ALBERT

Description: We use high-resolution zoom-in cosmological simulations of galaxies of Romano-Díaz et al., post-processing them with a panchromatic three-dimensional radiation transfer code to obtain the galaxy UV luminosity function (LF) at z ~= 6–12. The galaxies are followed in a rare, heavily overdense region within a ~5 density peak, which can host high- z quasars, and in an average density region, down to the stellar mass of M star  ~ 4 10 7 M . We find that the overdense regions evolve at a substantially accelerated pace – the most massive galaxy has grown to M star  ~ 8.4 10 10 M by z  = 6.3, contains dust of M dust  ~ 4.1 10 8 M , and is associated with a very high star formation rate, SFR ~ 745 M yr – 1 . The attained SFR– M star correlation results in the specific SFR slowly increasing with M star . Most of the UV radiation in massive galaxies is absorbed by the dust, its escape fraction f esc is low, increasing slowly with time. Galaxies in the average region have less dust, and agree with the observed UV LF. The LF of the overdense region is substantially higher, and contains much brighter galaxies. The massive galaxies are bright in the infrared (IR) due to the dust thermal emission, with L IR  ~ 3.7 10 12 L at z  = 6.3, while L IR  〈 10 11 L for the low-mass galaxies. Therefore, ALMA can probe massive galaxies in the overdense region up to z  ~ 10 with a reasonable integration time. The UV spectral properties of discy galaxies depend significantly upon the viewing angle. The stellar and dust masses of the most massive galaxy in the overdense region are comparable to those of the sub-millimetre galaxy found by Riechers et al. at z  = 6.3, while the modelled SFR and the sub-millimetre flux fall slightly below the observed one. Statistical significance of these similarities and differences will only become clear with the upcoming ALMA observations.

Description: We examine how the small-scale (〈kpc) variation of metallicity within a galaxy, which is found in nearby galaxies, affect the observational estimates of metallicity in the explosion sites of transient events such as core-collapse supernovae (CC SNe) and gamma-ray bursts (GRBs). Assuming the same luminosity, metallicity, and spatial distributions of H ii regions (hereafter HIIRs) as observed in M31, we compute the apparent metallicities that we would obtain when the spectrum of a target region is blended with those of surrounding HIIRs within the length-scale of typical spatial resolution. When the spatial resolution of spectroscopy is 0.5 kpc, which is typical for the existing studies of CC SN sites, we find that the apparent metallicities reflect the metallicities of target regions, but with significant systematic uncertainties in some cases. When the spatial resolution is 1.0 kpc, regardless of the target regions (which has a wide range of metallicity that spans ~0.6 dex for the M31 HIIRs), we always obtain the apparent metallicities similar to the average metallicity of the M31 HIIRs. Given that the apparent metallicities measured with kpc scale resolution do not necessarily reflect the immediate environment of the stellar explosions, the current observational estimates of high metallicities for some of the long GRB host galaxies do not rule out the hypothesis that the long GRBs are exclusively born in a low-metallicity environment.

Description: We use cosmological adaptive mesh refinement code enzo zoom-in simulations to study the long-term evolution of the collapsing gas within dark matter haloes at z . This direct collapse process is a leading candidate for rapid formation of supermassive black hole (SMBH) seeds. To circumvent the Courant condition at small radii, we apply the sink particle method, focusing on evolution on scales ~0.01–10 pc. The collapse proceeds in two stages, with the secondary runaway happening within the central 10 pc. The sink particles form when the collapsing gas requires additional refinement of the grid size at the highest refinement level. Their growth is negligible with the sole exception of the central seed which grows dramatically to M seed  ~ 2  x  10 6 M in ~2 Myr, confirming the feasibility of this path to the SMBH. The variability of angular momentum in the accreted gas results in the formation of two misaligned discs. Both discs lie within the Roche limit of the central seed. While the inner disc is geometrically thin and weakly asymmetric, the outer disc flares due to turbulent motions as a result of the massive inflow along a pair of penetrating filaments. The filamentary inflow determines the dominant Fourier modes in this disc – these modes have a non-self-gravitational origin. We do not confirm that m  = 1 is a dominant mode that drives the inflow in the presence of a central massive object. The overall configuration appears to be generic, and is expected to form when the central seed becomes sufficiently massive.

Description: 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.

Description: We use high-resolution zoom-in cosmological simulations of galaxies of Romano-Díaz et al., post-processing them with a panchromatic three-dimensional radiation transfer code to obtain the galaxy UV luminosity function (LF) at z ~= 6–12. The galaxies are followed in a rare, heavily overdense region within a ~5 density peak, which can host high- z quasars, and in an average density region, down to the stellar mass of M star  ~ 4 10 7 M . We find that the overdense regions evolve at a substantially accelerated pace – the most massive galaxy has grown to M star  ~ 8.4 10 10 M by z  = 6.3, contains dust of M dust  ~ 4.1 10 8 M , and is associated with a very high star formation rate, SFR ~ 745 M yr – 1 . The attained SFR– M star correlation results in the specific SFR slowly increasing with M star . Most of the UV radiation in massive galaxies is absorbed by the dust, its escape fraction f esc is low, increasing slowly with time. Galaxies in the average region have less dust, and agree with the observed UV LF. The LF of the overdense region is substantially higher, and contains much brighter galaxies. The massive galaxies are bright in the infrared (IR) due to the dust thermal emission, with L IR  ~ 3.7 10 12 L at z  = 6.3, while L IR  〈 10 11 L for the low-mass galaxies. Therefore, ALMA can probe massive galaxies in the overdense region up to z  ~ 10 with a reasonable integration time. The UV spectral properties of discy galaxies depend significantly upon the viewing angle. The stellar and dust masses of the most massive galaxy in the overdense region are comparable to those of the sub-millimetre galaxy found by Riechers et al. at z  = 6.3, while the modelled SFR and the sub-millimetre flux fall slightly below the observed one. Statistical significance of these similarities and differences will only become clear with the upcoming ALMA observations.