Monday, at Penn.
1308.3713
Heavy dust obscuration of z=7 galaxies in a cosmological hydrodynamic simulation
Kimm, Cen
HST observations show that galaxies at z~7 have very blue UV colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. Investigate UV and optical properties of the high-z galaxies in the standard CDM model using a high-resolution AMR cosmological hydro sims. For this purpose, perform panchromatic 3-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5e8-3e10 Msun with 3 parameters, the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (\fesc). The stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. Find that the heavily dust-attenuated galaxies (A_V~1.8) can also reasonably match modest UV-optical [rest-frame?] colors, blue UV slopes, as well as UV luminosity functions, provided that a significant fraction (~10%) of light directly escapes from them. The observed UV slope and scatter are better explained with a SMC-type extinction curve, whereas MW-type dust predicts too blue UV colors due to the 2175A bump. Expect that upcoming observations by ALMA will be able to test this heavily obscured model. [cf. paper by Mariska+Conroy]
1308.3719
Consequences of radiative and mechanical feedback from black holes in galaxy mergers
Choi, Naab, Ostriker, Johansson, Moster
Use hydro sims to study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disk galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to account for the global impact of AGN feedback. Compare 3 models: (1) no BH and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars which show winds with initial velocities of v_w ~ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity ~1000 km/s, similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of ~20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback, independent of their progenitor mass-ratios, follow the observed relations between stellar velocity dispersion and BH mass (M_BH-sigma) as well as X-ray luminosity (L_X-sigma) with 1e37.5 < L_X (0.3-8 keV) < 1e39.2 for velocity dispersions in the range of 120 km/s < sigma < 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. Also show that gas is more rapidly and impulsively stripped from the galactic centers driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model. However, the BH mass growth required to produce the observed galaxy size and central density evolution is inconsistent with the observed M_BH-sigma relation.
1308.3875
Initial results from a laboratory emulation of weak gravitational lensing measurements
Seshadri, Shapiro, Goodsall, Fucik, Hirata, Rhodes, Rowe, Smith
To validate the performance of the WFIRST IR detectors, performed a lab emulation of WL measurements: experiments used a custom precision projector system to image a target mask composed of a grid of pinholes, emulating stellar point sources, onto a 1.7 micron cut-off Teledyne HdCdTe/H2RG detector. Use a 880 nm LED illumination source and f/22 pupil stop to produce undersampled PSF similar to those expected from WFIRST. Also emulated the WFIRST image reconstruction strategy, using the IMage COMbination (IMCOM) algorithm to derive oversampled imaged from dithered, undersampled input images. Created shear maps for this data and computed shear correlation functions to mimic a real WL analysis. After removing only 2nd order polynomial fits to the shear maps, found that the correlation functions could be reduced to O(1e-6). This places a conservative upper limit on the detector-induced bias to the correlation function (under the given test conditions). This bias is two orders of magnitude lower than the expected WL signal. Restricted to scales relevant to DE analyses (sky separations > 0.5 arcmin), the bias is O(1e-7): comparable to the requirement for future weak lensing missions to avoid biasing cosmological parameter estimates. Experiment will need to be upgraded and repeated under different configurations to fully characterize the shape measurement performance of WFIRST IR detectors.
1308.3976
Pulsar scattering in space and time
Wucknitz
Report on a recent global VLBI experiment in which the simultaneous scatter broadening in the spatial and time domain is studied. Depending on the distribution of scattering screen(s), geometry predicts that the less spatially broadened parts of the signal arrive earlier than the more broadened parts. This means that over one pulse period, the size of the scattering disk should grow from pointlike to the maximum size. An equivalent description is that the pulse profile shows less temporal broadening on the longer baselines. Present first results that are consistent with the expected expanding rings. Also briefly discuss how the autocorrelations can be used for amplitude calibration. This requires a thorough investigation of the digitization and the sampler statistics and is not fully solved yet.
1308.4099
Null tests of the cosmological constant using supernovae
Yahya, Seikel, Clarkson, Maartens, Smith
In addition to using generic observational tests, one can also design tests that target the specific properties of the cosmological constant. These null tests do not rely on parameterizations of observables, but focus on quantities that are constant only if DE is a cosmological constant. Use SN data in null tests that are based on luminosity distance. In order to extract derivatives of the distance in a model-independent way, use Gaussian Processes [?]. Find that the concordance model is compatible with the Union 2.1 data, but the error bars are fairly large. Simulated datasets are generated for the DES SN survey and show that this survey will allow for a sharper null test of the cosmological constant if flat Universe is assumed. Allowing for spatial curvature degrades the power of the null test. [how exactly is the null test conducted?]
