48 research outputs found
Learning the relationship between galaxies spectra and their star formation histories using convolutional neural etworks and cosmological simulations
We present a new method for inferring galaxy star formation histories (SFH) using machine learning methods coupled with two cosmological hydrodynamic simulations. We train Convolutional Neural Networks to learn the relationship between synthetic galaxy spectra and high resolution SFHs from the EAGLE and Illustris models. To evaluate our SFH reconstruction we use Symmetric Mean Absolute Percentage Error (SMAPE), which acts as a true percentage error in the low-error regime. On dust-attenuated spectra we achieve high test accuracy (median SMAPE = 10.5%). Including the effects of simulated observational noise increases the error (12.5%), however this is alleviated by including multiple realisations of the noise, which increases the training set size and reduces overfitting (10.9%). We also make estimates for the observational and modelling errors. To further evaluate the generalisation properties we apply models trained on one simulation to spectra from the other, which leads to only a small increase in the error (median SMAPE ∼15%). We apply each trained model to SDSS DR7 spectra, and find smoother histories than in the VESPA catalogue. This new approach complements the results of existing SED fitting techniques, providing star formation histories directly motivated by the results of the latest cosmological simulations
AGN Feedback in SDSS-IV MaNGA: AGNs have Suppressed Central Star Formation Rates
Despite the importance of feedback from active galactic nuclei (AGNs) in
models of galaxy evolution, observational constraints on the influence of AGN
feedback on star formation remain weak. To this end, we have compared the star
formation trends of 279 low-redshift AGN galaxies with 558 inactive control
galaxies using integral field unit spectroscopy from the SDSS-IV MaNGA survey.
With a Gaussian process-based methodology, we reconstruct nonparametric star
formation histories in spatially resolved spaxels covering the face of each
galaxy. Based on galaxy-wide star formation rates (SFRs) alone, we find no
obvious signatures of AGN feedback. However, the AGN galaxies have
significantly suppressed central (kiloparsec-scale) SFRs, lying up to a factor
of below those of the control galaxies, providing direct observational
evidence of AGN feedback suppressing star formation. The suppression of central
SFRs in the AGN galaxies began in the central regions Gyr ago
(redshift ), taking place over a few gigayears. A small subset of
the AGN galaxies were rapidly driven to quiescence shortly before being
observed (in the last Myr), potentially indicating instances of
AGN-driven feedback. More frequently, however, star formation continues in the
AGN galaxies, with suppression primarily in the central regions. This is
suggestive of a picture in which integrated (Gyr-timescale) AGN feedback can
significantly affect central star formation, but may be inefficient in driving
galaxy-wide quenching in low-redshift galaxies, instead leaving them in the
green valley.Comment: 22 pages, 15 figures. Accepted for publication in Ap
A Hierarchy of Normalizing Flows for Modelling the Galaxy-Halo Relationship
Using a large sample of galaxies taken from the Cosmology and Astrophysics
with MachinE Learning Simulations (CAMELS) project, a suite of hydrodynamic
simulations varying both cosmological and astrophysical parameters, we train a
normalizing flow (NF) to map the probability of various galaxy and halo
properties conditioned on astrophysical and cosmological parameters. By
leveraging the learnt conditional relationships we can explore a wide range of
interesting questions, whilst enabling simple marginalisation over nuisance
parameters. We demonstrate how the model can be used as a generative model for
arbitrary values of our conditional parameters; we generate halo masses and
matched galaxy properties, and produce realisations of the halo mass function
as well as a number of galaxy scaling relations and distribution functions. The
model represents a unique and flexible approach to modelling the galaxy-halo
relationship.Comment: 8 pages, 2 figures, accepted for ICML 2023 Workshop on Machine
Learning for Astrophysic
Outshining by Recent Star Formation Prevents the Accurate Measurement of High-z Galaxy Stellar Masses
In this Letter, we demonstrate that the inference of galaxy stellar masses
via spectral energy distribution (SED) fitting techniques for galaxies formed
in the first billion years after the Big Bang carries fundamental uncertainties
