Engineering topics

Lindner, Robert R.

Publications and source records attributed to Lindner, Robert R..

8 records

DOE OSTI2017

Recovering Interstellar Gas Properties with Hi Spectral Lines: A Comparison between Synthetic Spectra and 21-SPONGE

We analyze synthetic neutral hydrogen (H i) absorption and emission spectral lines from a high-resolution, three-dimensional hydrodynamical simulation to quantify how well observational methods recover the physical properties of interstellar gas. We present a new method for uniformly decomposing H i spectral lines and estimating the properties of associated gas using the Autonomous Gaussian Decomposition (AGD) algorithm. We find that H i spectral lines recover physical structures in the simulation with excellent completeness at high Galactic latitude, and this completeness declines with decreasing latitude due to strong velocity-blending of spectral lines. The temperature and column density inferred from our decomposition and radiative transfer method agree with the simulated values within a factor of <2 for the majority of gas structures. We next compare synthetic spectra with observations from the 21-SPONGE survey at the Karl G. Jansky Very Large Array using AGD. We find more components per line of sight in 21-SPONGE than in synthetic spectra, which reflects insufficient simulated gas scale heights and the limitations of local box simulations. In addition, we find a significant population of low-optical depth, broad absorption components in the synthetic data which are not seen in 21-SPONGE. This population is not obvious in integrated or per-channel diagnostics, and reflects the benefit of studying velocity-resolved components. The discrepant components correspond to the highest spin temperatures (1000<T{sub s}<4000 K), which are not seen in 21-SPONGE despite sufficient observational sensitivity. We demonstrate that our analysis method is a powerful tool for diagnosing neutral interstellar medium conditions, and future work is needed to improve observational statistics and implementation of simulated physics.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

First detection of HCO{sup +} absorption in the Magellanic System

We present the first detection of HCO{sup +} absorption in the Magellanic System. Using the ATCA, we observed nine extragalactic radio continuum sources behind the Magellanic System and detected HCO{sup +} absorption toward one source located behind the leading edge of the Magellanic Bridge. The detection is located at an LSR velocity of v=214.0±0.4 km s{sup −1}, with an FWHM of Δv=4.5±1.0 km s{sup −1}, and an optical depth of τ(HCO{sup +})=0.10±0.02. Although there is abundant neutral hydrogen (H i) surrounding the sight line in position–velocity space, at the exact location of the absorber the H i column density is low, <10{sup 20} cm{sup −2}, and there is little evidence for dust or CO emission from Planck observations. While the origin and survival of molecules in such a diffuse environment remain unclear, dynamical events such as H i flows and cloud collisions in this interacting system likely play an important role.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

The 21-SPONGE H i absorption survey. I. Techniques and initial results

We present methods and results from “21 cm Spectral Line Observations of Neutral Gas with the EVLA” (21-SPONGE), a large survey for Galactic neutral hydrogen (H i) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median rms noise in optical depth of σ{sub τ}=9×10{sup −4} per 0.42 km s{sup −1} channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest H i absorption survey with this high sensitivity. We discuss the observations and data reduction strategies, as well as line fitting techniques. We prove that the VLA bandpass (BP) is stable enough to detect broad, shallow lines associated with warm H i, and we show that BP observations can be combined in time to reduce spectral noise. In combination with matching H i emission profiles from the Arecibo Observatory (∼3.′5 angular resolution), we estimate excitation (or spin) temperatures (T{sub s}) and column densities for Gaussian components fitted to sightlines along which we detect H i absorption (30/31). We measure temperatures up to T{sub s}∼1500 K for individual lines, showing that we can probe the thermally unstable interstellar medium (ISM) directly. However, we detect fewer of these thermally unstable components than expected from previous observational studies. We probe a wide range in column density between ∼10{sup 16} and >10{sup 21} cm{sup −2} for individual H i clouds. In addition, we reproduce the trend between cold gas fraction and average T{sub s} found by the Kim et al. synthetic observations of a hydrodynamic ISM simulation. Finally, we compare methods for estimating T{sub s} using H i observations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

The Atacama Cosmology Telescope: The LABOCA/ACT survey of clusters at all Redshifts

We present a multi-wavelength analysis of 11 Sunyaev–Zel’dovich effect (SZE)-selected galaxy clusters (10 with new data) from the Atacama Cosmology Telescope (ACT) southern survey. We have obtained new imaging from the Large APEX Bolometer Camera (345 GHz; LABOCA) on the Atacama Pathfinder EXperiment (APEX) telescope, the Australia Telescope Compact Array (2.1 GHz; ATCA), and the Spectral and Photometric Imaging Receiver (250, 350, and 500 μm; SPIRE) on the Herschel Space Observatory.{sup 24} Spatially resolved 345 GHz SZE increments with integrated signal-to-noise ratio (S/N)>5 are found in six clusters. We compute 2.1 GHz number counts as a function of cluster-centric radius and find significant enhancements in the counts of bright sources at projected radii θ<θ{sub 2500c}. By extrapolating in frequency, we predict that the combined signals from 2.1 GHz-selected radio sources and 345 GHz-selected submillimeter galaxies (SMGs) contaminate the 148 GHz SZE decrement signal by ∼5% and the 345 GHz SZE increment by ∼18%. After removing radio source and SMG emission from the SZE signals, we use ACT, LABOCA, and (in some cases) new Herschel SPIRE imaging to place constraints on the clusters’ peculiar velocities. The sample’s average peculiar velocity relative to the cosmic microwave background is 〈v{sub p}〉=153±383 km s{sup −1}.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

