VLA Observations Research Articles

AB Aur, a Rosetta stone for studies of planet formation

Context. Observational constraints on dust properties in protoplanetary disks are key to better understanding disk evolution, their dynamics, and the pathway to planet formation, but also surface chemistry, the main driver of chemical complexity. Aims. We continue our exploration of the protoplanetary disk around AB Aur by characterizing its dust properties at different millimeter wavelengths. Methods. We present new ALMA observations at 2.2 mm and VLA observations at 6.8 mm. Together with previous ALMA and NOEMA observations at 0.87 and 1.1 mm, these new observations are used to compute global spectral index profiles as well as spectral index maps to probe the dust properties throughout the disk. On the interpretation side, we present the results of a simple isothermal slab model to help constrain dust properties along the non-axisymmetric ring of continuum emission outside the millimeter cavity. We also present new results of dust radiative transfer calculations based on a disk-planet hydrodynamical simulation to explain how the azimuthal contrast ratio of the ring emission varies with millimeter wavelength. Results. The spectral energy distribution and the radial profiles of the spectral index indicate that the radiation from the compact source towards the center is not dominated by dust thermal emission, but most likely by free-free emission originating in the radio jet; it constitutes 93% of the emission at 6.8 mm, and 37% at 0.87 mm. The protoplanetary disk has a typical spectral index of 2.3, computed using the 0.87, 1.1, and 2.2 mm bands. We estimate a dust disk mass of 8 × 10−5 M⊙ which, assuming a mean gas-to-dust ratio of 40, gives a total disk mass of 3.2 × 10−3 M⊙. The azimuthal contrast ratio of the ring outside the millimeter cavity is smaller at 2.2 mm than at 1.1 mm, in agreement with previous findings. The VLA image shows several knots of 5σ emission all along the ring, which, with the help of our dust radiative transfer calculations, are consistent with the ring emission being nearly axisymmetric at that wavelength. The decrease in the azimuthal contrast ratio of the ring emission from 0.87 to 6.8 mm can be explained by a dust-losing decaying vortex at the outer edge of a planet gap.

The interaction of a large-scale nuclear wind with the high velocity HII region G0.17+0.15

Abstract We investigate the nature of a Galactic center source, G0.17+0.15, lying along the northern extension of the Radio Arc near l ∼ 0.2○. G0.17+0.15 is an HII region located toward the eastern edge of the radio bubble, embedded within the highly polarized Galactic center eastern Lobe where a number of radio filaments appear to cross through the HII region. We report the detection of hydrogen and helium recombination lines with a radial velocity exceeding 140 km s−1 based on GBT and VLA observations. The morphology of G0.17+0.15, aided by kinematics, and spectral index characteristics, suggests the presence of an external pressure dragging and shredding the ionized gas. We argue that this ionized cloud is interacting with a bundle of radio filaments and is entrained by the ram pressure of the radio bubble, which itself is thought to be produced by cosmic-ray driven outflows at the Galactic center. In this interpretation, the gas streamers on the western side of G0.17+0.15 are stripped, accelerated from 0 to δv ∼ 35 km s−1 over a time scale roughly 8 × 104 years, implying that ablating ram pressure is ∼700 eV cm−3, comparable to the ∼103 eVcm−3 cosmic-ray driven wind pressure in the Galactic center region.

Radio WISSH: tuning on the most luminous quasars in the Universe

AbstractIn the past years, the results obtained by the WISSH quasar project provided a novel general picture on the distinctive multi-band properties of hyper-luminous (Lbol > 1047 erg/s) quasars at high redshift (z ∼ 2-4), unveiling interesting relations among active galactic nuclei, winds and interstellar medium, in these powerful sources at cosmic noon. Since 2022, we are performing a systematic and statistically-significant VLA study of the radio properties of WISSH. We carried out high-resolution VLA observations aiming at: 1) identifying young radio source from the broad-band spectral shape of these objects; 2) sample an unexplored high redshift/high luminosity regime, tracking possible evolutionary effects on the radio-loud/radio-quiet dichotomy; 3) quantifying orientation effects on the observed winds/outflows properties.

