Abstract
The Gaia Sausage is the major accretion event that built the stellar halo of the Milky Way galaxy. Here, we provide dynamical and chemical evidence for a second substantial accretion ...episode, distinct from the Gaia Sausage. The Sequoia Event provided the bulk of the high-energy retrograde stars in the stellar halo, as well as the recently discovered globular cluster FSR 1758. There are up to six further globular clusters, including ω Centauri, as well as many of the retrograde substructures in Myeong et al., associated with the progenitor dwarf galaxy, named the Sequoia. The stellar mass in the Sequoia galaxy is ∼5 × 10 M⊙ , whilst the total mass is ∼1010 M⊙ , as judged from abundance matching or from the total sum of the globular cluster mass. Although clearly less massive than the Sausage, the Sequoia has a distinct chemodynamical signature. The strongly retrograde Sequoia stars have a typical eccentricity of ∼0.6, whereas the Sausage stars have no clear net rotation and move on predominantly radial orbits. On average, the Sequoia stars have lower metallicity by ∼0.3 dex and higher abundance ratios as compared to the Sausage. We conjecture that the Sausage and the Sequoia galaxies may have been associated and accreted at a comparable epoch.
Abstract
We fit the rotation curves of isolated dwarf galaxies to directly measure the stellar mass–halo mass relation (M⋆–M200) over the mass range 5 × 105 ≲ M⋆/M⊙ ≲ 108. By accounting for cusp-core ...transformations due to stellar feedback, we find a monotonic relation with little scatter. Such monotonicity implies that abundance matching should yield a similar M⋆–M200 if the cosmological model is correct. Using the ‘field galaxy’ stellar mass function from the Sloan Digital Sky Survey (SDSS) and the halo mass function from the Λ cold dark matter Bolshoi simulation, we find remarkable agreement between the two. This holds down to M200 ∼ 5 × 109 M⊙, and to M200 ∼ 5 × 108 M⊙ if we assume a power-law extrapolation of the SDSS stellar mass function below M⋆ ∼ 107 M⊙. However, if instead of SDSS we use the stellar mass function of nearby galaxy groups, then the agreement is poor. This occurs because the group stellar mass function is shallower than that of the field below M⋆ ∼ 109 M⊙, recovering the familiar ‘missing satellites’ and ‘too big to fail’ problems. Our result demonstrates that both problems are confined to group environments and must, therefore, owe to ‘galaxy formation physics’ rather than exotic cosmology. Finally, we repeat our analysis for a Λ Warm Dark Matter cosmology, finding that it fails at 68 per cent confidence for a thermal relic mass of mWDM < 1.25 keV, and mWDM < 2 keV if we use the power-law extrapolation of SDSS. We conclude by making a number of predictions for future surveys based on these results.
Abstract
We exploit the first Gaia data release to study the properties of the Galactic stellar halo as traced by RR Lyrae. We demonstrate that it is possible to select a pure sample of RR Lyrae ...using only photometric information available in the Gaia+2MASS catalogue. The final sample contains about 21 600 RR Lyrae covering an unprecedented fraction ( ∼ 60 per cent) of the volume of the Galactic inner halo (R < 28 kpc). We study the morphology of the stellar halo by analysing the RR Lyrae distribution with parametric and non-parametric techniques. Taking advantage of the uniform all-sky coverage, we test halo models more sophisticated than usually considered in the literature, such as those with varying flattening, tilts and/or offset of the halo with respect to the Galactic disc. A consistent picture emerges: the inner halo is well reproduced by a smooth distribution of stars settled on triaxial density ellipsoids. The shortest axis is perpendicular to the Milky Way's disc, while the longest axis forms an angle of ∼70° with the axis connecting the Sun and the Galactic Centre. The elongation along the major axis is mild (p = 1.27), and the vertical flattening is shown to evolve from a squashed state with q ≈ 0.57 in the centre to a more spherical q ≈ 0.75 at the outer edge of our data set. Within the radial range probed, the density profile of the stellar halo is well approximated by a single power law with exponent α = −2.96. We do not find evidence of tilt or offset of the halo with respect to the Galaxy's disc.
Abstract
Dwarf spheroidal galaxies (dSphs) appear to be some of the most dark matter (DM)-dominated objects in the Universe. Their dynamical masses are commonly derived using the kinematics of stars ...under the assumption of equilibrium. However, these objects are satellites of massive galaxies (e.g. the Milky Way) and thus can be influenced by their tidal fields. We investigate the implication of the assumption of equilibrium focusing on the Sculptor dSph by means of ad hoc N-body simulations tuned to reproduce the observed properties of Sculptor following the evolution along some observationally motivated orbits in the Milky Way gravitational field. For this purpose, we used state-of-the-art spectroscopic and photometric samples of Sculptor’s stars. We found that the stellar component of the simulated object is not directly influenced by the tidal field, while ${\approx } 30\!-\!60{{\ \rm per\ cent}}$ of the mass of the more diffuse DM halo is stripped. We conclude that, considering the most recent estimate of the Sculptor proper motion, the system is not affected by the tides and the stellar kinematics represents a robust tracer of the internal dynamics. In the simulations that match the observed properties of Sculptor, the present-day dark-to-luminous mass ratio is ≈6 within the stellar half-light radius (≈0.3 kpc) and >50 within the maximum radius of the analysed data set (≈1.5○, ≈2 kpc).
