arXiv subjects

J. E. G. Peek

Publications and source records attributed to J. E. G. Peek.

At least 37 records · Page 2Linked to original sources

arXiv2021

Burton's Curse: The Impact of Bulk Flows on the Galactic Longitude-Velocity Diagram and the Illusion of a Continuous Perseus Arm

In this work we demonstrate that the Perseus Arm is not a continuous structure of molecular gas in the second quadrant. We first show that the observed, distanced-resolved velocity structure of the Galaxy in the outer disk is capable of creating illusory spiral arms, as was first proposed by Burton (1971). Second, we measure the distances to a collection of CO clouds at velocities consistent with the Perseus arm with $135^\circ < l < 160^\circ$. We find these distances using 3D dust maps from Green et al. (2019). We determine that these molecular cloud do not preferentially lie at the distance of a purported Perseus arm, but rather extend over 3 kpc in distance, with some evidence for a closer, high pitch angle structure between 1 and 1.5 kpc away. Finally, we demonstrate that velocity perturbations of the amplitude found near the Perseus arm can wreak havoc on our interpretation of the longitude-velocity diagram for more than half of the Milky Way disk.

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arXiv2021

The Future Of The Arecibo Observatory: The Next Generation Arecibo Telescope

The Arecibo Observatory (AO) is a multidisciplinary research and education facility that is recognized worldwide as a leading facility in astronomy, planetary, and atmospheric and space sciences. AO's cornerstone research instrument was the 305-m William E. Gordon telescope. On December 1, 2020, the 305-m telescope collapsed and was irreparably damaged. In the three weeks following the collapse, AO's scientific and engineering staff and the AO users community initiated extensive discussions on the future of the observatory. The community is in overwhelming agreement that there is a need to build an enhanced, next-generation radar-radio telescope at the AO site. From these discussions, we established the set of science requirements the new facility should enable. These requirements can be summarized briefly as: 5 MW of continuous wave transmitter power at 2 - 6 GHz, 10 MW of peak transmitter power at 430 MHz (also at 220MHz under consideration), zenith angle coverage 0 to 48 deg, frequency coverage 0.2 to 30 GHz and increased Field-of-View. These requirements determine the unique specifications of the proposed new instrument. The telescope design concept we suggest consists of a compact array of fixed dishes on a tiltable, plate-like structure with a collecting area equivalent to a 300m dish. This concept, referred to as the Next Generation Arecibo Telescope (NGAT), meets all of the desired specifications and provides significant new science capabilities to all three research groups at AO. This whitepaper presents a sample of the wide variety of the science that can be achieved with the NGAT, the details of the telescope design concept and the need for the new telescope to be located at the AO site. We also discuss other AO science activities that interlock with the NGAT in the white paper.

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arXiv2021

The Role of Machine Learning in the Next Decade of Cosmology

In recent years, machine learning (ML) methods have remarkably improved how cosmologists can interpret data. The next decade will bring new opportunities for data-driven cosmological discovery, but will also present new challenges for adopting ML methodologies and understanding the results. ML could transform our field, but this transformation will require the astronomy community to both foster and promote interdisciplinary research endeavors.

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arXiv2020

Predicting galaxy spectra from images with hybrid convolutional neural networks

Galaxies can be described by features of their optical spectra such as oxygen emission lines, or morphological features such as spiral arms. Although spectroscopy provides a rich description of the physical processes that govern galaxy evolution, spectroscopic data are observationally expensive to obtain. For the first time, we are able to robustly predict galaxy spectra directly from broad-band imaging. We present a powerful new approach using a hybrid convolutional neural network with deconvolution instead of batch normalization; this hybrid CNN outperforms other models in our tests. The learned mapping between galaxy imaging and spectra will be transformative for future wide-field surveys, such as with the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope, by multiplying the scientific returns for spectroscopically-limited galaxy samples.

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arXiv2020

The HI Structure of the Local Volume Dwarf Galaxy Pisces A

Dedicated HI surveys have recently led to a growing category of low-mass galaxies found in the Local Volume. We present synthesis imaging of one such galaxy, Pisces A, a low-mass dwarf originally confirmed via optical imaging and spectroscopy of neutral hydrogen (HI) sources in the Galactic Arecibo L-band Feed Array HI (GALFA-HI) survey. Using HI observations taken with the Karl G. Jansky Very Large Array (JVLA), we characterize the kinematic structure of the gas and connect it to the galaxy's environment and evolutionary history. While the galaxy shows overall ordered rotation, a number of kinematic features indicate a disturbed gas morphology. These features are suggestive of a tumultuous recent history, and represent $\sim 3.5$% of the total baryonic mass. We find a total baryon fraction $f_{\rm bary} = 0.13$ if we include these features. We also quantify the cosmic environment of Pisces A, finding an apparent alignment of the disturbed gas with nearby, large scale filamentary structure at the edge of the Local Void. We consider several scenarios for the origin of the disturbed gas, including gas stripping via ram pressure or galaxy-galaxy interactions, as well as accretion and ram pressure compression. Though we cannot rule out a past interaction with a companion, our observations best support the suggestion that the neutral gas morphology and recent star formation in Pisces A is a direct result of its interactions with the IGM.

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arXiv2020

Extracting the cold neutral medium from HI emission with deep learning: Implications for Galactic foregrounds at high latitude

Resolving the phase structure of neutral hydrogen (HI) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of HI temperature and density are limited by the availability of background continuum sources for measuring HI absorption. Here we test the use of deep learning for extracting HI properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction of cold neutral medium (f_CNM) and the correction to the optically-thin HI column density for optical depth (R_HI) from $21\rm\,cm$ emission alone. We restrict our analysis to high Galactic latitudes ($|b|>30 deg), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts f_CNM and R_HI by comparing the results with direct constraints from 21 cm absorption. By applying the network to the GALFA-HI survey, we generate large-area maps of f_CNM and R_HI. Although the overall contribution to the total HI column of cold neutral medium (CNM)-rich structures is small (~5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21 cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between HI column density and dust reddening (E(B-V)) declines with increasing R_HI, indicating that future efforts to quantify foreground Galactic E(B-V) using HI, even at high latitudes, should increase fidelity by accounting for HI phase structure.

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arXiv2020

DeepMerge: Classifying High-redshift Merging Galaxies with Deep Neural Networks

We investigate and demonstrate the use of convolutional neural networks (CNNs) for the task of distinguishing between merging and non-merging galaxies in simulated images, and for the first time at high redshifts (i.e. $z=2$). We extract images of merging and non-merging galaxies from the Illustris-1 cosmological simulation and apply observational and experimental noise that mimics that from the Hubble Space Telescope; the data without noise form a "pristine" data set and that with noise form a "noisy" data set. The test set classification accuracy of the CNN is $79\%$ for pristine and $76\%$ for noisy. The CNN outperforms a Random Forest classifier, which was shown to be superior to conventional one- or two-dimensional statistical methods (Concentration, Asymmetry, the Gini, $M_{20}$ statistics etc.), which are commonly used when classifying merging galaxies. We also investigate the selection effects of the classifier with respect to merger state and star formation rate, finding no bias. Finally, we extract Grad-CAMs (Gradient-weighted Class Activation Mapping) from the results to further assess and interrogate the fidelity of the classification model.

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arXiv2019

Petabytes to Science

A Kavli foundation sponsored workshop on the theme \emph{Petabytes to Science} was held 12$^{th}$ to 14$^{th}$ of February 2019 in Las Vegas. The aim of the this workshop was to discuss important trends and technologies which may support astronomy. We also tackled how to better shape the workforce for the new trends and how we should approach education and public outreach. This document was coauthored during the workshop and edited in the weeks after. It comprises the discussions and highlights many recommendations which came out of the workshop. We shall distill parts of this document and formulate potential white papers for the decadal survey.

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arXiv2019

The 3D Kinematics of Gas in the Small Magellanic Cloud

We investigate the kinematics of neutral gas in the Small Magellanic Cloud (SMC) and test the hypothesis that it is rotating in a disk. To trace the 3D motions of the neutral gas distribution, we identify a sample of young, massive stars embedded within it. These are stars with radial velocity measurements from spectroscopic surveys and proper motion measurements from Gaia, whose radial velocities match with dominant HI components. We compare the observed radial and tangential velocities of these stars with predictions from the state-of-the-art rotating disk model based on high-resolution 21 cm observations of the SMC from the Australian Square Kilometer Array Pathfinder telescope. We find that the observed kinematics of gas-tracing stars are inconsistent with disk rotation. We conclude that the kinematics of gas in the SMC are more complex than can be inferred from the integrated radial velocity field. As a result of violent tidal interactions with the LMC, non-rotational motions are prevalent throughout the SMC, and it is likely composed of distinct sub-structures overlapping along the line of sight.

