21 research outputs found
The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
We present an extensive study of the Sagittarius II (Sgr II) stellar system using MegaCam g and
i photometry, narrow-band, metallicity-sensitive calcium H&K doublet photometry and Keck
II/DEIMOS multiobject spectroscopy. We derive and refine the Sgr II structural and stellar
properties inferred at the time of its discovery. The colour–magnitude diagram implies Sgr II
is old (12.0 ± 0.5 Gyr) and metal poor. The CaHK photometry confirms the metal-poor nature
of the satellite ([Fe/H] CaHK = −2.32 ± 0.04 dex) and suggests that Sgr II hosts more than one
single stellar population (σ CaHK
[FeH] = 0.11+0.05 −0.03 dex). Using the Ca infrared triplet measured from
our highest signal-to-noise spectra, we confirm the metallicity and dispersion inferred from
the Pristine photometric metallicities ([Fe/H]spectro = −2.23 ± 0.05 dex, σspectro
[Fe/H] = 0.10+0.06 −0.04
dex). The velocity dispersion of the system is found to be σv = 2.7+1.3 −1.0 km s−1 after excluding
two potential binary stars. Sgr II’s metallicity and absolute magnitude (MV = −5.7 ± 0.1
mag) place the system on the luminosity–metallicity relation of the Milky Way dwarf galaxies
despite its small size. The low but resolved metallicity and velocity dispersions paint the picture
of a slightly dark-matter-dominated satellite (M/L = 23.0+32.8 −23.0 M L−1
). Furthermore, using
the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocentre of
118.4+28.4 −23.7 kpc and a pericentre of 54.8+3.3 −6.1 kpc. The orbit of Sgr II is consistent with the
trailing arm of the Sgr stream and indicates that it is possibly a satellite of the Sgr dSph that
was tidally stripped from the dwarf’s influence.ES, KY, and AA gratefully acknowledge funding by the Emmy
Noether programme from the Deutsche Forschungsgemeinschaft
(DFG). This work has been published under the framework of the
IdEx Unistra and benefits from a funding from the state managed
by theFrench National Research Agency as part of the investments
for the future program. NFM, RI, and NL gratefully acknowledge
support from the French National Research Agency (ANR) funded
project ‘Pristine’ (ANR-18-CE31-0017) along with funding from
CNRS/INSU through the Programme National Galaxies et Cosmologie and through the CNRS grant PICS07708. The authors
thank the International Space Science Institute (ISSI), Berne,
Switzerland for providing financial support and meeting facilities
to the international team ‘Pristine’. JIGH acknowledges financial
support from the Spanish Ministry project MINECO AYA2017-
86389-P, and from the Spanish MINECO under the 2013 Ramon y ´
Cajal program MINECO RYC-2013-14875.
BPML gratefully acknowledges support from FONDECYT postdoctoral fellowship No. 316051
Is Draco II one of the faintest dwarf galaxies? First study from Keck/DEIMOS spectroscopy
We present the first spectroscopic analysis of the faint and compact stellar
system Draco II (Dra II, M_V=-2.9+/-0.8, r_h=19^{+8}_{-6} pc), recently
discovered in the Pan-STARRS1 3{\pi} survey. The observations, conducted with
DEIMOS on the Keck II telescope, establish some of its basic characteristics:
the velocity data reveal a narrow peak with 9 member stars at a systemic
heliocentric velocity =-347.6^{+1.7}_{-1.8} km/s, thereby confirming Dra
II is a satellite of the Milky Way; we infer a velocity dispersion with
\sigma_{vr}=2.9+/-2.1 km/s (<8.4 km/s at the 95% confidence level), which
implies log_{10}(M_{1/2})=5.5^{+0.4}_{-0.6} and
log_{10}((M/L)_{1/2})=2.7^{+0.5}_{-0.8}, in Solar units; furthermore, very weak
Calcium triplet lines in the spectra of the high signal-to-noise member stars
imply [Fe/H]<-2.1, whilst variations in the line strengths of two stars with
similar colours and magnitudes suggest a metallicity spread in Dra II. These
new data cannot clearly discriminate whether Draco II is a star cluster or
amongst the faintest, most compact, and closest dwarf galaxies. However, the
sum of the three --- individually inconclusive --- pieces of evidence presented
here, seems to favour the dwarf galaxy interpretation.Comment: 5 pages, 4 figures, 1 table. Excepted for publication in MNRAS. Full
table 1 available upon request. v2: moderate revisions of the text,
conclusion unchange
Triangulum II: A Very Metal-poor and Dynamically Hot Stellar System
We present a study of the recently discovered compact stellar system
Triangulum II. From observations conducted with the DEIMOS spectrograph on Keck
II, we obtained spectra for 13 member stars that follow the CMD features of
this very faint stellar system and include two bright red giant branch stars.
