Mergers and the outside-in formation of dwarf spheroidals

Benítez-Llambay, Alejandro; Navarro, Julio F.; Abadi, Mario G.; Gottlöber, Stefan; Yepes, Gustavo; Hoffman, Yehuda; Steinmetz, Matthias

doi:10.1093/mnras/stv2722

Cited by 73 publications

(75 citation statements)

References 59 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These results have also been reproduced by simulations (e.g. Schroyen et al 2013;Revaz & Jablonka 2018), which have shown that the shape of these gradients strongly depends on the combination of the stellar mass, SFH and dynamical history of the system under consideration, although their strength could be influenced by merger events (Benítez-Llambay et al 2016) or environmental effects such as tidal stripping (Sales et al 2010).…”

Section: Metallicity Propertiessupporting

confidence: 62%

The Tucana dwarf spheroidal galaxy: not such a massive failure after all

Taibi

Battaglia

Rejkuba

et al. 2020

A&A

View full text Add to dashboard Cite

Context. Isolated Local Group (LG) dwarf galaxies have evolved most or all of their life unaffected by interactions with the large LG spirals and therefore offer the opportunity to learn about the intrinsic characteristics of this class of objects. Aims. Here we explore the internal kinematic and metallicity properties of one of the three isolated LG early-type dwarf galaxies, the Tucana dwarf spheroidal. This is an intriguing system, as it has been found in the literature to have an internal rotation of up to 16 km s −1 , a much higher velocity dispersion than dwarf spheroidals of similar luminosity, and a possible exception to the too-big-too-fail problem. Methods. We present the results of a new spectroscopic dataset from the Very Large Telescope (VLT) taken with the FORS2 instrument in the region of the Ca II triplet for 50 candidate red giant branch stars in the direction of the Tucana dwarf spheroidal. This yielded line-of-sight (l.o.s.) velocity and metallicity ([Fe/H]) measurements of 39 effective members, which doubles the number of Tucana's stars with such measurements. In addition, we re-reduce and include in our analysis the other two spectroscopic datasets presented in the literature, the VLT/FORS2 sample by Fraternali et al. (2009) and the VLT/FLAMES one by Gregory et al. (2019).Results. We measure a l.o.s. systemic velocity of 180 ± 1.3 km s −1 , consistently across the various datasets analyzed, and find that a dispersion-only model is moderately favored over models accounting also for internal rotation. Our best estimate of the internal l.o.s. velocity dispersion is 6.2 +1.6 −1.3 km s −1 , much smaller than the values reported in the literature and in line with similarly luminous dwarf spheroidals; this is consistent with NFW halos of circular velocities < 30 km s −1 . Therefore, Tucana does not appear to be an exception to the too-big-to-fail problem nor to live in a dark matter halo much more massive than those of its sibling. As for the metallicity properties, we do not find anything unusual; there are hints of the presence of a metallicity gradient but more data are needed to pin its presence down.Article number, page 2 of 26 S. Taibi et al.: Chemo-kinematics of the Tucana dSph

show abstract

Section: Metallicity Propertiessupporting

confidence: 62%

The Tucana dwarf spheroidal galaxy: not such a massive failure after all

Taibi

Battaglia

Rejkuba

et al. 2020

A&A

View full text Add to dashboard Cite

show abstract

“…Some of these differences could indicate an ancient merger, which would have dispersed the old stellar component and allowed the enriched gas to sink further in before forming stars (Benítez-Llambay et al 2016;Genina et al 2019). This would provide a plausible explanation for the radial offset between the original distribution of Fornax GCs and the present-day distributions of its stars.…”

Section: Discussionmentioning

confidence: 99%

Cusp or core? Revisiting the globular cluster timing problem in Fornax

Meadows

Navarro

Santos-Santos

et al. 2019

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We use N-body simulations to revisit the globular cluster (GC) "timing problem" in the Fornax dwarf spheroidal (dSph). In agreement with earlier work, we find that, due to dynamical friction, GCs sink to the center of dark matter halos with a cuspy inner density profile but "stall" at roughly 1/3 of the core radius (r core ) in halos with constant-density cores. The timescales to sink or stall depend strongly on the mass of the GC and on the initial orbital radius, but are essentially the same for either cuspy (NFW) or cored halos normalized to have the same total mass within r core . Arguing against a cusp on the basis that GCs have not sunk to the center is thus no different from arguing against a core, unless all clusters are today at ∼ (1/3) r core . This would imply a core radius exceeding ∼ 3 kpc, much larger than seems plausible in any core-formation scenario. (The average projected distance of Fornax GCs is R GC,Fnx ∼ 1 kpc and its effective radius is ∼ 700 pc.) A simpler explanation is that Fornax GCs have only been modestly affected by dynamical friction, as expected if clusters started orbiting at initial radii of order ∼ 1-2 kpc, just outside Fornax's present-day half-light radius but well within the tidal radius imprinted by Galactic tides. This is not entirely unexpected. Fornax GCs are significantly older and more metal-poor than most Fornax stars, and such populations in dSphs tend to be more spatially extended than their younger and more metal-rich counterparts. Contrary to some earlier claims, our simulations further suggest that GCs do not truly "stall" at ∼ 0.3 r core , but rather continue decaying toward the center, albeit at reduced rates. We conclude that dismissing the presence of a cusp in Fornax based on the spatial distribution of its GC population is unwarranted.

show abstract

“…Very recently, direct observational evidence for mergers between dwarf galaxies has been discovered (e.g., Martínez-Delgado et al 2012;Penny et al 2012;Rich et al 2012;Johnson 2013;Nidever et al 2013;Crnojević et al 2014;Paudel et al 2015;Stierwalt et al 2015). Furthermore, for the first time, the latest numerical simulations are able to reach the required resolution in order to study the effects of dwarf-dwarf mergers in a cosmological scenario (Klimentowski et al 2010;Kazantzidis et al 2011;Deason et al 2014;Benítez-Llambay et al 2016), and these demonstrate that dwarf-dwarf mergers are a viable mechanism to form dwarf spheroidals in the Local Group environment (Kazantzidis et al 2011).…”

Section: Introductionmentioning

confidence: 95%

The Next Generation Virgo Cluster Survey. Xxii. Shell Feature Early-Type Dwarf Galaxies in the Virgo Cluster*

Paudel

Smith

Duc

et al. 2017

ApJ

View full text Add to dashboard Cite

The Next Generation Virgo Cluster Survey is a deep (with a 2σ detection limit μ g =29 mag arcsec −2 in the g-band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes, and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint (μ g >25 mag arcsec−2 ) shells in three Virgo cluster early-type dwarf galaxies: VCC1361, VCC1447, and VCC1668. Among them, VCC1447 has an absolute magnitude M g =−11.71 mag and is the least massive galaxy with a shell system discovered to date. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located up to several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies, forms the observed shell systems.

show abstract

Mergers and the outside-in formation of dwarf spheroidals

Cited by 73 publications

References 59 publications

The Tucana dwarf spheroidal galaxy: not such a massive failure after all

The Tucana dwarf spheroidal galaxy: not such a massive failure after all

Cusp or core? Revisiting the globular cluster timing problem in Fornax

The Next Generation Virgo Cluster Survey. Xxii. Shell Feature Early-Type Dwarf Galaxies in the Virgo Cluster*

Contact Info

Product

Resources

About