1308.3713
Heavy dust obscuration of z=7 galaxies in a cosmological hydrodynamic simulation
Kimm, Cen
HST observations show that galaxies at z~7 have very blue UV colors, consistent with these systems being dominated by young stellar populations with moderate or little attenuation by dust. Investigate UV and optical properties of the high-z galaxies in the standard CDM model using a high-resolution AMR cosmological hydro sims. For this purpose, perform panchromatic 3-dimensional dust radiative transfer calculations on 198 galaxies of stellar mass 5e8-3e10 Msun with 3 parameters, the dust-to-metal ratio, the extinction curve, and the fraction of directly escaped light from stars (\fesc). The stellar mass function is found to be in broad agreement with Gonzalez et al., independent of these parameters. Find that the heavily dust-attenuated galaxies (A_V~1.8) can also reasonably match modest UV-optical [rest-frame?] colors, blue UV slopes, as well as UV luminosity functions, provided that a significant fraction (~10%) of light directly escapes from them. The observed UV slope and scatter are better explained with a SMC-type extinction curve, whereas MW-type dust predicts too blue UV colors due to the 2175A bump. Expect that upcoming observations by ALMA will be able to test this heavily obscured model. [cf. paper by Mariska+Conroy]
1308.3719
Consequences of radiative and mechanical feedback from black holes in galaxy mergers
Choi, Naab, Ostriker, Johansson, Moster
Use hydro sims to study the effect of AGN mechanical and radiation feedback on the formation of bulge dominated galaxies via mergers of disk galaxies. The merging galaxies have mass-ratios of 1:1 to 6:1 and include pre-existing hot gaseous halos to account for the global impact of AGN feedback. Compare 3 models: (1) no BH and no AGN feedback; (2) thermal AGN feedback; and (3) mechanical and radiative AGN feedback. The last model is motivated by observations of broad absorption line quasars which show winds with initial velocities of v_w ~ 10,000 km/s and also heating associated with the central AGN X-ray radiation. The primary changes in gas properties due to mechanical AGN feedback are lower thermal X-ray luminosity from the final galaxy - in better agreement with observations - and galactic outflows with higher velocity ~1000 km/s, similar to recent direct observations of nearby merger remnants. The kinetic energy of the outflowing gas is a factor of ~20 higher than in the thermal feedback case. All merger remnants with momentum-based AGN feedback, independent of their progenitor mass-ratios, follow the observed relations between stellar velocity dispersion and BH mass (M_BH-sigma) as well as X-ray luminosity (L_X-sigma) with 1e37.5 < L_X (0.3-8 keV) < 1e39.2 for velocity dispersions in the range of 120 km/s < sigma < 190 km/s. In addition, the mechanical feedback produces a much greater AGN variability. Also show that gas is more rapidly and impulsively stripped from the galactic centers driving a moderate increase in galaxy size and decrease in central density with the mechanical AGN feedback model. However, the BH mass growth required to produce the observed galaxy size and central density evolution is inconsistent with the observed M_BH-sigma relation.
1308.3875
Initial results from a laboratory emulation of weak gravitational lensing measurements
Seshadri, Shapiro, Goodsall, Fucik, Hirata, Rhodes, Rowe, Smith
To validate the performance of the WFIRST IR detectors, performed a lab emulation of WL measurements: experiments used a custom precision projector system to image a target mask composed of a grid of pinholes, emulating stellar point sources, onto a 1.7 micron cut-off Teledyne HdCdTe/H2RG detector. Use a 880 nm LED illumination source and f/22 pupil stop to produce undersampled PSF similar to those expected from WFIRST. Also emulated the WFIRST image reconstruction strategy, using the IMage COMbination (IMCOM) algorithm to derive oversampled imaged from dithered, undersampled input images. Created shear maps for this data and computed shear correlation functions to mimic a real WL analysis. After removing only 2nd order polynomial fits to the shear maps, found that the correlation functions could be reduced to O(1e-6). This places a conservative upper limit on the detector-induced bias to the correlation function (under the given test conditions). This bias is two orders of magnitude lower than the expected WL signal. Restricted to scales relevant to DE analyses (sky separations > 0.5 arcmin), the bias is O(1e-7): comparable to the requirement for future weak lensing missions to avoid biasing cosmological parameter estimates. Experiment will need to be upgraded and repeated under different configurations to fully characterize the shape measurement performance of WFIRST IR detectors.
1308.3976
Pulsar scattering in space and time
Wucknitz
Report on a recent global VLBI experiment in which the simultaneous scatter broadening in the spatial and time domain is studied. Depending on the distribution of scattering screen(s), geometry predicts that the less spatially broadened parts of the signal arrive earlier than the more broadened parts. This means that over one pulse period, the size of the scattering disk should grow from pointlike to the maximum size. An equivalent description is that the pulse profile shows less temporal broadening on the longer baselines. Present first results that are consistent with the expected expanding rings. Also briefly discuss how the autocorrelations can be used for amplitude calibration. This requires a thorough investigation of the digitization and the sampler statistics and is not fully solved yet.
1308.4099
Null tests of the cosmological constant using supernovae
Yahya, Seikel, Clarkson, Maartens, Smith
In addition to using generic observational tests, one can also design tests that target the specific properties of the cosmological constant. These null tests do not rely on parameterizations of observables, but focus on quantities that are constant only if DE is a cosmological constant. Use SN data in null tests that are based on luminosity distance. In order to extract derivatives of the distance in a model-independent way, use Gaussian Processes [?]. Find that the concordance model is compatible with the Union 2.1 data, but the error bars are fairly large. Simulated datasets are generated for the DES SN survey and show that this survey will allow for a sharper null test of the cosmological constant if flat Universe is assumed. Allowing for spatial curvature degrades the power of the null test. [how exactly is the null test conducted?]
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