Friday.
1211.1669
A deep x-ray view of the hot halo in the edge-on spiral galaxy NGC 891
Hodges-Kluck, Bregman
NGC 891 is similar to MW and has a hot X-ray emitting halo that could arise from accretion, a galactic fountain, or a combination of the two. The metallicity of the gas can help distinguish between these models. Report results from Chandra and XMM-Newton on temperature and metallicity of the hot halo of the galaxy. Find good fits for a thermal model with kT~0.2 keV and Z~0.1 solar, and rule out solar metallicity to >99% confidence. Result suggests accretion from the IGM as the origin of the hot halo. Suggests accretion from IGM as the origin for the hot halo. Also possible to fit a 2-temperature thermal model with solar metallicity with 0.1 keV and 0.25 keV temperatures; the cooling rate in the hot gas cannot explain the massive HI halo in the steady state. A galactic fountain model cannot eject enough mass to account for the HI halo, so speculate that the neutral halo may be bas from a prior outflow that has since cooled.
1211.1670
The first billion years project - IV: proto-galaxies reionising the universe
Paardekooper, Kochfar, Vecchia
Contribution of stars in galaxies to cosmic reionization depends on the SFH in the universe, the abundance of galaxies during reionization, the escape fraction of ionising photons and the clumping factor of the IGM. Compute SFR and clumping factor during reionization in a cosmological volume using a high-res hydrodynamical simulation. Post-process the output with detailed radiative transfer simulations to compute the escape fraction of ionizing photons (self-consistent model). Strong mass and redshift dependence of the escape fraction indicates that reionization occurred between z=15 and 10 and was mainly driven by proto-galaxies forming in DM haloes with masses between 1e7 and 8 Msun. More massive galaxies that are rare at these z and have significantly lower escape fractions contribute less photos to the reionization process than the more-aundant low-mass galaxies. SF in the low-mass haloes is suppressed by radiative feedback from reionization, therefore these proto-galaxies only contribute when the part of the universe they live in is still neutral. After z~10, massive galaxies become more abundant and provide most of the ionising photons. Find: Pop III stars are too short-lived and not frequent enough to have a major contribution to reionisation. Although the stellar component of the proto-galaxies that produce the bulk of ionising photons during reionization is too faint to be detected by the JWST, these sources are brightest in the H-alpha and Ly-alpha recombination lines, which will likely be detected by JWST in deep surveys.
1211.1673
The minimum-mass extrasolar nebula: in-situ formation of close-in super-earths
Chiang, Laughlin
Close-in super-Earths, with radii R=2-5 R_Earth and orbital periods P<100 days, orbit mor ethan half, and perhaps nearly all Sun-like stars in the universe. Use this population to construct the minimum-mass extrasolar nebula, the circumstellar disk of solar-composition solids and gas from which such planets formed (if they formed near theyr current locations and did not migrate).
1211.1695
Properties of gas clumps and gas clumping factor in the intra cluster medium
Vazza, Eckert, Simionescu, Brueggen, Ettori
The spatial distribution of gas inside galaxy clusters is not completely smooth, but may host gas clumps associated with substructures. These overdense gas substructures are generally a source of unresolved bias of X-ray observations towards high density gas, but their bright luminosity peaks may be resolved sources within the ICM, that deep X-ray exposures may be (already) capable to detect. Use simulations to investigate these features. Find: it is difficult to recover the real baryon fraction to better than 10-20% uncertainty. Observing bright X-ray clumps in the nearby universe (z<=0.3). Produce simple mock X-ray observations for several instruments (XMM, Suzaku and ROSAT) and extracted the statistics of potentially detectable bright clumps. Their small projected size makes it difficult to prove their existence based on X-ray morphology only. Preheating, AGN feedback and CR are found to have little impact on the statistical properties of gas clumps.
1211.1713
Pseudobulge formation as a dynamical rather than a secular process
Guedes, Mayer, Carollo, Madau
Bulge formed from what was initially a bar at high z, destroyed by minor mergers at z~3, reformed shortly after, and weakened again following a steady gas inflow at z<1. From the "Eris" galaxy simulation.
1211.1826
Evolution in cluster cores since z~1
Burke, Collins, Stott, Hilton
Large fraction of stellar mass in galaxy clusters is thought to be contained in the diffuse low surface brightness ICL. Being bound to the gravitational potential of the cluster rather than any individual galaxy, the ICL contains much information about the evolution of its host cluster and the interactions between the galaxies within, but difficult to study because of the low SB. First detection and measurement of flux in ICL at z~1. Find that the fraction of the total cluster light contained in ICL may have increase by factors of 2-4 since z~1, in contrast to recent findings for the lack of mass and scale size evolution found for brightest cluster galaxies. Results suggest that late time buildup in cluster cores may occur more through stripping than merging; discuss implications of results for hierarchical simulations.
1211.1889
Constraining the statistics of Population III binaries
Stacy, Bromm
Cosmo simulations of Pop III systems: overall mass function is top-heavy compared to that of MW. Use sink particle to represent each growing protostar, examine the binary characteristics of the multiple systems, resolving down to 20 AU. Find 36% binary fraction, with semi-major axis as large as 3000 AU. Distribution of orbital periods slightly peaked at <900 yr; distribution of mass ratios relatively flat. All sink particles formed within the ten minihaloes, ~50% are lost to mergers with larger sinks, and ~50% of the remaining sinks are ejected from their star-forming disks. The large binary fraction may have important implications for Pop III evolution and nucleosynthesis, as well as the final fate of the first stars.
