4307974
Distance to the Virgo cluster galaxy M100 from Hubble Space Telescope observations of Cepheids
Accurate distances to galaxies are critical for determining the present expansion rate of the Universe or Hubble constant (H0). An important step in resolving the current uncertainty in H0 is the measurement of the distance to the Virgo cluster of galaxies. New observations using the Hubble Space Telescope yield a distance of 17.1 ± 1.8 Mpc to the Virgo cluster galaxy M100. This distance leads to a value of H0 = 80 ± 17 km s−1 Mpc−1. A comparable value of H0 is also derived from the Coma cluster using independent estimates of its distance ratio relative to the Virgo cluster.
15067001
The Hubble Constant from the HST Key Project on the Extragalactic Distance Scale
The final efforts of the HST Key Project on the Extragalactic Distance Scale are presented. Four distance indicators, the Surface Brightness Fluctuation method, the Fundamental Plane for early-type galaxies, the Tully-Fisher relation and the Type Ia Supernovae, are calibrated using Cepheid distances to galaxies within 25 Mpc. The calibration is then applied to distant samples reaching cz~10000 km/s and (in the case of SNIa) beyond. By combining the constraints imposed on the Hubble constant by the four distance indicators, we obtain H0 = 71+/-6 km/s/Mpc.
17391793
The Hubble Space Telescope key project on the extragalactic distance scale XXIV: the calibration of Tully-Fisher relations and the value of the Hubble constant
This paper presents the calibration of BVRIH-0.5 Tully-Fisher relations based on Cepheid distances to 21 galaxies within 25 Mpc and 23 clusters within 10,000 km s-1. These relations have been applied to several distant cluster surveys in order to derive a value for the Hubble constant, H0, mainly concentrating on an I-band all-sky survey by Giovanelli and collaborators, consisting of total I magnitudes and 50% line width data for ~550 galaxies in 16 clusters. For comparison, we also derive the values of H0 using surveys in the B and V bands by Bothun and collaborators, and in H band by Aaronson and collaborators. Careful comparisons with various other databases from the literature suggest that the H-band data, which have isophotal magnitudes extrapolated from aperture magnitudes rather than total magnitudes, are subject to systematic uncertainties. Taking a weighted average of the estimates of Hubble constants from four surveys, we obtain H0 = 71 ± 4 (random) ± 7 (systematic). We have also investigated how the value of H0 is affected by various systematic uncertainties, such as the internal extinction correction method used, Tully-Fisher slopes and shapes, a possible metallicity dependence of the Cepheid period-luminosity relation, and cluster population incompleteness bias.
119525918
The Extragalactic Distance Scale Key Project. VIII. The Discovery of Cepheids and a New Distance to NGC 3621 Using the Hubble Space Telescope
We report on the discovery of Cepheids in the field spiral galaxy NGC 3621, based on observations made with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope (HST). NGC 3621 is one of 18 galaxies observed as a part of the HST Key Project on the Extragalactic Distance Scale, which aims to measure the Hubble constant to 10% accuracy. Sixty-nine Cepheids with periods in the range 9-60 days were observed over 12 epochs using the F555W filter, and over four epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent packages, DAOPHOT II/ALLFRAME and DoPHOT. Period-luminosity relations in the V and I bands were constructed using 36 fairly isolated Cepheids present in our set of 69 variables. Extinction-corrected distance moduli relative to the LMC of 10.63 ? 0.09 and 10.56 ? 0.10 mag were obtained using the ALLFRAME and DoPHOT data, respectively. True distance moduli of 29.13 ? 0.18 and 29.06 ? 0.18 mag, corresponding to distances of 6.3 ? 0.7 and 6.1 ? 0.7 Mpc, were obtained by assuming values of ?0 = 18.50 ? 0.10 mag and E(V - I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.
