arXiv subjects

Jarle Brinchmann

Publications and source records attributed to Jarle Brinchmann.

At least 19 recordsLinked to original sources

arXiv2026

The Mysterious Case of Iron in XMPs: Anomalous High log(Fe/O) Observed in Extremely Metal-Poor Galaxies HSCJ1631+4426 and SDSSJ0811+4730

We present integral field spectroscopic observations of two local extremely metal-poor galaxies (XMPs), HSCJ1631+4426 and SDSSJ0811+4730, obtained with the Keck Cosmic Web Imager (KCWI) over the wavelength range $3545-5529$ {\AA} at a spectral sampling of 0.5 {\AA}, capturing bright nebular emission lines essential for determining gas-phase metallicity and chemical enrichment measurements. Using integrated spectra, we derive oxygen abundances of $\rm12+\log(O/H)=7.079\pm0.010$ and $6.926\pm0.004$, and elevated Fe/O ratios of $\rm\log(Fe/O)=-1.57\pm0.17$ and $-1.28\pm0.07$, for HSCJ1631+4426 and SDSSJ0811+4730 respectively. Each galaxy is fully contained within the $\sim$8'' field of view, with 0.15'' spaxels providing spatially resolved information. These measurements indicate unusually efficient iron enhancement at extremely low metallicity; Fe/O ratios approach or exceed solar despite oxygen abundances of only $\sim$2% solar, inconsistent with enrichment from core-collapse supernovae alone or delayed Type Ia supernovae given the young ages of the systems. Comparison with chemical evolution models suggests rare, highly energetic explosions such as bright hypernovae and/or pair-instability supernovae are likely responsible. Our results reinforce the growing evidence that XMPs can reflect the nucleosynthetic processes of early energetic stellar explosions, serving as local laboratories for chemical enrichment pathways prevalent in the early Universe.

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arXiv2026

Tracing the dynamical and structural complexity of spiral galaxy centres

The formation of late-type galaxies has traditionally been described via two pathways: one producing pressure-supported classical bulges, the other rotationally supported pseudo-bulges. Early studies relied on photometric decompositions assuming an exponential disk extrapolated inwards. Recent high-resolution observations, however, reveal a far more complex landscape in disk galaxy centres. We investigated the morphology of central stellar components in intermediate-to-massive spiral galaxies, focusing on disentangling cold, warm, and hot orbital contributions, critically reassessing the standard approach of extrapolating the exponential disk profile inwards. We developed GLANCE (Galactic archaeoLogy via chronochemicAl and dyNamiCal modElling), a tool for photometric, chronochemical, and dynamical galaxy analysis, applied to 8 high-resolution MUSE galaxies to derive stellar population properties and decompose orbits into cold, warm, hot, and counter-rotating (CR) components. We uncovered remarkable structural diversity in the dynamically cold central component: one galaxy displays an exponential profile throughout, while the majority exhibit either a pronounced central drop resembling a doughnut-shaped structure or a compact inner disk significantly steeper than the outer disk. Most galaxies hosting nuclear disks are classifiable as classical bulges - hot, old, red, high bulge-to-total ratio - contrasting with galaxies showing a central cold-component deficit. Beyond the bulge, cold plus warm orbit contributions remain below the total, indicating non-negligible hot or CR orbits with S\'ersic indexes consistently above unity. These results highlight the composite nature of disk galaxy centres and the need for decomposition methods that avoid extrapolating the outer disk inwards, requiring large IFS samples across a broad mass range, complemented by simulations such as IllustrisTNG50.

