30 research outputs found
Are we observing a NSC in course of formation in the NGC 4654 galaxy?
We use direct -body simulations to explore some possible scenarios for the
future evolution of two massive clusters observed toward the center of
NGC\,4654, a spiral galaxy with mass similar to that of the Milky Way. Using
archival HST data, we obtain the photometric masses of the two clusters,
M and M, their half-light
radii, pc and pc, and their projected
distances from the photometric center of the galaxy (both pc). The
knowledge of the structure and separation of these two clusters ( pc)
provides a unique view for studying the dynamics of a galactic central zone
hosting massive clusters. Varying some of the unknown clusters orbital
parameters, we carry out several -body simulations showing that the future
evolution of these clusters will inevitably result in their merger. We find
that, mainly depending on the shape of their relative orbit, they will merge
into the galactic center in less than 82 Myr. In addition to the tidal
interaction, a proper consideration of the dynamical friction braking would
shorten the merging times up to few Myr. We also investigate the possibility to
form a massive NSC in the center of the galaxy by this process. Our analysis
suggests that for low eccentricity orbits, and relatively long merger times,
the final merged cluster is spherical in shape, with an effective radius of few
parsecs and a mass within the effective radius of the order of
. Because the central density of such a cluster is
higher than that of the host galaxy, it is likely that this merger remnant
could be the likely embryo of a future NSC.Comment: 10 Pages, 11 Figures, 2 Tables. Published in MNRA
The Milky Way like galaxy NGC 6384 and its nuclear star cluster at high NIR spatial resolution using LBT/ARGOS commissioning data
We analyse high spatial resolution near infra-red (NIR) imaging of NGC6384, a
Milky Way like galaxy, using ARGOS commissioning data at the Large Binocular
Telescope (LBT). ARGOS provides a stable PSF AO
correction of the ground layer across the LUCI2 NIR camera field
by using six laser guide stars (three per telescope) and a natural guide star
for tip-tilt sensing and guiding. Enabled by this high spatial resolution we
analyse the structure of the nuclear star cluster (NSC) and the central
kiloparsec of NGC6384. We find via 2D modelling that the NSC (pc) is surrounded by a small (pc)
and a larger Sersi\'c (pc), all embedded within the
NGC\,6384 large-scale boxy/X-shaped bulge and disk. This proof-of-concept study
shows that with the high spatial resolution achieved by ground-layer AO we can
push such analysis to distances previously only accessible from space.
SED-fitting to the NIR and optical HST photometry allowed to leverage the
age-metallicity-extinction degeneracies and derive the effective NSC properties
of an young to old population mass ratio of with , Age$_{\rm old,\
young}\!=\!10.9\pm1.3\pm62\%=\!-0.11\pm0.160.33\pm39\%E(B\!-\!V)\!=\!0.63$ and
1.44mag.Comment: 12 pages (+9 appendix), 11 figures, Accepted in MNRA
The Discovery of a Gravitationally Lensed Quasar at z = 6.51
Strong gravitational lensing provides a powerful probe of the physical
properties of quasars and their host galaxies. A high fraction of the most
luminous high-redshift quasars was predicted to be lensed due to magnification
bias. However, no multiple imaged quasar was found at z>5 in previous surveys.
We report the discovery of J043947.08+163415.7, a strongly lensed quasar at
z=6.51, the first such object detected at the epoch of reionization, and the
brightest quasar yet known at z>5. High-resolution HST imaging reveals a
multiple imaged system with a maximum image separation theta ~ 0.2", best
explained by a model of three quasar images lensed by a low luminosity galaxy
at z~0.7, with a magnification factor of ~50. The existence of this source
suggests that a significant population of strongly lensed, high redshift
quasars could have been missed by previous surveys, as standard color selection
techniques would fail when the quasar color is contaminated by the lensing
galaxy.Comment: 8 pages, 4 figures, submitted to ApJ
ALMA Observations of the Sub-kpc Structure of the Host Galaxy of a z= 6.5 Lensed Quasar: A Rotationally-Supported Hyper-Starburst System at the Epoch of Reionization
We report ALMA observations of the dust continuum and {\cii} emission of the
host galaxy of J0439+1634, a gravitationally lensed quasar at .
