Observed Properties Of Galaxies Research Articles

Dwarf galaxies as a probe of a primordially magnetized Universe

Aims. The true nature of primordial magnetic fields (PMFs) and their role in the formation of galaxies remains elusive. To shed light on these unknowns, we investigated their impact by varying two sets of properties: (i) accounting for the effect of PMFs on the initial matter power spectrum and (ii) accounting for their magneto-hydrodynamical effects on the formation of galaxies. By comparing both, we can determine the dominant agent in shaping galaxy evolution. Methods. We used the magneto-hydrodynamics code RAMSES to generate multiple new zoom-in simulations for eight different host halos of dwarf galaxies across a wide luminosity range of 103 − 106 L⊙. These halos were selected from a ΛCDM cosmological box, tracking their evolution down to redshift z = 0. We explored a variety of primordial magnetic field (comoving) strengths of Bλ ranging from 0.05 to 0.50 nG. Results. We find that magnetic fields in the interstellar medium not only modify star formation processes in dwarf spheroidal galaxies, but these fields also entirely prevent the formation of stars in less compact, ultra-faint galaxies with halo masses and stellar masses below, respectively, ∼2.5 × 109 and 3 × 106 M⊙. At high redshifts, the impact of PMFs on host halos of dwarf galaxies through the modification of the matter power spectrum is more dominant than the influence of magneto-hydrodynamics in shaping their gaseous structure. Through the amplification of small perturbations ranging in mass from 107 to 109 M⊙ in the ΛCDM+PMFs matter power spectrum, primordial fields expedite the formation of the first dark matter halos, leading to an earlier onset and a higher star formation rate at redshifts of z > 9. We investigated the evolution of various energy components and demonstrated that magnetic fields with an initial strength of Bλ ≥ 0.05 nG exhibit a strong growth of magnetic energy, accompanied by a saturation phase that begins soon after the growth phase. These trends persist consistently, regardless of the initial conditions or whether it is the classical ΛCDM model or ΛCDM modified by PMFs. Lastly, we investigated the impact of PMFs on the present-time observable properties of dwarf galaxies, namely: the half light radius, V-band luminosity, mean metallicity, and velocity dispersion profile. We find that PMFs with moderate strengths of Bλ ≤ 0.10 nG show an impressive agreement with the scaling relations of the observed Local Group dwarfs. However, stronger fields lead to larger sizes and higher velocity dispersions.

Closing the Gap between Observed Low-mass Galaxy H i Kinematics and Cold Dark Matter Predictions

Testing the standard cosmological model (ΛCDM) at small scales is challenging. Galaxies that inhabit low-mass dark matter halos provide an ideal test bed for dark matter models by linking observational properties of galaxies at small scales (low mass, low velocity) to low-mass dark matter halos. However, the observed kinematics of these galaxies do not align with the kinematics of the dark matter halos predicted to host them, obscuring our understanding of the low-mass end of the galaxy–halo connection. We use deep H i observations of low-mass galaxies at high spectral resolution in combination with cosmological simulations of dwarf galaxies to better understand the connection between dwarf galaxy kinematics and low-mass halos. Specifically, we use H i line widths to directly compare to the maximum velocities in a dark matter halo and find that each deeper measurement approaches the expected one-to-one relationship between the observed kinematics and the predicted kinematics in ΛCDM. We also measure baryonic masses and place these on the baryonic Tully–Fisher relation (BTFR). Again, our deepest measurements approach the theoretical predictions for the low-mass end of this relation, a significant improvement on similar measurements based on line widths measured at 50% and 20% of the peak. Our data also hint at the rollover in the BTFR predicted by hydrodynamical simulations of ΛCDM for low-mass galaxies.

Reinterpreting fundamental plane correlations with machine learning

Abstract This work explores the relationships between galaxy sizes and related observable galaxy properties in a large volume cosmological hydrodynamical simulation. The objectives of this work are to develop a better understanding of both the correlations between galaxy properties and the influence of environment on galaxy physics in order to build an improved model for the galaxy sizes, building off of the fundamental plane. With an accurate intrinsic galaxy size predictor, the residuals in the observed galaxy sizes can potentially be used for multiple cosmological applications, including making measurements of galaxy velocities in spectroscopic samples, estimating the rate of cosmic expansion, and constraining the uncertainties in the photometric redshifts of galaxies. Using projection pursuit regression, the model accurately predicts intrinsic galaxy sizes and have residuals which have limited correlation with galaxy properties. The model decreases the spatial correlation of galaxy size residuals by a factor of ∼ 5 at small scales compared to the baseline correlation when the mean size is used as a predictor.

