile. We found hints for prolate rotation of order ${\sim}2 \, \mathrm{km} \, \mathrm{s}^{-1}$ in the MMT data set, but further observations are required to verify this. The flattened metal-rich population invalidates assumptions built into simple dynamical mass estimators, so we computed new astrophysical dark matter annihilation (J) and decay profiles based on the rounder, hotter metal-poor population and inferred $\log _{10}{(J(0{^{\circ}_{.}}5)/{\rm GeV^{2} \, cm^{-5}})}\approx 19.1$ for the Keck data set. Our results paint a more complex picture of the evolution of UMi than previously discussed.

The gas-loss evolution in dwarf spheroidal galaxies: Supernova feedback and environment effects in the case of the local group galaxy Ursa Minor

In this work, we performed two distinct non-cosmological, three-dimensional hydrodynamic simulations that evolved the gas component of a galaxy similar to the classical dwarf spheroidal galaxy Ursa Minor. Both simulations take into account types II and Ia supernovae feedback constrained by chemical evolution models, while ram-pressure stripping mechanism is added into one of them considering an intergalactic medium and a galactic velocity that resemble what is observed nowadays for the Ursa Minor galaxy. Our results show no difference in the amount of gas left inside the galaxy until 400 Myr of evolution. Moreover, the ram-pressure wind was stalled and inverted by thermal pressure of the interstellar medium and supernovae feedback during the same interval.

Too big to fail in light of Gaia

ABSTRACT We point out an anticorrelation between the central dark matter (DM) densities of the bright Milky Way dwarf spheroidal galaxies (dSphs) and their orbital pericenter distances inferred from Gaia data. The dSphs that have not come close to the Milky Way centre (like Fornax, Carina and Sextans) are less dense in DM than those that have come closer (like Draco and Ursa Minor). The same anticorrelation cannot be inferred for the ultrafaint dSphs due to large scatter, while a trend that dSphs with more extended stellar distributions tend to have lower DM densities emerges with ultrafaints. We discuss how these inferences constrain proposed solutions to the Milky Way’s too-big-to-fail problem and provide new clues to decipher the nature of DM.