A New Approach for Simulating Galaxy Cluster Properties

We describe a subgrid model for including galaxies into hydrodynamical cosmological simulations of galaxy cluster evolution. Each galaxy construct- or galcon- is modeled as a physically extended object within which star formation, galactic winds, and ram pressure stripping of gas are modeled analytically. Galcons are initialized at high redshift (z~3) after galaxy dark matter halos have formed but before the cluster has virialized. Each galcon moves self-consistently within the evolving cluster potential and injects mass, metals, and energy into intracluster (IC) gas through a well-resolved spherical interface layer. We have implemented galcons into the Enzo adaptive mesh refinement code and carried out a simulation of cluster formation in a LambdaCDM universe. With our approach, we are able to economically follow the impact of a large number of galaxies on IC gas. We compare the results of the galcon simulation with a second, more standard simulation where star formation and feedback are treated using a popular heuristic prescription. One advantage of the galcon approach is explicit control over the star formation history of cluster galaxies. Using a galactic SFR derived from the cosmic star formation density, we find the galcon simulation produces a lower stellar fraction, a larger gas core radius, a more isothermal temperature profile, and a flatter metallicity gradient than the standard simulation, in better agreement with observations.Comment: 4 pages, 2 figures, submitted for publication in ApJ

Photometric Properties of Lyman-break Galaxies at z=3 in Cosmological SPH Simulations

We study the photometric properties of Lyman-break galaxies (LBGs) formed by redshift z=3 in a set of large cosmological smoothed-particle hydrodynamics simulations of the Lambda cold dark matter (CDM) 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 boxsize 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-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_{star} ~ 1e10 Msun/h, a conclusion broadly consistent with earlier studies based on hydrodynamic simulations of the Lamda CDM 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.Comment: 12 pages, 8 figures, Error in AB magnitude calculation corrected. Figures in the original published version in MNRAS contain error except Fig.5 & 6, but the basic conclusions are unchanged. Higher resolution version available at http://cfa-www.harvard.edu/~knagamine/lbg.ps.g

Hydrodynamical Simulations of Galaxy Clusters with Galcons

We present our recently developed {\em galcon} approach to hydrodynamical cosmological simulations of galaxy clusters - a subgrid model added to the {\em Enzo} adaptive mesh refinement code - which is capable of tracking galaxies within the cluster potential and following the feedback of their main baryonic processes. Galcons are physically extended galactic constructs within which baryonic processes are modeled analytically. By identifying galaxy halos and initializing galcons at high redshift ($z \sim 3$, well before most clusters virialize), we are able to follow the evolution of star formation, galactic winds, and ram-pressure stripping of interstellar media, along with their associated mass, metals and energy feedback into intracluster (IC) gas, which are deposited through a well-resolved spherical interface layer. Our approach is fully described and all results from initial simulations with the enhanced {\em Enzo-Galcon} code are presented. With a galactic star formation rate derived from the observed cosmic star formation density, our galcon simulation better reproduces the observed properties of IC gas, including the density, temperature, metallicity, and entropy profiles. By following the impact of a large number of galaxies on IC gas we explicitly demonstrate the advantages of this approach in producing a lower stellar fraction, a larger gas core radius, an isothermal temperature profile in the central cluster region, and a flatter metallicity gradient than in a standard simulation

Star formation rate and metallicity of damped Lyman-alpha absorbers in cosmological SPH simulations

We study the distribution of the star formation rate and metallicity of damped Lyman-alpha absorbers using cosmological SPH simulations of the Lambda cold dark matter model in the redshift range z=0-4.5. Our approach includes a phenomenological model of galactic wind. We find that there is a positive correlation between the projected stellar mass density and the neutral hydrogen column density (NHI) of DLAs for high NHI systems, and that there is a good correspondence in the spatial distribution of stars and DLAs in the simulations. The evolution of typical star-to-gas mass ratios in DLAs can be characterised by an increase from about 2 at z=4.5 to 3 at z=3, to 10 at z=1, and finally to 20 at z=0. We also find that the projected SFR density in DLAs follows the Kennicutt law well at all redshifts, and the simulated values are consistent with the recent observational estimates of this quantity by Wolfe et al. (2003a,b). The rate of evolution in the mean metallicity of simulated DLAs as a function of redshift is mild, and is consistent with the rate estimated from observations. The predicted metallicity of DLAs is generally sub-solar in our simulations, and there is a significant scatter in the distribution of DLA metallicity for a given NHI. However, we find that the median metallicity of simulated DLAs is close to that of Lyman-break galaxies, which is higher than the values typically observed for DLAs by nearly an order of magnitude. This discrepancy with observations could be due to an inadequate treatment of SN feedback in our current simulations, perhaps indicating that metals are not expelled efficiently enough from DLAs by outflows. Alternatively, the current observations might be missing the majority of the high metallicity DLAs due to selection effects. (abridged)Comment: 18 pages, 15 figures. Accepted to MNRAS. More visual presentations and the version with high resolution figures are available at http://cfa-www.harvard.edu/~knagamine/DLA-pics

