Gravitational lensing by elliptical galaxies

The fraction of high-redshift sources which are multiply-imaged by intervening galaxies is strongly dependent on the cosmological constant, and so can be a useful probe of the cosmological model. However its power is limited by various systematic (and random) uncertainties in the calculation of lensing probabilities, one of the most important of which is the dynamical normalisation of elliptical galaxies. Assuming ellipticals' mass distributions can be modelled as isothermal spheres, the mass normalisation depends on: the velocity anisotropy; the luminosity density; the core radius; and the area over which the velocity dispersion is measured. The differences in the lensing probability and optical depth produced by using the correct normalisation can be comparable to the differences between even the most extreme cosmological models. The existing data is not sufficient to determine the correct normalisation with enough certainty to allow lensing statistics to be used to their full potential. However, as the correct lensing probability is almost certainly higher than is usually assumed, upper bounds on the cosmological constant are not weakened by these possibilities.Comment: MNRAS, in press; 13 pages, 22 figure

Gravitational lensing in galaxy redshift surveys

Gravitationally-lensed quasars should be discovered as a by-product of large galaxy redshift surveys, being discovered spectroscopically when a low-redshift galaxy exhibits high-redshift quasar emission lines. The number of lenses expected is higher than previously estimated, mainly due to the fact that the presence of the quasar images brings faint deflector galaxies above the survey limit. Thus the a posteriori likelihood of the discovery of Q 2237+0305 in the Center for Astrophysics redshift survey is approximately 0.03. In the future, the 2 degree Field survey should yield at least 10 lensed quasars, and the Sloan Digitial Sky Survey up to 100.Comment: Gravitational Lensing: Recent Progress and Future Goals, C.S. Kochanek & T.G. Brainerd, eds., in press; 2 pages, 1 figur

Using the 2dF galaxy redshift survey to detect gravitationally-lensed quasars

Galaxy redshift surveys can be used to detect gravitationally-lensed quasars if the spectra obtained are searched for the quasars' emission lines. Previous investigations of this possibility have used simple models to show that the 2 degree Field (2dF) redshift survey could yield several tens of new lenses, and that the larger Sloan Digital Sky Survey should contain an order of magnitude more. However the particular selection effects of the samples were not included in these calculations, limiting the robustness of the predictions; thus a more detailed simulation of the 2dF survey was undertaken here. The use of an isophotal magnitude limit reduces both the depth of the sample and the expected number of lenses, but more important is the Automatic Plate Measuring survey's star-galaxy separation algorithm, used to generate the 2dF input catalogue. It is found that most quasar lenses are classed as merged stars, with only the few lenses with low-redshift deflectors likely to be classified as galaxies. Explicit inclusion of these selection effects implies that the 2dF survey should contain 10 lenses on average. The largest remaining uncertainty is the lack of knowledge of the ease with which any underlying quasars can be extracted from the survey spectra.Comment: MNRAS, in press; 14 pages, 19 figure

Who rules the centre of care? : an institutional ethnography exploring patient experiences within the New Zealand primary care setting : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Nursing, Massey University, Manawatū, New Zealand

Improving ‘patient experience’ is at the forefront of international quality improvement agendas and is prioritised by dominant frameworks such as the Institute for Healthcare Improvement’s ‘Triple Aim.’ To gather knowledge of this priority measure, New Zealand developed a set of ‘system level measures’ to benchmark and compare data between local, national and international health systems. The primary care patient experience survey, introduced as a system level measure, is purported to measure ‘patient experience.’ The survey produces official reports of a person/patient-centred primary care system. However, the findings in this report differ from what I learned talking with patients about their actual experience. This project uses the tools of institutional ethnography to begin an inquiry from the accounts of patients. To generate these accounts, I asked people about their experience of being a patient (N = 10). The intention is to learn about what patients say, know and do. I then asked seven clinicians (general practitioners, nurse practitioners, and registered nurses) about their experience, again focusing on what they say, know and do. The analysis reveals that some frontline patients and clinicians reported care practices that explicitly challenge their ability to be at or put patients at the centre of care. In some instances, practices purported to enhance person-centred care instead appear to place the person at an even greater distance from the centre, generating new work for patients without a clear benefit for the patient doing such work. Examples investigated include ‘GP triage’ and ‘team-based practice.’ From these findings, I followed what patients and clinicians say, know and do into the institution of primary care. At this level I talked with other key stakeholders of primary care and patient experience; people in management and governance, practice owners, strategy writers, survey writers, and primary care researchers (N = 11). I asked people in these positions about what they say and know, with the intention of using this knowledge to make sense of what can be said and done at the frontline of primary care. I found that standardising practices (e.g. 15 minute appointments, consultations limited to one issue per appointment, fee for service) constrain the clinician (and by proxy the patient) to what can be said and done during an episode of primary care. These practices are powerfully controlled by the private business model of primary care despite significant public funding. I found that patients and clinicians undertake significant workarounds to support care priorities such as continuity of care and timely access to care. Yet, the measurement of the “person-centredness” of primary care (the survey), renders invisible these actions of both patients and clinicians. The implications of these findings suggest that primary care, as it is presently organised, reorganised and protected by its principle protagonists, shifts the work of person-centred practices onto the frontline of primary care. The frontline of primary care is, at present, invisibly attempting to save this system from failure through their best efforts at addressing patient need

