Size-scaling of clump instabilities in turbulent, feedback regulated disks

We explore the scaling between the size of star-forming clumps and rotational support in massively star-forming galactic disks. The analysis relies on simulations of a clumpy galaxy at $z=2$ and the observed DYNAMO sample of rare clumpy analogs at $z\approx0.1$ to test a predictive clump size scaling proposed by \citet{Fisher2017ApJ...839L...5F} in the context of the Violent Disk Instability (VDI) theory. We here determine the clump sizes using a recently presented 2-point estimator, which is robust against resolution/noise effects, hierarchical clump substructure, clump-clump overlap and other galactic substructure. After verifying Fisher's clump scaling relation for the DYNAMO observations, we explore whether this relation remains characteristic of the VDI theory, even if realistic physical processes, such as local asymetries and stellar feedback, are included in the model. To this end, we rely on hydrodynamic zoom-simulations of a Milky Way-mass galaxy with four different feedback prescriptions. We find that, during its marginally stable epoch at $z=2$, this mock galaxy falls on the clump scaling relation, although its position on this relation depends on the feedback model. This finding implies that Toomre-like stability considerations approximately apply to large ($\sim\rm kpc$) instabilities in marginally stable turbulent disks, irrespective of the feedback model, but also emphasizes that the global clump distribution of a turbulent disk depends strongly on feedback.Comment: Accepted by ApJ, no changes made. 11 pages, 4 figure

Dynamic equilibrium sets atomic content of galaxies across cosmic time

We analyze 88 independent high-resolution cosmological zoom-in simulations of disk galaxies in the NIHAO simulations suite to explore the connection between the atomic gas fraction and angular momentum of baryons throughout cosmic time. The study is motivated by the analytic model of \citet{obreschkow16}, which predicts a relation between the atomic gas fraction $f_{\rm atm}$ and the global atomic stability parameter $q \equiv j\sigma / (GM)$, where $M$ and $j$ are the mass and specific angular momentum of the galaxy (stars+cold gas) and $\sigma$ is the velocity dispersion of the atomic gas. We show that the simulated galaxies follow this relation from their formation ($z\simeq4$) to present within $\sim 0.5$ dex. To explain this behavior, we explore the evolution of the local Toomre stability and find that $90\%$--$100\%$ of the atomic gas in all simulated galaxies is stable at any time. In other words, throughout the entire epoch of peak star formation until today, the timescale for accretion is longer than the timescale to reach equilibrium, thus resulting in a quasi-static equilibrium of atomic gas at any time. Hence, the evolution of $f_{\rm atm}$ depends on the complex hierarchical growth history primarily via the evolution of $q$. An exception are galaxies subject to strong environmental effects.Comment: 12 pages, 7 figures; accepted to Ap

DUVET Survey: Mapping Outflows in the Metal-Poor Starburst Mrk 1486

We present a method to characterize star-formation driven outflows from edge-on galaxies and apply this method to the metal-poor starburst galaxy, Mrk 1486. Our method uses the distribution of emission line flux (from H$\beta$ and [OIII] 5007) to identify the location of the outflow and measure the extent above the disk, the opening angle, and the transverse kinematics. We show that this simple technique recovers a similar distribution of the outflow without requiring complex modelling of line-splitting or multi-Gaussian components, and is therefore applicable to lower spectral resolution data. In Mrk 1486 we observe an asymmetric outflow in both the location of the peak flux and total flux from each lobe. We estimate an opening angle of $17-37^{\circ}$ depending on the method and assumptions adopted. Within the minor axis outflows, we estimate a total mass outflow rate of $\sim2.5$ M$_{\odot}$ yr$^{-1}$, which corresponds to a mass loading factor of $\eta=0.7$. We observe a non-negligible amount of flux from ionized gas outflowing along the edge of the disk (perpendicular to the biconical components), with a mass outflow rate $\sim0.9$ M$_{\odot}$ yr$^{-1}$. Our results are intended to demonstrate a method that can be applied to high-throughput, low spectral resolution observations, such as narrow band filters or low spectral resolution IFS that may be more able to recover the faint emission from outflows.Comment: 12 Pages, 6 Figure

A giant galaxy in the young Universe with a massive ring

In the local (redshift z~0) Universe, collisional ring galaxies make up only ~0.01% of galaxies and are formed by head-on galactic collisions that trigger radially propagating density waves. These striking systems provide key snapshots for dissecting galactic disks and are studied extensively in the local Universe. However, not much is known about distant (z>0.1) collisional rings. Here we present a detailed study of a ring galaxy at a look-back time of 10.8 Gyr (z=2.19). Compared with our Milky Way, this galaxy has a similar stellar mass, but has a stellar half-light radius that is 1.5-2.2 times larger and is forming stars 50 times faster. The large, diffuse stellar light outside the star-forming ring, combined with a radial velocity on the ring and an intruder galaxy nearby, provides evidence for this galaxy hosting a collisional ring. If the ring is secularly evolved, the implied large bar in a giant disk would be inconsistent with the current understanding of the earliest formation of barred spirals. Contrary to previous predictions, this work suggests that massive collisional rings were as rare 11 Gyr ago as they are today. Our discovery offers a unique pathway for studying density waves in young galaxies, as well as constraining the cosmic evolution of spiral disks and galaxy groups.Comment: Author's version for the main article (10 pages). The Supplementary Information (22 pages) and a combined pdf are provided here http://astronomy.swin.edu.au/~tyuan/paper Published version available online http://dx.doi.org/10.1038/s41550-020-1102-