Saturday. Will stay home and cure my cough.
1301.3497
How robust are predictions of galaxy clustering?
Contreras, Baugh, Norberg, Padilla
Durham and Munich SAM both use Nillennium, but use independent algorithms to construct halo merger histories. Compare the predicted HODs and correlation functions for galaxy samples defined by stellar mass, cold gas mass and SFR. The predictions for the HOD are remarkably similar for samples ranked by stellar mass. The predicted bias averaged over 5-25 Mpc/h is consistent between models to within 10%. At small pair separations, there is a difference in the predicted clustering. This arises because the Durham models allow some satellite galaxies to merge with the central galaxy in a halo when they are still associated with resolved sub halos. The agreement between the models is less good for samples defined by cold gas mass or SFR, with the small scale clustering differing by an order of magnitude, reflecting the uncertainty in the modeling of star formation. The model prediction in these cases are qualitatively similar, with a markedly shallower slope for the correlation function than is found for stellar mass selected samples and with the HOD displaying an asymmetric peak for central galaxies. Provide illustrative parametric fits to the HODs predicted by the models. Results reveal the current limitations on the physics of galaxy formation from galaxy clustering measurements and the ability of future galaxy surveys to measure dark energy.
1301.3588
Impact of the non-Gaussian covariance of the weak lensing power spectrum and bispectrum on cosmological parameter estimation
Sato, Nishimichi
As the title says: how bad is it if Gaussian approximation doesn't work for calculating covariance matrices? Focus on its impact on the cosmo parameter estimations. Use N-body sims, carry Fisher matrix forecasts for tomographic WL surveys with 3 source redshifts. Show consistency of simulation with fitting formulae; then investigate the covariance matrix. Shape noise contributes a significant fraction to total error budget, mitigates impact of the non-Gaussian error; find that the non-G error degrads the cumulative S/N up to the maximum multipole of 2000 by a factor of about 2 (3) in the power (bi-) spectrum analysis. Impact on final cosmological parameter forecast with 6 parameters can be as large as 15% in the size of the one-dimensional statistical error. Show how DE FoM affected by non-G error.
1301.3624
Precision modeling of redshift-space distortions from multi-point propagator expansion
Taruya, Nishimichi, Bernardeau
As the title says.
1301.3905
Feedback-regulated star formation in molecular clouds and galactic discs
Faucher-Giguere, Quataert, Hopkins
Present a two-zone theory for feedback-regulated SF in galactic discs, consistently connecting the galaxy-averaged SF law with SF proceeding in GMCs. Focus on galaxies with gas surface density Sigma_g > 100 Msun/pc^2. In this theory, the galactic disc consists of Toomre-mass [?] GMCs embedded in a volume-filling ISM. Radiation pressure on dust disperses GMCs and most SNe explode in the volume-filling medium. A galaxy-averaged SF law is derived by balancing the momentum input from SNe feedback with the gravitational weight of the disc gas. The star formation law is in good agreement with observations for a CO conversion factor depending continuously on Sigma_g. Argue that the galaxy-averaged SF efficiency per free fall time, epsilon_ff^gal, is only a weak function of the efficiency with which GMCs convert their gas into stars. This is possible because the rate limiting step for SF is the rate at which GMCs form: for large efficiency of SF in GMCs, the Toomre Q parameter obtains a value slightly above unity so that the GMC formation rate is consistent with the galaxy-averaged SF law. Contrast results with other theories of turbulence-regulated SF and discuss predictions of this model. Show that the galaxy-averaged SF efficiency per free fall time is non-universal (from data compilation in literature), and increases with increasing gas fraction, as predicted by this model. Also predict that the fraction of the disc gas mass in bound GMCs decreases for increasing values of the GMC SF efficiency. This is qualitatively consistent with the smooth molecular gas distribution inferred in local ultra-luminous IR galaxies and the small mass fraction in giant clumps in high-z galaxies.
1301.4024
Properties of dust grains probed with extinction curves
Nozawa, Fukugita
Study the property of dust grain n NW and SMC using extinction curves from UV to NIR. Confirm that graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: The parmaeters are tightly constrained to be q=3.5 pm 0.2 for the size distribution a^-q and the maximum radius a_max=0.24pm0.05 um, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus H column density, E(B-V)/N_H. If we take the solar elemental abundance as a standard for the MW, >56% of carbon should be in graphite dust, while it is < 40% in the SMC. This disparity and the relative abundance explain the difference of the two curves. Find that 50-60% of C may not necessarily be in graphite but in the amorphous or the glassy phase, or up to 15% in SiC. Fe may also be in the metallic phase or up to ~80% in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions the parameters of the grain size remain unchanged. The mass density of dust grains relative to H is rho_dust/rho_H = 1/120 for the MW and 1/760 for the SMC under some abundance constraints. Underline the importance of the wavelength-dependence slope of the extinction curve in the NIR in constructing the dust model: if A_lambda propto lambda^-gamma with gamma~1.6, the power-law grain-size model fails, whereas it works if gamma~1.8-2.0.
