Among the many monuments in the city of Washington, there is one only a block from the National Mall which offers a more human scale than the better-known commemorations of the sacrifices of war and ...the drive and inspiration of presidents, while giving the imagination wings to span the Universe. In front of the National Academy of Sciences, amid a grove of elm and holly trees that has made it a pleasant diversion for countless groups of schoolchildren during sultry Washington summers, is a statue of Albert Einstein. Sculptor Robert Berks has depicted him seated in thought, holding a tablet as if to echo traditional depictions of Moses bearing the tablets of the Law. Einstein's single tablet also depicts law three equations characteristic of Einsteins's major contributions to physics. Two of them date from his "miracle year" of a century ago. That year, 1905, saw his publication first of his explanation of the emission of electric current from certain metals (the photoelectric effect) in terms of the particle-like behavior of light work which was the primary driver for his Nobel Prize in 1921 followed quickly by the first revolution of relativity. This paper, "Zur Elektrodynamik bewegter Kiirper" or "On the electrodynamics of moving bodies", hid within a dry and pedestrian title a content which was explosive in both literal and metaphorical senses for physics, astrophysics, philosophy, and even the world balance of power. The tablet (Fig. 1.1) recognizes this with the most familiar equation in all of physics: E = mc2. The middle line of the tablet shows the relation between the energy of incoming radiation and electrons liberated by the photoelectric effect. The uppermost equation comes from the second of Einstein's revolutions, the formulation of general relativity. This work appeared only in 1916, after a digression as Einstein mastered the new mathematical tools it required. The bottom equation on the tablet relates the curvature of space to the density of mass and energy a discovery which superseded the physics of Newton, after two centuries, with an understanding which is at once more accurate and vastly stranger in concept.
Type Ia supernovae (SNe Ia) are used as 'standard candles' for cosmological distance scales. To fit their light-curve shape-absolute luminosity relation, one needs to assume an intrinsic colour and a ...likelihood of host galaxy extinction or a convolution of these, a colour distribution prior. The host galaxy extinction prior is typically assumed to be an exponential drop-off for the current supernova programmes (...). We explore the validity of this prior using the distribution of extinction values inferred when two galaxies accidentally overlap (an occulting galaxy pair). We correct the supernova luminosity distances from the SDSS-III supernova projects (SDSS-SN) by matching the host galaxies to one of three templates from occulting galaxy pairs based on the host galaxy mass and the AV-bias-prior-scale (t0) relation from Jha et al. We find that introducing an AV prior that depends on host mass results in lowered luminosity distances for the SDSS-SN on average but it does not reduce the scatter in individual measurements. This points, in our view, to the need for many more occulting galaxy templates to match to SN Ia host galaxies to rule out this possible source of scatter in the SN Ia distance measurements. We match occulting galaxy templates based on both mass and projected radius and we find that one should match by stellar mass first with radius as a secondary consideration. We discuss the caveats of the current approach: the lack of enough radial coverage, the small sample of priors (occulting pairs with HST data), the effect of gravitationally interacting as well as occulting pairs, and whether an exponential distribution is appropriate. Our aim is to convince the reader that a library of occulting galaxy pairs observed with HST will provide sufficient priors to improve (optical) SN Ia measurements to the next required accuracy in cosmology. (ProQuest: ... denotes formulae/symbols omitted.)
Type Ia supernovae (SNe Ia) are used as 'standard candles' for cosmological distance scales. To fit their light-curve shape-absolute luminosity relation, one needs to assume an intrinsic colour and a ...likelihood of host galaxy extinction or a convolution of these, a colour distribution prior. The host galaxy extinction prior is typically assumed to be an exponential drop-off for the current supernova programmes (...). We explore the validity of this prior using the distribution of extinction values inferred when two galaxies accidentally overlap (an occulting galaxy pair). We correct the supernova luminosity distances from the SDSS-III supernova projects (SDSS-SN) by matching the host galaxies to one of three templates from occulting galaxy pairs based on the host galaxy mass and the AV-bias-prior-scale (t0) relation from Jha et al. We find that introducing an AV prior that depends on host mass results in lowered luminosity distances for the SDSS-SN on average but it does not reduce the scatter in individual measurements. This points, in our view, to the need for many more occulting galaxy templates to match to SN Ia host galaxies to rule out this possible source of scatter in the SN Ia distance measurements. We match occulting galaxy templates based on both mass and projected radius and we find that one should match by stellar mass first with radius as a secondary consideration. We discuss the caveats of the current approach: the lack of enough radial coverage, the small sample of priors (occulting pairs with HST data), the effect of gravitationally interacting as well as occulting pairs, and whether an exponential distribution is appropriate. Our aim is to convince the reader that a library of occulting galaxy pairs observed with HST will provide sufficient priors to improve (optical) SN Ia measurements to the next required accuracy in cosmology. (ProQuest: ... denotes formulae/symbols omitted.)
