THE ULTRAVIOLET UPTURN IN ELLIPTICAL GALAXIES AND ENVIRONMENTAL EFFECTS

Journal Article · Mon Aug 01 04:00:00 EDT 2011 · Astrophysical Journal, Supplement Series

DOI:https://doi.org/10.1088/0067-0049/195/2/22· OSTI ID:21560343

Yi, Sukyoung K; Lee, Jihye; Sheen, Yun-Kyeong; Suh, Hyewon; Oh, Kyuseok ^[1]; Jeong, Hyunjin ^[2]

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1. Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of)
2. Yonsei University Observatory, Yonsei University, Seoul 120-749 (Korea, Republic of)

It is suspected that the ultraviolet (UV) upturn phenomenon in elliptical galaxies and extended horizontal-branch stars in globular clusters have a common origin. An extremely high abundance of helium (Y {approx} 0.4) allows for a working hypothesis, but its origin is unclear. Peng and Nagai proposed that primordial helium sedimentation in dark halos over cosmic timescales may lead to extreme helium abundances in galaxy cluster centers. In this scenario, UV upturn should be restricted to brightest cluster galaxies (BCGs) only. This is a clear and testable prediction. We present tests of this hypothesis using galaxy clusters from Yoon et al. that were detected by both the Sloan Digital Sky Survey and the Galaxy Evolution Explorer Medium Imaging Survey. Using a new UV classification scheme based on far-UV, near-UV, and optical photometry we found that only 5% of cluster elliptical galaxies show a UV upturn, while 27% and 68% are classified as 'recent star formation' and 'UV-weak' ellipticals, respectively. The data reveal a modest positive dependence of the UV upturn fraction on galaxy velocity dispersion, which is in agreement with the earlier findings of Burstein et al. and possibly with the helium sedimentation theory. However, we do not see any dependency on rank or luminosity of galaxies. Besides, BCGs do not show any marked difference in UV upturn fraction or strength, which is inconsistent with the prediction. We conclude that the aforementioned helium sedimentation theory and its inferred environmental effects are not supported by the available data.

• OSTI ID: 21560343
• Journal Information: Astrophysical Journal, Supplement Series, Journal Name: Astrophysical Journal, Supplement Series Journal Issue: 2 Vol. 195; ISSN 0067-0049; ISSN APJSA2
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
ELECTROMAGNETIC RADIATION
ELEMENTS
EVOLUTION
FLUIDS
GALAXIES
GALAXY CLUSTERS
GASES
HELIUM
NONMETALS
PHOTOMETRY
RADIATIONS
RARE GASES
ULTRAVIOLET RADIATION