1301.4201
Chemical enrichment of Damped Lyman Alpha systems as a direct constraint on Population III star formation
Kulkarni, Rollinde, Hennawi, Vangioni
DLAs can be used to measure gas-phase metallicities at large cosmological lookback times with high precision. Relative abundances can still be measured accurately deep into the reionization epoch (z>6) using transitions redward of Lya. Study chemical evolution of DLAs using a constrained model for evolution of galaxies and IGM to determine: the degree to which DLA abundance measurements can probe PopIII enrichment. Find that if the critical metallicity of Pop III to II transition is <1e-4 Zsun, the cosmic Population III SFR is zero for z<8. Nevertheless, at high redshift (z~6), Pop III chemical signatures are retained in low-mass galaxies (halo mass < 1e9 Msun). This is because photoioinzation feedback suppresses SF in these galaxies until relatively low z (z~10), and the chemical record of early Pop III SF is retained. Model DLAs as these galaxies by assigning to them a mass-dependent HI absorption cross section and predict distribution of DLA abundance ratios. Find that these distributions are anchored towards abundance ratios set by Pop II yields, but exhibit a tail that depends on the Pop III IMF for z>5. Thus, a sample of DLA abundance measurements at high z holds the promise to constraint Pop III IMF. A sample just 10 DLAs with relative abundances measured to an accuracy of 0.1 dex is sufficient to constrain the Pop III IMF at 4-sigma. These constraints may prove stronger than other probes such as metal-poor stars and individual DLAs. Results provide a global picture of the cosmic thermal, ionization, and chemical evolution, and can rule out certain Pop III scenarios.
1301.3497
How robust are predictions of galaxy clustering?
Contreras, Baugh, Norberg, Padilla
Durham and Munich SAM both use Nillennium, but use independent algorithms to construct halo merger histories. Compare the predicted HODs and correlation functions for galaxy samples defined by stellar mass, cold gas mass and SFR. The predictions for the HOD are remarkably similar for samples ranked by stellar mass. The predicted bias averaged over 5-25 Mpc/h is consistent between models to within 10%. At small pair separations, there is a difference in the predicted clustering. This arises because the Durham models allow some satellite galaxies to merge with the central galaxy in a halo when they are still associated with resolved sub halos. The agreement between the models is less good for samples defined by cold gas mass or SFR, with the small scale clustering differing by an order of magnitude, reflecting the uncertainty in the modeling of star formation. The model prediction in these cases are qualitatively similar, with a markedly shallower slope for the correlation function than is found for stellar mass selected samples and with the HOD displaying an asymmetric peak for central galaxies. Provide illustrative parametric fits to the HODs predicted by the models. Results reveal the current limitations on the physics of galaxy formation from galaxy clustering measurements and the ability of future galaxy surveys to measure dark energy.
1301.3588
Impact of the non-Gaussian covariance of the weak lensing power spectrum and bispectrum on cosmological parameter estimation
Sato, Nishimichi
As the title says: how bad is it if Gaussian approximation doesn't work for calculating covariance matrices? Focus on its impact on the cosmo parameter estimations. Use N-body sims, carry Fisher matrix forecasts for tomographic WL surveys with 3 source redshifts. Show consistency of simulation with fitting formulae; then investigate the covariance matrix. Shape noise contributes a significant fraction to total error budget, mitigates impact of the non-Gaussian error; find that the non-G error degrads the cumulative S/N up to the maximum multipole of 2000 by a factor of about 2 (3) in the power (bi-) spectrum analysis. Impact on final cosmological parameter forecast with 6 parameters can be as large as 15% in the size of the one-dimensional statistical error. Show how DE FoM affected by non-G error.
1301.3624
Precision modeling of redshift-space distortions from multi-point propagator expansion
Taruya, Nishimichi, Bernardeau
As the title says.
