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Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Leitherer, Claus; Byler, Nell; Lee, Janice; Levesque, Emily

Description

We analyze far-ultraviolet spectra and ancillary data of the super star cluster SSC-N and its surrounding H II region in the nearby dwarf galaxy II Zw 40. From the ultraviolet spectrum, we derive a low internal reddening of E(B − V) = 0.07 ± 0.03, a mass of (9.1 ± 1.0) × 105 Me, a bolometric luminosity of (1.1 ± 0.1) × 109 Le, a number of ionizing photons of (6 ± 2) × 1052 s −1 , and an age of (2.8 ± 0.1) Myr. These parameters agree with the values derived from optical and radio data,...[Show more]

dc.contributor.authorLeitherer, Claus
dc.contributor.authorByler, Nell
dc.contributor.authorLee, Janice
dc.contributor.authorLevesque, Emily
dc.date.accessioned2020-09-18T04:48:10Z
dc.identifier.issn0004-637X
dc.identifier.urihttp://hdl.handle.net/1885/210651
dc.description.abstractWe analyze far-ultraviolet spectra and ancillary data of the super star cluster SSC-N and its surrounding H II region in the nearby dwarf galaxy II Zw 40. From the ultraviolet spectrum, we derive a low internal reddening of E(B − V) = 0.07 ± 0.03, a mass of (9.1 ± 1.0) × 105 Me, a bolometric luminosity of (1.1 ± 0.1) × 109 Le, a number of ionizing photons of (6 ± 2) × 1052 s −1 , and an age of (2.8 ± 0.1) Myr. These parameters agree with the values derived from optical and radio data, indicating no significant obscured star formation, absorption of photons by dust, or photon leakage. SSC-N and its nebulosity are an order of magnitude more massive and luminous than 30 Doradus and its ionizing cluster. Photoionization modeling suggests a high ionization parameter and a C/O ratio where C is between primary and secondary. We calculate diagnostic emission-line ratios and compare SSC-N to local star-forming galaxies. The SSC-N nebula does not coincide with the locus defined by local galaxies. Rather, it coincides with the location of “Green Pea” galaxies, objects that are often considered nearby analogs of the galaxies reionizing the universe. Most stellar features are well reproduced by synthetic spectra. However, the SSC-N cluster has strong, broad, stellar He II λ1640 emission that cannot be reproduced, suggesting a deficit of He-enhanced stars with massive winds in the models. We discuss possible sources for the broad He II emission, including very massive stars and/or enhanced mixing processes.
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherIOP Publishing
dc.rights© 2018. The American Astronomical Society
dc.sourceThe Astrophysical Journal
dc.titlePhysical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume865
dc.date.issued2018
local.identifier.absfor020103 - Cosmology and Extragalactic Astronomy
local.identifier.absfor020110 - Stellar Astronomy and Planetary Systems
local.identifier.ariespublicationu4485658xPUB1610
local.publisher.urlhttp://iopscience.iop.org/0004-637X
local.type.statusPublished Version
local.contributor.affiliationLeitherer, Claus, Space Telescope Science Institute
local.contributor.affiliationByler, Nell, College of Science, ANU
local.contributor.affiliationLee, Janice, Caltech-IPAC
local.contributor.affiliationLevesque, Emily, University of Washington
local.description.embargo2037-12-31
local.bibliographicCitation.issue1
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage16
local.identifier.doi10.3847/1538-4357/aada84
local.identifier.absseo970102 - Expanding Knowledge in the Physical Sciences
dc.date.updated2020-06-23T00:55:51Z
local.identifier.scopusID2-s2.0-85053924073
local.identifier.thomsonID000445277100008
CollectionsANU Research Publications

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