The UV Upturn: From M32 to Distant Clusters

Abstract

I review the observational constraints on the stars responsible for the upturn in the UV spectra of ellipticals, ranging from galaxies in the local Universe to distant clusters. In nearby galaxies, this UV upturn is produced by a minority population of extreme horizontal branch (EHB) stars, with the large variations observed in the UV-to-optical flux ratio driven by variations in the number of EHB stars, and not the type of UV-bright stars. Deep UV images of the nearest elliptical galaxy, M32, show that it has a well-populated EHB, even though it has the weakest UV upturn of any known elliptical galaxy. However, M32 suffers from a striking dearth of the hot post-HB stars expected from canonical evolutionary theory. As we observe to larger lookback times in more distant galaxy clusters, the UV upturn fades, as predicted by theories of stellar and galactic evolution, but does so gradually. Because the EHB stars do not appear suddenly in the Universe, their presence is likely driven by a large dispersion in the parameters that govern HB morphology.

8 pages, latex, 4 figures. To appear in "Extreme Horizontal Branch Stars and Related Objects," ed. P. Maxted, Astrophysics & Space Science

References in corpus (4)

• Detection and Photometry of Hot Horizontal Branch Stars in the Core of M32
• Far-UV Emission from Elliptical Galaxies at z=0.55
• Far-Ultraviolet Emission from Elliptical Galaxies at z=0.33
• Photospheric Abundances of the Hot Stars in NGC1399 and Limits on the Fornax Cluster Cooling Flow

Cited by in corpus (24)

• The GALEX Ultraviolet Atlas of Nearby Galaxies
• A binary model for the UV-upturn of elliptical galaxies (MNRAS version)
• Stellar Evolution in NGC 6791: Mass Loss on the Red Giant Branch and the Formation of Low Mass White Dwarfs
• GALEX UV Color Relations for Nearby Early-Type Galaxies
• Systematics of the Ultraviolet Rising flux in a GALEX/SDSS sample of Early-type Galaxies
• Ultraviolet Morphologies and Star-Formation Rates of CLASH Brightest Cluster Galaxies
• M31* and its circumnuclear environment
• GALEX Ultraviolet Photometry of Globular Clusters in M31: Three Year Results and a Catalog
• Star Formation Activity in CLASH Brightest Cluster Galaxies
• Nucleosynthesis in helium-enriched asymptotic giant branch models: Implications for Heavy Element Enrichment in Omega Centauri
• The SAURON project - XVIII. The integrated UV-linestrength relations of early-type galaxies
• Evolution of the UV Excess in Early-Type Galaxies
• Impact of young stellar components on quiescent galaxies: deconstructing cosmic chronometers
• Some Stars are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies
• Modelling the UV spectrum of SDSS-III/BOSS galaxies: hints towards the detection of the UV upturn at high-z
• AGB Connection and Ultraviolet Luminosity Excess in Elliptical Galaxies
• The GALEX Ultraviolet Virgo Cluster Survey (GUViCS). VII.: BCG UV upturn and the FUV-NUV color up to redshift 0.35
• UV bright red-sequence galaxies: how do UV upturn systems evolve in redshift and stellar mass?
• UV upturn versus UV weak galaxies: differences and similarities of their stellar populations unveiled by a de-biased sample
• A Survey for EHB Stars in the Galactic Bulge
• Evolution of the Ultraviolet Upturn at $0.3<z<1$: exploring helium rich stellar populations
• Discovery of an extended Horizontal Branch in the Large Magellanic Cloud globular cluster NGC1835
• The Ultraviolet Upturn in field Luminous Red Galaxies at $0.3<z<0.7$
• Horizontal Branch Stars and the Ultraviolet Universe