15 research outputs found
Dark influences: imprints of dark satellites on dwarf galaxies
In the context of the current CDM cosmological model small dark
matter haloes are abundant and satellites of dwarf galaxies are expected to be
predominantly dark. Since low mass galaxies have smaller baryon fractions
interactions with these satellites may leave particularly dramatic imprints. We
uncover the influence of the most massive of these dark satellites on disky
dwarf galaxies and the possible dynamical and morphological transformations
that result from these interactions. We use a suite of carefully set-up,
controlled simulations of isolated dwarf galaxies. The primary dwarf galaxies
have solely a stellar disk in the dark matter halo and the secundaries are
completely devoid of baryons. We vary the disk mass, halo concentration,
initial disk thickness and inclination of the satellite orbit. The disky dwarf
galaxies are heated and disrupted due to the minor merger event, more extremely
for higher satellite over disk mass ratios, and the morphology and kinematics
are significantly altered. Moreover, for less concentrated haloes the minor
merger can completely destroy the disk leaving a low-luminosity spheroidal-like
galaxy instead. We conclude that dwarf galaxies are very much susceptible to
being disturbed by dark galaxies and that even a minor merger event can
significantly disrupt and alter the structure and kinematics of a dwarf galaxy.
This process may be seen as a new channel for the formation of dwarf spheroidal
galaxies.Comment: 16 pages, 13 figures, A&A accepted. For movies or a higher resolution
version see http://www.astro.rug.nl/~starkenb/dwarfsanddarks.htm
Dark influences III. Structural characterization of minor mergers of dwarf galaxies with dark satellites
In the current concordance cosmology small halos are expected to be
completely dark and can significantly perturb low-mass galaxies during minor
merger interactions. These interactions may well contribute to the diversity of
the dwarf galaxy population. Dwarf galaxies in the field are often observed to
have peculiarities in their structure, morphology, and kinematics, as well as
strong bursts of star formation without apparent cause. We aim to characterize
the signatures of minor mergers of dwarf galaxies with dark satellites to aid
their observational identification. We explore and quantify a variety of
structural, morphological, and kinematic indicators of merging dwarf galaxies
and their remnants using a suite of hydrodynamical simulations. The most
sensitive indicators of mergers with dark satellites are large asymmetries in
the gaseous and stellar distributions, enhanced central surface brightness and
starbursts, and velocity offsets and misalignments between the cold gas and
stellar components. In general, merging systems span a wide range of values of
the most commonly used indicators, while isolated objects tend to have more
confined values. Interestingly, we find in our simulations that a significantly
off-centered burst of star formation can pinpoint the location of the dark
satellite. Observational systems with such characteristics are perhaps the most
promising for unveiling the presence of the hitherto, missing satellites.Comment: 9 pages, 7 figures. Accepted in A&
How cosmological merger histories shape the diversity of stellar haloes
We introduce and apply a new approach to probe the response of galactic
stellar haloes to the interplay between cosmological merger histories and
galaxy formation physics. We perform dark-matter-only, zoomed simulations of
two Milky Way-mass hosts and make targeted, controlled changes to their
cosmological histories using the genetic modification technique. Populating
each history's stellar halo with a semi-empirical, particle-tagging approach
then enables a controlled study, with all instances converging to the same
large-scale structure, dynamical and stellar mass at as their reference.
These related merger scenarios alone generate an extended spread in stellar
halo mass fractions (1.5 dex) comparable to the observed population. Largest
scatter is achieved by growing late () major mergers that spread out
existing stars to create massive, in-situ dominated stellar haloes. Increasing
a last major merger at brings more accreted stars into the inner
regions, resulting in smaller scatter in the outskirts which are predominantly
built by subsequent minor events. Exploiting the flexibility of our
semi-empirical approach, we show that the diversity of stellar halo masses
across scenarios is reduced by allowing shallower slopes in the stellar
mass--halo mass relation for dwarf galaxies, while it remains conserved when
central stars are born with hotter kinematics across cosmic time. The
merger-dependent diversity of stellar haloes thus responds distinctly to
assumptions in modelling the central and dwarf galaxies respectively, opening
exciting prospects to constrain star formation and feedback at different
galactic mass-scales with the coming generation of deep, photometric
observatories.Comment: Main text 11 pages, 7 figures. Submitted to MNRAS, comments welcom
On the origin of star-gas counterrotation in low-mass galaxies
Stars in galaxies form from the cold rotationally supported gaseous disks
that settle at the center of dark matter halos. In the simplest models, such
angular momentum is acquired early on at the time of collapse of the halo and
preserved thereafter, implying a well-aligned spin for the stellar and gaseous
component. Observations however have shown the presence of gaseous disks in
counterrotation with the stars. We use the Illustris numerical simulations to
study the origin of such counterrotation in low mass galaxies ( - ), a sample where mergers have
not played a significant role. Only of our sample shows a
counterrotating gaseous disk at . These counterrotating disks arise in
galaxies that have had a significant episode of gas removal followed by the
acquisition of new gas with misaligned angular momentum. In our simulations, we
identify two main channels responsible for the gas loss: a strong feedback
burst and gas stripping during a fly-by passage through a more massive group
environment. Once settled, counterrotation can be long-lived with several
galaxies in our sample displaying misaligned components consistently for more
than Gyr. As a result, no major correlation with the present day
