AGC 226067: A possible interacting low-mass system

We present Arecibo, GBT, VLA and WIYN/pODI observations of the ALFALFA source AGC 226067. Originally identified as an ultra-compact high velocity cloud and candidate Local Group galaxy, AGC 226067 is spatially and kinematically coincident with the Virgo cluster, and the identification by multiple groups of an optical counterpart with no resolved stars supports the interpretation that this systems lies at the Virgo distance (D=17 Mpc). The combined observations reveal that the system consists of multiple components: a central HI source associated with the optical counterpart (AGC 226067), a smaller HI-only component (AGC 229490), a second optical component (AGC 229491), and extended low surface brightness HI. Only ~1/4 of the single-dish HI emission is associated with AGC 226067; as a result, we find M_HI/L_g ~ 6 Msun/Lsun, which is lower than previous work. At D=17 Mpc, AGC 226067 has an HI mass of 1.5 x 10^7 Msun and L_g = 2.4 x 10^6 Lsun, AGC 229490 (the HI-only component) has M_HI = 3.6 x 10^6 Msun, and AGC 229491 (the second optical component) has L_g = 3.6 x 10^5 Lsun. The nature of this system of three sources is uncertain: AGC 226067 and AGC 229490 may be connected by an HI bridge, and AGC 229490 and AGC 229491 are separated by only 0.5'. The current data do not resolve the HI in AGC 229490 and its origin is unclear. We discuss possible scenarios for this system of objects: an interacting system of dwarf galaxies, accretion of material onto AGC 226067, or stripping of material from AGC 226067.Comment: Accepted for publication in A&A. 6 pages, 4 figure

Gas Accretion and Star Formation Rates

Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the alpha-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

Time course of plasma urea and urinary urea excretion in patients with a prolonged ICU stay

Whereas urinary creatinine excretion (UCE) is an established marker of muscle mass, both in critically ill and non-critically ill patients, analysis of urinary urea excretion (UUE) may allow estimation of proteolysis that is associated with critical illness. We evaluated the time courses of plasma urea and creatinine as well UUE and UCE in critically ill patients with a prolonged ICU stay. Our goal was to evaluate changes in plasma urea and creatinine in conjunction with their urinary excretion, to get a better understanding of urea handling in ICU patients. From 2002 to 2021, plasma urea and creatinine, UUE and UCE were determined in routinely obtained 24 h urine samples between ICU admission and day 30, in adult patients with an ICU-stay ≥ 28d. Urea-to-creatinine ratios in plasma and urine were calculated. Patients with stage 3 acute kidney injury (AKI) were excluded. Analyses were performed separately for females and males and for patients with and without acute renal failure to account for respectively differences in muscle mass and impaired renal function. Of 47,120 patients, who were admitted to the ICU between 2002 and 2021, 638 patients met the inclusion criteria. During the first 10 days mean ± SD plasma urea increased from 9.7 ± 6.0 mmol/L at ICU admission to 12.4 ± 7.9 mmol/L (P &lt; 0.001) on day 11 and decreased afterwards with a rate of 0.1 mmol/l/d. UUE peaked at 590 ± 317 mmol/day on day 13 whereas UCE peaked already on day 4. Males had higher plasma urea, plasma creatinine, UUE and UCE than females. Plasma and urinary urea-to-creatinine ratio (UCR) stabilized after day 7, with a gradual increase in plasma UCR and urinary UCR between day 7 and day 30. Similar courses, although less pronounced, were seen in patients without AKI. The course of urea in critically ill patients is characterized by an initial rise of both plasma urea and urinary urea excretion, presumably due to increased catabolism of endogenous and exogenous protein in the first week of ICU admission. Subsequently, UUE and UCE declined steadily in a rate that was comparable to the known loss of muscle mass during ICU admission of approximately 1%/day.</p

