Abstract
We present simulated galaxy spectral energy distributions (SEDs) from the far-ultraviolet (FUV) through the far-infrared (FIR), created using hydrodynamic simulations and radiative transfer ...calculations, suitable for the validation of SED modeling techniques. SED modeling is an essential tool for inferring star formation histories from nearby galaxy observations, but it is fraught with difficulty due to our incomplete understanding of stellar populations, chemical enrichment processes, and the nonlinear, geometry-dependent effects of dust on our observations. Our simulated SEDs will allow us to assess the accuracy of these inferences against galaxies with known ground truth. To create the SEDs, we use simulated galaxies from the Numerical Investigation of Hundred Astrophysical Objects suite and the radiative transfer code Stellar Kinematics Including Radiative Transfer. We explore different subgrid post-processing recipes, using color distributions and their dependence on axis ratios of galaxies in the nearby Universe to tune and validate them. We find that subgrid post-processing recipes that mitigate limitations in the temporal and spatial resolution of the simulations are required for producing FUV to FIR photometry that statistically reproduce the colors of galaxies in the nearby Universe. With this paper, we release resolved photometry and spatially integrated spectra for our sample galaxies, each from a range of different viewing angles. Our simulations predict that there is a large variation in attenuation laws among galaxies, and that from any particular viewing angle that energy balance between dust attenuation and re-emission can be violated by up to a factor of 3. These features are likely to affect SED modeling accuracy.
We study the hot and cold circum-galactic medium (CGM) of 86 galaxies of the cosmological, hydrodynamical simulation suite, Numerical Investigation of a Hundred Astrophysical Objects (NIHAO). NIHAO ...allows a study of how the z = 0 CGM varies across five orders of magnitude of stellar mass using O VI and H I as proxies for hot and cold gas. The cool H I covering fraction and column density profiles match observations well, particularly in the inner CGM. O VI shows increasing column densities with mass, a trend seemingly echoed in the observations. As in multiple previous simulations, the O VI column densities in simulations are lower than observed and optically thick H I does not extend as far out as in observations. We take a look at the collisional ionization fraction of O VI as a function of halo mass. We make observable predictions of the bipolarity of outflows and their effect on the general shape of the CGM. Bipolar outflows can be seen out to around 40 kpc in intermediate- and low-mass haloes (M sub( Halo) < 10 super( 11) M...), but outside that radius, the CGM is too well mixed to detect an elongated shape. Larger haloes have extended gas discs beyond the stellar disc that dominate the shape of the inner CGM. The simulated CGM is remarkably spherical even in low-mass simulations. The chemical enrichment of both halo and disc gas follow expected increasing trends as a function of halo mass that are well fit with power laws. These relations can be used in non-hydrodynamic models, such as semi-analytic models. (ProQuest: ... denotes formulae/symbols omitted.)
We analyse the properties of dark matter haloes in the cold-plus-warm dark matter (CWDM) cosmologies. We study their dependence on the fraction and velocity dispersion of the warm particle, keeping ...the free-streaming scale fixed. To this end, we consider three models with the same free-streaming: (1) a mixture of 90 per cent of CDM and 10 per cent of WDM with the mass 1 keV; (2) a mixture of 50 per cent of CDM and 50 per cent of WDM with the mass 5 keV and (3) pure WDM with the mass 10 keV. 'Warm' particles have rescaled -Dirac spectrum of primordial velocities (as non-resonantly produced sterile neutrinos would have). We compare the properties of haloes among these models and with a ΛCDM with the same cosmological parameters. We demonstrate that although these models have the same free-streaming length and the suppression of matter spectra are similar at scales probed by the Lyman α forest (comoving wave-numbers k < 3-5 h Mpc−1), the resulting properties of haloes with masses below ∼1011 M are different due to the different behaviour of matter power spectra at smaller scales. In particular, we find that while the number of galaxies remains the same as in the ΛCDM case, their density profiles become much less concentrated and hence in better agreement with current observational constraints. Our results imply that a single parameter (e.g. free-streaming length) description of these models is not enough to fully capture their effects on the structure formation process.
