scholarly journals The UV Upturn in Elliptical Galaxies

1995 ◽  
Vol 164 ◽  
pp. 239-248
Author(s):  
H.C. Ferguson
Keyword(s):  
Galaxy Evolution ◽  
Open Cluster ◽  
Elliptical Galaxies ◽  
Asymptotic Giant Branch ◽  
Star Mass ◽  
Uv Emission ◽  
Stellar Component ◽  
Red Clump ◽  
Ehb Stars ◽  
Uv Upturn

The hot stellar component in elliptical galaxies offers clues to both stellar evolution and galaxy evolution. Current observations suggest that extreme horizontal branch (EHB) stars dominate the far-UV emission from galaxies with the strongest “UV upturns,” while post asymptotic giant branch (PAGB) stars are probably significant contributors for weaker galaxies. Spectra near the Lyman limit indicate that a rather narrow range of temperature (and hence EHB star mass) is required. However, other arguments suggest that most of the helium-burning stars in elliptical galaxies are in the red clump. The HB star mass distribution therefore appears to be strongly bimodal. Such bimodality is qualitatively reproduced by two radically different stellar population models, (those of Lee and Bressan et al.), both of which require that the galaxies be very old. However, the Galactic open cluster NGC 6791 also contains EHB stars and exhibits strong bimodality, indicating that old age may not necessarily be a requirement for the UV upturn phenomenon.

scholarly journals UV Bright Stars and Planetary Nebulae in Elliptical Galaxies

1995 ◽  
Vol 10 ◽  
pp. 493-497
Author(s):  
Henry C. Ferguson
Keyword(s):  
Uv Spectroscopy ◽  
Mass Function ◽  
Elliptical Galaxies ◽  
Asymptotic Giant Branch ◽  
Uv Emission ◽  
Luminosity Functions ◽  
The Galaxy ◽  
Low Mass ◽  
Red Giant ◽  
Ehb Stars

AbstractFar UV observations and optical studies of planetary nebula luminosity functions (PNLFs) offer complementary views of the late phases of stellar evolution in elliptical galaxies and spiral galaxy bulges. UV spectroscopy reveals that the hot stellar population is composite, with a mix of temperatures that varies from galaxy to galaxy. This changing mix is most likely due to changes in the relative numbers of stars that channel through the Post-Asymptotic Giant Branch (PAGB), Post-Early-AGB (PEAGB) and Extreme Horizontal Branch (EHB) phases of evolution. EHB stars appear to dominate the integrated λ < 2000 Å flux from galaxies with the strongest far-UV emission, but are too faint to resolve individually in even the nearest galaxies. Far UV images of M31 and M32 reveal a population of hot stars that are much brighter, but do not account for the majority of the far-UV flux. The sources detected are most likely low-mass PAGB stars (0.55 < M/M⊙ < 0.59). In contrast, the PNLF probes the PAGB star mass function at values greater than ∼ 0.6 M⊙. For a given galaxy the relative numbers of stars in these different branches of evolution are determined by the age and chemical evolution of the galaxy and by the physics of mass loss on the red giant branch. We review current constraints on the mass function of hot evolved stars in elliptical galaxies, highlight a few puzzles, and outline where future observations might contribute.

scholarly journals Binary Evolutionary Models

2008 ◽  
Vol 4 (S252) ◽  
pp. 349-357
Author(s):  
Z. Han ◽  
Ph. Podsiadlowski
Keyword(s):  
Globular Clusters ◽  
A Priori ◽  
Elliptical Galaxies ◽  
Ultraviolet Excess ◽  
Sdb Stars ◽  
Binary Model ◽  
Type Ia ◽  
Binary Evolution ◽  
Ehb Stars ◽  
Uv Upturn

