Driving Galactic Outflows with Magnetic Fields at Low and High Redshift

Although galactic outflows play a key role in our understanding of the evolution of galaxies, the exact mechanism by which galactic outflows are driven is still far from being understood and, therefore, our understanding of associated feedback mechanisms that control the evolution of galaxies is still plagued by many enigmas. In this work, we present a simple toy model that can provide insight on how non-axisymmetric instabilities in galaxies (bars, spiral arms, warps) can lead to local exponential magnetic field growth by radial flows beyond the equipartition value by at least two orders of magnitude on a timescale of a few 100 Myr. Our predictions show that the process can lead to galactic outflows in barred spiral galaxies with a mass-loading factor η ≈ 0.1, in agreement with our numerical simulations. Moreover, our outflow mechanism could contribute to an understanding of the large fraction of barred spiral galaxies that show signs of galactic outflows in the chang-es survey. Extending our model shows the importance of such processes in high-redshift galaxies by assuming equipartition between magnetic energy and turbulent energy. Simple estimates for the star formation rate in our model together with cross correlated masses from the star-forming main sequence at redshifts z ∼ 2 allow us to estimate the outflow rate and mass-loading factors by non-axisymmetric instabilities and a subsequent radial inflow dynamo, giving mass-loading factors of η ≈ 0.1 for galaxies in the range of M ⋆ = 109–1012 M ⊙, in good agreement with recent results of sinfoni and kmos 3D.

FROM GLOBAL TO SPATIALLY RESOLVED IN LOW-REDSHIFT GALAXIES

Our understanding of the structure, composition and evolution of galaxies hasstrongly improved in the last decades, mostly due to new results based on large spectro-scopic and imaging surveys. In particular, the nature of ionized gas, its ionization mech-anisms, its relation with the stellar properties and chemical composition, the existence ofscaling relations that describe the cycle between stars and gas, and the corresponding evo-lution patterns have been widely explored and described. More recently, the introduction ofadditional techniques, in particular integral field spectroscopy, and their use in large galaxysurveys, have forced us to re-interpret most of those recent results from a spatially resolvedperspective. This review is aimed to complement recent efforts to compile and summarizethis change of paradigm in the interpretation of galaxy evolution. To this end we replicatepublished results, and present novel ones, based on the largest compilation of IFS data ofgalaxies in the nearby universe to date.

Large Metallicity Variations in the Galactic Interstellar Medium

Metals in the neutral Interstellar Medium (ISM) of galaxies are crucial for the formation and evolution of galaxies, stars, cosmic dust, molecules, and planets. However, understanding the metal abundances in the neutral ISM is complicated by the presence of cosmic dust. Large quantities of metals are missing from the observable gas-phase because they are incorporated into dust grains. This phenomenon is called dust depletion. Until recently, the metallicity of the neutral ISM in the vicinity of the Sun was assumed to be Solar. In this paper we directly measure the metallicity of the neutral ISM, by quantifying dust depletion without making as- sumptions on the gas metallicity, using Hubble Space Telescope (HST) and Very Large Telescope (VLT) spectra of 25 hot bright stars. We find that the dust-corrected metal- licity in the neutral ISM in our Galaxy is not always Solar, but shows large variations spreading over a factor of 10 and including many regions of low metallicity, down to ∼ 17% Solar and possibly below. Pristine gas infalling towards the Galactic disk in the form of intermediate and high-velocity clouds could cause the observed chemical inhomogeneities on scales of tens of pc. This has a profound impact for the chemical evolution of galaxies.

Constraints on the star formation histories of galaxies in the Local Cosmological Volume

ABSTRACT The majority of galaxies with current star formation rates (SFRs), $\rm SFR_{\rm o} \ge 10^{-3} \, M_\odot\,yr^{-1}$, in the Local Cosmological Volume, where observations should be reliable, have the property that their observed SFRo is larger than their average SFR. This is in tension with the evolution of galaxies described by delayed-τ models, according to which the opposite would be expected. The tension is apparent in that local galaxies imply the star formation time-scale τ ≈ 6.7 Gyr, much longer than the 3.5–4.5 Gyr obtained using an empirically determined main sequence at several redshifts. Using models where the SFR is a power law in time of the form ∝(t − t1)η for t1 = 1.8 Gyr (with no stars forming prior to t1) implies that η = 0.18 ± 0.03. This suggested near-constancy of a galaxy’s SFR over time raises non-trivial problems for the evolution and formation time of galaxies, but is broadly consistent with the observed decreasing main sequence with increasing age of the Universe.

Tidal evolution of galaxies in the most massive cluster of IllustrisTNG-100

We study the tidal evolution of galaxies in the most massive cluster of the IllustrisTNG-100 simulation. For the purpose of this work, we selected 112 galaxies with the largest stellar masses at present and followed their properties over time. Using their orbital history, we divided the sample into unevolved (infalling), weakly evolved (with one pericenter passage), and strongly evolved (with multiple pericenters). The samples are clearly separated by the value of the integrated tidal force from the cluster the galaxies experienced during their entire evolution and their properties depend strongly on this quantity. As a result of tidal stripping, the galaxies of the weakly evolved sample lost between 10 and 80% of their dark mass and less than 10% of stars, while those in the strongly evolved one lost more than 70% of dark mass and between 10 and 55% of stellar mass, and are significantly less, or not at all dark-matter dominated. While 33% of the infalling galaxies do not contain any gas, this fraction increases to 67% for the weakly evolved sample, and to 100% for the strongly evolved sample. The strongly evolved galaxies lose their gas earlier and faster (within 2–6 Gyr), but the process can take up to 4 Gyr from the first pericenter passage. These galaxies are redder and more metal rich, and at redshift z = 0.5, the population of galaxies in the cluster becomes predominantly red. As a result of tidal stirring, the morphology of the galaxies evolves from oblate to prolate and their rotation is diminished, thus the morphology-density relation is reproduced in the simulated cluster. The strongly evolved sample contains at least six convincing examples of tidally induced bars and six more galaxies that had their bars enhanced by their interaction with the cluster.

Cosmic ray driven galactic winds

Galactic winds constitute a primary feedback process in the ecology and evolution of galaxies. They are ubiquitously observed and exhibit a rich phenomenology, whose origin is actively investigated both theoretically and observationally. Cosmic rays have been widely recognized as a possible driving agent of galactic winds, especially in Milky–Way like galaxies. The formation of cosmic ray-driven winds is intimately connected with the microphysics of the cosmic ray transport in galaxies, making it an intrinsically non-linear and multiscale phenomenon. In this complex interplay, the cosmic ray distribution affects the wind launching and, in turns, is shaped by the presence of winds. In this review, we summarize the present knowledge of the physics of cosmic rays involved in the wind formation and of the wind hydrodynamics. We also discuss the theoretical difficulties connected with the study of cosmic ray-driven winds and possible future improvements and directions.