arXiv subjects

W. J. G. de Blok

Publications and source records attributed to W. J. G. de Blok.

At least 19 recordsLinked to original sources

arXiv2026

HI rotation curves and mass-size relation for 568 galaxies from the Apertif Wide-area Extragalactic Survey

The extended HI rotation curves of galaxies are one of the most powerful tools for studying galaxy evolution and for testing different dark matter and modified gravity models. However, their sample sizes have historically been limited to a few hundred galaxies, mostly due to the survey speed of radio interferometers. Here, we present a first data release of HI kinematic models from the Apertif Wide-area Extragalactic Survey (AWES). Starting from 1924 galaxies detected in HI, we constructed 568 reliable kinematic models, which provide rotation curves, velocity dispersion profiles, surface density profiles, and HI disk geometries. This dataset constitutes the largest homogeneous HI rotation curve sample to date. The HI disks of the modeled galaxies span three orders of magnitude in HI mass, have outer rotation velocities between ~20 and ~300 km/s, and extend from 2 to more than 60 kpc. The number of data points of the rotation curves ranges from 3 to 23, with a peak value at 4 and a broad tail to larger values. The rotation curves display a variety of inner shapes, but in general, they tend to become flat at large radii. Based on the HI surface density profiles derived during the kinematic modeling, we studied the HI mass-size relation with a large homogeneous sample of 213 galaxies. The relation is very tight, with an observed scatter along the mass direction of ~0.101 dex and an inferred intrinsic scatter along the same direction of only 0.067 +/- 0.007 dex. The best fitting slope is 1.96 +/- 0.03 when fitting for mass as a function of size, indicating that HI disks have a constant average surface density.

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arXiv2026

Options for Compression of radio interferometry data: lossy compression of visibilities and lossless compression of uv-visibility grids for the MHONGOOSE survey

Next generation radio astronomy telescopes are challenging existing data reduction paradigms. With ever more antennas, larger bandwidths, and sometimes multiple primary beams, they often generate more observed data products than can readily be stored long-term. Thus, data storage becomes a major cost driver and processing constraint. In this paper, we test two methods of addressing this problem: grid-stacking, a two-stage lossless compression solution; and the lossy compression of the raw visibilities before traditional processing. To demonstrate these solutions we utilised a deep imaging pipeline based on software for the ASKAP telescope, ASKAPSoft, but applied to a strong source (NGC1566) from the deep MeerKAT HI spectral line project, MHONGOOSE. The grid-stacking solution reproduces the spectrum from traditional processing to within better than 0.7%, and also allows for the reconstruction of other weighting scales without significant computing costs. In comparison, image-stacking also reproduces the spectrum from the traditional processing, to within better than 3% but with worse image residuals in the cube. The lossy compression, even at a near ten-fold reduction in file size, reproduces the spectra almost perfectly (to better than ~0.01% in all cases). Thus both compression methods are promising solutions, and we discuss considerations for their application.

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arXiv2026

AGN Feeding & Feedback Over the Galactic Scales

Active Galactic Nuclei (AGN) are key drivers of galaxy evolution, triggered by cold gas accreting onto a super-massive black hole. However, the processes regulating this gas accretion (feeding) and how AGN alter the interstellar medium to affect star formation (feedback) remain poorly understood. A major observational challenge is the vast range of spatial scales involved: AGN fuelling and jet-ejection occur over the sub-pc scales, while AGN feedback shocks and heats the ISM preventing star formation over the galactic and circum-galactic scales. Moreover, it is unclear how short stochastic AGN episodes are connected with the long timescales of gas accretion and star formation. In this manuscript, we illustrate how SKAO will provide the unprecedented opportunity to solve the observational limitations of AGN feeding and feedback studies by observing hundreds of nearby AGN down to low radio powers ($10^{21}$ W Hz$^{-1}$). Simultaneous SKA-Low and Mid observations of nearby galaxies will trace the thermal emission associated with star formation and AGN feedback and the synchrotron emission of their jets of relativistic plasma. These broad-band radio observations enable the detailed characterisation of the AGN duty-cycle, unravelling the time-scales of the nuclear activities. Reaching in 10 hours neutral atomic hydrogen (HI) column density sensitivities $\sim 10^{19}$ cm$^{-2}$ at arcsecond resolution, SKA AA4 observations will trace the typical low column density of HI gas in AGN inflows and outflows, to understand the impact AGN feedback over the full galaxy and trace fuelling processes from the environment onto the SMBH. Combining SKA with mm, sub-mm and optical Integral Field Spectrographic observations at comparable arcsecond resolution will provide an exhaustive understanding of the link between multi-phase AGN feeding and feedback processes and star formation.

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arXiv2026

Deep HI observations of cold gas inflow and outflow

A major question in galaxy evolution is how galaxies acquire sufficient gas to sustain their star formation rates. HI observations with high angular resolution and sensitivity to very low column densities are some of the important observational ingredients that are currently still missing. Answers to these questions are necessary for a correct interpretation of observations of galaxy evolution in the high-redshift universe and will provide crucial input for the sub-grid physics in hydrodynamical simulations of galaxy evolutions. In this chapter we discuss the progress that has been made over the past years, describe the various processes that lead to inflow and outflow of gas, and discuss how SKA-Mid AA4 observations can contribute to further understanding these important aspects of galaxy evolution using deep observations of nearby individual disk and dwarf galaxies.

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arXiv2026

HI Galaxy Science with the SKA

This chapter introduces the contributions of the HI galaxy science in this volume reviewing the latest developments and urgent questions in HI galaxy science, providing guiding principles for a layered set of future key science projects. The key science will include: a complete censuses of HI morphologies and kinematics at sub-kpc and 1 km/s resolution within and around galaxies in the nearby Universe; a measurement of the cosmic HI mass density and HI mass function evolution at least up to z~1; an improved understanding of the Universe at z>1, particularly the balance between cold molecular and cool atomic gas. We also provide a view of the synergistic multi-wavelength surveys available in 2028+ in the southern hemisphere. This effort will improve our understanding of the baryon cycle across a significant fraction of the cosmic history, including the processes of gas accretion, consumption and removal as well as AGN and star formation feedback. Based on these science goals, the earlier proposed three-tiered survey strategy remains, but survey parameters and predictions are adjusted according to AA* and AA4 developments. This chapter is an update of the earlier "Advancing Astrophysics with the Square Kilometre Array" chapter 'HI Science with the SKA' by Staveley-Smith & Oosterloo.

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arXiv2026

The ultra-deep HI radial profiles of late-type galaxies from MHONGOOSE

Galaxy discs have a finite extent, yet how and where their neutral atomic hydrogen (HI) components end is not fully understood. The existence of a break in the HI disc at column densities of $\sim10^{19}$ cm$^{-2}$ has been debated since early 21-cm observations of the spiral galaxy NGC 3198. We present the HI radial profiles of 16 star-forming, late-type galaxies from the MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey spanning a range of HI mass from $10^{7}$ M$_\odot$ to $10^{10}$ M$_\odot$. We probed via spectral stacking their HI discs down to inclination-corrected column densities of a few times $10^{17}$ cm$^{-2}$ at kpc resolution. The HI radial profiles of high-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$) galaxies are characterised by a inner plateau, followed by a knee at column densities of $\sim5\times10^{20}$ cm$^{-2}$, but no edges are unambiguously identified. The HI radial profiles of low-mass (M$_{\rm {HI}}>10^{9}$ M$_\odot$) galaxies shows a steeper decline and also no edges. We found that the profiles are self-similar when normalised to the radius at which a mass surface density of 0.01 M$_\odot$ pc$^{-2}$ is reached, in agreement with recent literature results, but we also found a possible correlation between the normalisation radius and the environment, suggesting that environment contributes to the shaping of the HI distribution in galaxies. The emerging picture is that the diverse morphology of the HI radial profiles is difficult to interpret, and future studies with a larger sample are necessary for quantifying the contribution of internal and external processes acting at different levels for different galaxies.

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arXiv2026

HI absorption in MHONGOOSE -- Spin temperatures and cold neutral medium in nearby disk galaxies

Combined HI emission-absorption studies constrain the spin temperature and phase structure of the neutral atomic hydrogen interstellar medium (ISM), but have largely been limited to the Milky Way and the Local Group. We extend this technique to galaxies at distances of 7-22 Mpc using deep data from the MeerKAT HI Observations of Nearby Galactic Objects - Observing Southern Emitters (MHONGOOSE) survey, and quantify the detection fraction and Cold Neutral Medium (CNM) properties at these distances. We search for HI absorption toward 56 background continuum sources in 21 out of the 30 MHONGOOSE galaxies (with nine galaxies lacking suitable background sources), and detect absorption associated with the galaxies' HI disks in three cases: one sight line in NGC 289 and two in NGC 7424. This corresponds to detection rates of 3/56 (5 percent) for the full sample and 3/31 (10 percent) for a clean sub-sample of sight lines, considering only unresolved background sources behind 14 low-inclination galaxies. Detections occur only where both the continuum flux and the foreground \HI column density are high, with optical-depth sensitivity as the primary limiting factor. For the detected sight lines, we model the absorption and emission spectra to derive spin temperatures and CNM fractions using the standard combined emission-absorption method. The CNM spin temperatures and line widths are comparable to Local Group measurements, but the inferred CNM fractions are systematically lower. We argue that this difference is primarily a resolution effect: at the distances of our galaxies, the emission spectra average over several hundred parsecs, diluting structured CNM relative to the smoother Warm Neutral Medium (WNM). This demonstrates that emission-absorption analyses can be extended beyond the Local Group, provided that care is taken in constructing representative emission spectra.

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arXiv2025

The MeerKAT Fornax Survey VI. The collapse of the galaxy HI Mass Function in Fornax

We present the deepest HI mass Function (HIMF) ever measured, outside the Local Group. The observations are part of the MeerKAT Fornax Survey and cover a 4 x 4 deg^2 field, corresponding to ~ Rvir. The 3$σ$ detection limit is log(MHI/Msun) = 5.7 for a 50 km/s-wide point source. We detect HI in 35 galaxies and 44 clouds with no optical counterparts. Using deep optical images from the Fornax Deep Survey, we show that the clouds are a distinct population, separated by a four magnitude gap from the faintest HI-detected galaxies. The majority (33 out of 44) of the clouds are associated with the two galaxies with the most HI in the cluster -- NGC 1365 and NGC 1427A, although the clouds contribute a negligible amount to the total MHI budget. By performing a SNR analysis and computing the Rauzy statistic on the HI detections, we demonstrate that our catalogue is complete down log(MHI/Msun) = 6, and we are therefore able to probe the HIMF down to this level. We find an abrupt drop of the number density of HI-detected galaxies at log(MHI/Msun) = 7, signifying a clear absence of galaxies between 6 < log(MHI/Msun) < 7. We use the modified maximum likelihood method to fit a Schechter function down to log(MHI/Msun) > 7, the range where the HIMF follows a power-law. The measured low-mass slope is $α$ = -1.31 $\pm$ 0.13, with a characteristic knee mass of log(M*/Msun) = 10.52 $\pm$ 1.89. The low-mass slope matches the slope in the field, while the knee is defined by a single galaxy and is unconstrained. Below log(MHI/Msun) = 7, there is a sharp departure from a Schechter function, and we report the first robust measurement of the collapse of a HIMF. For the HIMF below log(MHI/Msun) = 7 to follow a power-law, tens of galaxies are needed -- a factor ~ six higher than what is observed. The collapse of the Fornax HIMF is likely due to the rapid removal of HI from low-mass galaxies.

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arXiv2025

The inside-out quenching of the MHONGOOSE galaxy NGC 1371

We present the deepest 21-cm spectral line and 1.4 GHz broad-band continuum observations of nearby early-type spiral galaxy NGC 1371 as part of the MeerKAT HI Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey. We found the neutral atomic hydrogen (HI) mostly distributed in a regularly rotating disc with a hole $\sim5$ kpc wide around the galactic centre. The continuum observations reveal, within the HI hole, emission from one of the lowest luminosity AGN known to date and from two unique $\sim10$-kpc wide bipolar bubbles never observed before in this galaxy. The properties of the bubbles suggest that they may result from the impact of the low-power radio jet propagating within the gaseous disk instead of perpendicular to it. We found indication for jet-induced ionised outflows within the HI hole but no molecular gas (upper limit of $M_{\text{H$_2$}}<2\times10^5\text{ M$_\odot$}$) is detected. The emerging picture is that the gas in the central regions has been rapidly depleted by the stellar bar or, despite its low power, the AGN in NGC 1371 is efficiently heating and/or removing the gas through the jets and possibly by radiative winds, leading to the inside-out quenching of the galaxy.