Several open questions on galaxy formation and evolution have their roots in the lack of a universal star formation law that could univocally link the gas properties, such as its density, to the star ...formation rate (SFR) density. In a recent paper we used a sample of nearby disc galaxies to infer the volumetric star formation (VSF) law, a tight correlation between the gas and the SFR volume densities derived under the assumption of hydrostatic equilibrium for the gas disc. However, due to the dearth of information about the vertical distribution of the SFR in these galaxies, we could not find a unique slope for the VSF law, but two alternative values. In this paper, we use the scale height of the SFR density distribution in our Galaxy adopting classical Cepheids (age ≲200 Myr) as tracers of star formation. We show that this latter is fully compatible with the flaring scale height expected from gas in hydrostatic equilibrium. These scale heights allowed us to convert the observed surface densities of gas and SFR into the corresponding volume densities. Our results indicate that the VSF law ρSFR ∝ ραgas ρ SFR ∝ ρ gas α $ \rho_\mathrm{SFR} \propto \rho_\mathrm{gas}^\alpha $ with α ≈ 2 is valid in the Milky Way as well as in nearby disc galaxies.
Context.
Isolated local group (LG) dwarf galaxies have evolved most or all of their life unaffected by interactions with the large LG spirals and therefore offer the opportunity to learn about the ...intrinsic characteristics of this class of objects.
Aims.
Our aim is to explore the internal kinematic and metallicity properties of one of the three isolated LG early-type dwarf galaxies, the Tucana dwarf spheroidal. This is an intriguing system, as it has been found in the literature to have an internal rotation of up to 16 km s
−1
, a much higher velocity dispersion than dwarf spheroidals of similar luminosity, and a possible exception to the too-big-too-fail problem.
Methods.
We present the results of a new spectroscopic dataset that we procured from the Very Large Telescope (VLT) taken with the FORS2 instrument in the region of the Ca II triplet for 50 candidate red giant branch stars in the direction of the Tucana dwarf spheroidal. These yielded line-of-sight (l.o.s.) velocity and metallicity (Fe/H) measurements of 39 effective members that double the number of Tucana’s stars with such measurements. In addition, we re-reduce and include in our analysis the other two spectroscopic datasets presented in the literature, the VLT/FORS2 sample by Fraternali et al. (2009, A&A, 499, 121), and the VLT/FLAMES one from Gregory et al. (2019, MNRAS, 485, 2010).
Results.
Across the various datasets analyzed, we consistently measure a l.o.s. systemic velocity of 180 ± 1.3 km s
−1
and find that a dispersion-only model is moderately favored over models that also account for internal rotation. Our best estimate of the internal l.o.s. velocity dispersion is 6.2
−1.3
+1.6
km s
−1
, much smaller than the values reported in the literature and in line with similarly luminous dwarf spheroidals; this is consistent with NFW halos of circular velocities < 30 km s
−1
. Therefore, Tucana does not appear to be an exception to the too-big-to-fail problem, nor does it appear to reside in a dark matter halo much more massive than those of its siblings. As for the metallicity properties, we do not find anything unusual; there are hints of the presence of a metallicity gradient, but more data are needed to pinpoint its presence.
Resveratrol is a natural polyphenolic compound present in plants and red wine with many potential health benefits. This compound has various anti-inflammatory and anti-tumor properties and can ...improve cellular mitochondrial activity. This trial was designed to evaluate the effect on the outcome of IVF of Resveratrol supplementation in women > 35 years with good ovarian reserve (AMH > 1.2 ng/ml). Women were randomized to receive or placebo or Resveratrol (150 mg per day) for three months preceding the ovarian stimulation (OS). All patients were stimulated with a starting dose of recombinant FSH ranging between 150 and 300 IU according to age and ovarian reserve. GnRH antagonist flexible protocol was adopted for pituitary suppression. Triggering was performed with urinary hCG (10.000 IU).
The study was conducted between January 2019 and December 2022 with aa total of 37 cases and 33 controls were recruited. No statistically significant differences in the number of oocytes retrieved, biochemical pregnancy, clinical pregnancy and live birth rates were observed between women treated with resveratrol and control group. A statistically significant increase in the follicle output rate (FORT) and follicle-to oocyte index (FOI) was observed in women treated with resveratrol-based nutraceutical (0.92 versus 0.77 p = 0.02, and 0.77 versus 0.64 p = 0.006, respectively).
Preliminary results from this study indicate that pre-treatment with resveratrol may improve ovarian sensitivity to exogenous FSH, which in turn may decrease the risk of hypo-response to OS in advanced reproductive age women.
We recently described a complex multisystem syndrome in which mild‐moderate myopia segregated as an independent trait. A plethora of genes has been related to sporadic and familial myopia. More ...recently, in Chinese patients severe myopia (MYP25, OMIM:617238) has been linked to mutations in P4HA2 gene. Seven family members complaining of reduced distance vision especially at dusk underwent complete ophthalmological examination. Whole‐exome sequencing was performed to identify the gene responsible for myopia in the pedigree. Moderate myopia was diagnosed in the family which was associated to the novel missense variant c.1147A > G p.(Lys383Glu) in the prolyl 4‐hydroxylase,alpha‐polypeptide 2 (P4HA2) gene, which catalyzes the formation of 4‐hydroxyproline residues in the collagen strands. In vitro studies demonstrated P4HA2 mRNA and protein reduced expression level as well as decreased collagen hydroxylation and deposition in mutated fibroblast primary cultures compared to healthy cell lines. This study suggests that P4HA2 mutations may lead to myopic axial elongation of eyeball as a consequence of quantitative and structural alterations of collagen. This is the first confirmatory study which associates a novel dominant missense variant in P4HA2 with myopia in Caucasian patients. Further studies in larger cohorts are advisable to fully clarify genotype‐phenotype correlations.
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