arXiv subjects

Brian Mason

Publications and source records attributed to Brian Mason.

34 records · Page 2Linked to original sources

arXiv2019

The Radio Universe at Low Surface Brightness: Feedback & accretion in the circumgalactic medium

Massive galaxies at high-z are known to co-evolve with their circumgalactic medium (CGM). If we want to truly understand the role of the CGM in the early evolution of galaxies and galaxy-clusters, we need to fully explore the multi-phase nature of the CGM. We present two novel science cases that utilize low-surface-brightness observations in the radio regime to better understand the CGM around distant galaxies. At the lowest temperatures, observations of widespread molecular gas are providing evidence for the cold baryon cycle that grows massive galaxies. At the highest temperatures, observations of the Sunyaev-Zeldovich Effect are starting to reveal the effect of quasar feedback onto the hot gas in the CGM. We discuss the critical role that radio interferometers with compact configurations in the millimeter regime will play over the next decade in understanding the crucial role of the multi-phase CGM in galaxy evolution.

astro-ph.GA↗

arXiv2019

The MESAS Project: Long wavelength follow-up observations of Sirius A

Modeling the submillimeter to centimeter emission of stars is challenging due to a lack of sensitive observations at these long wavelengths. We launched an ongoing campaign to obtain new observations entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS). Here we present ALMA, GBT, and VLA observations of Sirius A, the closest main-sequence A-type star, that span from 1.4 to 9.0 millimeters. These observations complement our previous millimeter data on Sirius A and are entirely consistent with the PHOENIX stellar atmosphere models constructed to explain them. We note that accurate models of long wavelength emission from stars are essential not only to understand fundamental stellar processes, but also to determine the presence of dusty debris in spatially unresolved observations of circumstellar disks.

astro-ph.SR↗

arXiv2019

A High-resolution SZ View of the Warm-Hot Universe

The Sunyaev-Zeldovich (SZ) effect was first predicted nearly five decades ago, but has only recently become a mature tool for performing high resolution studies of the warm and hot ionized gas in and between galaxies, groups, and clusters. Galaxy groups and clusters are powerful probes of cosmology, and they also serve as hosts for roughly half of the galaxies in the Universe. In this white paper, we outline the advances in our understanding of thermodynamic and kinematic properties of the warm-hot universe that can come in the next decade through spatially and spectrally resolved measurements of the SZ effects. Many of these advances will be enabled through new/upcoming millimeter/submillimeter (mm/submm) instrumentation on existing facilities, but truly transformative advances will require construction of new facilities with larger fields of view and broad spectral coverage of the mm/submm bands.

astro-ph.CO↗

arXiv2019

Direct Detection of Quasar Feedback Via the Sunyaev-Zeldovich Effect

The nature and energetics of feedback from thermal winds in quasars can be constrained via observations of the Sunyaev-Zeldovich Effect (SZE) induced by the bubble of thermal plasma blown into the intergalactic medium by the quasar wind. In this letter, we present evidence that we have made the first detection of such a bubble, associated with the hyperluminous quasar HE0515-4414. The SZE detection is corroborated by the presence of extended emission line gas at the same position angle as the wind. Our detection appears on only one side of the quasar, consistent with the SZE signal arising from a combination of thermal and kinetic contributions. Estimates of the energy in the wind allow us to constrain the wind luminosity to the lower end of theoretical predictions, ~0.01% of the bolometric luminosity of the quasar. However, the age we estimate for the bubble, ~0.1 Gyr, and the long cooling time, ~0.6 Gyr, means that such bubbles may be effective at providing feedback between bursts of quasar activity.

astro-ph.GA↗

arXiv2018

Science with an ngVLA: The Sunyaev-Zeldovich Effect from Quasar and Starburst Winds

The Sunyaev-Zeldovich Effect (SZE) can be used to detect the hot bubbles in the intergalactic medium blown by energetic winds from AGN and starbursts. By directly constraining the kinetic luminosity, age and total energy of the outflow, it offers the promise of greatly increasing our understanding of the effects of wind feedback on galaxy evolution. Detecting the SZE in these winds is very challenging, at the edge of what is possible using existing facilities. The scale of the signal (10-100 kpc) is, however, well matched to interferometers operating at mm wavelengths for objects at z~1. Thus this could become a major science area for the ngVLA, especially if the design of the core is optimized for sensitivity on angular scales of >1 arcsec in the 90 GHz band.

