Deep Chandra observations of NGC 1404 : cluster plasma physics revealed by an infalling early-type galaxy

The intracluster medium (ICM), as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics under extreme conditions that cannot yet be achieved on Earth. NGC 1404 is a bright elliptical galaxy that is being gas stripped as it falls through the ICM of the Fornax Cluster. We use the new {\sl Chandra} X-ray observations of NGC 1404 to study ICM microphysics. The interstellar medium (ISM) of NGC 1404 is characterized by a sharp leading edge, 8 kpc from the galaxy center, and a short downstream gaseous tail. Contact discontinuities are resolved on unprecedented spatial scales (0\farcs5=45\,pc) due to the combination of the proximity of NGC 1404, the superb spatial resolution of {\sl Chandra}, and the very deep (670 ksec) exposure. At the leading edge, we observe sub-kpc scale eddies generated by Kelvin-Helmholtz instability and put an upper limit of 5\% Spitzer on the isotropic viscosity of the hot cluster plasma. We also observe mixing between the hot cluster gas and the cooler galaxy gas in the downstream stripped tail, which provides further evidence of a low viscosity plasma. The assumed ordered magnetic fields in the ICM ought to be smaller than 5\,μG to allow KHI to develop. The lack of evident magnetic draping layer just outside the contact edge is consistent with such an upper limit

Detection of a Compact Nuclear Radio Source in the Local Group Elliptical Galaxy M32

The Local Group compact elliptical galaxy M32 hosts one of the nearest candidate super-massive black holes (SMBHs), which has a previously suggested X-ray counterpart. Based on sensitive observations taken with the {\it Karl G. Jansky} Very Large Array (VLA), we detect for the first time a compact radio source coincident with the nucleus of M32, which exhibits an integrated flux density of $\sim$$47.3\pm6.1$ $\mu$Jy at 6.6 GHz. We discuss several possibilities for the nature of this source, favoring an origin of the long-sought radio emission from the central SMBH, for which we also revisit the X-ray properties based on recently acquired {\sl Chandra} and {\sl XMM-Newton} data. Our VLA observations also discover radio emission from three previously known optical planetary nebulae in the inner region of M32.Comment: 13 pages, 2 figures, accepted by ApJ Letter

Detection of a Star Forming Galaxy in the Center of a Low-Mass Galaxy Cluster

Brightest Cluster Galaxies (BCGs) residing in the centers of galaxy clusters are typically quenched giant ellipticals. A recent study hinted that star-forming galaxies with large disks, so-called superluminous spirals and lenticulars, are the BCGs of a subset of galaxy clusters. Based on the existing optical data it was not possible to constrain whether the superluminous disk galaxies reside at the center of galaxy clusters. In this work, we utilize XMM-Newton X-ray observations of five galaxy clusters to map the morphology of the intracluster medium (ICM), characterize the galaxy clusters, determine the position of the cluster center, and measure the offset between the cluster center and the superluminous disk galaxies. We demonstrate that one superluminous lenticular galaxy, 2MASX J10405643-0103584, resides at the center of a low-mass ($M_{\rm 500} = 10^{14} \ \rm{M_{\odot}}$) galaxy cluster. This represents the first conclusive evidence that a superluminous disk galaxy is the central BCG of a galaxy cluster. We speculate that the progenitor of 2MASX J10405643-0103584 was an elliptical galaxy, whose extended disk was re-formed due to the merger of galaxies. We exclude the possibility that the other four superluminous disk galaxies reside at the center of galaxy clusters, as their projected distance from the cluster center is $150-1070$ kpc, which corresponds to $(0.27-1.18)R_{\rm 500}$. We conclude that these clusters host quiescent massive elliptical galaxies at their center.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical Journa