The Dynamics of A2125 Miller, Neal A; Owen, Frazer N; Hill, John M ...
The Astrophysical journal,
10/2004, Letnik:
613, Številka:
2
Journal Article
Recenzirano
We present 371 galaxy velocities in the field of the very rich cluster A2125 (z approximately 0.25). These were determined using optical spectroscopy collected over several years from both the WIYN ...3.5 m telescope and NOAO Mayall 4 m telescope. Prior studies at a variety of wavelengths (radio, optical, and X-ray) have indicated that A2125 is a likely cluster-cluster merger, a scenario that we are able to test using our large velocity database. We identified 224 cluster galaxies, which were subjected to a broad range of statistical tests using both positional and velocity information to evaluate the cluster dynamics and substructure. The tests confirmed the presence of substructures within the A2125 system at high significance, demonstrating that A2125 is a complex dynamical system. Comparison of the test results with existing simulations strengthens the merger hypothesis and provides clues about the merger geometry and stage. The merger model for the system can reconcile A2125's low X-ray temperature and luminosity with its apparently high richness and might also explain A2125's high fraction of active galaxies identified in prior radio and optical studies.
The emission spectra of 29 spiral galaxies with low-ionization emission have been studied in detail, using synthetic galaxy spectra to correct the observed spectra for the contribution of starlight. ...The resulting emission-line intensities and ratios have been compared to published models of shock-heated and power-law photoionized plasmas. The observed spectra are best described by models in which a weak flat-spectrum (power-law) radiation field photoionizes the gas; this nonthermal continuum is generally too weak to be seen directly in the optical. Broad H-alpha emission, extending over a total velocity range as great as 4000 km/s, is identified in several 'normal' nuclei with strong low-ionization emission. The inferred nonthermal continuum and observed broad permitted lines indicate the presence of low-luminosity active nuclei in most, if not all, spiral galaxies.
We present a set of 180 active galactic nucleus (AGN) candidates based on color selection from the IRAS slow-scan deep observations, with color criteria broadened from the initial Point Source ...Catalog samples so as to include similar objects with redshifts up to z = 1 and allowing for two-band detections. Spectroscopic identifications have been obtained for 80 (44%); some additional identifications are secure based on radio detections or optical morphology, although yet unobserved spectroscopically. These spectroscopic identifications include 13 type 1 Seyfert galaxies, 17 type 2 Seyferts, 29 starburst galaxies, 7 LINER systems, and 13 emission-line galaxies so heavily reddened as to remain of ambiguous classification. The optical magnitudes range from R = 12.0 to 20.5; the counts suggest that incompleteness is important fainter than R = 15.5. Redshifts extend to z = 0.51, with a significant part of the sample at z > 0.2. Even with the relaxed color criteria, this sample includes slightly more AGNs than star-forming systems among those where the spectra contain enough diagnostic feature to make the distinction. The active nuclei include several broad-line objects with strong Fe II emission, and composite objects with the absorption-line signatures of fading starbursts. These AGNs with warm far-IR colors have little overlap with the "red AGNs" identified with 2MASS; only a single Seyfert 1 was detected by 2MASS with J - K > 2. Some reliable IRAS detections have either very faint optical counterparts or only absorption-line galaxies, potentially being deeply obscured AGNs. The IRAS detections include a newly identified symbiotic star, and several possible examples of the "Vega phenomenon," including dwarfs as cool as type K. Appendices detail these candidate stars, and the optical-identification content of a particularly deep set of high-latitude IRAS scans (probing the limits of optical identification from IRAS data alone).
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