astro-ph.GA↗

arXiv2018

Science with an ngVLA: The ngVLA Reference Design

The next-generation Very Large Array (ngVLA) is an astronomical observatory planned to operate at centimeter wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 to 116 GHz). The observatory will be a synthesis radio telescope constituted of approximately 244 reflector antennas each of 18 meters diameter, and 19 reflector antennas each of 6 meters diameter, operating in a phased or interferometric mode. We provide a technical overview of the Reference Design of the ngVLA. This Reference Design forms a baseline for a technical readiness assessment and the construction and operations cost estimate of the ngVLA. The concepts for major system elements such as the antenna, receiving electronics, and central signal processing are presented.

astro-ph.IM↗

arXiv2018

The Next Generation Very Large Array: A Technical Overview

The next-generation Very Large Array (ngVLA) is an astronomical observatory planned to operate at centimeter wavelengths (25 to 0.26 centimeters, corresponding to a frequency range extending from 1.2 GHz to 116 GHz). The observatory will be a synthesis radio telescope constituted of approximately 214 reflector antennas each of 18 meters diameter, operating in a phased or interferometric mode. We provide an overview of the current system design of the ngVLA. The concepts for major system elements such as the antenna, receiving electronics, and central signal processing are presented. We also describe the major development activities that are presently underway to advance the design.

astro-ph.IM↗

arXiv2018

Anomalous microwave emission from spinning nanodiamonds around stars

Several interstellar environments produce 'anomalous microwave emission', with brightness-peaks at tens-of-gigahertz frequencies. The emission's origins are uncertain - rapidly-spinning nano-particles could emit electric-dipole radiation, but polycyclic aromatic hydrocarbons proposed as the carrier are now found not to correlate with Galactic signals. The difficulty is to identify co-spatial sources over long lines of sight. Here we identify anomalous microwave emission in three proto-planetary discs. These are the only known systems that host hydrogenated nano-diamonds, in contrast to very common detection of polycyclic aromatic hydrocarbons. Spectroscopy locates the nano-diamonds close to the host-stars, at physically-constrained temperatures. Developing disc models, we reproduce the emission with diamonds 0.75-1.1 nanometres in radius, holding less than or equal to 1-2 per cent of the carbon budget. The microwave-emission:stellar-luminosity ratios are approximately constant, allowing nano-diamonds to be ubiquitous but emitting below detection thresholds in many star-systems. This can unify the findings with similar-sized diamonds found within solar system meteorites. As nano-diamond spectral absorption is seen in interstellar sightlines, these particles are also a candidate for generating galaxy-scale anomalous microwave emission.

astro-ph.SR↗

arXiv2017

Galaxy Cluster Pressure Profiles as Determined by Sunyaev Zel'dovich Effect Observations with MUSTANG and Bolocam II: Joint Analysis of Fourteen Clusters

We present pressure profiles of galaxy clusters determined from high resolution Sunyaev-Zel'dovich (SZ) effect observations of fourteen clusters, which span the redshift range $ 0.25 < z < 0.89$. The procedure simultaneously fits spherical cluster models to MUSTANG and Bolocam data. In this analysis, we adopt the generalized NFW parameterization of pressure profiles to produce our models. Our constraints on ensemble-average pressure profile parameters, in this study $γ$, $C_{500}$, and $P_0$, are consistent with those in previous studies, but for individual clusters we find discrepancies with the X-ray derived pressure profiles from the ACCEPT2 database. We investigate potential sources of these discrepancies, especially cluster geometry, electron temperature of the intracluster medium, and substructure. We find that the ensemble mean profile for all clusters in our sample is described by the parameters: $[γ,C_{500},P_0] = [0.3_{-0.1}^{+0.1}, 1.3_{-0.1}^{+0.1}, 8.6_{-2.4}^{+2.4}]$, for cool core clusters: $[γ,C_{500},P_0] = [0.6_{-0.1}^{+0.1}, 0.9_{-0.1}^{+0.1}, 3.6_{-1.5}^{+1.5}]$, and for disturbed clusters: $[γ,C_{500},P_0] = [0.0_{-0.0}^{+0.1}, 1.5_{-0.2}^{+0.1},13.8_{-1.6}^{+1.6}]$. Four of the fourteen clusters have clear substructure in our SZ observations, while an additional two clusters exhibit potential substructure.