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arXiv2025

Exploring the potential for kinematically colder HI component as a tracer for star-forming gas in nearby galaxies

Atomic hydrogen (HI) dominates the mass of the cold interstellar medium, undergoing thermal condensation to form molecular gas and fuel star formation. Kinematically colder HI components, identified via kinematic decomposition of HI 21 cm data cubes, serve as a crucial transition phase between diffuse warm neutral gas and molecular hydrogen (H$_{2}$). We analyse these colder HI components by decomposing HI 21 cm data cubes of seven nearby galaxies - Sextans A, NGC 6822, WLM, NGC 5068, NGC 7793, NGC 1566, and NGC 5236 - spanning metallicities (0.1 < $Z/Z_{\odot}$ < 1.0) and physical scales (53-1134 pc). Using a velocity dispersion threshold of 6 km s$^{-1}$, we classify the kinematically distinct components into narrow (colder) and broad (warmer). Cross-correlation analysis between the narrow HI components and H$_{2}$ or star formation rate (SFR) surface density at different spatial scales reveals that dwarf galaxies exhibit the strongest correlation at ~500-700 pc. The radially binned narrow HI fraction, $f_{\rm n} = I_{\rm narrowHI}/I_{\rm totalHI}$, in dwarf galaxies shows no clear trend with metallicity or SFR, while in spirals, $f_{\rm n}$ is lower in inner regions with higher metallicity and SFR. We find that the dataset resolution significantly impacts the results, with higher physical resolution data yielding a higher median $f_{\rm n}$, $\langle f_{\rm n} \rangle$, per galaxy. With this considered, dwarf galaxies consistently exhibit a larger $f_{\rm n}$ than spiral galaxies. These findings highlight the critical role of cold HI in regulating star formation across different galactic environments and emphasise the need for high-resolution HI observations to further unravel the connection between atomic-to-molecular gas conversion and galaxy evolution.

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arXiv2025

HI within and around observed and simulated galaxy discs -- Comparing MeerKAT observations with mock data from TNG50 and FIRE-2

Atomic hydrogen (HI) is an ideal tracer of gas flows in and around galaxies, and it is uniquely observable in the nearby Universe. Here we make use of wide-field (~1 square degree), spatially resolved (down to 22"), high-sensitivity (~$10^{18}$ cm$^{-2}$) HI observations of 5 nearby galaxies with stellar mass of $5\times10^{10}$ M$_\odot$, taken with the MeerKAT radio telescope. Four of these were observed as part of the MHONGOOSE survey. We characterise their main HI properties and compare these with synthetic HI data from a sample of 25 similarly massive star-forming galaxies from the TNG50 (20) and FIRE-2 (5) suites of cosmological hydrodynamical simulations. Globally, the simulated systems have HI and molecular hydrogen (H$_2$) masses in good agreement with the observations, but only when the H$_2$ recipe of Blitz & Rosolowsky (2006) is employed. The other recipes that we tested overestimate the H$_2$-to-HI mass fraction by up to an order of magnitude. On a local scale, we find two main discrepancies between observed and simulated data. First, the simulated galaxies show a more irregular HI morphology than the observed ones due to the presence of HI with column density $<10^{20}$ cm$^{-2}$ up to ~100 kpc from the galaxy centre, in spite of the fact that they inhabit more isolated environments than the observed targets. Second, the simulated galaxies and in particular those from the FIRE-2 suite, feature more complex and overall broader HI line profiles than the observed ones. We interpret this as being due to the combined effect of stellar feedback and gas accretion, which lead to a large-scale gas circulation that is more vigorous than in the observed galaxies. Our results indicate that, with respect to the simulations, gentler processes of gas inflows and outflows are at work in the nearby Universe, leading to more regular and less turbulent HI discs.

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arXiv2025

Uncovering Extraplanar Gas in UGCA 250 with the Ultra-deep MHONGOOSE Survey

We use the neutral atomic hydrogen (HI) observations of the edge-on galaxy UGCA 250, taken as part of the MeerKAT HI Observations of Nearby Galactic Objects - Observing Southern Emitters (MHONGOOSE) survey to investigate the amount, morphology, and kinematics of extraplanar gas. The combination of high column density sensitivity and high spatial resolution of the survey over a large field of view is ideal for studying the underlying physics governing the extraplanar gas. These data reveal 9 additional detections within the field of view along with UGCA 250, with 8 of them being within $\sim$ 200 km s$^{-1}$ of the galaxy's systemic velocity. The galaxy seems to have a tail-like feature extending away from it in the southern direction up to $\sim$ 41 kpc (in projection). We also detect a cloud at anomalous velocities, but we did not find any optical counterpart. We construct a detailed tilted ring model for this edge-on galaxy to gain a deeper understanding of the vertical structure of its neutral hydrogen. The model that best matches the data features a thick disc with a scale height of $\sim$ 3$\pm$1 kpc and an HI mass of about 15$\%$ of the total HI mass. This extraplanar gas is detected for the first time in UGCA 250. Our analysis favours a mixed origin for the extraplanar gas in UGCA 250, likely arising from a combination of internal stellar feedback and external tidal interactions.

