Naomi McClure-Griffiths

Bio: Naomi McClure-Griffiths is an academic researcher from Australian National University. The author has contributed to research in topics: Galactic plane & Galaxy. The author has an hindex of 58, co-authored 272 publications receiving 12064 citations. Previous affiliations of Naomi McClure-Griffiths include Max Planck Society & University of Minnesota.

HI4PI: a full-sky H i survey based on EBHIS and GASS

Abstract: Deutsche Forschungsgemeinschaft (DFG) [KA1265/5-1, KA1265/5-2, KE757/71, KE757/7-2, KE757/7-3, KE757/11-1.]; International Max Planck Research School for Astronomy and Astrophysics at the Universities of Bonn and Cologne (IMPRS Bonn/Cologne); Estonian Research Council [IUT26-2]; European Regional Development Fund [TK133]; Australian Research Council Future Fellowship [FT150100024]; NSF CAREER grant [AST-1149491]

The VLA Galactic Plane Survey

Abstract: The VLA Galactic Plane Survey (VGPS) is a survey of H I and 21 cm continuum emission in the Galactic plane between longitude 18° and 67° with latitude coverage from |b| < 13 to |b| < 23. The survey area was observed with the Very Large Array in 990 pointings. Short-spacing information for the H I line emission was obtained by additional observations with the Green Bank Telescope. H I spectral line images are presented with a resolution of 1' × 1' × 1.56 km s-1 (FWHM) and an rms noise of 2 K per 0.824 km s-1 channel. Continuum images made from channels without H I line emission have 1' (FWHM) resolution. The VGPS images reveal structures of atomic hydrogen and 21 cm continuum as large as several degrees with unprecedented resolution in this part of the Galaxy. With the completion of the VGPS, it is now possible for the first time to assess the consistency between arcminute-resolution surveys of Galactic H I emission. VGPS images are compared with images from the Canadian Galactic Plane Survey (CGPS) and the Southern Galactic Plane Survey (SGPS). In general, the agreement between these surveys is impressive, considering the differences in instrumentation and image-processing techniques used for each survey. The differences between VGPS and CGPS images are small, 6 K (rms) in channels in which the mean H I brightness temperature in the field exceeds 80 K. A similar degree of consistency is found between the VGPS and SGPS. The agreement we find between arcminute-resolution surveys of the Galactic plane is a crucial step toward combining these surveys into a single uniform data set that covers 90% of the Galactic disk: the International Galactic Plane Survey. The VGPS data will be made available on the World Wide Web through the Canadian Astronomy Data Centre.

Science with ASKAP: The Australian square-kilometre-array pathfinder

Abstract: The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries. The SKA will be 50 times more sensitive than any existing radio facility. A majority of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from 300 MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is aimed squarely in this frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phase-array feed systems on parabolic reflectors. This large field-of-view makes ASKAP an unprecedented synoptic telescope poised to achieve substantial advances in SKA key science. The central core of ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of the sites selected by the international community as a potential location for the SKA. Following an introductory description of ASKAP, this document contains 7 chapters describing specific science programmes for ASKAP. In summary, the goals of these programmes are as follows: The combination of location, technological innovation and scientific program will ensure that ASKAP will be a world-leading radio astronomy facility, closely aligned with the scientific and technical direction of the SKA. A brief summary chapter emphasizes the point, and considers discovery space.

The Southern Galactic Plane Survey: H I Observations and Analysis

Abstract: We describe the H I component of the Southern Galactic Plane Survey (SGPS). The SGPS is a large-scale project to image at arcminute resolution the H I spectral line and 21 cm continuum emission in parts of the plane of the Milky Way. The survey covers Galactic longitudes 253° ≤ l ≤ 358° and latitudes |b| ≤ 15 (SGPS I), plus a first quadrant extension covering 5° ≤ l ≤ 20° and |b| ≤ 15 (SGPS II). The survey combines data from the Australia Telescope Compact Array and the Parkes Radio Telescope for sensitivity to angular scales ranging from 2' to several degrees. The combined data cover 325 deg2 and have an rms sensitivity of 1.6 K. Here we describe the H I observations and data reduction in detail and present examples from the final data products. The complete data set is publicly available through the Australia Telescope National Facility's H I Surveys archive. This data set provides an unprecedented view of the neutral component of interstellar hydrogen in the inner Milky Way.

The Southern Galactic Plane Survey: HI Observations and Analysis

Abstract: We describe the HI component of the Southern Galactic Plane Survey (SGPS). The SGPS is a large-scale project to image at arcminute resolution the HI spectral line and 21 cm continuum emission in parts of the plane of the Milky Way. The survey covers Galactic longitudes 253 deg < l < 358 deg and latitudes |b| <1.5 deg (SGPS I), plus a first quadrant extension covering 5 deg < l < 20 deg and |b| <1.5 deg (SGPS II). The survey combines data from the Australia Telescope Compact Array and the Parkes Radio Telescope for sensitivity to angular scales ranging from 2 arcminutes to several degrees. The combined data cover 325 sq-deg and have an rms sensitivity of 1.6 K. Here we describe the HI observations and data reduction in detail, and present examples from the final data products. The complete dataset is publicly available through the Australia Telescope National Facility's HI Surveys archive. This dataset provides an unprecedented view of the neutral component of interstellar hydrogen in the inner Milky Way.

