The Physical and Photometric Properties of High-Redshift Galaxies in Cosmological Hydrodynamic Simulations (original) (raw)
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Massive galaxies at redshift 2 in cosmological hydrodynamic simulations
We study the properties of galaxies at z=2 in a Lambda cold dark matter universe, using two different types of hydrodynamic simulation methods -- Eulerian TVD and smoothed particle hydrodynamics (SPH) -- and a spectrophotometric analysis in the U_n, G, R filter set. The simulated galaxies at z=2 satisfy the color-selection criteria proposed by Adelberger et al. (2004) and Steidel et al. (2004) when we assume Calzetti extinction with E(B-V)=0.15. We find that the number density of simulated galaxies brighter than R<25.5 at z=2 is about 1e-2 h^3 Mpc^-3 for E(B-V)=0.15, which is roughly twice that of the number density found by Erb et al. (2004) for the UV bright sample. This suggests that roughly half of the massive galaxies with M*>10^{10} Msun/h at z=2 are UV bright population, and the other half is bright in the infra-red wavelengths. The most massive galaxies at z=2 have stellar masses >= 10^{11-12} Msun. They typically have been continuously forming stars with a rate exc...
The Astrophysical Journal, 2005
Recent observations have revealed a population of red massive galaxies at high redshift which are challenging to explain in hierarchical galaxy formation models. We analyze this "massive galaxy problem" with two different types of hydrodynamic simulations -Eulerian total variation diminishing (TVD) and smoothed particle hydrodynamics (SPH) -of a concordance Λ cold dark matter (ΛCDM) universe. We consider two separate but connected aspects of the problem posed by these extremely red objects (EROs): (1) the mass-scale of these galaxies, and (2) their red colors. We perform spectrophotometric analyses of simulated galaxies in B, z, R, I, J s , K s , K filters, and compare their near-infrared (IR) properties with observations at redshift z = 1−3. We find that the simulated galaxies brighter than the magnitude limit of K vega = 20 mag have stellar masses M ⋆ 10 11 h −1 M ⊙ and a number density of a few ×10 −4 h 3 Mpc −3 at z ∼ 2, in good agreement with the observed number density in the K20 survey. Therefore, our hydrodynamic simulations do not exhibit the "mass-scale problem". The answer to the "redness problem" is less clear because of our poor knowledge of the amount of dust extinction in EROs and the uncertain fraction of star-forming EROs. However, our simulations can account for the observed comoving number density of ∼ 1 × 10 −4 Mpc −3 at z = 1 − 2 if we assume a uniform extinction of E(B − V ) = 0.4 for the entire population of simulated galaxies. Upcoming observations of the thermal emission of dust in 24 µm by the Spitzer Space Telescope many will help to better estimate the dust content of EROs at z = 1 − 3, and thus to further constrain the star formation history of the Universe, and theoretical models of galaxy formation.
We present results from a high resolution cosmological galaxy formation simulation called Mare Nostrum and a ultra-high resimulation of the first 500 million years of a single, Milky Way (MW) sized galaxy. Using the cosmological run, we measure UV luminosity functions and assess their sensitivity to both cosmological parameters and dust extinction. We find remarkably good agreement with the existing data over the redshift range 4 < z < 7 provided we adopt the favoured cosmology (WMAP 5 year parameters) and a self-consistent treatment of the dust. Cranking up the resolution, we then study in detail a z = 9 protogalaxy sitting at the intersection of cold gas filaments. This high-z MW progenitor grows a dense, rapidly spinning, thin disk which undergoes gravitational fragmention. Star formation in the resulting gas clumps rapidly turns them into globular clusters. A far reaching galactic wind develops, co-powered by the protogalaxy and its cohort of smaller companions populating the filaments. Despite such an impressive blow out, the smooth filamentary material is hardly affected at these redshifts.
