Star formation in low density HI gas around the Elliptical Galaxy NGC2865

Abstract

Interacting galaxies surrounded by HI tidal debris are ideal sites for the study of young clusters and tidal galaxy formation. The process that triggers star formation in the low-density environments outside galaxies is still an open question. New clusters and galaxies of tidal origin are expected to have high metallicities for their luminosities. Spectroscopy of such objects is, however, at the limit of what can be done with existing 8-10m class telescopes, which has prevented statistical studies of these objects. NGC2865 is an UV-bright merging elliptical galaxy with shells and extended HI tails. The regions observed in this work were previously detected using multi-slit imaging spectroscopy. We obtain new multislit spectroscopy of six young star-forming regions around NGC2865, to determine their redshifts and metallicities. The six emission-line regions are located 16-40 kpc from NGC2865 and they have similar redshifts. They have ages of ~10Myears and an average metallicity of 12+log(O/H) ~ 8.6, suggesting a tidal origin for the regions. It is noted that they coincide with an extended HI tail, which has projected density of N${}_{HI}$ < 10${}^{19}$ cm${}^{-2}$, and displays a low surface brightness counterpart. These regions may represent the youngest of the three populations of star clusters already identified in NGC2865. The high, nearly-solar, oxygen abundances found for the six regions in the vicinity of NGC2865 suggest that they were formed by pre-enriched material from the parent galaxy, from gas removed during the last major merger. Given the mass and the location of the HII regions, we can speculate that these young star-forming regions are potential precursors of globular clusters that will be part of the halo of NGC2865 in the future. Our result supports the use of the multi-slit imaging spectroscopy as a useful tool for finding nearly-formed stellar systems around galaxies.

7 pages, 2 figures accepted in A&A

References in corpus (14)

• A parsec-resolution simulation of the Antennae galaxies: Formation of star clusters during the merger
• High-resolution simulations of galaxy mergers: Resolving globular cluster formation
• Cold Molecular Gas in Merger Remnants: I. Formation of Molecular Gas Disks
• VCC 2062: an old Tidal Dwarf Galaxy in the Virgo Cluster?
• The GALEX UV emission in shell galaxies: tracing galaxy "rejuvenation" episodes
• Polychromatic View of Intergalactic Star Formation in NGC 5291
• The K luminosity-metallicity relation for dwarf galaxies and the tidal dwarf galaxies in the tails of HCG 31
• Globular cluster systems of six shell galaxies
• An HI Threshold for Star Cluster Formation in Tidal Debris
• Isolated ellipticals and their globular cluster systems III. NGC 2271, NGC 2865, NGC 3962, NGC 4240 and IC 4889
• Tidal Tails of Minor Mergers: Star Formation Efficiency in the Western Tail of NGC 2782
• Intermediate-age Globular Clusters in Four Galaxy Merger Remnants
• A census of H$\alpha$ emitters in the intergalactic medium of the NGC 2865 system
• Molecular gas in Arp 94: Implications for intergalactic star formation

Cited by in corpus (1)

• Stellar Abundances at the Center of Early Type Galaxies with Fine Structure