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Probing Cluster Formation under Extreme Conditions: Super Star Clusters in Blue Compact Galaxies
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The numerous and massive young star clusters in blue compact galaxies (BCG) are used to investigate the properties of their hosts. We test whether BCGs follow claimed relations between the cluster population and their hosts, such as the cluster specific luminosity in the U band, TL(U), and the star formation rate density ΣSFR; the V bandluminosity of the brightest youngest cluster, Mbrightest, and the mean star formation Vrate (SFR); the cluster formation efficiency versus the ΣSFR. We find that BCGs fairly well reproduce the relations, supporting a scenario where cluster formation and environmental properties of the host are correlated. They occupy, in all the diagrams, the regions of higher SFRs, suggesting the extreme nature of the starburst operating in these systems. We suggest that the BCG environment has most likely favoured the compression and collapse of the giant molecular clouds, enhancing the local star formation efficiency, so that massive clusters have been formed. The cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) in BCGs is higher than the 8-10 % reported from quiescent spirals and dwarf starburst galaxies. BCGs have a cluster formation efficiency comparable to luminous IR galaxies and spiral starburst nuclei (the averaged value is ∼ 30 %).

Identifiers
URN: urn:nbn:se:su:diva-52677OAI: oai:DiVA.org:su-52677DiVA: diva2:388552
Available from: 2011-01-17 Created: 2011-01-17 Last updated: 2012-01-11Bibliographically approved
In thesis
1. Super Star Clusters in Blue Compact Galaxies: Evidence for a near-infrared flux excess and properties of the starburst phase
Open this publication in new window or tab >>Super Star Clusters in Blue Compact Galaxies: Evidence for a near-infrared flux excess and properties of the starburst phase
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Luminous Blue compact galaxies (BCGs) are metal-poor actively star-forming systems, characterised by bright ultraviolet and blue luminosities. Hubble Space Telescope high-resolution data have revealed that the luminous star-forming knots in these galaxies are composed of hundreds of young massive star clusters. In this work we present a systematic study of the star cluster populations in BCGs with important implications for the formation history of their host systems. The studied galaxies show recently increased star formation rates and a high fraction of massive clusters, probably as a result of minor/major merger events. The age distributions have a peak of cluster formation at only 3 - 4 Myr, unveiling a unique sample of clusters still partially embedded. A considerable fraction of clusters (30 - 50 %), mainly younger than 10 Myr, shows an observed flux excess between 0.8 and 2.2 μm. This so-called near-infrared (NIR) excess is impossible to reproduce even with the most recent spectral synthesis models (that include a self-consistent treatment of the photoionized gas). The origin of the NIR excess, which still remains unexplained, challenges our understanding of the cluster formation process under extreme conditions.

The results achieved in this work have produced important insights into the cluster formation process in BCGs. We suggest that the BCG environment has most likely favoured the compression and collapse of giant molecular clouds into compact massive star clusters. The cluster formation efficiency (i.e., the fraction of star formation happening in star clusters) in BCGs is higher than the reported 8 - 10 %, for quiescent spirals and local star-forming galaxies. Luminous BCGs have a cluster formation efficiency comparable to luminous infrared galaxies and spiral starburst nuclei (the averaged value is  about 30 %), suggesting an important role of the merger event in the cluster formation.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2011. 56 p.
Keyword
starburst galaxy-extragalactic star clusters-dwarf merger
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-52681 (URN)978-91-7447-215-8 (ISBN)
Public defence
2011-02-18, sal FB53, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Accepted. Paper 5: Manuscript. Paper 6: Manuscript.Available from: 2012-01-11 Created: 2011-01-17 Last updated: 2012-01-11Bibliographically approved

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