astro-ph.CO↗

arXiv2014

Evidence for Large Grains in the Star-forming Filament OMC-2/3

We present a new 3.3 mm continuum map of the OMC-2/3 region. When paired with previously published maps of 1.2mm continuum and NH3-derived temperature, we derive the emissivity spectral index of dust emission in this region, tracking its changes across the filament and cores. We find that the median value of the emissivity spectral index is 0.9, much shallower than previous estimates in other nearby molecular clouds. We find no significant difference between the emissivity spectral index of dust in the OMC-2/3 filament and the starless or protostellar cores. Furthermore, the temperature and emissivity spectral index, beta, are anti-correlated at the 4 sigma level. The low values of the emissivity spectral index found in OMC-2/3 can be explained by the presence of millimeter-sized dust grains in the dense regions of the filaments to which these maps are most sensitive. Alternatively, a shallow dust emissivity spectral index may indicate non-powerlaw spectral energy distributions, significant free-free emission, or anomalous microwave emission. We discuss the possible implications of millimeter-sized dust grains compared to the alternatives.

astro-ph.GA↗

arXiv2013

Bounds on Dark Matter Properties from Radio Observations of Ursa Major II using the Green Bank Telescope

Radio observations of the Ursa Major II dwarf spheroidal galaxy obtained using the Green Bank Telescope are used to place bounds on WIMP dark matter properties. Dark matter annihilation releases energy in the form of charged particles which emit synchrotron radiation in the magnetic field of the dwarf galaxy. We compute the expected synchrotron radiation intensity from WIMP annihilation to various primary channels. The predicted synchrotron radiation is sensitive to the distribution of dark matter in the halo, the diffusion coefficient D_0, the magnetic field strength B, the particle mass m_χ, the annihilation rate <σv>, and the annihilation channel. Limits on <σv>, m_χ, B, and D_0 are obtained for the e^+ e^-, μ^+ μ^-, τ^+ τ^-, and b \bar b channels. Constraints on these parameters are sensitive to uncertainties in the measurement of the dark matter density profile. For the best fit halo parameters derived from stellar kinematics, we exclude 10 GeV WIMPs annihilating directly to e^+ e^- at the thermal rate <σv> = 2.18 x 10^{-26} cm^3/s at the 2σlevel, for B > 0.6 microGauss (1.6 microGauss) and D_0 = 0.1 (1.0) x the Milky Way diffusion value.

astro-ph.CO↗

arXiv2012

The search for habitable worlds: 1. The viability of a starshade mission

As part of NASA's mission to explore habitable planets orbiting nearby stars, this paper explores the detection and characterization capabilities of a 4-m space telescope plus 50-m starshade located at the Earth-Sun L2 point, a.k.a. the New Worlds Observer (NWO). Our calculations include the true spectral types and distribution of stars on the sky, an iterative target selection protocol designed to maximize efficiency based on prior detections, and realistic mission constraints. We carry out both analytical calculations and simulated observing runs for a wide range in exozodiacal background levels (ε = 1 - 100 times the local zodi brightness) and overall prevalence of Earth-like terrestrial planets (η\oplus = 0.1 - 1). We find that even without any return visits, the NWO baseline architecture (IWA = 65 mas, limiting FPB = 4\times10-11) can achieve a 95% probability of detecting and spectrally characterizing at least one habitable Earth-like planet, and an expectation value of ~3 planets found, within the mission lifetime and ΔV budgets, even in the worst-case scenario (η\oplus = 0.1 and ε = 100 zodis for every target). This achievement requires about one year of integration time spread over the 5 year mission, leaving the remainder of the telescope time for UV-NIR General Astrophysics. Cost and technical feasibility considerations point to a "sweet spot" in starshade design near a 50-m starshade effective diameter, with 12 or 16 petals, at a distance of 70,000-100,000 km from the telescope.