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arXiv2025

The multi-wavelength Tully-Fisher relation in the TNG50 cosmological simulation

The Tully-Fisher relation (TFR) is one of the most important and widely used empirical correlations in extragalactic astronomy. Apart from its importance as a secondary distance indicator, the TFR relation serves as a test for galaxy evolution models, because it connects the baryonic and dark matter components of galaxies. We aim at simulating the multi-wavelength TFR relation from UV to mid-infrared wavelengths for the TNG50 cosmological simulation at $z = 0$, and at comparing the results with observational TFR studies. We want to compare the wavelength dependence of the slope and scatter with the observed values, and search for secondary parameters that reduce the scatter in the TFR. We select a large sample of simulated late-type, disc-dominated galaxies from the TNG50 simulation. For each galaxy, we use the SKIRT radiative transfer code to generate realistic synthetic global fluxes in 12 UV to mid-infrared broadbands and synthetic integrated HI line profiles. We use bivariate linear regression to determine the TFR in each band, and we search for a second TFR parameter by correlating the residuals with different physical parameters. Our TNG50 TFR reproduces the characteristic behaviour of the observed TFR in many studies: the TFR becomes steeper and tighter as we move from UV/optical to infrared wavelengths. The slope changes from $-7.46 \pm 0.14~{\text{mag}}~{\text{dex}}^{-1}$ in the NUV band to $-9.66 \pm 0.09~{\text{mag}}~{\text{dex}}^{-1}$ in the IRAC [4.5] band. Quantitatively, our slopes are well within the spread of different observational results. The ${\textit{u}} - {\textit{r}}$ colour or the sSFR can significantly reduce the scatter in the UV and optical bands. Using ${\textit{u}} - {\textit{r}}$ colour as second parameter, the modified TFR has a roughly constant intrinsic tightness of over the entire UV to MIR range. The combination of the TNG50...

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arXiv2024

Searching for HI around MHONGOOSE Galaxies via Spectral Stacking

The observed star formation rates of galaxies in the Local Universe suggests that they are replenishing their gas reservoir across cosmic time. Cosmological simulations predict that this accretion of fresh gas can occur in a hot or a cold mode, yet the existence of low column density ($\sim10^{17}$ cm$^{-2}$) neutral atomic hydrogen (HI) tracing the cold mode has not been unambiguously confirmed by observations. We present the application of unconstrained spectral stacking to attempt to detect the emission from this HI in the Circum-Galactic Medium (CGM) and Inter-Galactic Medium (IGM) of 6 nearby star forming galaxies from the MHONGOOSE sample for which full-depth observations are available. Our stacking procedure consists of a standard spectral stacking algorithm coupled with a one-dimensional spectral line finder designed to extract reliable signal close to the noise level. In agreement with previous studies, we found that the amount of signal detected outside the HI disk is much smaller than implied by simulations. Furthermore, the column density limit that we achieve via stacking ($\sim10^{17}$ cm$^{-2}$) suggests that direct detection of the neutral CGM/IGM component might be challenging in the future, even with the next generation of radio telescopes.

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arXiv2024

The spatially resolved relation between dust, gas, and metal abundance with the TYPHOON survey

We present the spatially resolved relationship between the dust-to-gas mass ratio (DGR) and gas-phase metallicity (Zgas or 12+log(O/H)) (i.e., DGR-Zgas relation) of 11 nearby galaxies with a large metallicity range (1.5 dex of 12+log(O/H)) at (sub-)kpc scales. We used the large field-of-view (> 3') optical pseudo-Integral Field Spectroscopy data taken by the TYPHOON/PrISM survey, covering the optical size of galaxies, combining them with multi-wavelength data (far-UV to far-IR, CO, and HI 21 cm radio). A large scatter of DGR in the intermediate metallicity galaxies (8.0 < 12+log(O/H) < 8.3) is found, which is in line with dust evolution models, where grain growth begins to dominate the mechanism of dust mass accumulation. In the lowest metallicity galaxy of our sample, Sextans A (12+log(O/H) < 7.6), the star-forming regions have significantly higher DGR values (by 0.5-2 dex) than the global estimates from literature at the same metallicity but aligns with the DGR values from metal depletion method from Damped Lyman Alpha systems and high hydrogen gas density regions of Sextans A. Using dust evolution models with a Bayesian MCMC approach suggests: 1) a high SN dust yield and 2) a negligible amount of photofragmentation by UV radiation, although we note that our sample in the low-metallicity regime is limited to Sextans A. On the other hand, it is also possible that while metallicity influences DGR, gas density also plays a role, indicating an early onset of dust grain growth in the dust mass build-up process despite its low metallicity.

