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Register a new userA test of Radial Acceleration Relation for the {it Giles et al Chandra} cluster sample
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We carry out a test of the radial acceleration relation (RAR) for a sample of 10 dynamically relaxed and cool-core galaxy clusters imaged by the Chandra X-ray telescope, which was studied in Giles et al. For this sample, we observe that the best-fit RAR shows a very tight residual scatter equal to 0.09 dex. We obtain an acceleration scale of $1.59 times 10^{-9} m/s^2$, which is about an order of magnitude higher than that obtained for galaxies. Furthermore, the best-fit RAR parameters differ from those estimated from some of the previously analyzed cluster samples, which indicates that the acceleration scale found from the RAR could be of an emergent nature, instead of a fundamental universal scale.
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We carry out a test of the radial acceleration relation (RAR) for galaxy clusters from two different catalogs compiled in literature, as an independent cross-check of two recent analyses, which reached opposite conclusions. The datasets we considered include a Chandra sample of 12 clusters and the X-COP sample of 12 clusters. For both the samples, we find that the residual scatter is small (0.11-0.14 dex), although the best-fit values for the Chandra sample have large error bars. Therefore, we argue that at least one of these cluster samples (X-COP) obeys the radial acceleration relation. However, since the best-fit parameters are discrepant with each other as well as the previous estimates, we argue that the RAR is not universal. For both the catalogs, the acceleration scale, which we obtain is about an order of magnitude larger than that obtained for galaxies, and is agreement with both the recent estimates.
The dark matter halo surface density, given by the product of the dark matter core radius ($r_c$) and core density ($rho_c$) has been shown to be a constant for a wide range of isolated galaxy systems. Here, we carry out a test of this {em ansatz} using a sample of 17 relaxed galaxy groups observed using Chandra and XMM-Newton, as an extension of our previous analysis with galaxy clusters. We find that $rho_c propto r_c^{-1.35^{+0.16}_{-0.17}}$, with an intrinsic scatter of about 27.3%, which is about 1.5 times larger than that seen for galaxy clusters. Our results thereby indicate that the surface density is discrepant with respect to scale invariance by about 2$sigma$, and its value is about four times greater than that for galaxies. Therefore, the elevated values of the halo surface density for groups and clusters indicate that the surface density cannot be a universal constant for all dark matter dominated systems. Furthermore, we also implement a test of the radial acceleration relation for this group sample. We find that the residual scatter in the radial acceleration relation is about 0.32 dex and a factor of three larger than that obtained using galaxy clusters. The acceleration scale which we obtain is in-between that seen for galaxies and clusters.
We study the radial acceleration relation (RAR) between the total ($a_{rm tot}$) and baryonic ($a_{rm bary}$) centripetal acceleration profiles of central galaxies in the cold dark matter (CDM) paradigm. We analytically show that the RAR is intimately connected with the physics of the quasi-adiabatic relaxation of dark matter in the presence of baryons in deep potential wells. This cleanly demonstrates how the mean RAR and its scatter emerge in the low-acceleration regime ($10^{-12},{rm m,s}^{-2}lesssim a_{rm bary}lesssim10^{-10},{rm m,s}^{-2}$) from an interplay between baryonic feedback processes and the distribution of CDM in dark halos. Our framework allows us to go further and study both higher and lower accelerations in detail, using analytical approximations and a realistic mock catalog of $sim342,000$ low-redshift central galaxies with $M_rleq-19$. We show that, while the RAR in the baryon-dominated, high-acceleration regime ($a_{rm bary}gtrsim10^{-10},{rm m,s}^{-2}$) is very sensitive to details of the relaxation physics, a simple `baryonification prescription matching the relaxation results of hydrodynamical CDM simulations is remarkably successful in reproducing the observed RAR without any tuning. And in the (currently unobserved) ultra-low-acceleration regime ($a_{rm bary}lesssim 10^{-12},{rm m,s}^{-2}$), the RAR is sensitive to the abundance of diffuse gas in the halo outskirts, with our default model predicting a distinctive break from a simple power-law-like relation for HI-deficient, diffuse gas-rich centrals. Our mocks also show that the RAR provides more robust, testable predictions of the $Lambda$CDM paradigm at galactic scales, with implications for alternative gravity theories, than the baryonic Tully-Fisher relation.
Galaxies covering several orders of magnitude in stellar mass and a variety of Hubble types have been shown to follow the Radial Acceleration Relation (RAR), a relationship between $g_{rm obs}$, the observed circular acceleration of the galaxy, and $g_{rm bar}$, the acceleration due to the total baryonic mass of the galaxy. For accelerations above $10^{10}~{rm m , s}^{-2}$, $g_{rm obs}$ traces $g_{rm bar}$, asymptoting to the 1:1 line. Below this scale, there is a break in the relation such that $rm g_{rm obs} sim g_{rm bar}^{1/2}$. We show that the RAR slope, scatter and the acceleration scale are all natural consequences of the well-known baryonic Tully-Fisher relation (BTFR). We further demonstrate that galaxies with a variety of baryonic and dark matter (DM) profiles and a wide range of dark halo and galaxy properties (well beyond those expected in CDM) lie on the RAR if we simply require that their rotation curves satisfy the BTFR. We explore conditions needed to break this degeneracy: sub-kpc resolved rotation curves inside of cored DM-dominated profiles and/or outside $gg 100,$kpc could lie on BTFR but deviate in the RAR, providing new constraints on DM.
We present the results of work involving a statistically complete sample of 34 galaxy clusters, in the redshift range 0.15$le$z$le$0.3 observed with $Chandra$. We investigate the luminosity-mass ($LM$) relation for the cluster sample, with the masses obtained via a full hydrostatic mass analysis. We utilise a method to fully account for selection biases when modeling the $LM$ relation, and find that the $LM$ relation is significantly different than the relation modelled when not account for selection effects. We find that the luminosity of our clusters is 2.2$pm$0.4 times higher (when accounting for selection effects) than the average for a given mass, its mass is 30% lower than the population average for a given luminosity. Equivalently, using the $LM$ relation measured from this sample without correcting for selection biases would lead to the underestimation by 40% of the average mass of a cluster with a given luminosity. Comparing the hydrostatic masses to mass estimates determined from the $Y_{X}$ parameter, we find that they are entirely consistent, irrespective of the dynamical state of the cluster.
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