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A. Green

Publications and source records attributed to A. Green.

At least 19 recordsLinked to original sources
arXiv2025

LMC+: Large-scale mapping of [CII] and [OIII] in the LMC molecular ridge, I. Dataset and line ratio analyses

The fundamental process of star formation in galaxies involves the interplay between the fueling of star formation via molecular gas and the feedback from recently formed massive stars. This process, by which galaxies evolve, is also closely connected to the intrinsic properties of the interstellar medium (ISM). To study the role that different molecular and atomic phases of the ISM play in star formation, and to characterize their physical conditions, we zoom into our nearest neighboring galaxy, the Large Magellanic Cloud (LMC; 50 kpc). The LMC offers a view of the ISM and star formation conditions in a low metallicity environment similar to, in that regard, the epoch of the peak of star formation in the earlier universe. We present an unprecedentedly detailed analysis of a well-known star-forming regions (SFRs) at a spatial resolution of a few pc. We mapped a 610pcx260pc region in the LMC molecular ridge in [CII] and the [OIII] using the FIFI-LS instrument on the SOFIA telescope. We compare the data with the distribution of the CO (2-1) emission from ALMA, the modeled TIR luminosity as well as Spitzer/MIPS continuum and Halpha. We also provide a detailed description of the observing strategy and the data reduction. We find that [CII] and [OIII] emission is associated with the SFRs in the molecular ridge, but also extends throughout the mapped region, not obviously associated with ongoing star formation. The CO emission is clumpier than the [CII] emission and we find plentiful [CII] present where there is little CO emission, possibly holding important implications for CO-dark gas. We find a clear trend of the [CII]/TIR ratio decreasing with increasing TIR. This suggests a strong link between the [CII]-deficit and the local physical conditions instead of global properties.

astro-ph.GA↗
arXiv2025

Object Detection with Deep Learning for Rare Event Search in the GADGET II TPC

In the pursuit of identifying rare two-particle events within the GADGET II Time Projection Chamber (TPC), this paper presents a comprehensive approach for leveraging Convolutional Neural Networks (CNNs) and various data processing methods. To address the inherent complexities of 3D TPC track reconstructions, the data is expressed in 2D projections and 1D quantities. This approach capitalizes on the diverse data modalities of the TPC, allowing for the efficient representation of the distinct features of the 3D events, with no loss in topology uniqueness. Additionally, it leverages the computational efficiency of 2D CNNs and benefits from the extensive availability of pre-trained models. Given the scarcity of real training data for the rare events of interest, simulated events are used to train the models to detect real events. To account for potential distribution shifts when predominantly depending on simulations, significant perturbations are embedded within the simulations. This produces a broad parameter space that works to account for potential physics parameter and detector response variations and uncertainties. These parameter-varied simulations are used to train sensitive 2D CNN object detectors. When combined with 1D histogram peak detection algorithms, this multi-modal detection framework is highly adept at identifying rare, two-particle events in data taken during experiment 21072 at the Facility for Rare Isotope Beams (FRIB), demonstrating a 100% recall for events of interest. We present the methods and outcomes of our investigation and discuss the potential future applications of these techniques.

physics.ins-det↗
arXiv2023

Global Characterization of a Laser-Generated Neutron Source

Laser-driven neutron sources are routinely produced by the interaction of laser-accelerated protons with a converter. They present complementary characteristics to those of conventional accelerator-based neutron sources (e.g. short pulse durations, enabling novel applications like radiography). We present here results from an experiment aimed at performing a global characterization of the neutrons produced using the Titan laser at the Jupiter Laser Facility (Livermore, USA), where protons were accelerated from 23 $\mu m$ thick plastic targets and directed onto a LiF converter to produce neutrons. For this purpose, several diagnostics were used to measure these neutron emissions, such as CR-39, activation foils, Time-of-Flight detectors and direct measurement of $^{7}$Be residual activity in the LiF converters. The use of these different, independently operating diagnostics enables comparison of the various measurements performed to provide a robust characterization. These measurements led to a neutron yield of $2.10^{9}$ neutrons per shot with a modest angular dependence, close to that simulated.

physics.acc-ph↗
arXiv2016

Ultra-High Gradient Channeling Acceleration in Nanostructures: Design/Progress of Proof-of-Concept (POC) Experiments

This paper describes simulation analyses on beam and laser (X-ray)-driven accelerations in effective nanotube models obtained from Vsim and EPOCH codes. Experimental setups to detect wakefields are also outlined with accelerator facilities at Fermilab and NIU. In the FAST facility, the electron beamline was successfully commissioned at 50 MeV and it is being upgraded toward higher energies for electron accelerator R&D. The 50 MeV injector beamline of the facility is used for X-ray crystal-channeling radiation with a diamond target. It has been proposed to utilize the same diamond crystal for a channeling acceleration POC test. Another POC experiment is also designed for the NIU accelerator lab with time-resolved electron diffraction. Recently, a stable generation of single-cycle laser pulses with tens of Petawatt power based on thin film compression (TFC) technique has been investigated for target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA). The experimental plan with a nanometer foil is discussed with an available test facility such as Extreme Light Infrastructure - Nuclear Physics (ELI-NP).

physics.acc-ph↗
arXiv2015

Beamed neutron emission driven by laser accelerated light ions

We report on the experimental observation of beam-like neutron emission with peak flux of the order of 10^9 n/sr, from light nuclei reactions in a pitcher-catcher scenario, by employing MeV ions driven by high power laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of 70 degrees, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher-catcher materials indicates the dominant reactions being d(p, n+p)^1H and d(d,n)^3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles are most likely related to the directionality and high energy of the projectile ions.

physics.plasm-ph↗
arXiv2015

Calibration of Time Of Flight Detectors Using Laser-driven Neutron Source

Calibration of three scintillators (EJ232Q, BC422Q and EJ410) in a time-of-flight (TOF) arrangement using a laser drive-neutron source is presented. The three plastic scintillator detectors were calibrated with gamma insensitive bubble detector spectrometers, which were absolutely calibrated over a wide range of neutron energies ranging from sub MeV to 20 MeV. A typical set of data obtained simultaneously by the detectors are shown, measuring the neutron spectrum emitted from a petawatt laser irradiated thin foil.

physics.ins-det↗
arXiv2015

Generation of a neutral, high-density electron-positron plasma in the laboratory

We report on the laser-driven generation of purely neutral, relativistic electron-positron pair plasmas. The overall charge neutrality, high average Lorentz factor ($γ_{e/p} \approx 15$), small divergence ($θ_{e/p} \approx 10 - 20$ mrad), and high density ($n_{e/p}\simeq 10^{15}$cm$^{-3}$) of these plasmas open the pathway for the experimental study of the dynamics of this exotic state of matter, in regimes that are of relevance to electron-positron astrophysical plasmas.

physics.plasm-ph↗
arXiv2015

The SAMI Galaxy Survey: instrument specification and target selection

The SAMI Galaxy Survey will observe 3400 galaxies with the Sydney-AAO Multi-object Integral-field spectrograph (SAMI) on the Anglo-Australian Telescope (AAT) in a 3-year survey which began in 2013. We present the throughput of the SAMI system, the science basis and specifications for the target selection, the survey observation plan and the combined properties of the selected galaxies. The survey includes four volume limited galaxy samples based on cuts in a proxy for stellar mass, along with low-stellar mass dwarf galaxies all selected from the Galaxy And Mass Assembly (GAMA) survey. The GAMA regions were selected because of the vast array of ancillary data available, including ultraviolet through to radio bands. These fields are on the celestial equator at 9, 12, and 14.5 hours, and cover a total of 144 square degrees (in GAMA-I). Higher density environments are also included with the addition of eight clusters. The clusters have spectroscopy from 2dFGRS and SDSS and photometry in regions covered by the Sloan Digital Sky Survey (SDSS) and/or VLT Survey Telescope/ATLAS. The aim is to cover a broad range in stellar mass and environment, and therefore the primary survey targets cover redshifts 0.004 < z < 0.095, magnitudes r$_{pet}$ < 19.4, stellar masses $10^{7} - 10^{12}$ M$_{sol}$, and environments from isolated field galaxies through groups to clusters of $10^{15}$ M$_{sol}$.

astro-ph.GA↗
arXiv2014

The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for galaxies of all types

We take advantage of the first data from the Sydney-AAO Multi-object Integral field (SAMI) Galaxy Survey to investigate the relation between the kinematics of gas and stars, and stellar mass in a comprehensive sample of nearby galaxies. We find that all 235 objects in our sample, regardless of their morphology, lie on a tight relation linking stellar mass ($M_{*}$) to internal velocity quantified by the $S_{0.5}$ parameter, which combines the contribution of both dispersion ($σ$) and rotational velocity ($V_{rot}$) to the dynamical support of a galaxy ($S_{0.5}=\sqrt{0.5V_{rot}^{2}+σ^{2}}$). Our results are independent of the baryonic component from which $σ$ and $V_{rot}$ are estimated, as the $S_{0.5}$ of stars and gas agree remarkably well. This represents a significant improvement compared to the canonical $M_{*}$ vs. $V_{rot}$ and $M_{*}$ vs. $σ$ relations. Not only is no sample pruning necessary, but also stellar and gas kinematics can be used simultaneously, as the effect of asymmetric drift is taken into account once $V_{rot}$ and $σ$ are combined. Our findings illustrate how the combination of dispersion and rotational velocities for both gas and stars can provide us with a single dynamical scaling relation valid for galaxies of all morphologies across at least the stellar mass range 8.5$<log(M_{*}/M_{\odot})<$11. Such relation appears to be more general and at least as tight as any other dynamical scaling relation, representing a unique tool for investigating the link between galaxy kinematics and baryonic content, and a less biased comparison with theoretical models.

astro-ph.GA↗
arXiv2014

Characterisation of deuterium spectra from laser driven multi-species sources by employing differentially filtered image plate detectors in Thomson spectrometers

A novel method for characterising the full spectrum of deuteron ions emitted by laser driven multi-species ion sources is discussed. The procedure is based on using differential filtering over the detector of a Thompson parabola ion spectrometer, which enables discrimination of deuterium ions from heavier ion species with the same charge-to-mass ratio (such as C6+, O8+, etc.). Commonly used Fuji Image plates were used as detectors in the spectrometer, whose absolute response to deuterium ions over a wide range of energies was calibrated by using slotted CR-39 nuclear track detectors. A typical deuterium ion spectrum diagnosed in a recent experimental campaign is presented.

physics.plasm-ph↗
arXiv2013

The Pulsar Search Collaboratory: Discovery and Timing of Five New Pulsars

We present the discovery and timing solutions of five new pulsars by students involved in the Pulsar Search Collaboratory (PSC), a NSF-funded joint program between the National Radio Astronomy Observatory and West Virginia University designed to excite and engage high-school students in Science, Technology, Engineering, and Mathematics (STEM) and related fields. We encourage students to pursue STEM fields by apprenticing them within a professional scientific community doing cutting edge research, specifically by teaching them to search for pulsars. The students are analyzing 300 hours of drift-scan survey data taken with the Green Bank Telescope at 350 MHz. These data cover 2876 square degrees of the sky. Over the course of five years, more than 700 students have inspected diagnostic plots through a web-based graphical interface designed for this project. The five pulsars discovered in the data have spin periods ranging from 3.1 ms to 4.8 s. Among the new discoveries are - PSR J1926-1314, a long period, nulling pulsar; PSR J1821+0155, an isolated, partially recycled 33-ms pulsar; and PSR J1400-1438, a millisecond pulsar in a 9.5-day orbit whose companion is likely a white dwarf star.

astro-ph.SR↗
arXiv2012

GASKAP -- The Galactic ASKAP Survey

A survey of the Milky Way disk and the Magellanic System at the wavelengths of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule will be carried out with the Australian Square Kilometre Array Pathfinder telescope. The survey will study the distribution of HI emission and absorption with unprecedented angular and velocity resolution, as well as molecular line thermal emission, absorption, and maser lines. The area to be covered includes the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg, spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific goals, from studies of galaxy evolution to star formation, with particular contributions to understanding stellar wind kinematics, the thermal phases of the interstellar medium, the interaction between gas in the disk and halo, and the dynamical and thermal states of gas at various positions along the Magellanic Stream.

astro-ph.GA↗
arXiv2009

The case for a directional dark matter detector and the status of current experimental efforts

