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

2020 ◽  
Vol 635 ◽  
pp. A152 ◽  
Author(s):  
S. Taibi ◽  
G. Battaglia ◽  
M. Rejkuba ◽  
R. Leaman ◽  
N. Kacharov ◽  
...  
Keyword(s):  
Internal Rotation ◽  
Velocity Dispersion ◽  
Dwarf Galaxies ◽  
Opportunity To Learn ◽  
Dark Matter Halo ◽  
Very Large Telescope ◽  
Systemic Velocity ◽  
Dwarf Spheroidals ◽  
Red Giant ◽  
Giant Branch Stars

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. Our aim is to 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 that we procured 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. These yielded line-of-sight (l.o.s.) velocity and metallicity ([Fe/H]) measurements of 39 effective members that double 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, A&A, 499, 121), and the VLT/FLAMES one from Gregory et al. (2019, MNRAS, 485, 2010). Results. Across the various datasets analyzed, we consistently measure a l.o.s. systemic velocity of 180 ± 1.3 km s−1 and find that a dispersion-only model is moderately favored over models that also account for internal rotation. Our best estimate of the internal l.o.s. velocity dispersion is 6.2−1.3+1.6 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 does it appear to reside in a dark matter halo much more massive than those of its siblings. 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 pinpoint its presence.

scholarly journals A dwarf disrupting – Andromeda XXVII and the North West Stream

2019 ◽  
Vol 490 (2) ◽  
pp. 2905-2917 ◽  
Author(s):  
Janet Preston ◽  
Michelle L M Collins ◽  
Rodrigo A Ibata ◽  
Erik J Tollerud ◽  
R Michael Rich ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Mean Values ◽  
North West ◽  
The North ◽  
Systemic Velocity ◽  
Andromeda Galaxy ◽  
Single Structure ◽  
Red Giant ◽  
Non Gaussian ◽  
Giant Branch Stars

ABSTRACT We present a kinematic and spectroscopic analysis of 38 red giant branch stars, in seven fields, spanning the dwarf spheroidal galaxy Andromeda XXVII and the upper segment of the North West Stream. Both features are located in the outer halo of the Andromeda galaxy at a projected radius of 50–80 kpc, with the stream extending for ∼3° on the sky. Our data are obtained as part of the PAndAS survey and enables us to confirm that Andromeda XXVII’s heliocentric distance is 827 ± 47 kpc and spectroscopic metallicity is $-2.1^{+0.4}_{-0.5}$. We also re-derive Andromeda XXVII’s kinematic properties, measuring a systemic velocity  = $-526.1^{+10.0}_{-11.0}$ km s−1 and a velocity dispersion that we find to be non-Gaussian but for which we derive a formal value of 27.0$^{+2.2}_{-3.9}$ km s−1. In the upper segment of the North West Stream we measure mean values for the metallicity = −1.8 ± 0.4, systemic velocity  = −519.4 ± 4.0 km s−1, and velocity dispersion  = 10.0 ± 4.0 km s−1. We also detect a velocity gradient of 1.7 ± 0.3 km s−1 kpc−1 on an infall trajectory towards M31. With a similar gradient, acting in the same direction, in the lower segment we suggest that the North West Stream is not a single structure. As the properties of the upper segment of the North West Stream and Andromeda XXVII are consistent within 90 per cent confidence limits, it is likely that the two are related and plausible that Andromeda XXVII is the progenitor of this stream.

scholarly journals Lithium abundance in lower red giant branch stars of Omega Centauri

2018 ◽  
Vol 618 ◽  
pp. A134 ◽  
Author(s):  
A. Mucciarelli ◽  
M. Salaris ◽  
L. Monaco ◽  
P. Bonifacio ◽  
X. Fu ◽  
...  
Keyword(s):  
High Resolution ◽  
Globular Clusters ◽  
Stellar System ◽  
The Other ◽  
Large Telescope ◽  
Lithium Abundance ◽  
Very Large Telescope ◽  
Red Giant ◽  
Giant Branch Stars ◽  
Branch Star

