45 research outputs found
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
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
Unveiling the complex circumgalactic medium: a comparative study of merging and non-interacting galaxy groups
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
A Glimpse of the Stellar Populations and Elemental Abundances of Gravitationally Lensed, Quiescent Galaxies at with Keck Deep Spectroscopy
Gravitational lenses can magnify distant galaxies, allowing us to discover
and characterize the stellar populations of intrinsically faint, quiescent
galaxies that are otherwise extremely difficult to directly observe at high
redshift from ground-based telescopes. Here, we present the spectral analysis
of two lensed, quiescent galaxies at discovered by the ASTRO 3D
Galaxy Evolution with Lenses survey: AGEL1323 (,
, ) and AGEL0014 (,
, ). We measured the age, [Fe/H], and [Mg/Fe] of the two
lensed galaxies using deep, rest-frame-optical spectra (S/N
40\AA) obtained on the Keck I telescope. The ages of AGEL1323 and
AGEL0014 are Gyr and Gyr, respectively,
indicating that most of the stars in the galaxies were formed less than 2 Gyr
after the Big Bang. Compared to nearby quiescent galaxies of similar masses,
the lensed galaxies have lower [Fe/H] and [Mg/H]. Surprisingly, the two
galaxies have comparable [Mg/Fe] to similar-mass galaxies at lower redshifts,
despite their old ages. Using a simple analytic chemical evolution model
connecting the instantaneously recycled element Mg with the mass-loading
factors of outflows averaged over the entire star formation history, we found
that the lensed galaxies may have experienced enhanced outflows during their
star formation compared to lower-redshift galaxies, which may explain why they
quenched early.Comment: 18 pages, 11 figures, submitted to ApJ; comments welcom
CD4 T lymphocyte autophagy is upregulated in the salivary glands of primary Sjögren’s syndrome patients and correlates with focus score and disease activity
Background: Primary Sjögren’s syndrome (pSS) is a common chronic autoimmune disease characterized by
lymphocytic infiltration of exocrine glands and peripheral lymphocyte perturbation. In the current study, we
aimed to investigate the possible pathogenic implication of autophagy in T lymphocytes in patients with pSS.
Methods: Thirty consecutive pSS patients were recruited together with 20 patients affected by sicca syndrome a
nd/or chronic sialoadenitis and 30 healthy controls. Disease activity and damage were evaluated according to SS
disease activity index, EULAR SS disease activity index, and SS disease damage index. T lymphocytes were analyzed
for the expression of autophagy-specific markers by biochemical, molecular, and histological assays in peripheral
blood and labial gland biopsies. Serum interleukin (IL)-23 and IL-21 levels were quantified by enzyme-linked
immunosorbent assay.
Results: Our study provides evidence for the first time that autophagy is upregulated in CD4+ T lymphocyte salivary
glands from pSS patients. Furthermore, a statistically significant correlation was detected between lymphocyte
autophagy levels, disease activity, and damage indexes. We also found a positive correlation between autophagy
enhancement and the increased salivary gland expression of IL-21 and IL-23, providing a further link between innate
and adaptive immune responses in pSS.
Conclusions: These findings suggest that CD4+ T lymphocyte autophagy could play a key role in pSS pathogenesis.
Additionally, our data highlight the potential exploitation of T cell autophagy as a biomarker of disease activity and
provide new ground to verify the therapeutic implications of autophagy as an innovative drug target in pSS