Stellar Body Research Articles

The MeerKAT Fornax Survey

We present MeerKAT Fornax Survey H I observations of NGC 1427A, a blue irregular galaxy with a stellar mass of ∼2 × 109 M⊙ located near the centre of the Fornax galaxy cluster. Thanks to the excellent resolution (1–6 kpc spatially, 1.4 km s−1 in velocity) and H I column density sensitivity (∼4 × 1019 to ∼1018 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 H I 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 H I (4 × 108 M⊙) and to be 3 times longer (70 kpc) than in previous observations. In fact, we detect scattered H I 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 H I tail and the peculiar kinematics of H I 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 H I and stars within the disturbed stellar body; the abundant kinematically anomalous H I; and the inversion of the H I velocity gradient near the base of the H I 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 H I in the perturbed outer stellar body and in the tidal tails.

H i studies of extremely metal-poor dwarfs in voids – I

ABSTRACT We present and discuss the results of the Giant Metrewave Radio Telescope H i 21-cm line mapping for five isolated low-mass (M$_{\rm bary}$$\sim$(2–8)$\times 10^7$ M$\odot$) eXtremely Metal Poor dwarfs [12+$\log$(O/H) = 7.13–7.28], selected from the nearby void galaxy sample. All the studied void dwarfs show disturbed morphology in the H i maps with the angular resolutions of $\sim 11$ to $\sim 40\,{\rm arcsec}$. We examine the H i morphology and velocity field and the relative orientation of their stellar and gas body spins. We discuss the overall non-equilibrium state of their gas and the possible origin and evolution of the studied void dwarfs. The most straightforward interpretation of the ubiquitous phenomenon of the gas component non-equilibrium state in these and similar void dwarfs is the cold accretion from the void filaments and/or minor mergers. The cold gas accretion in voids could be linked to the presence of small filaments that constitute the substructure of voids.

The Statistical Mechanics of Ideal Magnetohydrodynamic Turbulence and a Solution of the Dynamo Problem

We review and extend the theory of ideal, homogeneous, incompressible, magnetohydrodynamic (MHD) turbulence. The theory contains a solution to the ‘dynamo problem’, i.e., the problem of determining how a planetary or stellar body produces a global dipole magnetic field. We extend the theory to the case of ideal MHD turbulence with a mean magnetic field that is aligned with a rotation axis. The existing theory is also extended by developing the thermodynamics of ideal MHD turbulence based on entropy. A mathematical model is created by Fourier transforming the MHD equations and dynamical variables, resulting in a dynamical system consisting of the independent Fourier coefficients of the velocity and magnetic fields. This dynamical system has a large but finite-dimensional phase space in which the phase flow is divergenceless in the ideal case. There may be several constants of the motion, in addition to energy, which depend on the presence, or lack thereof, of a mean magnetic field or system rotation or both imposed on the magnetofluid; this leads to five different cases of MHD turbulence that must be considered. The constants of the motion (ideal invariants)—the most important being energy and magnetic helicity—are used to construct canonical probability densities and partition functions that enable ensemble predictions to be made. These predictions are compared with time averages from numerical simulations to test whether or not the system is ergodic. In the cases most pertinent to planets and stars, nonergodicity is observed at the largest length-scales and occurs when the components of the dipole field become quasi-stationary and dipole energy is directly proportional to magnetic helicity. This nonergodicity is evident in the thermodynamics, while dipole alignment with a rotation axis may be seen as the result of dynamical symmetry breaking, i.e., ‘broken ergodicity’. The relevance of ideal theoretical results to real (forced, dissipative) MHD turbulence is shown through numerical simulation. Again, an important result is a statistical solution of the ‘dynamo problem’.

