500 research outputs found
The Ultraviolet View of the Magellanic Clouds from GALEX: A First Look at the LMC Source Catalog
The Galaxy Evolution Exporer (GALEX) has performed unprecedented imaging
surveys of the Magellanic Clouds (MC) and their surrounding areas including the
Magellanic Bridge (MB) in near-UV (NUV, 1771-2831\AA) and far-UV (FUV,
1344-1786\AA) bands at 5" resolution. Substantially more area was covered in
the NUV than FUV, particularly in the bright central regions, because of the
GALEX FUV detector failure. The 5 depth of the NUV imaging varies
between 20.8 and 22.7 (ABmag). Such imaging provides the first sensitive view
of the entire content of hot stars in the Magellanic System, revealing the
presence of young populations even in sites with extremely low star-formation
rate surface density like the MB, owing to high sensitivity of the UV data to
hot stars and the dark sky at these wavelengths.
The density of UV sources is quite high in many areas of the LMC and SMC.
Crowding limits the quality of source detection and photometry from the
standard mission pipeline processing. We performed custom-photometry of the
GALEX data in the MC survey region ( from the LMC,
from the SMC). After merging multiple detections of sources in overlapping
images, the resulting catalog we have produced for the LMC contains nearly 6
million unique NUV point sources within 15 and is briefly presented
herein. This paper provides a first look at the GALEX MC survey and highlights
some of the science investigations that the entire catalog and imaging dataset
will make possible.Comment: 16 pages, 8 figures; J. Adv. Space Res. (2013
Assembly of Disk Galaxies from the Peak of Cosmic Star-Formation to Today
It was once accepted that galaxies form and maintain thin gas disks at early times. As gas is collisional, its disordered motions should be suppressed quickly. With angular momentum conserved, galaxies should be rotationally-supported within a few galaxy crossing times of their initial formation. The results presented over the chapters of this thesis challenge this picture.
We track the evolution of the ionized gas kinematics of star-forming galaxies from z = 2 to the present day, covering 10 Gyrs in cosmic time. First, as a part of a Keck/MOSFIRE spectroscopic survey, we determine that z = 2 (3 Gyr after the Big Bang) is still a period of active disk formation. The majority of massive star-forming galaxies at this time have disk-like characteristics — their kinematics are dominated by rotation, they are consistent with a marginally stable disk model, and they form a Tully-Fisher relation — but with disordered motions much higher than galaxies today. These galaxies are unlike disks today — less than 30% of galaxies at all masses have rotational motions at least 3x higher than their disordered motions. Lower mass galaxies are still in the early stages of disk assembly — their kinematics are often dominated by disordered motions and they fall short of the Tully-Fisher relation. Combining this sample with a similar one at z < 1, we find that all star-forming galaxy populations, on average, increase in rotational-support with time from z = 2 to now. This happens through a dramatic decline in disordered motions, and a mild increase in rotational motions. By the present day, nearly all star-forming galaxies above a stellar mass of 10^9.5 Msun have formed rotationally-supported disks with regular disk-like morphologies, while below this mass a galaxy may or may not form a disk. To better understand potential biases when interpreting these and other observations, we compare mock images and spectra of realistic hydrodynamic simulations against their intrinsic dynamical state. We determine that late-stager mergers are indistinguishable from disks in seeing-limited kinematic data. This implies that the fraction of galaxies that are measured to be “disks” from seeing-limited observations at z = 2 is only an upper-limit on the true disk fraction. Using theoretically-derived close pair fractions at z = 2, we determine that this effect is significant for low mass galaxies — up to a factor of 2 difference between observed and true disk fractions — but insignificant for high mass galaxies
CLEAR II: Evidence for Early Formation of the Most Compact Quiescent Galaxies at High Redshift
The origin of the correlations between mass, morphology, quenched fraction,
and formation history in galaxies is difficult to define, primarily due to the
uncertainties in galaxy star-formation histories. Star-formation histories are
better constrained for higher redshift galaxies, observed closer to their
formation and quenching epochs. Here we use "non-parametric" star-formation
histories and a nested sampling method to derive constraints on the formation
and quenching timescales of quiescent galaxies at . We model deep
HST grism spectroscopy and photometry from the CLEAR (CANDELS Lyman
Emission at Reionization) survey. The galaxy formation redshifts,
(defined as the point where they had formed 50\% of their stellar mass) range
from (shortly prior to the observed epoch) up to . \editone{We find that early formation redshifts are correlated with high
stellar-mass surface densities, 10.25, where is the stellar mass within 1~pkpc (proper kpc).