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arXiv2026

The MUSE-Faint survey V. The binary fraction of Leo T

The Leo T dwarf galaxy, the faintest and least massive galaxy known to have recent star formation ($\leq 1~Gyr$), exhibits a high dynamical mass-to-light ratio based on its stellar velocity dispersion ($7.07^{+1.29}_{-1.12}~\mathrm{km\ s^{-1}}$), indicating extreme dark matter dominance. We present the first measurement of the binary fraction of Leo T using MUSE-Faint multi-epoch spectroscopy. We also determine the binary fraction for both young and old stellar populations separately and gain insights into binary properties in more metal-poor environments than the Milky Way or Magellanic Clouds. Finally, we investigate the potential impact of binaries on the inferred stellar velocity dispersion. We employed a forward model methodology combining empirical scaling relations to predict stellar velocity variations and a constrained binary distribution from the literature. To estimate the close binary fraction, we limited the maximum semi-major axis ($a < 10~\mathrm{au}$) and repeated the analysis with a semi-amplitude threshold ($\geq~10~ \mathrm{km\ s^{-1}}$) to check the impact on the inferred stellar velocity dispersion.} The overall binary fraction of Leo T is estimated to be $55^{+40}_{-9} \%$, consistent with similar systems. The close binary fraction ($a < 10~\mathrm{au}$) is $30^{+34}_{-9} \%$, which is aligned with low-metallicity environments. We found a lower binary fraction for the older stellar population ($15^{+43}_{-15} \%$) when compared to the younger population ($35^{+40}_{-6} \%$). Finally, we found no significant inflation of the velocity dispersion estimate due to binary motions when compared to the dispersion inferred from the co-added spectra. This suggests that the co-added spectra effectively provide period-averaged velocities of the stars, thus mitigating the impact of binaries on the overall velocity dispersion measurement.

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arXiv2026

Illuminating the Physics of Cosmic Origin and Evolution: A UK Space Frontiers 2035 White Paper

Understanding the Universe's origins and evolution remains one of the most fundamental challenges in modern cosmology. This white paper explores three key science priorities in this field: unravelling the physics of cosmic inflation, investigating the accelerating expansion of the Universe, and precisely measuring the sum of the neutrino masses. Achieving these goals requires a dedicated survey to map the large-scale structure at high redshift in unprecedented detail. We describe how this can be achieved through a mission concept called SIRMOS, providing a high-throughput, highly multiplexed spectroscopic capability to obtain accurate redshifts for over 100 million galaxies over a wide sky area. Such a survey would leverage the deepest existing wide-area photometric catalogues for targeting, with spectra offering continuous 1.25-2.5~$\mu$m wavelength coverage at moderate resolution, allowing precise redshift measurements in the $1<z<4$ range with minimal bias. We outline the scientific opportunities this presents. Recent years have seen significant advances in instrumentation, including digital micromirror devices, complex telescope mirrors, large detector arrays, and data processing pipelines. While these technologies have been demonstrated in terrestrial applications, such a survey is a unique opportunity to apply these proven capabilities in space to address fundamental questions in cosmology. Participation in such a mission will simultaneously deliver a compelling science case, help align UK Space Agency and STFC strategies, demonstrate the UK's growing capability in end-to-end space missions, and strengthen the national space economy through high-value industrial participation.

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arXiv2025

The radial acceleration relation at the EDGE of galaxy formation: testing its universality in low-mass dwarf galaxies