Evidence of a Polar Cyclone on Uranus From VLA Observations

AbstractWe present observations of Uranus in northern spring with the Very Large Array from 0.7 to 5 cm. These observations reveal details in thermal emission from Uranus' north pole at 10s of bars, including a dark collar near 80°N and a bright spot at the polar center. The bright central spot resembles observations of polar emission on Saturn and Neptune at shallower pressures. We constrain the variations in temperature and NH3/H2S abundances which could explain these features. We find that the brightness temperature of the polar spot can be recreated through 5 K temperature gradients and/or 10× depletion of NH3 or H2S vapor between 10 and 20 bars, both consistent with the presence of a cyclonic polar vortex. The contrast of the polar spot may have increased since 2015, which would suggest seasonal evolution of Uranus' polar circulation at depth.

Multifrequency analysis of the radio emission from a post-merger galaxy CGCG 292-057

ABSTRACT Galaxies exhibiting a specific large-scale extended radio emission, such as X-shaped radio galaxies, belong to a rare class of winged radio galaxies. The morphological evolution of these radio sources is explained using several theoretical models, including galaxy mergers. However, such a direct link between a perturbed radio morphology and a galaxy merger remains observationally sparse. Here, we investigate a unique radio galaxy J1159+5820, whose host CGCG 292-057 displays the optical signature of a post-merger system with a distinct tidal tail feature, and an X-shaped radio morphology accompanied by an additional pair of inner lobes. We observed the target on a wide range of radio frequencies ranging from 147 to 4959 MHz, using dedicated GMRT and VLA observations, and supplemented it with publicly available survey data for broad-band radio analysis. Particle injection models were fitted to radio spectra of lobes and different parts of the wings. Spectral ageing analysis performed on the lobes and the wings favours a fast jet realignment model with a reorientation time-scale of a few million years. We present our results and discuss the possible mechanisms for the formation of the radio morphology.

H i 21 cm Extended Structures to the Northeast and Southwest of NGC 5595: VLA Observations of the Disk Galaxy Pair NGC 5595 and NGC 5597

We report VLA B-configuration observations of the H i 21 cm line on the close disk galaxy pair NGC 5595 and NGC 5597. At the angular resolution of the observations, ∼7.″1 × 4.″2, while most of the H i 21 cm in NGC 5595 and NGC 5597 has the same extent as the optical disk, we have detected for the first time extended structures (streamers) to the northeast (NE) and southwest (SW) of NGC 5595 with no counterparts in blue, red optical (continuum), 20 cm radio continuum, or Hα spectral line emission. One structure is extended by ∼45″ to the NE with blueshifted velocities, and the other is extended by ∼20″ to the SW with redshifted velocities with respect to the systemic velocity. No H i 21 cm emission is detected from the innermost central (nuclear) regions of either galaxy. Lower angular resolution H i 21 cm imaging indicates the nonexistence of any intergalactic hydrogen atomic H i 21 cm gas as tails or bridges between the two galaxies. Our new 20 cm radio continuum emission image of NGC 5597 shows a strong unresolved elongated structure in the central region, in the NE–SW direction, very similar to the spatial location of the innermost Hα spectral line emission. There is no 20 cm continuum emission from its northern spiral arm. In NGC 5595, the 20 cm radio continuum image shows no continuum emission from the NE or SW extended structures with H i 21 cm emission.

The multiwavelength view of shocks in the fastest nova V1674 Her

ABSTRACT Classical novae are shock-powered multiwavelength transients triggered by a thermonuclear runaway on an accreting white dwarf. V1674 Her is the fastest nova ever recorded (time to declined by two magnitudes is t2 = 1.1 d) that challenges our understanding of shock formation in novae. We investigate the physical mechanisms behind nova emission from GeV γ-rays to cm-band radio using coordinated Fermi-LAT, NuSTAR, Swift, and VLA observations supported by optical photometry. Fermi-LAT detected short-lived (18 h) 0.1–100 GeV emission from V1674 Her that appeared 6 h after the eruption began; this was at a level of (1.6 ± 0.4) × 10−6 photons cm−2 s−1. Eleven days later, simultaneous NuSTAR and Swift X-ray observations revealed optically thin thermal plasma shock-heated to kTshock = 4 keV. The lack of a detectable 6.7 keV Fe Kα emission suggests super-solar CNO abundances. The radio emission from V1674 Her was consistent with thermal emission at early times and synchrotron at late times. The radio spectrum steeply rising with frequency may be a result of either free-free absorption of synchrotron and thermal emission by unshocked outer regions of the nova shell or the Razin–Tsytovich effect attenuating synchrotron emission in dense plasma. The development of the shock inside the ejecta is unaffected by the extraordinarily rapid evolution and the intermediate polar host of this nova.

Ammonia Abundance Derived from Juno MWR and VLA Observations of Jupiter

The vertical distribution of trace gases in planetary atmospheres can be obtained with observations of the atmosphere’s thermal emission. Inverting radio observations to recover the atmospheric structure, however, is nontrivial, and the solutions are degenerate. We propose a modeling framework to prescribe a vertical distribution of trace gases that combines a thermochemical equilibrium model with a vertical temperature structure and compare these results to models where ammonia can vary between predefined pressure nodes. We compare these model to nadir brightness temperatures and limb-darkening parameters, together with their uncertainties, which we reduced from the raw Juno Microwave Radiometer (MWR) data set. We then apply this framework to MWR observations during Juno’s first years of operation (perijove passes 1–12) and to longitudinally averaged latitude scans taken with the upgraded Very Large Array. We use the model to constrain the distribution of ammonia between −60° and 60° latitude and down to 100 bars. We constrain the ammonia abundance to be ppm ( solar abundance) and find a depletion of ammonia down to a depth of ∼20 bars, which supports the existence of processes that deplete the atmosphere below the ammonia and water cloud layers. At the equator we find an increase of ammonia with altitude, while the zones and belts in the midlatitudes can be traced down to levels where the atmosphere is well mixed. The latitudinal variation in the ammonia abundance appears to be opposite to that shown at higher altitudes, which supports the existence of a stacked-cell circulation model.

Interferometric Observations of the Water Fountain Candidates OH 16.3−3.0 and IRAS 19356+0754

AbstractWater Fountains (WFs), located between the AGB and PN phases of stellar evolution, may provide significant clues on the shaping process of PNe. We present new VLA observations of the WF candidates OH 16.3-3.0 and IRAS 19356+0754. We detect H2O and OH maser and radio continuum emission towards OH 16.3-3.0. We suggest that the OH maser emission of OH 16.3-3.0 is associated with an aspherical circumstellar envelope due to its spatio-kinematics and peculiar spectral profile. We could not confirm the candidates as bona fide WFs because of the narrow velocity spread (OH 16.3-3.0) or non-detection (IRAS 19356+0754) of H2O maser emission. Further monitoring could help to discern their nature.

Turbulence and Accretion: A High-resolution Study of the B5 Filaments

High-resolution observations of the Perseus B5 “core” have previously revealed that this subsonic region actually consists of several filaments that are likely in the process of forming a quadruple stellar system. Since subsonic filaments are thought to be produced at the ∼0.1 pc sonic scale by turbulent compression, a detailed kinematic study is crucial to test such a scenario in the context of core and star formation. Here we present a detailed kinematic follow-up study of the B5 filaments at a 0.009 pc resolution using the VLA and GBT combined observations fitted with multicomponent spectral models. Using precisely identified filament spines, we find a remarkable resemblance between the averaged width profiles of each filament and Plummer-like functions, with filaments possessing FWHM widths of ∼0.03 pc. The velocity dispersion profiles of the filaments also show decreasing trends toward the filament spines. Moreover, the velocity gradient field in B5 appears to be locally well ordered (∼0.04 pc) but globally complex, with kinematic behaviors suggestive of inhomogeneous turbulent accretion onto filaments and longitudinal flows toward a local overdensity along one of the filaments.

The Nearby Dwarf Irregular Galaxy IC 1613 and Its Complex Bubble Region: Chandra and VLA Observations

Abstract We observed the nearby irregular galaxy IC 1613 with the Chandra X-ray Observatory, for 49.9 ks using the ACIS S3 chip, and with the VLA at 6 cm for 0.7 hr. The Chandra observation targeted the extensive bubble region in the northeast quadrant. We detect 31 sources within the D 25 diameter above a significance of 3σ corresponding to a point-source luminosity limit L X of ≈2 × 1035 erg s−1 (0.3–8 keV band). The VLA observation covered the entire galaxy with an angular resolution of 5″. We detect 11 sources: five do not fall on the ACIS chips, four fall on the S3 CCD, and two sit on the edge of the S2 CCD. We also describe corresponding Spitzer IRAC and MIPS images. Our detected source list matches the lists of two previous global point-source analyses except at the faint end. With the exception of one bright supernova remnant, the sources appear to be low-luminosity stellar sources (e.g., RS CVn stars) or X-ray binaries, or background objects. We identify one candidate supersoft source. All but one of the sources have at least one optical or infrared counterpart; three sources have radio counterparts. We describe our search for diffuse emission from the bubble region. We assign an upper limit of ≈5 × 1035 erg s−1 on the integrated flux and ≈1.4 × 1030 erg s−1 pc−2 on the surface brightness emission in the 0.5–2 keV band from that region.

The radio source in Abell 980: A Detached-Double-Double Radio Galaxy?

Abstract It is argued that the new morphological and spectral information gleaned from the recently published LoFAR Two metre Sky Survey data release 2 (LoTSS-2 at 144 MHz) observations of the cluster Abell 980 (A980), in combination with its existing GMRT and VLA observations at higher frequencies, provide the much-needed evidence to strengthen the proposal that the cluster’s radio emission comes mainly from two double radio sources, both produced by the brightest cluster galaxy (BCG) in two major episodes of jet activity. The two radio lobes left from the previous activity have become diffuse and developed an ultra-steep radio spectrum while rising buoyantly through the confining hot intra-cluster medium (ICM) and, concomitantly, the host galaxy has drifted to the cluster centre and entered a new active phase manifested by a coinciding younger double radio source. The new observational results and arguments presented here bolster the case that the old and young double radio sources in A980 conjointly represent a ‘double-double’ radio galaxy whose two lobe pairs have lost colinearity due to the (lateral) drift of their parent galaxy, making this system by far the most plausible case of a ‘Detached-Double-Double Radio Galaxy’ (dDDRG).

The fast radio burst FRB 20201124A in a star-forming region: Constraints to the progenitor and multiwavelength counterparts

We present the results of a multiwavelength campaign targeting FRB 20201124A, the third closest repeating fast radio burst (FRB), which was recently localized in a nearby (z = 0.0978) galaxy. Deep VLA observations led to the detection of quiescent radio emission, which was also marginally visible in X-rays with Chandra. Imaging at 22 GHz allowed us to resolve the source on a scale of ≳1″ and locate it at the position of the FRB, within an error of 0.2″. The EVN and e-MERLIN observations sampled small angular scales, from 2 to 100 mas, providing tight upper limits on the presence of a compact source and evidence for diffuse radio emission. We argue that this emission is associated with enhanced star formation activity in the proximity of the FRB, corresponding to a star formation rate (SFR) of ≈10 M⊙ yr−1. The surface SFR at the location of FRB 20201124A is two orders of magnitude larger than what is typically observed in other precisely localized FRBs. Such a high SFR is indicative of this FRB source being a newborn magnetar produced from a supernova explosion of a massive star progenitor. Upper limits to the X-ray counterparts of 49 radio bursts observed in our simultaneous FAST, SRT, and Chandra campaign are consistent with a magnetar scenario.

Radio Proper Motions of the Energetic Pulsar PSR J1813–1749

Abstract PSR J1813–1749 has peculiarities that make it a very interesting object of study. It is one of the most energetic and the most scattered pulsars known. It is associated with HESS J1813–178, one of the brightest and most compact TeV sources in the sky. Recently, Ho et al. used archival X-ray Chandra observations separated by more than 10 yr and determined that the total proper motion of PSR J1813–1749 is ∼66 mas yr−1, corresponding to a velocity of ∼1900 km s−1 for a distance of 6.2 kpc. These results would imply that this pulsar is the fastest neutron star known in the Galaxy and, by estimating the angular separation with respect to the center of the associated supernova remnant, has an age of only ∼300 yr, making it one of the youngest pulsars known. Using archival high angular resolution VLA observations taken over 12 yr we have estimated the radio proper motions of PSR J1813–1748 to be much smaller: ( μ α · cos ( δ ) , μ δ ) = (−5.0 ± 3.7, −13.2 ± 6.7) mas yr−1, or a total proper motion of 14.8 ± 5.9 mas yr−1. The positions referenced against quasars make our results reliable. We conclude that PSR J1813–1749 is not a very fast moving source. Its kinematic age using the new total proper motion is ∼1350 yr. This age is consistent within a factor of a few with the characteristic age of the pulsar and with the age estimated from the broadband spectral energy distribution of HESS J1813–178, as well as the age of the associated supernova remnant.

SiO Outflows as Tracers of Massive Star Formation in Infrared Dark Clouds

Abstract To study the early phases of massive star formation, we present ALMA observations of SiO(5−4) emission and VLA observations of 6 cm continuum emission toward 32 Infrared Dark Cloud clumps, spatially resolved down to ≲0.05 pc. Out of the 32 clumps, we detect SiO emission in 20 clumps, and in 11 of them the SiO emission is relatively strong and likely tracing protostellar outflows. Some SiO outflows are collimated, while others are less ordered. For the six strongest SiO outflows, we estimate basic outflow properties. In our entire sample, where there is SiO emission, we find 1.3 mm continuum and infrared emission nearby, but not vice versa. We build the spectral energy distributions (SEDs) of cores with 1.3 mm continuum emission and fit them with radiative transfer models. The low luminosities and stellar masses returned by SED fitting suggest these are early-stage protostars. We see a slight trend of increasing SiO line luminosity with bolometric luminosity, which suggests more powerful shocks in the vicinity of more massive YSOs. We do not see a clear relation between the SiO luminosity and the evolutionary stage indicated by L/M. We conclude that, as a protostar approaches a bolometric luminosity of ∼102 L ⊙, the shocks in the outflow are generally strong enough to form SiO emission. The VLA 6 cm observations toward the 15 clumps with the strongest SiO emission detect emission in four clumps, which is likely from shock-ionized jets associated with the more massive ones of these protostellar cores.

Hidden Treasures in the Unknown 3CR Extragalactic Radio Sky: A Multiwavelength Approach

We present the analysis of multi-wavelength observations of seven extragalactic radio sources, listed as unidentified in the Third Cambridge Revised Catalog (3CR). X-ray observations, performed during Chandra Cycle 21, were compared to VLA, WISE and Pan-STARRS observations in the radio, infrared and optical bands, respectively. All sources in this sample lack a clear optical counterpart, and are thus missing their redshift and optical classification. In order to confirm the X-ray and infrared radio counterparts of core and extended components, here we present for the first time radio maps obtained manually reducing VLA archival data. As in previous papers on the Chandra X-ray snapshot campaign, we report X-ray detections of radio cores and two sources, out of the seven presented here, are found to be members of galaxy clusters. For these two cluster sources (namely, 3CR 409 and 3CR 454.2), we derived surface brightness profiles in four directions. For all seven sources, we measured X-ray intensities of the radio sources and we also performed standard X-ray spectral analysis for the four sources (namely, 3CR 91, 3CR 390, 3CR 409 and 3CR 428) with the brightest nuclei (more than 400 photons in the 2'' nuclear region). We also detected extended X-ray emission around 3CR 390 and extended X-ray emission associated with the northern jet of 3CR 158. This paper represents the first attempt to give a multi-wavelength view of the unidentified radio sources listed in the 3CR catalog.

A lack of constraints on the cold opaque H i mass: H i spectra in M31 and M33 prefer multicomponent models over a single cold opaque component

ABSTRACT Previous work has argued that atomic gas mass estimates of galaxies from 21-cm H i emission are systematically low due to a cold opaque atomic gas component. If true, this opaque component necessitates a $\sim 35{{\ \rm per\ cent}}$ correction factor relative to the mass from assuming optically thin H i emission. These mass corrections are based on fitting H i spectra with a single opaque component model that produces a distinct ‘top-hat’ shaped line profile. Here, we investigate this issue using deep, high spectral resolution H i VLA observations of M31 and M33 to test if these top-hat profiles are instead superpositions of multiple H i components along the line of sight. We fit both models and find that ${\gt}80{{\ \rm per\ cent}}$ of the spectra strongly prefer a multicomponent Gaussian model while ${\lt}2{{\ \rm per\ cent}}$ prefer the single opacity-corrected component model. This strong preference for multiple components argues against previous findings of lines of sight dominated by only cold H i. Our findings are enabled by the improved spectral resolution (0.42 ${\rm km\, s^{-1}}$), whereas coarser spectral resolution blends multiple components together. We also show that the inferred opaque atomic ISM mass strongly depends on the goodness-of-fit definition and is highly uncertain when the inferred spin temperature has a large uncertainty. Finally, we find that the relation of the H i surface density with the dust surface density and extinction has significantly more scatter when the inferred H i opacity correction is applied. These variations are difficult to explain without additionally requiring large variations in the dust properties. Based on these findings, we suggest that the opaque H i mass is best constrained by H i absorption studies.

