1305.5254
The stellar mass growth of brightest cluster galaxies in the IRAC shallow cluster survey
Lin (YT), et al
The details of the stellar mass assembly of BCGs remain an unresolved problem in galaxy formation. Construct a sample of clusters that form an evolutionary sequence, and apply it to the Spitzer IRAC Shallow Cluster Survey (ISCS) to examine the evolution of BCGs in progenitors of present-day clusters with mass of 2.5-4.5e14 Msun. Follow the cluster mass growth history extracted from a high-res cosmo sim, and then use an empirical method that infers the cluster mass based on the ranking of cluster luminosity to select high-z clusters of appropriate mass from ISCS to be progenitors of the given set of z=0 clusters. Find that, between z=1.5 and0 .5, the BCGs have grown in stellar mass by a factor of 2.3, which is well matched by the predictions from a state-of-the-art SAM. Below z=0.5 see hints of differences in behavior between the model and observation.
1305.5256
Non-parameteric method for measuring gas inhomogeneities from X-ray observations of galaxy clusters
Morandi, Nagai, Cui
Non-parametric method to measure inhomogeneities in the ICM from X-ray observations of galaxy clusters. Analyze mock Chandra X-ray observations of simulated clusters; show that new method enables the accurate recovery of the 3D gas density and gas clumping factor profiles out to large radii of galaxy clusters. Then apply this method to observations of Abell 1935 and present the first determination of the gas clumping factor from the X-ray cluster data. Find that the gas clumping factor in Abell 1835 increases with radius and reaches ~2-3 at r=R200. This is in good agreement with the predictions of hydro sims, but it is significantly below the values inferred from recent Suzaku observations. Further show that the radial increasing gas clumping factor causes flattening of the derived entropy profile of the ICM and affects physical interpretation of the cluster gas structure, especially at the large cluster-centric radii. New technique should be used for improving the understanding of the cluster structure and to advance the use of galaxy clusters as cosmological probes, by helping to exploit rich datasets provided by Chandra and XMM-Newton X-ray space telescopes.
1305.5257
Deep LBT/LUCI spectroscopy of a Lyman-alpha emitter candidate at z~7.7
Jiang, ... Egami, et al
A non-detection of Lya emission line of the z~7.7 candidate (brightest among the 4 candidates). Puts a strong constraint on the LF at the bright end.
1305.5265
On the offset of barred galaxies from the black hole M_BH-sigma relationship
Brown et al
Use collisionless N-body sims to determine how the growth of a SMBH influences the nuclear kinematics in both barred and unbarred galaxies. In the presence of a bar, the increase in the velocity dispersion sigma (within the effective radius) due to the growth of an SMBH is on average <=10%, whereas the increase is only ~4% in an unbarred galaxy. In a barred galaxy, the increase results from a combination of three separate factors: (a) orientation and inclination effects, (b) angular momentum transport by the bar that results in an increase in the central mass density, (c) an increase in the vertical and radial velocity anisotropy of stars in the vicinity of the SMBH. In contrast the growth of the SMBH in an unbarred galaxy causes the velocity distribution in the inner part of the nucleus to become less radially anisotropic. Argue that using an axisymmetric stellar dynamical modeling code to measure SMBH masses in barred galaxies could result in a slight overestimate of the derived M_BH. Conclude that the growth of a black hole in the presence of a bar could result in an offset in sigma, perhaps partially accounting for the claimed offset of barred galaxies and pseudo-bulges from the M-BH-sigma relation for unbarred galaxies. If the BH grows significantly in a pre-existing barred galaxy, the resultant secular evolution would alter both the mass and velocity dispersion of the host bulge.
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