ERGO-ML: comparing IllustrisTNG and HSC galaxy images via contrastive learning

ABSTRACT Modern cosmological hydrodynamical galaxy simulations provide tens of thousands of reasonably realistic synthetic galaxies across cosmic time. However, quantitatively assessing the level of realism of simulated universes in comparison to the real one is difficult. In this paper of the Extracting Reality from Galaxy Observables with Machine Learning series, we utilize contrastive learning to directly compare a large sample of simulated and observed galaxies based on their stellar-light images. This eliminates the need to specify summary statistics and allows to exploit the whole information content of the observations. We produce survey-realistic galaxy mock data sets resembling real Hyper Suprime-Cam (HSC) observations using the cosmological simulations TNG50 and TNG100. Our focus is on galaxies with stellar masses between 109 and 1012 M⊙ at z = 0.1–0.4. This allows us to evaluate the realism of the simulated TNG galaxies in comparison to actual HSC observations. We apply the self-supervised contrastive learning method Nearest Neighbour Contrastive Learning to the images from both simulated and observed data sets (g-, r-, i-bands). This results in a 256-dimensional representation space, encoding all relevant observable galaxy properties. First, this allows us to identify simulated galaxies that closely resemble real ones by seeking similar images in this multidimensional space. Even more powerful, we quantify the alignment between the representations of these two image sets, finding that the majority (≳ 70 per cent) of the TNG galaxies align well with observed HSC images. However, a subset of simulated galaxies with larger sizes, steeper Sérsic profiles, smaller Sérsic ellipticities, and larger asymmetries appears unrealistic. We also demonstrate the utility of our derived image representations by inferring properties of real HSC galaxies using simulated TNG galaxies as the ground truth.

The correlations between galaxy properties in different environments of the cosmic web

Abstract We study the correlations between (u-r) colour, stellar mass, specific star formation rate (sSFR) and metallicity of galaxies in different geometric environments of the cosmic web using a volume limited sample from the SDSS. The geometric environment at the location of each galaxy is determined using the eigenvalues of the tidal tensor in three dimensions. We use the Pearson correlation coefficient (PCC) and the normalized mutual information (NMI) to quantify the correlations between these galaxy properties in sheets, filaments and clusters after matching the stellar mass distributions of the galaxies in these environments. A two-tailed t-test assesses the statistical significance of the observed differences between these relations in different geometric environments. The null hypothesis can be rejected at >99.99% significance level in most of the cases, suggesting that the scaling relations between the observable galaxy properties are susceptible to the geometric environments of the cosmic web.

Spiral shocks induced in a galactic gaseous disk: Hydrodynamic understanding of observational properties of spiral galaxies

Context. We investigate the properties of spiral shocks in a steady, adiabatic, non-axisymmetric, self-gravitating, mass-outflowing accretion disk around a compact object. Aims. We obtained the accretion-ejection solutions in a galactic disk and applied them to spiral galaxies in order to investigate the possible physical connections between some observational quantities of galaxies. Methods. We considered the self-gravitating disk potential to examine the properties of the galactic gaseous disk. We obtained spiral shock-induced accretion-ejection solutions following the point-wise self-similar approach. Results. We observed that the self-gravitating disk profoundly affects the dynamics of the spiral structure of the disk and the properties of the spiral shocks. We find that the observational dispersion between the pitch angle and shear rate and between the pitch angle and star formation rate in spiral galaxies contains some important physical information. Conclusions. There are large differences among the star formation rates of galaxies with similar pitch angles. These differences may be explained by the different star formation efficiencies caused by distinct galactic ambient conditions.

