19 research outputs found
Intermediate-mass black holes in Globular Clusters
For a sample of nine Galactic globular clusters we measured the inner
kinematic profiles with integral-field spectroscopy that we combined with
existing outer kinematic measurements and HST luminosity profiles. With this
information we are able to detect the crucial rise in the velocity-dispersion
profile which indicates the presence of a central black hole. In addition,
N-body simulations compared to our data will give us a deeper insight in the
properties of clusters with black holes and stronger selection criteria for
further studies. For the first time, we obtain a homogeneous sample of globular
cluster integral- field spectroscopy which allows a direct comparison between
clusters with and without an intermediate-mass black hole.Comment: 4 pages, 2 figures. To appear in the conference proceedings "Reading
the book of globular clusters with the lens of stellar evolution", Mem. S. A.
It. Eds. P. Ventura, C. Charbonnel, M. Castellani and M. Di Criscienz
Revealing the Formation of the Milky Way Nuclear Star Cluster via Chemo-Dynamical Modeling
The Milky Way nuclear star cluster (MW NSC) has been used as a template to
understand the origin and evolution of galactic nuclei and the interaction of
nuclear star clusters with supermassive black holes. It is the only nuclear
star cluster with a supermassive black hole where we can resolve individual
stars to measure their kinematics and metal abundance to reconstruct its
formation history. Here, we present results of the first chemo-dynamical model
of the inner 1 pc of the MW NSC using metallicity and radial velocity data from
the KMOS spectrograph on the Very Large Telescope. We find evidence for two
kinematically and chemically distinct components in this region. The majority
of the stars belong to a previously known super-solar metallicity component
with a rotation axis perpendicular to the Galactic plane. However, we identify
a new kinematically distinct sub-solar metallicity component which contains
about 7\% of the stars and appears to be rotating faster than the main
component with a rotation axis that may be misaligned. This second component
may be evidence for an infalling star cluster or remnants of a dwarf galaxy,
merging with the MW NSC. These measurements show that the combination of
chemical abundances with kinematics is a promising method to directly study the
MW NSC's origin and evolution.Comment: 6 pages, 5 figures, accepted to ApJ Letter
Self-consistent modelling of the Milky Way's Nuclear Stellar Disc
© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stac639The Nuclear Stellar Disc (NSD) is a flattened high-density stellar structure that dominates the gravitational field of the Milky Way at Galactocentric radius pc. We construct axisymmetric self-consistent equilibrium dynamical models of the NSD in which the distribution function is an analytic function of the action variables. We fit the models to the normalised kinematic distributions (line-of-sight velocities + VIRAC2 proper motions) of stars in the NSD survey of Fritz et al., taking the foreground contamination due to the Galactic Bar explicitly into account using an -body model. The posterior marginalised probability distributions give a total mass of , roughly exponential radial and vertical scale-lengths of pc and pc respectively, and a velocity dispersion km/s that decreases with radius. We find that the assumption that the NSD is axisymmetric provides a good representation of the data. We quantify contamination from the Galactic Bar in the sample, which is substantial in most observed fields. Our models provide the full 6D (position+velocity) distribution function of the NSD, which can be used to generate predictions for future surveys. We make the models publicly available as part of the software package AGAMA.Peer reviewedFinal Accepted Versio
Early formation and recent starburst activity in the nuclear disk of the Milky Way
The nuclear disk is a dense stellar structure at the centre of the Milky Way, with a radius of ~150 pc (ref. 1). It has been a place of intense star formation in the past several tens of millions of years1-3, but its overall formation history has remained unknown2. Here, we report that the bulk of its stars formed at least 8 Gyr ago. After a long period of quiescence, a starburst event followed about 1 Gyr ago that formed roughly 5% of its mass within ~100 Myr, in what may arguably have been one of the most energetic events in the history of the Milky Way. Star formation continued subsequently on a lower level, creating a few per cent of the stellar mass in the past ~500 Myr, with an increased rate up to ~30 Myr ago. Our findings contradict the previously accepted paradigm of quasi-continuous star formation at the Galactic Centre4. The long quiescent phase agrees with the overall quiescent history of the Milky Way2,5 and suggests that our Galaxy's bar may not have existed until recently, or that gas transport through the bar was extremely inefficient during a long stretch of the Milky Way's life. Consequently, the central black hole may have acquired most of its mass already in the early days of the Milky Way
PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628
We combine archival HST and new JWST imaging data, covering the ultraviolet
to mid-infrared regime, to morphologically analyze the nuclear star cluster
(NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200
pc x 400 pc cavity, lacking both dust and gas. We find roughly constant values
for the effective radius (r_eff ~ 5 pc) and ellipticity ({\epsilon} ~ 0.05),
while the S\'ersic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and
PA ~ 130{\deg} to 90{\deg}, respectively. In the mid-infrared, r_eff ~ 12pc,
{\epsilon} ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90{\deg}. The NSC has a
stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V,
confirmed when using multi-wavelength data, and in agreement with the
literature value. Fitting the spectral energy distribution, excluding the
mid-infrared data, yields a main stellar population's age of (8 +- 3) Gyr with
a metallicity of Z = 0.012 +- 0.006. There is no indication of any significant
star formation over the last few Gyr. Whether gas and dust were dynamically
kept out or evacuated from the central cavity remains unclear. The best-fit
suggests an excess of flux in the mid-infrared bands, with further indications
that the center of the mid-infrared structure is displaced with respect to the
optical center of the NSC. We discuss five potential scenarios, none of them
fully explaining both the observed photometry and structure.Comment: 26 pages, 10 figures, 6 tables. Accepted for publication by ApJ
The JWST Galactic Center Survey -- A White Paper
The inner hundred parsecs of the Milky Way hosts the nearest supermassive
black hole, largest reservoir of dense gas, greatest stellar density, hundreds
of massive main and post main sequence stars, and the highest volume density of
supernovae in the Galaxy. As the nearest environment in which it is possible to
simultaneously observe many of the extreme processes shaping the Universe, it
is one of the most well-studied regions in astrophysics. Due to its proximity,
we can study the center of our Galaxy on scales down to a few hundred AU, a
hundred times better than in similar Local Group galaxies and thousands of
times better than in the nearest active galaxies. The Galactic Center (GC) is
therefore of outstanding astrophysical interest. However, in spite of intense
observational work over the past decades, there are still fundamental things
unknown about the GC. JWST has the unique capability to provide us with the
necessary, game-changing data. In this White Paper, we advocate for a JWST
NIRCam survey that aims at solving central questions, that we have identified
as a community: i) the 3D structure and kinematics of gas and stars; ii)
ancient star formation and its relation with the overall history of the Milky
Way, as well as recent star formation and its implications for the overall
energetics of our galaxy's nucleus; and iii) the (non-)universality of star
formation and the stellar initial mass function. We advocate for a large-area,
multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy
in the form of a Treasury GO JWST Large Program that is open to the community.
We describe how this survey will derive the physical and kinematic properties
of ~10,000,000 stars, how this will solve the key unknowns and provide a
valuable resource for the community with long-lasting legacy value.Comment: This White Paper will be updated when required (e.g. new authors
joining, editing of content). Most recent update: 24 Oct 202
On the origin of a rotating metal-poor stellar population in the Milky Way Nuclear Cluster
We explore the origin of a population of stars recently detected in the inner parsec of the Milky
Way Nuclear Cluster (NC), which exhibit sub-solar metallicity and a higher rotation compared to
the dominant population. Using state-of-the-art N-body simulations, we model the infall of massive
stellar systems into the Galactic center, both of Galactic and extra-galactic origin. We show that
the newly discovered population can either be the remnant of a massive star cluster formed a few
kpc away from the Galactic center (Galactic scenario) or be accreted from a dwarf galaxy originally
located at 10-100 kpc (extragalactic scenario) and that reached the Galactic center