The large-scaled magnetic fields in intergalactic space may contain detailed information of the primordial magnetic fields produced in the early Universe. The generation of the cosmological ...matter-antimatter asymmetry may produce helical magnetic fields via CP (charge conjugation and parity) violating interactions during matter-genesis. Thus, the study of the intergalactic magnetic field (IGMF) could provide a new window on early-Universe cosmology. IGMFs deflect the electron-positron pairs produced by TeV gamma-rays from blazars, resulting in broadened beams of cascade GeV gamma-rays known as pair halos. In the presence of helical IGMFs, cascade GeV gamma-rays at different energies from a distant source fall into patterns in the observation plane in the GeV gamma-ray sky that have a similar chirality. These signatures of the IGMF on the gamma-ray emission from extragalactic sources, i.e. pair halos and helical patterns, can be observed using data from the Fermi Large Area Telescope (Fermi-LAT). In this dissertation, I describe methods for probing the IGMF using gamma-ray observations. I report on the results of a search for gamma-ray pair halos with a stacking analysis of low-redshift blazars using data from Fermi-LAT. For this analysis we used a number of a priori selection criteria, including the spatial and spectral properties of the Fermi sources. The angular distribution of ∼ 1 GeV photons around 24 stacked isolated high-synchrotron-peaked BL Lacs with redshift z < 0.5 shows an excess over that of point-like sources. A frequentist test yields a p-value of p ∼ 0.01 for the extended emission against the point-source hypothesis. A Bayesian estimation provides the common logarithm of Bayes factors > 2, consistent with expectations for pair halos produced in the IGMF with strength of ∼ 10-17 to 10-15 Gauss. In addition, I present a search for parity violating signatures of helical IGMFs in the GeV gamma-ray sky. In this study, the IGMF helicity is examined by evaluating a parity-odd statistic using gamma-ray data obtained from Fermi-LAT observations at high galactic latitudes. The resulting negative values of the parity-odd statistic imply that there is an excess of left-handed spirals in the gamma-ray sky, indicating a left-handed helicity consistent with a helical magnetic field with strength of ∼ 10 -14 Gauss on ∼ 10 Mpc scales.
The luminosities and velocity dispersions of the extinction-corrected Balmer
emission lines of giant HII regions in nearby galaxies exhibit a tight
correlation (~0.35 dex scatter). There are few ...constraints, however, on whether
giant HII regions at significant lookback times follow an L-sigma relation,
given the angular resolution and sensitivity required to study them
individually. We measure the luminosities and velocity dispersions of H-alpha
and H-beta emission from 11 HII regions in Sp1149, a spiral galaxy at redshift
z=1.49 multiply imaged by the MACS J1149 galaxy cluster. Sp1149 is also the
host galaxy of the first-known strongly lensed supernova with resolved images,
SN Refsdal. We employ archival Keck-I OSIRIS observations, and newly acquired
Keck-I MOSFIRE and Large Binocular Telescope LUCI long-slit spectra of Sp1149.
When we use the GLAFIC simply parameterized lens model, we find that the
H-alpha luminosities of the HII regions at z=1.49 are a factor of 6.4+2.9-2.0
brighter than predicted by the low-redshift L-sigma relation we measure from
Very Large Telescope MUSE spectroscopy. If the lens model is accurate, then the
HII regions in Sp1149 differ from their low-redshift counterparts. We identify
an HII region in Sp1149 that is dramatically brighter (by 2.03+-0.44 dex) than
our low-redshift L-sigma relation predicts given its low velocity dispersion.
Finally, the HII regions in Sp1149 are consistent, perhaps surprisingly, with
the z=0 star-forming locus on the Baldwin-Phillips-Terlevich diagram.