Jellyfish galaxies with the IllustrisTNG simulations – citizen-science results towards large distances, low-mass hosts, and high redshifts

ABSTRACT We present the ‘Cosmological Jellyfish’ project – a citizen-science classification program to identify jellyfish (JF) galaxies within the IllustrisTNG cosmological simulations. JF are satellite galaxies that exhibit long trailing gas features – ‘tails’ – extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of $\sim 80\, 000$ satellite galaxies spanning an unprecedented range of stellar masses, $10^{8.3}{-}10^{12.3}\, \mathrm{M_\odot }$, and host masses, $M_\mathrm{200,c}=10^{10.4}{-}10^{14.6}\, \mathrm{M_\odot }$ back to z = 2. Based on this sample, $\sim 90\, 000$ galaxy images were presented to volunteers in the citizen-science Zooniverse platform, who were asked to determine whether the galaxy image resembles a JF. Based on volunteer votes, each galaxy received a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a data set of 5307 visually identified JF galaxies. We find that JF is common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of $M_\mathrm{200,c}\sim 10^{11.5}{-}10^{13}\, \mathrm{M_\odot }$, radial positions within hosts exceeding the virial radius R200, c, and at high redshift up to z = 2. The full data set of our JF scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations.

Jellyfish galaxies with the IllustrisTNG simulations - No enhanced population-wide star formation according to TNG50

ABSTRACT Due to ram-pressure stripping (RPS), jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity + magnetohydrodynamical simulation, with an average spatial resolution of 50–200 pc in the star-forming regions of galaxies, to quantify the star formation activity and star formation rates (SFRs) of more than 700 jellyfish galaxies at z = 0–1 with stellar masses $10^{8.3-10.8} \ {\rm M}_\odot$ in hosts with mass $10^{10.5-14.3} \ {\rm M}_\odot$. We extract their global SFRs, the SFRs within their main stellar body versus within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction, and host halo mass. According to TNG50, star formation and RPS can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analogue satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch.

The MeerKAT Fornax Survey

The MeerKAT Fornax Survey maps the distribution and kinematics of atomic neutral hydrogen gas (H I) in the nearby Fornax galaxy cluster using the MeerKAT telescope. The 12 deg2 survey footprint covers the central region of the cluster out to ∼Rvir and stretches south-west out to ∼2Rvir to include the NGC 1316 galaxy group. The H I column density sensitivity (3σ over 25 km s−1) ranges from 5 × 1019 cm−2 at a resolution of ∼10″ (∼1 kpc at the 20 Mpc distance of Fornax) down to ∼1018 cm−2 at ∼1′ (∼6 kpc), and slightly below this level at the lowest resolution of ∼100″ (∼10 kpc). The H I mass sensitivity (3σ over 50 km s−1) is 6 × 105 M⊙. The H I velocity resolution is 1.4 km s−1. In this paper, we describe the survey design and H I data processing, and we present a sample of six galaxies with long, one-sided, starless H I tails (only one of which was previously known) radially oriented within the cluster and with measurable internal velocity gradients. We argue that the joint properties of the H I tails represent the first unambiguous evidence of ram pressure shaping the distribution of H I in the Fornax cluster. The disturbed optical morphology of all host galaxies supports the idea that the tails consist of H I that was initially pulled out of the galaxies’ stellar body by tidal forces. Ram pressure was then able to further displace the weakly bound H I and give the tails their current direction, length, and velocity gradient.

The neutrino pair annihilation around a massive source with an f(R) global monopole

In this work we investigate the neutrino pair annihilation around a gravitational object involving an f(R) global monopole. We derive and calculate the ratio meaning that the energy deposition per unit time is over that in the Newtonian case. It is found that the greater influence from f(R) theory leads more energy to set free from the annihilation with greater ratio value. It is important that the existence of global monopole makes a sharp increase in the ratio , causing heavier gamma-ray burst. We also discuss the derivative as a function of radius r of the star to show the similar features, that is the considerable modification of Einstein's gravity and the global monopole with unified theory order will raise the amount of more greatly. The stellar body with f(R) global monopole can be well qualified as a source of gamma-ray bursts. Moreover, we can select the factor to be comparable with the accelerating universe while regulating the parameter η for the global monopole in order to make the ratio curves coincide with the results from astronomy. It is possible to probe the monopole from astrophysical observations.