A tight correlation between the baryonic and observed acceleration of galaxies has been reported over a wide range of mass ($10^8 < M_{\rm bar}/{\rm M}_\odot < 10^{11}$) - the Radial Acceleration Relation (RAR). This has been interpreted as evidence that dark matter is actually a manifestation of some modified weak-field gravity theory. In this paper, we study the radially resolved RAR of 12 nearby dwarf galaxies, with baryonic masses in the range $10^4 < M_{\rm bar}/{\rm M}_\odot < 10^{7.5}$, using a combination of literature data and data from the MUSE-Faint survey. We use stellar line-of-sight velocities and the Jeans modelling code GravSphere to infer the mass distributions of these galaxies, allowing us to compute the RAR. We compare the results with the EDGE simulations of isolated dwarf galaxies with similar stellar masses in a $\Lambda$CDM cosmology. We find that most of the observed dwarf galaxies lie systematically above the low-mass extrapolation of the RAR. Each galaxy traces a locus in the RAR space that can have a multi-valued observed acceleration for a given baryonic acceleration, while there is significant scatter from galaxy to galaxy. Our results indicate that the RAR does not apply to low-mass dwarf galaxies and that the inferred baryonic acceleration of these dwarfs does not contain enough information, on its own, to derive the observed acceleration. The simulated EDGE dwarfs behave similarly to the real data, lying systematically above the extrapolated RAR. We show that, in the context of modified weak-field gravity theories, these results cannot be explained by differential tidal forces from the Milky Way, nor by the galaxies being far from dynamical equilibrium, since none of the galaxies in our sample seems to experience strong tides. As such, our results provide further evidence for the need for invisible dark matter in the smallest dwarf galaxies.

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arXiv2025

JADES NIRSpec Spectroscopy of GN-z11: Evidence for Wolf-Rayet contribution to stellar populations at 430 Myr after Big Bang?

We investigate the unusual emission line luminosity ratios observed in the JADES NIRSpec spectroscopy of GN-z11, which reveal exceptionally strong emission lines and a significant detection of the rarely observed N III] $\lambda1748-1753$Å multiplet. These features suggest an elevated N/O abundance, challenging existing models of stellar populations and nebular emission. To assess whether Wolf-Rayet (WR) stars can account for the observed line ratios, we construct a suite of stellar and nebular models incorporating high-resolution stellar spectral libraries, enabling a more accurate treatment of WR evolution and its influence on the ionising radiation field. We find that the inclusion of WR stars is essential for reproducing the observed position of GN-z11 in the C III]/He II versus C III]/C iv diagnostic plane, resolving discrepancies from previous studies. The model-derived metallicity (0.07$\lesssim$Z/Z$_{\odot}\lesssim$0.15), ionisation parameter ($\log\,U$$\approx$-2) and stellar ages are consistent with the literature estimates. However, our models under-predict the N III/O III] ratio, suggesting that WR stars alone cannot fully explain the nitrogen enrichment. This suggests that additional mechanisms, such as rapid chemical enrichment in a young, metal-poor environment, may be necessary to explain the nitrogen excess. While our models successfully reproduce most observed line ratios, further refinements to the models are needed to fully characterise the stellar populations and the enrichment processes of high-redshift galaxies like GN-z11.

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arXiv2024

Large-Scale Stellar Age-Velocity Spiral Pattern in NGC 4030

The processes driving the formation and evolution of late-type galaxies (LTGs) continue to be a debated subject in extragalactic astronomy. Investigating stellar kinematics, especially when combined with age estimates, provides crucial insights into the formation and subsequent development of galactic discs. Post-processing of exceptionally high-quality Integral Field Spectroscopy (IFS) data of NGC 4030 acquired with the Multi Unit Spectroscopic Explorer (MUSE), clearly reveals a striking grand design spiral pattern in the velocity dispersion map not previously detected in other galaxies. This pattern spatially correlates with HII regions, suggesting that stars currently being born exhibit lower velocity dispersion as compared to surrounding areas where star formation (SF) is less active. We examine the age-velocity relation (AVR) and propose that its configuration might be shaped by a combination of heating mechanisms, seemingly consistent with findings from recent high-resolution cosmological zoom-in simulations. The complex structure of the uncovered AVR of NGC 4030 support the hypothesis that stellar populations initially inherit the velocity dispersion σ of the progenitor cold molecular gas, which depends on formation time and galactocentric distance, subsequently experiencing kinematic heating by cumulative gravitational interactions during their lifetime. While advancing our understanding of the AVR, these findings offer a new framework for investigating disk heating mechanisms, and their role in the evolution of galactic disks.