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arXiv2019

Realizing the potential of astrostatistics and astroinformatics

This Astro2020 State of the Profession Consideration White Paper highlights the growth of astrostatistics and astroinformatics in astronomy, identifies key issues hampering the maturation of these new subfields, and makes recommendations for structural improvements at different levels that, if acted upon, will make significant positive impacts across astronomy.

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arXiv2019

Small-Scale HI Channel Map Structure is Cold: Evidence from Na I Absorption at High Galactic Latitudes

The spatial distribution of neutral hydrogen (H I) emission is a powerful probe of interstellar medium physics. The small-scale structure in H I channel maps is often assumed to probe the velocity field rather than real density structures. In this work we directly test this assumption, using high-resolution GALFA-H I observations and 50,985 quasar spectra from SDSS. We measure the equivalent widths of interstellar Na I D$_1$ and Na I D$_2$ absorption, and robustly conclude that they depend more strongly on the column density of small-scale structure in H I than on either the large-scale H I structure or the total H I column. This is inconsistent with the hypothesis that small-scale channel map structure is driven by velocity crowding. Instead, the data favor the interpretation that this emission structure predominantly originates in cold, dense interstellar material, consistent with a clumpy cold neutral medium.

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arXiv2019

Do Androids Dream of Magnetic Fields? Using Neural Networks to Interpret the Turbulent Interstellar Medium

The interstellar medium (ISM) of galaxies is composed of a turbulent magnetized plasma. In order to quantitatively measure relevant turbulent parameters of the ISM, a wide variety of statistical techniques and metrics have been developed that are often tested using numerical simulations and analytic formalism. These metrics are typically based on the Fourier power spectrum, which does not capture the Fourier phase information that carries the morphological characteristics of images. In this work we use density slices of magnetohydrodyanmic turbulence simulations to demonstrate that a modern tool, convolutional neural networks, can capture significant information encoded in the Fourier phases. We train the neural network to distinguish between two simulations with different levels of magnetization. We find that, even given a tiny slice of simulation data, a relatively simple network can distinguish sub-Alfvénic (strong magnetic field) and super-Alfvénic (weak magnetic field) turbulence >98% of the time, even when all spectral amplitude information is stripped from the images. In order to better understand how the neural network is picking out differences betweem the two classes of simulations we apply a neural network analysis method called "saliency maps". The saliency map analysis shows that sharp ridge-like features are a distinguishing morphological characteristic in such simulations. Our analysis provides a way forward for deeper understanding of the relationship between magnetohydrodyanmic turbulence and gas morphology and motivates further applications of neural networks for studies of turbulence. We make publicly available all data and software needed to reproduce our results.

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arXiv2019

Robust Archives Maximize Scientific Accessibility

We present a bibliographic analysis of Chandra, Hubble, and Spitzer publications. We find (a) archival data are used in >60% of the publication output and (b) archives for these missions enable a much broader set of institutions and countries to scientifically use data from these missions. Specifically, we find that authors from institutions that have published few papers from a given mission publish 2/3 archival publications, while those with many publications typically have 1/3 archival publications. We also show that countries with lower GDP per capita overwhelmingly produce archival publications, while countries with higher GDP per capital produce guest observer and archival publications in equal amounts. We argue that robust archives are thus not only critical for the scientific productivity of mission data, but also the scientific accessibility of mission data. We argue that the astronomical community should support archives to maximize the overall scientific societal impact of astronomy, and represent an excellent investment in astronomy's future.

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arXiv2019

The Physical Nature of Neutral Hydrogen Intensity Structure

We investigate the physical properties of structures seen in channel map observations of 21-cm neutral hydrogen (HI) emission. HI intensity maps display prominent linear structures that are well aligned with the ambient magnetic field in the diffuse interstellar medium (ISM). Some literature hold that these structures are "velocity caustics", fluctuations imprinted by the turbulent velocity field, and are not three-dimensional density structures in the ISM. We test this hypothesis by stacking probes of the density field -- broadband far infrared (FIR) emission and the integrated HI column density (NHI) -- at the locations of linear HI intensity structures. We find that the HI intensity features are real density structures and not velocity caustics. We generalize the investigation to all small-scale structure in HI channel maps, and analyze this correlation as a function of velocity channel width, finding no measurable contribution from velocity caustics to the HI channel map emission. Further, we find that small-scale HI channel maps structures have elevated FIR/NHI, implying that this emission originates from a colder, denser phase of the ISM than the surrounding material. The data are consistent with a multi-phase diffuse ISM in which small-scale structures in narrow HI channel maps are preferentially cold neutral medium (CNM) that is anisotropically distributed and aligned with the local magnetic field. The shallow spatial power spectrum (SPS) of narrow HI channels is often attributed to velocity caustics. We conjecture instead that the small-scale structure and narrow linewidths typical of CNM explain the observed relationship between the SPS and channel width.

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arXiv2019

The Panchromatic Circumgalactic Medium

Galaxies are surrounded by extended atmospheres, which are often called the circumgalactic medium (CGM) and are the least understood part of galactic ecosystems. The CGM serves as a reservoir of both diffuse, metal-poor gas accreted from the intergalactic medium, and metal-rich gas that is either ejected from galaxies by energetic feedback or stripped from infalling satellites. As such, the CGM is empirically multi-phased and complex in dynamics. Significant progress has been made in the past decade or so in observing the cosmic-ray/B-field, as well as various phases of the CGM. But basic questions remain to be answered. First, what are the energy, mass, and metal contents of the CGM? More specifically, how are they spatially distributed and partitioned in the different components? Moreover, how are they linked to properties of host galaxies and their global clustering and intergalactic medium environments? Lastly, what are the origin, state, and life-cycle of the CGM? This question explores the dynamics of the CGM. Here we illustrate how these questions may be addressed with multi-wavelength observations of the CGM.

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arXiv2019

Astro2020 Science White Paper: The Next Decade of Astroinformatics and Astrostatistics

Over the past century, major advances in astronomy and astrophysics have been largely driven by improvements in instrumentation and data collection. With the amassing of high quality data from new telescopes, and especially with the advent of deep and large astronomical surveys, it is becoming clear that future advances will also rely heavily on how those data are analyzed and interpreted. New methodologies derived from advances in statistics, computer science, and machine learning are beginning to be employed in sophisticated investigations that are not only bringing forth new discoveries, but are placing them on a solid footing. Progress in wide-field sky surveys, interferometric imaging, precision cosmology, exoplanet detection and characterization, and many subfields of stellar, Galactic and extragalactic astronomy, has resulted in complex data analysis challenges that must be solved to perform scientific inference. Research in astrostatistics and astroinformatics will be necessary to develop the state-of-the-art methodology needed in astronomy. Overcoming these challenges requires dedicated, interdisciplinary research. We recommend: (1) increasing funding for interdisciplinary projects in astrostatistics and astroinformatics; (2) dedicating space and time at conferences for interdisciplinary research and promotion; (3) developing sustainable funding for long-term astrostatisics appointments; and (4) funding infrastructure development for data archives and archive support, state-of-the-art algorithms, and efficient computing.

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arXiv2019

Understanding the circumgalactic medium is critical for understanding galaxy evolution

Galaxies evolve under the influence of gas flows between their interstellar medium and their surrounding gaseous halos known as the circumgalactic medium (CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a key role in the long cycles of accretion, feedback, and recycling of gas that drive star formation. In order to fully understand the physical processes at work within galaxies, it is therefore essential to have a firm understanding of the composition, structure, kinematics, thermodynamics, and evolution of the CGM. In this white paper we outline connections between the CGM and galactic star formation histories, internal kinematics, chemical evolution, quenching, satellite evolution, dark matter halo occupation, and the reionization of the larger-scale intergalactic medium in light of the advances that will be made on these topics in the 2020s. We argue that, in the next decade, fundamental progress on all of these major issues depends critically on improved empirical characterization and theoretical understanding of the CGM. In particular, we discuss how future advances in spatially-resolved CGM observations at high spectral resolution, broader characterization of the CGM across galaxy mass and redshift, and expected breakthroughs in cosmological hydrodynamic simulations will help resolve these major problems in galaxy evolution.

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arXiv2019

High-Dimensional Dust Mapping

Galactic interstellar dust has a profound impact not only on our observations of objects throughout the Universe, but also on the morphology, star formation, and chemical evolution of the Galaxy. The advent of massive imaging and spectroscopic surveys (particularly in the infrared) places us on the threshold of being able to map the properties and dynamics of dust and the interstellar medium (ISM) in three dimensions throughout the Milky Way disk and bulge. These developments will enable a fundamentally new understanding of dust properties, including how grains respond to their local environment and how those environments affect dust attenuation of background objects of interest. Distance-resolved maps of dust motion also hold great promise for tracing the flow of interstellar material throughout the Galaxy on a variety of scales, from bar-streaming motions to the collapse and dissolution of individual molecular clouds. These advances require optical and infrared imaging of stars throughout the Galactic midplane, stretching many kiloparsecs from the Sun, matched with very dense spectroscopic coverage to probe the ISM's fine-grained structure.

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