Complexity and the departure from spheroidicity

In this work we investigate the effect of spheroidicity on complexity in self-gravitating, static systems. Utilizing the anisotropic generalisation of the Vaidya–Tikekar superdense stellar model, we employ the complexity factor to connect the spheroidal parameter to the pressure anisotropy and density inhomogeneity. Our findings indicate that deviation from spherical symmetry lead to a higher degree of complexity within the stellar body. We further show the equation of state of parameter is inherently linked to the complexity factor thus demonstrating that the nature of matter in self-gravitating bounded systems plays an important role in the effect of pressure anisotropy and density inhomogeneities.

Recent Formation of a Spiral Disk Hosting Progenitor Globular Clusters at the Center of the Perseus Brightest Cluster Galaxy. I. Spiral Disk

Abstract We address the nature and origin of a spiral disk at the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus cluster, that spans a radius of ∼5 kpc. By comparing stellar absorption lines measured in long-slit optical spectra with synthetic spectra for single stellar populations, we find that fitting of these lines requires two stellar populations: (i) a very young population that peaks in radial velocity at ±250 km s−1 of the systemic velocity within a radius of ∼720 pc of the nucleus, a 1σ velocity dispersion significantly lower than 140 km s−1, and an age of 0.15 ± 0.05 Gyr; and (ii) a very old population having a constant radial velocity with a radius corresponding to the systemic velocity, a much broader velocity dispersion of ∼250 km s−1, and an age of around 10 Gyr. We attribute the former to a post-starburst population associated with the spiral disk, and the latter to the main stellar body of NGC 1275 along the same sight line. If the spiral disk is the remnant of a cannibalized galaxy, then its progenitor would have had to retain an enormous amount of gas in the face of intensive ram-pressure stripping so as to form a total initial mass in stars of ∼3 × 109 M ⊙. More likely, the central spiral originally comprised a gaseous body accreted over the distant past from a residual cooling flow, before experiencing a starburst ∼0.15 Gyr ago to form its stellar body.

Recent Formation of a Spiral Disk Hosting Progenitor Globular Clusters at the Center of the Perseus Brightest Cluster Galaxy. II. Progenitor Globular Clusters

Abstract We address the nature and origin of super star clusters (SSCs) discovered by Holtzman et al. within a radius of ∼5 kpc from the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus Cluster. We show that, in contrast with the much more numerous population of SSCs subsequently discovered up to ∼30 kpc from the center of this galaxy, the central SSC population have maximal masses an order of magnitude higher and a mass function with a shallower power-law slope. Furthermore, whereas the outer SSC population have ages spanning a few Myr to at least ∼1 Gyr, the central SSC population have ages strongly concentrated around ∼500 Myr with a 1σ dispersion of ∼100 Myr. These SSCs share a close spatial and temporal relationship with the “central spiral,” which also has a radius ∼5 kpc centered on NGC 1275 and a characteristic stellar age of ∼150 Myr. We argue that both the central SSC population and the central spiral formed from gas deposited by a residual cooling flow, with the SSCs forming first followed by the formation of the stellar body of the central spiral ∼300–400 Myr later. The ages of the central SSC population imply that they are able to withstand very strong tidal fields near the center of NGC 1275, making them genuine progenitor globular clusters. Evidently, a spiral disk hosting progenitor globular clusters has recently formed at the center of a giant elliptical galaxy.

Discovery of a Damped Lyα Absorber Originating in a Spectacular Interacting Dwarf Galaxy Pair at z = 0.026

Abstract We present the discovery of neutral gas detected in both damped Lyα absorption (DLA) and H i 21 cm emission outside of the stellar body of a galaxy, the first such detection in the literature. A joint analysis between the Cosmic Ultraviolet Baryon Survey and the MeerKAT Absorption Line Survey reveals an H i bridge connecting two interacting dwarf galaxies (log (M star/M ⊙) = 8.5 ± 0.2) that host a z = 0.026 DLA with log[N(H i)/cm−2] = 20.60 ± 0.05 toward the QSO J2339−5523 (z QSO = 1.35). At impact parameters of d = 6 and 33 kpc, the dwarf galaxies have no companions more luminous than ≈0.05L * within at least Δv = ±300 km s−1 and d ≈ 350 kpc. The H i 21 cm emission is spatially coincident with the DLA at the 2σ–3σ level per spectral channel over several adjacent beams. However, H i 21 cm absorption is not detected against the radio-bright QSO; if the background UV and radio sources are spatially aligned, the gas is either warm or clumpy (with a spin temperature to covering factor ratio T s /f c > 1880 K). Observations with VLT-MUSE demonstrate that the α-element abundance of the ionized interstellar medium (ISM) is consistent with the DLA (≈10% solar), suggesting that the neutral gas envelope is perturbed ISM gas. This study showcases the impact of dwarf–dwarf interactions on the physical and chemical state of neutral gas outside of star-forming regions. In the SKA era, joint UV and H i 21 cm analyses will be critical for connecting the cosmic neutral gas content to galaxy environments.

