Determining the extragalactic extinction law with SALT. II. Additional sample

We present new results from an on-going programme to study the dust extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern African Large Telescope (SALT) during its performance-verification phase. The wavelength dependence of the dust extinction for seven galaxies is derived in six spectral bands ranging from the near-ultraviolet atmospheric cutoff to the near-infrared. The derivation of an extinction law is performed by fitting model galaxies to the unextinguished parts of the image in each spectral band, and subtracting from these the actual images. We compare our results with the derived extinction law in the Galaxy and find them to run parallel to the Galactic extinction curve with a mean total-to-selective extinction value of 2.71+-0.43. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them to range from 10^4 to 10^7 Solar masses. We study the case of the well-known dust-lane galaxy NGC2685 for which HST/WFPC2 data is available to test the dust distribution on different scales. Our results imply a scale-free dust distribution across the dust lanes, at least within ~1 arcsec (~60 pc) regions.Comment: 11 pages, 7 figures, 3 tables. Accepted for publication in MNRAS. R-band contour maps and B-R colour-index maps are low-resolution versions of those used in the MNRAS versio

Dust and Ionized Gas Association in E/S0 Galaxies with Dust Lanes: Clues to their Origin

We present results from an on-going programme to study the dust and ionized gas in E/S0 galaxies with dust lanes. Our data, together with results from previous studies of E/S0 galaxies, are used to demonstrate the tight relationship between these two components. This relationship is discussed in light of our current understanding of the nature and origin of the interstellar medium (ISM), and in particular in the context of the interplay between the different multi-temperature components. We show that focusing on dust obscured regions as tracers of the ISM, and on their properties, serves as independent evidence for the external origin of the dust and ionized gas.Comment: 11 pages, 5 figures, 3 tables. MNRAS in pres

A candidate polar-ring galaxy in the Subaru Deep Field

We discuss the properties of an object in the Subaru Deep Field (SDF) classified as a galaxy in on-line data bases and revealed on the Subaru images as a genuine polar-ring galaxy (PRG) candidate. We analyse available photometric data and conclude that this object consists of a >5 Gyr old early-type central body surrounded by a faint, narrow inner ring tilted at a ~25 deg angle relative to the polar axis of the host galaxy. The halo surrounding the main stellar body exhibits a diversity of spatially extended stellar features of low surface brightness, including a faint asymmetric stellar cloud and two prominent loops. These faint features, together with the unperturbed morphology of the central host, are clear signs of a recent coalescence of two highly unequal mass galaxies, most likely a pre-existing early-type galaxy and a close-by gas-rich dwarf galaxy. The presumed stellar remnants observed near the edges of the ring, including possibly the surviving captured companion itself, indicate that the merger is still taking place.Comment: 6 pages, 5 figures, 1 table. Accepted for publication in MNRA

Hoag's Object: Evidence for Cold Accretion onto an Elliptical Galaxy

(Abridged) We present new photometric and spectroscopic observations of the famous Hoag's Object, a peculiar ring galaxy with a central roundish core. The nature of Hoag's Object is still under controversial discussion. Previous studies demonstrated that a major accretion event that took place at least 2-3 Gyr ago can account for the observational evidence. However, the role of internal nonlinear mechanisms in forming the outer ring was not yet completely ruled out. These new data, together with HI and optical information from the literature, are used to demonstrate that Hoag's Object is a relatively isolated system surrounded by a luminous quasi-spiral pattern and a massive, low-density HI disc. The main stellar body is an old, mildly triaxial elliptical galaxy with very high angular momentum. We review previous formation scenarios of Hoag's Object in light of the new data and conclude that the peculiar morphology could not represent a late phase in barred early-type galaxies evolution. In addition, no observational evidence supports late merging events in the evolution of the galaxy, although further tests are required before safely dismissing this idea. We propose a new scenario where the elliptical core formed in the early Universe with the HI disc forming shortly after the core by prolonged "cold" accretion of primordial gas from the intergalactic medium. The low gas density does not allow intense star formation to occur everywhere in the disc, but only along a tightly wound spiral pattern of enhanced density induced by the triaxial gravitational potential.Comment: 18 pages, 12 figures. MNRAS in press, minor changes to match published versio

UGC 4599: A Photometric Study of the Nearest Hoag-Type Ring Galaxy

We present a photometric study of UGC 4599, a low-luminosity galaxy superficially resembling Hoag's Object in that on sky survey images it appears to be a complete ring surrounding a roundish core. The nature of the outer ring of Hoag-type galaxies is still debated and may be related either to slow secular evolution or to environmental processes, such as galaxy-galaxy interactions. we show that in UGC 4599 (a) the nearly round central body follows well an r^1/4 light profile almost all the way to the centre, (b) the isophotes are strongly twisted with a sharp 45 deg transition at a radius of r~6 arcsec, (c) the blue ring seems to have reached near-equilibrium configuration with the central body, (d) the ring is actually composed of a one-and-a-half turn spiral feature, and (e) one side of the spiral shows conspicuous star formation in the form of at least nine HII regions, revealed by their H_alpha emission. Based on the photometric data, together with HI information from the literature, we characterize UGC 4599 as an elliptical-like object surrounded by a luminous ring and a massive, extremely extended HI disc. Given its observed properties, we rule out UGC 4599 as representing a late phase in barred early-type galaxies evolution. We discuss the origin of UGC 4599 and conclude that this galaxy could be the result of a major interaction between two gas-rich spiral galaxies that took place at least 5 Gyr ago. However, deep optical imaging and a detailed stellar population analysis are required to determine whether the large gas reservoir could have been accreted directly from the intergalactic medium onto a pre-existing elliptical galaxy in the early Universe. A detailed kinematical study will shed light on the exact nature of the central body and the ring of UGC 4599.Comment: 14 pages, 6 figures and 5 tables. Accepted for publication in MNRAS. The abstract is abridged compared to the published versio

