137 research outputs found
The ALMaQUEST Survey - V. The non-universality of kpc-scale star formation relations and the factors that drive them
ABSTRACT
Using a sample of âŒ15â000 kpc-scale star-forming spaxels in 28 galaxies drawn from the ALMA-MaNGA QUEnching and STar formation (ALMaQUEST) survey, we investigate the galaxy-to-galaxy variation of the âresolvedâ SchmidtâKennicutt relation (rSK; âÎŁSFR), the âresolvedâ star-forming main sequence (rSFMS; ÎŁââÎŁSFR), and the âresolvedâ molecular gas main sequence (rMGMS; ÎŁââ). The rSK relation, rSFMS, and rMGMS all show significant galaxy-to-galaxy variation in both shape and normalization, indicating that none of these relations is universal between galaxies. The rSFMS shows the largest galaxy-to-galaxy variation and the rMGMS the least. By defining an âoffsetâ from the average relations, we compute a ÎrSK, ÎrSFMS, ÎrMGMS for each galaxy, to investigate correlations with global properties. We find the following correlations with at least 2Ï significance: The rSK is lower (i.e. lower star formation efficiency) in galaxies with higher Mâ, larger Sersic index, and lower specific SFR (sSFR); the rSFMS is lower (i.e. lower sSFR) in galaxies with higher Mâ and larger Sersic index; and the rMGMS is lower (i.e. lower gas fraction) in galaxies with lower sSFR. In the ensemble of all 15â000 data points, the rSK relation and rMGMS show equally tight scatters and strong correlation coefficients, compared with a larger scatter and weaker correlation in the rSFMS. Moreover, whilst there is no correlation between ÎrSK and ÎrMGMS in the sample, the offset of a galaxyâs rSFMS does correlate with both of the other two offsets. Our results therefore indicate that the rSK and rMGMS are independent relations, whereas the rSFMS is a result of their combination.ERC
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Are galactic star formation and quenching governed by local, global, or environmental phenomena?
We present an analysis of star formation and quenching in the SDSS-IV
MaNGA-DR15, utilising over 5 million spaxels from 3500 local galaxies. We
estimate star formation rate surface densities () via dust
corrected flux where possible, and via an empirical relationship
between specific star formation rate (sSFR) and the strength of the 4000
Angstrom break (D4000) in all other cases. We train a multi-layered artificial
neural network (ANN) and a random forest (RF) to classify spaxels into `star
forming' and `quenched' categories given various individual (and groups of)
parameters. We find that global parameters (pertaining to the galaxy as a
whole) perform collectively the best at predicting when spaxels will be
quenched, and are substantially superior to local/ spatially resolved and
environmental parameters. Central velocity dispersion is the best single
parameter for predicting quenching in central galaxies. We interpret this
observational fact as a probable consequence of the total integrated energy
from AGN feedback being traced by the mass of the black hole, which is well
known to correlate strongly with central velocity dispersion. Additionally, we
train both an ANN and RF to estimate values directly via
regression in star forming regions. Local/ spatially resolved parameters are
collectively the most predictive at estimating in these
analyses, with stellar mass surface density at the spaxel location ()
being by far the best single parameter. Thus, quenching is fundamentally a
global process but star formation is governed locally by processes within each
spaxel.ERC Advanced Grant: 695671 "Quench
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How do central and satellite galaxies quench? - Insights from spatially resolved spectroscopy in the MaNGA survey
We investigate how star formation quenching proceeds within central and
satellite galaxies using spatially resolved spectroscopy from the SDSS-IV MaNGA
DR15. We adopt a complete sample of star formation rate surface densities
(), derived in Bluck et al. (2020), to compute the distance
at which each spaxel resides from the resolved star forming main sequence
( relation): . We study
galaxy radial profiles in , and luminosity weighted
stellar age (), split by a variety of intrinsic and environmental
parameters. Via several statistical analyses, we establish that the quenching
of central galaxies is governed by intrinsic parameters, with central velocity
dispersion () being the most important single parameter. High mass
satellites quench in a very similar manner to centrals. Conversely, low mass
satellite quenching is governed primarily by environmental parameters, with
local galaxy over-density () being the most important single
parameter. Utilising the empirical - relation, we estimate
that quenching via AGN feedback must occur at , and is marked by steeply rising radial