owing to the loss of star formation history (SFH) information from the very
first episodes of star formation in the integrated spectra of galaxies. While
this early star formation can contribute substantially to the total stellar
mass of high-redshift systems, ongoing star formation at the time of detection
outshines the residual light from earlier bursts, hampering the determination
of accurate stellar masses. As a result, order of magnitude uncertainties in
stellar masses can be expected. We demonstrate this potential problem via
direct numerical simulation of galaxy formation in a cosmological context. In
detail, we carry out two cosmological simulations with significantly different
stellar feedback models which span a significant range in star formation
history burstiness. We compute the mock SEDs for these model galaxies at z=7
via 3D dust radiative transfer calculations, and then backwards fit these SEDs
with Prospector SED fitting software. The uncertainties in derived stellar
masses that we find for z>7 galaxies motivate the development of new techniques
and/or star formation history priors to model early Universe star formation.Comment: Submitted to ApJL, comments welcom
The SFR-M <sub>∗</sub> Correlation Extends to Low Mass at High Redshift
To achieve a fuller understanding of galaxy evolution, SED fitting can be
used to recover quantities beyond stellar masses (M) and star formation
rates (SFRs). We use Star Formation Histories (SFHs) reconstructed via the
Dense Basis method of Iyer \& Gawiser (2017) for a sample of galaxies
at in the CANDELS GOODS-S field to study the nature and evolution of
the SFR-M correlation. The reconstructed SFHs represent trajectories in
SFR-M space, enabling us to study galaxies at epochs earlier than observed
by propagating them backwards in time along these trajectories. We study the
SFR-M correlation at using both direct fits to galaxies
observed at those epochs and SFR-M trajectories of galaxies observed at
lower redshifts. The SFR-M correlations obtained using the two approaches
are found to be consistent with each other through a KS test. Validation tests
using SFHs from semi-analytic models and cosmological hydrodynamical
simulations confirm the sensitivity of the method to changes in the slope,
normalization and shape of the SFR-M correlation. This technique allows us
to further probe the low-mass regime of the correlation at high-z by
dex and over an effective volume of larger than possible with
just direct fits. We find that the SFR-M correlation is consistent with
being linear down to M at . The evolution of the
correlation is well described by , where is the age of the universe in Gyr.Comment: 22 pages, 10 figures. Accepted for publication in Ap
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
CDM not dead yet: massive high-z Balmer break galaxies are less common than previously reported
Early JWST observations that targeted so-called double-break sources
(attributed to Lyman and Balmer breaks at ), reported a previously unknown
population of very massive, evolved high-redshift galaxies. This surprising
discovery led to a flurry of attempts to explain these objects' unexpected
existence including invoking alternatives to the standard CDM
cosmological paradigm. To test these early results, we adopted the same
double-break candidate galaxy selection criteria to search for such objects in
the JWST images of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS), and
found a sample of 19 sources over five independent CANUCS fields that cover a
total effective area of arcmin at . However, (1) our SED
fits do not yield exceptionally high stellar masses for our candidates, while
(2) spectroscopy of five of the candidates shows that while all five are at
high redshifts, their red colours are due to high-EW emission lines in
star-forming galaxies rather than Balmer breaks in massive, evolved systems.
Additionally, (3) field-to-field variance leads to differences of
dex in the maximum stellar masses measured in the different fields, suggesting
that the early single-field JWST observations may have suffered from cosmic
variance and/or sample bias. Finally, (4) we show that the presence of even a
single massive outlier can dominate conclusions from small samples such as
those in early JWST observations. In conclusion, we find that the double-break
sources in CANUCS are not sufficiently massive or numerous to warrant
questioning the standard CDM paradigm.Comment: V2: correction of display problem of Fig.1 in Chrome browser.
Submitted to MNRAS, 10 pages (+4 in Appendix), 5 figures (+4), 1 table (+1