A Thirty Kiloparsec Chain of 'Beads on a String' Star Formation Between Two Merging Early Type Galaxies in the Core of a Strong-Lensing Galaxy Cluster

摘要

New Hubble Space Telescope ultraviolet and optical imaging of thestrong-lensing galaxy cluster SDSS J1531+3414 (z=0.335) reveals two centrallydominant elliptical galaxies participating in an ongoing major merger. Theinteraction is at least somewhat rich in cool gas, as the merger is associatedwith a complex network of nineteen massive superclusters of young stars (orsmall tidal dwarf galaxies) separated by ~1 kpc in projection from one another,combining to an estimated total star formation rate of ~5 solar masses peryear. The resolved young stellar superclusters are threaded by narrow H-alpha,[O II], and blue excess filaments arranged in a network spanning ~27 kpc acrossthe two merging galaxies. This morphology is strongly reminiscent of thewell-known "beads on a string" mode of star formation observed on kpc-scales inthe arms of spiral galaxies, resonance rings, and in tidal tails betweeninteracting galaxies. Nevertheless, the arrangement of this star formationrelative to the nuclei of the two galaxies is difficult to interpret in adynamical sense, as no known "beads on a string" systems associated withkpc-scale tidal interactions exhibit such lopsided morphology relative to themerger participants. In this Letter we present the images and follow-upspectroscopy, and discuss possible physical interpretations for the uniquearrangement of the young stellar clusters. While we suggest that thismorphology is likely to be dynamically short-lived, a more quantitativeunderstanding awaits necessary multiwavelength follow-up, including opticalintegral field spectroscopy, ALMA sub-mm interferometry, and Chandra X-rayimaging.