Multi-messenger observations of a binary neutron star merger

Abstract: On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of $\sim 1.7\,{\rm{s}}$ with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of ${40}_{-8}^{+8}$ Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 $\,{M}_{\odot }$. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at $\sim 40\,{\rm{Mpc}}$) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position $\sim 9$ and $\sim 16$ days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

Star Formation in the Milky Way and Nearby Galaxies

Abstract: We review progress over the past decade in observations of large-scale star formation, with a focus on the interface between extragalactic and Galactic studies. Methods of measuring gas contents and star-formation rates are discussed, and updated prescriptions for calculating star-formation rates are provided. We review relations between star formation and gas on scales ranging from entire galaxies to individual molecular clouds.

Theory of Star Formation

Abstract: We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation—turbulence, magnetic fields, and self-gravity— are highly nonlinear and multidimensional. Physical arguments are used to identify and explain the features and scalings involved in star formation, and results from numerical simulations are used to quantify these effects. We divide star formation into large-scale and small-scale regimes and review each in turn. Large scales range from galaxies to giant molecular clouds (GMCs) and their substructures. Important problems include how GMCs form and evolve, what determines the star formation rate (SFR), and what determines the initial mass function (IMF). Small scales range from dense cores to the protostellar systems they beget. We discuss formation of both low- and high-mass stars, including ongoing accretion. The development of winds and outflows is increasingly well understood, as are the mechanisms governing angular momentum transport in disks. Although outstanding questions remain, the framework is now in place to build a comprehensive theory of star formation that will be tested by the next generation of telescopes.

Three Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Polarization Analysis

Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) has mapped the entire sky in five frequency bands between 23 and 94 GHz with polarization-sensitive radiometers. We present 3 year full-sky maps of the polarization and analyze them for foreground emission and cosmological implications. These observations open up a new window for understanding how the universe began and help set a foundation for future observations. WMAP observes significant levels of polarized foreground emission due to both Galactic synchrotron radiation and thermal dust emission. Synchrotron radiation is the dominant signal at l < 50 and ν 40 GHz, while thermal dust emission is evident at 94 GHz. The least contaminated channel is at 61 GHz. We present a model of polarized foreground emission that captures the large angular scale characteristics of the microwave sky. After applying a Galactic mask that cuts 25.7% of the sky, we show that the high Galactic latitude rms polarized foreground emission, averaged over l = 4-6, ranges from ≈5 μK at 22 GHz to 0.6 μK at 61 GHz. By comparison, the levels of intrinsic CMB polarization for a ΛCDM model with an optical depth of τ = 0.09 and assumed tensor-to-scalar ratio r = 0.3 are ≈0.3 μK for E-mode polarization and ≈0.1 μK for B-mode polarization. To analyze the maps for CMB polarization at l < 16, we subtract a model of the foreground emission that is based primarily on a scaling WMAP's 23 GHz map. In the foreground-corrected maps, we detect l(l + 1)C/2π = 0.086 ± 0.029 (μK)2. This is interpreted as the result of rescattering of the CMB by free electrons released during reionization at zr = 10.9 for a model with instantaneous reionization. By computing the likelihood of just the EE data as a function of τ we find τ = 0.10 ± 0.03. When the same EE data are used in the full six-parameter fit to all WMAP data (TT, TE, EE), we find τ = 0.09 ± 0.03. Marginalization over the foreground subtraction affects this value by δτ < 0.01. We see no evidence for B modes, limiting them to l(l + 1)C/2π = -0.04 ± 0.03 (μK)2. We perform a template fit to the E-mode and B-mode data with an approximate model for the tensor scalar ratio. We find that the limit from the polarization signals alone is r < 2.2 (95% CL), where r is evaluated at k = 0.002 Mpc-1. This corresponds to a limit on the cosmic density of gravitational waves of ΩGWh2 < 5 × 10-12. From the full WMAP analysis, we find r < 0.55 (95% CL) corresponding to a limit of ΩGWh2 < 1 × 10-12 (95% CL). The limit on r is approaching the upper bound of predictions for some of the simplest models of inflation, r ~ 0.3.

Planck 2018 results: XI. Polarized dust foregrounds

Abstract: The study of polarized dust emission has become entwined with the analysis of the cosmic microwave background (CMB) polarization. We use new Planck maps to characterize Galactic dust emission as a foreground to the CMB polarization. We present Planck EE, BB, and TE power spectra of dust polarization at 353 GHz for six nested sky regions covering from 24 to 71 % of the sky. We present power-law fits to the angular power spectra, yielding evidence for statistically significant variations of the exponents over sky regions and a difference between the values for the EE and BB spectra. The TE correlation and E/B power asymmetry extend to low multipoles that were not included in earlier Planck polarization papers. We also report evidence for a positive TB dust signal. Combining data from Planck and WMAP, we determine the amplitudes and spectral energy distributions (SEDs) of polarized foregrounds, including the correlation between dust and synchrotron polarized emission, for the six sky regions as a function of multipole. This quantifies the challenge of the component separation procedure required for detecting the reionization and recombination peaks of primordial CMB B modes. The SED of polarized dust emission is fit well by a single-temperature modified blackbody emission law from 353 GHz to below 70 GHz. For a dust temperature of 19.6 K, the mean spectral index for dust polarization is $\beta_{\rm d}^{P} = 1.53\pm0.02 $. By fitting multi-frequency cross-spectra, we examine the correlation of the dust polarization maps across frequency. We find no evidence for decorrelation. If the Planck limit for the largest sky region applies to the smaller sky regions observed by sub-orbital experiments, then decorrelation might not be a problem for CMB experiments aiming at a primordial B-mode detection limit on the tensor-to-scalar ratio $r\simeq0.01$ at the recombination peak.