environment or structural properties might remain, except for a slight
preference for early type morphologies and a lower than average gas content at
a given stellar mass.Comment: 16 pages, 11 figures. Submitted to ApJ. Comments welcom
Decoupling the rotation of stars and gas - II. The link between black hole activity and simulated IFU kinematics in IllustrisTNG
Funding: UK Science and Technology Funding Council ( STFC) via an PhD studentship (grant number ST/N504427/1) (CD).We study the relationship between supermassive black hole (BH) feedback, BH luminosity and the kinematics of stars and gas for galaxies inIllustrisTNG. We use galaxies with mock MaNGA observations to identify kinematic misalignment at z = 0 (difference in rotation of stars and gas), for which we follow the evolutionary history of BH activity and gas properties over the last 8 Gyrs. Misaligned low mass galaxies (Mstel 1010.2Mâ) with misalignment typically have similar BH luminosities, show lower gas fractions, and have typically lower gas phase metallicity over the last 8 Gyrs in comparison to the high mass aligned.Publisher PDFPeer reviewe
IQ Collaboratory III: The Empirical Dust Attenuation Framework -- Taking Hydrodynamical Simulations with a Grain of Dust
We present the Empirical Dust Attenuation (EDA) framework -- a flexible
prescription for assigning realistic dust attenuation to simulated galaxies
based on their physical properties. We use the EDA to forward model synthetic
observations for three state-of-the-art large-scale cosmological hydrodynamical
simulations: SIMBA, IllustrisTNG, and EAGLE. We then compare the optical and UV
color-magnitude relations, and , of the
simulations to a and UV complete SDSS galaxy sample using
likelihood-free inference. Without dust, none of the simulations match
observations, as expected. With the EDA, however, we can reproduce the observed
color-magnitude with all three simulations. Furthermore, the attenuation curves
predicted by our dust prescription are in good agreement with the observed
attenuation-slope relations and attenuation curves of star-forming galaxies.
However, the EDA does not predict star-forming galaxies with low since
simulated star-forming galaxies are intrinsically much brighter than
observations. Additionally, the EDA provides, for the first time, predictions
on the attenuation curves of quiescent galaxies, which are challenging to
measure observationally. Simulated quiescent galaxies require shallower
attenuation curves with lower amplitude than star-forming galaxies. The EDA,
combined with forward modeling, provides an effective approach for shedding
light on dust in galaxies and probing hydrodynamical simulations. This work
also illustrates a major limitation in comparing galaxy formation models: by
adjusting dust attenuation, simulations that predict significantly different
galaxy populations can reproduce the same UV and optical observations.Comment: 26 pages, 15 figure
The Diversity and Variability of Star Formation Histories in Models of Galaxy Evolution
Understanding the variability of galaxy star formation histories (SFHs)
across a range of timescales provides insight into the underlying physical
processes that regulate star formation within galaxies. We compile the SFHs of
galaxies at from an extensive set of models, ranging from cosmological
hydrodynamical simulations (Illustris, IllustrisTNG, Mufasa, Simba, EAGLE),
zoom simulations (FIRE-2, g14, and Marvel/Justice League), semi-analytic models
(Santa Cruz SAM) and empirical models (UniverseMachine), and quantify the
variability of these SFHs on different timescales using the power spectral
density (PSD) formalism. We find that the PSDs are well described by broken
power-laws, and variability on long timescales ( Gyr) accounts for
most of the power in galaxy SFHs. Most hydrodynamical models show increased
variability on shorter timescales ( Myr) with decreasing stellar
mass. Quenching can induce dex of additional power on timescales
Gyr. The dark matter accretion histories of galaxies have remarkably
self-similar PSDs and are coherent with the in-situ star formation on
timescales Gyr. There is considerable diversity among the different models
in their (i) power due to SFR variability at a given timescale, (ii) amount of
correlation with adjacent timescales (PSD slope), (iii) evolution of median
PSDs with stellar mass, and (iv) presence and locations of breaks in the PSDs.
The PSD framework is a useful space to study the SFHs of galaxies since model
predictions vary widely. Observational constraints in this space will help
constrain the relative strengths of the physical processes responsible for this
variability.Comment: 31 pages, 17 figures (+ appendix). Resubmitted to MNRAS after
responding to referee's comments. Comments are welcome
The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations
Understanding the rate at which stars form is central to studies of galaxy
formation. Observationally, the star formation rates (SFRs) of galaxies are
measured using the luminosity in different frequency bands, often under the
assumption of a time-steady SFR in the recent past. We use star formation
histories (SFHs) extracted from cosmological simulations of star-forming
galaxies from the FIRE project to analyze the time-scales to which the
H and far-ultraviolet (FUV) continuum SFR indicators are sensitive.
In these simulations, the SFRs are highly time variable for all galaxies at
high redshift, and continue to be bursty to z=0 in dwarf galaxies. When FIRE
SFHs are partitioned into their bursty and time-steady phases, the best-fitting
FUV time-scale fluctuates from its ~10 Myr value when the SFR is time-steady to
>~100 Myr immediately following particularly extreme bursts of star formation
during the bursty phase. On the other hand, the best-fitting averaging
time-scale for H is generally insensitive to the SFR variability in
the FIRE simulations and remains ~5 Myr at all times. These time-scales are
shorter than the 100 Myr and 10 Myr time-scales sometimes assumed in the
literature for FUV and H, respectively, because while the FUV
emission persists for stellar populations older than 100 Myr, the
time-dependent luminosities are strongly dominated by younger stars. Our
results confirm that the ratio of SFRs inferred using H vs. FUV can
be used to probe the burstiness of star formation in galaxies.Comment: 14 pages, 10 figures, accepted to MNRA