We present Li, Na, Al, and Fe abundances of 199 lower red giant branch star members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ∼ 1 dex with a prominent tail towards lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ∼ 1 dex are found at metallicities lower than [Fe/H] ∼ –1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all metallicities. The most metal-poor stars exhibit a clear Li–Na anti-correlation, where about 30% of the sample have A(Li) lower than ∼0.8 dex, while these stars represent a small fraction of normal globular clusters. Most of the stars with [Fe/H] > –1.6 dex are Li poor and Na rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich, and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.

scholarly journals Neutron-capture elements in dwarf galaxies

2019 ◽  
Vol 631 ◽  
pp. A171 ◽  
Author(s):  
Á. Skúladóttir ◽  
C. J. Hansen ◽  
S. Salvadori ◽  
A. Choplin
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Relative Contribution ◽  
History Of ◽  
Red Giant ◽  
Process Element ◽  
Giant Branch Stars

The heavy elements (Z >  30) are created in neutron (n)-capture processes that are predicted to happen at vastly different nucleosynthetic sites. To study these processes in an environment different from the Milky Way, we targeted the n-capture elements in red giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO VLT/FLAMES spectra, we measured the chemical abundances of Y, Ba, La, Nd, and Eu in 98 stars covering the metalliticy range −2.4 < [Fe/H] < −0.9. This is the first paper in a series about the n-capture elements in dwarf galaxies, and here we focus on the relative and absolute timescales of the slow (s)- and rapid (r)-processes in Sculptor. From the abundances of the s-process element Ba and the r-process element Eu, it is clear that the r-process enrichment occurred throughout the entire chemical evolution history of Sculptor. Furthermore, there is no evidence for the r-process to be significantly delayed in time relative to core-collapse supernovae. Neutron star mergers are therefore unlikely the dominant (or only) nucleosynthetic site of the r-process. However, the products of the s-process only become apparent at [Fe/H] ≈ −2 in Sculptor, and the s-process becomes the dominant source of Ba at [Fe/H] ≳ −2. We tested the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor. Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg] increase towards younger ages. However, there is an offset in the trends, where the abundance ratios of [Y/Mg] in Sculptor are significantly lower than those of the Milky Way at any given age. This is most likely caused by metallicity dependence of yields from the s-process, as well as by a different relative contribution of the s-process to core-collapse supernovae in these galaxies. Comparisons of our results with data of the Milky Way and the Fornax dwarf spheroidal galaxy furthermore show that these chemical clocks depend on both metallicity and environment.

scholarly journals A VLT/FORS2 spectroscopic survey of individual stars in a transforming dwarf galaxy

2016 ◽  
Vol 11 (S321) ◽  
pp. 28-30
Author(s):  
G. Battaglia ◽  
N. Kacharov ◽  
M. Rejkuba
Keyword(s):  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Common Type ◽  
Line Of Sight ◽  
Cosmological Context ◽  
Formation And Evolution ◽  
Red Giant ◽  
Giant Branch Stars ◽  
Shed Light ◽  
The Phoenix

AbstractUnderstanding the properties of dwarf galaxies is important not only to put them in their proper cosmological context, but also to understand the formation and evolution of the most common type of galaxies. Dwarf galaxies are divided into two main classes, dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs), which differ from each other mainly because the former are gas-rich objects currently forming stars, while the latter are gas-deficient with no on-going star formation. Transition types (dT) are thought to represent dIs in the process of losing their gas, and can therefore shed light into the possible process of dwarf irregulars (dIrrs) becoming gas-deficient, passively evolving galaxies. Here we present preliminary results from our wide-area VLT/FORS2 MXU spectroscopic survey of the Phoenix dT, from which we obtained line-of-sight velocities and metallicities from the nIR Ca II triplet lines for a large sample of individual Red Giant Branch stars.

scholarly journals Kinematic and metallicity properties of the Aquarius dwarf galaxy from FORS2 MXU spectroscopy

2020 ◽  
Vol 634 ◽  
pp. A10 ◽  
Author(s):  
L. Hermosa Muñoz ◽  
S. Taibi ◽  
G. Battaglia ◽  
G. Iorio ◽  
M. Rejkuba ◽  
...  
Keyword(s):  
Near Infrared ◽  
Velocity Dispersion ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Major Axis ◽  
Stellar Feedback ◽  
Stellar Component ◽  
Red Giant ◽  
Gas Loss ◽  
The Individual

