Monday. Wrote to Yookyung last night, to Aaron this morning.
1201.5640
On the magnetic flux problem in star formation
Braithwaite
Strong magnetic fields play a crucial role in the removal of angular momentum from collapsing clouds and protostellar discs, and are necessary for the formation of disc winds as well as jets from the inner disc. Strong large-scale poloidal magnetic fields are observed in protostellar discs at all radii down to ~10 Rsun. But by the time the star is visible virtually all of the original magnetic flux has vanished. Explore mechanisms for removing this flux during the formation of the protostar once it is magnetically disconnected from the parent cloud, looking at both radiative and convective protostars. Includes numerical investigation of buoyant magnetic field removal from convective stars. Find: if the star goes through a fully convective phase, all remaining flux can easily be removed from the protostar, essentially on an Alfven timescale. On the other hand if the protostar has no fully convective phase then some flux can be retained, the quantity depending on the net magnetic helicity, which is probably small. Only some fraction of the flux is visible at the stellar surface. Look at how the same mechanisms could prevent flux from accreting onto the star, meaning that mass would only accrete as fast as it is able to slip past the flux.
1201.5641
Absorption signatures of warm-hot gas at low redshift: Broad Lya absorbers
Tepper-Garcia, Richter, Schaye, Booth, Vecchia, Theuns
Investigate the physical state of HI absorbing gas at low z (~0.25) using hydrosims, focusing on broad (>40km/s) Lya absorbers (BLAs), believed to originate in shock-heated gas in the Warm-Hot Intergalactic medium (WHIM). The fiducial model, which includes radiative cooling by heaving elements and feedback by SNe and AGN, predicts that by z=0.25 nearly 60% of the gas mass ends up at densities and temperatures characteristic of the WHIM and find that half of this fraction is due to outflows. The standard HI observables (distribution of HI column densities N_HI, distribution of Doppler parameters b_HI, b_HI-NHI correlation) and the BLA line number density predicted by simulations are in good agreement with observations. BLAs arase in gas that is hotter, more highly ionised and more enriched than the gas giving rise to typical Lya forest absorbers. Although the majority of the BLAs arise in warm-hot (log(T/K)~5) gas at low (log Delta < 1.5) densities, their line width correlates only weakly with the gas temperature, and is thus a poor indicator of the thermal state of the gas. Detectable BLAs account for only a small fraction of the true baryon content of the WHIM at low redshift. In order to detect the bulk of the mass in this gas phase, a sensitivity at least one order magnitude better than achieved by current UV spectrographs is required. Argue that BLAs mostly trace gas that has been shock-heated and enriched by outflows and that they therefore provide an important window on a poorly understood feedback process.
1201.5642
On the detection of ionizing radiation arising from SF galaxies at z~3-4: looking for analogs for "Stellar Reionizers"
Vanzella, ... Grogin, Koekemoer, Newman, et al
Use spatially resolved, multi-band photometry in the GOODS-S field to constrain the nature of candidate Lyman continuum (LyC) emitters at redshift z~3.7 identified using imaging below the Lyman limit. In 18 candidates, the light centroid of the candidate LyC emission is offset from that of the LBG by up to 1.5". Fit the SED of the LyC candidates to spectral populations synthesis models to measure photo-z and stellar population parameters. Also discuss the differences in the UV colors between the LBG and the LyC candidates, and how to estimate the escape fraction of ionizing radiation (f_esc) in cases, where the lyC emission is spatially offset from the host galaxy. In all but one case, conclude that the candidate LyC emission is most likely due to lower redshift interlopers. Argue that the majority of similar measurements reported in the literature need further investigation before it can be firmly concluded that LyC emission is detected. Only a single surviving LyC candidate is a LBG at z=3.795, which shows the bluest (B-V) color among LBGs at similar redshift, a stellar mass of 2e9 Msun, weak interstellar absorption lines and a flat UV spectral slope with no Lya in emission. Estimate f_esc in the range 25-100%, depending on the dust and intergalactic attenuation.
1201.5644
First cosmological constraints on the proton-to-electron mass ratio from observations of rotational transitions of methanol
Ellingsen, Voronkov, Breen, Lovell
Used Australia telescope compact array to measure the absorption from the 12.2 GHz transition of methanol towards the z=0.89 lensing galaxy in the PKS B 1830-211 gravitational lens system. Comparison of the velocity of the main absorption feature with the published absorption spectrum from the (different) transition of methanol shows that they differ by -0.6 pm 1.6 km/s. Can use these observations to constrain the changes in the proton-to-electron mass ration from z=0.89 to present to 0.8pm2.1e-7. This result is consistent, and of similar precision to recent observations at z=0.68 achieved through comparison of a variety of rotational and inversion transitions, and approximately a factor of 2 better than previous constraints obtained in this source. Future observations that incorporate additional rotational methanol transitions can improve results by factor of 5-10.
1201.5662
Temperature structure and mass-temperature scatter in galaxy clusters
Ventimiglia, Voit, Rasia
The T_HBR (the ratio of hardband to broadband spectral-fit temperatures) is a substructure indicator, that is found to be modestly correlated to the scatter in the M-T_X relation.
