ABSTRACT
We present a new model for the evolution of gas phase metallicity gradients in galaxies from first principles. We show that metallicity gradients depend on four ratios that collectively ...describe the metal equilibration time-scale, production, transport, consumption, and loss. Our model finds that most galaxy metallicity gradients are in equilibrium at all redshifts. When normalized by metal diffusion, metallicity gradients are governed by the competition between radial advection, metal production, and accretion of metal-poor gas from the cosmic web. The model naturally explains the varying gradients measured in local spirals, local dwarfs, and high-redshift star-forming galaxies. We use the model to study the cosmic evolution of gradients across redshift, showing that the gradient in Milky Way-like galaxies has steepened over time, in good agreement with both observations and simulations. We also predict the evolution of metallicity gradients with redshift in galaxy samples constructed using both matched stellar masses and matched abundances. Our model shows that massive galaxies transition from the advection-dominated to the accretion-dominated regime from high to low redshifts, which mirrors the transition from gravity-driven to star formation feedback-driven turbulence. Lastly, we show that gradients in local ultraluminous infrared galaxies (major mergers) and inverted gradients seen both in the local and high-redshift galaxies may not be in equilibrium. In subsequent papers in this series, we show that the model also explains the observed relationship between galaxy mass and metallicity gradients, and between metallicity gradients and galaxy kinematics.
We present 0 2 resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations at 870 m in a stellar mass-selected sample of 85 massive ( ) star-forming galaxies (SFGs) at in the ...CANDELS/3D-Hubble Space Telescope fields of UDS and GOODS-S. We measure the effective radius of the rest-frame far-infrared (FIR) emission for 62 massive SFGs. They are distributed over wide ranges of FIR size from to . The effective radius of the FIR emission is smaller by a factor of than the effective radius of the optical emission and is smaller by a factor of than the half-mass radius. Taking into account potential extended components, the FIR size would change only by ∼10%. By combining the spatial distributions of the FIR and optical emission, we investigate how galaxies change the effective radius of the optical emission and the stellar mass within a radius of 1 kpc, . The compact starburst puts most of the massive SFGs on the mass-size relation for quiescent galaxies (QGs) at z ∼ 2 within 300 Myr if the current star formation activity and its spatial distribution are maintained. We also find that within 300 Myr, ∼38% of massive SFGs can reach the central mass of , which is around the boundary between massive SFGs and QGs. These results suggest an outside-in transformation scenario in which a dense core is formed at the center of a more extended disk, likely via dissipative in-disk inflows. Synchronized observations at ALMA 870 m and James Webb Space Telescope 3-4 m will explicitly verify this scenario.
ABSTRACT
We study the effect of the gas accretion rate ($\dot{M}_{\rm accr}$) on the radial gas metallicity profile (RMP) of galaxies using the eagle cosmological hydrodynamic simulations, focusing ...on central galaxies of stellar mass M⋆ ≳ 109 M⊙ at z ≤ 1. We find clear relations between $\dot{M}_{\rm accr}$ and the slope of the RMP (measured within an effective radius), where higher $\dot{M}_{\rm accr}$ are associated with more negative slopes. The slope of the RMPs depends more strongly on $\dot{M}_{\rm accr}$ than on stellar mass, star formation rate (SFR), or gas fraction, suggesting $\dot{M}_{\rm accr}$ to be a more fundamental driver of the RMP slope of galaxies. We find that eliminating the dependence on stellar mass is essential for pinning down the properties that shape the slope of the RMP. Although $\dot{M}_{\rm accr}$ is the main property modulating the slope of the RMP, we find that it causes other correlations that are more easily testable observationally: At fixed stellar mass, galaxies with more negative RMP slopes tend to have higher gas fractions and SFRs, while galaxies with lower gas fractions and SFRs tend to have flatter metallicity profiles within an effective radius.
We present precise measurements of the growth rate of cosmic structure for the redshift range 0.1 < z < 0.9, using redshift-space distortions in the galaxy power spectrum of the WiggleZ Dark Energy ...Survey. Our results, which have a precision of around 10 per cent in four independent redshift bins, are well fitted by a flat Λ cold dark matter (ΛCDM) cosmological model with matter density parameter Ωm= 0.27. Our analysis hence indicates that this model provides a self-consistent description of the growth of cosmic structure through large-scale perturbations and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic oscillations. We achieve robust results by systematically comparing our data with several different models of the quasi-linear growth of structure including empirical models, fitting formulae calibrated to N-body simulations, and perturbation theory techniques. We extract the first measurements of the power spectrum of the velocity divergence field, P
θθ(k), as a function of redshift (under the assumption that
, where g is the galaxy overdensity field), and demonstrate that the WiggleZ galaxy-mass cross-correlation is consistent with a deterministic (rather than stochastic) scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h Mpc−1. Measurements of the cosmic growth rate from the WiggleZ Survey and other current and future observations offer a powerful test of the physical nature of dark energy that is complementary to distance-redshift measures such as supernovae and baryon acoustic oscillations.