Resolved Star Formation in TNG100 Central and Satellite Galaxies

Recent cosmological hydrodynamical simulations have produced populations of numerical galaxies whose global star-forming properties are in good agreement with those of observed galaxies. Proper modeling of energetic feedback from supernovae and active galactic nuclei is critical to the ability of simulations to reproduce observed galaxy properties, and historically, such modeling has proven to be a challenge. Here, we analyze the local properties of central and satellite galaxies in the z = 0 snapshot of the TNG100 simulation as a test of feedback models. We generate a face-on projection of stellar particles in TNG100 galaxies, from which we demonstrate the existence of a resolved star-forming main sequence (ΣSFR–Σ* relation) with a slope and normalization that is in reasonable agreement with previous studies. We also present radial profiles of various galaxy populations for two parameters: the distance from the resolved main-sequence line (ΔΣSFR) and the luminosity-weighted stellar age (Age L ). We find that, on average, high-mass central and satellite galaxies quench from the inside out, while low-mass central and satellite galaxies have similar, flatter profiles. Overall, we find that, with the exception of the starburst population, the TNG100 feedback models yield simulated galaxies whose radial distributions of Age L and ΔΣSFR agree with those of observed galaxies.

Learning to concentrate: multi-tracer forecasts on local primordial non-Gaussianity with machine-learned bias

Local primordial non-Gaussianity (LPNG) is predicted by many non-minimal models of inflation, and creates a scale-dependent contribution to the power spectrum of large-scale structure (LSS) tracers, whose amplitude is characterized by bϕ .Knowledge of bϕ for the observed tracer population is therefore crucial for learning about inflation from LSS.Recently, it has been shown that the relationship between linear bias b1 and bϕ for simulated halos exhibits significant secondary dependence on halo concentration.We leverage this fact to forecast multi-tracer constraints on f loc NL.We train a machine learning model on observable properties of simulated IllustrisTNG galaxies to predict bϕ for samples constructed to approximate DESI emission line galaxies (ELGs) and luminous red galaxies (LRGs). We find σ(f loc NL) = 2.3, and σ(f loc NL = 3.7, respectively.These forecasted errors are roughly factors of 3, and 35% improvements over the single-tracer case for each sample, respectively.When considering both ELGs and LRGs in their overlap region, we forecast σ(f loc NL) = 1.5 is attainable with our learned model, more than a factor of 3 improvement over thesingle-tracer case,while the ideal split by bϕ could reach σ(f loc NL) < 1.We also perform multi-tracer forecasts for upcoming spectroscopic surveys targeting LPNG (MegaMapper, SPHEREx) and show that splitting tracer samples by bϕ can lead to an order-of-magnitude reduction in projected σ(f loc NL for these surveys.

ERGO-ML: towards a robust machine learning model for inferring the fraction of accreted stars in galaxies from integral-field spectroscopic maps

ABSTRACT Quantifying the contribution of mergers to the stellar mass of galaxies is key for constraining the mechanisms of galaxy assembly across cosmic time. However, the mapping between observable galaxy properties and merger histories is not trivial: cosmological galaxy simulations are the only tools we have for calibration. We study the robustness of a simulation-based inference of the ex situ stellar mass fraction of nearby galaxies to different observables – integrated and spatially resolved – and to different galaxy formation models – IllustrisTNG and EAGLE – with machine learning. We find that at fixed simulation, the fraction of accreted stars can be inferred with very high accuracy, with an error ∼5 per cent (10 per cent) from 2D integral-field spectroscopic maps (integrated quantities) throughout the considered stellar mass range. A bias (&amp;gt; 5 per cent) and an increase in scatter by a factor of 2 are introduced when testing with a different simulation, revealing a lack of generalization to distinct galaxy-formation models. Interestingly, upon using only stellar mass and kinematics maps in the central galactic regions for training, we find that this bias is removed and the ex situ stellar mass fraction can be recovered in both simulations with &amp;lt;15 per cent scatter, independently of the training set’s origin. This opens up the door to a potential robust inference of the accretion histories of galaxies from existing integral field unit surveys, such as MaNGA, covering a similar field of view and containing spatially resolved spectra for tens of thousands of nearby galaxies.

