Searching for Large Scale Structure in Deep Radio Surveys

(Abridged Abstract) We calculate the expected amplitude of the dipole and higher spherical harmonics in the angular distribution of radio galaxies. The median redshift of radio sources in existing catalogues is z=1, which allows us to study large scale structure on scales between those accessible to present optical and infrared surveys, and that of the Cosmic Microwave Background (CMB). The dipole is due to 2 effects which turn out to be of comparable magnitude: (i) our motion with respect to the CMB, and (ii) large scale structure, parameterised here by a family of Cold Dark Matter power-spectra. We make specific predictions for the Green Bank (87GB) and Parkes-MIT-NRAO (PMN) catalogues. For these relatively sparse catalogues both the motion and large scale structure dipole effects are expected to be smaller than the Poisson shot-noise. However, we detect dipole and higher harmonics in the combined 87GB-PMN catalogue which are far larger than expected. We attribute this to a 2 % flux mismatch between the two catalogues. We also investigate the existence and extent of the Supergalactic Plane in the above catalogues. In a strip of +- 10 deg of the standard Supergalactic equator, we find a 3-sigma detection in PMN, but only 1-sigma in 87GB.Comment: 15 pages, 5 ps figures, Latex, Submitted to MNRA

Clusters of galaxies in the microwave band: influence of the motion of the Solar System

In this work we consider the changes of the SZ cluster brightness, flux and number counts induced by the motion of the Solar System with respect to the frame defined by the cosmic microwave background (CMB). These changes are connected with the Doppler effect and aberration and exhibit a strong spectral and spatial dependence. The correction to the SZ cluster brightness and flux has an amplitude and spectral dependence, which is similar to the first order cluster peculiar velocity correction to the thermal SZ effect. Due to the change in the received cluster CMB flux the motion of the Solar System induces a dipolar asymmetry in the observed number of clusters above a given flux level. Similar effects were discussed for $\gamma$-ray bursts and radio galaxies, but here, due to the very peculiar frequency-dependence of the thermal SZ effect, the number of observed clusters in one direction of the sky can be both, decreased or increased depending on the frequency band. A detection of this asymmetry should be possible using future full sky CMB experiments with mJy sensitivities.Comment: 7 pages, 6 figures, submitted to Astronomy and Astrophysics, corrected pdf-proble

The velocity field of 2MRS Ks=11.75 galaxies: constraints on beta and bulk flow from the luminosity function

Using the nearly full sky Ks=11.75 2MASS Redshift Survey [2MRS]of ~45,000 galaxies we reconstruct the underlying peculiar velocity field and constrain the cosmological bulk flow within ~100. These results are obtained by maximizing the probability to estimate the absolute magnitude of a galaxy given its observed apparent magnitude and redshift. At a depth of ~60 Mpc/h we find a bulk flow Vb=(90\pm65,-230\pm65,50\pm65) km/s in agreement with the theoretical predictions of the LCDM model. The reconstructed peculiar velocity field that maximizes the likelihood is characterized by the parameter beta=0.323 +/- 0.08. Both results are in agreement with those obtained previously using the ~23,000 galaxies of the shallower Ks=11.25 2MRS survey. In our analysis we find that the luminosity function of 2MRS galaxies is poorly fitted by the Schechter form and that luminosity evolves such that objects become fainter with increasing redshift according to L(z)=L(z=0)(1+z)^(+2.7 +/-0.15).Comment: 10 pages, 6 figure

Dipoles in the Sky

We perform observational tests of statistical isotropy using data from large-scale structure surveys spanning a wide range of wavelengths. Using data from 2MASS, 2MRS, and NVSS galaxies, and BATSE gamma-ray bursts, we constrain the amplitude and direction of dipolar modulations in the number count of sources projected along the line of sight. We pay particular attention to the treatment of systematic errors and selection effects, and carefully distinguish between different sources of dipole signal previously considered in the literature. Dipole signals detected in these surveys are consistent with the standard, statistically isotropic expectation, except for the NVSS result, which is likely biased by remaining systematics in the data. We place constraints on the amplitude of any intrinsic dipole driven by novel physics in the early universe.Comment: 36 pages, 20 figures. v3: minor additions to theory section; matches the published MNRAS versio

Small-Scale Fluctuations in Cosmic X-ray Background : A Power Spectrum Approach

Equations to investigate fluctuations in cosmic X-ray background radiation due to point-like sources at high-redshift are formulated in a systematic way. The angular power spectrum of X-ray background fluctuations is investigated from large-scales to small-scales in various cosmological models such as open universe models and models with the cosmological constant, assuming a simple evolution model of the sources. The effect of epoch-dependent bias is demonstrated for small-angle fluctuations. The contribution from shot noise fluctuations is also discussed.Comment: 12 pages, 4 figures, Phys.Rev.D in pres

Joining a Discourse Community: How Graduate Students Learn to Speak like Astronomers