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arXiv2024

The Blue Multi Unit Spectroscopic Explorer (BlueMUSE) on the VLT: science drivers and overview of instrument design

BlueMUSE is a blue-optimised, medium spectral resolution, panoramic integral field spectrograph under development for the Very Large Telescope (VLT). With an optimised transmission down to 350 nm, spectral resolution of R$\sim$3500 on average across the wavelength range, and a large FoV (1 arcmin$^2$), BlueMUSE will open up a new range of galactic and extragalactic science cases facilitated by its specific capabilities. The BlueMUSE consortium includes 9 institutes located in 7 countries and is led by the Centre de Recherche Astrophysique de Lyon (CRAL). The BlueMUSE project development is currently in Phase A, with an expected first light at the VLT in 2031. We introduce here the Top Level Requirements (TLRs) derived from the main science cases, and then present an overview of the BlueMUSE system and its subsystems fulfilling these TLRs. We specifically emphasize the tradeoffs that are made and the key distinctions compared to the MUSE instrument, upon which the system architecture is built.

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arXiv2024

Spatially-resolved Spectroscopic Analysis of Ly$α$ Haloes: Radial Evolution of the Ly$α$ Line Profile out to 60 kpc

The extended Ly$α$ haloes (LAHs) have been found to be prevalent around high-redshift star-forming galaxies. However, the origin of the LAHs is still a subject of debate. Spatially resolved analysis of Ly$α$ profiles provides an important diagnostic. We analyse the average spatial extent and spectral variation of the circumgalactic LAHs by stacking a sample of 155 Ly$α$ emitters (LAEs) at redshift $3<z<4$ in the MUSE Extremely Deep Field. Our analysis reveals that, with respect to the Ly$α$ line of the target LAE, the peak of the Ly$α$ line at large distances becomes increasingly more blueshifted up to a projected distance of 60 kpc ($\approx 3 \times$ virial radius), with a velocity offset of $\approx$ 250 km/s. This trend is evident in both the mean and median stacks, suggesting that it is a general property of our LAE sample, which typically has a Ly$α$ luminosity $\mathrm{\approx 10^{41.1} erg\,s^{-1}}$. However, due to the absence of systemic redshift data, it remains unclear whether the Ly$α$ line peak at large projected distances is less redshifted compared to the inner regions or truly blueshifted with respect to the systemic velocity. We explore various scenarios to explain the large-scale kinematics of the Ly$α$ line.

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arXiv2024

WST -- Widefield Spectroscopic Telescope: Motivation, science drivers and top-level requirements for a new dedicated facility

In this paper, we describe the wide-field spectroscopic survey telescope (WST) project. WST is a 12-metre wide-field spectroscopic survey telescope with simultaneous operation of a large field-of-view (3 sq. degree), high-multiplex (20,000) multi-object spectrograph (MOS), with both a low and high-resolution modes, and a giant 3x3 arcmin2 integral field spectrograph (IFS). In scientific capability, these specifications place WST far ahead of existing and planned facilities. In only 5 years of operation, the MOS would target 250 million galaxies and 25 million stars at low spectral resolution, plus 2 million stars at high resolution. Without need for pre-imaged targets, the IFS would deliver 4 billion spectra offering many serendipitous discoveries. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work in synergy with future ground and space-based facilities. We show how it can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; the origin of stars and planets; and time domain and multi-messenger astrophysics. WST's uniquely rich dataset may yield unforeseen discoveries in many of these areas. The telescope and instruments are designed as an integrated system and will mostly use existing technology, with the aim to minimise the carbon footprint and environmental impact. We will propose WST as the next European Southern Observatory (ESO) project after completion of the 39-metre ELT.

