Emission line ratios for the Circumgalactic Medium and the "Bimodal" Nature of Galaxies

We find significantly different diagnostic emission line ratios for the circumgalactic gas associated with galaxies of stellar masses above and below $10^{10.4}$ M$_\odot$ using SDSS spectroscopy. Specifically, in a sample of 17,393 galaxies, intersected by 18,535 lines of sight at projected radii between 10 and 50 kpc, we stack measured fluxes for nebular strong emission lines, [O {\small III}] $\lambda$5007, H$\alpha$ and [N {\small II}] $\lambda6583$, and find that the gas surrounding the lower mass galaxies exhibits similar line ratios to those of gas ionized by star formation and that surrounding the higher mass galaxies similar to those of gas ionized by AGN or shocks. This finding highlights yet another characteristic of galaxies that is distinctly different above and below this stellar mass threshold, but one that is more closely connected to the gas accretion behavior hypothesized to be responsible for this dichotomy.Comment: 5 pages, 3 figures, accepted by ApJ

Partizipation und Beteiligungsrechte bei Vorhaben und Planungen des Naturschutzes und aufgrund von Entscheidungen nach dem Naturschutzrecht

Für alle diese Aspekte ist entscheidend, dass Naturschutz hierbei nicht verengt verstanden wird, sondern als eine vernetzende und umfassende Aufgabe, die mit dem gesamten Umweltaufgabenbereich durchdrungen ist und die notwendigen Bezüge insbesondere zur Landnutzung und der Land- und Forstwirtschaft und diesbezüglichen Kooperationen herstellt. Partizipationen sind also nicht bilateral oder einseitig auszugestalten. Sie müssen darauf gerichtet sein, zu tragfähigen und konsensualen Entscheidungen zwischen verschiedenen Akteuren im Raum zu kommen. Naturschutz ist verbunden mit dem Ressourcenschutz und einer nachhaltigen Wirtschaftsweise. Daher muss Naturschutz ökonomischen und sozialen Anforderungen gleichermaßen das Augenmerk schenken, um ihnen angemessen gerecht zu werden. Nur in diesem Dreiklang sind Erfolge dauerhaft erreichbar

The survival of gas clouds in the Circumgalactic Medium of Milky Way-like galaxies

Observational evidence shows that low-redshift galaxies are surrounded by extended haloes of multiphase gas, the so-called 'circumgalactic medium' (CGM). To study the survival of relatively cool gas (T < 10^5 K) in the CGM, we performed a set of hydrodynamical simulations of cold (T = 10^4 K) neutral gas clouds travelling through a hot (T = 2x10^6 K) and low-density (n = 10^-4 cm^-3) coronal medium, typical of Milky Way-like galaxies at large galactocentric distances (~ 50-150 kpc). We explored the effects of different initial values of relative velocity and radius of the clouds. Our simulations were performed on a two-dimensional grid with constant mesh size (2 pc) and they include radiative cooling, photoionization heating and thermal conduction. We found that for large clouds (radii larger than 250 pc) the cool gas survives for very long time (larger than 250 Myr): despite that they are partially destroyed and fragmented into smaller cloudlets during their trajectory, the total mass of cool gas decreases at very low rates. We found that thermal conduction plays a significant role: its effect is to hinder formation of hydrodynamical instabilities at the cloud-corona interface, keeping the cloud compact and therefore more difficult to destroy. The distribution of column densities extracted from our simulations are compatible with those observed for low-temperature ions (e.g. SiII and SiIII) and for high-temperature ions (OVI) once we take into account that OVI covers much more extended regions than the cool gas and, therefore, it is more likely to be detected along a generic line of sight.Comment: 12 pages, 10 figures. Accepted for publication in MNRA