A numerical study of the impact of jet magnetic topology on radio galaxy evolution

ABSTRACT The propagation of active galactic nucleus jets depends both on the environment into which they propagate and on their internal structure. To test the impact that different magnetic topologies have on the observable properties of radio galaxies on kpc scales, we conducted a series of magnetohydrodynamic simulations of jets injected with different magnetic field configurations propagating into a gaseous atmosphere modelled on the Perseus cluster. The simulations show that the structure of the field affects the collimation and propagation of the jets on cluster scales and thus the morphology of the radio lobes inflated by the jets, due to both magnetic collimation and the development of dynamical instabilities in jets with different magnetic topologies. In all cases, the simulations show a distinct reversal of the synchrotron spectral age gradient in the radio lobes about a dynamical time after the jets turn off due to large-scale circulation inside the radio lobe, driven primarily by buoyancy, which could provide a way to constrain the age of radio sources in cluster environments without the need for detailed spectral modelling and thus constrain the radio-mode feedback efficiency. We suggest a robust diagnostic to search for such age gradients in multifrequency radio data.

Constraining cosmic ray transport with observations of the circumgalactic medium

ABSTRACT Recent theoretical studies predict that the circumgalactic medium (CGM) around low-redshift, ∼L* galaxies could have substantial non-thermal pressure support in the form of cosmic rays. However, these predictions are sensitive to the specific model of cosmic ray transport employed, which is theoretically and observationally underconstrained. In this work, we propose a novel observational constraint for calculating the lower limit of the radially averaged, effective cosmic ray transport rate, ${\kappa _{\rm eff}^{\rm min}}$. Under a wide range of assumptions (so long as cosmic rays do not lose a significant fraction of their energy in the galactic disc, regardless of whether the cosmic ray pressure is important or not in the CGM), we demonstrate a well-defined relationship between ${\kappa _{\rm eff}^{\rm min}}$ and three observable galaxy properties: the total hydrogen column density, the average star formation rate, and the gas circular velocity. We use a suite of Feedback in Realistic Environments 2 galaxy simulations with a variety of cosmic ray transport physics to demonstrate that our analytical model of ${\kappa _{\rm eff}^{\rm min}}$ is a robust lower limit of the true cosmic ray transport rate. We then apply our new model to calculate ${\kappa _{\rm eff}^{\rm min}}$ for galaxies in the COS-Halos sample, and confirm this already reveals strong evidence for an effective transport rate that rises rapidly away from the interstellar medium to values ${\kappa _{\rm eff}^{\rm min}}\gtrsim 10^{30\!-\!31}\, {\rm cm}^2\, {\rm s}^{-1}$ (corresponding to anisotropic streaming velocities of $v^{\rm stream}_{\rm eff} \gtrsim 1000\, {\rm km}\, {\rm s}^{-1}$) in the diffuse CGM, at impact parameters larger than 50–100 kpc. We discuss how future observations can provide qualitatively new constraints in our understanding of cosmic rays in the CGM and intergalactic medium.

Semi-analytic forecasts for Roman – the beginning of a new era of deep-wide galaxy surveys

ABSTRACT The Nancy Grace Roman Space Telescope, NASA’s next flagship observatory, will redefine deep-field galaxy survey with a field of view two orders of magnitude larger than Hubble and an angular resolution of matching quality. These future deep-wide galaxy surveys necessitate new simulations to forecast their scientific output and to optimize survey strategies. In this work, we present five realizations of 2-deg2 light cones, containing a total of ≳25 million simulated galaxies with −16 ≳ MUV ≳ −25 spanning z ∼ 0 to 10. This data set enables a new set of experiments with the impacts of survey size on the derived galaxy formation and cosmological constraints. The intrinsic and observable galaxy properties are predicted using a well-established, physics-based semi-analytic modelling approach. We provide forecasts for number density, cosmic SFR, field-to-field variance, and angular two-point correlation functions, and demonstrate how the future wide-field surveys will be able to improve these measurements relative to current generation surveys. We also present a comparison between these light cones and others that have been constructed with empirical models. The mock light cones are designed to facilitate the exploration of multi-instrument synergies and connecting with current generation instruments and legacy surveys. In addition to Roman, we also provide photometry for a number of other instruments on upcoming facilities, including Euclid and Rubin, as well as the instruments, that are part of many legacy surveys. Full object catalogues and data tables for the results presented in this work are made available through a web-based, interactive portal.

