72 research outputs found
How well do local relations predict gas-phase metallicity gradients? : results from SDSS-IV MaNGA
Gas-phase metallicity gradients in galaxies provide important clues to those galaxies’ formation histories. Using SDSS-IV MaNGA data, we previously demonstrated that gas metallicity gradients vary systematically and significantly across the galaxy mass–size plane: at stellar masses beyond approximately 1010 M , more extended galaxies display steeper gradients (in units of dex/Re) at a given stellar mass. Here, we set out to develop a physical interpretation of these findings by examining the ability of local ∼kpc-scale relations to predict the gradient behaviour along the mass–size plane. We find that local stellar mass surface density, when combined with total stellar mass, is sufficient to reproduce the overall mass–size trend in a qualitative sense. We further find that we can improve the predictions by correcting for residual trends relating to the recent star formation histories of star-forming regions. However, we find as well that the most extended galaxies display steeper average gradients than predicted, even after correcting for residual metallicity trends with other local parameters. From these results, we argue that gas-phase metallicity gradients can largely be understood in terms of known local relations, but we also discuss some possible physical causes of discrepant gradients
SDSS-IV MaNGA: when is morphology imprinted on galaxies?
It remains an open question as to how long ago the morphology that we see in a present-day galaxy was typically imprinted. Studies of galaxy populations at different redshifts reveal that the balance of morphologies has changed over time, but such snapshots cannot uncover the typical time-scales over which individual galaxies undergo morphological transformation, nor which are the progenitors of today’s galaxies of different types. However, these studies also show a strong link between morphology and star formation rate (SFR) over a large range in redshift, which offers an alternative probe of morphological transformation. We therefore derive the evolution in SFR and stellar mass of a sample of 4342 galaxies in the SDSS-IV MaNGA survey through a stellar population ‘fossil record’ approach, and show that the average evolution of the population shows good agreement with known behaviour from previous studies. Although the correlation between a galaxy’s contemporaneous morphology and SFR is strong over a large range of lookback times, we find that a galaxy’s present-day morphology only correlates with its relatively recent (∼2Gyr) star formation history. We therefore find strong evidence that morphological transitions to galaxies’ current appearance occurred on time-scales as short as a few billion years
Integral-field kinematics and stellar populations of early-type galaxies out to three half-light radii
Funding: STFC grant ST/K502339/1 during the course of this work (NFB), Leverhulme Trust Early Career Fellowship (AW).We observed twelve nearby HI -detected early-type galaxies (ETGs) of stellar mass ∼ 1010 M⊙ ≤ M* ≤1011 M⊙ with the Mitchell Integral-Field Spectrograph, reaching approximately three half-light radii in most cases. We extracted line-of-sight velocity distributions for the stellar and gaseous components. We find little evidence of transitions in the stellar kinematics of the galaxies in our sample beyond the central effective radius, with centrally fast-rotating galaxies remaining fast-rotating and centrally slow-rotating galaxies likewise remaining slow-rotating. This is consistent with these galaxies having not experienced late dry major mergers; however, several of our objects have ionised gas that is misaligned with respect to their stars,suggesting some kind of past interaction. We extract Lick index measurements of the commonly-used Hβ, Fe5015, Mg, b, Fe5270 and Fe5335 absorption features, and we find most galaxies to have flat Hβ gradients and negative Mg, b gradients. We measure gradients of age, metallicity and abundance ratio for our galaxies using spectral fitting, and for the majority of our galaxies find negative age and metallicity gradients. We also find the stellar mass-to-light ratios to decrease with radius for most of the galaxies in our sample. Our results are consistent with a view in which intermediate-mass ETGs experience mostly quiet evolutionary histories, but in which many have experienced some kind of gaseous interaction in recent times.PostprintPeer reviewe
SDSS-IV MaNGA: spatially resolved dust attenuation in spiral galaxies
Dust attenuation in star-forming spiral galaxies affects stars and gas in
different ways due to local variations in dust geometry. We present spatially
resolved measurements of dust attenuation for a sample of 232 such star-forming
spiral galaxies, derived from spectra acquired by the SDSS-IV MaNGA survey. The
dust attenuation affecting the stellar populations of these galaxies (obtained
using full spectrum stellar population fitting methods) is compared with the
dust attenuation in the gas (derived from the Balmer decrement). Both of these
attenuation measures increase for local regions of galaxies with higher star
formation rates; the dust attenuation affecting the stellar populations
increases more so than the dust attenuation in the gas, causing the ratio of
the dust attenuation affecting the stellar populations to the dust attenuation
in the gas to decrease for local regions of galaxies with higher star formation
rate densities. No systematic difference is discernible in any of these dust
attenuation quantities between the spiral arm and inter-arm regions of the
galaxies. While both the dust attenuation in the gas and the dust attenuation
affecting the stellar populations decrease with galactocentric radius, the
ratio of the two quantities does not vary with radius. This ratio does,
however, decrease systematically as the stellar mass of the galaxy increases.
