34 research outputs found
Measuring the physical imprints of gas flows in galaxies I: Accretion rate histories
Galaxies are expected to accrete pristine gas from their surroundings to
sustain their star formation over cosmic timescales. Its lower abundance
affects the metallicity of the ISM in which stars are born, leaving chemical
imprints in the stellar populations. We measure the amount of pristine gas that
galaxies accrete during their lifetime, using information on the ages and
abundances of their stellar populations and a chemical evolution model. We also
aim to determine the efficiency of star formation over time. We derived star
formation histories and metallicity histories for a sample of 8523 galaxies
from the MaNGA survey. We use the former to predict the evolution of the
metallicity in a closed-box scenario, and estimate for each epoch the gas
accretion rate required to match these predictions with the measured stellar
metallicity. Using only chemical parameters, we find that the history of gas
accretion depends on the mass of galaxies. More massive galaxies accrete more
gas and at higher redshifts than less massive galaxies, which accrete their gas
over longer periods. We also find that galaxies with a higher star formation
rate at z = 0 have a more persistent accretion history for a given mass. The
star formation efficiency shows similar correlations: early-type galaxies and
higher-mass galaxies had a higher efficiency in the past, and it declined such
that they are less efficient in the present. Our analysis of individual
galaxies shows that compactness affects the peak star formation efficiency that
galaxies reach, and that the slope of the efficiency history of galaxies with
current star formation is flat. Our results support the hypothesis that a
steady and substantial supply of pristine gas is required for persistent star
formation in galaxies. Once they lose access to this gas supply, star formation
comes to a halt.Comment: 17 pages, 11 figures. Accepted at A&
CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass and radius
We study the components of cool and warm/hot gas in the circumgalactic medium
(CGM) of simulated galaxies and address the relative production of OVI by
photoionization versus collisional ionization, as a function of halo mass,
redshift, and distance from the galaxy halo center. This is done utilizing two
different suites of zoom-in hydro-cosmological simulations, VELA (6 halos;
) and NIHAO (18 halos; to ), which provide a broad theoretical basis
because they use different codes and physical recipes for star formation and
feedback. In all halos studied in this work, we find that collisional
ionization by thermal electrons dominates at high redshift, while
photoionization of cool or warm gas by the metagalactic radiation takes over
near . In halos of and above, collisions become
important again at , while photoionization remains significant down to
for less massive halos. In halos with , at most of the photoionized OVI is in a
warm, not cool, gas phase (~K). We also find that
collisions are dominant in the central regions of halos, while photoionization
is more significant at the outskirts, around , even in massive
halos. This too may be explained by the presence of warm gas or, in lower mass
halos, by cool gas inflows
Galactoseismology in cosmological simulations: Vertical perturbations by dark matter, satellite galaxies and gas
Only recently, complex models that include the global dynamics from dwarf
satellite galaxies, dark matter halo structure, gas infalls, and stellar disk
in a cosmological context became available to study the dynamics of disk
galaxies such as the Milky Way (MW). We use a MW model from a high-resolution
hydrodynamical cosmological simulation named GARROTXA to establish the
relationship between the vertical disturbances seen in its galactic disk and
multiple perturbations, from the dark matter halo, satellites and gas.
We calculate the bending modes in the galactic disk in the last 6 Gyr of
evolution. To quantify the impact of dark matter and gas we compute the
vertical acceleration exerted by these components onto the disk and compare
them with the bending behavior with Fourier analysis. We find complex bending
patterns at different radii and times, such as an inner retrograde mode with
high frequency, as well as an outer slower retrograde mode excited at different
times. The amplitudes of these bending modes are highest during the early
stages of the thin disk formation and reach up to 8.5 km s-1 in the late disk
evolution. We find that the infall of satellite galaxies leads to a tilt of the
disk, and produces anisotropic gas accretion with subsequent star formation
events, and supernovae, creating significant vertical accelerations onto the
disk plane. The misalignment between the disk and the inner stellar/dark matter
triaxial structure, formed during the ancient assembly of the galaxy, creates a
strong vertical acceleration on the stars.
We conclude that several agents trigger the bending of the stellar disk and
its phase spirals in this simulation, including satellite galaxies, dark
sub-halos, misaligned gaseous structures, and the inner dark matter profile,
which coexist and influence each other, making it challenging to establish
direct causality
Kinematic analysis of the Large Magellanic Cloud using Gaia DR3
Context: The high quality of the Gaia mission data is allowing to study the
internal kinematics of the Large Magellanic Cloud (LMC) in unprecedented
detail, providing insights on the non-axisymmetric structure of its disc. Aims:
To define and validate an improved selection strategy to distinguish the LMC
stars from the Milky Way foreground. To check the possible biases that assumed
parameters or sample contamination from the Milky Way can introduce in the
analysis of the internal kinematics of the LMC using Gaia data. Methods: Our
selection is based on a supervised Neural Network classifier using as much as
of the Gaia DR3 data as possible. We select three samples of candidate LMC
stars with different degrees of completeness and purity; we validate them using
different test samples and we compare them with the Gaia Collaboration paper
sample. We analyse the resulting velocity profiles and maps, and we check how
these results change when using also the line-of-sight velocities, available
for a subset of stars. Results: The contamination in the samples from Milky Way
stars affects basically the results for the outskirts of the LMC, and the
absence of line-of-sight velocities does not bias the results for the
kinematics in the inner disc. For the first time, we perform a kinematic
analysis of the LMC using samples with the full three dimensional velocity
information from Gaia DR3. Conclusions: The dynamics in the inner disc is
mainly bar dominated; the kinematics on the spiral arm over-density seem to be
dominated by an inward motion and a rotation faster than that of the disc in
the piece of the arm attached to the bar; contamination of MW stars seem to
dominate the outer parts of the disc and mainly affects old evolutionary
phases; uncertainties in the assumed disc morphological parameters and
line-of-sight velocity of the LMC can in some cases have significant effects.
[ABRIDGED
THE AGORA HIGH-RESOLUTION GALAXY SIMULATIONS COMPARISON PROJECT. II. ISOLATED DISK TEST
Using an isolated Milky Way-mass galaxy simulation, we compare results from nine state-of-the-art gravito-hydrodynamics codes widely used in the numerical community. We utilize the infrastructure we have built for the AGORA High-resolution Galaxy Simulations Comparison Project. This includes the common disk initial conditions, common physics models (e.g., radiative cooling and UV background by the standardized package Grackle) and common analysis toolkit yt, all of which are publicly available. Subgrid physics models such as Jeans pressure floor, star formation, supernova feedback energy, and metal production are carefully constrained across code platforms. With numerical accuracy that resolves the disk scale height, we find that the codes overall agree well with one another in many dimensions including: gas and stellar surface densities, rotation curves, velocity dispersions, density and temperature distribution functions, disk vertical heights, stellar clumps, star formation rates, and Kennicutt-Schmidt relations. Quantities such as velocity dispersions are very robust (agreement within a few tens of percent at all radii) while measures like newly formed stellar clump mass functions show more significant variation (difference by up to a factor of ∼3). Systematic differences exist, for example, between mesh-based and particle-based codes in the low-density region, and between more diffusive and less diffusive schemes in the high-density tail of the density distribution. Yet intrinsic code differences are generally small compared to the variations in numerical implementations of the common subgrid physics such as supernova feedback. Our experiment reassures that, if adequately designed in accordance with our proposed common parameters, results of a modern high-resolution galaxy formation simulation are more sensitive to input physics than to intrinsic differences in numerical schemes
Galactic archaeology with asteroseismology and spectroscopy: Red giants observed by CoRoT and APOGEE
With the advent of the space missions CoRoT and Kepler, it has recently become feasible to determine precise asteroseismic masses and relative ages for large samples of red giant stars. We present the CoRoGEE dataset, obtained from CoRoT light curves for 606 red giants in two fields of the Galactic disc that have been co-observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). We used the Bayesian parameter estimation code PARAM to calculate distances, extinctions, masses, and ages for these stars in a homogeneous analysis, resulting in relative statistical uncertainties of ≲2% in distance, ~4% in radius, ~9% in mass and ~25% in age. We also assessed systematic age uncertainties stemming from different input physics and mass loss. We discuss the correlation between ages and