72 research outputs found
Links between Galaxy Structure and Stellar Populations
In this thesis we analyse the observational relations between galaxy structure and global stellar population properties to determine the dependencies between a galaxy's star formation and mass assembly histories. Stellar population parameters correlate with a range of galaxy properties, but it is unclear which relations are causal and which are the result of another underlying trend. The well-established correlations between mass and other galaxy properties are often considered evidence for mass driving a galaxy's evolution. However, we find that, at fixed mass, stellar population properties show significant dependence on size, indicating that the size of a galaxy is also an important property tracing, and possibly influencing, its evolution. The focus of the thesis is to quantitatively compare trends between various stellar population properties and key galaxy structural parameters, in particular the galaxy's mass (M), gravitational potential (M/R) and surface density (M/R^2), to determine which relations are intrinsically tighter and are therefore more likely to reflect a causal relation. We start by analysing a sample of 625 early-type galaxies (ETGs) from the SAMI survey. We show that, compared to correlations with mass, metallicity [Z/H] correlates strongly with M/R, while age correlates best with M/R^2. For [alpha/Fe], a proxy for star formation duration, we find comparable results for M/R and M/R^2, with both being significantly stronger correlations than the [alpha/Fe]--M relation. First, we concur with previous studies in finding that gravitational potential is the primary regulator of global metallicity by determining the escape velocity required for metal-rich supernova ejecta to escape the system and avoid being recycled into later stellar generations. Second, to explain the age and [alpha/Fe] correlations with M/R^2, we propose two possible mechanisms: (a)~the correlations arise as results of compactness-driven quenching mechanisms, and/or (b)~as fossil records of the \Sigma_SFR ~ \Sigma_gas relation in their disk-dominated progenitors. To test these conclusions, we study the ages and metallicities of 2085 star-forming galaxies (SFGs) from the SDSS Legacy survey. By investigating whether these relations are also present in earlier phases of galaxy evolution, we narrow the range of possible physical mechanisms responsible for producing them. As with the trends found in ETGs, we find that in SFGs age correlates best with M/R^2 and [Z/H] correlates best with M/R. Showing that the age--M/R^2 relation exists in star-forming galaxies demonstrates it must originate before quenching. We conclude that the age--M/R^2 relation is consistent with compact galaxies forming earlier, perhaps driven by higher gas fractions in the early Universe causing older galaxies to form more compactly during their in-situ formation phase. Lastly we investigate the change in age and metallicity relations for quiescent galaxies from intermediate redshift (0.60<z<0.76), using the LEGA-C survey, to z<0.11 using the SAMI survey. We find that, as for their low-redshift counterparts, the metallicity of quiescent galaxies at 0.60<z<0.76 correlates with M/R. This supports the hypothesis that the relation arises because the gravitational potential regulates the gas escape velocity. On the other hand, we find no correlation between age and M/R^2 in the LEGA-C sample, despite there being a strong relation at low redshift. We consider this change in the age--M/R^2 relation in the context of the redshift evolution of the star-forming and quiescent populations in the mass--size plane and find our results can be explained as a consequence of galaxies forming more compactly at higher redshift, and remaining compact throughout their evolution. The age--M/R^2 relation at z=0 results from the build-up of the quiescent and star-forming populations from galaxies that formed over a range of redshifts and therefore with a range of surface densities
Gravitational Potential and Surface Density Drive Stellar Populations -- II. Star-Forming Galaxies
Stellar population parameters correlate with a range of galaxy properties,
but it is unclear which relations are causal and which are the result of
another underlying trend. In this series, we quantitatively compare trends
between stellar population properties and galaxy structural parameters in order
to determine which relations are intrinsically tighter, and are therefore more
likely to reflect a causal relation. Specifically, we focus on the galaxy
structural parameters of mass , gravitational potential ,
and surface mass density . In Barone et al. (2018) we found
that for early-type galaxies the age- and [Z/H]- relations show
the least intrinsic scatter as well as the least residual trend with galaxy
size. In this work we study the ages and metallicities measured from full
spectral fitting of 2085 star-forming galaxies from the SDSS Legacy Survey,
selected so all galaxies in the sample are probed to one effective radius. As
with the trends found in early-type galaxies, we find that in star-forming
