153 research outputs found
Chemodynamics of green pea galaxies - I. Outflows and turbulence driving the escape of ionizing photons and chemical enrichment
We investigate the ionized gas kinematics, physical properties, and chemical abundances of Sloan Digital Sky Survey J142947, a Green Pea galaxy at redshift z ⌠0.17 with strong, double-peak Ly α emission and indirect evidence of Lyman continuum (LyC) leakage. Using high-dispersion spectroscopy, we perform a multicomponent analysis of emission-line profiles. Our model consistently fits all lines as a narrow component with intrinsic velocity dispersion Ï âŒ 40 km s-1, and two broader blue-shifted components with Ï âŒ 90 and âŒ250 km s-1. We find electron densities and temperatures, ionization conditions, and direct O/H and N/O abundances for each component. A highly ionized, metal-poor, young and compact starburst dominates narrow emission, showing evidence of hard radiation fields and elevated N/O. The blue-shifted broader components are consistent with highly turbulent, possibly clumpy ionized gas at the base of a strong photoionized outflow, which accounts for âł50 per cent of the integrated emission-line fluxes. The outflow is dense and metal-enriched compared to the HII regions, with expansion velocities larger than those obtained from UV interstellar absorption lines under standard assumptions. Some of these metals may be able to escape, with outflows loading factors comparable to those found in high-z galaxies of similar SFR/Area. Our findings depict a two-stage starburst picture; hard radiation fields from young star clusters illuminate a turbulent and clumpy ISM that has been eroded by SNe feedback. Whilst UV data suggest an extended Ly α halo with high average HI column density, LyC photons could only escape from SDSS J142947 through low HI density channels or filaments in the ISM approaching density-bounded conditions, traced by outflowing gas.Fil: Hogarth, L.. Colegio Universitario de Londres; Reino UnidoFil: AmorĂn, R.. Universidad de La Serena; ChileFil: VĂlchez, J. M.. Instituto de AstrofĂsica de AndalucĂa - Csic; EspañaFil: HĂ€gele, Guillermo Federico. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Cardaci, Monica Viviana. Instituto de AstrofĂsica de la Plata (conicet- Universidad Nacional de la Plata); ArgentinaFil: PĂ©rez Montero, E.. Instituto de AstrofĂsica de AndalucĂa - Csic; EspañaFil: Firpo, VerĂłnica. Gemini Observatorysouthern Operations Center; ChileFil: Jaskot, A.. Williams College; Estados UnidosFil: ChĂĄvez, R.. Instituto de RadioastronomĂa y AstrofĂsica; MĂ©xic
Observational Constraints on Superbubble X-ray Energy Budgets
The hot, X-ray-emitting gas in superbubbles imparts energy and enriched
material to the interstellar medium (ISM) and generates the hot ionized medium,
the ISM's high-temperature component. The evolution of superbubble energy
budgets is not well understood, however, and the processes responsible for
enhanced X-ray emission in superbubbles remain a matter of debate. We present
Chandra ACIS-S observations of two X-ray-bright superbubbles in the Large
Magellanic Cloud (LMC), DEM L50 (N186) and DEM L152 (N44), with an emphasis on
disentangling the true superbubble X-ray emission from non-related diffuse
emission and determining the spatial origin and spectral variation of the X-ray
emission. An examination of the superbubble energy budgets shows that on the
order of 50% of the X-ray emission comes from regions associated with supernova
remnant (SNR) impacts. We find some evidence of mass-loading due to swept-up
clouds and metallicity enrichment, but neither mechanism provides a significant
contribution to the X-ray luminosities. We also find that one of the
superbubbles, DEM L50, is likely not in collisional ionization equilibrium. We
compare our observations to the predictions of the standard Weaver et al. model
and to 1-D hydrodynamic simulations including cavity supernova impacts on the
shell walls. Our observations show that mass-loading due to thermal evaporation
from the shell walls and SNR impacts are the dominant source of enhanced X-ray
luminosities in superbubbles. These two processes should affect most
superbubbles, and their contribution to the X-ray luminosity must be considered
when determining the energy available for transport to the ISM.Comment: 25 pages, 11 figures, accepted for publication in Ap
Toxicity and recovery in the pregnant mouse after gestational exposure to the cyanobacterial toxin, cylindrospermopsin
Cylindrospermopsin (CYN) is a tricyclic alkaloid toxin produced by fresh water cyanobacterial species worldwide. CYN has been responsible for both livestock and human poisoning after oral exposure. This study investigated the toxicity of CYN to pregnant mice exposed during different segments of gestation. The course of recovery and individual responses to the toxin were evaluated. Adverse effects of CYN were monitored up to 7 weeks post-dosing by clinical examination, histopathology, biochemistry and gene expression. Exposure on gestational days (GD) 8â12 induced significantly more lethality than GD13â17 exposure. Periorbital, gastrointestinal and distal tail hemorrhages were seen in both groups. Serum markers indicative of hepatic injury (alanine amino transferase, aspartate amino transferase and sorbitol dehydrogenase)were increased in both groups; markers of renal dysfunction (blood urea nitrogen and creatinine) were elevated in the GD8â12 animals. Histopathology was observed in the liver (centrilobular necrosis) and kidney (interstitial inflammation) in groups exhibiting abnormal serum markers. The expression profiles of genes involved in ribosomal biogenesis, xenobiotic and lipid metabolism, inflammatory response and oxidative stress were altered 24 h after the final dose. One week after dosing, gross, histological and serum parameters had returned to normal, although increased liver/body weight ratio and one instance of gastrointestinal bleeding was found in the GD13â17 group. Gene expression changes persisted up to 2 weeks post-dosing and returned to normal by 4 weeks. Responses of individual animals to CYN exposure indicated highly significant inter-animal variability within the treated groups
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