ALBERT

Beschreibung: The Bullet Cluster has provided some of the best evidence for the cold dark matter (CDM) model via direct empirical proof of the existence of collisionless dark matter, while posing a serious challenge owing to the unusually high inferred pairwise velocities of its progenitor clusters. Here, we investigate the probability of finding such a high-velocity pair in large-volume N -body simulations, particularly focusing on differences between halo-finding algorithms. We find that algorithms that do not account for the kinematics of infalling groups yield vastly different statistics and probabilities. When employing the rockstar halo finder that considers particle velocities, we find numerous Bullet-like pair candidates that closely match not only the high pairwise velocity, but also the mass, mass ratio, separation distance, and collision angle of the initial conditions that have been shown to produce the Bullet Cluster in non-cosmological hydrodynamic simulations. The probability of finding a high pairwise velocity pair among haloes with M halo  ≥ 10 14 M is 4.6  x  10 –4 using rockstar , while it is 34  x  lower using a friends-of-friends (FoF)-based approach as in previous studies. This is because the typical spatial extent of Bullet progenitors is such that FoF tends to group them into a single halo despite clearly distinct kinematics. Further requiring an appropriately high average mass among the two progenitors, we find the comoving number density of potential Bullet-like candidates to be of the order of 10 –10 Mpc –3 . Our findings suggest that CDM straightforwardly produces massive, high relative velocity halo pairs analogous to Bullet Cluster progenitors, and hence the Bullet Cluster does not present a challenge to the CDM model.

Beschreibung: Low-luminosity Type II supernovae (LL SNe II) make up the low explosion energy end of core-collapse SNe, but their study and physical understanding remain limited. We present SN 2016aqf, an LL SN II with extensive spectral and photometric coverage. We measure a V-band peak magnitude of −14.58 mag, a plateau duration of ∼100 d, and an inferred 56Ni mass of 0.008 ± 0.002 M⊙. The peak bolometric luminosity, Lbol ≈ 1041.4 erg s−1, and its spectral evolution are typical of other SNe in the class. Using our late-time spectra, we measure the [O i] λλ6300, 6364 lines, which we compare against SN II spectral synthesis models to constrain the progenitor zero-age main-sequence mass. We find this to be 12 ± 3 M⊙. Our extensive late-time spectral coverage of the [Fe ii] λ7155 and [Ni ii] λ7378 lines permits a measurement of the Ni/Fe abundance ratio, a parameter sensitive to the inner progenitor structure and explosion mechanism dynamics. We measure a constant abundance ratio evolution of $0.081^{+0.009}_{-0.010}$ and argue that the best epochs to measure the ratio are at ∼200–300 d after explosion. We place this measurement in the context of a large sample of SNe II and compare against various physical, light-curve, and spectral parameters, in search of trends that might allow indirect ways of constraining this ratio. We do not find correlations predicted by theoretical models; however, this may be the result of the exact choice of parameters and explosion mechanism in the models, the simplicity of them, and/or primordial contamination in the measured abundance ratio.

Beschreibung: The instantaneous H i content of galaxies is thought to be governed by recent accretion and environment. We examine these effects within a cosmological hydrodynamic simulation that includes a heuristic galactic outflow model that reproduces basic observed trends of H i in galaxies. We show that this model reproduces the observed H i mass function in bins of stellar mass, as well as the H i richness ( $M_{\rm H\,\small {I}}$ / M * ) versus local galaxy density. For satellite galaxies in massive ( 10 12 M ) haloes, the H i richness distribution is bimodal and the median drops towards the largest halo masses. The depletion time-scale of H i entering a massive halo is more rapid, in contrast to the specific star formation rate which shows little variation in the attenuation rate versus halo mass. This suggests that, up to the halo mass scales probed here ( 10 14 M ), star formation is mainly attenuated by starvation, but H i is additionally removed by stripping once a hot gaseous halo is present. In low-mass haloes, the H i richness of satellites is independent of radius, while in very massive haloes they become gas-poor towards the centre, confirming the increasing strength of the stripping with halo mass. Mergers somewhat increase the H i richness and its scatter about the mean relation, tracking the metallicity in a way consistent with it arising from inflow fluctuations, while star formation is significantly boosted relative to H i .

Beschreibung: The instantaneous H i content of galaxies is thought to be governed by recent accretion and environment. We examine these effects within a cosmological hydrodynamic simulation that includes a heuristic galactic outflow model that reproduces basic observed trends of H i in galaxies. We show that this model reproduces the observed H i mass function in bins of stellar mass, as well as the H i richness ( $M_{\rm H\,\small {I}}$ / M * ) versus local galaxy density. For satellite galaxies in massive ( 10 12 M ) haloes, the H i richness distribution is bimodal and the median drops towards the largest halo masses. The depletion time-scale of H i entering a massive halo is more rapid, in contrast to the specific star formation rate which shows little variation in the attenuation rate versus halo mass. This suggests that, up to the halo mass scales probed here ( 10 14 M ), star formation is mainly attenuated by starvation, but H i is additionally removed by stripping once a hot gaseous halo is present. In low-mass haloes, the H i richness of satellites is independent of radius, while in very massive haloes they become gas-poor towards the centre, confirming the increasing strength of the stripping with halo mass. Mergers somewhat increase the H i richness and its scatter about the mean relation, tracking the metallicity in a way consistent with it arising from inflow fluctuations, while star formation is significantly boosted relative to H i .

