The nature and origin of disky elliptical galaxies

The observational trend that disky elliptical galaxies exhibit younger luminosity- weighted ages than boxy ellipticals is investigated. The presence of a possible young stellar disk embedded in these galaxies is explored by comparing kinematics derived from the near-infrared Calcium II triplet (around 8600 Å) and Hβ (4863 Å) Balmer line, thought to be sensitive to older and younger stars respectively. Using synthetic stellar population spectra of these two wavelength regions, it is found that a young disk component produces observable differences in the kinematics derived from the two wavelength regions. Specifically, very young disks produce differences in the Gauss-Hermite coefficients, h(_3) and h(_4). Disks with an intermediate age produce offsets in the rotation velocities. Older disks produce clear two-component structure in the derived LOSVDs. Thus, diagnostic indicators are established which can be applied to observations. A comparison is presented of the major- and minor-axis kinematics derived from the Calcium II triplet and Hβ absorption features for a small sample of disky elliptical galaxies with enhanced Hβ absorption strength, indicative of a young component. For two galaxies in the sample, NGC 584 and NGC 821, Hβ gives a rotation velocity higher than that from the Calcium II triplet. These offsets are not consistent with the spectral models, since the offsets in velocity are not accompanied by the expected offsets in the other LOSVD parameters. This implies that the disks have either formed over time with a modest star- formation rate; or that the young stars in these systems are present in both the disk and spheroid components. From dynamical modelling of ground-based integral-field spectroscopy combined with HST STIS data, the disky elliptical NGC 821 is found to have a mass-to-light ratio of 4.12± 0.06 in I-band solar units, and harbours a central black hole of mass (3.41 ± 0.68) x 10(^7) M(_ʘ). This black hole mass is consistent with Gebhardt et al. (2002), who use the same STIS data with their independent modelling code. The phase-space distribution of the orbits in the model shows evidence for a two-component structure, which corresponds to a slowly rotating spheroidal component superimposed with a flattened, strongly rotating component. This second component, which has properties similar to a disk, accounts for 15% of the total system mass. Applying the two-component stellar population models, a disk of this mass would have formed 6 Gyr ago to produce the observed Hβ absorption. Such a disk is not consistent with the long-slit observations, as no offset was found between the Calcium II triplet and Hβ velocity dispersions. However, this cannot be strongly excluded due to the effects of metallicity and disk velocity dispersion on the spectral modelling

The Spectral Energy Distribution of Powerful Starburst Galaxies I : Modelling the Radio Continuum

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We have acquired radio-continuum data between 70MHz and 48 GHz for a sample of 19 southern starburst galaxies at moderate redshifts (0.067 < z < 0.227) with the aim of separating synchrotron and free-free emission components. Using a Bayesian framework, we find the radio continuum is rarely characterized well by a single power law, instead often exhibiting lowfrequency turnovers below 500 MHz, steepening at mid to high frequencies, and a flattening at high frequencies where free-free emission begins to dominate over the synchrotron emission. These higher order curvature components may be attributed to free-free absorption across multiple regions of star formation with varying optical depths. The decomposed synchrotron and free-free emission components in our sample of galaxies form strong correlations with the total-infrared bolometric luminosities. Finally, we find that without accounting for free-free absorption with turnovers between 90 and 500MHz the radio continuum at low frequency (v < 200 MHz) could be overestimated by upwards of a factor of 12 if a simple power-law extrapolation is used from higher frequencies. The mean synchrotron spectral index of our sample is constrained to be α = -1.06, which is steeper than the canonical value of -0.8 for normal galaxies. We suggest this may be caused by an intrinsically steeper cosmic ray distribution.Peer reviewe

The Role of Nutrition in COVID-19 Susceptibility and Severity of Disease: A Systematic Review.

BACKGROUND Many nutrients have powerful immunomodulatory actions with the potential to alter susceptibility to coronavirus disease 2019 (COVID-19) infection, progression to symptoms, likelihood of severe disease, and survival. OBJECTIVE The aim was to review the latest evidence on how malnutrition across all its forms (under- and overnutrition and micronutrient status) may influence both susceptibility to, and progression of, COVID-19. METHODS We synthesized information on 13 nutrition-related components and their potential interactions with COVID-19: overweight, obesity, and diabetes; protein-energy malnutrition; anemia; vitamins A, C, D, and E; PUFAs; iron; selenium; zinc; antioxidants; and nutritional support. For each section we provide: 1) a landscape review of pertinent material; 2) a systematic search of the literature in PubMed and EMBASE databases, including a wide range of preprint servers; and 3) a screen of 6 clinical trial registries. All original research was considered, without restriction to study design, and included if it covered: 1) severe acute respiratory syndrome coronavirus (CoV) 2 (SARS-CoV-2), Middle East respiratory syndrome CoV (MERS-CoV), or SARS-CoV viruses and 2) disease susceptibility or 3) disease progression, and 4) the nutritional component of interest. Searches took place between 16 May and 11 August 2020. RESULTS Across the 13 searches, 2732 articles from PubMed and EMBASE, 4164 articles from the preprint servers, and 433 trials were returned. In the final narrative synthesis, we include 22 published articles, 38 preprint articles, and 79 trials. CONCLUSIONS Currently there is limited evidence that high-dose supplements of micronutrients will either prevent severe disease or speed up recovery. However, results of clinical trials are eagerly awaited. Given the known impacts of all forms of malnutrition on the immune system, public health strategies to reduce micronutrient deficiencies and undernutrition remain of critical importance. Furthermore, there is strong evidence that prevention of obesity and type 2 diabetes will reduce the risk of serious COVID-19 outcomes. This review is registered at PROSPERO as CRD42020186194