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Register a new userThe masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data
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Added by
Crist\\'obal Sif\\'on
Publication date
2015
fields
Physics
and research's language is
English
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We use the first 100 sq. deg. of overlap between the Kilo-Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey to determine the galaxy halo mass of ~10,000 spectroscopically-confirmed satellite galaxies in massive ($M > 10^{13}h^{-1}{rm M}_odot$) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro-Frenk-White (NFW) density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses $log M_{rm sub} /(h^{-1}{rm M}_odot) approx 11.7 - 12.2$ consistent across group-centric distance within the errorbars. Given their typical stellar masses, $log M_{rm star,sat}/(h^{-2}{rm M}_odot) sim 10.5$, such total masses imply stellar mass fractions of $M_{rm star,sat} /M_{rm sub} approx 0.04 h^{-1}$ . The average subhalo hosting these satellite galaxies has a mass $M_{rm sub} sim 0.015M_{rm host}$ independent of host halo mass, in broad agreement with the expectations of structure formation in a $Lambda$CDM universe.
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We constrain the average halo ellipticity of ~2 600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modeling the signal with an elliptical Navarro-Frenk-White (NFW) profile on scales < 250 kpc, which roughly corresponds to half the virial radius, and assuming that the BCG is perfectly aligned with the dark matter, we find an average halo ellipticity of e_h=0.38 +/- 0.12. This agrees well with results from cold-dark-matter-only simulations, which typically report values of e_h ~ 0.3. On larger scales, the lensing signal around the BCGs does not trace the dark matter distribution well, and the distribution of group satellites provides a better proxy for the halos orientation instead, leading to a 3--4 sigma detection of a non-zero halo ellipticity at scales between 250 kpc and 750 kpc. Our results suggest that the distribution of stars enclosed within a certain radius forms a good proxy for the orientation of the dark matter within that radius, which has also been observed in hydrodynamical simulations.
We study the stellar-to-halo mass relation of central galaxies in the range 9.7<log_10(M_*/h^-2 M_sun)<11.7 and z<0.4, obtained from a combined analysis of the Kilo Degree Survey (KiDS) and the Galaxy And Mass Assembly (GAMA) survey. We use ~100 deg^2 of KiDS data to study the lensing signal around galaxies for which spectroscopic redshifts and stellar masses were determined by GAMA. We show that lensing alone results in poor constraints on the stellar-to-halo mass relation due to a degeneracy between the satellite fraction and the halo mass, which is lifted when we simultaneously fit the stellar mass function. At M_sun>5x10^10 h^-2 M_sun, the stellar mass increases with halo mass as ~M_h^0.25. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8x10^11 h^-1 M_sun with a value of M_h/M_*=56_-10^+16 [h]. We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues.
We present predictions for the galaxy-galaxy lensing profile from the EAGLE hydrodynamical cosmological simulation at redshift z=0.18, in the spatial range 0.02 < R/(Mpc/h) < 2, and for five logarithmically equi-spaced stellar mass bins in the range 10.3 < $log_{10}$(Mstar/ $M_{odot}$) < 11.8. We compare these excess surface density profiles to the observed signal from background galaxies imaged by the Kilo Degree Survey around spectroscopically confirmed foreground galaxies from the GAMA survey. Exploiting the GAMA galaxy group catalogue, the profiles of central and satellite galaxies are computed separately for groups with at least five members to minimise contamination. EAGLE predictions are in broad agreement with the observed profiles for both central and satellite galaxies, although the signal is underestimated at R$approx$0.5-2 Mpc/h for the highest stellar mass bins. When central and satellite galaxies are considered simultaneously, agreement is found only when the selection function of lens galaxies is taken into account in detail. Specifically, in the case of GAMA galaxies, it is crucial to account for the variation of the fraction of satellite galaxies in bins of stellar mass induced by the flux-limited nature of the survey. We report the inferred stellar-to-halo mass relation and we find good agreement with recent published results. We note how the precision of the galaxy-galaxy lensing profiles in the simulation holds the potential to constrain fine-grained aspects of the galaxy-dark matter connection.
We investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the GAMA survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric KiDS survey. We use GAMA groups with an apparent richness larger than 4 to identify samples with comparable mean host halo masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes. We measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of $0.85^{+0.37}_{-0.25}$, which is consistent with the $Lambda$CDM prediction. Our galaxy groups have typical masses of $10^{13} M_{odot}/h$, naturally complementing previous studies of halo assembly bias on galaxy cluster scales.
We utilize the galaxy shape catalogue from the first-year data release of the Subaru Hyper Suprime-cam Survey (HSC) to study the dark matter content of galaxy groups in the Universe using weak gravitational lensing. As our lens sample, we use galaxy groups that have been spectroscopically selected from the Galaxy Mass and Assembly galaxy survey in approximately 100 sq. degrees of the sky that overlap with the HSC survey. We restrict our analysis to the 1587 groups with at least five group members. We divide these galaxy groups into six bins each of galaxy group luminosity and group member velocity dispersion and measure the coherent tangential ellipticity pattern on background HSC galaxies imprinted by weak gravitational lensing. We measure the weak lensing signal with a signal-to-noise ratio of 55 and 51 for these two different selections, respectively. We use a Bayesian halo model framework to infer the halo mass distribution of our galaxy groups binned in the two different observable properties and obtain constraints on the power-law scaling relation between mean halo masses and the two group observable properties. We obtain a 5 percent constraint on the amplitude of the scaling relation between halo mass and group luminosity with $langle Mrangle = (0.81pm0.04)times10^{14}h^{-1}M_odot$ for $L_{rm grp}=10^{11.5}h^{-2}L_odot$, and a power-law index of $alpha=1.01pm0.07$. We also obtain a 5-percent constraint on the amplitude of the scaling relation between halo mass and velocity dispersion with $langle Mrangle=(0.93pm0.05)times10^{14}h^{-1}M_odot$ for $sigma=500{,rm kms}^{-1}$ and a power-law index $alpha=1.52pm0.10$, although these scaling relations are sensitive to the exact cuts applied to the number of group members. Comparisons with similar scaling relations from the literature indicate that our results are consistent, but have significantly reduced errors.
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