# Embedded Spiral Patterns in the Cool Core of the Massive Cluster of Galaxies Abell 1835

## TL;DR

This study reveals spiral patterns in the cool core of galaxy cluster Abell 1835 using Chandra X-ray data, showing temperature differences but pressure equilibrium, indicating a possible off-axis minor merger influence.

## Contribution

First detailed analysis of spiral patterns in Abell 1835's cool core, highlighting their properties and potential merger origin.

## Key findings

- Spiral patterns have a radius of 70 kpc with two arms.
- Temperature differences exist between spiral arms, but pressure is balanced.
- Cluster exhibits features of a typical cool core with minor merger signs.

## Abstract

We present the properties of intracluster medium (ICM) in the cool core of the massive cluster of galaxies Abell 1835 obtained with the data by $ Chandra$ $X$-$ray$ $Observatory$. We find distinctive spiral patterns with the radius of 70 kpc (or 18 arcsec) as a whole in the residual image of X-ray surface brightness after the 2-dimensional ellipse model of surface brightness is subtracted. The size is smaller by a factor of 2 -- 4 than that of other clusters known to have a similar pattern. The spiral patterns consist of two arms. One of them appears as positive, and the other does as negative excesses in the residual image. Their X-ray spectra show that the ICM temperatures in the positive- and negative-excess regions are $5.09^{+0.12}_{-0.13}$ keV and $6.52^{+0.18}_{-0.15}$ keV, respectively. In contrast, no significant difference is found in the abundance or pressure, the latter of which suggests that the ICM in the two regions of the spiral patterns is in pressure equilibrium or close. The spatially-resolved X-ray spectroscopy of the central region ($r<40$ arcsec) divided into 92 sub-regions indicates that Abell 1835 is a typical cool core cluster. We also find that the spiral patterns extend from the cool core out to the hotter surrounding ICM. The residual image reveals some lumpy sub-structure in the cool core. The line-of-sight component of the disturbance velocity responsible for the sub-structures is estimated to be lower than 600 km/s. Abell 1835 may be now experiencing an off-axis minor merger.