scholarly journals M31 Globular Cluster Metallicities and Ages

2002 ◽  
Vol 207 ◽  
pp. 58-61
Author(s):  
Pauline Barmby
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Globular Cluster ◽  
Chemical Enrichment ◽  
Detailed Explanation ◽  
Age Gap ◽  
Small Delay ◽  
Age Of The Universe ◽  
Lower Limits ◽  
The Universe

Globular cluster ages are more than just lower limits to the age of the universe; the distribution of ages constraints the timescales for galaxy formation and chemical evolution. Globular cluster populations with different metallicities have now been detected in many galaxies, and understanding how these populations formed requires knowing their relative ages. We examined the relative ages of the two M31 globular cluster populations using their color and luminosity distributions and found that the metal-rich clusters could be up to 50% younger than the metal-poor clusters. While a small delay in the formation of metal-rich clusters might be imposed by chemical enrichment timescales, a large age gap demands a more detailed explanation. I outline several possibilities and their promises and problems.

scholarly journals Hipparcos subdwarfs and globular cluster ages: towards reliable absolute ages

1997 ◽  
Vol 189 ◽  
pp. 433-438 ◽  
Author(s):  
F. Pont ◽  
M. Mayor ◽  
C. Turon
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Large Fraction ◽  
Age Determination ◽  
Colour Scale ◽  
Minimum Age ◽  
Age Of The Universe ◽  
Robust Prediction ◽  
The Universe ◽  
Cluster Age

The maximum age of galactic globular clusters provides the best observational constraint on the minimum age of the Universe. One of the main “missing link” in the globular cluster age determination has been the lack of a precise calibration, with local subdwarfs, of the position of the subdwarf sequence at different [Fe/H].Hipparcos data may change this situation. As many precise parallaxes become available for local subdwarfs, the distance to globular clusters can be estimated directly from ZAMS fitting to the subdwarf locus. The ages can then be inferred from the turnoff luminosity (a robust prediction of stellar evolution models), rather than using secondary indicators such as Horizontal-Branch position, or indicators depending on the uncertain colour scale such as turnoff colour.Combining Hipparcos parallaxes with [Fe/H] values determined with the CORAVEL spectrometer, we are studying the position of the subdwarfs in the Colour-Magnitude Diagram from a sample of more than 900 subdwarf candidates. Preliminary results are presented here. It is shown that the distances of many subdwarfs had been underestimated in previous studies, mainly because a large fraction of them is in fact evolved off the main sequence into the turnoff or the subgiant branch.

scholarly journals Observational Searches for Star-Forming Galaxies at z > 6

2016 ◽  
Vol 33 ◽  
Author(s):  
Steven L. Finkelstein
Keyword(s):  
Galaxy Evolution ◽  
Galaxy Formation ◽  
Cosmic Time ◽  
Mass Function ◽  
Star Forming ◽  
Chemical Enrichment ◽  
Large Samples ◽  
Galaxy Formation And Evolution ◽  
Observational Techniques ◽  
The Universe

AbstractAlthough the universe at redshifts greater than six represents only the first one billion years (< 10%) of cosmic time, the dense nature of the early universe led to vigorous galaxy formation and evolution activity which we are only now starting to piece together. Technological improvements have, over only the past decade, allowed large samples of galaxies at such high redshifts to be collected, providing a glimpse into the epoch of formation of the first stars and galaxies. A wide variety of observational techniques have led to the discovery of thousands of galaxy candidates at z > 6, with spectroscopically confirmed galaxies out to nearly z = 9. Using these large samples, we have begun to gain a physical insight into the processes inherent in galaxy evolution at early times. In this review, I will discuss (i) the selection techniques for finding distant galaxies, including a summary of previous and ongoing ground and space-based searches, and spectroscopic follow-up efforts, (ii) insights into galaxy evolution gleaned from measures such as the rest-frame ultraviolet luminosity function, the stellar mass function, and galaxy star-formation rates, and (iii) the effect of galaxies on their surrounding environment, including the chemical enrichment of the universe, and the reionisation of the intergalactic medium. Finally, I conclude with prospects for future observational study of the distant universe, using a bevy of new state-of-the-art facilities coming online over the next decade and beyond.

scholarly journals Thousands of Milky Ways: galaxy satellites and building blocks

2009 ◽  
Vol 5 (S262) ◽  
pp. 240-243
Author(s):  
Nelson Padilla ◽  
Claudia Lagos ◽  
Sofía Cora
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Galactic Nuclei ◽  
Building Blocks ◽  
Chemical Enrichment ◽  
Stellar Formation ◽  
History Of ◽  
The Universe