Beschreibung: We have simulated the formation of a massive galaxy cluster ( $M_{200}^{\rm crit}$ = 1.1 x 10 15 h –1 M ) in a cold dark matter universe using 10 different codes ( ramses , 2 incarnations of arepo and 7 of gadget ), modelling hydrodynamics with full radiative subgrid physics. These codes include smoothed-particle hydrodynamics (SPH), spanning traditional and advanced SPH schemes, adaptive mesh and moving mesh codes. Our goal is to study the consistency between simulated clusters modelled with different radiative physical implementations – such as cooling, star formation and thermal active galactic nucleus (AGN) feedback. We compare images of the cluster at z = 0, global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. We find that, with respect to non-radiative simulations, dark matter is more centrally concentrated, the extent not simply depending on the presence/absence of AGN feedback. The scatter in global quantities is substantially higher than for non-radiative runs. Intriguingly, adding radiative physics seems to have washed away the marked code-based differences present in the entropy profile seen for non-radiative simulations in Sembolini et al.: radiative physics + classic SPH can produce entropy cores, at least in the case of non cool-core clusters. Furthermore, the inclusion/absence of AGN feedback is not the dividing line -as in the case of describing the stellar content – for whether a code produces an unrealistic temperature inversion and a falling central entropy profile. However, AGN feedback does strongly affect the overall stellar distribution, limiting the effect of overcooling and reducing sensibly the stellar fraction.

Beschreibung: We have exploited the Hubble Space Telescope ( HST ) Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) J and H -band Wide Field Camera 3 (WFC3)/infrared (IR) imaging to study the properties of (sub-)millimetre galaxies within the Great Observatories Origins Deep Survey South (GOODS-South) field. After using the deep radio (Very Large Array 1.4 GHz) and Spitzer (Infrared Array Camera 8 μm) imaging to identify galaxy counterparts for the (sub-)millimetre sources, we have then utilized the new CANDELS WFC3/IR imaging in two ways. First, the addition of new deep near-IR photometry from both HST and (at K band) the VLT to the existing GOODS-South data base has enabled us to derive improved photometric redshifts and stellar masses, confirming that the (sub-)millimetre sources are massive (〈 M * 〉 = 2.2  x 10 11  ± 0.2 M ) galaxies at z ~= 1-3. Secondly, we have exploited the depth and resolution of the WFC3/IR imaging to determine the sizes and morphologies of the galaxies at rest-frame optical wavelengths rest  〉 4000 Å. Specifically, we have fitted two-dimensional axisymmetric galaxy models to the WFC3/IR images, varying luminosity, axial ratio, half-light radius r 1/2 and Sérsic index n . Crucially, the wavelength and depth of the WFC3/IR imaging enables modelling of the mass-dominant galaxy, rather than the blue high surface-brightness features which often dominate optical (rest-frame ultraviolet) images of (sub-)millimetre galaxies, and can confuse visual morphological classification. As a result of this analysis, we find that 〉95 per cent of the rest-frame optical light in almost all of the (sub-)millimetre galaxies is well described by either a single exponential disc ( n  ~= 1), or a multiple-component system in which the dominant constituent is disc like. We demonstrate that this conclusion is completely consistent with the results of recent high-quality ground-based K -band imaging sampling even longer rest-frame wavelengths, and explain why it is so. These massive disc galaxies are reasonably extended (〈 r 1/2 〉 = 4.5 ± 0.5 kpc; median r 1/2  = 4.0 kpc), consistent with the sizes of other massive star-forming discs at z  ~= 2. In many cases, we find evidence of blue clumps within the sources, with the mass-dominant disc component becoming more significant at longer wavelengths. Finally, only a minority of the sources show evidence for a major galaxy–galaxy interaction. Taken together, these results support the view that most (sub-)millimetre galaxies at z  ~= 2 are simply the most extreme examples of normal star-forming galaxies at that era. Interestingly, the only two bulge-dominated galaxies are also the two lowest redshift sources in the sample ( z  ~= 1), a result which may reflect the structural evolution of high-mass galaxies in general.

