Related papers: Revisit of cosmic age problem
We present new high signal-to-noise spectroscopic data on the M31 globular cluster system, obtained with the Hectospec multifiber spectrograph on the 6.5m MMT. More than 300 clusters have been observed at a resolution of 5A. The primary…
New age determinations of the galactic disk globular clusters 47 Tuc, M71 and NGC6352 have been performed with our up-to-date alpha-enhanced stellar models. We find that all three clusters are about 9.2 Gyr old and therefore coeval with the…
In a recent striking discovery, Dunlop {\bf \it et al} observed a galaxy at redshift z=1.55 with an estimated age of 3.5 Gyr. This is incompatible with age estimates for a flat matter dominated universe unless the Hubble constant is less…
Recently H(z) data obtained from differential ages of galaxies have been proposed as a new geometrical probe of dark energy. In this paper we use those data, combined with other background tests (CMB shift and SNIa data), to constrain a set…
We present integrated photometry and color-magnitude diagrams (CMDs) for 24 star clusters in M33, of which 12 were previously uncataloged. These results are based on Advanced Camera for Surveys observations from the Hubble Space Telescope…
In this note, we test the original holographic dark energy model with some old high redshift objects. The main idea is very simple: the universe cannot be younger than its constituents. We find that the original holographic dark energy…
Our proposed cosmological framework, which is based on fractional quantum cosmology, aims to address the issue of synchronicity in the age of the universe. To achieve this, we have developed a new fractional $\Lambda$CDM cosmological model.…
Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that…
Globular Clusters (GCs) in the Milky Way are the primary laboratories for establishing the ages of the oldest stellar populations and for measuring the color-magnitude relation of stars. In infrared (IR) color-magnitude diagrams (CMDs), the…
There have been a number of studies dedicated to identification of fossil galaxy groups, arguably groups with a relatively old formation epoch. Most of such studies identify fossil groups, primarily based on a large luminosity gap, which is…
We present explicit expressions for the calculation of cosmological look back time, for zero cosmological constant and arbitrary density parameter $\Omega$, which, in the limit as redshift becomes infinite, give the age of the universe. The…
Using multi-wavelength imaging from the Wide Field Camera 3 on the Hubble Space Telescope we study the stellar cluster populations of two adjacent fields in the nearby face-on spiral galaxy, M83. The observations cover the galactic centre…
The Magellanic Clouds host a large population of massive (> 10^4 Msun) star clusters with ages ranging from a few Myr to 12 Gyr. In nearly all cases, close inspection of their CMDs reveals features that deviate from expectations of a…
We put constraints on the main cosmological parameters of different spatially flat cosmological models by combining the recent clustering results of XMM-Newton soft (0.5-2 keV) X-ray sources, which have a redshift distribution with median…
We present a sample of 11 M31 Cepheids in stellar clusters, derived from the overlap of the Panchromatic Hubble Andromeda Treasury (PHAT) cluster catalog and the Pan-STARRS1 (PS1) disk Cepheid catalog. After identifying the PS1 Cepheids in…
Nine presently known "young" Galactic globular clusters, which have ages / 3 Gyr smaller than the oldest clusters of similar metallicity, all have RGC > 15 kpc. Furthermore these young globulars are found to have below-average luminosities.…
I review the challenges and problems facing the standard cosmological model, involving an $\Omega=1$ Universe dominated by non-baryonic dark matter, which arise due to: age estimates of the universe, estimates of the baryon fraction of the…
The formation details of globular clusters (GCs) are still poorly understood due to their old ages and the lack of detailed observations of their formation. A large variety of models for the formation and evolution of GCs have been created…
There is a deep cosmological mystery: although dependent on very different underlying physics, the timescales of structure formation, of galaxy cooling (both radiatively and against the CMB), and of vacuum domination do not differ by many…
We present our new, fully-automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo…