36 research outputs found
GALACTICNUCLEUS: A high-angular-resolution imaging survey of the Galactic centre. IV. Extinction maps and de-reddened photometry
The extreme extinction (\,mag) and its variation on arc-second
scales towards the Galactic centre hamper the study of its stars. Their
analysis is restricted to the near infrared (NIR) regime, where the extinction
curve can be approximated by a broken power law. Therefore, correcting for
extinction is fundamental to analyse the structure and stellar population of
the central regions of our Galaxy. We aim to, (1) discuss different strategies
to de-redden the photometry and check the usefulness of extinction; (2) build
extinction maps for the NIR bands and make them publicly available; (3)
create a de-reddened catalogue of the GALACTICNUCLEUS (GNS) survey, identifying
foreground stars; and (4) perform a preliminary analysis of the de-reddened
luminosity functions (KLFs). We used photometry from the GNS survey to
create extinction maps for the whole catalogue. We took red clump (RC) and red
giant stars of similar brightnesses as a reference to build the maps and
de-reddened the GNS photometry. We discussed the limitations of the process and
analysed non-linear effects of the de-reddening. We obtained high resolution
() extinction maps with low uncertainties (\,\%) and
computed average extinctions for each of the regions covered by the GNS. We
checked that our maps effectively correct the differential extinction reducing
the spread of the RC features by a factor of . We assessed the validity
of the broken power law approach computing two equivalent extinction maps
using either and photometry for the same reference stars and
obtained compatible average extinctions within the uncertainties. Finally, we
analysed de-reddened KLFs for different lines of sight and found that the
regions belonging to the NSD contain a homogeneous stellar population that is
significantly different from that in the innermost bulge regions.Comment: Updated to the final version accepted for publication in Astronomy &
Astrophysics. 17 pages, 11 figure
GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre III. Evidence for wavelength dependence of the extinction curve in the near-infrared
The characterisation of the extinction curve in the near infrared (NIR) is
fundamental to analyse the structure and stellar population of the Galactic
centre (GC), whose analysis is hampered by the extreme interstellar extinction
( mag) that varies on arc-second scales. Recent studies indicate
that the behaviour of the extinction curve might be more complex than
previously assumed, pointing towards a variation of the extinction curve as a
function of wavelength. We aim at analysing the variations of the extinction
index, , with wavelength, line-of-sight, and absolute extinction,
extending previous analysis to a larger area of the innermost regions of the
Galaxy. We analysed the whole GALACTICNUCLEUS survey, a high-angular resolution
() NIR survey specially designed to observe the GC in
unprecedented detail. It covers a region of \,pc, comprising
fields in the nuclear stellar disc, the inner bulge, and the transition region
between them. We applied two independent methods based on red clump (RC) stars
to constrain the extinction curve and analysed its variation superseding
previous studies. We used more than 165,000 RC stars and increased
significantly the size of the regions analysed to confirm that the extinction
curve varies with the wavelength. We estimated a difference between the obtained extinction indices,
and . We also concluded that there is no
significant variation of the extinction curve with wavelength, with the
line-of-sight or the absolute extinction. Finally, we computed the ratios
between extinctions, and ,
consistent with all the regions of the GALACTICNUCLEUS catalogue.Comment: 10 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre I. Catalog of Variable Sources
We used four-year baseline HST/WFC3 IR observations of the Galactic Centre in
the F153M band (1.53 micron) to identify variable stars in the central
~2.3'x2.3' field. We classified 3845 long-term (periods from months to years)
and 76 short-term (periods of a few days or less) variables among a total
sample of 33070 stars. For 36 of the latter ones, we also derived their periods
(<3 days). Our catalog not only confirms bright long period variables and
massive eclipsing binaries identified in previous works, but also contains many
newly recognized dim variable stars. For example, we found \delta Scuti and RR
Lyrae stars towards the Galactic Centre for the first time, as well as one BL
Her star (period < 1.3 d). We cross-correlated our catalog with previous
spectroscopic studies and found that 319 variables have well-defined stellar
types, such as Wolf-Rayet, OB main sequence, supergiants and asymptotic giant
branch stars. We used colours and magnitudes to infer the probable variable
types for those stars without accurately measured periods or spectroscopic
information. We conclude that the majority of unclassified variables could
potentially be eclipsing/ellipsoidal binaries and Type II Cepheids. Our source
catalog will be valuable for future studies aimed at constraining the distance,
star formation history and massive binary fraction of the Milky Way nuclear
star cluster.Comment: has been accepted to be published in MNRAS, 64 pages, 26 figures. The
complete lists of table 3, 4, 8 and 9 will be published onlin
Near-Infrared Variability Study of the Central 2.3 arcmin x 2.3 arcmin of the Galactic Centre II. Identification of RR Lyrae Stars in the Milky Way Nuclear Star Cluster
Because of strong and spatially highly variable interstellar extinction and
extreme source crowding, the faint (K>15) stellar population in the Milky Way's
nuclear cluster is still poorly studied. RR Lyrae stars provide us with a tool
to estimate the mass of the oldest, relative dim stellar population. Recently,
we analyzed HST/WFC3/IR observations of the central 2.3'x2.3' of the Milky Way
and found 21 variable stars with periods between 0.2 and 1d. Here, we present a
further comprehensive analysis of these stars. The period-luminosity
relationship of RR Lyrae is used to derive their extinctions and distances.