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arXiv2024

The Wide-field Spectroscopic Telescope (WST) Science White Paper

The Wide-field Spectroscopic Telescope (WST) is proposed as a new facility dedicated to the efficient delivery of spectroscopic surveys. This white paper summarises the initial concept as well as the corresponding science cases. WST will feature simultaneous operation of a large field-of-view (3 sq. degree), a high multiplex (20,000) multi-object spectrograph (MOS) and a giant 3x3 sq. arcmin integral field spectrograph (IFS). In scientific capability these requirements place WST far ahead of existing and planned facilities. Given the current investment in deep imaging surveys and noting the diagnostic power of spectroscopy, WST will fill a crucial gap in astronomical capability and work synergistically with future ground and space-based facilities. This white paper shows that WST can address outstanding scientific questions in the areas of cosmology; galaxy assembly, evolution, and enrichment, including our own Milky Way; origin of stars and planets; time domain and multi-messenger astrophysics. WST's uniquely rich dataset will deliver unforeseen discoveries in many of these areas. The WST Science Team (already including more than 500 scientists worldwide) is open to the all astronomical community. To register in the WST Science Team please visit https://www.wstelescope.com/for-scientists/participate

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arXiv2024

Robust bounds on ALP dark matter from dwarf spheroidal galaxies in the optical MUSE-Faint survey

Nearby dwarf spheroidal galaxies are ideal targets in the search for indirect dark matter (DM) signals. In this work, we analyze MUSE spectroscopic observations of a sample of five galaxies, composed of both classical and ultra-faint dwarf spheroidals. The goal is to search for radiative decays of axion-like particles (ALPs) in the mass range of 2.7-5.3 eV. After taking into account the uncertainties associated with the DM spatial distribution in the galaxies, we derive robust bounds on the effective ALP-two-photon coupling. They lie well below the QCD axion band and are significantly more constraining than limits from other probes, in the relevant mass range. We also test the possible presence of a positive signal, concluding that none of the channels selected for this analysis, i.e., not affected by large background contamination, is exhibiting such evidence.

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arXiv2024

Large-scale excess HI absorption around $z\approx4$ galaxies detected in a background galaxy spectrum in the MUSE eXtremely Deep Field

Observationally mapping the relation between galaxies and the intergalactic medium (IGM) is of key interest for studies of cosmic reionization. Diffuse hydrogen gas has typically been observed in HI Lyman-$α$ (Ly$α$) absorption in the spectra of bright background quasars. However, it is important to extend these measurements to background galaxies as quasars become increasingly rare at high redshift and rarely probe closely separated sight-lines. Here we use deep integral field spectroscopy in the MUSE eXtremely Deep Field to demonstrate the measurement of the Ly$α$ transmission at $z\approx4$ in absorption to a background galaxy at $z=4.77$. The HI transmission is consistent with independent quasar sight-lines at similar redshifts. Exploiting the high number of spectroscopic redshifts of faint galaxies (500 between $z=4.0-4.7$ within a radius of 8 arcmin) that are tracers of the density field, we show that Ly$α$ transmission is inversely correlated with galaxy density, i.e. transparent regions in the Ly$α$ forest mark under-dense regions at $z\approx4$. Due to large-scale clustering, galaxies are surrounded by excess HI absorption over the cosmic mean out to 4 cMpc/h. We also find that redshifts from the peak of the Ly$α$ line are typically offset from the systemic redshift by +170 km/s. This work extends results from $z\approx 2 - 3$ to higher redshifts and demonstrates the power of deep integral field spectroscopy to simultaneously measure the ionization structure of the IGM and the large-scale density field in the early Universe.