Gravitational lensing boosts the source-plane resolution to \sim0\farcs15
. The lensing model derived from the ALMA data is
consistent with the fiducial model in \citet{fan19} based on {\it HST} imaging.
The host galaxy of J0439+1634 can be well-fitted by a S\'ersic profile
consistent with an exponential disk, both in the far-infrared (FIR) continuum
and the {\cii} emission. The overall magnification is for the
continuum and for the {\cii} line. The host galaxy of J0439+1634
is a compact ultra-luminous infrared galaxy, with a total star formation rate
(SFR) of after correcting for lensing and
an effective radius of kpc. The resolved regions in J0439+1634 follow
the ``{\cii} deficit," where the {\cii}-to-FIR ratio decreases with FIR surface
brightness. The reconstructed velocity field of J0439+1634 appears to be
rotation-like. The maximum line-of-sight rotation velocity of 130 km/s at a
radius of 2 kpc. However, our data cannot be fit by an axisymmetric thin
rotating disk, and the inclination of the rotation axis, , remains
unconstrained. We estimate the dynamical mass of the host galaxy to be
. J0439+1634 is likely to have a high
gas-mass fraction and an oversized SMBH compared to local relations. The SFR of
J0439+1634 reaches the maximum possible values, and the SFR surface density is
close to the highest value seen in any star-forming galaxy currently known in
the universe.Comment: 14 pages, 7 figures. Accepted by Ap
Supermassive black holes in cosmological simulations - II : the AGN population and predictions for upcoming X-ray missions
In large-scale hydrodynamical cosmological simulations, the fate of massive galaxies is mainly dictated by the modelling of feedback from active galactic nuclei (AGNs). The amount of energy released by AGN feedback is proportional to the mass that has been accreted on to the black holes (BHs), but the exact subgrid modelling of AGN feedback differs in all simulations. While modern simulations reliably produce populations of quiescent massive galaxies at z = 10(45) erg s(-1) (although this is sensitive to AGN variability), and leads to smaller fractions of AGN in massive galaxies than in the observations at zPeer reviewe
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A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. III. Discrete Multicomponent Population-dynamical Models Based on the Jeans Equations
We present comprehensive multicomponent dynamical models of M54 (NGC 6715), the nuclear star cluster of the Sagittarius (Sgr) dwarf galaxy, which is undergoing a tidal disruption in the Milky Way halo. Previous papers in this series used a large MUSE mosaic data set to identify multiple stellar populations in the system and study their kinematic differences. Here, we use Jeans-based dynamical models that fit the population properties (mean age and metallicity), spatial distributions, and kinematics simultaneously. They provide a solid physical explanation for our previous findings. Population-dynamical models deliver a comprehensive view of the whole system, and allow us to disentangle the different stellar populations. We explore their dynamical interplay and confirm our previous findings about the build-up of Sgr’s nuclear cluster via contributions from globular cluster stars, Sgr inner field stars, and in situ star formation. We explore various parameterizations of the gravitational potential and show the importance of a radially varying mass-to-light ratio for the proper treatment of the mass profile. We find a total dynamical mass within M54's tidal radius (∼75 pc) of 1.60 ± 0.07 × 106 M ⊙ in excellent agreement with N-body simulations. Metal-poor globular cluster stars contribute about 65% of the total mass or 1.04 ± 0.05 × 106 M ⊙. Metal-rich stars can be further divided into young and intermediate-age populations, which contribute 0.32 ± 0.02 × 106 M ⊙ (20%) and 0.24 ± 0.02 × 106 M ⊙ (15%), respectively. Our population-dynamical models successfully distinguish the different stellar populations in Sgr’s nucleus because of their different spatial distributions, ages, metallicities, and kinematic features