chemical abundance patterns of field stars over a broad radial range of the Milky Way disc (5 kpc <RGal< 14 kpc), focussing on the [α/Fe]-[Fe/H]-age plane in five radial bins of the Galactic disc. We find an overall agreement with the expectations of pure chemical-evolution models computed before the present data were available, especially for the outer regions. However, our data also indicate that a significant fraction of stars now observed near and beyond the solar neighbourhood migrated from inner regions. Mock CoRoGEE observations of a chemodynamical Milky Way disc model indicate that the number of high-metallicity stars in the outer disc is too high to be accounted for even by the strong radial mixing present in the model. The mock observations also show that the age distribution of the [α/Fe]-enhanced sequence in the CoRoGEE inner-disc field is much broader than expected from a combination of radial mixing and observational errors. We suggest that a thick-disc/bulge component that formed stars for more than 3 Gyr may account for these discrepancies. Our results are subject to future improvements due to (a) the still low statistics, because our sample had to be sliced into bins of Galactocentric distances and ages; (b) large uncertainties in proper motions (and therefore guiding radii); and (c) corrections to the asteroseismic mass-scaling relation. The situation will improve not only upon the upcoming Gaia data releases, but also with the foreseen increase in the number of stars with both seismic and spectroscopic information
Kinematics of symmetric Galactic longitudes to probe the spiral arms of the Milky Way with
Aims. We model the effects of the spiral arms of the Milky Way on the disk stellar kinematics in the Gaia observable space. We also estimate the Gaia capabilities of detecting the predicted signatures.
Methods. We use both controlled orbital integrations in analytic potentials and self-consistent simulations. We introduce a new strategy to investigate the effects of spiral arms, which consists of comparing the stellar kinematics of symmetric Galactic longitudes (+l and −l), in particular the median transverse velocity as determined from parallaxes and proper motions. This approach does not require the assumption of an axisymmetric model because it involves an internal comparison of the data.
Results. The typical differences between the transverse velocity in symmetric longitudes in the models are of the order of ~2 km s-1, but can be larger than 10 km s-1 for certain longitudes and distances. The longitudes close to the Galactic centre and to the anti-centre are those with larger and smaller differences, respectively. The differences between the kinematics for +l and −l show clear trends that depend strongly on the properties of spiral arms. Thus, this method can be used to quantify the importance of the effects of spiral arms on the orbits of stars in the different regions of the disk, and to constrain the location of the arms, main resonances and, thus, pattern speed. Moreover, the method allows us to test different origin scenarios of spiral arms and the dynamical nature of the spiral structure (e.g. grand design versus transient multiple arms). We estimate the number of stars of each spectral type that Gaia will observe in certain representative Galactic longitudes, their characteristic errors in distance and transverse velocity, and the error in computing the median velocity as a function of distance. We will be able to measure the median transverse velocity exclusively with Gaia data, with precision smaller than ~1 km s-1 up to distances of ~4–6 kpc for certain giant stars, and up to ~2–4 kpc and better kinematic precision (≲0.5 km s-1) for certain sub-giants and dwarfs. These are enough to measure the typical signatures seen in the models.
Conclusions. The Gaia catalogue will allow us to use the presented approach successfully and improve significantly upon current studies of the dynamics of the spiral arms of our Galaxy. We also show that a similar strategy can be used with line-of-sight velocities, which could be applied to Gaia data and to upcoming spectroscopic surveys
Large scale characterization of the stellar velocity distribution in the galactic disk
Test particle simulations of Milky Way type galactic disks are being conducted to map the evolution of the stellar large scale kinematic response to the bar and spiral structure. Second and third order moments of the velocity distribution function prove to be good indicators of both, the velocity ellipsoid misalignment near the arms and the bar, and the degree of kinematic substructure in the UV plane, that is, the presence of moving groups. A large scale analysis all through the galactic disk allows to establish the kinematic behavior near resonances and the correlation between the kinematic parameters and properties of the non-axisymmetric components, such as its transient nature or its mass overdensity. N-body simulaions are being run in order to test these results in self-consistent models
Erratum: Phase spirals in cosmological simulations of Milky Way-sized galaxies
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