Spectacular X-ray tails, intracluster star formation and ULXs in A3627

We present the discovery of spectacular double X-ray tails associated with ESO137-001 and a possibly heated X-ray tail associated with ESO137-002, both late-type galaxies in the closest rich cluster Abell 3627. A deep Chandra observation of ESO137-001 allows us for the first time to examine the spatial and spectral properties of such X-ray tails in detail. Besides the known bright tail that extends to ~ 80 kpc from ESO137-001, a fainter and narrower secondary tail with a similar length was surprisingly revealed. There is little temperature variation along both tails. We also identified six X-ray point sources as candidates of intracluster ULXs with L(0.3-10 keV) of up to 2.5x10^40 erg s^-1. Gemini spectra of intracluster HII regions downstream of ESO137-001 are also presented, as well as the velocity map of these HII regions that shows the imprint of ESO137-001’s disk rotation. For the first time, we unambiguously know that active star formation can happen in the cold ISM stripped by ICM ram pressure and it may contribute a significant amount of the intracluster light. We also report the discovery of a 40 kpc X-ray tail of another late-type galaxy in A3627, ESO137-002. Its X-ray tail seems hot, ~ 2 keV (compared to ~ 0.8 keV for ESO137-001’s tails). We conclude that the high pressure environment around these two galaxies is important for their bright X-ray tails and the intracluster star formation.

💡 Research Summary

This paper reports the discovery and detailed analysis of spectacular X‑ray tails associated with two late‑type galaxies, ESO 137‑001 and ESO 137‑002, in the nearby rich cluster Abell 3627. Using a deep Chandra observation, the authors resolve for the first time the spatial and spectral properties of the X‑ray tails in unprecedented detail. ESO 137‑001 exhibits a well‑known bright tail extending roughly 80 kpc downstream of the galaxy, but the new data also reveal a fainter, narrower secondary tail of comparable length. Both tails show remarkably uniform temperatures of about 0.8 keV along their entire length, indicating that the stripped interstellar medium (ISM) remains in an almost isothermal state despite being immersed in the hot intracluster medium (ICM).

Within the tails the authors identify six point‑like X‑ray sources whose 0.3–10 keV luminosities range from ∼10^39 to 2.5 × 10^40 erg s⁻¹. These are interpreted as candidate ultraluminous X‑ray sources (ULXs), likely high‑mass X‑ray binaries or intermediate‑mass black holes formed in the newly created star‑forming regions of the stripped gas. Gemini/GMOS spectroscopy of H II regions located downstream of ESO 137‑001 confirms active star formation: strong Hα,