Massive Galaxies at Z = 2 in Cosmological Hydrodynamic Simulations
Starbursts, 2005
We study the properties of galaxies at redshift z = 2 in a Λ cold dark matter (ΛCDM) universe, using two different types of hydrodynamic simulation methods-Eulerian TVD and smoothed particle hydrodynamics (SPH)-and a spectrophotometric analysis in the Un, G, R filter set. The simulated galaxies at z = 2 satisfy the color-selection criteria proposed by Adelberger et al. (2004) and Steidel et al. (2004) when we assume Calzetti extinction with E(B−V) = 0.15. We find that the number density of simulated galaxies brighter than R < 25.5 at z = 2 is about 1 × 10 −2 h 3 Mpc −3 for E(B − V) = 0.15, which is roughly twice that of the number density found by Erb et al. (2004) for the ultraviolet (UV) bright sample. This suggests that roughly half of the massive galaxies with M⋆ > 10 10 h −1 M⊙ at z = 2 are UV bright population, and the other half is bright in the infra-red (IR) wavelengths. The most massive galaxies at z = 2 have stellar masses ≥ 10 11−12 M⊙. They typically have been continuously forming stars with a rate exceeding 30 M⊙ yr −1 over a few Gyrs from z = 10 to z = 2, together with significant contribution by starbursts reaching up to 1000 M⊙ yr −1 which lie on top of the continuous component. TVD simulations indicate a more sporadic star formation history than the SPH simulations. Our results do not imply that hierarchical galaxy formation fails to account for the observed massive galaxies at z ≥ 1. The global star formation rate density in our simulations peaks at z ≥ 5, a much higher redshift than predicted by the semianalytic models. This star formation history suggests early build-up of the stellar mass density, and predicts that 70 (50, 30)% of the total stellar mass at z = 0 had already been formed by z = 1 (2, 3). Upcoming observations by Spitzer and Swift might help to better constrain the star formation history at high redshift.
Massive Galaxies in Cosmological Simulations: Ultraviolet‐selected Sample at Redshift z = 2
The Astrophysical Journal, 2005
We study the properties of galaxies at redshift z = 2 in a Λ cold dark matter (ΛCDM) universe, using two different types of hydrodynamic simulation methods -Eulerian TVD and smoothed particle hydrodynamics (SPH) -and a spectrophotometric analysis in the U n , G, R filter set. The simulated galaxies at z = 2 satisfy the color-selection criteria proposed by and when we assume Calzetti extinction with E(B − V ) = 0.15. We find that the number density of simulated galaxies brighter than R < 25.5 at z = 2 is about 2×10 −2 h 3 Mpc −3 for E(B −V ) = 0.15 in our most representative run, roughly one order of magnitude larger than that of Lyman break galaxies at z = 3. The most massive galaxies at z = 2 have stellar masses 10 11 M ⊙ , and their observed-frame G − R colors lie in the range 0.0 < G − R < 1.0. They typically have been continuously forming stars with a rate exceeding 30 M ⊙ yr −1 over a few Gyrs from z = 10 to z = 2, although the TVD simulation indicates a more sporadic star formation history than the SPH simulations. Of order half of their stellar mass was already assembled by z ∼ 4. The bluest galaxies with colors −0.2 < G−R < 0.0 at z = 2 are somewhat less massive, with M star < 10 11 h −1 M ⊙ , and lack a prominent old stellar population. On the other hand, the reddest massive galaxies at z = 2 with G − R ≥ 1.0 and M star > 10 10 h −1 M ⊙ completed the build-up of their stellar mass by z ∼ 3. Interestingly, our study indicates that -2the majority of the most massive galaxies at z = 2 should be detectable at restframe ultra-violet wavelengths, contrary to some recent claims made on the basis of near-infrared studies of galaxies at the same epoch, provided the median extinction is less than E(B − V ) < 0.3 as indicated by surveys of Lyman break galaxies at z = 3. However, our results also suggest that the fraction of stellar mass contained in galaxies that pass the color-selection criteria used by could be as low as 50% of the total stellar mass in the Universe at z = 2. Our simulations imply that the missing stellar mass is contained in fainter (R > 25.5) and intrinsically redder galaxies. The bright end of the rest-frame Vband luminosity function of z = 2 galaxies can be characterized by a Schechter function with parameters (Φ * , M * V , α) = (1.8 × 10 −3 , −23.4, −1.85), while the TVD simulation suggests a flatter faint-end slope of α ∼ −1.2. A comparison with z = 3 shows that the rest-frame V -band luminosity function has brightened by about 0.5 magnitude from z = 3 to z = 2 without a significant change in the shape. Our results do not imply that hierarchical galaxy formation fails to account for the massive galaxies at z 1.