1301.3905
Feedback-regulated star formation in molecular clouds and galactic discs
Faucher-Giguere, Quataert, Hopkins
Present a two-zone theory for feedback-regulated SF in galactic discs, consistently connecting the galaxy-averaged SF law with SF proceeding in GMCs. Focus on galaxies with gas surface density Sigma_g > 100 Msun/pc^2. In this theory, the galactic disc consists of Toomre-mass [?] GMCs embedded in a volume-filling ISM. Radiation pressure on dust disperses GMCs and most SNe explode in the volume-filling medium. A galaxy-averaged SF law is derived by balancing the momentum input from SNe feedback with the gravitational weight of the disc gas. The star formation law is in good agreement with observations for a CO conversion factor depending continuously on Sigma_g. Argue that the galaxy-averaged SF efficiency per free fall time, epsilon_ff^gal, is only a weak function of the efficiency with which GMCs convert their gas into stars. This is possible because the rate limiting step for SF is the rate at which GMCs form: for large efficiency of SF in GMCs, the Toomre Q parameter obtains a value slightly above unity so that the GMC formation rate is consistent with the galaxy-averaged SF law. Contrast results with other theories of turbulence-regulated SF and discuss predictions of this model. Show that the galaxy-averaged SF efficiency per free fall time is non-universal (from data compilation in literature), and increases with increasing gas fraction, as predicted by this model. Also predict that the fraction of the disc gas mass in bound GMCs decreases for increasing values of the GMC SF efficiency. This is qualitatively consistent with the smooth molecular gas distribution inferred in local ultra-luminous IR galaxies and the small mass fraction in giant clumps in high-z galaxies.
1301.4024
Properties of dust grains probed with extinction curves
Nozawa, Fukugita
Study the property of dust grain n NW and SMC using extinction curves from UV to NIR. Confirm that graphite-silicate mixture of grains yields the observed extinction curve with the simple power-law distribution of the grain size but with a cutoff at some maximal size: The parmaeters are tightly constrained to be q=3.5 pm 0.2 for the size distribution a^-q and the maximum radius a_max=0.24pm0.05 um, for both MW and SMC. The abundance of grains, and hence the elemental abundance, is constrained from the reddening versus H column density, E(B-V)/N_H. If we take the solar elemental abundance as a standard for the MW, >56% of carbon should be in graphite dust, while it is < 40% in the SMC. This disparity and the relative abundance explain the difference of the two curves. Find that 50-60% of C may not necessarily be in graphite but in the amorphous or the glassy phase, or up to 15% in SiC. Fe may also be in the metallic phase or up to ~80% in magnetite rather than in silicates, so that the Mg/Fe ratio in astronomical olivine is arbitrary. With these substitutions the parameters of the grain size remain unchanged. The mass density of dust grains relative to H is rho_dust/rho_H = 1/120 for the MW and 1/760 for the SMC under some abundance constraints. Underline the importance of the wavelength-dependence slope of the extinction curve in the NIR in constructing the dust model: if A_lambda propto lambda^-gamma with gamma~1.6, the power-law grain-size model fails, whereas it works if gamma~1.8-2.0.
1301.4201
Chemical enrichment of Damped Lyman Alpha systems as a direct constraint on Population III star formation
Kulkarni, Rollinde, Hennawi, Vangioni
DLAs can be used to measure gas-phase metallicities at large cosmological lookback times with high precision. Relative abundances can still be measured accurately deep into the reionization epoch (z>6) using transitions redward of Lya. Study chemical evolution of DLAs using a constrained model for evolution of galaxies and IGM to determine: the degree to which DLA abundance measurements can probe PopIII enrichment. Find that if the critical metallicity of Pop III to II transition is <1e-4 Zsun, the cosmic Population III SFR is zero for z<8. Nevertheless, at high redshift (z~6), Pop III chemical signatures are retained in low-mass galaxies (halo mass < 1e9 Msun). This is because photoioinzation feedback suppresses SF in these galaxies until relatively low z (z~10), and the chemical record of early Pop III SF is retained. Model DLAs as these galaxies by assigning to them a mass-dependent HI absorption cross section and predict distribution of DLA abundance ratios. Find that these distributions are anchored towards abundance ratios set by Pop II yields, but exhibit a tail that depends on the Pop III IMF for z>5. Thus, a sample of DLA abundance measurements at high z holds the promise to constraint Pop III IMF. A sample just 10 DLAs with relative abundances measured to an accuracy of 0.1 dex is sufficient to constrain the Pop III IMF at 4-sigma. These constraints may prove stronger than other probes such as metal-poor stars and individual DLAs. Results provide a global picture of the cosmic thermal, ionization, and chemical evolution, and can rule out certain Pop III scenarios.
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