Almost half of all graduate students leave their doctoral programs without finishing. Who leaves, taking which skills and strengths with them, is still poorly understood, however, because it is hard to measure exactly what graduate students learn in their doctoral programs. Since the expertise required of a PhD holder is highly dependent on discipline, the development of a better understanding of graduate education and attrition requires studying the process at the departmental level.This is a qualitative study of the cultural values and norms of academic astronomy, as transmitted through the socialization of graduate students into giving talks, asking questions, and participating in departmental speaking events. This study also looks at the conflicts that arise when implicit cultural norms, which are practiced but remain unacknowledged, are inconsistent with the official, explicit values and norms for speaking in astronomy.Doctoral students and faculty members in a single astronomy department, at a large western university, filled out a short survey about the stakes involved in astronomy speaking events. A subset of these individuals was interviewed in-depth about the goals of, and their experiences with, five departmental speaking events: Coffee Hour, Journal Club, research talks, Thesis defense talks, and Colloquia. These interviewees were: (1) graduate students who had given a verbal presentation at one of these events, and (2) graduate students and faculty members who were in the audience at a graduate student's presentation.The desired outcomes which were expressed for these speaking events included: (1) lively, informal discussion among all participants, (2) increasing graduate student verbal participation in these events as they "learn to speak like astronomers," and (3) the utility of these events in helping graduate students learn and practice their speaking and reasoning skills related to astronomy research. In practice these goals were not achieved due to: (1) the ubiquitous, but unacknowledged practice of judging others' speech performance to come to negative conclusions about those individuals' intentions, intellectual abilities or efforts, (2) a lack of feedback for graduate students on their verbal performances, and (3) a lack of faculty members making explicit their own solutions to the inherent dilemmas of academic speaking

Joining a discourse community: How graduate students learn to speak like astronomers

Almost half of all graduate students leave their doctoral programs without finishing. Who leaves, taking which skills and strengths with them, is still poorly understood, however, because it is hard to measure exactly what graduate students learn in their doctoral programs. Since the expertise required of a PhD holder is highly dependent on discipline, the development of a better understanding of graduate education and attrition requires studying the process at the departmental level. This is a qualitative study of the cultural values and norms of academic astronomy, as transmitted through the socialization of graduate students into giving talks, asking questions, and participating in departmental speaking events. This study also looks at the conflicts that arise when implicit cultural norms, which are practiced but remain unacknowledged, are inconsistent with the official, explicit values and norms for speaking in astronomy. Doctoral students and faculty members in a single astronomy department, at a large western university, filled out a short survey about the stakes involved in astronomy speaking events. A subset of these individuals was interviewed in-depth about the goals of, and their experiences with, five departmental speaking events: Coffee Hour, Journal Club, research talks, Thesis defense talks, and Colloquia. These interviewees were: (1) graduate students who had given a verbal presentation at one of these events, and (2) graduate students and faculty members who were in the audience at a graduate student’s presentation. The desired outcomes which were expressed for these speaking events included: (1) lively, informal discussion among all participants, (2) increasing graduate student verbal participation in these events as they “learn to speak like astronomers,” and (3) the utility of these events in helping graduate students learn and practice their speaking and reasoning skills related to astronomy research. In practice these goals were not achieved due to: (1) the ubiquitous, but unacknowledged practice of judging others’ speech performance to come to negative conclusions about those individuals’ intentions, intellectual abilities or efforts, (2) a lack of feedback for graduate students on their verbal performances, and (3) a lack of faculty members making explicit their own solutions to the inherent dilemmas of academic speaking

Comprehensive examination of tattoo removal using a 150 ps Nd:YAG laser in a porcine model

Abstract This study aimed to investigate the efficacy of a Nd:YAG laser with a pulse duration of 150 ps at different laser parameters. The effects on multiple-colored tattoos with such ultrashort pulses has not been previously described in the literature. In vivo experiments were conducted on porcine skin to analyze the fragmentation efficiency of five different tattoo colors using different wavelengths, pulse energies, and spot sizes. The results showed that the optimal tattoo clearance to safety ratio for blue, green, red, and yellow tattoos with a 532 nm wavelength was 0.96–2.39 J/cm2. The laser with a wavelength of 1064 nm demonstrated the highest efficacy in eliminating black tattoos, with positive results observed for green and blue pigments at a fluence of 3.02 J/cm2. The study provides valuable insights into the efficacy of laser treatment with 150 ps for removing tattoos of different colors using different laser parameters. This information can help dermatologists and practitioners perform more efficient and effective tattoo removal with fewer side effects

Joining A Discourse Community: How Graduate Students Learn To Speak Like Astronomers

"Almost half of all graduate students leave their doctoral programs without finishing. Who leaves, taking which skills and strengths with them, is still poorly understood, however, because it is hard to measure exactly what graduate students learn in their doctoral programs. Since the expertise required of a PhD holder is highly dependent on discipline, the development of a better understanding of graduate education and attrition requires studying the process at the departmental level. This is a qualitative study of the cultural values and norms of academic astronomy, as transmitted through the socialization of graduate students into giving talks, asking questions, and participating in departmental speaking events. This study also looks at the conflicts that arise when implicit cultural norms, which are practiced but remain unacknowledged, are inconsistent with the official, explicit values and norms for speaking in astronomy. Doctoral students and faculty members in a single astronomy department, at a large western university, filled out a short survey about the stakes involved in astronomy speaking events. A subset of these individuals was interviewed in-depth about the goals of, and their experiences with, five departmental speaking events: Coffee Hour, Journal Club, research talks, Thesis defense talks, and Colloquia. These interviewees were: (1) graduate students who had given a verbal presentation at one of these events, and (2) graduate students and faculty members who were in the audience at a graduate student’s presentation. The desired outcomes which were expressed for these speaking events included: (1) lively, informal discussion among all participants, (2) increasing graduate student verbal participation in these events as they “learn to speak like astronomers,” and (3) the utility of these events in helping graduate students learn and practice their speaking and reasoning skills related to astronomy research. In practice these goals were not achieved due to: (1) the ubiquitous, but unacknowledged practice of judging others’ speech performance to come to negative conclusions about those individuals’ intentions, intellectual abilities or efforts, (2) a lack of feedback for graduate students on their verbal performances, and (3) a lack of faculty members making explicit their own solutions to the inherent dilemmas of academic speaking.