AUTONOMOUS GAUSSIAN DECOMPOSITION

We present a new algorithm, named Autonomous Gaussian Decomposition (AGD), for automatically decomposing spectra into Gaussian components. AGD uses derivative spectroscopy and machine learning to provide optimized guesses for the number of Gaussian components in the data, and also their locations, widths, and amplitudes. We test AGD and find that it produces results comparable to human-derived solutions on 21 cm absorption spectra from the 21 cm SPectral line Observations of Neutral Gas with the EVLA (21-SPONGE) survey. We use AGD with Monte Carlo methods to derive the H i line completeness as a function of peak optical depth and velocity width for the 21-SPONGE data, and also show that the results of AGD are stable against varying observational noise intensity. The autonomy and computational efficiency of the method over traditional manual Gaussian fits allow for truly unbiased comparisons between observations and simulations, and for the ability to scale up and interpret the very large data volumes from the upcoming Square Kilometer Array and pathfinder telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

The radio relics and halo of El Gordo, a massive z = 0.870 cluster merger

We present 610 MHz and 2.1 GHz imaging of the massive Sunyaev-Zel'dovich Effect selected z = 0.870 cluster merger ACT-CL J0102–4915 ({sup E}l Gordo{sup )}, obtained with the Giant Metrewave Radio Telescope and the Australia Telescope Compact Array (ATCA), respectively. We detect two complexes of radio relics separated by 3.'4 (1.6 Mpc) along the system's northwest-to-southeast collision axis that have high integrated polarization fractions (33%) and steep spectral indices (α between 1 and 2; S {sub ν}∝ν{sup –α}), consistent with creation via Fermi acceleration by shocks in the intracluster medium triggered by the cluster collision. From the spectral index of the relics, we compute a Mach number M=2.5{sub −0.3}{sup +0.7} and shock speed of 2500{sub −300}{sup +400} km s{sup −1}. With our wide-bandwidth, full-polarization ATCA data, we compute the Faraday depth φ across the northwest relic and find a range of values spanning Δφ = 30 rad m{sup –2}, with a mean value of (φ) = 11 rad m{sup –2} and standard deviation σ{sub φ} = 6 rad m{sup –2}. With the integrated line-of-sight gas density derived from new Chandra X-ray observations, our Faraday depth measurement implies B {sub ∥} ∼ 0.01 μG in the cluster outskirts. The extremely narrow shock widths in the relics (d {sub shock} ≤ 23 kpc), caused by the short synchrotron cooling timescale of relativistic electrons at z = 0.870, prevent us from placing a meaningful constraint on the magnetic field strength B using cooling time arguments. In addition to the relics, we detect a large (r {sub H} ≅ 1.1 Mpc radius), powerful (log (L {sub 1.4}/W Hz{sup –1}) = 25.66 ± 0.12) radio halo with a shape similar to El Gordo's 'bullet'-like X-ray morphology. The spatially resolved spectral-index map of the halo shows the synchrotron spectrum is flattest near the relics, along the system's collision axis, and in regions of high T {sub gas}, all locations associated with recent energy injection. The spatial and spectral correlation between the halo emission and cluster X-ray properties supports primary-electron processes like turbulent reacceleration as the halo production mechanism. The halo's integrated 610 MHz to 2.1 GHz spectral index is a relatively flat α = 1.2 ± 0.1, consistent with the cluster's high T {sub gas} in view of previously established global scaling relations. El Gordo is the highest-redshift cluster known to host a radio halo and/or radio relics, and provides new constraints on the non-thermal physics in clusters at z > 0.6.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

EXCITATION TEMPERATURE OF THE WARM NEUTRAL MEDIUM AS A NEW PROBE OF THE Lyα RADIATION FIELD

We use the Karl G. Jansky Very Large Array to conduct a high-sensitivity survey of neutral hydrogen (H I) absorption in the Milky Way. In combination with corresponding H I emission spectra obtained mostly with the Arecibo Observatory, we detect a widespread warm neutral medium component with excitation temperature 〈T{sub s}〉=7200{sub −1200}{sup +1800} K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Lyα scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that H I absorption can be used to constrain the Lyα radiation field, a critical quantity for studying the energy balance in the ISM and intergalactic medium yet notoriously difficult to model because of its complicated radiative transfer, in and around galaxies nearby and at high redshift.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

DETECTION OF IRON K{alpha} EMISSION FROM A COMPLETE SAMPLE OF SUBMILLIMETER GALAXIES

We present an X-ray stacking analysis of a sample of 38 submillimeter galaxies (SMGs) with (z) = 2.6 discovered at {>=}4{sigma} significance in the Lockman Hole North with the MAMBO array. We find a 5{sigma} detection in the stacked soft band (0.5-2.0 keV) image, and no significant detection in the hard band (2.0-8 keV). We also perform rest-frame spectral stacking based on spectroscopic and photometric redshifts and find a {approx}4{sigma} detection of Fe K{alpha} emission with an equivalent width of EW {approx}> 1 keV. The centroid of the Fe K{alpha} emission lies near 6.7 keV, indicating a possible contribution from highly ionized Fe XXV or Fe XXVI; there is also a slight indication that the line emission is more spatially extended than the X-ray continuum. This is the first X-ray analysis of a complete, flux-limited sample of SMGs with statistically robust radio counterparts.

79 ASTRONOMY AND ASTROPHYSICS↗