1506.03453
A bright year for tidal disruptions?
Metzger, Stone
When a star is tidally disrupted by a SMBH, roughly half of its mass falls back to the BH at super-Eddington rates. Being tenuously gravitationally bound and unable to cool radiatively, only a small fraction f_in<<1 of the returning debris will likely be incorporated into the disk and accrete, with the vast majority instead becoming unbound in an outflow of velocity ~1e4 km/s. This slow outflow spreads laterally, encasing the BH. For months or longer, the outflow remains sufficiently neutral to block hard EUV and X-ray radiation from the hot inner disk, which instead become trapped in a radiation-dominated nebula. Ionizing nebular radiation heats the inner edge of the ejecta to temperatures of T>few 1e4 K, converting the emission to optical/near-UV wavelengths where photons more readily escape due to the lower opacity. This can explain the unexpectedly low and temporally constant effective temperatures of optically-discovered TDE flares. For BHs with relatively high masses M_BH>1e7 Msun the ejecta can become ionized at an earlier stage, or for a wider range of viewing angles, producing a TDE flare which is instead dominated by thermal X-ray emission. Predict total radiated energies consistent with those of observed TDE flares, and ejecta velocities that agree with the measured emission line widths. The peak optical luminosity for M_BH<1e6 Msun is suppressed due to adiabatic losses in the inner disk wind, possibly contributing to the unexpected dearth of optical TDEs in galaxies with low mass BHs. In the classical picture, where f_in~1, TDEs de-spin SMBHs and cap their maximum spins well below theoretical accretion physics limits. This cap is greatly relaxed in the model, and existing Fe K-alpha spin measurements provide suggestive preliminary evidence that f_in<1.
1506.03536
Lensing measurements of the ellipticity of LRG dark matter halos
Clampitt, Jain
Lensing measurements of the shapes of DM haloes can provide tests of gravity theories and possible DM interactions. Measure the quadrupole WL signal from the elliptical halos of 70k SDSS LRGs. Use a new estimator that nulls the spherical halo lensing signal, isolating the shear due to anisotropy in the DM distribution. One of the two Cartesian components of the estimator is insensitive to the primary systematic, a spurious alignment of lens and source ellipticities, allowing to make robust measurements of halo ellipticity. The best-fit value for the ellipticity of the surface mass density is 0.24, which translates to an axis ratio of 0.78. Rule out the hypothesis of no ellipticity at the 4-sigma confidence level, and ellipticity <0.12 (axis ratio > 0.89) at the 2-sigma level. Discuss how the measurement of halo ellipticity are revised to higher values using estimates of the misalignment of mass and light from simulations. Finally, apply the same techniques to a smaller sample of redMaPPer galaxy clusters and obtain a 3-sigma measurement of cluster ellipticity. Discuss how the improved signal to noise properties of the estimator can enable studies of halo shapes for different galaxy populations with upcoming surveys.
1506.03715
Records of sunspot and aurora during CE 960-1279 in the Chinese chronicle of the Song dynasty
Hayakawa, et al
The Songshi chronicle contains a record of continuous observations with well-formatted reports conducted as a policy of the government; a brief comparison of the frequency of observations of sunspots and auroras and the observations of radioisotopes as an indicator of the solar activity during corresponding periods is provided. This paper is the first step of the project in which they survey and compile the records of sunspots and aurora in historical documents from various locations and languages, ultimately providing it to the science community as online data.
1506.03817
Weak-lensing-iferred scaling realtions of galaxy clusters in the RCS2: mass-richness, mass-concentration, mass-bias and more
van Uitert, Gilbank, Hoekstra, Semboloni, Gladders, Yee
Study a sample of ~1e4 galaxy clusters in 0.2<z<0.8 with masses M_200>5e13 Msun/h_70, discovered in RCS2. The depth and excellent image quality of the RCS2 enables detection of the cluster-mass cross-correlation up to z~0.7. To obtain cluster masses, concentrations and halo biases, fit a cluster halo model simultaneously to the lensing signal and to the projected density profile of RCS members, as the latter provides tight constraints on the cluster miscentering distribution. Parameterize the mass-richness relation as M_200=A (N_200/20)^alpha, and find A=(16.7±1.2)e13 Msun/h_70 and alpha=0.73±0.09 at low z (0.2<z<0.35). At intermediate redshift (0.35<z<0.55), find a higher normalization, which points at a fractional increase of the richness towards lower z caused by the build-up of the red-sequence. The miscentering distribution is well constrained. Only ~30% of the BCGs coincide with the peak of the DM distribution. The distribution of the remaining BCGs are modeled with a 2d-Gaussian, whose width increases from 0.2 to 0.4 Mpc/h_70 towards higher masses; the ratio of width and r_200 is constant with mass and has an average value of 0.43±0.01. The mass-concentration and mass-bias relation agree fairly well with literature results at low z, but have a higher normalization at higher redshifts, which may be due to selection and projection effects. The concentration of the satellite distribution decreases with mass and is correlated with the concentration of the halo.