AbstractA semi-analytic model of galaxy formation with and without active galactic nuclei feedback is used to study the nature of possible building blocks (BBs) of z = 0 galaxies, including those of Milky-Way types. We find that BBs can show an important range of properties arising from environmental variables such as host halo mass, and whether a galaxy is a satellite within its host halo; the stellar formation histories are comparatively faster and the chemical enrichment is more efficient in BBs than in surviving satellites, in accordance with recent metallicity measurements for the Milky Way. These results can be used in combination with observational constraints to continue probing the ability of the cold dark-matter scenario to reproduce the history of galaxy demography in the Universe.

scholarly journals Modelling the Chemical Evolution

2009 ◽  
Vol 5 (S265) ◽  
pp. 325-335
Author(s):  
Gerhard Hensler ◽  
Simone Recchi
Keyword(s):  
Chemical Evolution ◽  
Metal Enrichment ◽  
Element Abundances ◽  
Chemical Enrichment ◽  
Direct Observations ◽  
Trace Back ◽  
Astrophysical Objects ◽  
The One ◽  
The Universe ◽  
Insight Into

AbstractAdvanced observational facilities allow to trace back the chemical evolution of the Universe, on the one hand, from local objects of different ages and, secondly, by direct observations of redshifted objects. The chemical enrichment serves as one of the cornerstones of cosmological evolution. In order to understand this chemical evolution in morphologically different astrophysical objects models are constructed based on analytical descriptions or numerical methods. For the comparison of their chemical issues, as there are element abundances, gradients, and ratios, with observations not only the present-day values are used but also their temporal evolution from the first era of metal enrichment. Here we will provide some insight into basics of chemical evolution models, highlight advancements, and discuss a few applications.

scholarly journals Chemical enrichment and feedback in low metallicity environments: constraints on galaxy formation

2008 ◽  
Vol 4 (S255) ◽  
pp. 134-141
Author(s):  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Chemical Properties ◽  
Building Blocks ◽  
Formation Mechanisms ◽  
Chemical Enrichment ◽  
Stellar Feedback ◽  
R Process

AbstractChemical evolution models for dwarf metal poor galaxies, including dwarf irregulars and dwarf spheroidals will be presented. The main ingredients necessary to build detailed models of chemical evolution including stellar nucleosynthesis, supernova progenitors, stellar lifetimes and stellar feedback will be discussed. The stellar feedback will be analysed in connection with the development of galactic winds in dwarf galaxies and their effects on the predicted abundances and abundance ratios. Model results concerning α-elements (O, Mg, Si, Ca), Fe and s-and r-process elements will be discussed and compared with the most recent observational data for metal poor galaxies of the Local Group. We will show how the study of abundance ratios versus abundances can represent a very powerful tool to infer constraints on galaxy formation mechanisms. In this framework, we will discuss whether, on the basis of their chemical properties, the dwarf galaxies of the Local Group could have been the building blocks of the Milky Way.

scholarly journals The Cosmic Chemical Evolution as seen by the Brightest Events in the Universe

2009 ◽  
Vol 5 (S265) ◽  
pp. 139-146 ◽  
Author(s):  
Sandra Savaglio
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Gamma Ray ◽  
Host Galaxies ◽  
First Stars ◽  
Galaxy Surveys ◽  
Galaxy Formation And Evolution ◽  
Formation And Evolution ◽  
Field Galaxy ◽  
The Universe

AbstractGamma-ray bursts (GRBs) are the brightest events in the universe. They have been used in the last five years to study the cosmic chemical evolution, from the local universe to the first stars. The sample size is still relatively small when compared to field galaxy surveys. However, GRBs show a universe that is surprising. At z > 2, the cold interstellar medium in galaxies is chemically evolved, with a mean metallicity of about 1/10 solar. At lower redshift (z < 1), metallicities of the ionized gas are relatively low, on average 1/6 solar. Not only is there no evidence of redshift evolution in the interval 0 < z < 6.3, but also the dispersion in the ~30 objects is large. This suggests that the metallicity of host galaxies is not the physical quantity triggering GRB events. From the investigation of other galaxy parameters, it emerges that active star-formation might be a stronger requirement to produce a GRB. Several recent striking results strongly support the idea that GRB studies open a new view on our understanding of galaxy formation and evolution, back to the very primordial universe at z ~ 8.

scholarly journals Evolution of Metals and Stars in Damped Lyman-Alpha Galaxies

2005 ◽  
Vol 13 ◽  
pp. 566-571
Author(s):  
Varsha P. Kulkarni
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Current Data ◽  
Star Formation History ◽  
Lyman Alpha ◽  
Quasar Spectra ◽  
Formation History ◽  
Age Of The Universe ◽  
Line Imaging ◽  
The Universe