Determining the extragalactic extinction law with SALT

We present CCD imaging observations of early-type galaxies with dark lanes obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We derive the extinction law by the extragalactic dust in the dark lanes in the spectral range 1.11mu m^{-1} < lambda^{-1} < 2.94 mu m^{-1} by fitting model galaxies to the unextinguished parts of the image, and subtracting from these the actual images. We find that the extinction curves run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic enviroment are similar to those of the Milky Way. The ratio of the total V band extinction to the selective extinction between the V and B bands is derived for each galaxy with an average of 2.82+-0.38, compared to a canonical value of 3.1 for the Milky Way. The similar values imply that galaxies with well-defined dark lanes have characteristic dust grain sizes similar to those of Galactic dust.Comment: 20 pages, 15 figures and 4 tables. Accepted for publication in MNRA

Repurposing Metformin in Nondiabetic People With HIV:Influence on Weight and Gut Microbiota

Background. People with HIV (PWH) taking antiretroviral therapy (ART) may experience weight gain, dyslipidemia, increased risk of non-AIDS comorbidities, and long-term alteration of the gut microbiota. Both low CD4/CD8 ratio and chronic inflammation have been associated with changes in the gut microbiota of PWH. The antidiabetic drug metformin has been shown to improve gut microbiota composition while decreasing weight and inflammation in diabetes and polycystic ovary syndrome. Nevertheless, it remains unknown whether metformin may benefit PWH receiving ART, especially those with a low CD4/CD8 ratio. Methods. In the Lilac pilot trial, we recruited 23 nondiabetic PWI I receiving ART for more than 2 years with a low CD4/CD8 ratio ( Results. Metformin decreased weight in PWH, and weight loss was inversely correlated with plasma levels of the satiety factor GDF-15. Furthermore, metformin changed the gut microbiota composition by increasing the abundance of anti-inflammatory bacteria such as butyrate-producing species and the protective Akkermansia muciniphila. Conclusions. Our study provides the first evidence that a 12-week metformin treatment decreased weight and favored anti-inflammatory bacteria abundance in the microbiota of nondiabetic ART-treated PWH. Larger randomized placebo-controlled clinical trials with longer metformin treatment will be needed to further investigate the role of metformin in reducing inflammation and the risk of non-AIDS comorbidities in ART-treated PWH

CXCL13 as a Biomarker of Immune Activation During Early and Chronic HIV Infection

Background: CXCL13 is preferentially secreted by Follicular Helper T cells (TFH) to attract B cells to germinal centers. Plasma levels of CXCL13 have been reported to be elevated during chronic HIV-infection, however there is limited data on such elevation during early phases of infection and on the effect of ART. Moreover, the contribution of CXCL13 to disease progression and systemic immune activation have been partially defined. Herein, we assessed the relationship between plasma levels of CXCL13 and systemic immune activation.Methods: Study samples were collected in 114 people living with HIV (PLWH) who were in early (EHI) or chronic (CHI) HIV infection and 35 elite controllers (EC) compared to 17 uninfected controls (UC). A subgroup of 11 EHI who initiated ART and 14 who did not were followed prospectively. Plasma levels of CXCL13 were correlated with CD4 T cell count, CD4/CD8 ratio, plasma viral load (VL), markers of microbial translocation [LPS, sCD14, and (1→3)-β-D-Glucan], markers of B cell activation (total IgG, IgM, IgA, and IgG1-4), and inflammatory/activation markers like IL-6, IL-8, IL-1β, TNF-α, IDO-1 activity, and frequency of CD38+HLA-DR+ T cells on CD4+ and CD8+ T cells.Results: Plasma levels of CXCL13 were elevated in EHI (127.9 ± 64.9 pg/mL) and CHI (229.4 ± 28.5 pg/mL) compared to EC (71.3 ± 20.11 pg/mL), and UC (33.4 ± 14.9 pg/mL). Longitudinal analysis demonstrated that CXCL13 remains significantly elevated after 14 months without ART (p &lt; 0.001) and was reduced without normalization after 24 months on ART (p = 0.002). Correlations were observed with VL, CD4 T cell count, CD4/CD8 ratio, LPS, sCD14, (1→3)-β-D-Glucan, total IgG, TNF-α, Kynurenine/Tryptophan ratio, and frequency of CD38+HLA-DR+ CD4 and CD8 T cells. In addition, CMV+ PLWH presented with higher levels of plasma CXCL13 than CMV- PLWH (p = 0.005).Conclusion: Plasma CXCL13 levels increased with HIV disease progression. Early initiation of ART reduces plasma CXCL13 and B cell activation without normalization. CXCL13 represents a novel marker of systemic immune activation during early and chronic HIV infection and may be used to predict the development of non-AIDS events