FDG-PET/CT in intensive care patients with bloodstream infection

BACKGROUND: 2-Deoxy-2-[18F]fluoro-D-glucose (FDG) positron emission tomography (PET)/computed tomography (CT) is an advanced imaging technique that can be used to examine the whole body for an infection focus in a single examination in patients with bloodstream infection (BSI) of unknown origin. However, literature on the use of this technique in intensive care patients is scarce. The purpose of this study was to evaluate the diagnostic yield of FDG-PET/CT in intensive care patients with BSI. METHODS: In this retrospective cohort study, all intensive care patients from our Dutch university medical center who had culture-proven BSI between 2010 and 2020 and underwent FDG-PET/CT to find the focus of infection were included. Diagnostic performance was calculated and logistic regression analysis was performed to evaluate the association between FDG-PET/CT outcome and C-reactive protein level (CRP), leukocyte count, duration of antibiotic treatment, duration of ICU stay, quality of FDG-PET/CT, and dependency on mechanical ventilation. In addition, the impact of FDG-PET/CT on clinical treatment was evaluated. RESULTS: 30 intensive care patients with BSI were included. In 21 patients, an infection focus was found on FDG-PET/CT which led to changes in clinical management in 14 patients. FDG-PET/CT achieved a sensitivity of 90.9% and specificity of 87.5% for identifying the focus of infection. Poor quality of the FDG-PET images significantly decreased the likelihood of finding an infection focus as compared to reasonable or good image quality (OR 0.16, P = 0.034). No other variables were significantly associated with FDG-PET/CT outcome. No adverse events during the FDG-PET/CT procedure were reported. CONCLUSION: FDG-PET/CT has a high diagnostic yield for detecting the infection focus in patients with BSI admitted to intensive care. Poor PET image quality was significantly associated with a decreased likelihood of finding the infection focus in patients with BSI. This could be improved by adequate dietary preparation and cessation of intravenous glucose and glucose-regulating drugs. Recent advances in PET/CT technology enable higher image quality with shorter imaging time and may contribute to routinely performing FDG-PET/CT in intensive care patients with BSI of unknown origin

The dwarf galaxy population as revealed by ALFALFA

The combination of sensitivity and large sky coverage of the ALFALFA HI survey has enabled the detection of difficult to observe low mass galaxies in large numbers, including dwarf galaxies overlooked in optical surveys. Three different, but connected, studies of dwarf galaxies from the ALFALFA survey are of particular interest: SHIELD (Survey of HI in Extremely Low-mass Dwarfs), candidate gas-rich ultra- faint dwarf galaxies, and the (Almost) Dark population. SHIELD is a systematic multiwavelength study of all dwarf galaxies from ALFALFA with MHI &lt; 107.2 M☉ and clear optical counterparts. Candidate gas-rich ultra-faint dwarf galaxies extend the dwarf galaxy population to even lower masses. These galaxies are identified as isolated HI clouds with no discernible optical counterpart but subsequent observations reveal that some are extremely faint, gas- dominated galaxies. Leo P, discovered first as an HI detection, and then found to be an actively star-forming galaxy, bridges the gap between these candidate galaxies and the SHIELD sample. The (Almost) Dark sample consists of galaxies whose optical counterparts are overlooked in current optical surveys but which are clear detections in ALFALFA. This sample includes field gas-rich ultra-diffuse galaxies. Coma P, with a peak surface brightness of only ~26.4 mag arcsec-2 in g', demonstrates the sort of extreme low surface brightness galaxy that can be discovered in an HI survey

Extracellular matrix turnover in severe COVID-19 is reduced by corticosteroids

BACKGROUND: Severe and critical COVID-19 is characterized by pulmonary viral infection with SARS-CoV-2 resulting in local and systemic inflammation. Dexamethasone (DEX) has been shown to improve outcomes in critically ill patients; however, its effect on tissue remodeling, particularly collagen turnover, remains unclear. This study investigated the association between circulating extracellular matrix (ECM) remodeling neo-epitopes and COVID-19 severity, their relationship with mortality, and the effect of DEX on these markers.METHODS: We conducted a multi-center prospective cohort study involving 226 COVID-19 patients: 157 with severe disease admitted to the ward and 69 with critical disease admitted to the ICU. Plasma samples were collected at ICU admission and at discharge or death. Circulating collagen degradation (C3M, C4Ma3, and C6M) and synthesis (PRO-C3, PRO-C4, and PRO-C6) neo-epitopes were measured. Longitudinal analysis of ECM neo-epitope changes during ICU stay and their association with mortality was performed, along with an evaluation of the impact of DEX treatment on these markers.RESULTS: Critically ill patients exhibited higher levels of collagen degradation (reflecting inflammatory driven ECM destruction) (C3M, C6M) and collagen synthesis (strongly related to fibroblast activity) (PRO-C3, PRO-C6) neo-epitopes than severe patients. Increased collagen turnover, measured during ICU stay, was associated with mortality. Non-survivors displayed rising levels of collagen degradation and synthesis markers over time, whereas survivors had stable or declining levels. In non-survivors without DEX treatment, C6M and PRO-C6 levels were significantly increased, whereas these elevations were less pronounced in patients treated with DEX.CONCLUSION: Our findings suggest that elevated collagen turnover is associated with poor outcomes in critically ill COVID-19 patients. DEX treatment appeared to attenuate ECM remodeling, although this effect was not linked to improved survival. Further studies are needed to confirm these observations and better understand the role of ECM remodeling in COVID-19 and the potential therapeutic impact of corticosteroids.</p

[18F]FDG PET/CT identifies infectious and inflammatory foci in persistent critical illness.