profiles in the green valley, indicating `inside-out' quenching. On the other
hand, environmental quenching occurs at over-densities of 10 - 30 times the
average galaxy density at z0.1, and is marked by steeply declining
profiles, indicating `outside-in' quenching. Finally,
through an analysis of stellar metallicities, we conclude that both intrinsic
and environmental quenching must incorporate significant starvation of gas
supply.ERC
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The ALMaQUEST Survey: The Molecular Gas Main Sequence and the Origin of the Star-forming Main Sequence
The origin of the star forming main sequence ( i.e., the relation between
star formation rate and stellar mass, globally or on kpc-scales; hereafter
SFMS) remains a hotly debated topic in galaxy evolution. Using the ALMA-MaNGA
QUEnching and STar formation (ALMaQUEST) survey, we show that for star forming
spaxels in the main sequence galaxies, the three local quantities,
star-formation rate surface density (\sigsfr), stellar mass surface density
(\sigsm), and the \h2~mass surface density (\sigh2), are strongly correlated
with one another and form a 3D linear (in log) relation with dispersion. In
addition to the two well known scaling relations, the resolved SFMS (\sigsfr~
vs. \sigsm) and the Schmidt-Kennicutt relation (\sigsfr~ vs. \sigh2; SK
relation), there is a third scaling relation between \sigh2~ and \sigsm, which
we refer to as the `molecular gas main sequence' (MGMS). The latter indicates
that either the local gas mass traces the gravitational potential set by the
local stellar mass or both quantities follow the underlying total mass
distributions. The scatter of the resolved SFMS ( dex) is the
largest compared to those of the SK and MGMS relations ( 0.2 dex).
A Pearson correlation test also indicates that the SK and MGMS relations are
more strongly correlated than the resolved SFMS. Our result suggests a scenario
in which the resolved SFMS is the least physically fundamental and is the
consequence of the combination of the SK and the MGMS relations
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Towards robust determination of non-parametric morphologies in marginal astronomical data: Resolving uncertainties with cosmological hydrodynamical simulations
Quantitative morphologies, such as asymmetry and concentration, have long
been used as an effective way to assess the distribution of galaxy starlight in
large samples. Application of such quantitative indicators to other data
products could provide a tool capable of capturing the 2-dimensional
distribution of a range of galactic properties, such as stellar mass or
star-formation rate maps. In this work, we utilize galaxies from the Illustris
and IllustrisTNG simulations to assess the applicability of concentration and
asymmetry indicators to the stellar mass distribution in galaxies.
Specifically, we test whether the intrinsic values of concentration and
asymmetry (measured directly from the simulation stellar mass particle maps)
are recovered after the application of measurement uncertainty and a point
spread function (PSF). We find that random noise has a non-negligible
systematic effect on asymmetry that scales inversely with signal-to-noise,
particularly at signal-to-noise less than 100. We evaluate different methods to
correct for the noise contribution to asymmetry at very low signal-to-noise,
where previous studies have been unable to explore due to systematics. We
present algebraic corrections for noise and resolution to recover the intrinsic
morphology parameters. Using Illustris as a comparison dataset, we evaluate the
robustness of these fits in the presence of a different physics model, and
confirm these correction methods can be applied to other datasets. Lastly, we
provide estimations for the uncertainty on different correction methods at
varying signal-to-noise and resolution regimes.STFC
ER
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The ALMaQUEST Survey. VII. Star Formation Scaling Relations of Green Valley Galaxies
We utilize the ALMA-MaNGA QUEnch and STar formation (ALMaQUEST) survey to
investigate the kpc-scale scaling relations, presented as the resolved star
forming main sequence (rSFMS: vs. ), the
resolved Schmidt-Kennicutt relation (rSK: vs. ), and the resolved molecular gas main sequence (rMGMS: vs. ), for 11478 star-forming and 1414 retired spaxels
(oversampled by a factor of ) located in 22 green valley (GV) and 12
main sequence (MS) galaxies. For a given galaxy type (MS or GV), the retired
spaxels are found to be offset from the sequences formed by the star-forming
spaxels on the rSFMS, rSK, and rMGMS planes, toward lower absolute values of
sSFR, SFE, and by 1.1, 0.6, and 0.5 dex. The scaling
relations for GV galaxies are found to be distinct from that of the MS
galaxies, even if the analyses are restricted to the star-forming spaxels only.
