This is the fourth paper in the series "Continuum Halos in Nearby Galaxies - an EVLA Survey" (Irwin et al. 2012). The overall aims of the CHANG-ES project are to investigate the occurrence, origin and nature of radio halos, to probe the disk-halo interface, and to investigate in-disk emission. We seek to understand connections between radio halos and the host disk and its environment, and to investigate the magnetic fields in these galaxies and their halos. This covers a wide variety of science, including cosmic ray transport and wind speeds, the nature and origin of galactic magnetic fields, the far-infrared radiation - radio continuum correlation, cosmic rays and high-energy modelling, disk star formation rates and presence or absence of active galactic nuclei (AGN). Note that in this context, we use the word "halo" to refer to gas, dust, cosmic rays and the magnetic field above and below the galaxy disk, not to be confused with stellar or dark matter halos. Specifically, we call emission on larger scales, i.e. scale height z > 1 kpc, halo emission, while the disk-halo interface is at 0.2 < z < 1 kpc (Irwin et al. 2012).
Magnetic fields in the halos of edge-on galaxies, and their commonly X-shaped behaviour (magnetic field lines outside the projected galaxy’s disk are bending away from the disk with increasing vertical components) are discussed in the review by Krause (2009) (also see references therein). Their intensities and degree of uniformity can be estimated from the total and polarized synchrotron emission, but many uncertainties pertaining to their structures and origins in external galaxies remain (Haverkorn & Heesen 2012).
With CHANG-ES, we have observed thirty-five nearby edge-on galaxies in the radio continuum in L and C bands (centred at approximately 1.5 and 6 GHz, respectively), in three array configurations (B, C, D; in B-configuration only L-band was observed) of the Karl G. Jansky Very Large Array (hereafter VLA). The recently enhanced VLA allows us to trace radio continuum emission at levels fainter than previously possible via its wide bandwidth capabilities. Moreover, observing on a variety of angular scales, the VLA provides distinct advantages in understanding disk-halo and halo features. For example, both faint diffuse emission and distinct filamentary structures can be investigated through the combined use of compact and extended configurations. The low frequencies, chosen because of their sensitivity to synchrotron emission, in combination with observing all polarization products, enables us to derive information about the halo magnetic fields and cosmic rays.
Our thirty-five edge-on galaxies have inclinations higher than 75 degrees. They also adhere to limitations on declination (more than −23 degrees in order to be observed with sufficient uv coverage with the VLA), as well as optical diameter (4' < d25 < 15') and flux density (S1.4 GHz ≥ 23 mJy). Three galaxies (NGC 5775, NGC 4565 and NGC 4244) just outside of these criteria were included in the sample as well, due to evidence for extra-planar gas and availability of good ancillary data. We refer to Table 1 of Irwin et al. (2012) (Paper I) for details of the galaxy sample.
The full project, with its motivation and science goals, is presented in detail in Irwin et al. (2012) (Paper I). Two other papers, Irwin et al. (2012) (Paper II) and 182013Irwin et al. (2013) (Paper III), present detailed results of CHANG-ES observations of NGC 4631 and UGC 10288, respectively.
In this, the fourth CHANG-ES paper, we present all observations which were carried out in the shortest baseline array configuration, D, and display each galaxy of the survey with its results in the appendix. In particular, we show the Stokes I maps and spectral index maps for each of the galaxies in the two frequency bands, as well as the polarization map with apparent B-vectors superposed, as derived from the Stokes Q and U maps. These data products are available for download at http://www.queensu.ca/changes.
Additionally, new star formation rates and flux densities are presented.
The paper is organized as follows: in Section 2 we give a description of the sample selection, the setup of the observations and observation details. Section 3 describes the data reduction with calibration procedures and Section 4 presents the resulting data products, which are displayed in the appendix. Analysis is presented in Section 5 and the conclusions can be found in Section 6.