PURPOSE: Some ICU patients remain critically ill despite reversal of the original admission diagnosis, driven by a cascade of events resulting in new and persistent organ failure. Secondary infections and systemic inflammation are important components of this cascade and may be visualised using [ 18F]FDG PET/CT. The aim of this dual centre retrospective study was to assess the ability of [ 18F]FDG PET/CT to identify infectious and inflammatory foci in patients with persistent critical illness and to evaluate its impact on subsequent therapy management. METHODS: We included patients admitted to the ICU between 2017 and 2024, in whom a [ 18F]FDG PET/CT scan was performed ten days or more after ICU admission. [ 18F]FDG PET/CT reports were reviewed for diagnoses, and clinical records were reviewed to determine if this diagnosis was new, which diagnostics were performed before the PET/CT, and which therapeutic changes were made directly after the PET/CT. The relation between inflammatory parameters and [ 18F]FDG PET/CT findings were studied using t-test or ANOVA. RESULTS: Forty-seven patients with persistent critical illness were included from two university medical centres. The median interval between admission and PET/CT was 21 days (IQR 14-28). In 43 patients (91%) a potential infectious or inflammatory focus was detected, of which 34 (72%) were previously unknown. The [ 18F]FDG PET/CT was utilized late in the diagnostic work-up since a median of 7 (IQR 6.0-8.0) diagnostic procedures were performed prior to the PET/CT. In 26 (55%) patients therapy change was reported within 48 h after the PET/CT. CONCLUSION: [ 18F]FDG PET/CT detected a considerable number of (new) infectious and inflammatory foci in patients with persistent critical illness, often followed by a change in therapy. Further research is needed to establish the role of [ 18F]FDG PET/CT in these patients

Transcriptome Kinetics of Circulating Neutrophils during Human Experimental Endotoxemia

Polymorphonuclear cells (neutrophils) play an important role in the systemic inflammatory response syndrome and the development of sepsis. These cells are essential for the defense against microorganisms, but may also cause tissue damage. Therefore, neutrophil numbers and activity are considered to be tightly regulated. Previous studies have investigated gene transcription during experimental endotoxemia in whole blood and peripheral blood mononuclear cells. However, the gene transcription response of the circulating pool of neutrophils to systemic inflammatory stimulation in vivo is currently unclear. We examined neutrophil gene transcription kinetics in healthy human subjects (n = 4) administered a single dose of endotoxin (LPS, 2 ng/kg iv). In addition, freshly isolated neutrophils were stimulated ex vivo with LPS, TNFα, G-CSF and GM-CSF to identify stimulus-specific gene transcription responses. Whole transcriptome microarray analysis of circulating neutrophils at 2, 4 and 6 hours after LPS infusion revealed activation of inflammatory networks which are involved in signaling of TNFα and IL-1α and IL-1β. The transcriptome profile of inflammatory activated neutrophils in vivo reflects extended survival and regulation of inflammatory responses. These changes in neutrophil transcriptome suggest a combination of early activation of circulating neutrophils by TNFα and G-CSF and a mobilization of young neutrophils from the bone marrow

Gaia

We use the first Gaia data release, combined with RAVE and APOGEE spectroscopic surveys, to investigate the origin of halo stars within <~3 kpc from the Sun. We identify halo stars kinematically, as moving with a relative speed of at least 220 km/s with respect to the local standard of rest. These stars are in general more metal-poor than the disk, but surprisingly, half of our halo sample is comprised of stars with [Fe/H]>-1. The orbital directions of these metal-rich halo stars are preferentially aligned with the disk rotation, in sharp contrast with the isotropic orbital distribution of the more metal-poor halo stars. We find similar properties in the Latte cosmological zoom-in simulation of a Milky Way-like galaxy from the FIRE project. In Latte, metal-rich halo stars formed primarily inside of the solar circle, while lower-metallicity halo stars preferentially formed at larger distances (extending beyond the virial radius). This suggests that metal-rich halo stars in the Solar neighborhood in fact formed in-situ within the Galactic disk rather than having been accreted from satellite systems. These stars, currently on halo-like orbits, therefore have likely undergone substantial radial migration/heating.Comment: 16 pages, 11 figures, submitted to Ap