Context. Dwarf galaxies found in isolation in the Local Group (LG) are unlikely to have interacted with the large LG spirals, and therefore environmental effects such as tidal and ram-pressure stripping should not be the main drivers of their evolution. Aims. We provide insight into the internal mechanisms shaping LG dwarf galaxies by increasing our knowledge of the internal properties of isolated systems. Here we focus on the evolved stellar component of the Aquarius dwarf galaxy, whose kinematic and metallicity properties have only recently started to be explored. Methods. Spectroscopic data in the region of the near-infrared Ca II triplet lines has been obtained with FORS2 at the Very Large Telescope for 53 red giant branch (RGB) stars. These data are used to derive line-of-sight (l.o.s.) velocities and [Fe/H] of the individual RGB stars. Results. We derive a systemic velocity of −142.2+1.8−1.8 km s−1, in agreement with previous determinations from both the HI gas and stars. The internal kinematics of Aquarius appears to be best modelled by a combination of random motions (l.o.s. velocity dispersion of 10.3+1.6−1.3 km s−1) and linear rotation (with a gradient −5.0+1.6−1.9 km s−1 arcmin−1) along a PA = 139+17−27 deg, broadly consistent with the optical projected major axis. This rotation signal is significantly misaligned or even counter-rotating to that derived from the HI gas. We also find the tentative presence of a mild negative metallicity gradient and indications that the metal-rich stars have a colder velocity dispersion than the metal-poor ones. Conclusions. This work represents a significant improvement with respect to previous measurements of the RGB stars of Aquarius as it doubles the number of member stars already studied in the literature. We speculate that the misaligned rotation between the HI gas and evolved stellar component might have been the result of recent accretion of HI gas, or re-accretion after gas-loss due to internal stellar feedback.

scholarly journals Stellar chemo-kinematics of the Cetus dwarf spheroidal galaxy

2018 ◽  
Vol 618 ◽  
pp. A122 ◽  
Author(s):  
S. Taibi ◽  
G. Battaglia ◽  
N. Kacharov ◽  
M. Rejkuba ◽  
M. Irwin ◽  
...  
Keyword(s):  
Dark Matter ◽  
Local Group ◽  
Great Majority ◽  
Dark Matter Halo ◽  
Early Type ◽  
Absolute Deviation ◽  
Dwarf Spheroidal Galaxies ◽  
Galaxy Groups ◽  
Very Large Telescope ◽  
Red Giant

Context. The great majority of early-type dwarf galaxies, in the Local Group as well as in other galaxy groups, are found in the vicinity of much larger galaxies, making it hard to disentangle the role of internal versus external effects in driving their evolution. Aims. In order to minimize environmental effects and gain an insight into the internal mechanisms that shape the properties of these systems, we study one of the few dwarf spheroidal galaxies of the Local Group found in isolation: Cetus. This system is of particular interest since it does not follow the Local Group morphology-density relation. Methods. We obtained Very Large Telescope (VLT) FORS2 spectra (R ∼ 2600) in the region of the nIR CaII triplet lines for 80 candidate red giant branch (RGB) stars. The analysis yielded line-of-sight velocities and metallicities ([Fe/H]) for 54 bona fide member stars. Results. The kinematic analysis shows that Cetus is a mainly pressure-supported (σv = 110−1.3+1.6 km s−1), dark-matter-dominated system (M1/2/LV = 23.9−8.9+9.7 M⊙/L⊙) with no significant signs of internal rotation. We find Cetus to be a metal-poor system with a significant metallicity spread (median [Fe/H]= − 1.71 dex, median-absolute-deviation = 0.49 dex), as expected for its stellar mass. We report the presence of a mild metallicity gradient compatible with those found in other dwarf spheroidals of the same luminosity; we trace the presence of a stellar population gradient also in the spatial distribution of stars in different evolutionary phases in ancillary SuprimeCam photometric data. There are tentative indications of two chemo-kinematically distinct sub-populations, with the more metal-poor stars showing a hotter kinematics than the metal-richer ones. Furthermore, the photometric dataset reveals the presence of a foreground population that most likely belongs to the Sagittarius stream. Conclusions. This study represents an important step forward in assessing the internal kinematics of the Cetus dwarf spheroidal galaxy as well as the first wide-area spectroscopic determination of its metallicity properties. With our analysis, Cetus adds to the growing scatter in stellar-dark matter halo properties in low-mass galactic systems. The presence of a metallicity gradient akin to those found in similarly luminous and pressure-supported systems inhabiting very different environments may hint at metallicity gradients in Local Group early-type dwarfs being driven by internal mechanisms.

