scholarly journals The Shapes and Ages of Elliptical Galaxies

1996 ◽  
Vol 171 ◽  
pp. 359-359
Author(s):  
Roelof S. de Jong ◽  
Roger L. Davies
Keyword(s):  
Elliptical Galaxies ◽  
Population Synthesis ◽  
Range Of Values ◽  
Normal Perception

Normally elliptical galaxies are thought to be old, evolved systems, but recently a controversy has arisen over the age of ellipticals. Measurements by Gonzáles (1993, Ph.D. thesis, UCSC) show that the Hβ absorption indices of ellipticals span a range of values. Population synthesis models indicate that the Hβ index is a good age indicator and hence, contrary to normal perception, the ages of ellipticals seem to span a range of values.

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.

scholarly journals The Age of Elliptical Galaxies in Clusters

1996 ◽  
Vol 171 ◽  
pp. 473-473
Author(s):  
Bodo Ziegler ◽  
Ralf Bender
Keyword(s):  
Velocity Dispersion ◽  
Elliptical Galaxies ◽  
Population Synthesis ◽  
Small Scatter ◽  
Hubble Time

Nearby cluster ellipticals follow a very tight relation between velocity dispersion σ and Mg absorption (e.g. Bender et al. 1993, ApJ411, 153). The small scatter in Mg implies that the age and metallicity spread at a given σ in ellipticals is smaller than 15% (applying Worthey's population synthesis models 1994, ApJS95, 107). This means that ellipticals cannot have formed continuously over the Hubble time and ongoing merger processes represent only a tail of latecomers.

scholarly journals Contamination of RR Lyrae stars from Binary Evolution Pulsators

2015 ◽  
Vol 5 (1) ◽  
pp. 24-28
Author(s):  
P. Karczmarek
Keyword(s):  
Mass Transfer ◽  
Binary System ◽  
Synthesis Method ◽  
Population Synthesis ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Low Mass ◽  
Binary Evolution ◽  
Lyrae Stars ◽  
Range Of Values

A Binary Evolution Pulsator (BEP) is a low-mass (0.26 𝔐☉) member of a binary system, which pulsates as a result of a former mass transfer to its companion. The BEP mimics RR Lyrae-type pulsations, but has completely different internal structure and evolution history. Although there is only one known BEP (OGLE-BLG-RRLYR-02792), it has been estimated that approximately 0.2% of objects classified as RR Lyrae stars can be undetected Binary Evolution Pulsators. In the present work, this contamination value is re-evaluated using the population synthesis method. The output falls inside a range of values dependent on tuning the parameters in the StarTrack code, and varies from 0.06% to 0.43%.

scholarly journals The Hβ Index As a Chronometer of Extragalactic Globular Cluster Systems

2002 ◽  
Vol 207 ◽  
pp. 721-723
Author(s):  
Hyun-chul Lee ◽  
Suk-Jin Yoon ◽  
Young-Wook Lee
Keyword(s):  
Globular Cluster ◽  
Elliptical Galaxies ◽  
Systematic Difference ◽  
Population Synthesis ◽  
Milky Way Galaxy ◽  
Cluster Systems ◽  
The Mean ◽  
Globular Cluster System ◽  
First Time ◽  
Monotonically Decrease

For the first time, we have taken into account the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity in our population synthesis models and they result that the integrated Hβ index is significantly affected by the presence of blue HB stars. As a matter of fact, due to the systematic HB morphology variation, it is found that Hβ does not monotonically decrease as metallicity increases at given ages, but shows a kind of wavy feature. According to our models, a systematic difference between the globular cluster system in the Milky Way Galaxy and that in NGC 1399 in the Hβ vs. Mg2 plane is explained if globular cluster systems in giant elliptical galaxies are a couple of billion years older, in the mean, than the Galactic counterpart.

scholarly journals Evolution of binary stars and its implications for evolutionary population synthesis