Quiescent galaxies with the highest stellar-mass surface density, , } show a \textit{minimum} formation
redshift: all such objects in our sample have . Quiescent
galaxies with lower surface density, $\log \Sigma_1 / (M_\odot\
\mathrm{kpc}^{-2}) = 9.5 - 10.25z_{50}
\simeq 1.5 - 8\log\Sigma_1/(M_\odot\ \mathrm{kpc}^{-2})>10.25$ uniquely identifies galaxies
that formed in the first few Gyr after the Big Bang, and we discuss the
implications this has for galaxy formation models.Comment: 13 pages, 7 figures, accepted for publication in ApJ. Includes an
interactive online appendix (https://vince-ec.github.io/appendix/appendix
z~2: An Epoch of Disk Assembly
We explore the evolution of the internal gas kinematics of star-forming
galaxies from the peak of cosmic star-formation at to today.
Measurements of galaxy rotation velocity , which quantify ordered
motions, and gas velocity dispersion , which quantify disordered
motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a
continuous baseline in redshift from to , spanning 10 Gyrs. At
low redshift, nearly all sufficiently massive star-forming galaxies are
rotationally supported (). By , the percentage of
galaxies with rotational support has declined to 50 at low stellar mass
() and 70 at high stellar mass
(). For , the percentage
drops below 35 for all masses. From to now, galaxies exhibit
remarkably smooth kinematic evolution on average. All galaxies tend towards
rotational support with time, and it is reached earlier in higher mass systems.
This is mostly due to an average decline in by a factor of 3 since a
redshift of 2, which is independent of mass. Over the same time period,
increases by a factor of 1.5 for low mass systems, but does not
evolve for high mass systems. These trends in and with
time are at a fixed stellar mass and should not be interpreted as evolutionary
tracks for galaxy populations. When galaxy populations are linked in time with
abundance matching, not only does decline with time as before, but
strongly increases with time for all galaxy masses. This enhances the
evolution in . These results indicate that is a
period of disk assembly, during which the strong rotational support present in
today's massive disk galaxies is only just beginning to emerge.Comment: 12 pages, 8 figures, submitted to Ap
Optical Polarization and Spectral Variability in the M87 Jet
During the last decade, M87's jet has been the site of an extraordinary
variability event, with one knot (HST-1) increasing by over a factor 100 in
brightness. Variability was also seen on timescales of months in the nuclear
flux. Here we discuss the optical-UV polarization and spectral variability of
these components, which show vastly different behavior. HST-1 shows a highly
significant correlation between flux and polarization, with P increasing from
at minimum to >40% at maximum, while the orientation of its electric
vector stayed constant. HST-1's optical-UV spectrum is very hard
(, ), and displays "hard lags"
during epochs 2004.9-2005.5, including the peak of the flare, with soft lags at
later epochs. We interpret the behavior of HST-1 as enhanced particle
acceleration in a shock, with cooling from both particle aging and the
relaxation of the compression. We set 2 upper limits of
parsecs and 1.02 on the size and advance speed of the flaring region. The
slight deviation of the electric vector orientation from the jet PA, makes it
likely that on smaller scales the flaring region has either a double or twisted
structure. By contrast, the nucleus displays much more rapid variability, with
a highly variable electric vector orientation and 'looping' in the
plane. The nucleus has a much steeper spectrum () but
does not show UV-optical spectral variability. Its behavior can be interpreted
as either a helical distortion to a steady jet or a shock propagating through a
helical jet.Comment: 14 pages, 7 figures, ApJ, in pres