Metal-poor nuclear star clusters in two dwarf galaxies near Centaurus A suggesting formation from the in-spiraling of globular clusters
Studies of nucleated dwarf galaxies can constrain the scenarios for the formation and evolution of nuclear star clusters (NSC) in
low-mass galaxies and give us insights on the origin of ultra compact dwarf galaxies (UCDs). We report the discovery of a NSC
in the dwarf galaxy KKs58 and investigate its properties together with those of another NSC in KK197. Both NSCs are hosted by
dwarf elliptical galaxies of the Centaurus group. Combining ESO VLT MUSE data with photometry from VLT FORS2, CTIO Blanco
DECam, and HST ACS, as well as high-resolution spectroscopy from VLT UVES, we analyse the photometric, kinematic and stellar
population properties of the NSCs and their host galaxies. We confirm membership of the NSCs based on their radial velocities and
location close to the galaxy centres. We also confirm the membership of two globular clusters (GCs) and detect oblate rotation in the
main body of KK197. Based on high signal-to-noise spectra taken with MUSE of the NSCs of both KKs58 and KK197 we measure
low metallicities, [Fe/H] = −1.75 ± 0.06 dex and [Fe/H] = −1.84 ± 0.05 dex, and stellar masses of 7.3 × 105 M and 1.0 × 106 M ,
respectively. Both NSCs are more metal-poor than their hosts that have metallicities of −1.35±0.23 dex (KKs58) and −0.84±0.12 dex
(KK197). This can be interpreted as NSC formation via the in-spiral of GCs. The masses, sizes and metallicities of the two NSCs
place them among other NSCs, but also among the known UCDs of the Centaurus group. This indicates that NSCs might constitute
the progenitors of a part of the low-mass UCDs, although their properties are almost indistinguishable from typical GCs.OM is grateful to the Swiss National Science Foundation for financial support.
GvdV acknowledges funding from the European Research Council (ERC) under
the European Union’s Horizon 2020 research and innovation programme under
grant agreement No 724857 (Consolidator Grant ArcheoDyn). HJ acknowledges
support from the Australian Research Council through the Discovery Project
DP150100862
New insights into the star formation histories of candidate intermediate-age early-type galaxies from K'-band imaging of globular clusters
We investigate age and metallicity distributions of bright globular clusters
(GCs) in the candidate intermediate-age early-type galaxies NGC 3610, NGC 584
and NGC 3377 using a combination of new Gemini/NIRI K'-band imaging and
existing optical V,I photometry from HST data. The V-I vs I-K' colour-colour
diagram is found to break the age-metallicity degeneracy present in optical
colours, as I-K' primarily measures a populations' metallicity and is
relatively insensitive, unlike optical spectroscopy, to the effect of hot
horizontal branch (HB) stars, known to be present in massive old GCs. We derive
GCs' photometric age, Z and masses. In general, metal-poor ([Z/H]<-0.7dex) GCs
are older than more metal-rich GCs. For the most massive GCs (M>6x10^5 M_sol)
in NGC 3610 with available spectroscopic data, photometric ages are older by ~2
Gyr, and this difference is more pronounced for the metal-poor GCs. However,
photometric and spectroscopic metallicities are in good agreement. We suggest
that this indicates the presence of a hot HB in these massive clusters, which
renders spectroscopic ages from Balmer line strengths to be underestimated. To
support this suggestion we show that all Galactic GCs with M>6x10^5 M_sol
feature hot HBs, except 47 Tuc. Using the relation between the most massive GC
mass and the galaxy's SFR, we find that the galaxies' peak SFR was attained at
the epoch of the formation of the oldest (metal-poor) GCs. Age and [Z/H]
distributions of the metal-rich GCs are broad, indicating prolonged galaxy star
formation histories. The peak value of the age and [Z/H] distributions of the
GCs correlates with host galaxy integrated age and [Z/H], showing that GCs can
indeed be used as relevant proxies of the star formation histories of
galaxies.(Abridged)Comment: Accepted by MNRAS; 18 pages, 12 figures, 6 tables (v2 added
references