External gas accretion provides a fresh gas supply to the active S0 galaxy NGC 5077

In early-type galaxies, externally accreted gas is thought to be the main source of gas replenishment at late times. We use MUSE integral field spectroscopy data to study the active S0 galaxy NGC 5077, which is known to have disturbed dynamics that are indicative of a past external interaction. We confirm the presence of a stellar kinematically distinct core with a diameter of 2.8 kpc that is counter-rotating with respect to the main stellar body of the galaxy. We find that the counter-rotating core consists of an old stellar population that is not significantly different from the rest of the galaxy. The ionised gas is strongly warped and extends out to 6.5 kpc in the polar direction and in a filamentary structure. The gas dynamics is complex, with significant changes in the position angle as a function of radius. The ionised gas line ratios are consistent with LINER excitation by the active galactic nucleus, both in the nucleus and at kiloparsec scales. We discover a nuclear outflow with projected velocity V ∼ 400 km s−1, consistent with a hollow outflow cone intersecting the plane of the sky. The properties of the misaligned gas match predictions from numerical simulations of misaligned gas infall after a gas-rich merger. The warp and change in the gas orientation as a function of radius are consistent with gas relaxation due to stellar torques; these are stronger at small radii where the gas aligns faster than in the outer regions, driving gas to the nucleus. The stellar and gas dynamics indicate that NGC 5077 has had at least two external interactions, one that resulted in the formation of the counter-rotating core, followed by the second, late-time external gas accretion. NGC 5077 illustrates the importance of external interactions in the replenishment of the galaxy gas reservoir and the nuclear gas content available for black hole fuelling.

Modelling magnetohydrodynamic equilibrium in magnetars with applications to continuous gravitational wave production

ABSTRACT Possessing the strongest magnetic fields in our Universe, magnetars mark an extremum of physical phenomena. The strength of their magnetic fields is sufficient to deform the shape of the stellar body, and when the rotational and magnetic axes are not aligned, these deformations lead to the production of gravitational waves (GWs) via a time-varying quadrupole moment. Such gravitational radiation differs from signals presently detectable by the Laser Interferometer Gravitational-Wave Observatory. These signals are continuous rather than the momentary ‘chirp’ waveforms produced by binary systems during the phases of inspiral, merger, and ringdown. Here, we construct a computational model for magnetar stellar structure with strong internal magnetic fields. We implement an n = 1 polytropic equation of state (EOS) and adopt a mixed poloidal and toroidal magnetic field model constrained by the choice of EOS. We utilize fiducial values for magnetar magnetic field strength and various stellar physical attributes. Via computational simulation, we measure the deformation of magnetar stellar structure to determine upper bounds on the strength of continuous GWs formed as a result of these deformations inducing non-axisymmetric rotation. We compute predictions of upper limit GW strain values for sources in the McGill Magnetar Catalog, an index of all detected magnetars.

