2019, Hill, Vanessa, Skúladóttir, Ása, Tolstoy, Eline, Venn, Kim A., Shetrone, Matthew D., Jablonka, Pascale, Primas, Francesca, Battaglia, Giuseppina, de Boer, Thomas J. L., François, Patrick, Helmi, Amina, Kaufer, Andreas, Letarte, Bruno, Starkenburg, Else, Spite, Monique

We present detailed chemical abundances for 99 red-giant branch stars in the centre of the Sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution VLT/FLAMES spectroscopy. The abundances of Li, Na, -elements (O, Mg, Si, Ca Ti), iron-peak elements (Sc, Cr, Fe, Co, Ni, Zn), and r- and s-process elements (Ba, La, Nd, Eu) were all derived using stellar atmosphere models and semi-automated analysis techniques. The iron abundances populate the whole metallicity distribution of the galaxy with the exception of the very low metallicity tail, 2:3 [Fe/H] 0:9. There is a marked decrease in [ /Fe] over our sample, from the Galactic halo plateau value at low [Fe/H] and then, after a “knee”, a decrease to sub-solar [ /Fe] at high [Fe/H]. This is consistent with products of core-collapse supernovae dominating at early times, followed by the onset of supernovae type Ia as early as 12 Gyr ago. The s-process products from low-mass AGB stars also participate in the chemical evolution of Sculptor on a timescale comparable to that of supernovae type Ia. However, the r-process is consistent with having no time delay relative to core-collapse supernovae, at least at the later stages of the chemical evolution in Sculptor. Using the simple and well-behaved chemical evolution of Sculptor, we further derive empirical constraints on the relative importance of massive stars and supernovae type Ia to the nucleosynthesis of individual iron-peak and -elements. The most important contribution of supernovae type Ia is to the iron-peak elements: Fe, Cr, and Mn. There is, however, also a modest but non-negligible contribution to both the heavier -elements: S, Ca and Ti, and some of the iron-peak elements: Sc and Co. We see only a very small or no contribution to O, Mg, Ni, and Zn from supernovae type Ia in Sculptor. The observed chemical abundances in Sculptor show no evidence of a significantly di erent initial mass function, compared to that of the Milky Way. With the exception of neutron-capture elements at low [Fe/H], the scatter around mean trends in Sculptor for [Fe=H] 2:3 is extremely low, and compatible with observational errors. Combined with the small scatter in the age-elemental abundances relation, this calls for an effcient mixing of metals in the gas in the centre of Sculptor since 12 Gyr ago.

2022, Taibi, S., Battaglia, G., Leaman, R., Brooks, A., Riggs, C., Munshi, F., Revaz, Y., Jablonka, P.

Aims. We explore correlations between the strength of metallicity gradients in Local Group dwarf galaxies and their stellar mass, star formation history timescales, and environment. Methods. We performed a homogeneous analysis of literature spectroscopic data of red giant stars and determined radial metallicity profiles for 30 Local Group dwarf galaxies. This is the largest compilation of this type to date. Results. The dwarf galaxies in our sample show a variety of metallicity profiles, most of them decreasing with radius and some with rather steep profiles. The derived metallicity gradients as a function of the half-light radius, [Fe/H](R/Re), show no statistical differences when compared with the morphological type of the galaxies, nor with their distance from the Milky Way or M31. No correlations are found with either stellar mass or star formation timescales. In particular, we do not find the linear relation between [Fe/H](R/Re) and the galaxy median age t50, which has been reported in the literature for a set of simulated systems. On the other hand, the high angular momentum in some of our galaxies does not seem to affect the gradient strengths. The strongest gradients in our sample are observed in systems that are likely to have experienced a past merger event. When these merger candidates are excluded, the analysed dwarf galaxies show mild gradients (ã-0.1 dex Re-1) with little scatter between them, regardless of their stellar mass, dynamical state, and their star formation history. These results agree well with different sets of simulations presented in the literature that were analysed using the same method as for the observed dwarf galaxies. Conclusions. The interplay between the multitude of factors that could drive the formation of metallicity gradients likely combine in complex ways to produce in general comparable mild [Fe/H](R/Re) values, regardless of stellar mass and star formation history. The strongest driver of steep gradients seems to be previous dwarf-dwarf merger events in a system.

2022, Pechetti, Renuka, Seth, Anil, Kamann, Sebastian, Caldwell, Nelson, Strader, Jay, den Brok, Mark, Luetzgendorf, Nora, Neumayer, Nadine, Voggel, Karina

We investigate the presence of a central black hole (BH) in B023-G078, M31's most massive globular cluster. We present high-resolution, adaptive-optics assisted, integral-field spectroscopic kinematics from Gemini/NIFS that show a strong rotation (∼20 km s-1) and a velocity dispersion rise toward the center (37 km s-1). We combine the kinematic data with a mass model based on a two-component fit to HST ACS/HRC data of the cluster to estimate the mass of a putative BH. Our dynamical modeling suggests a >3σ detection of a BH component of (1σ uncertainties). The inferred stellar mass of the cluster is , consistent with previous estimates, thus the BH makes up 1.5% of its mass. We examine whether the observed kinematics are caused by a collection of stellar mass BHs by modeling an extended dark mass as a Plummer profile. The upper limit on the size scale of the extended mass is 0.56 pc (95% confidence), which does not rule out an extended mass. There is compelling evidence that B023-G078 is the tidally stripped nucleus of a galaxy with a stellar mass >109 M o˙, including its high-mass, two-component luminosity profile, color, metallicity gradient, and spread in metallicity. Given the emerging evidence that the central BH occupation fraction of >109 M o˙ galaxies is high, the most plausible interpretation of the kinematic data is that B023-G078 hosts a central BH. This makes it the strongest BH detection in a lower-mass (<107 M o˙) stripped nucleus, and one of the few dynamically detected intermediate-mass BHs.