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arXiv2024

Neutral Atomic Hydrogen Surveys: past, present and future

Neutral atomic hydrogen (HI) observations are fundamental to understand the dynamics of galaxies, their assembly, the fuelling of their star formation and environmental interactions. HI studies have so far been limited by the capabilities of single-dish radio telescopes or synthesis arrays to either small samples or low resolution and sensitivities. Now, the Square Kilometer Array precursors and pathfinders are providing a novel view of the HI in and around galaxies allowing wide-field high resolution deep surveys in nearby galaxies. We give an overview of past, current and future HI surveys consistently comparing their HI column density and spatial resolutions highlighting their main scientific key goals and results.

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arXiv2024

The MeerKAT Fornax Survey. III. Ram-pressure stripping of the tidally interacting galaxy NGC 1427A in the Fornax cluster

We present MeerKAT Fornax Survey HI observations of NGC 1427A, a blue irregular galaxy with a stellar mass of 2e+9 Msun located near the centre of the Fornax galaxy cluster. Thanks to the excellent resolution (1 to 6 kpc spatially, 1.4 km/s in velocity) and HI column density sensitivity (4e+19/cm^2 to 1e+18/cm^2 depending on resolution), our data deliver new insights on the long-debated interaction of this galaxy with the cluster environment. We confirm the presence of a broad, one-sided, starless HI tail stretching from the outer regions of the stellar body and pointing away from the cluster centre. We find the tail to have 50% more HI (4e+8 Msun) and to be 3 times longer (70 kpc) than in previous observations. In fact, we detect scattered HI clouds out to 300 kpc from the galaxy in the direction of the tail -- possibly the most ancient remnant of the passage of NGC 1427A through the intracluster medium of Fornax. Both the velocity gradient along the HI tail and the peculiar kinematics of HI in the outer region of the stellar body are consistent with the effect of ram pressure given the line-of-sight motion of the galaxy within the cluster. However, several properties cannot be explained solely by ram pressure and suggest an ongoing tidal interaction. This includes: the close match between dense HI and stars within the disturbed stellar body; the abundant kinematically-anomalous HI; and the inversion of the HI velocity gradient near the base of the HI tail. We rule out an interaction with the cluster tidal field, and conclude that NGC 1427A is the result of a high-speed galaxy encounter or of a merger started at least 300 Myr ago, where ram pressure shapes the distribution and kinematics of the HI in the perturbed outer stellar body and in the tidal tails.

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arXiv2024

Neutral atomic and molecular gas dynamics in the nearby spiral galaxies NGC 1512, NGC 4535, and NGC 7496

Neutral atomic gas (HI) effectively traces galactic dynamics across mid to large galactocentric radii. However, its limitations in observing small-scale changes within the central few kiloparsecs, coupled with the often observed HI deficit in galactic centers, necessitates using molecular gas emission as a preferred tracer in these regions. Understanding the dynamics of both neutral atomic and molecular gas is crucial for a more complete understanding of how galaxies evolve, funnel gas from the outer disk into their central parts, and eventually form stars. In this work we aim to quantify the dynamics of both, the neutral atomic and molecular gas, in the nearby spiral galaxies NGC 1512, NGC 4535, and NGC 7496 using new MeerKAT-HI observations together with ALMA CO (2-1) observations from the PHANGS collaboration. We use the analysis tool 3D-Barolo to fit tilted ring models to the HI and CO observations. A combined approach of using the HI to constrain the true disk orientation parameters before applying these to the CO datasets is tested. This paper sets expectations for the results of the upcoming high-resolution HI coverage of many galaxies in the PHANGS-ALMA sample using MeerKAT or VLA, to establish a robust methodology for characterizing galaxy orientations and deriving dynamics from combining new HI with existing CO data.

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