A photometric and kinematic analysis of UDG1137+16 (dw1137+16): Probing ultradiffuse galaxy formation in a group environment

ABSTRACT The dominant physical formation mechanism(s) for ultradiffuse galaxies (UDGs) is still poorly understood. Here, we combine new, deep imaging from the Jeanne Rich Telescope with deep integral field spectroscopy from the Keck II telescope to investigate the formation of UDG1137+16 (dw1137+16). Our new analyses confirm both its environmental association with the low density UGC 6594 group, along with its large size of 3.3 kpc and status as a UDG. The new imaging reveals two distinct stellar components for UDG1137+16, indicating that a central stellar body is surrounded by an outer stellar envelope undergoing tidal interaction. Both the components have approximately similar stellar masses. From our integral field spectroscopy, we measure a stellar velocity dispersion within the half-light radius (15 ± 4 km s−1) and find that UDG1137+16 is similar to some other UDGs in that it is likely dark matter dominated. Incorporating literature measurements, we also examine the current state of UDG observational kinematics. Placing these data on the central stellar velocity dispersion–stellar mass relation, we suggest there is little evidence for UDG1137+16 being created through a strong tidal interaction. Finally, we investigate the constraining power current dynamical mass estimates (from stellar and globular cluster velocity dispersions) have on the total halo mass of UDGs. As most are measured within the half-light radius, they are unable to accurately constrain UDG total halo masses.

Spectroscopic study of MATLAS-2019 with MUSE: An ultra-diffuse galaxy with an excess of old globular clusters

The MATLAS deep imaging survey has uncovered a plethora of dwarf galaxies in the low density environment it has mapped. A fraction of them are unusually extended and have low surface brightness. Among these so-called ultra-diffuse galaxies, a few seem to host an excess of globular clusters (GCs). With the integral field unit spectrograph MUSE we have observed one of these galaxies – MATLAS J15052031+0148447 (MATLAS-2019) – located toward the nearby group NGC 5846 and measured its systemic velocity, age, and metallicity, and that of its GC candidates. For the stellar body of MATLAS-2019 we derive a metallicity of −1.33−0.01+0.19 dex and an age of 11.2−0.8+1.8 Gyr. For some of the individual GCs and the stacked GC population, we derive consistent ages and metallicities. From the 11 confirmed GCs and using a Markov Chain Monte Carlo approach we derived a dynamical mass-to-light ratio of 4.2−3.4+8.6 M⊙/L⊙. This is at the lower end of the luminosity-mass scaling relation defined by the Local Group dwarf galaxies. Furthermore, we could not confirm or reject the possibility of a rotational component in the GC system. If present, this would further modify the inferred mass. Follow-up observations of the GC population and of the stellar body of the galaxy are needed to assess whether this galaxy lacks dark matter, as was suggested for the pair of dwarf galaxies in the field of NGC 1052, or if this is a misinterpretation arising from systematic uncertainties of the method commonly used for these systems and the large uncertainties of the individual GC velocities.

New H i observations of KK 69. Is KK 69 a dwarf galaxy in transition?

We present new HI data of the dwarf galaxy KK 69, obtained with the Giant Metrewave Radio Telescope (GMRT) with a signal-to-noise ratio that almost double previous observations. We carried out a Gaussian spectral decomposition and stacking methods to identify the cold neutral medium (CNM) and the warm neutral medium (WNM) of the HI gas. We found that 30% of the total HI gas, which corresponds to a mass of approx. 10^7 Mo, is in the CNM phase. The distribution of the HI in KK 69 is not symmetric. Our GMRT HI intensity map of KK 69 overlaid onto a Hubble Space Telescope image reveals an offset of approx. 4 kpc between the HI high-density region and the stellar body, indicating it may be a dwarf transitional galaxy. The offset, along with the potential truncation of the HI body, are evidence of interaction with the central group spiral galaxy NGC 2683, indicating the HI gas is being stripped from KK 69. Additionally, we detected extended HI emission of a dwarf galaxy member of the group as well as a possible new galaxy located near the north-eastern part of the NGC 2683 HI disk.

Geodesic congruences and a collapsing stellar distribution in f(T) theories

Teleparallel Gravity (TG) describes gravitation as a torsional- rather than curvature-based effect. As in curvature-based constructions of gravity, several different formulations can be proposed, one of which is the Teleparallel equivalent of General Relativity (TEGR) which is dynamically equivalent to GR. In this work, we explore the evolution of a spatially homogeneous collapsing stellar body in the context of two important modifications to TEGR, namely f (T) gravity which is the TG analogue of f (R) gravity, and a nonminimal coupling with a scalar field which has become popular in TG for its effects in cosmology. We explore the role of geodesic deviation to study the congruence of nearby particles in lieu of the Raychaudhuri equation. We find f (T) models that satisfy the null energy condition and describe interesting collapse profiles. In the case of a nonminimally coupled scalar field, we also find potential collapse models with intriguing scalar field evolution profiles.