The dark side of galaxy stellar populations – II. The dependence of star-formation histories on halo mass and on the scatter of the main sequence

ABSTRACT Nearby galaxies are the end result of their cosmological evolution, which is predicted to be influenced by the growth of their host dark matter haloes. This co-evolution potentially leaves signatures in present-day observed galaxy properties, which might be essential to further understand how the growth and properties of galaxies are connected to those of their host haloes. In this work, we study the evolutionary histories of nearby galaxies both in terms of their host haloes and the scatter of the star-forming main sequence by investigating their time-resolved stellar populations using absorption optical spectra drawn from the Sloan Digital Sky Survey. We find that galaxy star-formation histories depend on the masses of their host haloes, and hence they shape the evolution of the star-forming main sequence over cosmic time. Additionally, we also find that the scatter around the z = 0 star-forming main sequence is not (entirely) stochastic, as galaxies with currently different star-formation rates have experienced, on average, different star-formation histories. Our findings suggest that dark matter haloes might play a key role in modulating the evolution of star formation in galaxies, and thus of the main sequence, and further demonstrate that galaxies at different evolutionary stages contribute to the observed scatter of this relation.

ERGO-ML I: inferring the assembly histories of IllustrisTNG galaxies from integral observable properties via invertible neural networks

ABSTRACT A fundamental prediction of the ΛCDM cosmology is the hierarchical build-up of structure and therefore the successive merging of galaxies into more massive ones. As one can only observe galaxies at one specific time in the cosmic history, this merger history remains, in principle, unobservable. By using the TNG100 simulation of the IllustrisTNG project, we show that it is possible to infer the unobservable stellar assembly and merger history of central galaxies from their observable properties by using machine learning techniques. In particular, in this first paper of ERGO-ML (Extracting Reality from Galaxy Observables with Machine Learning), we choose a set of seven observable integral properties of galaxies to infer the stellar ex-situ fraction, the average merger lookback times and mass ratios, and the lookback time and stellar mass of the last major merger. To infer the posterior distribution for these parameters and hence estimate the uncertainties in the predictions, we use a conditional Invertible Neural Network (cINN). We find that the stellar ex-situ fraction and the time of the last major merger are well-determined by the selected set of observables, that the mass-weighted merger mass ratio is unconstrained, and that, beyond stellar mass, stellar morphology and stellar age are the most informative properties. Finally, we show that the cINN recovers the remaining unexplained scatter and secondary cross-correlations. Overall, this is a first step towards a tool that can be applied to large galaxy surveys in order to infer unobservable properties of the galaxies’ past, enabling empirical studies of galaxy evolution enriched by cosmological simulations.

The dark side of galaxy stellar populations – I. The stellar-to-halo mass relation and the velocity dispersion–halo mass relation

ABSTRACT The growth and properties of galaxies are thought to be closely connected to the ones of their host dark matter haloes. Despite the importance of this so-called galaxy–halo connection, the potential role of dark matter haloes in regulating observed galaxy properties remains yet to be fully understood. In this work, we derive the ages, metallicites, and [Mg/Fe] abundances from optical spectra from the Sloan Digital Sky Survey of nearby central galaxies, and study them in terms of their host haloes. We investigate how the scatter in the stellar-to-halo mass relation and the velocity dispersion–halo mass relation correlates with these stellar population parameters. In addition, we also study the differences when distinguishing between different galaxy morphologies and environments. We find that the ages and chemical enrichment of galaxies are not fully determined by their stellar masses or velocity dispersion, but also depend on the mass of the host haloes. Our findings suggest that the velocity dispersion is the best proxy of the stellar population parameters with halo mass playing a secondary yet noticeable role. We interpret that the origin of the correlation between the scatter of these relations and the ages and metallicities might be related to different halo formation times.

Observational measures of halo properties beyond mass

ABSTRACT Different properties of dark matter haloes, including growth rate, concentration, interaction history, and spin, correlate with environment in unique, scale-dependent ways. While these halo properties are not directly observable, galaxies will inherit their host haloes’ correlations with environment. In this paper, we show how these characteristic environmental signatures allow using measurements of galaxy environment to constrain which dark matter halo properties are most tightly connected to observable galaxy properties. We show that different halo properties beyond mass imprint distinct scale-dependent signatures in both the galaxy two-point correlation function and the distribution of distances to galaxies’ kth nearest neighbours, with features strong enough to be accessible even with low-resolution (e.g. grism) spectroscopy at higher redshifts. As an application, we compute observed two-point correlation functions for galaxies binned by half-mass radius at $z$ = 0 from the Sloan Digital Sky Survey, showing that classic galaxy size models (i.e. galaxy size being proportional to halo spin) as well as other recent proposals show significant tensions with observational data. We show that the agreement with observed clustering can be improved with a simple empirical model in which galaxy size correlates with halo growth.