Using multiple approaches, we classify our sample as four RRc, four RRab and
three candidates, ten binaries. Especially, the four RRabs show sawtooth light
curves and fall exactly onto the Oosterhoff I division in the Bailey diagram.
Compared to the RRabs reported by Minniti et al, 2016, our new RRabs have
higher extinction (A_K>1.8) and should be closer to the Galactic Centre. The
extinction and distance of one RRab match those for the nuclear star cluster
given in previous works. We perform simulations and find that after correcting
for incompleteness, there could be no more than 40 RRabs within the nuclear
star cluster and in our field-of-view. Through comparing with the known
globular clusters of the Milky Way, we estimate that if there exists an old,
metal-poor (-1.5<[Fe/H]<-1) stellar population in the Milky Way nuclear star
cluster on a scale of 5x5pc, then it contributes at most 4.7x10^5 solar mass,
i.e., ~18% of the stellar mass.Comment: 33 pages, 10 figures. The paper has been accepted to be published in
MNRA
Jeans modelling of the Milky Way's nuclear stellar disc
The nuclear stellar disc (NSD) is a flattened stellar structure that
dominates the gravitational potential of the Milky Way at Galactocentric radii
. In this paper, we construct
axisymmetric Jeans dynamical models of the NSD based on previous photometric
studies and we fit them to line-of-sight kinematic data of APOGEE and SiO maser
stars. We find that (i) the NSD mass is lower but consistent with the mass
independently determined from photometry by Launhardt et al. (2002). Our
fiducial model has a mass contained within spherical radius
of and a total
mass of . (ii) The NSD
might be the first example of a vertically biased disc, i.e. with ratio between
the vertical and radial velocity dispersion . Observations
and theoretical models of the star-forming molecular gas in the central
molecular zone suggest that large vertical oscillations may be already
imprinted at stellar birth. However, the finding
depends on a drop in the velocity dispersion in the innermost few tens of
parsecs, on our assumption that the NSD is axisymmetric, and that the available
(extinction corrected) stellar samples broadly trace the underlying light and
mass distributions, all of which need to be established by future observations
and/or modelling. (iii) We provide the most accurate rotation curve to date for
the innermost of our Galaxy.Comment: Accepted for publication in MNRA
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
Kinematics of Galactic Centre clouds shaped by shear-seeded solenoidal turbulence
The Central Molecular Zone (CMZ; the central ~ 500 pc of the Galaxy) is a
kinematically unusual environment relative to the Galactic disc, with high
velocity dispersions and a steep size-linewidth relation of the molecular
clouds. In addition, the CMZ region has a significantly lower star formation
rate (SFR) than expected by its large amount of dense gas. An important factor
in explaining the low SFR is the turbulent state of the star-forming gas, which
seems to be dominated by rotational modes. However, the turbulence driving
mechanism remains unclear. In this work, we investigate how the Galactic
gravitational potential affects the turbulence in CMZ clouds. We focus on the
CMZ cloud G0.253+0.016 (`the Brick'), which is very quiescent and unlikely to
be kinematically dominated by stellar feedback. We demonstrate that several
kinematic properties of the Brick arise naturally in a cloud-scale
hydrodynamics simulation that takes into account the Galactic gravitational
potential. These properties include the line-of-sight velocity distribution,
the steepened size-linewidth relation, and the predominantly solenoidal nature
of the turbulence. Within the simulation, these properties result from the
Galactic shear in combination with the cloud's gravitational collapse. This is
a strong indication that the Galactic gravitational potential plays a crucial
role in shaping the CMZ gas kinematics, and is a major contributor to
suppressing the SFR by inducing predominantly solenoidal turbulent modes.Comment: 7 pages, 8 figures; accepted to MNRAS (July 24th 2023