astro-ph.IM↗

arXiv2011

Field Scanner Design for MUSTANG of the Green Bank Telescope

MUSTANG is a bolometer camera for the Green Bank Telescope (GBT) working at a frequency of 90 GHz. The detector has a field of view of 40 arcseconds. To cancel out random emission change from atmosphere and other sources, requires a fast scanning reflecting system with a few arcminute ranges. In this paper, the aberrations of an off-axis system are reviewed. The condition for an optimized system is provided. In an optimized system, as additional image transfer mirrors are introduced, new aberrations of the off-axis system may be reintroduced, resulting in a limited field of view. In this paper, different scanning mirror arrangements for the GBT system are analyzed through the ray tracing analysis. These include using the subreflector as the scanning mirror, chopping a flat mirror and transferring image with an ellipse mirror, and chopping a flat mirror and transferring image with a pair of face-to-face paraboloid mirrors. The system analysis shows that chopping a flat mirror and using a well aligned pair of paraboloids can generate the required field of view for the MUSTUNG detector system, while other systems all suffer from larger off-axis aberrations added by the system modification. The spot diagrams of the well aligned pair of paraboloids produced is only about one Airy disk size within a scanning angle of about 3 arcmin.

astro-ph.IM↗

arXiv2011

New High-Resolution Sunyaev-Zel'dovich Observations with GBT+MUSTANG

We present recent high angular resolution (9") Sunyaev-Zel'dovich effect (SZE) observations with MUSTANG, a 90-GHz bolometric receiver on the Green Bank Telescope. MUSTANG has now imaged several massive clusters of galaxies in some of the highest-resolution SZE imaging to date, revealing complex pressure substructure within the hot intra-cluster gas in merging clusters. We focus on three merging, intermediate redshift clusters here: MACS J0744.8+3927, MACS J0717.5+3745, RX J1347.5-1145. In one of these merging clusters, MACS J0744.8+3927, the MUSTANG observation has revealed shocked gas that was previously undetected in X-ray observations. Our preliminary results for MACS J0717.5+3745 demonstrate the complementarity these observations provide when combined with X-ray observations of the thermal emission and radio observations of the non-thermal emission. And finally, by revisiting RX J1347.5-1145, we note an inter- esting correlation between its radio emission and the SZE data. While observations of the thermal SZE probe the line of sight integral of thermal electron pressure through a cluster, these redshift independent observations hold great potential for aiding the interpretation of non-thermal astrophysics in high-z clusters.

astro-ph.CO↗

arXiv2006

Polaris: Mass and Multiplicity

Polaris, the nearest and brightest classical Cepheid, is a member of at least a triple system. It has a wide ($18''$) physical companion, the F-type dwarf Polaris B. Polaris itself is a single-lined spectroscopic binary with an orbital period of 30 years (Kamper, 1996, JRASC, 90, 140). By combining {\it Hipparcos} measurements of the instantaneous proper motion with long-term measurements and the Kamper radial-velocity orbit, Wielen et al. (2000, A&A, 360, 399) have predicted the astrometric orbit of the close companion. Using the {\it Hubble Space Telescope} and the Advanced Camera for Surveys' High-Resolution Channel with an ultraviolet (F220W) filter, we have now directly detected the close companion. Based on the Wielen et al. orbit, the {\it Hipparcos} parallax, and our measurement of the separation ($0.176''$ $\pm$ $0.002''$), we find a preliminary mass of 5.0 $\pm$ 1.5 M$_{\odot}$ for the Cepheid and 1.38 $\pm$ 0.61 M$_{\odot}$ for the close companion. These values will be refined by additional {\it HST} observations scheduled for the next 3 years. We have also obtained a {\it Chandra} ACIS-I image of the Polaris field. Two distant companions C and D are not X-rays sources and hence are not young enough to be physical companions of the Cepheid. There is one additional stellar X-ray source in the field, located $253''$ from Polaris A, which is a possible companion. Further investigation of such a distant companion is valuable to confirm the full extent of the system.

astro-ph↗

arXiv1994

Solar Neutrino Oscillations in the Moon

The first three quarters of this paper consists of a pedagogical review of neutrino oscillations, including vacuum oscillations, constant density matter oscillations and variable density matter oscillations. We then address the question of whether MSW solar neutrino oscillations in the moon could be observed during a solar eclipse. For the small angle MSW solution, the effect is unmeasureable; for the large angle solution, we find an enhancement in the rate which can be as large as a factor of two. Since the center of the Sun, as seen from a typical solar neutrino detector (through a transparent Earth) is covered for roughly three hours per decade, a world-wide event rate of a few solar neutrino events per hour might be sufficient to observe this effect. This work constituted the undergraduate senior thesis of Brian Mason, and has been submitted to the American Journal of Physics.

hep-ph↗