17,762 research outputs found
Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: Galaxies in the Coma I Cloud
The membership of some galaxies in the nearby (d ~ 12 Mpc) Coma I cloud is
uncertain. Here we present globular cluster luminosity functions (GCLFs) from
the HST for two bright ellipticals which may belong to this group. After
fitting the GCLF, we find a turnover magnitude of m_V^0 = 23.23 +/- 0.11 for
NGC 4278 and m_V^0 = 23.07 +/- 0.13 for NGC 4494. Our limiting magnitude is
about two magnitudes fainter than these values, making this data among the most
complete GCLFs published to date. The fitted GCLF dispersions (~ 1.1 mag.) are
somewhat smaller than typical values for other ellipticals. Assuming an
absolute turnover magnitude of M_V^0 = -7.62, and after applying a small
metallicity correction, we derive distance modulii of (m -- M) = 30.61 +/- 0.14
for NGC 4278 and 30.50 +/- 0.15 for NGC 4494. These distance estimates are
compared to other methods, and lie within the published range of values. We
conclude that both galaxies lie at the same distance and are both members of
the Coma I cloud.Comment: 13 pages, Latex. Full paper also available at
http://www.ucolick.org/~forbes/home.htm
Globular Clusters and Galaxy Formation
Globular clusters provide a unique probe of galaxy formation and evolution.
Here I briefly summarize the known observational properties of globular cluster
systems. One re-occurring theme is that the globular cluster systems of spirals
and ellipticals are remarkably similar. Photometry, and the limited spectra
available, are consistent with metal-poor clusters forming before the main
spheroid component is established and the metal-rich ones forming at the same
time as the spheroid in a burst of star formation. These observations are
compared to a model for globular cluster formation in a LCDM hierarchical
universe. One model result reported here is that S_N is determined at early
times and little affected by late epoch mergers.Comment: 2 pages, Latex, 2 figures, To appear in the proceedings of Galaxy
Evolution: Theory and Observations, ed. V. Avila-Reese, C. Firmani, C. Frenk,
C. Allen, RevMexA
The Globular Cluster Systems of Ellipticals and Spirals
In this overview of the key properties of globular cluster (GC) systems I
show that the GCs in elliptical and spiral host galaxies have more in common
than previously thought. After contrasting these properties I briefly comment
on GC formation.Comment: 6 pages, Latex, 4 figures, To appear in the proceedings of IAU Symp.
207, "Extragalactic Star Clusters", eds. Grebel, Geisler, Minnit
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Completing the design spectra for graphs with six vertices and eight edges
Apart from two possible exceptions, the design spectrum has been determined for every graph with six vertices and at most eight edges. The purpose of this note is to establish the existence of the two missing designs, both of order 32
Improved Soundness for QMA with Multiple Provers
We present three contributions to the understanding of QMA with multiple
provers:
1) We give a tight soundness analysis of the protocol of [Blier and Tapp,
ICQNM '09], yielding a soundness gap Omega(1/N^2). Our improvement is achieved
without the use of an instance with a constant soundness gap (i.e., without
using a PCP).
2) We give a tight soundness analysis of the protocol of [Chen and Drucker,
ArXiV '10], thereby improving their result from a monolithic protocol where
Theta(sqrt(N)) provers are needed in order to have any soundness gap, to a
protocol with a smooth trade-off between the number of provers k and a
soundness gap Omega(k^2/N), as long as k>=Omega(log N). (And, when
k=Theta(sqrt(N)), we recover the original parameters of Chen and Drucker.)
3) We make progress towards an open question of [Aaronson et al., ToC '09]
about what kinds of NP-complete problems are amenable to sublinear
multiple-prover QMA protocols, by observing that a large class of such examples
can easily be derived from results already in the PCP literature - namely, at
least the languages recognized by a non-deterministic RAMs in quasilinear time.Comment: 24 pages; comments welcom
Passive laser irradiation as a tool for optical catalysis
The mechanisms of absorption, emission, and scattering of photons form the foundations of optical interactions between light and matter. In the vast majority of such interactions there is a significant interplay and energy exchange between the radiation field and the material components. In absorption for example, modes of the field are depopulated by photons whose energy is at resonance with a molecular transition producing excited material states. In all such optical phenomena, the initial state of the radiation field differs in mode occupation to its final state. However, certain optical processes can involve off-resonance laser beams that are unchanged on interaction with the material: the output light, after interaction, is identical to the laser input. Such off-resonance interactions include forward Rayleigh scattering, responsible for the wellknown gradient force in optical trapping, and the laser-induced intermolecular interaction commonly termed optical binding; in both processes, an intense beam delivers its effect without suffering change. It is possible for beams detuned from resonance to provide not only techniques for optomechanical and optical manipulation, but also to passively influence other important and functional interactions such as absorption from a resonant beam, or energy transfer. Such effects can be grouped under the banner of ‘optical catalysis’, since they can significantly influence resonant processes. Furthermore, off-resonance photonics affords a potential to impact on chemical interactions, as in the passive modification of rotational constants and phase transitions. To date, apart from optical manipulation, the potential applicability of passive photonics, particularly in the realm of chemical physics and materials science, has received little attention. Here we open up this field, highlighting the distinct and novel role that off-resonance laser beams and the ensuing photonics can play
UBRI Photometry of Globular Clusters in the Leo Group Galaxy NGC 3379
We present wide area UBRI photometry for globular clusters around the Leo
group galaxy NGC 3379. Globular cluster candidates are selected from their
B-band magnitudes and their (U-B)o vs (B-I)o colours. A colour-colour selection
region was defined from photometry of the Milky Way and M31 globular cluster
systems. We detect 133 globular cluster candidates which, supports previous
claims of a low specific frequency for NGC 3379. The Milky Way and M31 reveal
blue and red subpopulations, with (U-B)o and (B-I)o colours indicating mean
metallicities similar to those expected based on previous spectroscopic work.
The stellar population models of Maraston (2003) and Brocato etal (2000) are
consistent with both subpopulations being old, and with metallicities of [Fe/H]
\~ -1.5 and -0.6 for the blue and red subpopulations respectively. The models
of Worthey (1994) do not reproduce the (U-B)o colours of the red (metal-rich)
subpopulation for any modelled age. For NGC 3379 we detect a blue subpopulation
with similar colours and presumably age/metallicity, to that of the Milky Way
and M31 globular cluster systems. The red subpopulation is less well defined,
perhaps due to increased photometric errors, but indicates a mean metallicity
of [Fe/H] ~ -0.6.Comment: 12 pages, Latex, 10 figures, 1 table, submitted for publication in
MNRAS, Fig. 11 available in source file or from [email protected]
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