Galaxy-cluster gravitational lenses enable the study of faint galaxies even
at large lookback times, and, recently, time-delay constraints on the Hubble
constant. There have been few tests, however, ...of lens model predictions
adjacent to the critical curve (<8") where the magnification is greatest. In a
companion paper, we use the GLAFIC lens model to constrain the Balmer L-sigma
relation for HII regions in a galaxy at redshift z=1.49 strongly lensed by the
MACS J1149 galaxy cluster. Here we perform a detailed comparison between the
predictions of ten cluster lens models which employ multiple modeling
assumptions with our measurements of 11 magnified giant HII regions. We find
that that the models predict magnifications an average factor of 6.2 smaller, a
2-sigma tension, than that inferred from the HII regions under the assumption
that they follow the low-redshift L-sigma relation. To evaluate the possibility
that the lens model magnifications are strongly biased, we next consider the
flux ratios among knots in three images of Sp1149, and find that these are
consistent with model predictions. Moreover, while the mass-sheet degeneracy
could in principle account for a factor of ~6 discrepancy in magnification, the
value of H0 inferred from SN Refsdal's time delay would become implausibly
small. We conclude that the lens models are not likely to be highly biased, and
that instead the HII regions in Sp1149 are substantially more luminous than the
low-redshift Balmer L-sigma relation predicts.
We report the discovery of transients among star clusters in a distant galaxy that is gravitationally lensed by a foreground galaxy cluster, and explore whether these transients correspond to: (i) ...intrinsic variations associated with stellar outbursts; or (ii) extrinsic variations imposed through microlensing by intraclusters stars along, perhaps, with primordial black holes. From images at two epochs separated by nearly a year, we discovered ten such transients -- displaying brightness variations of \(\sim\)10\%--20\% -- among 55 persistent knots identified as young star clusters in the Dragon arc. Two of these transients are associated with a triply-lensed star cluster, permitting a test of intrinsic variability by checking whether their light variations are repeated among the different lensed counterparts with a suitable time delay given their different light arrival times at the observer. Despite considerable care in constructing a lens model for Abell 370 that is optimized at the Dragon arc, we found that the predicted lensing magnifications are not sufficiently accurate to provide a definitive test of intrinsic variability based only on two images -- although such a test will become feasible as more observations are made. On the other hand, we perform simulations demonstrating that the observed level of brightness variations, as well as the observed transient event rate, can be explained entirely by stellar microlensing: as stars in the background star cluster move across the sky relative to intracluster stars, changes in their individual brightnesses can result in an overall change in the brightness of their parent star cluster.
We present the highest resolution images to date of caustics formed by wave dark matter (\(\psi\)DM) fluctuations near the critical curves of cluster gravitational lenses. We describe the basic ...magnification features of \(\psi\)DM in the source plane at high macromodel magnification and discuss specific differences between the \(\psi\)DM and standard cold dark matter (CDM) models. The unique generation of demagnified counterimages formed outside the Einstein radius for \(\psi\)DM is highlighted. Substructure in CDM cannot generate such demagnified images of positive parity, thus providing a definitive way to distinguish \(\psi\)DM from CDM. Highly magnified background sources with sizes \(r\approx 1pc\), or approximately a factor of ten smaller than the expected de Broglie wavelength of \(\psi\)DM, offer the best possibility of discriminating between \(\psi\)DM and CDM. These include objects such as very compact stellar clusters at high redshift that JWST is finding in abundance.