120455459
Long-period variables in the Large Magellanic Cloud. II. Infrared photometry, spectral classification, AGB evolution, and spatial distribution
Infrared JHK photometry and visual spectra have been obtained for a large sample of long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Various aspects of the asymptotic giant branch (AGB) evolution of LPVs are discussed using these data. The birth/death rate of LPVs of different ages in the LMC is compared with the birth rates of appropriate samples of planetary nebulas, clump stars, Cepheids, and OH/IR stars. It appears that there are much fewer large-amplitude LPVs per unit galactic stellar mass in the LMC than in the Galaxy. It is suggested that this may be due to the fact that the evolved intermediate-age AGB stars in the LMC often turn into carbon stars, which tend to have smaller pulsation amplitudes than M stars. There is also a major discrepancy between the number of LPVs in the LMC (and in the Galaxy) and the number predicted by the theories of AGB evolution, pulsation, and mass loss. A distance modulus to the LMC of 18.66 + or - 0.05 is derived by comparing the LMC LPVs with P about 200 days with the 47 Tucanae Mira variables in the (K, log P) plane. 64 refs.
197531313
The HST Key Project on the Extragalactic Distance Scale. XXVIII. Combining the Constraints on the Hubble Constant
Since the launch of the Hubble Space Telescope nine years ago, Cepheid distances to 25 galaxies have been determined for the purpose of calibrating secondary distance indicators. A variety of these can now be calibrated, and the accompanying papers by Sakai, Kelson, Ferrarese, and Gibson employ the full set of 25 galaxies to consider the Tully-Fisher relation, the fundamental plane of elliptical galaxies, Type Ia supernovae, and surface brightness fluctuations. 
When calibrated with Cepheid distances, each of these methods yields a measurement of the Hubble constant and a corresponding measurement uncertainty. We combine these measurements in this paper, together with a model of the velocity field, to yield the best available estimate of the value of H_0 within the range of these secondary distance indicators and its uncertainty. 
The result is H_0 = 71 +/- 6 km/sec/Mpc. The largest contributor to the uncertainty of this 67% confidence level result is the distance of the Large Magellanic Cloud, which has been assumed to be 50 +/- 3 kpc.
18693900
TeV Gamma-Ray Observations of the Perseus and Abell 2029 Galaxy Clusters
Galaxy clusters might be sources of TeV gamma rays emitted by high-energy protons and electrons accelerated by large-scale structure formation shocks, galactic winds, or active galactic nuclei. Furthermore, gamma rays may be produced in dark matter particle annihilation processes at the cluster cores. We report on observations of the galaxy clusters Perseus and A2029 using the 10 m Whipple Cerenkov telescope during the 2003-2004 and 2004-2005 observing seasons. We apply a two-dimensional analysis technique to scrutinize the clusters for TeV emission. In this paper we first determine flux upper limits on TeV gamma-ray emission from point sources within the clusters. Second, we derive upper limits on the extended cluster emission. We subsequently compare the flux upper limits with EGRET upper limits at 100 MeV and theoretical models. Assuming that the gamma-ray surface brightness profile mimics that of the thermal X-ray emission and that the spectrum of cluster cosmic rays extends all the way from thermal energies to multi-TeV energies with a differential spectral index of -2.1, our results imply that the cosmic-ray proton energy density is less than 7.9% of the thermal energy density for the Perseus Cluster.
121643265
The Science benefits and Preliminary Design of the Southern hemisphere Gravitational Wave Detector AIGO.
The proposed southern hemisphere gravitational wave detector AIGO increases the projected average baseline of the global array of ground based gravitational wave detectors by a factor ~4. This allows the world array to be substantially improved. The orientation of AIGO allows much better resolution of both wave polarisations. This enables better distance estimates for inspiral events, allowing unambiguous optical identification of host galaxies for about 25% of neutron star binary inspiral events. This can allow Hubble Law estimation without optical identification of an outburst, and can also allow deep exposure imaging with electromagnetic telescopes to search for weak afterglows. This allows independent estimates of cosmological acceleration and dark energy as well as improved understanding of the physics of neutron star and black hole coalescences. This paper reviews and summarises the science benefits of AIGO and presents a preliminary conceptual design.