AbstractIn this talk, we present the general principles of binary evolution and give two examples. The first example is the formation of subdwarf B stars (sdBs) and their application to the long-standing problem of ultraviolet excess (also known as UV-upturn) in elliptical galaxies. The second is for the progenitors of type Ia supernovae (SNe Ia). We discuss the main binary interactions, i.e., stable Roche lobe overflow (RLOF) and common envelope (CE) evolution, and show evolutionary channels leading to the formation of various binary-related objects. In the first example, we show that the binary model of sdB stars of Han et al. (2002, 2003) can reproduce field sdB stars and their counterparts, extreme horizontal branch (EHB) stars, in globular clusters. By applying the binary model to the study of evolutionary population synthesis, we have obtained an “a priori” model for the UV-upturn of elliptical galaxies and showed that the UV-upturn is most likely resulted from binary interactions. This has major implications for understanding the evolution of the UV excess and elliptical galaxies in general. In the second example, we introduce the single degenerate channel and the double degenerate channel for the progenitors of SNe Ia. We give the birth rates and delay time distributions for each channel and the distributions of companion stars at the moment of SN explosion for the single degenerate channel, which would help to search for the remnant companion stars observationally.

Updates on the Ultraviolet Emission from Asymptotic Giant Branch Stars

2018 ◽  
Vol 14 (S343) ◽  
pp. 474-475
Author(s):  
Rodolfo Montez ◽  
Sofia Ramstedt ◽  
Joel H. Kastner ◽  
Wouter Vlemmings
Keyword(s):  
Galaxy Evolution ◽  
Initial Study ◽  
Asymptotic Giant Branch ◽  
Asymptotic Giant Branch Stars ◽  
Agb Stars ◽  
Ultraviolet Emission ◽  
Uv Emission ◽  
The Galaxy ◽  
Chromospheric Emission ◽  
Giant Branch Stars

AbstractA comprehensive study of UV emission from asymptotic giant branch (AGB) stars with the Galaxy Evolution Explorer (GALEX) revealed that out of the 316 observed AGB stars, 57% were detected in the near-UV (NUV) bandpass and 12% were detected in the far-UV (FUV) bandpass (Montez et al. 2017). A cross-match between our sample and Gaia DR2 results in parallax estimates for 90% of the sample of AGB stars, compared to only 30% from Hipparcos. This increase allowed us to further probe trends and conclusions of our initial study. Specifically, that the detection of UV emission from AGB stars is subject to proximity and favorable lines of sight in our Galaxy. These improved results support the notion that some of the GALEX-detected UV emission is intrinsic to AGB stars, likely due to a combination of photospheric and chromospheric emission.

scholarly journals UV bright red-sequence galaxies: how do UV upturn systems evolve in redshift and stellar mass?

2019 ◽  
Vol 492 (2) ◽  
pp. 2996-3011 ◽  
Author(s):  
M L L Dantas ◽  
P R T Coelho ◽  
R S de Souza ◽  
T S Gonçalves
Keyword(s):  
Emission Line ◽  
Galaxy Evolution ◽  
Stellar Mass ◽  
Sloan Digital Sky Survey ◽  
Uv Emission ◽  
Mass Assembly ◽  
Matched Data ◽  
Line Classification ◽  
Uv Upturn ◽  
Red Sequence

ABSTRACT The so-called ultraviolet (UV) upturn of elliptical galaxies is a phenomenon characterized by the up-rise of their fluxes in bluer wavelengths, typically in the 1200–2500 Å range. This work aims at estimating the rate of occurrence of the UV upturn over the entire red-sequence population of galaxies that show significant UV emission. This assessment is made considering it as function of three parameters: redshift, stellar mass, and – what may seem counter-intuitive at first – emission-line classification. We built a multiwavelength spectrophotometric catalogue from the Galaxy Mass Assembly survey, together with aperture-matched data from Galaxy Evolution Explorer Medium-Depth Imaging Survey (MIS) and Sloan Digital Sky Survey, covering the redshift range between 0.06 and 0.40. From this sample, we analyse the UV emission among UV bright galaxies, by selecting those that occupy the red-sequence locus in the (NUV− r) × (FUV−NUV) chart; then, we stratify the sample by their emission-line classes. To that end, we make use of emission-line diagnostic diagrams, focusing the analysis in retired/passive lineless galaxies. Then, a Bayesian logistic model was built to simultaneously deal with the effects of all galaxy properties (including emission-line classification or lack thereof). The main results show that retired/passive systems host an up-rise in the fraction of UV upturn for redshifts between 0.06 and 0.25, followed by an in-fall up to 0.35. Additionally, we show that the fraction of UV upturn hosts rises with increasing stellar mass.

scholarly journals Abundance analysis of red clump stars in the old, inner disc, open cluster NGC 4337: a twin of NGC 752?