A randomly chosen star in today's universe is most likely to live in a galaxy with stellar mass between the Milky Way and Andromeda. It remains uncertain, however, how the structural evolution of ...these bulge-disk systems proceeded. Most of the unobscured star formation we observe by building Andromeda progenitor s at 0.7 < z < 1.5 occurs in disks, but 90% of their star formation is reprocessed by dust and remains unaccounted for. Here we map rest-500 m dust continuum emission in an Andromeda progenitor at z = 1.25 to probe where it is growing through dust-obscured star formation. Combining resolved dust measurements from the NOthern Extended Millimeter Array interferometer with Hubble Space Telescope H maps and multicolor imaging (including new data from the Hubble Deep UV Legacy Survey, HDUV), we find a bulge growing by dust-obscured star formation: while the unobscured star formation is centrally suppressed, the dust continuum is centrally concentrated, filling the ring-like structure that is evident in the H and UV emission. Reflecting this, the dust emission is more compact than the optical/UV tracers of star formation with re(dust) = 3.4 kpc, re(H )/re(dust) = 1.4, and re(UV)/re(dust) = 1.8. Crucially, however, the bulge and disk of this galaxy are building simultaneously; although the dust emission is more compact than the rest-optical emission (re(optical)/re(dust) = 1.4), it is somewhat less compact than the stellar mass (re(M*)/re(dust) = 0.9). Taking the rest-500 m emission as a tracer, the expected structural evolution can be accounted for by star formation: it will grow in size by Δre/ΔM* ∼ 0.3 and in central surface density by Δ cen/ΔM* ∼ 0.9. Finally, our observations are consistent with a picture in which merging and disk instabilities drive gas to the center of galaxies, boosting global star formation rates above the main sequence and building bulges.
We present spatially resolved ALMA observations of the CO emission line in two massive galaxies at z = 2.5 on the star-forming main sequence. Both galaxies have compact dusty star-forming cores with ...effective radii of and in the 870 m continuum emission. The spatial extent of star-forming molecular gas is also compact with and , but more extended than the dust emission. Interpreting the observed position-velocity diagrams with dynamical models, we find the starburst cores to be rotation dominated with the ratio of the maximum rotation velocity to the local velocity dispersion of ( km s−1) and ( km s−1). Given that the descendants of these massive galaxies in the local universe are likely ellipticals with nearly an order of magnitude lower, the rapidly rotating galaxies would lose significant net angular momentum in the intervening time. The comparisons among dynamical, stellar, gas, and dust mass suggest that the starburst CO-to-H2 conversion factor of (K km s−1 pc−2)−1 is appropriate in the spatially resolved cores. The dense cores are likely to be formed in extreme environments similar to the central regions of local ultraluminous infrared galaxies. Our work also demonstrates that a combination of medium-resolution CO and high-resolution dust continuum observations is a powerful tool for characterizing the dynamical state of molecular gas in distant galaxies.
ABSTRACT
We exploit deep integral-field spectroscopic observations with KMOS/Very Large Telescope of 240 star-forming disks at
to dynamically constrain their mass budget. Our sample consists of ...massive (
) galaxies with sizes
. By contrasting the observed velocity and dispersion profiles with dynamical models, we find that on average the stellar content contributes
of the total dynamical mass, with a significant spread among galaxies (68th percentile range
). Including molecular gas as inferred from CO- and dust-based scaling relations, the estimated baryonic mass adds up to
of the total for the typical galaxy in our sample, reaching
at
. We conclude that baryons make up most of the mass within the disk regions of high-redshift star-forming disk galaxies, with typical disks at
being strongly baryon-dominated within
R
e
. Substantial object-to-object variations in both stellar and baryonic mass fractions are observed among the galaxies in our sample, larger than what can be accounted for by the formal uncertainties in their respective measurements. In both cases, the mass fractions correlate most strongly with measures of surface density. High-
galaxies feature stellar mass fractions closer to unity, and systems with high inferred gas or baryonic surface densities leave less room for additional mass components other than stars and molecular gas. Our findings can be interpreted as more extended disks probing further (and more compact disks probing less far) into the dark matter halos that host them.
In this letter we study the mean sizes of H clumps in turbulent disk galaxies relative to kinematics, gas fractions, and Toomre Q. We use ∼100 pc resolution HST images, IFU kinematics, and gas ...fractions of a sample of rare, nearby turbulent disks with properties closely matched to main-sequence galaxies (the DYNAMO sample). We find linear correlations of normalized mean clump sizes with both the gas fraction and the velocity dispersion-to-rotation velocity ratio of the host galaxy. We show that these correlations are consistent with predictions derived from a model of instabilities in a self-gravitating disk (the so-called "violent disk instability model"). We also observe, using a two-fluid model for Q, a correlation between the size of clumps and self-gravity-driven unstable regions. These results are most consistent with the hypothesis that massive star-forming clumps in turbulent disks are the result of instabilities in self-gravitating gas-rich disks, and therefore provide a direct connection between resolved clump sizes and this in situ mechanism.
ABSTRACT We measure the stellar specific angular momentum in four nearby (z 0.1) disk galaxies that have stellar masses near the break of the galaxy mass function but look like typical star-forming ...disks at z 2 in terms of their low stability (Q 1), clumpiness, high ionized gas dispersion (40−50 ), high molecular gas fraction (20%-30%), and rapid star formation ( ). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low values of our targets are similar to those expected in the population at higher z from the approximate theoretical scaling at fixed This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.
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