Low-mass galaxy assembly in simulations: regulation of early star formation by radiation from massive stars

Self Cite

From mock Hubble Space Telescope images, we quantify non-parametric statistics of galaxy morphology, thereby predicting the emergence of relationships among stellar mass, star formation, and observed rest-frame optical structure at 1 < z < 3. We measure automated diagnostics of galaxy morphology in cosmological simulations of the formation of 22 central galaxies with 9.3 < log 10 M * /M < 10.7. These highspatial-resolution zoom-in calculations enable accurate modeling of the rest-frame UV and optical morphology. Even with small numbers of galaxies, we find that structural evolution is neither universal nor monotonic: galaxy interactions can trigger either bulge or disc formation, and optically bulge-dominated galaxies at this mass may not remain so forever. Simulated galaxies with M * > 10 10 M contain relatively more disc-dominated light profiles than those with lower mass, reflecting significant disc brightening in some haloes at 1 < z < 2. By this epoch, simulated galaxies with specific star formation rates below 10 −9.7 yr −1 are more likely than normal starformers to have a broader mix of structural types, especially at M * > 10 10 M . We analyze a cosmological major merger at z ∼ 1.5 and find that the newly proposed MID morphology diagnostics trace later merger stages while Gini-M 20 trace earlier ones. MID is sensitive also to clumpy star-forming discs. The observability time of typical MID-enhanced events in our simulation sample is < 100 Myr. A larger sample of cosmological assembly histories may be required to calibrate such diagnostics in the face of their sensitivity to viewing angle, segmentation algorithm, and various phenomena such as clumpy star formation and minor mergers.

Section: Rp Versus No-rp Simulationsmentioning

confidence: 99%

Diverse structural evolution atz > 1 in cosmologically simulated galaxies

Snyder

Lotz

Moody

et al. 2015

Self Cite

“…The past several years have proven fruitful in this regard, with many published studies achieving substantial suppression in the conversion of baryons to stars on the scale of dwarf galaxy halos (Governato et al 2010;Sawala et al 2011;Simpson et al 2013;Munshi et al 2013;Governato et al 2015;Trujillo-Gomez et al 2015). As we show below, however, many of these studies have not quite reached the level of suppression that seems to be required by local galaxy counts.…”

Section: Introductionmentioning

confidence: 98%

Forged in fire: cusps, cores and baryons in low-mass dwarf galaxies

Oñorbe

Boylan-Kolchin

Bullock

et al. 2015

390

414

We present multiple ultra-high resolution cosmological hydrodynamic simulations of M 10 4−6.3 M dwarf galaxies that form within two M vir = 10 9.5−10 M dark matter halo initial conditions. Our simulations rely on the FIRE implementation of star formation feedback and were run with high enough force and mass resolution to directly resolve structure on the ∼ 200 pc scales. The resultant galaxies sit on the M vs. M vir relation required to match the Local Group stellar mass function via abundance matching. They have bursty star formation histories and also form with half-light radii and metallicities that broadly match those observed for local dwarfs at the same stellar mass. We demonstrate that it is possible to create a large (∼ 1 kpc) constant-density dark matter core in a cosmological simulation of an M 10 6.3 M dwarf galaxy within a typical M vir = 10 10 M halo -precisely the scale of interest for resolving the Too Big to Fail problem. However, these large cores are not ubiquitous and appear to correlate closely with the star formation histories of the dwarfs: dark matter cores are largest in systems that form their stars late (z 2), after the early epoch of cusp building mergers has ended. Our M 10 4 M dwarf retains a cuspy dark matter halo density profile that matches that of a dark-matter only run of the same system. Though ancient, most of the stars in our ultra-faint form after reionization; the UV field acts mainly to suppress fresh gas accretion, not to boil away gas that is already present in the proto-dwarf.

“…On the scale of dwarf galaxies (M200 ∼ 10 10−11 M⊙), a number of different groups have presented fully cosmological hydrodynamical simulations in which the dark matter halo expands (Mashchenko et al 2008;Governato et al 2012;Trujillo-Gomez et al 2015;Chan et al 2015;Tollet et al 2016). In these simulations stellar feedback was found to drive rapid (sub-dynamical) time variability of the potential.…”

Section: Introductionmentioning

confidence: 99%

NIHAO IX: the role of gas inflows and outflows in driving the contraction and expansion of cold dark matter haloes

Dutton

Macciò

Dekel³

et al. 2016

101

118

We use ∼ 100 cosmological galaxy formation 'zoom-in' simulations using the smoothed particle hydrodynamics code gasoline to study the effect of baryonic processes on the mass profiles of cold dark matter haloes. The haloes in our study range from dwarf (M 200 ∼ 10 10 M ⊙ ) to Milky Way (M 200 ∼ 10 12 M ⊙ ) masses. Our simulations exhibit a wide range of halo responses, primarily varying with mass, from expansion to contraction, with up to factor ∼ 10 changes in the enclosed dark matter mass at 1 per cent of the virial radius. Confirming previous studies, the halo response is correlated with the integrated efficiency of star formation:In addition, we report a new correlation with the compactness of the stellar system: ǫ R ≡ r 1/2 /R 200 . We provide an analytic formula depending on ǫ SF and ǫ R for the response of cold dark matter haloes to baryonic processes. An observationally testable prediction is that, at fixed mass, larger galaxies experience more halo expansion, while the smaller galaxies more halo contraction. This diversity of dark halo response is captured by a toy model consisting of cycles of adiabatic inflow (causing contraction) and impulsive gas outflow (causing expansion). For net outflow, or equal inflow and outflow fractions, f , the overall effect is expansion, with more expansion with larger f . For net inflow, contraction occurs for small f (large radii), while expansion occurs for large f (small radii), recovering the phenomenology seen in our simulations. These regularities in the galaxy formation process provide a step towards a fully predictive model for the structure of cold dark matter haloes.