1506.03823
Galaxy clusters and groups in the ALHAMBRA survey
Ascaso, et al
Present a catalogue of 348 galaxy clusters and groups with 0.2<z<1.2 selected in the 2.78 deg^2 ALHAMBRA survey. The high precision of the photometric redshifts, close to 1%, and the wide spread of the seven ALHAMBRA pointing ensure that this catalogue has better mass sensitivity and is less affected by cosmic variance than comparable samples. The detection has been carried out with the Bayesian Cluster Finder (BCF), whose performance has been checked in ALHAMBRA-like light-cone mock catalogues. Great care has been taken to ensure that the observable properties of the mocks photometry accurately correspond to those of real catalogues. From the simulations, expect to detect galaxy clusters and groups with both 70% completeness and purity down to dark matter halo masses of Mh~3e13Msun for z<0.85. Cluster redshifts are expected to be recovered with ~0.6% precision for z<1. Also expect to measure cluster masses with sigma_Mh|M*_CL~0.25-0.35 dex precision down to ~3e13Msun, masses which are 50% smaller than those reached by similar work. Compare these detections with previous optical, spectroscopic and X-rays work, finding an excellent agreement with the rates reported from the simulations. Also explored the overall properties of these detections such as the presence of a color-magnitude relation, the evolution of the photometric blue fraction and the clustering of these sources in the different ALHAMBRA fields. Despite the small numbers, observe tentative evidence that, for a fixed stellar mass, the environment is playing a crucial role at lower redshifts (z<0.5).
1506.03900
The BOSS-WIggleZ overlap region I: Baryon Acoustic Oscillations
Beutler, Blake, Koda, Marin, Seo, Cuesta, Schneider
Study the large-scale clustering of galaxies in the overlap region of the BOSS CMASS sample and the WIggleZ Dark Energy Survey. Calculate the auto-correlation and cross-correlation functions in the overlap region of he two datasets and detect BAO final in each of them. The BAO measurement from the cross-correlation function represents the first such detection between 2 different galaxy surveys. After applying density-field reconstruction, report distance-scale measurements D_V r^fid_s/r_s = (1970±47, 2132±67, 2100±200) Mpc from CMASS, the cross-correlation and WiggleZ, respectively. Use correlated mock realizations to calculate the covariance between the 2 BAO constraints. The distance scales derived from the 2 datasets are consistent, and are also robust against switching the displacement fields used for reconstruction between the 2 surveys. This approach can be used to construct a correlation matrix, permitting for the first time a rigorous combination of WiggleZ and CMASS BAO measurements. Using a volume-scaling technique, the result can also be used to combine WiggleZ and future CMASS DR12 results. Finally, use the cross-correlation function measurements to show that the relative velocity effect, a possible source of systematic uncertainty for the BAO technique is consistent with zero for the samples.
1506.03901
The BOSS-WIggleZ overlap region II: dependence of cosmic growth on galaxy type
Marin, Beutler, Blake, Koda, Kazin, Schneider
The anisotropic galaxy 2PCF allows measurement of the growth of large-scale structures from the effect of peculiar velocities on the clustering pattern. Present new measurements of the auto- and cross-correlation function multipoles of 69180 WiggleZ and 46380 BOSS-CMASS galaxies sharing an overlapping volume of ~0.2 (Gpc/h)^3. Analyzing the RSD of galaxy 2pt statistics for these two galaxy tracers, test for systematic errors in the modeling depending on galaxy type and investigate potential improvements in cosmological constraints. Build a large number of mock galaxy catalogues to examine the limits of different RSD models in terms of fitting scales and galaxy type, and to study the covariance of the measurements when performing joint fits. For the galaxy data, fitting the monopole and quadrupole of the WiggleZ 2PCF on scales 24<s<80 Mpc/h produces a measurement of the normalized growth rate f sigma_8(z=0.54)=0.409±0.059, whereas for the CMASS galaxies find a consistent constraint of f sigma8 (z=0.54)=0.413±0.054, in agreement with the LCDM-GR model of structure growth and with other survey measurements.
No comments:
Post a Comment