117041277
Gravitational-Wave Astronomy: Aspects of the Theory of Binary Sources and Interferometric Detectors
This thesis presents a study of several problems and issues in the nascent field of gravitational-wave astronomy. Multi-kilometer baseline interferometers are being built in the United States [the LIGO (Laser Interferometer Gravitational-wave Observatory) project] and similar projects are underway in Europe (the VIRGO and GE0600 projects) and Japan (the TAMA300 project). LIGO will begin operations very soon (the first science run is scheduled for 2002), and detectors in other countries will begin soon as well. We are thus about 5 years from using gravitational waves as a new window to probe astrophysical processes in the universe. Chapters 2, 3, and 4 of this thesis study gravitational waves from coalescences of compact bi­naries. Chapters 2 and 3 are a detailed examination, in collaboration with Eanna E. Flanagan, of binary black hole (BBH) coalescences. The birth rate of BBH systems in the universe is highly uncertain, so it is not immediately apparent how relevant they are to gravitational-wave astronomy. If such systems do in fact exist, we find that they will be visible to extremely large distances, far greater than the distances to which binary neutron star systems, for example, will be visible. This heightened visibility may compensate for the possible dearth of such binaries, making them an ex­tremely important and interesting source. We suggest ways in which numerical modeling of BBHs may aid gravitational-wave data analysis, and techniques that can be used in BBH event searches and waveform analysis. Chapter 4 analyzes the measurement of gravitational waves from the final merger of binary neutron star systems. Such waves depend on details of the composition of neutron stars, such as their equation of state, and may be driven by hydrodynamic and nuclear processes that occur in the final merger. Unfortunately, these waves are emitted at high frequencies where LIGO­ type detectors have poor sensitivity. Measuring such waves will require specialty "narrow-band" detectors. In this chapter, I present an algorithm for optimally configuring a network of multiple LIGO-type and narrow-band detectors to measure these merger waves. I find that improved 
theoret­ical modeling of the final merger will play an important role in designing such networks and in the analysis of their data. In Chapter 5, in collaboration with Patrick R. Brady, I analyze the stability of binary neutron star systems as they coalesce. Some rather controversial numerical calculations have found that neutron stars in binary systems are rendered unstable by their companion, and may collapse into black holes long before their final merger. This would have a huge impact on the gravitational waves such systems emit. The claimed effect is first-order in a particular expansion. Motivated by this claim, Brady and I perform a first-order expansion of the fluid and field equations of general relativity, in the limit in which one star is much smaller than the other. We find that no such effect can exist. Finally, Chapter 6 is an analysis, in collaboration with Kip S. Thorne, of seismic gravity-gradient noise, a noise source that may be of concern to future detector designs. This noise source arises from fluctuations in the density of the earth near and below a LIGO-type interferometer's test masses. It is gravitational in origin, and thus cannot be shielded. By carefully studying the geological structures in the earth near the two LIGO sites, considering the propagation of elastodynamic waves in such structures, and computing the gravitational fluctuations such waves cause, we find seismic gravity-gradient noise is likely to become unavoidable at frequencies below roughly 5 Hertz. This has strong implications on plans to improve the low frequency sensitivity of the LIGO detectors.
56110611
Black hole binary inspiral and trajectory dominance
Perimeter Institute for Theoretical Physics, Waterloo, ON N2L 2Y5, CanadaGravitational waves emitted during the inspiral, plunge and merger of a black holebinary carry linear momentum. This results in an astrophysically important recoil tothe nal merged black hole, a \kick" that can eject it from the nucleus of a galaxy.In a previous paper we showed that the puzzling partial cancellation of an earlykick by a late antikick, and the dependence of the cancellation on black hole spin,can be understood from the phenomenology of the linear momentum waveforms.Here we connect that phenomenology to its underlying cause, the spin-dependenceof the inspiral trajectories. This insight suggests that the details of plunge can be
1891241
How black holes get their kicks: Radiation recoil in binary black hole mergers
Gravitational waves from the coalescence of binary black holes carry linear momentum, causing center of mass recoil. This ``radiation rocket'' has important implications for systems with escape speeds of order the recoil velocity. We describe new recoil calculations using high precision black hole perturbation theory to estimate the magnitude of the recoil for the slow ``inspiral'' coalescence phase; coupled with a cruder calculation for the final ``plunge'', we estimate the total recoil imparted to a merged black hole. We find that velocities of many tens to a few hundred km/sec can be achieved fairly easily. The recoil probably never exceeds about 500 km/sec.