AlFoCS + Fornax3D: resolved star formation in the Fornax cluster with ALMA and MUSE

ABSTRACT We combine data from ALMA and MUSE to study the resolved (∼300 pc scale) star formation relation (star formation rate, SFR, versus molecular gas surface density) in cluster galaxies. Our sample consists of nine Fornax cluster galaxies, including spirals, ellipticals, and dwarfs, covering a stellar mass range of ∼108.8–1011 M⊙. CO(1-0) and extinction corrected Hα were used as tracers for the molecular gas mass and SFR, respectively. We compare our results with Kennicutt and Bigiel et al. Furthermore, we create depletion time maps to reveal small-scale variations in individual galaxies. We explore these further in FCC290, using the ‘uncertainty principle for star formation’ (Kruijssen & Longmore) to estimate molecular cloud lifetimes, which we find to be short (<10 Myr) in this galaxy. Galaxy-averaged depletion times are compared with other parameters such as stellar mass and cluster-centric distance. We find that the star formation relation in the Fornax cluster is close to those from Kennicutt and Bigiel et al., but overlaps mostly with the shortest depletion times predicted by Bigiel et al. This slight decrease in depletion time is mostly driven by dwarf galaxies with disturbed molecular gas reservoirs close to the virial radius. In FCC90, a dwarf galaxy with a molecular gas tail, we find that depletion times are a factor ≳10 higher in its tail than in its stellar body.

Atomic hydrogen clues to the formation of counterrotating stellar discs

ABSTRACT We present interferometric H i observations of six double-disc stellar counterrotator (‘2σ’) galaxies from the ATLAS3D sample. Three are detected in H i emission; two of these are new detections. NGC 7710 shows a modestly asymmetric H i disc, and the atomic gas in PGC 056772 is centrally peaked but too poorly resolved to identify the direction of rotation. IC 0719, the most instructive system in this study, shows an extended, strongly warped disc of ∼43 kpc diameter, with a faint tail extending towards its neighbour IC 0718. The gas has likely been accreted from this external source during an encounter whose geometry directed the gas into misaligned retrograde orbits (with respect to the primary stellar body of IC 0719). In the interior, where dynamical time-scales are shorter, the H i has settled into the equatorial plane forming the retrograde secondary stellar disc. This is the first direct evidence that a double-disc stellar counterrotator could be formed through the accretion of retrograde gas. However, the dominant formation pathway for the formation of 2σ galaxies is still unclear. The ATLAS3D sample shows some cases of the retrograde accretion scenario and also some cases in which a scenario based on an unusually well-aligned merger is more likely.

The Fornax 3D project: Globular clusters tracing kinematics and metallicities

Globular clusters (GCs) are found ubiquitously in massive galaxies and due to their old ages, they are regarded as fossil records of galaxy evolution. Spectroscopic studies of GC systems are often limited to the outskirts of galaxies, where GCs stand out against the galaxy background and serve as bright tracers of galaxy assembly. In this work, we use the capabilities of the Multi Unit Explorer Spectrograph (MUSE) to extract a spectroscopic sample of 722 GCs in the inner regions (≲3 Reff) of 32 galaxies in the Fornax cluster. These galaxies were observed as part of the Fornax 3D project, a MUSE survey that targets early and late-type galaxies within the virial radius of Fornax. After accounting for the galaxy background in the GC spectra, we extracted line-of-sight velocities and determined metallicities of a sub-sample of 238 GCs. We found signatures of rotation within GC systems, and comparing the GC kinematics and that of the stellar body shows that the GCs trace the spheroid of the galaxies. While the red GCs prove to closely follow the metallicity profile of the host galaxy, the blue GCs show a large spread of metallicities but they are generally more metal-poor than the host.