Tuesday.
1607.07445
The dark nemesis of galaxy formation: why hot haloes trigger black hole growth and bring star formation to an end
Bower, Schaye, Frenk, et al
Galaxies fall into 2 clearly distinct types: 'blue-sequence' galaxies that are rapidly forming young stars, and 'red-sequence' galaxies in which SF has almost completely ceased. Most galaxies more massive than 3e10 Msun follow the red-sequence while less massive central galaxies lie on the blue sequence. Show that these sequences are created by a competition between SF-driven outflows and gas accretion on to the SMBH at the galaxy's center. Develop a simple analytic model for this interaction. In galaxies less massive than 3e10 Msun, young stars and SNe drive a buoyant outflow that balances the rate of gas inflow. This prevents high gas densities building up in the central regions. More massive galaxies, however, are surrounded by a hot corona. Argue that above a halo mass of ~1e12 Msun, the SN-driven outflow is no longer buoyant and SF is unable to prevent the build up of gas in the central regions. This triggers a strongly non-linear response from the BH. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for SF. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. Show that the analytic model provides a good description of galaxy evolution in the EAGLE hydro sims, and demonstrate that, so long as SF-driven outflows are present, the transition mass scale is almost independent of sub grid parameter choice. The transition mass disappears entirely, however, if SF driven outflows are absent.
1607.07545
Cosmic shear measurement using autoconvolved images
Li, Zhang
Study the possibility of using quadruple moments of auto-convolved galaxy images to measure cosmic shear. The auto convolution of an image corresponds to the inverse Foureir transformation of its power spectrum. The new method has the following advantages: the smearing effect due to the PSF can be corrected by subtracting the quadrupole moments of the auto-convolved PSF; the centroid of the auto-convolved image is trivially identified; the systematic error due to noise can be directly removed in Fourier space; the PSF image can also contain noise, the effect of which can be similarly removed. With a large ensemble of simulated galaxy images, show that the new method can reach a sub-percent level accuracy in general conditions, albeit with increasingly large stamp size for galaxies of less compact profiles.
1607.07445
The dark nemesis of galaxy formation: why hot haloes trigger black hole growth and bring star formation to an end
Bower, Schaye, Frenk, et al
Galaxies fall into 2 clearly distinct types: 'blue-sequence' galaxies that are rapidly forming young stars, and 'red-sequence' galaxies in which SF has almost completely ceased. Most galaxies more massive than 3e10 Msun follow the red-sequence while less massive central galaxies lie on the blue sequence. Show that these sequences are created by a competition between SF-driven outflows and gas accretion on to the SMBH at the galaxy's center. Develop a simple analytic model for this interaction. In galaxies less massive than 3e10 Msun, young stars and SNe drive a buoyant outflow that balances the rate of gas inflow. This prevents high gas densities building up in the central regions. More massive galaxies, however, are surrounded by a hot corona. Argue that above a halo mass of ~1e12 Msun, the SN-driven outflow is no longer buoyant and SF is unable to prevent the build up of gas in the central regions. This triggers a strongly non-linear response from the BH. Its accretion rate rises rapidly, heating the galaxy's corona, disrupting the incoming supply of cool gas and starving the galaxy of the fuel for SF. The host galaxy makes a transition to the red sequence, and further growth predominantly occurs through galaxy mergers. Show that the analytic model provides a good description of galaxy evolution in the EAGLE hydro sims, and demonstrate that, so long as SF-driven outflows are present, the transition mass scale is almost independent of sub grid parameter choice. The transition mass disappears entirely, however, if SF driven outflows are absent.
1607.07545
Cosmic shear measurement using autoconvolved images
Li, Zhang
Study the possibility of using quadruple moments of auto-convolved galaxy images to measure cosmic shear. The auto convolution of an image corresponds to the inverse Foureir transformation of its power spectrum. The new method has the following advantages: the smearing effect due to the PSF can be corrected by subtracting the quadrupole moments of the auto-convolved PSF; the centroid of the auto-convolved image is trivially identified; the systematic error due to noise can be directly removed in Fourier space; the PSF image can also contain noise, the effect of which can be similarly removed. With a large ensemble of simulated galaxy images, show that the new method can reach a sub-percent level accuracy in general conditions, albeit with increasingly large stamp size for galaxies of less compact profiles.
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