1201.5697
"Evaporation" of a flavor-mixed particle from a gravitational potential
Medvedev
Demonstrate that a stable particle with flavor mixing, confined in a gravitational potential can gradually and irreversibly escape ("evaporate") from it. Effect due to mass eigenstate conversions which occur in interactions (scattering) of mass states with other particles even when the energy exchange between them is vanishing. The evaporation and conversion are quantum effects not related to flavor oscillations, particle decay, quantum tunneling or other well-known processes. These effects should have implications for cosmology: (1) cosmic neutrino background distortion and (2) softening of central cusps in DM haloes and smearing out or destruction of dwarf haloes.
1201.5742
Expected constraints on the galactic magnetic field using PLANCK data
Fauvet et al
Simulation shows that PLANCK should be able to recover the main properties of the Galactic magnetic field. An accurate reconstruction of the matter distribution would require an improved modelling of the ISM and the usage of extra data sets such as the rotation measurements of pulsars [???].
1201.5746
The cluster and large scale environments of quasars at z<0.9
Harris
Thesis: to study (1) the large scale environment over a large z range (2) the evolution as well as any change in environment with quasar luminosity and z, and (3) the orientation of quasar with respect to a galaxy cluster. Deficit of quasars lying close to cluster centers for 0.4<z<0.8 (preference for less dense environments). Position [?] of quasars as a function of absolute quasar magnitude does not change, nor the preferred orientation between the quasar and the cluster major axis for bright or faint quasars. Fe II emission discussed.
1201.5784
How to make an ultra-faint dwarf spheroidal galaxy: tidal stirring of disky dwarfs with shallow DM density profiles
Lokas, Kazantzidis, Mayer
Use n-body sims, reproduce tidal interactions between MW-sized host galaxies and rotationally supported dwarfs embedded in 1e9 Msun DM haloes. UFDs can be produced via the tidal stirring of disky dwarfs on relatively tight orbits, consistent with a redshift of accretion by the host galaxy of z~1, and with intermediate values for the halo inner density slopes. The inferred slopes in agreement other sims. Similarities in basic observational parameters. Tidal stirring of rotationally supported dwarfs is a viable mechanism for the formation of UFDs in the LG environment.
1201.5785
Do stellar winds play a decisive role in feeding AGN?
Davies, Burtscher, Dodds-Eden, de Xivry
Existence of starburst-AGN connection is undisputed, but no consensus on what the connection is. Begin by noting that mechanisms that drive gas inwards in disk galaxies are generally inefficient at removing angular momentum, leading to stalled inflows. Thus, a tiered series of such processes is required to bring gas to the smallest scales, each of which on its own may not correlate with the presence of an AGN. Similarly, each may be associated with a starburst event, making it important to discriminate between 'circumnuclear' and 'nuclear' star formation. Show that stellar feedback on scales of tens of parsecs plays a critical role in first hindering and then helping accretion. Argue: only after the initial turbulent phases of a starburst that gas from slow stellar winds can accrete efficiently to smaller scales. Implies that the properties of the obscuring torus are directly coupled to SF and that the torus must be a complex dynamical entity.
1201.5794
Connecting the cosmic web to the spin of dark haloes: implications for galaxy formation
Codis, Pichon, Devriendt, Slyz, Pogosyan, Dubois, Sousbie
Detect clear mass transition: the spin of DM haloes above a critical mass tends to be perpendicular to the closest filament, and aligned with the intermediate axis of the tidal tensor, whereas the spin of low-mass haloes is more likely to be aligned with the closest filament. The critical mass of 5e12 (Msun) is redshift dependent and scales as (1+z)^-2.5. Interpretation in terms of large-scale cosmic flows: most low-mass haloes are formed through the winding of flows embedded in misaligned walls; they acquire a spin parallel to the axis of the resulting filaments forming at the intersection of these walls. On the other hand, more massive haloes are typically the products of later mergers along such filaments, and thus acquire a spin perpendicular to this direction when their orbital angular momentum is converted into spin. Show that this scenario is consistent with both the measured excess probabilities of alignment wrt the eigen-directions of the tidal tensor, and halo merger histories. On a more qualitative level, it also seems compatible with 3d visualization of the structure of the cosmic web as traced by "smoothed" DM simulations or gas tracer particles. Provides extra support to the disk forming paradigm by Pichon+2011, as it extends it by characterizing the geometry of secondary infall at high z.
1201.5888
THe evolution of massive black holes and their spins in their galactic hosts
Barausse
Study the mass and spin evolution of massive BHs within a semi-analytical galaxy-formation model that follows the evolution of DM haloes among merger trees, as well as that of the baryonic components (hot gas, stellar and gaseous bulges, and stellar and gaseous galactic disks). Allows us to study the mass and spin evolution of massive black holes in a self-consistent way, by taking into account the effect of the gas present in galactic nuclei both during the accretion phases and during mergers. Also present predictions, as a function of redshift, for the fraction of gas-rich BH mergers, in which the spins prior to the merger are aligned due to the gravito-magnetic torques exerted by the circumbinary disk, as opposed to gas-poor mergers, in which the orientation of the spins before the merger is roughly isotropic. Predictions may be tested with e.g., eLISA.
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