The Column Density Distribution Function at z=0 from HI Selected Galaxies

We have measured the column density distribution function, f(N), at z=0 using 21-cm HI emission from galaxies selected from a blind HI survey. f(N) is found to be smaller and flatter at z=0 than indicated by high-redshift measurements of Damped Lyman-alpha (DLA) systems, consistent with the predictions of hierarchical galaxy formation. The derived DLA number density per unit redshift, dn/dz =0.058, is in moderate agreement with values calculated from low-redshift QSO absorption line studies. We use two different methods to determine the types of galaxies which contribute most to the DLA cross-section: comparing the power law slope of f(N) to theoretical predictions and analysing contributions to dn/dz. We find that comparison of the power law slope cannot rule out spiral discs as the dominant galaxy type responsible for DLA systems. Analysis of dn/dz however, is much more discriminating. We find that galaxies with log M_HI < 9.0 make up 34% of dn/dz; Irregular and Magellanic types contribute 25%; galaxies with surface brightness > 24 mag arcsec^{-2} account for 22% and sub-L* galaxies contribute 45% to dn/dz. We conclude that a large range of galaxy types give rise to DLA systems, not just large spiral galaxies as previously speculated.Comment: 13 pages, low resolution figures in the appendix, MNRAS accepte

Smooth matter and source size in microlensing simulations of gravitationally lensed quasars

Several gravitationally lensed quasars are observed with anomalous magnifications in pairs of images that straddle a critical curve. Simple theoretical arguments suggest that the magnification of these images should be approximately equivalent, whereas one image is observed to be significantly demagnified. Microlensing provides a possible explanation for this discrepancy. There are two key parameters when modelling this effect. The first, the fraction of smooth matter in the lens at the image positions, has been explored by Schechter and Wambsganss (2002). They have shown that the anomalous flux ratio observed in the lensed quasar MG 0414+0534 is a priori a factor of 5 more likely if the assumed smooth matter content in the lens model is increased from 0% to 93%. The second parameter, the size of the emission region, is explored in this paper, and shown to be more significant. We find that the broadening of the magnification probability distributions due to smooth matter content is washed out for source sizes that are predicted by standard models for quasars. We apply our model to the anomalous lensed quasar MG 0414+0534, and find a 95% upper limit of 2.62 x 10^(16) h^(-1/2) (M/Msun)^(1/2) cm on the radius of the I-band emission region. The smooth matter percentage in the lens is unconstrained.Comment: 6 pages, 6 figures. To be published in MNRA

Local Column Density Distribution Function from HI selected galaxies

The cross-section of sky occupied by a particular neutral hydrogen column density provides insight into the nature of Lyman-alpha absorption systems. We have measured this column density distribution at z=0 using 21-cm HI emission from a blind survey. A subsample of HI Parkes All Sky Survey (HIPASS) galaxies have been imaged with the Australia Telescope Compact Array (ATCA). The contribution of low HI mass galaxies 10^7.5 to 10^8 M_solar is compared to that of M_star (10^10 to 10^10.5 M_solar) galaxies. We find that the column density distribution function is dominated by low HI mass galaxies with column densities in the range 3x10^18 to 2x10^20 cm^-2. This result is not intuitively obvious. M_star galaxies may contain the bulk of the HI gas, but the cross-section presented by low HI mass galaxies 10^7.5 to 10^8 M_solar is greater at moderate column densities. This result implies that moderate column density Lyman-alpha absorption systems may be caused by a range of galaxy types and not just large spiral galaxies as originally thought.Comment: 5 pages, including 1 figure. To appear in "Extragalactic Gas at Low Redshift" (ASP Conf. Series, Weymann Conf.

What No One Mentions

Is how the birth comes together and in waves and you come to know one another in those hours like you’ll know one another ever after: which of you is afraid of pain, which of you is angry, which of you is stubborn, which of you is cautious and swaddled in memory. I knew Phoebe’s reluctance even while she was being born, and in it, I understood her intelligence. I knew then her life would be a burden to her, that she’d blame me for it, but also that she’d never let up, that she’d hold each one of her days fiercely in her teeth. Her birth took fifteen hours, and it was like we were working against each other, like she was raging for the remainder of darkness that she knew then as light. Womb-light, deeper than a bruise. She fought, and she knows in her muscles how I wanted her born, how I worked and wailed just to get her here