Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userProbing Galaxy Dark Matter Haloes in COSMOS with Weak Lensing Flexion
216
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Current theories of structure formation predict specific density profiles of galaxy dark matter haloes, and with weak gravitational lensing we can probe these profiles on several scales. On small scales, higher-order shape distortions known as flexion add significant detail to the weak lensing measurements. We present here the first detection of a galaxy-galaxy flexion signal in space-based data, obtained using a new Shapelets pipeline introduced here. We combine this higher-order lensing signal with shear to constrain the average density profile of the galaxy lenses in the Hubble Space Telescope COSMOS survey. We also show that light from nearby bright objects can significantly affect flexion measurements. After correcting for the influence of lens light, we show that the inclusion of flexion provides tighter constraints on density profiles than does shear alone. Finally we find an average density profile consistent with an isothermal sphere.
rate research
Read More
We study the shapes of galaxy dark matter haloes by measuring the anisotropy of the weak gravitational lensing signal around galaxies in the second Red-sequence Cluster Survey (RCS2). We determine the average shear anisotropy within the virial radius for three lens samples: all galaxies with 19<m_r<21.5, and the `red and `blue samples, whose lensing signals are dominated by massive low-redshift early-type and late-type galaxies, respectively. To study the environmental dependence of the lensing signal, we separate each lens sample into an isolated and clustered part and analyse them separately. We also measure the azimuthal dependence of the distribution of physically associated galaxies around the lens samples. We find that these satellites preferentially reside near the major axis of the lenses, and constrain the angle between the major axis of the lens and the average location of the satellites to <theta>=43.7 deg +/- 0.3 deg for the `all lenses, <theta>=41.7 deg +/- 0.5 deg for the `red lenses and <theta>=42.0 deg +/- 1.4 deg for the `blue lenses. For the `all sample, we find that the anisotropy of the galaxy-mass cross-correlation function <f-f_45>=0.23 +/- 0.12, providing weak support for the view that the average galaxy is embedded in, and preferentially aligned with, a triaxial dark matter halo. Assuming an elliptical Navarro-Frenk-White (NFW) profile, we find that the ratio of the dark matter halo ellipticity and the galaxy ellipticity f_h=e_h/e_g=1.50+1.03-1.01, which for a mean lens ellipticity of 0.25 corresponds to a projected halo ellipticity of e_h=0.38+0.26-0.25 if the halo and the lens are perfectly aligned. For isolated galaxies of the `all sample, the average shear anisotropy increases to <f-f_45>=0.51+0.26-0.25 and f_h=4.73+2.17-2.05, whilst for clustered galaxies the signal is consistent with zero. (abridged)
Cosmological simulations predict that galaxies are embedded into triaxial dark matter haloes, which appear approximately elliptical in projection. Weak gravitational lensing allows us to constrain these halo shapes and thereby test the nature of dark matter. Weak lensing has already provided robust detections of the signature of halo flattening at the mass scales of groups and clusters, whereas results for galaxies have been somewhat inconclusive. Here we combine data from five surveys (NGVSLenS, KiDS/KV450, CFHTLenS, CS82, and RCSLenS) in order to tighten observational constraints on galaxy-scale halo ellipticity for photometrically selected lens samples. We constrain $f_rm{h}$, the average ratio between the aligned component of the halo ellipticity and the ellipticity of the light distribution, finding $f_rm{h}=0.303^{+0.080}_{-0.079}$ for red lenses and $f_rm{h}=0.217^{+0.160}_{-0.159}$ for blue lenses when assuming elliptical NFW density profiles and a linear scaling between halo ellipticity and galaxy ellipticity. Our constraints for red galaxies constitute the currently most significant ($3.8sigma$) systematics-corrected detection of the signature of halo flattening at the mass scale of galaxies. Our results are in good agreement with expectations from the Millennium Simulation that apply the same analysis scheme and incorporate models for galaxy-halo misalignment. Assuming these misalignment models and the analysis assumptions stated above are correct, our measurements imply an average dark matter halo ellipticity for the studied red galaxy samples of $langle|epsilon_rm{h}|rangle=0.174pm 0.046$, where $|epsilon_{h}|=(1-q)/(1+q)$ relates to the ratio $q=b/a$ of the minor and major axes of the projected mass distribution. Similar measurements based on larger upcoming weak lensing data sets can help to calibrate models for intrinsic galaxy alignments. [abridged]