Physically Motivated Fit to Mass Surface Density Profiles Observed in Galaxies

Abstract Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ∼750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ( 7 &lt; log [ M ⋆ / M ⊙ ] &lt; 12 ). The propol fits are systematically better than Sérsic profiles when log ( M ⋆ / M ⊙ ) ≲ 9 and systematically worse when log ( M ⋆ / M ⊙ ) ≳ 10 . Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies.

Simultaneous Estimation of Large-scale Structure and Milky Way Dust Extinction from Galaxy Surveys

Abstract The high cosmological precision offered by the next generation of galaxy surveys hinges on improved corrections for Galactic dust extinction. We explore the possibility of estimating both the dust extinction and large-scale structure from a single photometric galaxy survey, making use of the predictable manner in which Milky Way dust affects the measured brightness and colors of galaxies in a given sky location in several redshift bins. To test our method, we use a synthetic catalog from a cosmological simulation designed to model the Vera C. Rubin Observatory Legacy Survey of Space and Time. At high Galactic latitude (∣b∣ ≳ 20°) and a resolution of 1° ( 7 ′ ), we predict the uncertainty in the measurement of dust extinction, E(B − V), to be 0.005 mag (0.015 mag). This is similar to the uncertainty of existing dust maps, illustrating the feasibility of our method. Simultaneous estimation of large-scale structure is predicted to recover the galaxy overdensity δ with a precision of ∼0.01 (∼0.05) at 1° ( 7 ′ ) resolution. We also introduce a Bayesian formalism that combines prior information from existing dust maps with the likelihood of Galactic dust extinction determined from the excursion of observed galaxy properties.

Tracing the local volume galaxy halo‐to‐stellar mass ratio with satellite kinematics

AbstractRapid advance has been made recently in accurate distance measurements for nearby ( Mpc) galaxies based on the magnitude of the tip of red giant branch stars resolved with the Hubble Space Telescope. We use observational properties of galaxies presented in the last version of Updated Nearby Galaxy Catalog to derive a halo mass of luminous galaxies via orbital motion of their companions. Our sample contains 298 assumed satellites with known radial velocities around 25 Milky Way‐like massive galaxies and 65 assumed satellites around 47 fainter dominant galaxies. The average total mass‐to‐K‐band luminosity ratio is for the luminous galaxies, increasing up to toward dwarfs. The bulge‐dominated luminous galaxies are characterized with , while the disk‐dominated spirals have . We draw attention to a particular subsample of luminous spiral galaxies with signs of declining rotation curve, which have a radial velocity dispersion of satellites less than 55 km s−1 and a poor dark matter halo with . We note that a fraction of quenched (dSph, dE) companions around Milky Way‐like galaxies decreases with their linear projected separation as .

A diffuse tidal dwarf galaxy destined to fade out as a “dark galaxy”

We have explored the properties of a peculiar object detected in deep optical imaging and located at the tip of an H I tail emerging from Hickson Compact Group 16. Using multiband photometry from infrared to ultraviolet, we were able to constrain its stellar age to 58−9+22 Myr with a rather high metallicity of [Fe/H] = −0.16−0.41+0.43 for its stellar mass of M⋆ = 4.2 × 106 M⊙, a typical signature of tidal dwarf galaxies. The structural properties of this object are similar to those of diffuse galaxies, with a round and featureless morphology, a large effective radius (reff = 1.5 kpc), and a low surface brightness (⟨μg⟩eff = 25.6 mag arcsec−2). Assuming that the object is dynamically stable and able to survive in the future, its fading in time via the aging of its stellar component will make it undetectable in optical observations in just ∼2 Gyr of evolution, even in the deepest current or future optical surveys. Its high H I mass, M(HI) = 3.9 × 108 M⊙, and future undetectable stellar component will make the object match the observational properties of dark galaxies, that is, dark matter halos that failed to turn gas into stars. Our work presents further observational evidence of the feasibility of H I tidal features becoming fake dark galaxies; it also shows the impact of stellar fading, particularly in high metallicity systems such as tidal dwarfs, in hiding aged stellar components beyond detection limits in optical observations.