2014 ◽  
Vol 568 ◽  
pp. A86 ◽  
Author(s):  
Giovanni Carraro ◽  
Lorenzo Monaco ◽  
Sandro Villanova
Keyword(s):  
Open Cluster ◽  
Red Clump

scholarly journals The Dark Halo – Spheroid Conspiracy

2012 ◽  
Vol 8 (S295) ◽  
pp. 208-208
Author(s):  
Rhea-Silvia Remus ◽  
Andreas Burkert ◽  
Klaus Dolag ◽  
Peter H. Johansson ◽  
Thorsten Naab ◽  
...  
Keyword(s):  
Elliptical Galaxies ◽  
Total Density ◽  
Dark Halo ◽  
Coma Cluster ◽  
Density Profiles ◽  
Stellar Component ◽  
Strong Lensing ◽  
The Galaxy ◽  
Good Agreement

AbstractObservational results from strong lensing and dynamical modeling indicate that the total density profiles of early-type galaxies are close to isothermal, i.e. ρtot ∝ rγ with γ ≈ −2. To understand the origin of this universal slope we study a set of simulated spheroids formed in cosmological hydrodynamical zoom-in simulations (see Oser et al. 2010 for more details). We find that the total stellar plus dark matter density profiles of all our simulations on average can be described by a power law with a slope of γ ≈ −2.1, with a tendency towards steeper slopes for more compact, lower mass ellipticals, while the total intrinsic velocity dispersion is flat for all simulations, independent of the values of γ. Our results are in good agreement with observations of Coma cluster ellipticals (Thomas et al. 2007) and results from strong lensing (Sonnenfeld et al. 2012). We find that for z ≳ 2 the majority of the stellar build-up occurs through in-situ star formation, i.e. the gas falls to the center of the galaxy and forms stars, causing the galaxy to be more compact and thus the stellar component to be more dominant. As a result, the total density slopes at z ≈ 2 are generally steeper (around γ ≈ −3). Between z = 2 and z = 0 galaxies grow mostly through dry merging, with each merging event shifting the slope more towards γ ≈ −2. We conclude from our simulations that the steepness of the slope of present day galaxies is a signature of the importance of mostly dry mergers in the formation of an elliptical, and suggest that all elliptical galaxies will with time end up in a configuration with a density slope of γ ≈ −2. For a more detailed analysis with a larger sample of simulations see Remus et al. (2013).

scholarly journals The Age Spread Among Galaxies and the Origin of the UV Radiation from Elliptical Galaxies

1995 ◽  
Vol 164 ◽  
pp. 448-449
Author(s):  
Young-Wook Lee ◽  
Jang-Hyun Park
Keyword(s):  
Uv Radiation ◽  
Spectral Energy Distribution ◽  
Type Systems ◽  
Elliptical Galaxies ◽  
Spectral Energy ◽  
Population Synthesis ◽  
Massive Galaxies ◽  
Metal Abundance ◽  
Inside Out ◽  
Uv Upturn

Recent UV observations of elliptical galaxies are interpreted as evidence for the global second parameter phenomenon of horizontal-branch (HB) morphology within, as well as between, these galaxies. In this picture, the origin of the UV radiation is mostly due to hot HB stars and their post-HB progeny produced by the metal-poor tail of the wide metallicity distribution expected to be present in these systems. The attractive feature of this model is that the bimodal temperature distributions of HB stars (and their progeny), required to generate the 2000 Å dip of the spectral energy distribution (SED), can naturally be reproduced from the standard HB population models with large range of metal abundance (see Lee 1994, ApJ, 430, L113). Detailed population synthesis models are presented, which reproduce the systematic variation of UV upturn among elliptical galaxies (Fig 1). If age is the major second parameter, as suggested by the fossil record in our Galaxy, the observed UV color gradient and the UV upturn-total mass (mean metallicity) correlation, within and between the early-type systems, would imply, respectively, (1) that most galaxies formed from the inside out, and (2) that there is age spread among galaxies, in the sense that more massive galaxies are older (and more metal-rich in the mean) than less massive galaxies as a result of more efficient star formation (and metal enrichment) in denser environments.

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