N-body simulations predict that dark matter haloes are described by specific density profiles on both galactic- and cluster-sized scales. Weak gravitational lensing through the measurements of their first and second order properties, shear and flexion, is a powerful observational tool for investigating the true shape of these profiles. One of the three-parameter density profiles recently favoured in the description of dark matter haloes is the Einasto profile. We present exact expressions for the shear and the first and second flexions of Einasto dark matter haloes derived using a Mellin-transform formalism in terms of the Fox H and Meijer G functions, that are valid for general values of the Einasto index. The resulting expressions can be written as series expansions that permit us to investigate the asymptotic behaviour of these quantities. Moreover, we compare the shear and flexion of the Einasto profile with those of different mass profiles including the singular isothermal sphere, the Navarro-Frenk-White profile, and the Sersic profile. We investigate the concentration and index dependences of the Einasto profile, finding that the shear and second flexion could be used to determine the halo concentration, whilst for the Einasto index the shear and first and second flexions may be employed. We also provide simplified expressions for the weak lensing properties and other lensing quantities in terms of the generalized hypergeometric function.
It is of great interest to measure the properties of substructures in dark matter halos at galactic and cluster scales. Here we suggest a method to constrain substructure properties using the variance of weak gravitational flexion in a galaxy-galaxy lensing context. We show the effectiveness of flexion variance in measuring substructures in N-body simulations of dark matter halos, and present the expected galaxy-galaxy lensing signals. We show the insensitivity of the method to the overall galaxy halo mass, and predict the methods signal-to-noise for a space-based all-sky survey, showing that the presence of substructure down to 10^9 M_odot halos can be reliably detected.
We present a study of the relation between dark matter halo mass and the baryonic content of host galaxies, quantified via luminosity and stellar mass. Our investigation uses 154 deg2 of Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) lensing and photometric data, obtained from the CFHT Legacy Survey. We employ a galaxy-galaxy lensing halo model which allows us to constrain the halo mass and the satellite fraction. Our analysis is limited to lenses at redshifts between 0.2 and 0.4. We express the relationship between halo mass and baryonic observable as a power law. For the luminosity-halo mass relation we find a slope of 1.32+/-0.06 and a normalisation of 1.19+0.06-0.07x10^13 h70^-1 Msun for red galaxies, while for blue galaxies the best-fit slope is 1.09+0.20-0.13 and the normalisation is 0.18+0.04-0.05x10^13 h70^-1 Msun. Similarly, we find a best-fit slope of 1.36+0.06-0.07 and a normalisation of 1.43+0.11-0.08x10^13 h70^-1 Msun for the stellar mass-halo mass relation of red galaxies, while for blue galaxies the corresponding values are 0.98+0.08-0.07 and 0.84+0.20-0.16x10^13 h70^-1 Msun. For red lenses, the fraction which are satellites tends to decrease with luminosity and stellar mass, with the sample being nearly all satellites for a stellar mass of 2x10^9 h70^-2 Msun. The satellite fractions are generally close to zero for blue lenses, irrespective of luminosity or stellar mass. This, together with the shallower relation between halo mass and baryonic tracer, is a direct confirmation from galaxy-galaxy lensing that blue galaxies reside in less clustered environments than red galaxies. We also find that the halo model, while matching the lensing signal around red lenses well, is prone to over-predicting the large-scale signal for faint and less massive blue lenses. This could be a further indication that these galaxies tend to be more isolated than assumed. [abridged]
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