scholarly journals SHαDE: survey description and mass–kinematics scaling relations for dwarf galaxies

2020 ◽  
Vol 498 (4) ◽  
pp. 5885-5903
Author(s):  
Dilyar Barat ◽  
Francesco D’Eugenio ◽  
Matthew Colless ◽  
Sarah M Sweet ◽  
Brent Groves ◽  
...  
Keyword(s):  
Dwarf Galaxies ◽  
Mass Range ◽  
Stellar Mass ◽  
Dark Matter Halo ◽  
High Spectral Resolution ◽  
Scaling Relation ◽  
Massive Galaxies ◽  
Very Large Telescope ◽  
Halo Masses ◽  
Stellar Masses

ABSTRACT The Study of H α from Dwarf Emissions (SHαDE) is a high spectral resolution (R = 13 500) H α integral field survey of 69 dwarf galaxies with stellar masses 106 &lt; M⋆ &lt; 109 M⊙. The survey used FLAMES on the ESO Very Large Telescope. SHαDE is designed to study the kinematics and stellar populations of dwarf galaxies using consistent methods applied to massive galaxies and at matching level of detail, connecting these mass ranges in an unbiased way. In this paper, we set out the science goals of SHαDE, describe the sample properties, outline the data reduction, and analysis processes. We investigate the log M⋆–log S0.5 mass–kinematics scaling relation, which has previously shown potential for combining galaxies of all morphologies in a single scaling relation. We extend the scaling relation from massive galaxies to dwarf galaxies, demonstrating this relation is linear down to a stellar mass of M⋆ ∼ 108.6 M⊙. Below this limit, the kinematics of galaxies inside one effective radius appears to be dominated by the internal velocity dispersion limit of the H α-emitting gas, giving a bend in the log M⋆–log S0.5 relation. Replacing stellar mass with total baryonic mass using gas mass estimate reduces the severity but does not remove the linearity limit of the scaling relation. An extrapolation to estimate the galaxies’ dark matter halo masses, yields a log Mh–log S0.5 scaling relation that is free of any bend, has reduced curvature over the whole mass range, and brings galaxies of all masses and morphologies on to the virial relation.

scholarly journals Distances from the tip of the red giant branch to the dwarf galaxies dw1335-29 and dw1340-30 in the Centaurus group

2018 ◽  
Vol 615 ◽  
pp. A96 ◽  
Author(s):  
Oliver Müller ◽  
Marina Rejkuba ◽  
Helmut Jerjen
Keyword(s):  
Spatial Distribution ◽  
Dwarf Galaxies ◽  
Group Membership ◽  
Optical Images ◽  
Test Models ◽  
Very Large Telescope ◽  
The Mean ◽  
Red Giant ◽  
Sobel Edge Detection ◽  
Artificial Star

Context. The abundance and spatial distribution of dwarf galaxies are excellent empirical benchmarks against which to test models of structure formation on small scales. The nearby Centaurus group, with its two subgroups centered on Cen A and M 83, stands out as an important alternative to the Local Group for scrutinizing cosmological model predictions in a group of galaxies context. Aims. We have obtained deep optical images of three recently discovered M 83 satellite galaxy candidates with the FORS2 instrument mounted on the Very Large Telescope. We aim to confirm their group membership and study their stellar population. Methods. Deep V I-band photometry was used to resolve the brightest stars in our targets. Artificial star tests are performed to estimate the completeness and uncertainties of the photometry. The color-magnitude diagrams reveal the red giant branch (RGB) stars, allowing us to use the Sobel edge detection method to measure the magnitude of the RGB tip and thus derive distances and group membership for our targets. The mean metallicity of the dwarf galaxies were further determined by fitting BASTI model isochrones to the mean RGB locus. Results. We confirm the two candidates, dw1335-29 and dw1340-30, to be dwarf satellites of the M 83 subgroup, with estimated distances of 5.03 ± 0.24 Mpc and 5.06 ± 0.24 Mpc, respectively. Their respective mean metallicities of ⟨[Fe/H]⟩ = −1.79 ± 0.4 and ⟨[Fe/H]⟩ = −2.27 ± 0.4 are consistent with the metallicity–luminosity relation for dwarf galaxies. The third candidate, dw1325-33, could not be resolved into stars due to insufficiently deep images, implying its distance must be larger than 5.3 Mpc. Using the two newly derived distances we assess the spatial distribution of the galaxies in the M 83 subgroup and discuss a potential plane-of-satellites around M 83.

