ABSTRACT
We explore a sample of 1492 galaxies with measurements of the mean stellar population properties and the spin parameter proxy, $\lambda _{R_{\rm {e}}}$, drawn from the SAMI Galaxy Survey. We ...fit a global $\alpha /\rm {Fe}$–σ relation, finding that ${\alpha /\rm {Fe}}=(0.395\pm 0.010)\rm {log}_{10}(\sigma)-(0.627\pm 0.002)$. We observe an anti-correlation between the residuals $\Delta \alpha /\rm {Fe}$ and the inclination-corrected $\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}$, which can be expressed as ${\Delta \alpha /\rm {Fe}}=(-0.057\pm 0.008){\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}}+(0.020\pm 0.003)$. The anti-correlation appears to be driven by star-forming galaxies, with a gradient of ${\Delta \alpha /\rm {Fe}}\sim (-0.121\pm 0.015){\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}}$, although a weak relationship persists for the subsample of galaxies for which star formation has been quenched. We take this to be confirmation that disc-dominated galaxies have an extended duration of star formation. At a reference velocity dispersion of 200 km s−1, we estimate an increase in half-mass formation time from ∼0.5 Gyr to ∼1.2 Gyr from low- to high-$\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}$ galaxies. Slow rotators do not appear to fit these trends. Their residual α-enhancement is indistinguishable from other galaxies with ${\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}}\lessapprox 0.4$, despite being both larger and more massive. This result shows that galaxies with ${\lambda _{\, R_{\rm {e}}}^{\rm {\, eo}}}\lessapprox 0.4$ experience a similar range of star formation histories, despite their different physical structure and angular momentum.
ABSTRACT
The Galaxy And Mass Assembly (GAMA) survey has morphologically identified a class of ‘Little Blue Spheroid’ (LBS) galaxies whose relationship to other classes of galaxies we now examine in ...detail. Considering a sample of 868 LBSs, we find that such galaxies display similar but not identical colours, specific star formation rates, stellar population ages, mass-to-light ratios, and metallicities to Sd-Irr galaxies. We also find that LBSs typically occupy environments of even lower density than those of Sd-Irr galaxies, where ∼65 per cent of LBS galaxies live in isolation. Using deep, high-resolution imaging from VST KiDS and the new Bayesian, 2D galaxy profile modelling code profit, we further examine the detailed structure of LBSs and find that their Sérsic indices, sizes, and axial ratios are compatible with those of low-mass elliptical galaxies. We then examine SAMI Galaxy survey integral field emission line kinematics for a subset of 62 LBSs and find that the majority (42) of these galaxies display ordered rotation with the remainder displaying disturbed/non-ordered dynamics. Finally, we consider potential evolutionary scenarios for a population with this unusual combination of properties, concluding that LBSs are likely formed by a mixture of merger and accretion processes still recently active in low-redshift dwarf populations. We also infer that if LBS-like galaxies were subjected to quenching in a rich environment, they would plausibly resemble cluster dwarf ellipticals.
Abstract
We present a novel Bayesian method, referred to as blobby3d, to infer gas kinematics that mitigates the effects of beam smearing for observations using integral field spectroscopy. The ...method is robust for regularly rotating galaxies despite substructure in the gas distribution. Modelling the gas substructure within the disc is achieved by using a hierarchical Gaussian mixture model. To account for beam smearing effects, we construct a modelled cube that is then convolved per wavelength slice by the seeing, before calculating the likelihood function. We show that our method can model complex gas substructure including clumps and spiral arms. We also show that kinematic asymmetries can be observed after beam smearing for regularly rotating galaxies with asymmetries only introduced in the spatial distribution of the gas. We present findings for our method applied to a sample of 20 star-forming galaxies from the SAMI Galaxy Survey. We estimate the global H α gas velocity dispersion for our sample to be in the range $\bar{\sigma }_v \sim$7, 30 km s−1. The relative difference between our approach and estimates using the single Gaussian component fits per spaxel is $\Delta \bar{\sigma }_v / \bar{\sigma }_v = - 0.29 \pm 0.18$ for the H α flux-weighted mean velocity dispersion.
The Antarctic plateau contains the best sites on earth for many forms of astronomy, but none of the existing bases was selected with astronomy as the primary motivation. In this article, we try to ...systematically compare the merits of potential observatory sites. We include South Pole, Domes A, C, and F, and also Ridge B (running northeast from Dome A), and what we call “Ridge A” (running southwest from Dome A). Our analysis combines satellite data, published results, and atmospheric models, to compare the boundary layer, weather, aurorae, airglow, precipitable water vapor, thermal sky emission, surface temperature, and the free atmosphere, at each site. We find that all Antarctic sites are likely to be compromised for optical work by airglow and aurorae. Of the sites with existing bases, Dome A is easily the best overall; but we find that Ridge A offers an even better site. We also find that Dome F is a remarkably good site. Dome C is less good as a thermal infrared or terahertz site, but would be able to take advantage of a predicted “OH hole” over Antarctica during spring.
The recent PNAS paper by Migliori et al. (1) attempts to explain the unusually strong temperature dependence of the bulk modulus of fcc plutonium (δ-Pu) by use of the disordered local moment (DLM) ...model. It is our opinion that this approach does not correctly incorporate the dynamic magnetism of δ-Pu. We provide the following note as commentary.
One of the most important considerations when planning the next generation of ground-based optical astronomical telescopes is to choose a site that has excellent 'seeing'-the jitter in the apparent ...position of a star that is caused by light bending as it passes through regions of differing refractive index in the Earth's atmosphere. The best mid-latitude sites have a median seeing ranging from 0.5 to 1.0 arcsec (refs 1-5). Sites on the Antarctic plateau have unique atmospheric properties that make them worth investigating as potential observatory locations. Previous testing at the US Amundsen-Scott South Pole Station has, however, demonstrated poor seeing, averaging 1.8 arcsec (refs 6, 7). Here we report observations of the wintertime seeing from Dome C (ref. 8), a high point on the Antarctic plateau at a latitude of 75° S. The results are remarkable: the median seeing is 0.27 arcsec, and below 0.15 arcsec 25 per cent of the time. A telescope placed at Dome C would compete with one that is 2 to 3 times larger at the best mid-latitude observatories, and an interferometer based at this site could work on projects that would otherwise require a space mission.
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