We present the case for a dark matter detector with directional sensitivity. This document was developed at the 2009 CYGNUS workshop on directional dark matter detection, and contains contributions from theorists and experimental groups in the field. We describe the need for a dark matter detector with directional sensitivity; each directional dark matter experiment presents their project's status; and we close with a feasibility study for scaling up to a one ton directional detector, which would cost around $150M.

astro-ph.CO↗
arXiv2007

The Molonglo Galactic Plane Survey (MGPS-2): Compact Source Catalogue

We present the first data release from the second epoch Molonglo Galactic Plane Survey (MGPS-2). MGPS-2 was carried out with the Molonglo Observatory Synthesis Telescope at a frequency of 843 MHz and with a restoring beam of 45 arcsec x 45 arcsec cosec(dec), making it the highest resolution large scale radio survey of the southern Galactic plane. It covers the range |b| < 10 deg and 245 deg < l < 365 deg and is the Galactic counterpart to the Sydney University Molonglo Sky Survey (SUMSS) which covers the whole southern sky with dec <= -30 deg (|b| > 10 deg). In this paper we present the MGPS-2 compact source catalogue. The catalogue has 48,850 sources above a limiting peak brightness of 10 mJy/beam. Positions in the catalogue are accurate to 1 arcsec - 2 arcsec. A full catalogue including extended sources is in preparation. We have carried out an analysis of the compact source density across the Galactic plane and find that the source density is not statistically higher than the density expected from the extragalactic source density alone. We also present version 2.0 of the SUMSS image data and catalogue which are now available online. The data consists of 629 4.3 deg x 4.3 deg mosaic images covering the 8100 deg^2 of sky with dec <= -30 deg and |b| > 10 deg. The catalogue contains 210,412 radio sources to a limiting peak brightness of 6 mJy/beam at dec <= -50 deg and 10 mJy/beam at dec > -50 deg. We describe the updates and improvements made to the SUMSS cataloguing process.

astro-ph↗
arXiv2006

An Atomic and Molecular Study of the Interstellar Medium Around the SNR RCW 103

We report on the detection of HCO+ and 12CO emission in the rotational transition J=1-0 in the vicinity of the shock front at the southern border of the supernova remnant RCW 103, where previous infrared observations suggest an interaction with a molecular cloud. The observations were carried out with the Australian Millimeter Radiotelescope at Mopra. We observed a depletion of HCO+ behind the supernova shock front. In addition, we studied the interstellar medium over an extended region towards RCW 103 based on archival 21 cm HI line observations from the Australia Telescope Compact Array (ATCA) and the Parkes Telescope. No atomic gas is observed in emission in coincidence with the molecular feature. This absence is interpreted in terms of self absorption processes.

astro-ph↗
arXiv2005

Measuring Active-Sterile Neutrino Oscillations with a Stopped Pion Neutrino Source

The question of the existence of light sterile neutrinos is of great interest in many areas of particle physics, astrophysics, and cosmology. Furthermore, should the MiniBooNE experiment at Fermilab confirm the LSND oscillation signal, then new measurements are required to identify the mechanism responsible for these oscillations. Possibilities include sterile neutrinos, CP or CPT violation, variable mass neutrinos, Lorentz violation, and extra dimensions. In this paper, we consider an experiment at a stopped pion neutrino source to determine if active-sterile neutrino oscillations with delta-m greater than 0.1 eV2 can account for the signal. By exploiting stopped pi+ decay to produce a monoenergetic nu_mu source, and measuring the rate of the neutral current reaction nu_x + 12C -> nu_x +12C* as a function of distance from the source, we show that a convincing test for active-sterile neutrino oscillations can be performed.

hep-ph↗
arXiv2005

The neutral gas in the environs of the Geminga gamma-ray pulsar

We present a high-resolution (24 arcsec) study of the HI interstellar gas distribution around the radio-quiet neutron star Geminga. Based on Very Large Array (VLA) and MPIfR Effelsberg telescope data, we analyzed a 40' x 40' field around Geminga. These observations have revealed the presence of a neutral gas shell, 0.4 pc in radius, with an associated HI mass of 0.8 Msun, which surrounds Geminga at a radial velocity compatible with the kinematical distance of the neutron star. In addition, morphological agreement is observed between the internal face of the HI shell and the brightest structure of Geminga's tail observed in X-rays.We explore the possibility that this morphological agreement is the result of a physical association.

astro-ph↗