scholarly journals A detailed study of Andromeda XIX, an extreme local analogue of ultradiffuse galaxies

2019 ◽  
Vol 491 (3) ◽  
pp. 3496-3514 ◽  
Author(s):  
Michelle L M Collins ◽  
Erik J Tollerud ◽  
R Michael Rich ◽  
Rodrigo A Ibata ◽  
Nicolas F Martin ◽  
...  
Keyword(s):  
Complex Dynamics ◽  
Dwarf Galaxy ◽  
Major Axis ◽  
Data Set ◽  
Central Surface ◽  
Systemic Velocity ◽  
Red Giant ◽  
The Masses ◽  
Giant Branch Stars ◽  
Tidal Processes

ABSTRACT With a central surface brightness of μ0 = 29.3 mag arcsec−2, and half-light radius of $r_{\rm half}=3.1^{+0.9}_{-1.1}$ kpc, Andromeda XIX (And XIX) is an extremely diffuse satellite of Andromeda. We present spectra for ∼100 red giant branch stars in this galaxy, plus 16 stars in a nearby stellar stream. With this exquisite data set, we re-derive the properties of And XIX, measuring a systemic velocity of 〈vr〉 = −109.0 ± 1.6 km s−1 and a velocity dispersion of $\sigma _{vr} = 7.8^{+1.7}_{-1.5}$ km s−1 (higher than derived in our previous work). We marginally detect a velocity gradient along the major axis of $\frac{{\rm d} v}{{\rm d}\chi }= -2.1\pm 1.8~{\rm km\, s}^{-1}$ kpc−1. We find its mass-to-light ratio is higher than galaxies of comparable stellar mass (${}[M/L]_{\rm half} = 278^{+146}_{-198}\, \mathrm{M}_\odot /\mathrm{L}_\odot$), but its dynamics place it in a halo with a similar total mass to these galaxies. This could suggest that And XIX is a ‘puffed up’ dwarf galaxy, whose properties have been altered by tidal processes, similar to its Milky Way counterpart, Antlia II. For the nearby stream, we measure $v_r=-279.2\pm 3.7~{\rm km\, s}^{-1}$, and $\sigma _v=13.8^{+3.5}_{-2.6}~{\rm km\, s}^{-1}$. We measure its metallicity, and find it to be more metal rich than And XIX, implying that the two features are unrelated. Finally, And XIX’s dynamical and structural properties imply it is a local analogue to ultradiffuse galaxies (UDGs). Its complex dynamics suggest that the masses of distant UDGs measured from velocity dispersions alone should be carefully interpreted.

Subaru Hyper Suprime-Cam Survey for the Local Group Dwarf Galaxies: Ursa Minor

2018 ◽  
Vol 14 (S344) ◽  
pp. 94-95
Author(s):  
Yutaka Komiyama
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Structural Parameters ◽  
Deep Imaging ◽  
Ursa Minor ◽  
Red Giant

AbstractWe have carried out a wide and deep imaging survey for the Local Group dwarf spheroidal galaxy Ursa Minor (UMi) using Hyper Suprime-Cam (HSC). The data cover out beyond the nominal tidal radius down to ~25 mag in i band, which is ~2 mag below the main sequence turn-off point. The structural parameters of UMi are derived using red giant branch (RGB) stars and sub-giant branch (SGB) stars, and the tidal radius is suggested to be larger than those estimated by the previous studies. It is also found that the distribution of bluer RGB/SGB stars is more extended than that of redder RGB/SGB stars. The fraction of binary systems is estimated to be ~0.4 from the morphology of the main sequences.

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