Sub-millimetre galaxies in cosmological hydrodynamic simulations: Source number counts and the spatial clustering

We use large cosmological Smoothed-Particle-Hydrodynamics simulations to study the formation and evolution of sub-millimetre galaxies (SMGs). In our previous work, we studied the statistical properties of ultra-violet selected star-forming galaxies at high redshifts. We populate the same cosmological simulations with SMGs by calculating the reprocess of stellar light by dust grains into far-infrared to millimetre wavebands in a self-consistent manner. We generate light-cone outputs to compare directly the statistical properties of the simulated SMGs with available observations. Our model reproduces the submm source number counts and the clustering amplitude. We show that bright SMGs with flux $S > 1$ mJy reside in halos with mass of $\sim 10^{13} M_{\odot}$ and have stellar masses greater than $10^{11}\sim \rm M_{\odot}$. The angular cross-correlation between the SMGs and Lyman-$\alpha$ emitters is significantly weaker than that between the SMGs and Lyman-break galaxies. The cross-correlation is also weaker than the auto-correlation of the SMGs. The redshift distribution of the SMGs shows a broad peak at $z \sim 2$, where Bright SMGs contribute significantly to the global cosmic star formation rate density. Our model predicts that there are hundreds of SMGs with $S > 0.1$ mJy at $z > 5$ per 1 square degree field. Such SMGs can be detected by ALMA.Comment: 11 pages, 13 figures, submitted to MNRA

Large-Scale Structure of Short-Lived Lyman\alpha Emitters

Recently discovered large-scale structure of Ly\alpha Emitters (LAEs) raises a novel challenge to the cold dark matter (CDM) cosmology. The structure is extended over more than 50 Mpc at redshift z=3.1, and exhibits a considerably weak angular correlation. Such properties of LAE distributions appear to be incompatible with the standard biased galaxy formation scenario in the CDM cosmology. In this paper, by considering the possibility that LAEs are short-lived events, we attempt to build up the picture of LAEs concordant with the CDM cosmology. We find that if the lifetime of LAEs is as short as (6.7 \pm 0.6) \times 10^7 yr, the distributions of simulated galaxies successfully match the extension and morphology of large-scale structure of LAEs at z=3.1, and also the weak angular correlation function. This result implies that LAEs at z=3.1 do not necessarily reside in high density peaks, but tends to be located in less dense regions, in a different way from the expectation by the standard biased galaxy formation scenario. In addition, we make a prediction for the angular correlation function of LAEs at redshifts higher than 3. It is found that the prediction deviates from that by the standard biased galaxy formation scenario even at redshifts 4 < z < 6.Comment: 5 pages, 4 figures, accepted for publication in MNRA

Physical Properties of UDF12 Galaxies in Cosmological simulations

We have performed a large cosmological hydrodynamics simulation tailored to the deep survey with the Hubble Space Telescope made in 2012, the so-called UDF12 campaign. After making a light-cone output, we have applied the same color selection criteria as the UDF12 campaign to select galaxies from our simulation, and then, have examined the physical properties of them as a proxy of the real observed UDF12 galaxies at $z > 7$. As a result, we find that the halo mass is almost linearly proportional to the observed ultraviolet (UV) luminosity ($4 \times 10^{11}~{\rm M_{\odot}}$ at $M_{\rm UV} = -21$). The dust attenuation and UV slope $\beta$ well correlates with the observed UV luminosity, which is consistent with observations quantitatively. The star formation rate (SFR) is also linearly proportional to the stellar mass and the specific SFR shows only a weak dependency on the mass. We also find an increasing star formation history with a time-scale of $\sim100$ Myr in the high-$z$ galaxies. An average metallicity weighted by the Lyman continuum luminosity reaches up to $>0.1$ Solar even at $z \sim 10$, suggesting a rapid metal enrichment. We also expect $\geq 0.1$ mJy at 350 GHz of the dust thermal emission from the galaxies with $H_{160} \leq 27$, which can be detectable with the Atacama Large Milimetre-submilimetre Array. The galaxies selected by the UDF12 survey contribute to only $52--12\%$ of the cosmic SFR density from $z \sim 7$ to $z \sim 10$, respectively. The James Webb Space Telescope will push the detection fraction up to $77--72\%$.Comment: re-Submitted to MNRAS; 16 pages; 14 figures; 1 tables

Star Formation and Chemical Enrichment in Protoclusters

We examine star formation and chemical enrichment in protoclusters (PCs) using cosmological zoom-in hydrodynamic simulations. We find that the total star formation rate (SFR) in all PC ($>10^{14.4}\,h^{-1}$M$_\odot$) reaches $>10^4\,\mathrm{M}_\odot \mathrm{yr}^{-1}$ at $z=3$, equivalent to the observed PCs. The SFR in the Core region accounts for about $30\%$ of the total star formation in the PC at $z\gtrsim1$, suggesting the importance of the outer regions to reveal the evolution of galaxy clusters. We find that the total SFR of PC is dominated by galaxies with $10^{10}\,\le\,(\mathrm{M}_\star/M_\odot)\,\le\,10^{11}$, while more massive galaxies dominate the SFR in the Core. For the chemical abundance evolution, we find that the higher-density region has a higher metallicity and faster evolution. We show that the [O/Fe] vs. [Fe/H] relation turns down in the Core at $z=3.4$ due to the enrichment of Fe by Type Ia supernovae. We find no environmental effects for the mass--metallicity relations (MZR) or $\log$(N/O) vs. $12+\log$(O/H) for galaxies. We find that the chemical enrichment in galaxy clusters proceeds faster in the high redshift Universe ($z>1$). Our work will benefit future tomographic observations, particularly using PCs as unique probes of accelerated structure formation and evolution in high-density regions of the universe.Comment: 19 pages, 18 figures, 2 tables, 2 appendices, Accepted for publication in MNRA