Tri II has a very negative radial velocity (=-383.7^{+3.0}_{-3.3} km/s)
that translates to ~ -264 km/s and confirms it is a Milky Way
satellite. We show that, despite the small data set, there is evidence that Tri
II has complex internal kinematics. Its radial velocity dispersion increases
from 4.4^{+2.8}_{-2.0} km/s in the central 2' to 14.1^{+5.8}_{-4.2} km/s
outwards. The velocity dispersion of the full sample is inferred to be
\sigma_{vr}=9.9^{+3.2}_{-2.2} km/s. From the two bright RGB member stars we
measure an average metallicity =-2.6+/-0.2, placing Tri II among the
most metal-poor Milky Way dwarf galaxies. In addition, the spectra of the
fainter member stars exhibit differences in their line widths that could be the
indication of a metallicity dispersion in the system. All these properties
paint a complex picture for Tri II, whose nature and current state are largely
speculative. The inferred metallicity properties of the system however lead us
to favor a scenario in which Tri II is a dwarf galaxy that is either disrupting
or embedded in a stellar stream.Comment: 8 pages, 6 figures, 2 tables. ApJ, in press. v2: only minor changes
to the tex
Recommended from our members
Lacerta I and Cassiopeia III. Two Luminous and Distant Andromeda Satellite Dwarf Galaxies Found in the 3Ï€ Pan-STARRS1 Survey
We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI (Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in stacked Pan-STARRS1 r P1- and i P1-band imaging data. Both are luminous systems (MV ~ –12) located at projected distances of 20fdg3 and 10fdg5 from M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with heliocentric distances of and , respectively, and corresponding M31-centric distances of 275 ± 7 kpc and . The brightest of recent Local Group member discoveries, these two new dwarf galaxies owe their late discovery to their large sizes ( arcmin or for Lac I; arcmin or 1456 ± 267 pc for Cas III) and consequently low surface brightness (μ0 ~ 26.0 mag arcsec–2), as well as to the lack of a systematic survey of regions at large radii from M31, close to the Galactic plane. This latter limitation is now alleviated by the 3π Pan-STARRS1 survey, which could lead to the discovery of other distant Andromeda satellite dwarf galaxies.Astronom
A Rogues’ Gallery of Andromeda's Dwarf Galaxies. I. A Predominance of Red Horizontal Branches
We present homogeneous, sub-horizontal branch photometry of twenty dwarf
spheroidal satellite galaxies of M31 observed with the Hubble Space Telescope.