Analysis of the radial profiles of the two dust attenuation measures suggests
that there is a disproportionately high concentration of birth clouds
(incorporating gas, young stars and clumpy dust) nearer to the centres of
star-forming spiral galaxies.Comment: 17 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Societ
SDSS-IV MaNGA : exploring the local scaling relations for N/O
We present, for the first time, the relationship between local stellar mass surface density, Σ*, and N/O derived from SDSS-IV MaNGA data, using a sample of 792,765 high signal-to-noise ratio star-forming spaxels. Using a combination of phenomenological modeling and partial correlation analysis, we find that Σ* alone is insufficient to predict the N/O in MaNGA spaxels and that there is an additional dependence on the local star formation rate surface density, ΣSFR. This effect is a factor of 3 stronger than the dependence of 12+log(O/H) on ΣSFR. Surprisingly, we find that the local N/O scaling relations also depend on the total galaxy stellar mass at fixed Σ* and the galaxy size at fixed stellar mass. We find that more compact galaxies are more nitrogen rich, even when Σ* and ΣSFR are controlled for. We show that ~50% of the variance of N/O is explained by the total stellar mass and size. Thus, the evolution of nitrogen in galaxies is set by more than just local effects and does not simply track the buildup of oxygen in galaxies. The precise form of the N/O–O/H relation is therefore sensitive to the sample of galaxies from which it is derived. This result casts doubt on the universal applicability of nitrogen-based strongline metallicity indicators derived in the local universe
SDSS-IV MaNGA: drivers of stellar metallicity in nearby galaxies
The distribution of stellar metallicities within and across galaxies is an excellent relic of the chemical evolution across cosmic time. We present a detailed analysis of spatially resolved stellar populations based on >2.6 million spatial bins from 7439 nearby galaxies in the Sloan Digital Sky Survey-IV (SDSS-IV) Mapping Nearby Galaxies at APO (MaNGA) survey. To account for accurate inclination corrections, we derive an equation for morphology-dependent determination of galaxy inclinations. Our study goes beyond the well-known global mass-metallicity relation and radial metallicity gradients by providing a statistically sound exploration of local relations between stellar metallicity [Z/H], stellar surface mass density Σ∗, and galactocentric distance in the global mass-morphology plane. We find a significant resolved mass density-metallicity relation Σ ZR for galaxies of all types and masses above 109.8 M⊙. Different radial distances make an important contribution to the spread of the relation. Particularly, in low- and intermediate-mass galaxies, we find that at fixed Σ∗ metallicity increases with radius independently of morphology. For high masses, this radial dependence is only observed in high Σ∗ regions of spiral galaxies. This result calls for a driver of metallicity, in addition to Σ∗ that promotes chemical enrichment in the outer parts of galaxies more strongly than in the inner parts. We discuss gas accretion, outflows, recycling, and radial migration as possible scenarios.The Science and Technology Facilities Council is acknowledged for support through the Consolidated Grant Cosmology and Astrophysics at Portsmouth, ST/S000550/1. JL is supported by the National Science Foundation under Grant No. 2009993. JKB-B acknowledges support from the grant IA-100420 (DGAPA-PAPIIT, UNAM), and funding from the CONACYT grants CF 19-39578, CB-285080, and FC-2016-01-1916
Improved annotation of 3' untranslated regions and complex loci by combination of strand-specific direct RNA sequencing, RNA-seq and ESTs
The reference annotations made for a genome sequence provide the framework
for all subsequent analyses of the genome. Correct annotation is particularly
important when interpreting the results of RNA-seq experiments where short
sequence reads are mapped against the genome and assigned to genes according to
the annotation. Inconsistencies in annotations between the reference and the
experimental system can lead to incorrect interpretation of the effect on RNA
expression of an experimental treatment or mutation in the system under study.
