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Is the escape velocity in star clusters linked to extended star formation histories? Using NGC 7252: W3 as a test case

Cabrera-Ziri, I and Bastian, N and Hilker, M and Davies, B and Schweizer, F and Kruijssen, JMD and Mejia-Narvaez, A and Niederhofer, F and Brandt, TD and Rejkuba, M and Bruzual, G and Magris, G (2016) Is the escape velocity in star clusters linked to extended star formation histories? Using NGC 7252: W3 as a test case. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 457 (1). pp. 809-821. ISSN 0035-8711

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Open Access URL: https://arxiv.org/pdf/1601.02024 (Accepted version)

Abstract

The colour–magnitude diagrams of some intermediate-age (1–2 Gyr) star clusters show unexpectedly broad main-sequence turnoffs, raising the possibility that these clusters have experienced more than one episode of star formation. Such a scenario predicts the existence of an extended main-sequence turnoff (eMSTO) only in clusters with escape velocities above a certain threshold (>15 km s−1), which would allow them to retain or accrete gas that eventually would fuel a secondary extended star formation episode. This paper presents a test of this scenario based on the study of the young and massive cluster NGC 7252: W3. We use the HST photometry from Wide Field Planetary Camera 2 and Wide Field Camera 3 images obtained with UV and optical filters, as well as MagE echellette spectrograph data from the Las Campanas Clay 6.5 m telescope, in order to construct the observed UV/optical Spectral energy distribution (SED) of NGC 7252: W3. The observations are then compared with synthetic spectra based on different star formation histories consistent with those of the eMSTO clusters. We find that the SED of this cluster is best fitted by a synthetic spectrum with a single stellar population of age
570^{+70}_{-62} Myr and mass 1.13^{+0.14}_{-0.13}\times 10^8  M⊙, confirming earlier works on NGC 7252:W3. We also estimate the lower limit on the central escape velocity of 193 km s−1. We rule out extended star formation histories, like those inferred for the eMSTO clusters in the Magellanic Clouds, at high confidence. We conclude that the escape velocity of a cluster does not dictate whether a cluster can undergo extended periods of star formation.

Item Type: Article
Additional Information: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Mon Not R Astron Soc (2016) 457 (1): 809-821 is available online at:http://dx.doi.org/10.1093/mnras/stv2977
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: OXFORD UNIV PRESS
Related URLs:
Date Deposited: 10 Apr 2017 10:58
Last Modified: 10 Apr 2017 10:58
DOI or Identification number: 10.1093/mnras/stv2977
URI: http://researchonline.ljmu.ac.uk/id/eprint/6232

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