It is found that for star-forming spaxels, sSFR, SFE, and in GV
galaxies are reduced by 0.36, 0.14, and 0.21 dex, respectively, compared
to those in MS galaxies. Therefore, the suppressed sSFR/SFE/ in
GV galaxies are associated with not only an increased proportion of retired
regions in GV galaxies but also a depletion of these quantities in star-forming
regions. Finally, the reduction of SFE and in GV galaxies
relative to MS galaxies is seen in both bulge and disk regions (albeit with
larger uncertainties), suggesting that statistically, quenching in the GV
population may persist from the inner to the outer regions
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ALMaQUEST. IV. The ALMA-MaNGA QUEnching and STar Formation (ALMaQUEST) Survey
The ALMaQUEST (ALMA-MaNGA QUEnching and STar formation) survey is a program
with spatially-resolved CO(1-0) measurements obtained with the Atacama
Large Millimeter Array (ALMA) for 46 galaxies selected from the Mapping Nearby
Galaxies at Apache Point Observatory (MaNGA) DR15 optical integral-field
spectroscopic survey. The aim of the ALMaQUEST survey is to investigate the
dependence of star formation activity on the cold molecular gas content at kpc
scales in nearby galaxies. The sample consists of galaxies spanning a wide
range in specific star formation rate (sSFR), including starburst (SB),
main-sequence (MS), and green valley (GV) galaxies. In this paper, we present
the sample selection and characteristics of the ALMA observations, and showcase
some of the key results enabled by the combination of spatially-matched stellar
populations and gas measurements. Considering the global (aperture-matched)
stellar mass, molecular gas mass, and star formation rate of the sample, we
find that the sSFR depends on both the star formation efficiency (SFE) and the
molecular gas fraction (), although the correlation with the
latter is slightly weaker. Furthermore, the dependence of sSFR on the molecular
gas content (SFE or ) is stronger than that on either the atomic
gas fraction or the molecular-to-atomic gas fraction, albeit with the small HI
sample size. On kpc scales, the variations in both SFE and
within individual galaxies can be as large as 1-2 dex thereby demonstrating
that the availability of spatially-resolved observations is essential to
understand the details of both star formation and quenching processes.STFC
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Fossil herbivore stable isotopes reveal middle Pleistocene hominin palaeoenvironment in âGreen Arabiaâ
Despite its largely hyper-arid and inhospitable climate today, the Arabian Peninsula is emerging as an important area for investigating Pleistocene hominin dispersals. Recently, a member of our own species was found in northern Arabia dating to c. 90 ka, while stone tools and fossil finds have hinted at an earlier, Middle Pleistocene, hominin presence. However, there remain few direct insights into Pleistocene environments, and associated hominin adaptations, that accompanied the movement of populations into this region. Here, we apply stable carbon and oxygen isotope analysis to fossil mammal tooth enamel (n=21) from the Middle Pleistocene locality of Tiâs al Ghadah in Saudi Arabia associated with newly-discovered lithics and probable cutmarks. The results demonstrate productive grasslands in the interior of the Arabian Peninsula c. 300-500 ka, as well as aridity levels similar to those found in open savanna settings in eastern Africa today. The association between this palaeoenvironmental information and the earliest traces for hominin activity in this part of the world lead us to argue that Middle Pleistocene hominin dispersal into the interior of the Arabian Peninsula required no major novel adaptation
Sedentary behaviour and biomarkers for cardiovascular disease and diabetes in mid-life: the role of television-viewing and sitting at work.
Knowledge of sedentary behaviour associations with health has relied mainly on television-viewing as a proxy and studies with other measures are less common. To clarify whether sedentary behaviour is associated with disease-risk, we examined associations for television-viewing and sitting at work
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