AbstractDamped Lyman-alpha absorbers in quasar spectra provide a unique tool to directly measure the abundances of elements in galaxies at red-shifts 0 < z < 5, and hence probe the chemical evolution of galaxies over > 90% of the age of the Universe. Since cosmic chemical evolution models predict the global metallicity of galaxies to increase with time, it is of great interest to determine whether DLAs actually show such a trend. We discuss statistical analysis of existing DLA Zn data to examine the metallicity-redshift relation, and a comparison of the observed data with models of cosmic chemical evolution. We also describe efforts to expand the DLA abundance sample at z < 1.5, where the current data are particularly sparse. Finally, we discuss emission-line imaging studies of the absorber galaxies and compare constraints on their star formation rates with models based on the global star formation history.

scholarly journals Constraints on Dark Matter Density and Axion Mass from the Large-Scale Structure of Spacetime

1987 ◽  
Vol 117 ◽  
pp. 491-491
Author(s):  
P.S. Joshi ◽  
B. Datta
Keyword(s):  
Dark Matter ◽  
Large Scale ◽  
Large Scale Structure ◽  
Maximum Density ◽  
Scale Structure ◽  
Axion Mass ◽  
Upper Limits ◽  
Age Of The Universe ◽  
Lower Limits ◽  
The Universe

On the basis of general properties of the large-scale structure of spacetime, we present new and general theoretical upper limits on the density of dark matter in the Universe, assuming a 90% content for the dark matter, and lower limits on the mass of the axion, assuming the dark matter to be made up of axions. These limits are derived in terms of the possible lower limits to the age of the Universe and the Hubble parameter. We find that for the age in the range (8–24) × 109yr, the maximum density of dark matter is in the range (1.25 × 10−28 −1.38 × 10−29) g cm−3 and the minimum value of axion mass in the ranges (0.36–2.39) × 10−5 eV and (1.44–9.51) × 10−5 eV.

scholarly journals The Main Sequence of the Very Old Globular Cluster NGC 6397

1980 ◽  
Vol 85 ◽  
pp. 423-423
Author(s):  
Gonzalo Alcaino ◽  
William Liller
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Narrow Range ◽  
Age Determination ◽  
The Sun ◽  
Age Of The Universe ◽  
The Universe ◽  
Photographic Photometry ◽  
Collapse Phase

We present photographic photometry for 1135 stars in the globular cluster NGC 6397, which, at a distance of 2.4 kpc, is most likely the second nearest globular to the Sun. The Racine wedge with the CTIO Yale 1 m telescope (Δm=3. 60 mag), the CTIO 4 m telescope (Δm=6. 83 mag) and the ESO 3.6 m telescope (Δm=3. 87 mag) was used to extend the photoelectric calibration from V≃16.1 to V≃20.7. The main sequence turnoff at V=16.7 and B-V=0.52 with respectively Mv =4.30 and (B-V)o =0.36 yields (m-M)v=12.40 and E(B-V)=0.16. Using the models of Iben and Rood (1970) and the isochrones of Demarque and McClure (1977), we deduce the cluster's age to be 17 × 109 years. This makes this object the oldest of the nine globular clusters with age determination and gives a lower limit to the age of the universe, rendering Ho ≤ 57 km sec−1 Mpc−1 if qo ≥ 0 is assumed. The large age spread of 6 billion years between NGC 6397 and 47 Tuc (the youngest counterpart with age data) indicates both that the protogalaxy underwent a slow collapse phase and that the abundances in globular clusters are lower for the oldest. The fact that the galactocentric distances for these clusters have the narrow range of 6 <R < 13 kpc makes it highly important to secure age data for extremely metal poor globulars far out in the halo.

scholarly journals Globular Clusters in Elliptical Galaxies: Constraints on Mergers

1999 ◽  
Vol 186 ◽  
pp. 181-184
Author(s):  
Duncan A. Forbes
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Elliptical Galaxies ◽  
Cluster System ◽  
Cluster Systems ◽  
Chemical Enrichment ◽  
Formation And Evolution ◽  
Globular Cluster System ◽  
Parent Galaxy

There exists a relationship between globular cluster mean metallicity and parent galaxy luminosity (e.g. Brodie & Huchra 1991; Forbes et al. 1996), which appears to be similar to that between stellar metallicity and galaxy luminosity. The globular cluster relation has a similar slope but is offset by about 0.5 dex to lower metallicity. The similarity of these relations suggests that both the globular cluster system and their parent galaxy have shared a common chemical enrichment history. If we can understand the formation and evolution of the globulars, we will also learn something about galaxy formation. With this aim in mind we have created the SAGES (Study of the Astrophysics of Globular clusters in Extragalactic Systems) project. Project members include Brodie, Elson, Forbes, Freeman, Grillmair, Huchra, Kissler–Patig and Schroder. We are using HST Imaging and Keck spectroscopy to study extragalactic globular cluster systems. Further details are given at http://www.ucolick.org/~mkissler/Sages/sages.html.

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