Beschreibung: Observed galaxies with high stellar masses or in dense environments have low specific star formation rates, i.e. they are quenched. Based on cosmological hydrodynamic simulations that include a prescription where quenching occurs in regions dominated by hot (〉10 5.4  K) gas, we argue that this hot gas quenching in haloes 〉10 12 M drives both mass quenching (i.e. central quenching) and environment quenching (i.e. satellite quenching). These simulations reproduce a broad range of locally observed trends among quenching, halo mass, stellar mass, environment, and distance to halo centre. Mass quenching is independent of environment because ~10 12 –10 13 M ‘mass quenching haloes’ inhabit a large range of environments. On the other hand, environment quenching is independent of stellar mass because galaxies of all stellar masses may live in dense environments as satellites of groups and clusters. As in observations, the quenched fraction of satellites increases with halo mass and decreases with distance to the centre of the group or cluster. We investigate pre-processing in group haloes, ejected former satellites, and hot gas that extends beyond the virial radius. The agreement of our model with key observational trends suggests that hot gas in massive haloes plays a leading role in quenching low-redshift galaxies.

Beschreibung: We investigate the Baryonic Tully–Fisher relation (BTFR) in the $(100, h^{-1}{ m Mpc})^3$simba hydrodynamical galaxy formation simulation together with a higher resolution $(25, h^{-1}{ m Mpc})^3$simba run, for over 10 000 disc-dominated, H i-rich galaxies. We generate simulated galaxy rotation curves from the mass distribution, which we show yields similar results to using the gas rotational velocities. From this, we measure the galaxy rotation velocity Vcirc using four metrics: $V_{ m max}, V_{ m flat}, V_{2R_e},$ and Vpolyex. We compare the predicted BTFR to the SPARC observational sample and find broad agreement. In detail, however, simba is biased towards higher Vcirc by up to 0.1 dex. We find evidence for the flattening of the BTFR in Vcirc 〉 300  km s−1 galaxies, in agreement with recent observational findings. simba’s rotation curves are more peaked for lower mass galaxies, in contrast with observations, suggesting overly bulge-dominated dwarf galaxies in our sample. We investigate for residuals around the BTFR versus H i mass, stellar mass, gas fraction, and specific star formation rate, which provide testable predictions for upcoming BTFR surveys. simba’s BTFR shows sub-optimal resolution mass convergence, with the higher resolution run lowering V in better agreement with data.

Beschreibung: Galaxies strongly self-regulate their growth via energetic feedback from stars, supernovae, and black holes, but these processes are among the least understood aspects of galaxy formation theory. We present an analytic galaxy evolution model that directly constrains such feedback processes from observed galaxy scaling relations. The equilibrium model, which is broadly valid for star-forming central galaxies that dominate cosmic star formation, is based on the ansatz that galaxies live in a slowly evolving equilibrium between inflows, outflows, and star formation. Using a Bayesian Monte Carlo Markov chain approach, we constrain our model to match observed galaxy scaling relations between stellar mass and halo mass, star formation rate, and metallicity from 0 〈  z  〈 2. A good fit ( 2   1.6) is achieved with eight free parameters. We further show that constraining our model to any two of the three data sets also produces a fit to the third that is within reasonable systematic uncertainties. The resulting best-fitting parameters that describe baryon cycling suggest galactic outflow scalings intermediate between energy and momentum-driven winds, a weak dependence of wind recycling time on mass, and a quenching mass scale that evolves modestly upwards with redshift. This model further predicts a stellar mass–star formation rate relation that is in good agreement with observations to z  ~ 6. Our results suggest that this simple analytic framework captures the basic physical processes required to model the mean evolution of stars and metals in galaxies, despite not incorporating many canonical ingredients of galaxy formation models such as merging or disc formation.

Beschreibung: We present the mufasa suite of cosmological hydrodynamic simulations, which employs the gizmo meshless finite mass (MFM) code including H 2 -based star formation, nine-element chemical evolution, two-phase kinetic outflows following scalings from the Feedback in Realistic Environments zoom simulations, and evolving halo mass-based quenching. Our fiducial (50 h –1 Mpc) 3 volume is evolved to z  = 0 with a quarter billion elements. The predicted galaxy stellar mass functions (GSMFs) reproduces observations from z  = 4 -〉 0 to 1.2 in cosmic variance, providing an unprecedented match to this key diagnostic. The cosmic star formation history and stellar mass growth show general agreement with data, with a strong archaeological downsizing trend such that dwarf galaxies form the majority of their stars after z  ~ 1. We run 25 and 12.5 h –1 Mpc volumes to z  = 2 with identical feedback prescriptions, the latter resolving all hydrogen-cooling haloes, and the three runs display fair resolution convergence. The specific star formation rates broadly agree with data at z  = 0, but are underpredicted at z  ~ 2 by a factor of 3, re-emphasizing a longstanding puzzle in galaxy evolution models. We compare runs using MFM and two flavours of smoothed particle hydrodynamics, and show that the GSMF is sensitive to hydrodynamics methodology at the ~ x 2 level, which is sub-dominant to choices for parametrizing feedback.