A Gaia-based Catalog of Candidate Stripped Nuclei and Luminous Globular Clusters in the Halo of Centaurus A

Voggel, Karina; Seth, Anil; Sand, David J.; Hughes, Allison; Strader, Jay; Crnojević, Denija; Caldwell, Nelson

doi:10.3847/1538-4357/ab6f69

Cited by 41 publications

(53 citation statements)

References 63 publications

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“…The simultaneous extraction of the metallicity of both the NSC and the galaxy stellar body showed that these NSCs are more metal-poor than their hosts, suggesting that they have formed through the process of in-spiraling GCs. Intriguingly, the masses, sizes, and metallicities of these two NSCs are consistent with the properties of known ultra-compact dwarfs (Misgeld & Hilker 2011;Voggel et al 2018Voggel et al , 2020Fahrion et al 2019a), suggesting that stripped nuclei of dwarf galaxies are the progenitors of low-mass ultra-compact dwarfs (Strader et al 2013).…”

Section: Introductionsupporting

confidence: 75%

The properties of dwarf spheroidal galaxies in the Cen A group

Müller

Fahrion

Rejkuba

et al. 2021

A&A

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Dwarf spheroidal galaxies (dSphs) have been extensively investigated in the Local Group, but their low luminosity and surface brightness make similar work in more distant galaxy groups challenging. Modern instrumentation unlocks the possibility of scrutinizing these faint systems in other environments, expanding the parameter space of group properties. We use MUSE spectroscopy to study the properties of 14 known or suspected dSph satellites of Cen A. Twelve targets are confirmed to be group members based on their radial velocities. Two targets are background galaxies at ∼50 Mpc: KK 198 is a face-on spiral galaxy, and dw1315-45 is an ultradiffuse galaxy with an effective radius of ∼2300 pc. The 12 confirmed dSph members of the Cen A group have old and metal-poor stellar populations and follow the stellar metallicity-luminosity relation defined by the dwarf galaxies in the Local Group. In the three brightest dwarf galaxies (KK 197, KKs 55, and KKs 58), we identify globular clusters, as well as a planetary nebula in KK 197, although its association with this galaxy and/or the extended halo of Cen A is uncertain. Using four discrete tracers, we measure the velocity dispersion and dynamical mass of KK 197. This dSph appears dark matter dominated and lies on the radial acceleration relation of star-forming galaxies within the uncertainties. It also is consistent with predictions stemming from modified Newtonian dynamics (MOND). Surprisingly, in the dwarf KK 203 we find an extended Hα ring. Careful examination of Hubble Space Telescope photometry reveals a very low level of star formation at ages between 30-300 Myr. The Hα emission is most likely linked to a ∼40 Myr old supernova remnant, although other possibilities for its origin cannot be entirely ruled out.

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Section: Introductionsupporting

confidence: 75%

The properties of dwarf spheroidal galaxies in the Cen A group

Müller

Fahrion

Rejkuba

et al. 2021

A&A

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“…Jennings et al 2015). GC-CAND also has a larger Gaia BP-RP excess factors similar to what is seen for GCs/Nuclei in nearby galaxies (Voggel et al 2020). Gaia proper motions have large errors at these faint magnitudes and its proper motion in RA direction is detected at 2.5 𝜎 level, which is not significant enough to clearly mark it as foreground star.…”

Section: The Progenitor Of the Blue Stellar Streamsupporting

confidence: 57%

Once in a blue stream: Detection of recent star formation in the NGC 7241 stellar stream with MEGARA