ABSTRACT
We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the impact of the threshold for star formation on the response of the dark matter (DM) ...halo to baryonic processes. The fiducial NIHAO threshold, $n=10\, {\rm cm}^{-3}$, results in strong expansion of the DM halo in galaxies with stellar masses in the range $10^{7.5} \lesssim {{M_{\rm star}}}\lesssim 10^{9.5} {{ {\rm M}_{\odot }}}$. We find that lower thresholds such as n = 0.1 (as employed by the EAGLE/APOSTLE and Illustris/AURIGA projects) do not result in significant halo expansion at any mass scale. Halo expansion driven by supernova feedback requires significant fluctuations in the local gas fraction on sub-dynamical times (i.e. $\lesssim $50 Myr at galaxy half-light radii), which are themselves caused by variability in the star formation rate. At one per cent of the virial radius, simulations with n = 10 have gas fractions of ≃0.2 and variations of ≃0.1, while n = 0.1 simulations have order of magnitude lower gas fractions and hence do not expand the halo. The observed DM circular velocities of nearby dwarf galaxies are inconsistent with CDM simulations with n = 0.1 and n = 1, but in a reasonable agreement with n = 10. Star formation rates are more variable for higher n, lower galaxy masses, and when star formation is measured on shorter time-scales. For example, simulations with n = 10 have up to 0.4 dex higher scatter in specific star formation rates than simulations with n = 0.1. Thus observationally constraining the sub-grid model for star formation, and hence the nature of DM, should be possible in the near future.
Abstract
Recent studies have found a dramatic difference between the observed number density evolution of low-mass galaxies and that predicted by semi-analytic models. Whilst models accurately ...reproduce the z = 0 number density, they require that the evolution occurs rapidly at early times, which is incompatible with the strong late evolution found in observational results. We report here the same discrepancy in two state-of-the-art cosmological hydrodynamical simulations, which is evidence that the problem is fundamental. We search for the underlying cause of this problem using two complementary methods. First, we consider a narrow range in stellar mass of log (M
star/(h
−2 M⊙)) = 9-9.5 and look for evidence of a different history of today's low-mass galaxies in models and observations. We find that the exclusion of satellite galaxies from the analysis brings the median ages and star formation rates of galaxies into reasonable agreement. However, the models yield too few young, strongly star-forming galaxies. Secondly, we construct a toy model to link the observed evolution of specific star formation rates with the evolution of the galaxy stellar mass function. We infer from this model that a key problem in both semi-analytic and hydrodynamical models is the presence of a positive instead of a negative correlation between specific star formation rate and stellar mass. A similar positive correlation is found between the specific dark matter halo accretion rate and the halo mass, indicating that model galaxies are growing in a way that follows the growth of their host haloes too closely. It therefore appears necessary to find a mechanism that decouples the growth of low-mass galaxies, which occurs primarily at late times, from the growth of their host haloes, which occurs primarily at early times. We argue that the current form of star formation-driven feedback implemented in most galaxy formation models is unlikely to achieve this goal, owing to its fundamental dependence on host halo mass and time.
Abstract
Many massive star-forming disc galaxies in the redshift range 3–0.5 are observed to have a clumpy morphology showing giant clumps of size ∼1 kpc and masses of about 107–1010 M⊙. The nature ...and fate of these giant clumps are still under debate. In this work, we use 19 high-resolution simulations of disc galaxies from the Numerical Investigations of Hundred Astrophysical Objects (NIHAO) sample to study the formation and evolution of clumps in the discs of high-redshift galaxies. We use mock Hubble Space Telescope-CANDELS observations created with the radiative transfer code grasil-3d to carry out, for the first time, a quantitative comparison of the observed fraction of clumpy galaxies and its evolution with redshift with simulations. We find a good agreement between the observed clumpy fraction and the one of the NIHAO galaxies. We find that dust attenuation can suppress intrinsically bright clumps and enhance less luminous ones. In our galaxy sample, we find clumps only in light (U band) from young stars but not in stellar mass surface density maps. This means that the NIHAO sample does not show clumpy stellar discs but rather a clumpy light distribution originating from clumpy star formation events. The clumps found in the NIHAO sample match observed age/colour gradients as a function of distance from the galaxy centre, but they show no sign of inward migration. Clumps in our simulations disperse on time-scales of about a hundred Myr and their contribution to bulge growth is negligible.