The core-collapse supernova of a massive star rapidly brightens when a shock, produced following the collapse of its core, reaches the stellar surface. As the shock-heated star subsequently expands ...and cools, its early-time light curve should have a simple dependence on the progenitor's size and therefore final evolutionary state. Measurements of the progenitor's radius from early light curves exist for only a small sample of nearby supernovae, and almost all lack constraining ultraviolet observations within a day of explosion. The several-day time delays and magnifying ability of galaxy-scale gravitational lenses, however, should provide a powerful tool for measuring the early light curves of distant supernovae, and thereby studying massive stellar populations at high redshift. Here we analyse individual rest-frame ultraviolet-through-optical exposures taken with the Hubble Space Telescope that simultaneously capture, in three separate gravitationally lensed images, the early phases of a supernova at redshift \(z \approx 3\) beginning within \(5.8\pm 3.1\) hr of explosion. The supernova, seen at a lookback time of \(\sim11.5\) billion years, is strongly lensed by an early-type galaxy in the Abell 370 cluster. We constrain the pre-explosion radius to be \(533^{+154}_{-119}\) solar radii, consistent with a red supergiant. Highly confined and massive circumstellar material at the same radius can also reproduce the light curve, but is unlikely since no similar low-redshift examples are known.
We present a new analysis of the rest-frame UV and optical spectra of a
sample of three $z>8$ galaxies discovered behind the gravitational lensing
cluster RX\,J2129.4+0009. We combine these ...observations with $z>7.5$ galaxies
from the literature, for which similar measurements are available. As already
pointed out in other studies, the high \oiii$\lambda$5007/\oii$\lambda$3727
ratios ($O_{32}$) and steep UV continuum slopes ($\beta$) are consistent with
the values observed for low redshift Lyman continuum emitters, suggesting that
such galaxies contribute to the ionizing budget of the intergalactic medium. We
construct a logistic regression model to estimate the probability of a galaxy
being a Lyman continuum emitter based on the measured \MUV, $\beta$, and
$O_{32}$. Using this probability and the UV luminosity function, we construct
an empirical model that estimates the contribution of high redshift galaxies to
reionization. The preferred scenario in our analysis shows that at $z\sim8$,
the average escape fraction of the galaxy population (i.e., including both LyC
emitters and non-emitters) varies with \MUV, with intermediate UV luminosity
($-19<M_{UV}<-16$) galaxies having larger escape fraction. Galaxies with faint
UV luminosity ($-16<M_{UV}<-13.5$) contribute most of the ionizing photons. The
relative contribution of faint versus bright galaxies depends on redshift, with
the intermediate UV galaxies becoming more important over time. UV bright
galaxies, although more likely to be LCEs at a given log($O_{32}$) and $\beta$,
contribute the least of the total ionizing photon budget.
Microlensed stars recently discovered by JWST & HST follow closely the
winding critical curve of A370 along all sections of the ``Dragon Arc"
traversed by the critical curve. These transients are ...fainter than
$m_{AB}>26.5$, corresponding to the Asymptotic Giant Branch (AGB) and
microlensed by diffuse cluster stars observed with $\simeq 18M_\odot/pc^2$, or
about $\simeq 1$\% of the projected dark matter density. Most microlensed stars
appear along the inner edge of the critical curve, following an asymmetric band
of width $\simeq 4$kpc that is skewed by $-0.7\pm0.2$kpc. Some skewness is
expected as the most magnified images should form along the inner edge of the
critical curve with negative parity, but the predicted shift is small $\simeq
-0.04$kpc and the band of predicted detections is narrow, $\simeq 1.4$kpc.
Adding CDM-like dark halos of $10^{6-8}M_\odot$ broadens the band as desired
but favours detections along the outer edge of the critical curve, in the wrong
direction, where sub-halos generate local Einstein rings. Instead, the
interference inherent to ``Wave Dark Matter" as a Bose-Einstein condensate
($\psi$DM) forms a symmetric band of critical curves that favours negative
parity detections. A de Broglie wavelength of $\simeq 10$pc matches well the
observed $4$kpc band of microlenses and predicts negative skewness $\simeq
-0.6$kpc, similar to the data. The implied corresponding boson mass is $\simeq
10^{-22}$eV, in good agreement with estimates from dwarf galaxy cores when
scaled by momentum. Further JWST imaging may reveal the pattern of critical
curves by simply ``joining the dots" between microlensed stars, allowing wave
corrugations of $\psi$DM to be distinguished from CDM sub-halos
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