Combining our new data for sixteen systems with archival data in the same
filters for another four, we show that Andromeda dwarf spheroidal galaxies
favor strikingly red horizontal branches or red clumps down to ~10^{4.2} Lsun
(M_V ~ -5.8). The age-sensitivity of horizontal branch stars implies that a
large fraction of the M31 dwarf galaxies have extended star formation histories
(SFHs), and appear inconsistent with early star formation episodes that were
rapidly shutdown. Systems fainter than ~10^{5.5} Lsun show the widest range in
the ratios and morphologies of red and blue horizontal branches, indicative of
both complex SFHs and a diversity in quenching timescales and/or mechanisms,
which is qualitatively different from what is currently known for faint Milky
Way (MW) satellites of comparable luminosities. Our findings bolster similar
conclusions from recent deeper data for a handful of M31 dwarf galaxies. We
discuss several sources for diversity of our data such as varying halo masses,
patchy reionization, mergers/accretion, and the environmental influence of M31
and the Milky Way on the early evolution of their satellite populations. A
detailed comparison between the histories of M31 and MW satellites would shed
signifiant insight into the processes that drive the evolution of low-mass
galaxies. Such a study will require imaging that reaches the oldest main
sequence turnoffs for a significant number of M31 companions.Comment: 11 pages, 5 figures, 2 tables. ApJ in press. v2: small tweaks to the
results and discussion sectio
Lacerta i and cassiopeia III. Two luminous and distant andromeda satellite dwarf galaxies found in the 3Ï€ pan-starrs1 survey
We report the discovery of two new dwarf galaxies, Lacerta I/Andromeda XXXI
(Lac I/And XXXI) and Cassiopeia III/Andromeda XXXII (Cas III/And XXXII), in
stacked Pan-STARRS1 r_P1- and i_P1-band imaging data. Both are luminous systems
(M_V ~ -12) located at projected distances of 20.3{\deg} and 10.5{\deg} from
M31. Lac I and Cas III are likely satellites of the Andromeda galaxy with
heliocentric distances of 756^{+44}_{-28} kpc and 772^{+61}_{-56} kpc,
respectively, and corresponding M31-centric distances of 275+/-7 kpc and
144^{+6}_{-4} kpc . The brightest of recent Local Group member discoveries,
these two new dwarf galaxies owe their late discovery to their large sizes (r_h
= 4.2^{+0.4}_{-0.5} arcmin or 912^{+124}_{-93} pc for Lac I; r_h =
6.5^{+1.2}_{-1.0} arcmin or 1456+/-267 pc for Cas III), and consequently low
surface brightness (\mu_0 ~ 26.0 mag/arcsec^2), as well as to the lack of a
systematic survey of regions at large radii from M31, close to the Galactic
plane. This latter limitation is now alleviated by the 3{\pi} Pan-STARRS1
survey, which could lead to the discovery of other distant Andromeda satellite
dwarf galaxies.Comment: 7 pages, 5 figures. Accepted for publication in Ap
A la recherche et la caractérisation des galaxies plus sombres dans le groupe local avec le relevé Pan-STARRS 1
This thesis uses the Panoramic Survey Telescope and Rapid Response System 1 Survey to find new Local Group satellites such as dwarf galaxies and globular clusters. This survey is instrumental in helping resolve tensions that have become apparent between observation and theories. In a first phase, a search algorithm is developed, discovering five new satellites. Though yielding five discoveries, this number is lower than one would expect, assuming isotropy of the dwarf galaxies. This leads to the second aim of this thesis, namely quantifying the detection limits of the PS1 Survey. The detection efficiency maps over the entire PS1 sky can be used as a stepping–stone towards the quantification of the (an)isotropy of the Milky Way satellites’ distribution. Using this information, the luminosity function of these satellites can be re–derived.Cette thèse utilise le relevé de donné du Panoramic Survey Telescope and Rapid Response System 1 Survey pour trouver de nouveaux satellites du Groupe Local: les galaxies naines et les amas globulaires. Le relevé est important pour résoudre les tensions entre les observations et les modèles. Premièrement, un algorithme de détection est développé, découvrant cinq nouveaux satellites. Bien que cinq découvertes soient faites, le nombre de découvertes est inférieur à ce qu’on s’attendrait, en présumant une distribution isotrope de galaxies naines. Ce résultat mène au deuxième objectif de la these: quantifier les limites de détections du relevé PS1. Les cartes d’efficacité de détection du ciel complet peuvent être utilisées pour quantifier la distribution (an)isotrope des galaxies satellites de la Voie Lactée. En outre, ces informations peuvent mener a redériver la fonction de luminosité des satellites
Iodide-Mediated Synthesis of Spirooxindolo Dihydrofurans from Iodonium Ylides and 3‑Alkylidene-2-oxindoles
An iodide-mediated reaction between
cyclic iodonium ylides of 1,3-dicarbonyls
and 3-alkylidene-2-oxindoles results in 3<i>H</i>-spiroÂ[furan-2,3′-indolin]-2′-ones.
The reaction was tolerant to substitutions on both the alkylidene
and ylide substrates and provided access to 19 new, densely functionalized
polycyclic spirocycles in typically high yield