Supplementary material for the article: Perusko, M.; van Roest, M.; Stanic-Vucinic, D.; Simons, P. J.; Pieters, R. H. H.; Cirkovic Velickovic, T.; Smit, J. J. Glycation of the Major Milk Allergen β-Lactoglobulin Changes Its Allergenicity by Alterations in Cellular Uptake and Degradation. Molecular Nutrition and Food Research 2018, 62 (17). https://doi.org/10.1002/mnfr.201800341
Supplementary material for: [https://doi.org/10.1002/mnfr.201800341]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2212
Figuring Out Gas & Galaxies In Enzo (FOGGIE) V: The Virial Temperature Does Not Describe Gas in a Virialized Galaxy Halo
The classical definition of the virial temperature of a galaxy halo excludes
a fundamental contribution to the energy partition of the halo: the kinetic
energy of non-thermal gas motions. Using simulations of low-redshift, galaxies from the FOGGIE project (Figuring Out Gas & Galaxies In Enzo)
that are optimized to resolve low-density gas, we show that the kinetic energy
of non-thermal motions is roughly equal to the energy of thermal motions. The
simulated FOGGIE halos have lower bulk temperatures than
expected from a classical virial equilibrium, owing to significant non-thermal
kinetic energy that is formally excluded from the definition of
. We derive a modified virial temperature explicitly including
non-thermal gas motions that provides a more accurate description of gas
temperatures for simulated halos in virial equilibrium. Strong bursts of
stellar feedback drive the simulated FOGGIE halos out of virial equilibrium,
but the halo gas cannot be accurately described by the standard virial
temperature even when in virial equilibrium. Compared to the standard virial
temperature, the cooler modified virial temperature implies other effects on
halo gas: (i) the thermal gas pressure is lower, (ii) radiative cooling is more
efficient, (iii) O VI absorbing gas that traces the virial temperature may be
prevalent in halos of a higher mass than expected, (iv) gas mass estimates from
X-ray surface brightness profiles may be incorrect, and (v) turbulent motions
make an important contribution to the energy balance of a galaxy halo.Comment: 30 pages, 14 figures, accepted to Ap
Beyond Spheroids and Discs: Classifications of CANDELS Galaxy Structure at 1.4 < z < 2 via Principal Component Analysis
Important but rare and subtle processes driving galaxy morphology and
star-formation may be missed by traditional spiral, elliptical, irregular or
S\'ersic bulge/disk classifications. To overcome this limitation, we use a
principal component analysis of non-parametric morphological indicators
(concentration, asymmetry, Gini coefficient, , multi-mode, intensity
and deviation) measured at rest-frame -band (corresponding to HST/WFC3 F125W
at 1.4 ) galaxy morphologies. Principal component analysis (PCA) quantifies
the correlations between these morphological indicators and determines the
relative importance of each. The first three principal components (PCs) capture
75 per cent of the variance inherent to our sample. We interpret the
first principal component (PC) as bulge strength, the second PC as dominated by
concentration and the third PC as dominated by asymmetry. Both PC1 and PC2
correlate with the visual appearance of a central bulge and predict galaxy
quiescence. PC1 is a better predictor of quenching than stellar mass, as as
good as other structural indicators (S\'ersic-n or compactness). We divide the
PCA results into groups using an agglomerative hierarchical clustering method.
Unlike S\'ersic, this classification scheme separates compact galaxies from
larger, smooth proto-elliptical systems, and star-forming disk-dominated clumpy
galaxies from star-forming bulge-dominated asymmetric galaxies. Distinguishing
between these galaxy structural types in a quantitative manner is an important
step towards understanding the connections between morphology, galaxy assembly
and star-formation.Comment: 31 pages, 24 figures, accepted for publication in MNRA
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