Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?

Martocchia, S.; Dalessandro, E.; Salaris, Maurizio; Larsen, Soeren S.; Rejkuba, M.

doi:10.1093/mnras/staa1482

Cited by 5 publications

(4 citation statements)

References 76 publications

(104 reference statements)

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“…While we have assumed an age of 13 Gyr for Fornax 4, some studies have reported a somewhat younger age of ∼10 Gyr (Buonanno et al 1999;Hendricks et al 2016;Martocchia et al 2020). Indeed, a younger age would be consistent with the less α-enhanced composition.…”

Section: Remarks On Globular Cluster Systems Of Individual Galaxiesmentioning

confidence: 80%

“…Despite a small radial velocity offset (6−9 km s −1 ; Larsen et al 2012;Hendricks et al 2016) between Fornax 4 and the field stars, the location of the cluster near the centre of the Fornax dSph has led to suggestions that it may be the nucleus (Hardy 2002;Strader et al 2003). This idea has recently been revisited by Martocchia et al (2020), who found a larger colour spread on the RGB than could be accounted for by the measurement errors, suggesting a metallicity spread of up to ≈0.5 dex. While this should not seriously affect the comparison of integrated-light measurements, a robust comparison with individual stars would require larger samples than the single star of Hendricks et al (2016).…”

Section: Remarks On Globular Cluster Systems Of Individual Galaxiesmentioning

confidence: 99%

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The chemical composition of globular clusters in the Local Group

Larsen

Eitner

Magg

et al. 2022

A&A

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We present detailed chemical abundance measurements for 45 globular clusters (GCs) associated with galaxies in (and, in one case, beyond) the Local Group. The measurements are based on new high-resolution integrated-light spectra of GCs in the galaxies NGC 185, NGC 205, M 31, M 33, and NGC 2403, combined with reanalysis of previously published observations of GCs in the Fornax dSph, WLM, NGC 147, NGC 6822, and the Milky Way. The GCs cover the range −2.8 < [Fe/H] < −0.1 and we determined abundances for Fe, Na, Mg, Si, Ca, Sc, Ti, Cr, Mn, Ni, Cu, Zn, Zr, Ba, and Eu. Corrections for non local thermodynamic equilibrium effects are included for Na, Mg, Ca, Ti, Mn, Fe, Ni, and Ba, building on a recently developed procedure. For several of the galaxies, our measurements provide the first quantitative constraints on the detailed composition of their metal-poor stellar populations. Overall, the GCs in different galaxies exhibit remarkably uniform abundance patterns of the α, iron-peak, and neutron-capture elements, with a dispersion of less than 0.1 dex in [α/Fe] for the full sample. There is a hint that GCs in dwarf galaxies are slightly less α-enhanced (by ∼0.04 dex on average) than those in larger galaxies. One GC in M 33 (HM33-B) resembles the most metal-rich GCs in the Fornax dSph (Fornax 4) and NGC 6822 (SC7) by having α-element abundances closer to scaled-solar values, possibly hinting at an accretion origin. A principal components analysis shows that the α-element abundances strongly correlate with those of Na, Sc, Ni, and Zn. Several GCs with [Fe/H] < −1.5 are deficient in Mg compared to other α-elements. We find no GCs with strongly enhanced r-process abundances as reported for metal-poor stars in some ultra-faint dwarfs and the Magellanic Clouds. The similarity of the abundance patterns for metal-poor GCs in different environments points to similar early enrichment histories and only allow for minor variations in the initial mass function.

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Section: Remarks On Globular Cluster Systems Of Individual Galaxiesmentioning

confidence: 80%

Section: Remarks On Globular Cluster Systems Of Individual Galaxiesmentioning

confidence: 99%

The chemical composition of globular clusters in the Local Group

Larsen

Eitner

Magg

et al. 2022

A&A

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“…A large core would stabilise the orbit of this GC to the 10 Gyr time scale, and even the intermediate coreNFW profile predicts inspiral time of ≈ 5 Gyr. GC4 is younger and more metal-rich compared to the other GCs [17,18], and it has been debated in the literature whether it is in fact the nuclear star cluster of Fornax [17,[80][81][82]. The LOS velocity of this GC, 8 km/s, appears potentially at odds with this interpretation [83].…”