Hyperfine Populations Prior to Muon Capture

It is shown that the 1S level hyperfine populations prior to muon capture will be statistical when either target or beam are unpolarised independent of the atomic level at which the hyperfine interaction becomes appreciable. This assertion holds in the absence of magnetic transitions during the cascade and is true because of minimal polarisation after atomic capture and selective feeding during the cascade.Comment: (revtex, 6 preprint pages, no figures

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 exceeding 30 Msun/yr over a few Gyrs from z=10 to z=2, together with significant contribution by starbursts reaching up to 1000 Msun/yr 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.Comment: 4 pages, Kluwer style files included. To appear in "Starbursts - from 30 Doradus to Lyman break galaxies" (IoA, Cambridge UK, Sep 2004; talk summary), Astrophysics & Space Science Library, eds. de Grijs R., Gonzalez Delgado R.M. (Kluwer: Dordrecht

The K20 survey. VI. The Distribution of the Stellar Masses in Galaxies up to z~2

We present a detailed analysis of the stellar mass content of galaxies up to z=2.5 in the K20 galaxy sample, that has a 92% spectroscopic completeness and a complete $UBVRIzJK_s$ multicolor coverage. We find that the M/L ratio decreases with redshift: in particular, the average M/L ratio of early type galaxies decreases with $z$, with a scatter that is indicative of a range of star--formation time-scales and redshift of formation. More important, the typical M/L of massive early type galaxies is larger than that of less massive ones, suggesting that their stellar population formed at higher z. The final K20 galaxy sample spans a range of stellar masses from M*=10^9Msun to M*=10^12Msun, with massive galaxies ($M*>10^11Msun) detected up to z~2. We compute the Galaxy Stellar Mass Function at various z, of which we observe only a mild evolution (i.e. by 20-30%) up to z~1. At z>1, the evolution of the GSMF appears to be much faster: at z~2, about 35% of the present day stellar mass in objects with M*~10^11Msun appear to have assembled. We also detect a change in the physical nature of the most massive galaxies, since at z>1 a population of massive star--forming galaxies progressively appears. We finally analyze our results in the framework of Lambda-CDM hierarchical models. First, we show that the large number of massive galaxies detected at high z does not violate any fundamental Lambda-CDM constraint based on the number of massive DM halos. Then, we compare our results with the predictions of renditions of both semianalytic and hydro-dynamical models, that range from severe underestimates to slight overestimates of the observed mass density at z<~2. We discuss how the differences among these models are due to the different implementation of the main physical processes. (Abridged)Comment: Accepted for publication on Astronomy & Astrophysic

Imaging the cool gas, dust, star formation, and AGN in the first galaxies

When, and how, did the first galaxies and supermassive black holes (SMBH) form, and how did they reionization the Universe? First galaxy formation and cosmic reionization are among the last frontiers in studies of cosmic structure formation. We delineate the detailed astrophysical probes of early galaxy and SMBH formation afforded by observations at centimeter through submillimeter wavelengths. These observations include studies of the molecular gas (= the fuel for star formation in galaxies), atomic fine structure lines (= the dominant ISM gas coolant), thermal dust continuum emission (= an ideal star formation rate estimator), and radio continuum emission from star formation and relativistic jets. High resolution spectroscopic imaging can be used to study galaxy dynamics and star formation on sub-kpc scales. These cm and mm observations are the necessary compliment to near-IR observations, which probe the stars and ionized gas, and X-ray observations, which reveal the AGN. Together, a suite of revolutionary observatories planned for the next decade from centimeter to X-ray wavelengths will provide the requisite panchromatic view of the complex processes involved in the formation of the first generation of galaxies and SMBHs, and cosmic reionization.Comment: 8 pages total. White paper submitted to the Astro 2010 Decadal Surve

Confusion background from compact binaries

URL to conference site: http://www.amaldi8.org/index.htmlDouble neutron stars are one of the most promizing sources for terrestrial gravitational wave interferometers. For actual interferometers and their planned upgrades, the probability of having a signal present in the data is small, but as the sensitivity improves, the detection rate increases and the waveforms may start to overlap, creating a confusion background, ultimately limiting the capabilities of future detectors. The third generation Einstein Telescope, with an horizon of z > 1 and very low frequency "seismic wall" may be affected by such confusion noise. At a minimum, careful data analysis will be require to separate signals which will appear confused. This result should be borne in mind when designing highly advanced future instruments