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تسجيل مستخدم جديدGemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. IV. Stephans Quintet
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We present a spectroscopic survey of 21 young massive clusters and complexes and one tidal dwarf galaxy candidate (TDG) in Stephans Quintet, an interacting compact group of galaxies. All of the selected targets lie outside the main galaxies of the system and are associated with tidal debris. We find clusters with ages between a few and 125 Myr and confirm the ages estimated through HST photometry by Fedotov et al. (2011), as well as their modelled interaction history of the Quintet. Many of the clusters are found to be relatively long-lived, given their spectrosopically derived ages, while their high masses suggest that they will likely evolve to eventually become intergalactic clusters. One cluster, T118, is particularly interesting, given its age (sim 125 Myr), high mass (sim 2times10^6 Modot) and position in the extreme outer end of the young tidal tail. This cluster appears to be quite extended (Reff sim 12 - 15 pc) compared to clusters observed in galaxy disks (Reff sim 3 - 4 pc), which confirms an effect we previously found in the tidal tails of NGC 3256, where clusters are similarly extended. We find that star and cluster formation can proceed at a continuous pace for at least sim 150 Myr within the tidal debris of interacting galaxies. The spectrum of the TDG candidate is dominated by a young population (sim 7 Myr), and assuming a single age for the entire region, has a mass of at least 10^6 Modot.
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Stephans Quintet (SQ) is a compact group of galaxies that exhibits numerous signs of interactions between its members. Using high resolution images of SQ in B438, V606, and I814 bands from the Early Release Science project obtained with the Wide Fiel
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ot connected with the main bodies of the galaxies, but roughly coincident with the X-ray halo of the group. We fitted the inferred dust emission spectral energy distribution of this extended source and the other main infrared emission components of SQ, including the intergalactic shock, to elucidate the mechanisms powering the dust and PAH emission, taking into account collisional heating by the plasma and heating through UV and optical photons. Combining the inferred direct and dust-processed UV emission to estimate the star formation rate (SFR) for each source we obtain a total SFR for SQ of 7.5 M(sun)/yr, similar to that expected for non-interacting galaxies with stellar mass comparable to the SQ galaxies. Although star formation in SQ is mainly occurring at, or external to the periphery of the galaxies, the relation of SFR per unit physical area to gas column density for the brightest sources is similar to that seen for star-formation regions in galactic disks. We also show that available sources of dust in the group halo can provide enough dust to produce up to L_{IR}approx 10^42 erg/s powered by collisional heating. Though a minority of the total infrared emission (which we infer to trace distributed star-formation), this is several times higher than the X-ray luminosity of the halo, so could indicate an important cooling mechanism for the hot IGM and account for the overall correspondence between FIR and X-ray emission.
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