Upper Limits on the Presence of Central Massive Black Holes in Two Ultra-compact Dwarf Galaxies in Centaurus A

Voggel, Karina; Seth, Anil; Neumayer, Nadine; Mieske, S.; Chilingarian, Igor; Ahn, Christopher; Baumgardt, Holger; Hilker, M.; Nguyen, Dieu D.; Romanowsky, Aaron J.; Walsh, Jonelle L.; Brok, Mark den; Strader, Jay

doi:10.3847/1538-4357/aabae5

Cited by 37 publications

(44 citation statements)

References 103 publications

(217 reference statements)

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“…For UCD 320, Voggel et al (2018) reported a singlecomponent structure (perhaps indicative of a globular cluster rather than a UCD galaxy), with M V = −10.39 mag and M * /L V = 2.64, and therefore one obtains a total stellar mass of 3.17 × 10 6 M . If this is a remnant nuclear star cluster, then from equation 9 one may expect it to contain a black hole with a mass equal to 5.5 × 10 4 M , i.e.…”

Section: Centaurus A: Ucd 320 and Ucd 330mentioning

confidence: 99%

A consistency test for determining whether ultracompact dwarf galaxies could be the remnant nuclei of threshed galaxies

Graham

2019

Monthly Notices of the Royal Astronomical Society

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It has been suggested that ultra-compact dwarf (UCD) galaxies are the "threshed" remains of larger galaxies. Simulations have revealed that extensive tidal-stripping may pare a galaxy back to its tightly-bound, compact nuclear star cluster. It has therefore been proposed that the two-component nature of UCD galaxies may reflect the original nuclear star cluster surrounded by the paltry remnants of its host galaxy. A simple quantitative test of this theory is devised and applied here. If the mass of the central black hole in UCD galaxies, relative to the mass of the UCD galaxies' inner stellar component, i.e. the suspected nuclear star cluster, matches with the (black hole mass)-(nuclear star cluster mass) relation observed in other galaxies, then it would provide quantitative support for the stripped galaxy scenario. Such consistency is found for four of the five UCD galaxies reported to have a massive black hole. This (black hole mass)-(nuclear star cluster mass) relation is then used to predict the central black hole mass in two additional UCD galaxies, and to reveal that NGC 205 and possibly NGC 404 (which only has an upper limit to its black hole mass) also follow this scaling relation.1 While grossly over-represented in some published scaling diagrams, at a given luminosity, just 0.5 percent of dwarf galaxies are "compact elliptical" galaxies (Chilingarian, private communication).

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Section: Centaurus A: Ucd 320 and Ucd 330mentioning

confidence: 99%

A consistency test for determining whether ultracompact dwarf galaxies could be the remnant nuclei of threshed galaxies

Graham

2019

Monthly Notices of the Royal Astronomical Society

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“…The comparison to known NSC-type UCDs shows that these are more massive, bigger and denser than FCC 47-UCD1. As UCDs are considered to be unrelaxed systems (Fellhauer & Kroupa 2002;Norris & Kannappan 2011;Voggel et al 2018), a colour gradient translates directly into a population gradient (instead of being an effect of mass segregation), where a slightly younger population is found at the center while the outskirts are dominated by a older, metal-poor population. Although we cannot find a significant colour gradient, we find the UCD to appear larger in the blue than the red filter by ∼ 10%, corresponding to a more extended metal-poor population.…”

Section: Ucd Propertiesmentioning

confidence: 99%

“…Both, top-heavy (Murray 2009;Dabringhausen et al 2009) and bottom-heavy IMFs (Mieske & Kroupa 2008) are discussed. While a SMBH presents a different explanation for the elevated M/L dyn for high mass UCDs (Mieske et al 2013), a search for SMBHs in two lower-mass UCDs (< 10 7 M ) around Centaurus A yielded a nondetection (Voggel et al 2018). Because of detection thresholds, the non detection of a central BH; however, does not disqualify a UCD from being a former nucleus of an accreted low-mass dwarf galaxy.…”

Section: Introductionmentioning

confidence: 96%

“…Generally, NSCs of dwarf galaxies have larger sizes and are more massive and brighter than typical GCs Sandoval et al 2015). SMBHs in UCDs would give direct evidence but are very difficult to measure in distant low-mass systems (Voggel et al 2018). In addition, the nuclei of dwarf galaxies are metal-poorer than their high-mass equivalents as dictated by the mass-metallicity relation (Spengler et al 2017) and thus have metallicities and colours comparable to the blue population of a GC system (Norris & Kannappan 2011;Sandoval et al 2015;Janz et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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Single metal-poor ultra compact dwarf galaxy at one kiloparsec distance from the low-mass elliptical galaxy FCC 47

Fahrion

Georgiev

Hilker

et al. 2019

A&A

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Context. Photometric surveys of galaxy clusters have revealed a large number of ultra compact dwarfs (UCDs) around predominantly massive elliptical galaxies. Their origin is still debated as some UCDs are considered to be the remnant nuclei of stripped dwarf galaxies while others seem to mark the high-mass end of the star cluster population. Aims. We aim to characterise the properties of a UCD found at very close projected distance (r proj = 1.1 kpc) from the centre of the low-mass (M ∼ 10 10 M ) early-type galaxy FCC 47. This is a serendipitous discovery from MUSE adaptive optics science verification data. We explore the potential origin of this UCD as either a massive cluster or the remnant nucleus of a dissolved galaxy. Methods. We use archival Hubble Space Telescope data to study the photometric and structural properties of FCC 47-UCD1. In the MUSE data, the UCD is unresolved, but we use its spectrum to determine the radial velocity and metallicity. Results. FCC 47-UCD1's surface brightness is best described by a single King profile with low concentration C = R t /R c ∼ 10 and large effective radius (r eff = 24 pc). Its integrated magnitude and a blue colour (M g = −10.55 mag, (g − z) = 1.46 mag) combined with with a metallicity of [M/H] = −1.12 ± 0.10 dex and an age > 8 Gyr obtained from the full fitting of the MUSE spectrum suggests a stellar population mass of M * = 4.87 × 10 6 M . The low S/N of the MUSE spectrum prevents detailed stellar population analysis. Due to the limited spectral resolution of MUSE, we can only give an upper limit on the velocity dispersion (σ < 17 km s −1 ), and consequently on its dynamical mass (M dyn < 1.3 × 10 7 M ). Conclusions. The origin of the UCD cannot be constrained with certainty. The low metallicity, old age and magnitude are consistent with a star cluster origin, whereas the extended size and high mass are consistent with an origin as the stripped nucleus of a dwarf galaxy with a initial stellar mass of a few 10 8 M .

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“…Supermassive black holes are found in most, but crucially not all, galactic nuclei. Perhaps all, and certainly most, nuclei also host a nuclear stellar cluster at the very centre (Neumayer & Walcher 2012, Voggel, et al 2018, Voggel et al 2019, Nguyen et al 2019. Intriguingly, some galactic nuclei are found to contain a nuclear stellar cluster but show no evidence for a supermassive black hole.…”

Section: Introductionmentioning

confidence: 99%

The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

Davies¹,

Askar²,

Church³

2019

Proc. IAU

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Supermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

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Upper Limits on the Presence of Central Massive Black Holes in Two Ultra-compact Dwarf Galaxies in Centaurus A

Cited by 37 publications

References 103 publications

A consistency test for determining whether ultracompact dwarf galaxies could be the remnant nuclei of threshed galaxies

A consistency test for determining whether ultracompact dwarf galaxies could be the remnant nuclei of threshed galaxies

Single metal-poor ultra compact dwarf galaxy at one kiloparsec distance from the low-mass elliptical galaxy FCC 47

The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

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