A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

Both in the Faraday Rotation Measure and the intrinsic polarization angle, new features are revealed to indicate a helical magnetic field operating along the jet of the bright active galactic nuclei 3C 273. The helical field has been suggested to be related to the formation and collimation of jets by magnetohydrodynamic models. The distribution of the RM shows a systematic gradient with respect to the jet axis, which is expected by a helical magnetic field. In addition, the helical field can consistently explain two types in the direction of the projected magnetic field: parallel and perpendicular to the jet axis. Further, if the helical magnetic field is generated by winding up of an initial field by rotation of the accretion disk, we can uniquely determine the direction of the disk rotation, since the jet is approaching us.

We improve the dynamical black hole (BH) mass estimates in three nearby low-mass early-type galaxies-NGC 205, NGC 5102, and NGC 5206. We use new HST /STIS spectroscopy to fit the star formation histories of the nuclei in these galaxies, and use these measurements to create local colormass-to-light ratio (M/L) relations. We then create new mass models from HST imaging and combined with adaptive optics kinematics, we use Jeans dynamical models to constrain their BH masses. The masses of the central BHs in NGC 5102 and NGC 5206 are both below one million solar masses and are consistent with our previous estimates, 9.12 +1.84 −1.53 × 10 5 M and 6.31 +1.06 −2.74 × 10 5 M (3σ errors), respectively. However, for NGC 205, the improved models suggests the presence of a BH for the first time, with a best-fit mass of 6.8 +95.6 −6.7 × 10 3 M (3σ errors). This is the least massive central BH mass in a galaxy detected using any method. We discuss the possible systematic errors of this measurement in detail. Using this BH mass, the existing upper limits of both X-ray, and radio emissions in the nucleus of NGC 205 suggest an accretion rate 10 −5 of the Eddington rate. We also discuss the color-M/L eff relations in our nuclei and find that the slopes of these vary significantly between nuclei. Nuclei with significant young stellar populations have steeper color-M/L eff relations than some previously published galaxy color-M/L eff relations.

As part of the mm-Wave Interferometric Survey of Dark Object Masses (WISDOM) project, we present an estimate of the mass of the supermassive black hole (SMBH) in the nearby fast-rotating early-type galaxy NGC4697. This estimate is based on Atacama Large Millimeter/submillimeter Array (ALMA) cycle-3 observations of the 12 CO(2-1) emission line with a linear resolution of 29 pc (0. 53). We find that NGC4697 hosts a small relaxed central molecular gas disc with a mass of 1.6×10 7 M , co-spatial with the obscuring dust disc visible in optical Hubble Space Telescope (HST) imaging. We also resolve thermal 1 mm continuum emission from the dust in this disc. NGC4697 is found to have a very low molecular gas velocity dispersion, σ gas =1.65 +0.68 −0.65 km s −1 . This seems to be partially because the giant molecular cloud mass function is not fully sampled, but other mechanisms such as chemical differentiation in a hard radiation field or morphological quenching also seem to be required. We detect a Keplerian increase of the rotation of the molecular gas in the very centre of NGC4697, and use forward modelling of the ALMA data cube in a Bayesian framework with the KIN-EMATIC MOLECULAR SIMULATION (KINMS) code to estimate a SMBH mass of (1.3 +0.18 −0.17 ) ×10 8 M and an i-band mass-to-light ratio of 2.14 +0.04 −0.05 M /L (at the 99% confidence level). Our estimate of the SMBH mass is entirely consistent with previous measurements from stellar kinematics. This increases confidence in the growing number of SMBH mass estimates being obtained in the ALMA era.