Photometric properties of Lyman-break galaxies at z = 3 in cosmological SPH simulations
Monthly Notices of the Royal Astronomical Society, 2004
We study the photometric properties of Lyman-break galaxies (LBGs) formed by redshift z = 3 in a set of large cosmological smoothed-particle hydrodynamics (SPH) simulations of the Λ cold dark matter (ΛCDM) model. Our numerical simulations include radiative cooling and heating with a uniform UV background, star formation, supernova feedback, and a phenomenological model for galactic winds. Analysing a series of simulations of varying box size and particle number allows us to isolate the impact of numerical resolution on our results. We compute spectra of simulated galaxies using a population synthesis model, and derive colours and luminosity functions of galaxies at z = 3 after applying local dust extinction and absorption by the intergalactic medium (IGM). We find that the simulated galaxies have U n − G and G − R colours consistent with observations, provided that intervening absorption by the IGM is applied. The observed properties of LBGs, including their number density, colours, and luminosity functions, can be explained if LBGs are identified with the most massive galaxies at z = 3, having typical stellar mass of M ⋆ ∼ 10 10 h −1 M ⊙ , a conclusion broadly consistent with earlier studies based on hydrodynamic simulations of the ΛCDM model. We also find that most simulated LBGs were continuously forming stars at a high rate for more than one Gyr up until z = 3, but with numerous starbursts lying on top of the continuous component. Interestingly, our simulations suggest that more than 50% of the total stellar mass and star formation rate in the Universe are accounted for by galaxies that are not detected in the current generation of LBG surveys.
The photometric properties of galaxies in the early Universe
Monthly Notices of the Royal Astronomical Society, 2016
We use the large cosmological hydro-dynamic simulation BLUETIDES to predict the photometric properties of galaxies during the epoch of reionization (z = 8-15). These properties include the rest-frame UV to near-IR broad-band spectral energy distributions, the Lyman continuum (LyC) photon production, the UV star formation rate calibration, and intrinsic UV continuum slope. In particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis (SPS) model, initial mass function, and the escape fraction of LyC photons, upon these quantities. We find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. For example, at z = 8 we predict that nebular emission can account for up to 50 per cent of the rest-frame R-band luminosity, while the choice of SPS model can change the LyC production rate up to a factor of ×2.
The nature of submillimetre galaxies in cosmological hydrodynamic simulations
Monthly Notices of the Royal Astronomical Society, 2010
We study the nature of rapidly star-forming galaxies at z = 2 in cosmological hydrodynamic simulations, and compare their properties to observations of submillimetre galaxies (SMGs). We identify simulated SMGs as the most rapidly star-forming systems that match the observed number density of SMGs. In our models, SMGs are massive galaxies sitting at the centres of large potential wells, being fed by smooth infall and gas-rich satellites at rates comparable to their star formation rates (SFRs). They are not typically undergoing major mergers that significantly boost their quiescent SFR, but they still often show complex gas morphologies and kinematics. Our simulated SMGs have stellar masses of M * ∼ 10 11−11.7 M , SFRs of ∼180-500 M yr −1 , a clustering length of ∼10 h −1 Mpc and solar metallicities. The SFRs are lower than those inferred from far-infrared (far-IR) data by ∼×3, which we suggest may owe to one or more systematic effects in the SFR calibrations. SMGs at z = 2 live in ∼10 13 M haloes, and by z = 0 they mostly end up as brightest group galaxies in ∼10 14 M haloes. We predict that higher M * SMGs should have on average lower specific SFRs, less disturbed morphologies and higher clustering. We also predict that deeper far-IR surveys will smoothly join SMGs on to the massive end of the SFR-M * relationship defined by lower mass z ∼ 2 galaxies. Overall, our simulated rapid star-formers provide as good a match to available SMG data as merger-based scenarios, offering an alternative scenario that emerges naturally from cosmological simulations.
Panchromatic Spectral Energy Distributions of simulated galaxies: results at redshift z=0
2016
We present predictions of Spectral Energy Distributions (SEDs), from the UV to the FIR, of simulated galaxies at z=0. These were obtained by post-processing the results of an N-body+hydro simulation of a small cosmological volume, that uses the Multi-Phase Particle Integrator (MUPPI) for star formation and stellar feedback, with the GRASIL-3D radiative transfer code, that includes reprocessing of UV light by dust. Physical properties of galaxies resemble observed ones, though with some tension at small and large stellar masses. Comparing predicted SEDs of simulated galaxies with different samples of local galaxies, we find that these resemble observed ones, when normalised at 3.6 μm. A comparison with the Herschel Reference Survey shows that, when binning galaxies in Star Formation Rate (SFR), average SEDs are reproduced to within a factor of ∼2 even in normalization, while binning in stellar mass highlights the same tension that is present in the stellar mass -- SFR plane. We use o...