Monday.
1502.03820
A clear age-velocity dispersion correlation in Andromeda's stellar disk
Dorman, ... Dalcanton, et al
The stellar kinematics of galactic disks are key to constraining disk formation and evolution processes. Measure (for the first time) the stellar age-velocity dispersion correlation in the inner 20 kpc (3.5 disk scale lengths) of M31 and show that it is dramatically different from that in the MW. Use optical Hubble ACS photometry of 5800 individual stars from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and Keck/DEIMOS radial velocity measurements of the same stars from the SPLASH survey. Show that the average line-of-sight velocity dispersion is a steadily increasing function of stellar age exterior to R=10kpc, increasing from 30 km/s for the young upper MS stars to 90 km/s for the old red giant branch stars. This monotonic increase implies that a continuous or recurring process contributed to the evolution of the disk. Both the slope and normalization of the dispersion vs. age relation are significantly larger than in the MW, allowing for the possibility that the disk of M31 has had a more violent history than the disk of the MW, more in line with cosmological predictions. Also find evidence for an inhomogeneous distribution of stars from a second kinematical component in addition to the dominant disk component. One of the largest and hottest high-dispersion patches is present in all age bins, and may be the signature of the end of the long bar.
1502.03821
Evidence for DM in the inner Milky Way
Iocco, Pato, Bertone
The ubiquitous presence of DM in the universe is today a central tenet in modern cosmology and astrophysics. Ranging from the smallest galaxies to the observable universe, the evidence for DM is compelling in dwarfs, spirals, galaxy clusters, as well as at cosmological scales. However, it has been historically difficult to pin down the DM contribution to the total mass density of the MW, particularly in the innermost regions of the Galaxy and in the solar neighborhood. Present an up-to-date compilation of MW rotation curve measurements, and compare it with state-of-the-art baryonic mass distribution models. Show that current data strongly disfavor baryons as the sole contribution to the galactic mass budget, even inside the solar circle. These findings demonstrate the existence of DM in the inner Galaxy while making no assumptions on its distribution. Anticipate that this result will compel new model-independent constraints on the DM local density and profile, thus reducing uncertainties on direct and indirect DM searches, and will shed new light on the structure and evolution of the Galaxy.
1502.03887
The impact of strong gravitational lensing on observed Lyman-break galaxy numbers at 4<z<8 in the GOODS and the XDF blank fields
Barone-Nugent, ... Treu, Oesch, et al
Detection of LBGs at high-z can be affected by GL induced by FG deflectors not only in galaxy clusters, but also in blank fields. Quantify the impact of strong magnification in the samples of B,V,i,z,&Y LBGs (4<z<8) observed in the XDF and GOODS/CANDELS fields, by investigating the proximity of dropouts to FG objects. Find that ~6% of bright LBGs (m_H160<26) at z~7 have been strongly lensed (mu>2) by FG objects. This fraction decreases from ~3.5% at z~6 to ~1.5% at z~4. Since the observed fraction of strongly lensed galaxies is a function of the shape of the LF, it can be used to derive Schechter parameters, alpha and M*, independently from galaxy number counts. The magnification bias analysis yields Shcechter-function parameters in close agreement with those determined from galaxy counts albeit with larger uncertainties. Extrapolation of the analysis to z>8 suggest that future surveys with JSWT, WFIRST and EUCLID should find excess LBGs at the bright-end, even if there is an intrinsic exponential cutoff of number counts. Finally, highlight how the magnification bias measurement near the detection limit can be used as probe of the population of galaxies too faint to be detected. Preliminary results using this novel idea suggest that the magnification bias at M_UV~-18 is not as strong as expected if alpha<-1.7 extends well below the current detection limits in the XDF. At face value this implies a flattening of the LF at M_UV-16.5. However, selection effects and completeness estimates are difficult to quantify precisely. Thus, no ruling out a steep LF extending to M_UV>-15.
1502.03972
Combining spectroscopic and photometric surveys using angular cross-correlations II: parameter constraints from different physical effects
Eriksen, Gaztanaga
In the previous paper, studied the effects of RSD, BAO and WL using angular cross-correlation. Provide a new forecast that explores the contribution in including different observables, physical effects (galaxy bias, WL, RSD, BAO) and approximations (non-linearities, Limber approximation, covariance between probes). The radial information is included by using the cross-correlation of separate narrow redshift bins. For the auto correlation the separation of galaxy pairs is mostly transverse, while the cross-correlations also includes a radial component. Study how this information adds to the FoM, which includes the DE EoS w(z) and the growth history, parameterized by gamma. Show that the Limber approximation and galaxy bias are the most critical ingredients to the modelling of correlations. Adding WL increases the FoM by 4.8, RSD by 2.1 and BAO by 1.3. Also explore how overlapping surveys perform under the different assumption and for different FoM. Qualitative conclusions depend on the survey choices and scales included, but find some clear tendencies that highlight the importance of combining different probes and can be used to guid and optimism survey strategies.
1502.03994
Cnostraints on a scale-depedent bias from galaxy clustering
Amendola, ... Branchini
Forecast the future constraints on scale-dependent parameterizations of galaxy bias and their impact on the estimate of cosmo params from the PS of galaxies measured in a spectroscopic redshift survey. For the latter, assume a wide survey at relatively large z, similar to the planned Euclid survey, as baseline for future experiments. To assess the impact of the bias, perform a Fisher matrix analysis and adopt two different parameterizations of scale-dependent bias. The fiducial model for galaxy bias are calibrated using a mock catalogs of Ha emitting galaxies mimicking the expected properties of the objects that will be targeted by the Euclid survey. In the analysis, obtained 2 main results: (1) allowing for a scale-dependent bias does not significantly increase the errors on the other cosmo params apart from the RMS amplitude of density fluctuations, sigma_8 and the growth index gamma, whose uncertainties increase by a factor up to two, depending on the bias model adopted. (2) find that the accuracy in the linear bias parameter b_0 can be estimated to within 1-2% at various z regardless of the fiducial model. The NL bias parameters have significantly large errors that depend on the model adopted. Despite this, in the more realistic scenarios departs from the simple linear bias prescription can be detected with a ~2 sigma significance at each z explored.
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