Martínez–Delgado¹,

Roca-Fàbrega²,

Paz³

et al. 2021

Preprint

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The census of stellar tidal streams around nearby massive galaxies has significantly grown from recent deep imaging of the low-surface brightness sky. In this work we study the striking case of a blue narrow stream with a possible globular clusterlike progenitor around the Milky Way-size galaxy NGC 7241 and its foreground dwarf companion. We present a follow-up spectroscopic study of this stream based on data taken with the MEGARA instrument at the 10.4-m Gran Telescopio Canarias using the integral field spectroscopy mode. Although our data suggest that this compact object in the stream is actually a foreground Milky Way halo star, we detect emission lines overlapping a less compact, bluer and fainter blob of the stream that is clearly visible in both ultra-violet and optical deep images. From its heliocentric systemic radial velocity derived from the [O ]𝜆5007Å lines (𝑉 syst = 1548.58±1.80 km s −1 ) and new UV and optical broad-band photometry, we conclude that this over-density could be the actual core of the stream, with an absolute magnitude of M𝑔 ∼ -10 and a 𝑔 − 𝑟 = 0.08 ± 0.11, consistent with a remnant of a low-mass dwarf satellite undergoing a current episode of star formation. From the width of the stream and assuming a circular orbit, we calculate that the progenitor mass is between 6.4 × 10 6 M − 2.7 × 10 7 M , which is typical of a dwarf galaxy, but its mass could be substantially lower if the stream is on a very radial orbit. These estimates also suggest that this is one of the lowest mass streams detected so far beyond the Local Group. We find that blue stellar streams containing star formation regions are commonly predicted by high-resolution cosmological simulations of galaxies lighter than the Milky Way. This scenario is consistent with the processes explaining the bursty star formation history of some dwarf satellites, which are followed by a gas depletion and a fast quenching once they enter within the virial radius of their host galaxies for the first time. Thus, it is likely that the stream's progenitor is suffering a star-formation burst comparable to those that have shaped the star-formation history of several Local Group dwarfs in the last few Gigayears.

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“…Spectroscopy of astronomical objects, however, needs longer exposure times than imaging. In other words, spectroscopy for all the star-like objects (point-sources) is unfortunately not feasible in practice (Voggel et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Detection of extragalactic Ultra-Compact Dwarfs and Globular Clusters using Explainable AI techniques

Mohammadi¹,

Mutatiina²,

Saifollahi³

et al. 2022

Preprint

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Compact stellar systems such as Ultra-compact dwarfs (UCDs) and Globular Clusters (GCs) around galaxies are known to be the tracers of the merger events that have been forming these galaxies. Therefore, identifying such systems allows to study galaxies mass assembly, formation and evolution. However, in the lack of spectroscopic information detecting UCDs/GCs using imaging data is very uncertain. Here, we aim to train a machine learning model to separate these objects from the foreground stars and background galaxies using the multi-wavelength imaging data of the Fornax galaxy cluster in 6 filters, namely u, g, r, i, J and Ks. The classes of objects are highly imbalanced which is problematic for many automatic classification techniques. Hence, we employ Synthetic Minority Over-sampling to handle the imbalance of the training data. Then, we compare two classifiers, namely Localized Generalized Matrix Learning Vector Quantization (LGMLVQ) and Random Forest (RF). Both methods are able to identify UCDs/GCs with a precision and a recall of > 93% and provide relevances that reflect the importance of each feature dimension for the classification. Both methods detect angular sizes as important markers for this classification problem. While it is astronomical expectation that color indices of u−i and i−K s are the most important colors, our analysis shows that colors such as g−r are more informative, potentially because of higher signal-to-noise ratio. Besides the excellent performance the LGMLVQ method allows further interpretability by providing the feature importance for each individual class, class-wise representative samples and the possibility for non-linear visualization of the data as demonstrated in this contribution. We conclude that employing machine learning techniques to identify UCDs/GCs can lead to promising results. Especially transparent methods allow further investigation and analysis of importance of the measurements for the detection problem and provide tools for non-linear visualization of the data.

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A Gaia-based Catalog of Candidate Stripped Nuclei and Luminous Globular Clusters in the Halo of Centaurus A

Cited by 41 publications

References 63 publications

The properties of dwarf spheroidal galaxies in the Cen A group

The properties of dwarf spheroidal galaxies in the Cen A group

Once in a blue stream: Detection of recent star formation in the NGC 7241 stellar stream with MEGARA

Detection of extragalactic Ultra-Compact Dwarfs and Globular Clusters using Explainable AI techniques

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