galaxies age correlates best with stellar surface mass density, and [Z/H]
correlates best with gravitational potential. We discuss multiple mechanisms
that could lead to these scaling relations. For the [Z/H]-- relation we
conclude that gravitational potential is the primary regulator of metallicity,
via its relation to the gas escape velocity. The age-- relation is
consistent with compact galaxies forming earlier, as higher gas fractions in
the early universe cause old galaxies to form more compactly during their
in-situ formation phase, and may be reinforced by compactness-related quenching
mechanisms.Comment: Accepted for publication in ApJ. 20 pages, 9 figures, 1 tabl
The gas-phase metallicities of star-forming galaxies in aperture-matched SDSS samples follow potential rather than mass or average surface density
We present a comparative study of the relation between the aperture-based
gas-phase metallicity and three structural parameters of star-forming galaxies:
mass (), average potential () and average surface mass density (; where is the effective radius). We use a
volume-limited sample drawn from the publicly available SDSS DR7, and base our
analysis on aperture-matched sampling by selecting sets of galaxies where the
SDSS fibre probes a fixed fraction of . We find that between 0.5
and 1.5 , the gas-phase metallicity correlates more tightly with
than with either or , in that for all
aperture-matched samples, the potential-metallicity relation has (i) less
scatter, (ii) higher Spearman rank correlation coefficient and (iii) less
residual trend with than either the mass-metallicity relation
and the average surface density-metallicity relation. Our result is broadly
consistent with the current models of gas enrichment and metal loss. However, a
more natural explanation for our findings is a local relation between the
gas-phase metallicity and escape velocity.Comment: Accepted by MNRAS; 17 pages, 11 figures, 1 tabl
Comparison of the Stellar Populations of Bulges and Discs using the MaNGA Survey
We use the MaNGA integral-field spectroscopic survey of low-redshift galaxies
to compare the stellar populations of the bulge and disc components, identified
from their Sersic profiles, for various samples of galaxies. Bulge dominated
regions tend to be more metal-rich and have slightly older stellar ages than
their associated disc dominated regions. The metallicity difference is
consistent with the deeper gravitational potential in bulges relative to discs,
which allows bulges to retain more of the metals produced by stars. The age
difference is due to star formation persisting longer in discs relative to
bulges. Relative to galaxies with lower stellar masses, galaxies with higher
stellar masses tend to have bulge dominated regions that are more metal-rich
and older (in light-weighted measurements) than their disc dominated regions.
This suggests high-mass galaxies quench from the inside out, while lower-mass
galaxies quench across the whole galaxy simultaneously. Early-type galaxies
tend to have bulge dominated regions the same age as their disc dominated
regions, while late-type galaxies tend to have disc dominated regions
significantly younger than their bulge dominated regions. Central galaxies tend
to have a greater metallicity difference between their bulge dominated regions
and disc dominated regions than satellite galaxies at similar stellar mass.
This difference may be explained by central galaxies being subject to mergers
or extended gas accretion bringing new, lower-metallicity gas to the disc,
thereby reducing the average metallicity and age of the stars; quenching of
satellite discs may also play a role.Comment: Accepted by PAS
Osteoblasts and Fibroblasts Interaction with a Porcine Acellular Dermal Matrix Membrane
The use of collagen membranes has remained the gold standard in GTR/GBR. In this study, the features and the biological activities of an acellular porcine dermis collagen matrix membrane applicable during dental surgery were investigated, and also by applying hydration with NaCl. Thus, two tested membranes were distinguished, the H-Membrane and Membrane, compared to the control cell culture plastic. The characterization was performed by SEM and histological analyses. In contrast, the biocompatibility was investigated on HGF and HOB cells at 3, 7, and 14 days by MTT for proliferation study; by SEM and histology for cell interaction study; and by RT-PCR for function-related genes study. In HOBs seeded on membranes, mineralization functions by ALP assay and Alizarin Red staining were also investigated. Results indicated that the tested membranes, especially when hydrated, can promote the proliferation and attachment of cells at each time. Furthermore, membranes significantly increased ALP and mineralization activities in HOBs as well as the osteoblastic-related genes ALP and OCN. Similarly, membranes significantly increased ECM-related and MMP8 gene expression in HGFs. In conclusion, the tested acellular porcine dermis collagen matrix membrane, mainly when it is hydrated, behaved as a suitable microenvironment for oral cells