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arXiv2023

Bipolar Outflows out to 10~kpc for Massive Galaxies at Redshift $z\approx 1$

Galactic outflows are believed to play a critical role in the evolution of galaxies by regulating their mass build-up and star formation. Theoretical models assumes bipolar shapes for the outflows that extends well into the circumgalctic medium (CGM), up to tens of kpc perpendicular to the galaxies. They have been directly observed in the local Universe in several individual galaxies, e.g., around the Milky Way and M82. At higher redshifts, cosmological simulations of galaxy formation predict an increase in the frequency and efficiency of galactic outflows due to the increasing star formation activity. Outflows are responsible for removing potential fuel for star formation from the galaxy, while at the same enriching the CGM and the intergalactic medium. These feedback processes, although incorporated as key elements of cosmological simulations, are still poorly constrained on CGM scales. Here we present an ultra-deep MUSE image of the mean MgII emission surrounding a sample of galaxies at z~1 that strongly suggests the presence of outflowing gas on physical scales of more than 10kpc. We find a strong dependence of the detected signal on the inclination of the central galaxy, with edge-on galaxies clearly showing enhanced MgII emission along the minor axis, while face-on galaxies display much weaker and more isotropic emission. We interpret these findings as supporting the idea that outflows typically have a bipolar cone geometry perpendicular to the galactic disk. We demonstrate that the signal is not dominated by a few outliers. After dividing the galaxy sample in subsamples by mass, the bipolar emission is only detected in galaxies with stellar mass $\mathrm{M_* \gtrsim 10^{9.5} M_\odot}$.

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arXiv2023

CLASSY VIII: Exploring the Source of Ionization with UV ISM diagnostics in local High-$z$ Analogs

In the current JWST era, rest-frame UV spectra play a crucial role in enhancing our understanding of the interstellar medium (ISM) and stellar properties of the first galaxies in the epoch of reionization (EoR, $z>6$). Here, we compare well-known and reliable optical diagrams sensitive to the main ionization source (i.e., star formation, SF; active galactic nuclei, AGN; shocks) to UV counterparts proposed in the literature - the so-called ``UV-BPT diagrams'' - using the HST COS Legacy Archive Spectroscopic SurveY (CLASSY), the largest high-quality, high-resolution and broad-wavelength range atlas of far-UV spectra for 45 local star-forming galaxies. In particular, we explore where CLASSY UV line ratios are located in the different UV diagnostic plots, taking into account state-of-the-art photoionization and shock models and, for the first time, the measured ISM and stellar properties (e.g., gas-phase metallicity, ionization parameter, carbon abundance, stellar age). We find that the combination of C III] $λλ$1907,9 He II $\lambda1640$ and O III] $λ$1666 can be a powerful tool to separate between SF, shocks and AGN at sub-solar metallicities. We also confirm that alternative diagrams without O III] $λ$1666 still allow us to define a SF-locus with some caveats. Diagrams including C IV $λλ$1548,51 should be taken with caution given the complexity of this doublet profile. Finally, we present a discussion detailing the ISM conditions required to detect UV emission lines, visible only in low gas-phase metallicity (12+log(O/H) $\lesssim8.3$) and high ionization parameter (log($U$) $\gtrsim-2.5$) environments. Overall, CLASSY and our UV toolkit will be crucial in interpreting the spectra of the earliest galaxies that JWST is currently revealing.

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arXiv2023

The first comprehensive study of a giant nebula around a radio-quiet quasar in the $z < 1$ Universe

We present the first comprehensive study of a giant, $\approx \! \! 70$ kpc-scale nebula around a radio-quiet quasar at $z<1$. The analysis is based on deep integral field spectroscopy with MUSE of the field of HE$\,$0238$-$1904, a luminous quasar at $z=0.6282$. The nebula emits strongly in $\mathrm{[O \, II]}$, $\rm H β$, and $\mathrm{[O \, III]}$, and the quasar resides in an unusually overdense environment for a radio-quiet system. The environment likely consists of two groups which may be merging, and in total have an estimated dynamical mass of $M_{\rm dyn}\approx 4\times 10^{13}$ to $10^{14}\ {\rm M_\odot}$. The nebula exhibits largely quiescent kinematics and irregular morphology. The nebula may arise primarily through interaction-related stripping of circumgalactic and interstellar medium (CGM/ISM) of group members, with some potential contributions from quasar outflows. The simultaneous presence of the giant nebula and a radio-quiet quasar in a rich environment suggests a correlation between such circum-quasar nebulae and environmental effects. This possibility can be tested with larger samples. The upper limits on the electron number density implied by the $\mathrm{[O \, II]}$ doublet ratio range from $\log(n_{\rm e, \, [O \, II]} / \mathrm{cm^{-3}}) < 1.2$ to $2.8$. However, assuming a constant quasar luminosity and negligible projection effects, the densities implied from the measured line ratios between different ions (e.g., $\mathrm{[O\,II]}$, $\mathrm{[O\,III]}$, and $\mathrm{[Ne\,V]}$) and photoionization simulations are often $10{-}400$ times larger. This large discrepancy can be explained by quasar variability on a timescale of $\approx 10^4{-}10^5$ years.