Until recently, the genome-wide annotation of 3-prime untranslated regions
received less attention than coding regions and the delineation of intron/exon
boundaries. In this paper, data produced for samples in Human, Chicken and A.
thaliana by the novel single-molecule, strand-specific, Direct RNA Sequencing
technology from Helicos Biosciences which locates 3-prime polyadenylation sites
to within +/- 2 nt, were combined with archival EST and RNA-Seq data. Nine
examples are illustrated where this combination of data allowed: (1) gene and
3-prime UTR re-annotation (including extension of one 3-prime UTR by 5.9 kb);
(2) disentangling of gene expression in complex regions; (3) clearer
interpretation of small RNA expression and (4) identification of novel genes.
While the specific examples displayed here may become obsolete as genome
sequences and their annotations are refined, the principles laid out in this
paper will be of general use both to those annotating genomes and those seeking
to interpret existing publically available annotations in the context of their
own experimental dataComment: 44 pages, 9 figure
Size, shade or shape? The contribution of galaxies of different types to the star-formation history of the Universe from SDSS-IV MaNGA
By fitting stellar populations to SDSS-IV MaNGA survey observations of ~7000
suitably-weighted individual galaxies, we reconstruct the star-formation
history of the Universe, which we find to be in reasonable agreement with
previous studies. Dividing the galaxies by their present-day stellar mass, we
demonstrate the downsizing phenomenon, whereby the more massive galaxies hosted
the most star-formation at earlier times. Further dividing the galaxy sample by
colour and morphology, we find that a galaxy's present-day colour tells us more
about its historical contribution to the cosmic star formation history than its
current morphology. We show that downsizing effects are greatest among galaxies
currently in the blue cloud, but that the level of downsizing in galaxies of
different morphologies depends quite sensitively on the morphological
classification used, due largely to the difficulty in classifying the smaller
low-mass galaxies from their ground-based images. Nevertheless, we find
agreement that among galaxies with stellar masses
, downsizing is most significant in
spirals. However, there are complicating factors. For example, for more massive
galaxies, we find that colour and morphology are predictors of the past star
formation over a longer timescale than in less massive systems. Presumably this
effect is reflecting the longer period of evolution required to alter these
larger galaxies' physical properties, but shows that conclusions based on any
single property don't tell the full story.Comment: 16 pages, 21 figures. Accepted for publication in MNRA
SDSS-IV MaNGA: Exploring the local scaling relations for N/O
We present, for the first time, the relationship between local stellar mass
surface density, , and N/O derived from SDSS-IV MaNGA
data, using a sample of high signal-to-noise ratio star-forming
spaxels. Using a combination of phenomenological modelling and partial
correlation analysis, we find that alone is insufficient
to predict the N/O in MaNGA spaxels, and that there is an additional dependence
on the local star formation rate surface density, . This
effect is a factor of stronger than the dependence of 12+log(O/H) on
. Surprisingly, we find that the local N/O scaling
relations also depend on the total galaxy stellar mass at fixed as
well as the galaxy size at fixed stellar mass. We find that more compact
galaxies are more nitrogen rich, even when and
are controlled for. We show that of the
variance of N/O is explained by the total stellar mass and size. Thus, the
evolution of nitrogen in galaxies is set by more than just local effects and
does not simply track the build up of oxygen in galaxies. The precise form of
the N/O-O/H relation is therefore sensitive to the sample of galaxies from
which it is derived. This result casts doubt on the universal applicability of
nitrogen-based strong-line metallicity indicators derived in the local
universe.Comment: 22 pages, 14 figures. Accepted for publication in the Astrophysical
Journa
Association studies of up to 1.2 million individuals yield new insights into the genetic etiology of tobacco and alcohol use.
Tobacco and alcohol use are leading causes of mortality that influence risk for many complex diseases and disorders1. They are heritable2,3 and etiologically related4,5 behaviors that have been resistant to gene discovery efforts6-11. In sample sizes up to 1.2 million individuals, we discovered 566 genetic variants in 406 loci associated with multiple stages of tobacco use (initiation, cessation, and heaviness) as well as alcohol use, with 150 loci evidencing pleiotropic association. Smoking phenotypes were positively genetically correlated with many health conditions, whereas alcohol use was negatively correlated with these conditions, such that increased genetic risk for alcohol use is associated with lower disease risk. We report evidence for the involvement of many systems in tobacco and alcohol use, including genes involved in nicotinic, dopaminergic, and glutamatergic neurotransmission. The results provide a solid starting point to evaluate the effects of these loci in model organisms and more precise substance use measures
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