We revealed the detailed structure of a vastly extended H$\alpha$-emittingnebula ("H$\alpha$ nebula") surrounding the starburst/merging galaxy NGC 6240by deep narrow-band imaging observations with the Subaru Suprime-Cam. Theextent of the nebula is $\sim$90 kpc in diameter and the total H$\alpha$luminosity amounts to $\approx 1.6 \times 10^{42}$ erg s$^{-1}$. The volumefilling factor and the mass of the warm ionized gas are$\sim$10$^{-4}$--10$^{-5}$ and $\sim$$5 \times 10^8$ $M_\odot$, respectively.The nebula has a complicated structure, which includes numerous filaments,loops, bubbles, and knots. We found that there is a tight spatial correlationbetween the H$\alpha$ nebula and the extended soft X-ray-emitting gas, both inlarge and small scales. The overall morphology of the nebula is dominated byfilamentary structures radially extending from the center of the galaxy. Alarge-scale bi-polar bubble extends along the minor axis of the main stellardisk. The morphology strongly suggests that the nebula was formed by intenseoutflows - superwinds - driven by starbursts. We also found three bright knotsembedded in a looped filament of ionized gas that show head-tail morphologiesin both emission-line and continuum, suggesting close interactions between theoutflows and star forming regions. Based on the morphology and surfacebrightness distribution of the H$\alpha$ nebula, we propose the scenario thatthree major episodes of starburst/superwind activities which were initiated$\sim$10$^2$ Myr ago formed the extended ionized gas nebula of NGC 6240.

This Letter presents a new, remarkably simple diagnostic specificallydesigned to derive chemical abundances for high redshift galaxies. It uses onlythe H \alpha, [N II] and [S II] emission lines, which can usually be observedin a single gating stetting, and is almost linear up to an abundance of 12+log(O/H) = 9.05. It can be used over the full abundance range encountered in highredshift galaxies. By its use of emission lines located close together inwavelength, it is also independent of reddening. Our diagnostic dependscritically on the calibration of the N/O ratio. However, by using realisticstellar atmospheres combined with the N/O vs. O/H abundance calibration derivedlocally from stars and H II regions, and allowing for the fact thathigh-redshift H II regions have both high ionisation parameters \emph{and} highgas pressures, we find that the observations of high-redshift galaxies can besimply explained by the models without having to invoke arbitrary changes inN/O ratio, or the presence of unusual quantities of Wolf-Rayet stars in thesegalaxies.

Mass models of galactic disks traditionally rely on axisymmetric density androtation curves, paradoxically acting as if their most remarkable asymmetricfeatures, such as lopsidedness or spiral arms, were not important. In thisarticle, we relax the axisymmetry approximation and introduce a methodologythat derives 3D gravitational potentials of disk-like objects and robustlyestimates the impacts of asymmetries on circular velocities in the diskmidplane. Mass distribution models can then be directly fitted to asymmetricline-of-sight velocity fields. Applied to the grand-design spiral M99, the newstrategy shows that circular velocities are highly nonuniform, particularly inthe inner disk of the galaxy, as a natural response to the perturbedgravitational potential of luminous matter. A cuspy inner density profile ofdark matter is found in M99, in the usual case where luminous and dark mattershare the same center. The impact of the velocity nonuniformity is to make theinner profile less steep, although the density remains cuspy. On another hand,a model where the halo is core dominated and shifted by 2.2-2.5 kpc from theluminous mass center is more appropriate to explain most of the kinematicallopsidedness evidenced in the velocity field of M99. However, the gravitationalpotential of luminous baryons is not asymmetric enough to explain thekinematical lopsidedness of the innermost regions, irrespective of the densityshape of dark matter. This discrepancy points out the necessity of anadditional dynamical process in these regions: possibly a lopsided distributionof dark matter.

