1202.1524
Comparison of convective overshooting models and their impact on abundances from integrated light spectroscopy of young (<3 Gyr) star clusters
Colucci, Bernstein
* convective overshoot: convection carrying material beyond an unstable region of the atmosphere into a stratified, stable region. Overshoot is caused by momentum of the convecting material, which carries the material beyond the unstable region. E.g., in the sun, the innermost part has heat of nuclear fusion carried outward by radiation, and by comvective circulation in the outer zone, but cool sinking material from the surface penetrates farther into the radiative zone than theory would suggest. This affects the heat transfer rate and the temperature of the solar interior which can be indirectly measured by helioseismology. The layer between the Sun's convective and radiative zone is called tachocline.
A ongoing program tot measure detailed chemical abundances in nearby galaxies. Use a sample of young to intermediate age clusters in the LMC with ages 10 Myr to 2 Gyr to evaluate the effect of isochrone parameters, specifically core convective overshooting, on Fe abundance results from high resolution, integrated light spectroscopy. Obtain fiducial Fe abundances from high resolution spectroscopy of the cluster individual member stars. Compare the Fe abundance results for the individual stars to the results for individual stars to the results from isochrones to determine whether isochrons with convective overshooting should be used in the integrated light analysis. Find that when using the isocrhones from the Teramo group, obtain more accurate results for young and intermediate age clusters over the entire age range when using isochrons without convective overshooting. While convective overshooting is not the only uncertain aspect of stellar evolution, it is one of the most readily parameterized ingredients in stellar evolution models, and thus important to evaluate for the specific models used in out integrated light analysis. This work demonstrates that this method for integrated light spectroscopy of star clusters can provide unique tests for future constraints on stellar evolution models of young and intermediate age clusters.
1202.1527
Effects of baryon mass loss on profiles of large galactic DM haloes
Ragone-Figueroa, Granato, Abadi
Assess effect of baryon mass loss on the inner structure of large galactic DM haloes; mass expulsion intended to mimic both the SNe and AGN feedback, as well as stellar pops. Study the AGN feedback in precursors of massive Early type galaxies (ETGs) which have been proposed to remove on a short timescale (few dynaimcal times) a substantial fraction of their baryons. In previous paper, evaluate the observational consequences of this process on galactic structure. Focus on the distribution of DM in the galactic region. Show that the inner region of the DM halo expands and its density profile flattens by a sizeable amount, with little dependence on the expulsion timescale. Evaluate the effect of the commonly made approximation of treating the baryonic component as a potential that changes in intensity without any variation in shape. This approximation leads to some underestimates of the halo expansion and its slope flattening. Conclude that cuspy density profiles ins ETGs could be difficult to reconcile with an effective AGN (or stellar) feedback during the evolution of these systems.
1202.1645
The Chandra view of the largest quasar lens SDSS J1029+2623
Ota, Oguri, Dai, Kochanek, Richards, Ofek, Blandford, Schrabback, Inada
Chandra observations of z_l=0.58 cluster lens: lensed quasar has the largest separation known. Clearly detect the x-ray emission both from the lensing cluster and the 3 lensed quasar images. Cluster temp kT=8.1 keV and luminosity L_X=9.6e44 erg/s. E-W elongation, NW subpeak (ongoing merger?). Xray mass appears to be consistent with EInstein radius of the system. Find significant absorption in the soft X-ray spectrum of quasar image C, which can be caused by an intervening material at either the lens or the source redshift. The x-ray flux ratios between the quasar images after correcting for absorption are in reasonable agreement with those at optical and radio wavelengths. This implies that microlensing effect is not significant for this system and DM substructure is mainly responsible for the anomalous flux ratios.
1202.1527
Effects of baryon mass loss on profiles of large galactic DM haloes
Ragone-Figueroa, Granato, Abadi
Assess effect of baryon mass loss on the inner structure of large galactic DM haloes; mass expulsion intended to mimic both the SNe and AGN feedback, as well as stellar pops. Study the AGN feedback in precursors of massive Early type galaxies (ETGs) which have been proposed to remove on a short timescale (few dynaimcal times) a substantial fraction of their baryons. In previous paper, evaluate the observational consequences of this process on galactic structure. Focus on the distribution of DM in the galactic region. Show that the inner region of the DM halo expands and its density profile flattens by a sizeable amount, with little dependence on the expulsion timescale. Evaluate the effect of the commonly made approximation of treating the baryonic component as a potential that changes in intensity without any variation in shape. This approximation leads to some underestimates of the halo expansion and its slope flattening. Conclude that cuspy density profiles ins ETGs could be difficult to reconcile with an effective AGN (or stellar) feedback during the evolution of these systems.
1202.1645
The Chandra view of the largest quasar lens SDSS J1029+2623
Ota, Oguri, Dai, Kochanek, Richards, Ofek, Blandford, Schrabback, Inada
Chandra observations of z_l=0.58 cluster lens: lensed quasar has the largest separation known. Clearly detect the x-ray emission both from the lensing cluster and the 3 lensed quasar images. Cluster temp kT=8.1 keV and luminosity L_X=9.6e44 erg/s. E-W elongation, NW subpeak (ongoing merger?). Xray mass appears to be consistent with EInstein radius of the system. Find significant absorption in the soft X-ray spectrum of quasar image C, which can be caused by an intervening material at either the lens or the source redshift. The x-ray flux ratios between the quasar images after correcting for absorption are in reasonable agreement with those at optical and radio wavelengths. This implies that microlensing effect is not significant for this system and DM substructure is mainly responsible for the anomalous flux ratios.
1202.1650
Inverse depolarizaton: a potential probe of internal faraday rotation and helical magnetic fields in extragalactic radio jets
Homan
* Faraday rotation: Interaction between light and magnetic field in a medium. Faraday effect causes a rotation of the plane of polarization which is linearly proportional to the component of the magnetic field in the direction of propagation.
* In interstellar medium: caused by free electrons, can be characterized as a difference in the refractive index seen by the two circularly polarized propagation modes. Hence, in contrast to the Faraday effect in solids or liquids, interstellar Faraday rotation has a simple dependence on the wavelength of light: beta (angle of rotation) = RM\lambda^2. RM depends on the number density of electrons n_e and the interstellar magnetic field B.
Recent observations: increasing fractional linear polarization with increasing wavelength in a small number of optically thin jet features ("inverse depolarization". Present a physical model that can explain this effect. Model: structural inhomogeneities in the jet magnetic field create cancellation of polarization along the LoS. Internal Faraday rotation, which increases like wavelength squared, acts to align the polarization from the far and near sides of the jet, leading to increased polarization at longer wavelengths. ...
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