We present 610 MHz and 2.1 GHz imaging of the massive Sunyaev Zel'dovich Effect (SZE)-selected z = 0.870 cluster merger ACT-CL J0102-4915 ("El Gordo"), obtained with the Giant Metre-wave Radio Telescope (GMRT) 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-tosoutheast collision axis that have high integrated polarization fractions (33%) and steep spectral indices (α between 1-2; S ν ∝ ν −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 +0.7 −0.3 and shock speed of 2500 +400 −300 km s −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 ∆φ = 30 rad m −2 , with a mean value of φ = 11 rad m −2 and standard deviation σ φ = 6 rad m −2 . With the integrated line-of-sight gas density derived from new Chandra Xray observations, our Faraday depth measurement implies B ∼ 0.01 µG in the cluster outskirts. The extremely narrow shock widths in the relics (d 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 H 1.1 Mpc radius), powerful (log(L 1.4 /W Hz −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 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 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. 2properties of galaxy clusters such as cosmic ray acceleration and magnetic field profiles. The geometry of relic systems can also be used to constrain the collision parameters of cluster mergers (van Weeren et al. 2011a).One challenge in using relics and halos to probe the energy content and magnetic field properties of clusters is their relative rarity. Only 30% of X-ray luminous clusters host halos (Venturi et al. 2007(Venturi et al. , 2008. Their presence is correlated with cluster mass and dynamical state, with the most massive and most dynamically disturbed clusters showing the highest frequencies of halos and relics (Cassano et al. 201...

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 (Hi) absorption with the Karl G. Jansky Very Large Array (VLA). With the upgraded capabilities of the VLA, we reach median root-mean-square (RMS) noise in optical depth of σ τ = 9 × 10 −4 per 0.42 km s −1 channel for the 31 sources presented here. Upon completion, 21-SPONGE will be the largest Hi 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 is stable enough to detect broad, shallow lines associated with warm Hi, and show that bandpass observations can be combined in time to reduce spectral noise. In combination with matching Hi emission profiles from the Arecibo Observatory (∼ 3.5 ′ angular resolution), we estimate excitation (or spin) temperatures (T s ) and column densities for Gaussian components fitted to sightlines along which we detect Hi absorption (30/31). We measure temperatures up to T 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 16 and > 10 21 cm −2 for individual Hi clouds. In addition, we reproduce the trend between cold gas fraction and average T s found by synthetic observations of a hydrodynamic ISM simulation by Kim et al. (2014). Finally, we investigate methods for estimating Hi T s and discuss their biases.

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.

We present deep 1.2 mm continuum mapping of a 566 arcmin 2 area within the Lockman Hole North field, previously a target of the Spitzer Wide-area Infrared Extragalactic (SWIRE) survey and extremely deep 20 cm mapping with the Very Large Array, which we have obtained using the Max-Planck millimeter bolometer (MAMBO) array on the IRAM 30 m telescope. After filtering, our full map has an RMS sensitivity ranging from 0.45 to 1.5 mJy beam −1 , with an average of 0.75 mJy beam −1 . Using the pixel flux distribution in a map made from our best data, we determine the shape, normalization, and approximate flux density cutoff for 1.2 mm number counts well below our nominal sensitivity and confusion limits. After validating our full dataset through comparison with this map, we successfully detect 41 1.2 mm sources with S/N > 4.0 and S 1.2 mm ≃ 2 − 5 mJy. We use the most significant of these detections to directly determine the integral number counts down to 1.8 mJy, which are consistent with the results of the pixel flux distribution analysis. 93% of our 41 individual detections have 20 cm counterparts, 49% have Spitzer/MIPS 24 µm counterparts, and one may have a significant Chandra X-ray counterpart. We resolve ≃ 3% of the cosmic infrared background (CIB) at 1.2 mm into significant detections, and directly estimate a 0.05 mJy faint-end cutoff for the counts that is consistent with the full intensity of the 1.2 mm CIB. The median redshift of our 17 detections with spectroscopic or robust photometric redshifts is z median = 2.3, and rises to z median = 2.9 when we include redshifts estimated from the radio/far-infrared spectral index. By using a nearest neighbor and angular correlation function analysis, we find evidence that our S/N > 4.0 detections are clustered at the 95% confidence level.

We use the Karl G. Jansky Very Large Array (VLA) to conduct a high-sensitivity survey of neutral hydrogen (Hi) absorption in the Milky Way. In combination with corresponding Hi emission spectra obtained mostly with the Arecibo Observatory, we detect a widespread warm neutral medium (WNM) component with excitation temperature T s = 7200 +1800 −1200 K (68% confidence). This temperature lies above theoretical predictions based on collisional excitation alone, implying that Ly-α scattering, the most probable additional source of excitation, is more important in the interstellar medium (ISM) than previously assumed. Our results demonstrate that Hi absorption can be used to constrain the Ly-α 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.