اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOn the Alignment of Galaxies in Clusters
49
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We explore the distribution of position angles (PA) of galaxies in clusters. We selected for study the isolated clusters, since the distribution of the galaxy orientation in clusters with close neighbors could be altered by gravitational influence of the latter. We assume that galaxies are aligned, if their number at one $90^o$ position angle interval is more than twice higher than at the other $90^o$ interval. We study the galaxy PA distribution at the outer regions of clusters with smaller space density, where the probability of the PA variation in the result of interactions between galaxies is smaller than at the dense central regions. We found that the alignment of galaxies is more often observed in poor clusters and concluded that originally galaxies were aligned, but in the result of accretion in time of field galaxies with arbitrary orientations and also due to the mutual interactions the relative number of aligned galaxies decreases.
قيم البحث
اقرأ أيضاً
We show that, provided the principal axes of the second velocity moment tensor of a stellar population are generally unequal and are oriented perpendicular to a set of orthogonal surfaces at each point, then those surfaces must be confocal quadric su
rfaces and the potential must be separable or Stackel. This is true under the mild assumption that the even part of the distribution function is invariant under time reversal $v_i rightarrow -v_i$ of each velocity component. In particular, if the second velocity moment tensor is everywhere exactly aligned in spherical polar coordinates, then the potential must be of Stackel form (excepting degenerate cases where two or more of the semiaxes of ellipsoid are everywhere the same). The theorem also has consequences for alignment in cylindrical polar coordinates, which is used in the popular Jeans Anisotropic Models (JAM). We analyse data on the radial velocities and proper motions of a sample of $sim 7400$ stars in the stellar halo of the Milky Way. We provide the distributions of the tilt angles or misalignments from the spherical polar coordinate systems. We show that in this sample the misalignment is always small (usually within $3^circ$) for radii between 7 and 12 kpc. The velocity anisotropy is very radially biased ($beta approx 0.7$), and almost invariant across the volume in our study. Finally, we construct a triaxial stellar halo in a triaxial NFW dark matter halo using a made-to-measure method. Despite the triaxiality of the potential, the velocity ellipsoid of the stellar halo is nearly spherically aligned within $sim6^circ$ for large regions of space, particularly outside the scale radius of the stellar halo. We conclude that the second velocity moment ellipsoid can be close to spherically aligned for a much wider class of potentials than the strong constraints that arise from exact alignment might suggest.
We investigated the influence of environment on cluster galaxies by examining the alignment of the brightest cluster galaxy (BCG) position angle with respect to the host cluster X-ray position angle. The cluster position angles were measured using hi
gh spatial resolution X-ray data taken from the Chandra ACIS archive, that significantly improved the determination of the cluster shape compared to the conventional method of using optical images. Meanwhile, those of the BCGs were measured using homogeneous dataset composed of high spatial resolution optical images taken with Suprime-Cam mounted on Subaru 8m telescope. We found a strong indication of an alignment between the cluster X-ray emission and optical light from BCGs, while we see no clear direct correlation between the degree of ellipticity of X-ray and optical BCG morphologies, despite the apparent alignment of two elliptical structures. We have also investigated possible dependence of the position angle alignment on the X-ray morphology of the clusters, and no clear trends are found. The fact that no trends are evident regarding frequency or degree of the alignment with respect to X-ray morphology may be consistent with an interpretation as a lack of dependence on the dynamical status of clusters.
We examine the alignment between Brightest Cluster Galaxies (BCGs) and their host clusters in a sample of 7031 clusters with 0.08<z<0.44 found using a matched-filter algorithm and an independent sample of 5744 clusters with 0.1<z<0.3 selected with th
e maxBCG algorithm, both extracted from the Sloan Digital Sky Survey Data Release 6 imaging data. We confirm that BCGs are preferentially aligned with the clusters major axis; clusters with dominant BCGs (>0.65 mag brighter than the mean of the second and third ranked galaxies) show stronger alignment than do clusters with less dominant BCGs at the 4.4 sigma level. Rich clusters show a stronger alignment than do poor clusters at the 2.3 sigma level. Low redshift clusters (z<0.26) show more alignment than do high redshift (z>0.26) clusters, with a difference significant at the 3.0 sigma level. Our results do not depend on the algorithm used to select the cluster sample, suggesting that they are not biased by systematics of either algorithm. The correlation between BCG dominance and cluster alignment may be a consequence of the hierarchical merging process which forms the cluster. The observed redshift evolution may follow from secondary infall at late redshifts.
We explore the dependence of UV upturn colours in early type cluster galaxies on the properties of their parent clusters (such as velocity dispersion and X-ray luminosity) and on the positions and kinematics of galaxies within them. We use a sample o
f 24 nearby clusters with highly complete spectroscopy and optical/infrared data to select a suitable sample of red sequence galaxies, whose FUV and NUV magnitudes we measure from archival GALEX data. Our results show that the UV upturn colour has no dependence on cluster properties and has the same range in all clusters. There is also no dependence on the projected position within clusters or on line-of-sight velocity. Therefore, our conclusion is that the UV upturn phenomenon is an intrinsic feature of cluster early type galaxies, irrespective of their cluster environment.
It has been shown, both in simulations and observationally, that the tidal field of a large galaxy can torque its satellites such that the major axis of satellite galaxies points towards their hosts. This so-called `shape alignment has been observed
in isolated Milky Way-like galaxies but not in `Local Group-like pairs. In this study, we investigate the shape alignment of satellite galaxies in galaxy pairs similar to the Local Group identified in the Sloan Digital Sky Survey Data Release 13 (SDSS DR13). By stacking tens of thousands of satellite galaxies around primary galaxy pairs, we find two statistically strong alignment signals. (1) The major axes of satellite galaxies located in the (projected) area between two primaries (the {it facing} region) tend to be perpendicular to the line connecting the satellite to its host (tangential alignment), while (2) the major axes of satellite galaxies located in regions away from the other host (the {it away} region) tend to be aligned with the line connecting the satellite to its host (radial alignment). These alignments are confirmed at $sim5sigma$ levels. The alignment signal increases with increasing primary brightness, decreasing pair separation, and decreasing satellite distance. The alignment signal is also found to be stronger in filamentary environments. These findings will shed light on understanding the mechanisms of how satellite galaxies are affected by the tidal field in galaxy pairs and will be useful for investigating galaxy intrinsic alignment in the analyses of weak gravitational lensing.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