High surface density, rapidly star-forming galaxies are observed to have$\approx 50-100\,{\rm km\,s^{-1}}$ line-of-sight velocity dispersions, whichare much higher than expected from supernova driving alone, but may arise fromlarge-scale gravitational instabilities. Using three-dimensional simulations oflocal regions of the interstellar medium, we explore the impact of highvelocity dispersions that arise from these disk instabilities. Parametrizingdisks by their surface densities and epicyclic frequencies, we conduct a seriesof simulations that probe a broad range of conditions. Turbulence is drivenpurely horizontally and on large scales, neglecting any energy input fromsupernovae. We find that such motions lead to strong global outflows in thehighly-compact disks that were common at high redshifts, but weak or negligiblemass loss in the more diffuse disks that are prevalent today. Substantialoutflows are generated if the one-dimensional horizontal velocity dispersionexceeds $\approx 35\,{\rm km\,s^{-1}},$ as occurs in the dense disks that havestar formation rate densities above $\approx 0.1\,{\rm M}_\odot\,{\rmyr}^{-1}\,{\rm kpc}^{-2}.$ These outflows are triggered by a thermal runaway,arising from the inefficient cooling of hot material coupled with successiveheating from turbulent driving. Thus, even in the absence of stellar feedback,a critical value of the star-formation rate density for outflow generation canarise due to a turbulent heating instability. This suggests that in stronglyself-gravitating disks, outflows may be enhanced by, but need not caused by,energy input from supernovae.

Following a number of conflicting studies of M87's mass profile, we undertakea dynamical analysis of multiple tracer populations to constrain its mass overa large radius range. We combine stellar kinematics in the central regions withthe dynamics of 612 globular clusters out to 200 kpc and satellite galaxiesextending to scales comparable with the virial radius. Using a spherical Jeansanalysis, we are able to disentangle the mass contributions from the dark andbaryonic components and set constraints on the structure of each. Assumingisotropy, we explore four different models for the dark matter halo and findthat a centrally-cored dark matter distribution is preferred. We infer astellar mass-to-light ratio $\Upsilon_{\star,v} = 6.9 \pm 0.1$ -- consistentwith a Salpeter-like IMF -- and a core radius $r_c = 67 \pm 20$ kpc. We thenintroduce anisotropy and find that, while the halo remains clearly cored, theradial stellar anisotropy has a strong impact on both $\Upsilon_{\star,v}$ andthe core's radius; here we find $\Upsilon_{\star,v} = 3.50_{-0.36}^{+0.32}$ --consistent with a Chabrier-like IMF -- and $r_c = 19.00_{-8.34}^{+8.38}$ kpc.Thus the presence of a core at the centre of the dark halo is robust againstanisotropy assumptions, while the stellar mass and core size are not. We areable to reconcile previously discrepant studies by showing that modelling theglobular cluster data alone leads to the very different inference of asuper-NFW cusp, thus highlighting the value of multiple-population modelling,and we point to the possible role of M87's AGN and the cluster environment informing the central dark matter core.

We measured the gas abundance profiles in a sample of 122 face-on spiralgalaxies observed by the CALIFA survey and included all spaxels whose lineemission was consistent with star formation. This type of analysis allowed usto improve the statistics with respect to previous studies, and to properlyestimate the oxygen distribution across the entire disc to a distance of up to3-4 disc effective radii (r$_e$). We confirm the results obtained fromclassical HII region analysis. In addition to the general negative gradient, anouter flattening can be observed in the oxygen abundance radial profile. Aninner drop is also found in some cases. There is a common abundance gradientbetween 0.5 and 2.0 r$_e$ of $\alpha_{O/H} = -\,0.075\,\rm{dex}/r_e$ with ascatter of $\sigma = 0.016\,\rm{dex}/r_e$ when normalising the distances to thedisc effective radius. By performing a set of Kolmogorov-Smirnov tests, wedetermined that this slope is independent of other galaxy properties, such asmorphology, absolute magnitude, and the presence or absence of bars. Inparticular, barred galaxies do not seem to display shallower gradients, aspredicted by numerical simulations. Interestingly, we find that most of thegalaxies in the sample with reliable oxygen abundance values beyond $\sim 2$effective radii (57 galaxies) present a flattening of the abundance gradient inthese outer regions. This flattening is not associated with any morphologicalfeature, which suggests that it is a common property of disc galaxies. Finally,we detect a drop or truncation of the abundance in the inner regions of 27galaxies in the sample; this is only visible for the most massive galaxies.