The most common cause of death among adults with diabetes is cardiovascular disease (CVD). In this concise review on pathogenesis of CVD in diabetes, the 4 common conditions, atherosclerosis, ...microangiopathy, diabetic cardiomyopathy, and cardiac autonomic neuropathy, are explored and illustrated to be caused by interrelated pathogenetic factors. Each of these diagnoses can present alone or, commonly, along with others due to overlapping pathophysiology. Although the spectrum of physiologic abnormalities that characterize the diabetes milieu is broad and go beyond hyperglycemia, the authors highlight the most relevant evidence supporting the current knowledge of potent factors that contribute to CVD in diabetes.
In this article, we will briefly review the history and progress of photonics in Latin America, describing the discipline's development over the years and its collaborations with the rest of the ...world's countries. Among the ten countries analyzed, we will focus mainly on the most developed players in the field, taking the three most significant in terms of scientific weight: Brazil, Mexico, and Argentina, and the very interesting, more recent developments acquired by Chile, Colombia, and Ecuador. On the other hand, we will also shortly review the activities we have developed in Argentina in nanophotonics, specifically in mechanical nanoresonators.
In this paper, we study the tidal stripping process for satellite galaxies orbiting around a massive host galaxy, and focus on its dependence on the morphology of both satellite and host galaxy. For ...this purpose, we use three different morphologies for the satellites: pure disc, pure bulge and a mixture bulge+disc. Two morphologies are used for the host galaxies: bulge+disc and pure bulge. We find that while the spheroidal stellar component experiences a constant power law like mass removal, the disc is exposed to an exponential mass-loss when the tidal radius of the satellite is of the same order of the disc scalelength. This dramatic mass-loss is able to completely remove the stellar component on time-scale of 100 Myr. As a consequence two satellites with the same stellar and dark matter masses, on the same orbit could either retain considerable fraction of their stellar mass after 10 Gyr or being completely destroyed, depending on their initial stellar morphology. We find that there are two characteristic time-scales describing the beginning and the end of the disc removal, whose values are related to the size of the disc. This result can be easily incorporated in semi-analytical models. We also find that the host morphology and the orbital parameters also have an effect on determining the mass removal, but they are of secondary importance with respect to satellite morphology. We conclude that satellite morphology has a very strong effect on the efficiency of stellar stripping and should be taken into account in modelling galaxy formation and evolution.
Flaviviruses include a highly diverse group of arboviruses with a global distribution and a high human disease burden. Most flaviviruses cycle between insects and vertebrate hosts; thus, they are ...obligated to use different cellular machinery for their replication and mount different mechanisms to evade specific antiviral responses. In addition to coding for viral proteins, the viral genome contains signals in RNA structures that govern the amplification of viral components and participate in triggering or evading antiviral responses. In this review, we focused on new information about host-specific functions of RNA structures present in the 3′ untranslated region (3′ UTR) of flavivirus genomes. Models and conservation patterns of RNA elements of distinct flavivirus ecological groups are revised. An intriguing feature of the 3′ UTR of insect-borne flavivirus genomes is the conservation of complex RNA structure duplications. Here, we discuss new hypotheses of how these RNA elements specialize for replication in vertebrate and invertebrate hosts, and present new ideas associating the significance of RNA structure duplication, small subgenomic flavivirus RNA formation, and host adaptation.
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