1211.1669
A deep x-ray view of the hot halo in the edge-on spiral galaxy NGC 891
Hodges-Kluck, Bregman
NGC 891 is similar to MW and has a hot X-ray emitting halo that could arise from accretion, a galactic fountain, or a combination of the two. The metallicity of the gas can help distinguish between these models. Report results from Chandra and XMM-Newton on temperature and metallicity of the hot halo of the galaxy. Find good fits for a thermal model with kT~0.2 keV and Z~0.1 solar, and rule out solar metallicity to >99% confidence. Result suggests accretion from the IGM as the origin of the hot halo. Suggests accretion from IGM as the origin for the hot halo. Also possible to fit a 2-temperature thermal model with solar metallicity with 0.1 keV and 0.25 keV temperatures; the cooling rate in the hot gas cannot explain the massive HI halo in the steady state. A galactic fountain model cannot eject enough mass to account for the HI halo, so speculate that the neutral halo may be bas from a prior outflow that has since cooled.
1211.1670
The first billion years project - IV: proto-galaxies reionising the universe
Paardekooper, Kochfar, Vecchia
Contribution of stars in galaxies to cosmic reionization depends on the SFH in the universe, the abundance of galaxies during reionization, the escape fraction of ionising photons and the clumping factor of the IGM. Compute SFR and clumping factor during reionization in a cosmological volume using a high-res hydrodynamical simulation. Post-process the output with detailed radiative transfer simulations to compute the escape fraction of ionizing photons (self-consistent model). Strong mass and redshift dependence of the escape fraction indicates that reionization occurred between z=15 and 10 and was mainly driven by proto-galaxies forming in DM haloes with masses between 1e7 and 8 Msun. More massive galaxies that are rare at these z and have significantly lower escape fractions contribute less photos to the reionization process than the more-aundant low-mass galaxies. SF in the low-mass haloes is suppressed by radiative feedback from reionization, therefore these proto-galaxies only contribute when the part of the universe they live in is still neutral. After z~10, massive galaxies become more abundant and provide most of the ionising photons. Find: Pop III stars are too short-lived and not frequent enough to have a major contribution to reionisation. Although the stellar component of the proto-galaxies that produce the bulk of ionising photons during reionization is too faint to be detected by the JWST, these sources are brightest in the H-alpha and Ly-alpha recombination lines, which will likely be detected by JWST in deep surveys.
1211.1673
The minimum-mass extrasolar nebula: in-situ formation of close-in super-earths
Chiang, Laughlin
Close-in super-Earths, with radii R=2-5 R_Earth and orbital periods P<100 days, orbit mor ethan half, and perhaps nearly all Sun-like stars in the universe. Use this population to construct the minimum-mass extrasolar nebula, the circumstellar disk of solar-composition solids and gas from which such planets formed (if they formed near theyr current locations and did not migrate).
1211.1695
Properties of gas clumps and gas clumping factor in the intra cluster medium
Vazza, Eckert, Simionescu, Brueggen, Ettori
The spatial distribution of gas inside galaxy clusters is not completely smooth, but may host gas clumps associated with substructures. These overdense gas substructures are generally a source of unresolved bias of X-ray observations towards high density gas, but their bright luminosity peaks may be resolved sources within the ICM, that deep X-ray exposures may be (already) capable to detect. Use simulations to investigate these features. Find: it is difficult to recover the real baryon fraction to better than 10-20% uncertainty. Observing bright X-ray clumps in the nearby universe (z<=0.3). Produce simple mock X-ray observations for several instruments (XMM, Suzaku and ROSAT) and extracted the statistics of potentially detectable bright clumps. Their small projected size makes it difficult to prove their existence based on X-ray morphology only. Preheating, AGN feedback and CR are found to have little impact on the statistical properties of gas clumps.
1211.1713
Pseudobulge formation as a dynamical rather than a secular process
Guedes, Mayer, Carollo, Madau
Bulge formed from what was initially a bar at high z, destroyed by minor mergers at z~3, reformed shortly after, and weakened again following a steady gas inflow at z<1. From the "Eris" galaxy simulation.
1211.1826
Evolution in cluster cores since z~1
Burke, Collins, Stott, Hilton
Large fraction of stellar mass in galaxy clusters is thought to be contained in the diffuse low surface brightness ICL. Being bound to the gravitational potential of the cluster rather than any individual galaxy, the ICL contains much information about the evolution of its host cluster and the interactions between the galaxies within, but difficult to study because of the low SB. First detection and measurement of flux in ICL at z~1. Find that the fraction of the total cluster light contained in ICL may have increase by factors of 2-4 since z~1, in contrast to recent findings for the lack of mass and scale size evolution found for brightest cluster galaxies. Results suggest that late time buildup in cluster cores may occur more through stripping than merging; discuss implications of results for hierarchical simulations.
1211.1889
Constraining the statistics of Population III binaries
Stacy, Bromm
Cosmo simulations of Pop III systems: overall mass function is top-heavy compared to that of MW. Use sink particle to represent each growing protostar, examine the binary characteristics of the multiple systems, resolving down to 20 AU. Find 36% binary fraction, with semi-major axis as large as 3000 AU. Distribution of orbital periods slightly peaked at <900 yr; distribution of mass ratios relatively flat. All sink particles formed within the ten minihaloes, ~50% are lost to mergers with larger sinks, and ~50% of the remaining sinks are ejected from their star-forming disks. The large binary fraction may have important implications for Pop III evolution and nucleosynthesis, as well as the final fate of the first stars.
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