In the 20 years since the initial observations were made for the NRAO VLA Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST), these pioneering programs have defined the state-of-the-art in centimeter radio sky surveys and produced a steady stream of excellent science. Given the enhanced capabilities of the Jansky Very Large Array (VLA), now is an appropriate time to discuss the scientific potential of new centimeter-wavelength sky surveys.
Continuum Halos in Nearby Galaxies - an EVLA Survey (CHANG-ES), was awarded 405 hours of observing time in the B, C and D array configurations. The survey aims to measure radio continuum emission of 35 nearby edge-on galaxies in C band (6 GHz) and L band (1.4 GHz). The edge-on inclination of the galaxies makes it possible to probe the structure and physics of disk-halo outflows. With 3 arrays of observations (B, C, and D), we will be able to examine, in detail, the disk-halo interface, as well as the larger scale halos that surround galaxies.
The Naval Research Laboratory (NRL) and NRAO announce the release of the Very Large Array (VLA) Low-frequency Sky Survey Redux (VLSSr). All data from the original VLSS survey has been re-imaged.
The VLSSr covers the sky above declinations -30 deg at a frequency of 74 MHz with 75 arcsec resolution and an average rms noise of 0.1 Jy/beam. It includes six previously unpublished fields and improved dynamic range in 95% of all fields. The clean bias has been halved and is now 0.66x the local rms. The largest angular size imaged has been roughly doubled to 36 arcmin, and the number of cataloged sources is increased by 35% to 95,000.
Improvements made include application of a substantially more accurate primary beam correction, smart-windowing to reduce clean bias, and the use of new automatic radio frequency interference removal and bright-source peeling algorithms. The original VLSS has been used as a starting sky model to enable higher-order Zernike fits to better model the ionospheric phase contributions.
Details of the improved reduction techniques can be found in W.M. Lane et al. (2012, Radio Science, 47, RS0K04) and a full description paper of the VLSSr is in preparation. Catalogs and images are on-line.
VLA-ANGST ("Very Large Array - ACS Nearby Galaxy Survey Treasury") is an NRAO Large Program to observe 35 nearby (distance <4Mpc) galaxies in the 21cm line of neutral atomic hydrogen (HI). All VLA-ANGST galaxies were observed at high spatial (~6", corresponding to ~100pc) and high spectral (0.65-2.6 km/s) resolution in the VLA B, C, and D array configurations. The galaxies are selected to map all gas-rich and actively star forming objects that are included in the "ACS Nearby Galaxy Survey Treasury" (ANGST). ANGST is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D < 4 Mpc). The ANGST observations allow derivation of spatially resolved star formation histories (SFHs). The high spatial resolution of the VLA-ANGST observations allow meaningful comparisons to these ANGST SFH maps, as well as to surveys at other wavelengths such as LVL, KINGFISH, and 11HUGS. In addition, THINGS, LITTLE THINGS, SHIELD, and VLA-ANGST all follow similar observation strategies and data reduction procedures for a combined sample of >100 galaxies.
LITTLE: The Local Irregulars That Trace Luminosity Extremes
THINGS: The HI Nearby Galaxy Survey
The LITTLE THINGS Survey was granted close to 376 hours of time with the Very Large Array (VLA) in the B, C, and D array configurations 2007-2008 to obtain deep HI-line maps of dwarf galaxies. The purpose is to determine how tiny galaxies form stars. Twenty-one dwarf irregular (dIm) and Blue Compact Dwarf (BCD) galaxies were observed, and are adding another 20 dwarfs with data from the VLA Archives. The new observations consist of 12 hours in B-array, 6 hours in C-array, and 2 hours in D-array for each galaxy. The channel separation is 2.6 km/s for 31 galaxies and 1.3 km/s for 11 galaxies.
The combined B/C/D arrays sample the galaxies at 6 arcsec, which is 110 pc at 3.7 Mpc, the average distance of our sample. This resolution shows clouds, shells, and turbulent structures that are important for star formation. We also produce maps at lower resolution that reveal the extended, low-density gas around star formation structures and trace the low density HI far beyond the stellar disks.
Science Team: Deidre Hunter (Lowell), Elias Brinks (Hertfordshire), Bruce Elmegreen (Watson Research Center), Michael Rupen (NRAO), Caroline Simpson (FIU), Fabian Walter (MPIfA), David Westpfahl (NM Tech), Lisa Young (NM Tech), Trisha Ashley (FIU), Phil Cigan (NM Tech), Dana Ficut-Vicus (Hertfordshire), Volker Heesen (Hertfordshire), Kim Herrmann (Lowell), Megan Johnson (NRAO), Se-Heon Oh (W Australia), Andreas Schruba (Caltech), Hong-Xin Zhang (Lowell).
The NVSS has mapped the sky north of -40 deg declination at 1.4 GHz. The principal data products are: (a) 4 deg X 4 deg continuum maps " cubes" with three planes containing Stokes I, Q, and U images; (b) source lists; and (c) processed (u,v) data sets. The maps have 45 arcsec FWHM resolution and nearly uniform rms noise, about 0.45 mJy/beam = 0.14 K (Stokes I) and 0.29 mJy/beam (Stokes Q and U). The rms uncertainties in right ascension and declination vary from 0.3 arcsec for strong (S > 30 mJy) point sources to 5 arcsec for the faintest (S ~ 2.5 mJy) detectable sources.
Science Team: J. J. Condon, W. D. Cotton, E. W. Greisen, and Q. F. Yin (NRAO-Charlottesville); R.A. Perley and G.B. Taylor (NRAO-Socorro); J.J. Broderick (Virginia Polytechnic).