Section: A Comments Regarding Gc Data Used In This Work (Gc-by-gc Dis...mentioning

confidence: 99%

Assessing the Fornax globular cluster timing problem in different models of dark matter

et al. 2021

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We investigate what the orbits of globular clusters (GCs) in the Fornax dwarf spheroidal (dSph) galaxy can teach us about dark matter (DM). This problem was recently studied for ultralight dark matter (ULDM). We consider two additional models: (i) fermionic degenerate dark matter (DDM), where Pauli blocking should be taken into account in the dynamical friction computation; and (ii) self-interacting dark matter (SIDM). We give a simple and direct Fokker-Planck derivation of dynamical friction, new in the case of DDM and reproducing previous results in the literature for ULDM and cold DM. ULDM, DDM and SIDM were considered in the past as leading to cores in dSphs, a feature that acts to suppress dynamical friction and prolong GC orbits. For DDM we derive a version of the cosmological free streaming limit that is independent of the DM production mechanism, finding that DDM cannot produce an appreciable core in Fornax without violating Lyα limits. If the Ly-α limit is discounted for some reason, then stellar kinematics data does allow a DDM core which could prolong GC orbits. For SIDM we find that significant prolongation of GC orbits could be obtained for values of the self-interaction cross section considered in previous works. In addition to reassessing the inspiral time using updated observational data, we give a new perspective on the so-called GC timing problem, demonstrating that for a cuspy cold DM profile dynamical friction predicts a z = 0 radial distribution for the innermost GCs that is independent of initial conditions. The observed orbits of Fornax GCs are consistent with this expectation with a mild apparent fine-tuning at the level of ∼ 25%.

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“…Schiavon et al 2013;Colucci et al 2014;Sakari et al 2016), the Fornax dwarf spheroidal (e.g. Larsen et al 2012Larsen et al , 2014Martocchia et al 2020a) and the Sagittarius dwarf (e.g. Carretta et al 2010;Fernández-Trincado et al 2021); (iii) they are only found in high-density environments, i.e.…”

Section: Introductionmentioning

confidence: 99%

On the Nitrogen variation in ∼2 Gyr old massive star clusters in the large Magellanic Cloud

Martocchia

Lardo

Rejkuba

et al. 2021

Monthly Notices of the Royal Astronomical Society

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We present ESO/VLT FORS2 low resolution spectroscopy of red giant branch stars in three massive, intermediate age (∼1.7 − 2.3 Gyr) star clusters in the Large Magellanic Cloud. We measure CH and CN index bands at 4300Å and 3883Å, as well as [C/Fe] and [N/Fe] abundance ratios for 24, 21 and 12 member stars of NGC 1978, NGC 1651, NGC 1783, respectively. We find a significant intrinsic spread in CN in NGC 1978 and NGC 1651, a signal of multiple stellar populations (MPs) within the clusters. On the contrary, we report a null CN spread in NGC 1783 within our measurement precision. For NGC 1978, we separated the two populations in the CN distribution and we translated the CN spread into an internal N variation Δ[N/Fe]=0.63 ± 0.49 dex. For NGC 1651 and NGC 1783, we put upper limits on the N abundance variations of Δ[N/Fe]≤0.2, 0.4 dex, respectively. The spectroscopic analysis confirms previous results from HST photometry, where NGC 1978 was found to host MPs in the form of N spreads, while slightly younger clusters (e.g. NGC 1783, < 2 Gyr old) were not, within the limits of the uncertainties. It also confirms that intermediate age massive clusters show lower N abundance variations with respect to the ancient globular clusters, although this is in part due to the effect of the first dredge up at these stellar masses, as recently reported in the literature. We stress the importance of future studies to estimate the initial N abundance variations, free of stellar evolutionary mixing processes, by observing unevolved stars in young clusters.

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Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?

Cited by 5 publications

References 76 publications

The chemical composition of globular clusters in the Local Group

The chemical composition of globular clusters in the Local Group

Assessing the Fornax globular cluster timing problem in different models of dark matter

On the Nitrogen variation in ∼2 Gyr old massive star clusters in the large Magellanic Cloud

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