2009 ◽  
Vol 5 (S262) ◽  
pp. 44-47
Author(s):  
Z. Han ◽  
X. Chen ◽  
F. Zhang ◽  
Ph. Podsiadlowski
Keyword(s):  
Binary System ◽  
Binary Stars ◽  
Elliptical Galaxies ◽  
Close Binary System ◽  
Close Binary ◽  
Population Synthesis ◽  
Blue Stragglers ◽  
Uv Excess ◽  
Hot Subdwarfs ◽  
Binary Evolution

AbstractMost stars are members of binaries, and the evolution of a star in a close binary system differs from that of an ioslated star due to the proximity of its companion star. The components in a binary system interact in many ways and binary evolution leads to the formation of many peculiar stars, including blue stragglers and hot subdwarfs. We will discuss binary evolution and the formation of blue stragglers and hot subdwarfs, and show that those hot objects are important in the study of evolutionary population synthesis (EPS), and conclude that binary interactions should be included in the study of EPS. Indeed, binary interactions make a stellar population younger (hotter), and the far-ultraviolet (UV) excess in elliptical galaxies is shown to be most likely resulted from binary interactions. This has major implications for understanding the evolution of the far-UV excess and elliptical galaxies in general. In particular, it implies that the far-UV excess is not a sign of age, as had been postulated prviously and predicts that it should not be strongly dependent on the metallicity of the population, but exists universally from dwarf ellipticals to giant ellipticals.

scholarly journals Ages of Giant Elliptical Galaxies as Evidence for the Cosmological Constant

1999 ◽  
Vol 183 ◽  
pp. 140-144
Author(s):  
Young-Wook Lee
Keyword(s):  
Cosmological Constant ◽  
Time Scale ◽  
Ad Hoc ◽  
Elliptical Galaxies ◽  
Alternative Interpretation ◽  
Population Synthesis ◽  
Compelling Evidence ◽  
Future Space ◽  
Scale Test ◽  
Ultraviolet Observations

There is a compelling evidence for old ages of giant elliptical galaxies, about 3 Gyrs older than our Galaxy, from space ultraviolet observations and new population synthesis models. Alternative interpretation requires ad-hoc assumptions yet it produces poor fitting to observational data. If confirmed by future space UV mission, this would provide evidence for non-zero cosmological constant from time scale test.

scholarly journals Diffuse LINER-type emission from extended disc regions of barred galaxies

2020 ◽  
Vol 496 (1) ◽  
pp. 36-48 ◽  
Author(s):  
S M Percival ◽  
P A James
Keyword(s):  
Line Emission ◽  
Elliptical Galaxies ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Population Synthesis ◽  
Full Sample ◽  
Barred Galaxies ◽  
Horizontal Branch Stars ◽  
Ambient Gas ◽  
Barred Spiral Galaxies

ABSTRACT We present a spectroscopic analysis of the central disc regions of barred spiral galaxies, concentrating on the region that is swept by the bar but not including the bar itself (the ‘star formation desert’ or SFD region). New spectroscopy is presented for 34 galaxies, and the full sample analysed comprises 48 SBa–SBcd galaxies. These data confirm the full suppression of SF within the SFD regions of all but the latest type (SBcd) galaxies. However, diffuse [N ii] and H α line emission is detected in all galaxies. The ubiquity and homogeneous properties of this emission from SBa to SBc galaxies favour post-asymptotic giant branch (p-AGB) stars as the source of this line excitation, rather than extreme blue horizontal branch stars. The emission-line ratios strongly exclude any contribution from recent SF, but are fully consistent with recent population synthesis modelling of p-AGB emission by other authors, and favour excitation dominated by ambient gas of approximately solar abundance, rather than ejecta from the AGB stars themselves. The line equivalent widths are also larger than those observed in many fully passive (e.g. elliptical) galaxies, which may also be a consequence of a greater ambient gas density in the SFD regions.

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