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arXiv2023

High-z galaxies with JWST and local analogues -- it is not only star formation

I present an analysis of the JWST NIRSpec data of SMACS 0723 released as Early Release Observations. As part of this three new redshifts are provided, bringing the total of reliable redshifts to 14. I propose a modification to the direct abundance determination method that reduces sensitivity to flux calibration uncertainties by a factor of ~3 and show that the resulting abundances are in good agreement with Bayesian photoionization models of the rest-frame optical spectrum. I also show that 6355 is most likely a narrow-line active galactic nucleus (AGN) with $M_* \sim 10^9$ Msun at z=7.66, and argue that 10612 might also have an AGN contribution to its flux through comparison to photoionization models and low-redshift analogues. Under the assumption that the lines come from star-formation I find that the galaxies have gas depletion times of ~$10^7$ years, comparable to similar galaxies locally. I also identify a population of possibly shock-dominated galaxies at z<3 whose near-IR emission lines plausibly come nearly all from shocks and discuss their implications. I close with a discussion of the potential for biases in the determination of the mass-metallicity relation using samples defined by detected [O III]4363 and show using low-z galaxies that this can lead to biases of up to 0.5 dex with a systematic trend with mass.

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arXiv2023

The MUSE-Faint survey. III. Constraining scalar field dark matter with Antlia B

Aims. We use the stellar line-of-sight velocities of Antlia B (Ant B), a faint dwarf galaxy in the NGC 3109 association, to derive constraints on the fundamental properties of scalar field dark matter (SFDM), which was originally proposed to solve the small-scale problems faced by cold dark matter models. Methods. We used the first spectroscopic observations of Ant B, a distant (d $\sim$ 1.35 Mpc) faint dwarf ($M_\text{V} = -9.7$, $M_\star \sim 8\times10^5$M$_\odot$), from MUSE-Faint, a survey of ultra-faint dwarfs conducted using the Multi Unit Spectroscopic Explorer. By measuring the line-of-sight velocities of stars in the $1'\times 1'$ field of view, we identified 127 stars as members of Ant B, which enabled us to model its dark matter density profile with the Jeans modelling code GravSphere. We implemented a model for SFDM into GravSphere and used this to place constraints on the self-coupling strength of this model. Results. We find a virial mass of ${M_{200} \approx 1.66^{+2.51}_{-0.92}\times 10^9}$ $M_\odot$ and a concentration parameter of ${c_{200}\approx 17.38^{+6.06}_{-4.20}}$ for Ant B. These results are consistent with the mass-concentration relations in the literature. We constrain the characteristic length scale of the repulsive self-interaction $R_{\text{TF}}$ of the SFDM model to $R_{\text{TF}} \lesssim 180$ pc ($68\%$ confidence level), which translates to a self-coupling strength of $\frac{g}{m^2c^4}\lesssim 5.2 \times 10^{-20}$ eV$^{-1}$cm$^3$. The constraint on the characteristic length scale of the repulsive self-interaction is inconsistent with the value required to match observations of the cores of dwarf galaxies in the Local Group, suggesting that the cored density profiles of those galaxies are not caused by SFDM.

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