Abstract
Interaction between the intracluster medium and the interstellar media of galaxies via ram-pressure stripping (RPS) has ample support from both observations and simulations of galaxies in clusters. Some, but not all of the observations and simulations show a phase of increased star formation compared to normal spirals. Examples of galaxies undergoing RPS induced star formation in clusters experiencing a merger have been identified in high resolution optical images supporting the existence of a star formation phase. We have selected Abell 3266 to search for ram-pressure induced star formation as a global property of a merging cluster. Abell 3266 (z = 0.0594) is a high mass cluster that features a high velocity dispersion, an infalling subcluster near to the line of sight, and a strong shock front. These phenomena should all contribute to making Abell 3266 an optimum cluster to see the global effects of RPS induced star formation. Using archival X-ray observations and published optical data, we cross-correlate optical spectral properties ([OII, Hβ]), indicative of starburst and post-starburst, respectively with ram-pressure, ρv2, calculated from the X-ray and optical data. We find that post-starburst galaxies, classified as E + A, occur at a higher frequency in this merging cluster than in the Coma cluster and at a comparable rate to intermediate redshift clusters. This is consistent with increased star formation due to the merger. However, both starburst and post-starburst galaxies are equally likely to be in a low or high ram pressure environment. From this result, we infer that the duration of the starburst phase must be very brief so that: 1) at any time only a small fraction of the galaxies in a high ram pressure environment show this effect, and 2) most post-starburst galaxies are in an environment of low ram pressure due to their continued orbital motion in the cluster.
Highlights
An estimated 20% of all galaxies are in clusters of galaxies [1]
Much of the metal enhancement must have originated from local galaxy evolutionary processes that are more efficient in the cluster center. [7] originally suggested that as galaxies move through the intracluster medium (ICM), there is a possibility that their interstellar medium (ISM) could be removed through RPS
We adopted the condition for high ram pressure used by [50] of 5 × 10−11 dynes∙cm−2
Summary
An estimated 20% of all galaxies are in clusters of galaxies [1]. These large structures are typically ~3 million light years or more in radius and are roughly circular in projection. The X-ray spectra from the plasma have a thermal bremsstrahlung continuum with emission lines from high ionization states of elements such as O, Fe, Si, and S. These elements are formed in stars and their presence in the ICM implies a connection to star formation, which takes place predominately in galaxies [2]. While studies of sedimentation of metals to the center of the cluster could account, at least in part, for the excess metals [5], inclusion of the intracluster magnetic field gives a prohibitively long time for this process [6]. Much of the metal enhancement must have originated from local galaxy evolutionary processes that are more efficient in the cluster center. Though there are competing galaxy evolutionary processes that favor the cluster center [9], images of gas removal in galaxies by RPS are evident in the jelly-fish galaxies
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