The EVLA: Prospects for HI

To continue the unparalleled success of the Very Large Array (VLA) for radio astronomy, the facility is currently being converted to become the 'Expanded VLA' (EVLA). The EVLA will radically improve the VLA in order to cover the full 0.93-50 GHz radio wavelength range without gaps, provide up to an order of magnitude better sensitivity, and to allow observations at much larger bandwidths and spectral resolution as currently possible. For observations of the 21 cm line of atomic neutral hydrogen (HI), the EVLA offers thousands of km/s velocity coverage at sub-km/s resolution for targeted observations as well as an improved spectral baseline stability. In addition, every L-band (21 cm) continuum or targeted HI observation can be set-up to simultaneously observe a full z=0-0.53 HI redshift survey at a velocity resolution of a few km/s. In turn, every HI observation will also yield deep radio continuum images of the field. These synergies will deliver a wealth of data which opens up a wide 'discovery space' to study the details of galaxy evolution and cosmology.Comment: to appear in the proceedings to the conference: "The Evolution of Galaxies through the Neutral Hydrogen Window", Arecibo, PR, US

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy

A Wideband Polarization Study of Cygnus A with the JVLA. I: The Observations and Data

We present results from deep, wideband, high spatial and spectral resolution observations of the nearby luminous radio galaxy Cygnus A with the Jansky Very Large Array. The high surface brightness of this source enables detailed polarimetric imaging, providing images at 0.75\arcsec, spanning 2 - 18 GHz, and at 0.30\arcsec (6 - 18 GHz). The fractional polarization from 2000 independent lines of sight across the lobes decreases strongly with decreasing frequency, with the eastern lobe depolarizing at higher frequencies than the western lobe. The depolarization shows considerable structure, varying from monotonic to strongly oscillatory. The fractional polarization in general increases with increasing resolution at a given frequency, as expected. However, there are numerous lines of sight with more complicated behavior. We have fitted the 0.3\arcsec images with a simple model incorporating random, unresolved fluctuations in the cluster magnetic field to determine the high resolution, high-frequency properties of the source and the cluster. From these derived properties, we generate predicted polarization images of the source at lower frequencies, convolved to 0.75\arcsec. These predictions are remarkably consistent with the observed emission. The observations are consistent with the lower-frequency depolarization being due to unresolved fluctuations on scales $\gtrsim$ 300 - 700 pc in the magnetic field and/or electron density superposed on a partially ordered field component. There is no indication in our data of the location of the depolarizing screen or the large-scale field, either, or both of which could be located throughout the cluster, or in a boundary region between the lobes and the cluster.Comment: 24 pages, 13 figures. The manuscript has been accepted for publication in The Astrophysical Journa

Radio galaxy evolution: what you can learn from a Brief Encounter

We describe the pitfalls encountered in deducing from classical double radio source observables (luminosity, spectral index, redshift and linear size) the essential nature of how these objects evolve. We discuss the key role played by hotspots in governing the energy distribution of the lobes they feed, and subsequent spectral evolution. We present images obtained using the new 74 MHz receivers on the VLA and discuss constraints which these enforce on models of the backflow and ages in classical doubles.Comment: invited talk at `Lifecycles of Radio Galaxies' workshop; eds John Biretta et a

SN2019dge: a Helium-rich Ultra-Stripped Envelope Supernova

We present observations of ZTF18abfcmjw (SN2019dge), a helium-rich supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.33 M_⊙) and low kinetic energy (≈1.3 × 10⁵⁰ erg). Early-time (<4 days after explosion) photometry reveals evidence of shock cooling from an extended helium-rich envelope of ~0.1 M_⊙ located ~1.2 × 10¹³ cm from the progenitor. Early-time He II line emission and subsequent spectra show signatures of interaction with helium-rich circumstellar material, which extends from ≳ 5 × 10¹³ cm to 2 × 10¹⁶ cm. We interpret SN2019dge as a helium-rich supernova from an ultra-stripped progenitor, which originates from a close binary system consisting of a mass-losing helium star and a low-mass main-sequence star or a compact object (i.e., a white dwarf, a neutron star, or a black hole). We infer that the local volumetric birth rate of 19dge-like ultra-stripped SNe is in the range of 1400–8200 Gpc⁻³ yr⁻¹ (i.e., 2%–12% of core-collapse supernova rate). This can be compared to the observed coalescence rate of compact neutron star binaries that are not formed by dynamical capture