The SAMI Galaxy Survey: gravitational potential and surface density drive stellar populations -- I. early-type galaxies
The well-established correlations between the mass of a galaxy and the
properties of its stars are considered evidence for mass driving the evolution
of the stellar population. However, for early-type galaxies (ETGs), we find
that color and stellar metallicity [Z/H] correlate more strongly with
gravitational potential than with mass , whereas stellar population
age correlates best with surface density . Specifically, for our sample
of 625 ETGs with integral-field spectroscopy from the SAMI Galaxy Survey,
compared to correlations with mass, the color--, [Z/H]--, and
age-- relations show both smaller scatter and less residual trend with
galaxy size. For the star formation duration proxy [/Fe], we find
comparable results for trends with and , with both being
significantly stronger than the [/Fe]- relation. In determining the
strength of a trend, we analyze both the overall scatter, and the observational
uncertainty on the parameters, in order to compare the intrinsic scatter in
each correlation. These results lead us to the following inferences and
interpretations: (1) the color-- diagram is a more precise tool for
determining the developmental stage of the stellar population than the
conventional color--mass diagram; and (2) gravitational potential is the
primary regulator of global stellar metallicity, via its relation to the gas
escape velocity. Furthermore, we propose the following two mechanisms for the
age and [/Fe] relations with : (a) the age-- and
[/Fe]-- correlations arise as results of compactness driven
quenching mechanisms; and/or (b) as fossil records of the
relation in their disk-dominated progenitors.Comment: 9 pages, 4 figures, 1 table Accepted to Ap
Resolved velocity profiles of galactic winds at Cosmic Noon
We study the kinematics of the interstellar medium (ISM) viewed "down the
barrel" in 20 gravitationally lensed galaxies during Cosmic Noon (). We use moderate-resolution spectra () from Keck/ESI and
Magellan/MagE to spectrally resolve the ISM absorption in these galaxies into
10 independent elements and use double Gaussian fits to quantify the
velocity structure of the gas. We find that the bulk motion of gas in this
galaxy sample is outflowing, with average velocity centroid
\left=-141 kms ( kms scatter)
measured with respect to the systemic redshift. 16 out of the 20 galaxies
exhibit a clear positive skewness, with a blueshifted tail extending to kms. We examine scaling relations in outflow velocities with
galaxy stellar mass and star formation rate (SFR), finding correlations
consistent with a momentum-driven wind scenario. Our measured outflow
velocities are also comparable to those reported for FIRE-2 and TNG50
cosmological simulations at similar redshift and galaxy properties. We also
consider implications for interpreting results from lower-resolution spectra.
We demonstrate that while velocity centroids are accurately recovered, the
skewness, velocity width, and probes of high velocity gas (e.g., ) are
subject to large scatter and biases at lower resolution. We find that
is required for accurate results for the gas kinematics of our
sample. This work represents the largest available sample of well-resolved
outflow velocity structure at , and highlights the need for good spectral
resolution to recover accurate properties.Comment: 42 pages, 37 figures (including appendix), Accepted for publication,
Ap
Inverse stellar population age gradients of post-starburst galaxies at z=0.8 with LEGA-C
We use deep, spatially resolved spectroscopy from the Large Early Galaxy Astrophysics Census Survey to study radial variations in the stellar population of 17 spectroscopically selected post-starburst (PSB) galaxies. We use spectral fitting to measure two Lick indices, H δA and Fe 4383 , and find that, on average, PSB galaxies have radially decreasing H δA and increasing Fe 4383 profiles. In contrast, a control sample of quiescent, non-PSB galaxies in the same mass range shows outwardly increasing H δA and decreasing Fe 4383 . The observed gradients are weak (≈−0.2 Å/Re), mainly due to seeing convolution. A two-SSP (simple stellar population) model suggests that intrinsic gradients are as strong as observed in local PSB galaxies (≈−0.8 Å/Re). We interpret these results in terms of inside-out growth (for the bulk of the quiescent population) versus star formation occurring last in the centre (for PSB galaxies). At z ≈ 0.8, central starbursts are often the result of gas-rich mergers, as evidenced by the high fraction of PSB galaxies with disturbed morphologies and tidal features (40 per cent). Our results provide additional evidence for multiple paths to quiescence: a standard path, associated with inside-out disc formation and with gradually decreasing star formation activity, without fundamental structural transformation, and a fast path, associated with centrally concentrated starbursts, leaving an inverse age gradient and smaller half-light radius
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