Fragmentation in the massive G31.41+0.31 protocluster

Context. ALMA observations at 1.4 mm and ~0.′′2 (~750 au) angular resolution of the Main core in the high-mass star-forming region G31.41+0.31 have revealed a puzzling scenario. On the one hand, the continuum emission looks very homogeneous and the core appears to undergo solid-body rotation, suggesting a monolithic core stabilized by the magnetic field; on the other hand, rotation and infall speed up toward the core center, where two massive embedded free-free continuum sources have been detected, pointing to an unstable core having undergone fragmentation. Aims. To establish whether the Main core is indeed monolithic or if its homogeneous appearance is due to a combination of large dust opacity and low angular resolution, we carried out millimeter observations at higher angular resolution and different wavelengths. Methods. We carried out ALMA observations at 1.4 mm and 3.5 mm that achieved angular resolutions of ~0.′′1 (~375 au) and ~0.′′075 (~280 au), respectively. VLA observations at 7 mm and 1.3 cm at even higher angular resolution, ~0.′′05 (~190 au) and ~0.′′07 (~260 au), respectively, were also carried out to better study the nature of the free-free continuum sources detected in the core. Results. The millimeter continuum emission of the Main core has been clearly resolved into at least four sources, A, B, C, and D, within 1″, indicating that the core is not monolithic. The deconvolved radii of the dust emission of the sources, estimated at 3.5 mm, are ~400–500 au; their masses range from ~15 to ~26 M⊙; and their number densities are several 109 cm−3. Sources A and B, located closer to the center of the core and separated by ~750 au, are clearly associated with two free-free continuum sources, likely thermal radio jets, and are brightest in the core. The spectral energy distribution of these two sources and their masses and sizes are similar and suggest a common origin. Source C has not been detected at centimeter wavelengths, while source D has been clearly detected at 1.3 cm. Source D is likely the driving source of an E–W SiO outflow previously detected in the region, which suggests that the free-free emission might be coming from a radio jet. Conclusions. The observations have confirmed that the Main core in G31 is collapsing, that it has undergone fragmentation, and that its homogeneous appearance previously observed at short wavelengths is a consequence of both high dust opacity and insufficient angular resolution. The low level of fragmentation together with the fact that the core is moderately magnetically supercritical, suggests that G31 could have undergone a phase of magnetically regulated evolution characterized by a reduced fragmentation efficiency, eventually leading to the formation of a small number of relatively massive dense cores.

VLBA Discovery of a Resolved Source in the Candidate Black Hole X-Ray Binary AT2019wey

Abstract AT2019wey is a Galactic low-mass X-ray binary with a candidate black hole accretor first discovered as an optical transient by ATLAS in 2019 December. It was then associated with an X-ray source discovered by SRG/eROSITA and SRG/ART-XC instruments in 2020 March. After a brightening in X-rays in 2020 August, VLA observations of the source revealed an optically thin spectrum that subsequently shifted to optically thick, as the source continued to brighten in the radio. This motivated us to observe AT2019wey with the VLBA. We found a resolved source that we interpret to be a steady compact jet, a feature associated with black hole X-ray binary systems in hard X-ray spectral states. The jet power is comparable to the accretion-disk X-ray luminosity. Here, we summarize the results from these observations.

Comparison of classical and Bayesian imaging in radio interferometry

CLEAN, the commonly employed imaging algorithm in radio interferometry, suffers from a number of shortcomings: In its basic version, it does not have the concept of diffuse flux, and the common practice of convolving the CLEAN components with the CLEAN beam erases the potential for super-resolution; it does not output uncertainty information; it produces images with unphysical negative flux regions; and its results are highly dependent on the so-called weighting scheme as well as on any human choice of CLEAN masks for guiding the imaging. Here, we present the Bayesian imaging algorithm resolve , which solves the above problems and naturally leads to super-resolution. We take a VLA observation of Cygnus A at four different frequencies and image it with single-scale CLEAN, multi-scale CLEAN, and resolve. Alongside the sky brightness distribution, resolve estimates a baseline-dependent correction function for the noise budget, the Bayesian equivalent of a weighting scheme. We report noise correction factors between 0.4 and 429. The enhancements achieved by resolve come at the cost of higher computational effort.