1309.2946
The effect of metal enrichment and galactic winds on galaxy formation in cosmological zoom simulations
Hirschmann ... Genzel, ... et al
Investigate differential effects of metal cooling and galactic stellar winds on the cosmological formation of individual galaxies with three sets of cosmological, hydrodynamical zoom simulations of 45 halos in the mass range 1e11 < M_halo<1e13 Msun. Models including both galactic winds and metal cooling (i) suppress early star formation at z>1 and predict reasonable SFHs, (ii) produce galaxies with high cold gas fractions (30-60%) at high z, (iii) significantly reduce the galaxy formation efficiencies for haloes < 1e12 Msun at all redshifts in agreement with observational and abundance matching constraints, (iv) result in high-redshift galaxies with reduced circular velocities matching the observed Tully-Fisher relation at z~2, and (v) significantly increase the sizes of low-mass galaxies (M*<3e10 Msun) at high z resulting in a weak size evolution - a trend in agreement with observations. However, the low redshift (z<0.5) SFRs of massive galaxies are higher than observed (up to 10x). No tested model predicts the observed size evolution for low-mass and high-mass galaxies simultaneously. Due to the delayed onset of SF in the wind models, the metal enrichment of gas and stars is delayed and agrees well with observational constraints. Metal cooling and stellar winds are both found to increase the ratio of in situ formed to formed to accreted stars - the relative importance of dissipative vs. dissipationless assembly. For halo masses below ~1e12 Msun, this is mainly caused by less stellar accretion and compares well to predictions from semi-analytical models but still differs from abundance matching models. For higher masses, the fraction of in situ stars is over-predicted due to the unrealistically high SFR at low redshifts.
1309.2950
A new method to measure the mass of galaxy clusters
Falco et al
Standard methods rely on various assumptions about the shape or the level of equilibrium of the cluster. Present a novel method of measuring cluster masses; complementary to most of the other methods, since it only uses kinematcial information from outside the virialized cluster. This method identifies objects, as galaxy sheets or filaments, in the cluster outer region, and infers the cluster mass by modeling how the massive cluster perturbs the motion of the structures from the Hubble flow. At the same time, this technique allows to constrain the 3-d orientation of the detected structures with a good accuracy. Use a cosmological numerical simulation to test the method. Apply the method to the Coma cluster, where 2 galaxy sheets are found, and the mass of the Coma is measured to be M_vir=9.2pm2.4e14 Msun in good agreement with previous measurements obtained with the standard methods.
1309.2954
Characterizing unknown systematics in large scale structure surveys
Agarwal, Ho, Meyers, Seo, Ross, .. Eisenstein, Muna, ... et al
Photometric LSS probe the largest volumes in the Universe, but are inevitably limited by systematic uncertainties. Imperfect photometric calibration leads to biases in measurements of the density fields of LSS tracers such as galaxies and quasars, and result in cosmological parameter estimation. Earlier studies have proposed using cross-correlations between different z slices or cross-correlations between different surveys to reduce the effects of such systematics. In this paper, develop a method to characterize unknown systematics. Demonstrate that while there is insufficient information to correct for unknown systematics in the data, can obtain an estimate of their magnitude. Define a parameter to estimate contamination from unknown systematics using cross-correlations between different redshifts slices and propose discarding bins in the angular PS that lie outside a certain contamination tolerance level. Show that this method improves estimates of the bias using simulated data and further apply it to photometric luminous red galaxies in SDSS as a case study.
1309.3053
The masses of local group dwarf spheroidal galaxies: not too small after all?
Collins, et al
A singular dSph halo mass profile derived from dSphs around the MW doesn't seem to apply to the 25 Andromeda dSphs: a profile with lower maximum circular velocity, and hence mass, is preferred for dSphs for the Galaxy. 3 outliers of And (XIX, XXI and XXV) have large half-light radii (>060 pc) and low velocity dispersions (sigma_v<5 km/s); likely caused by tidal interactions from the host galaxy. Also discuss the masses of all Local Group dSphs in the context of the 'too big to fail problem', and conclude that these are potentially reconcilable with theoretical predictions when the full scope of baryonic physics and observational uncertainties are taken into account.
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