The Lyman-$\alpha$ (Ly$\alpha$) emission line has been ubiquitously used to
confirm and study high redshift galaxies. We report on the line morphology as
seen in the 2D spectra from the VIMOS Ultra ...Deep Survey in a sample of 914
Ly$\alpha$ emitters from a parent sample of 4192 star-forming galaxies at
$2<z_\mathrm{spec}\lesssim6$. The study of the spatial extent of Ly$\alpha$
emission provides insight into the escape of Ly$\alpha$ photons from galaxies.
We classify the line emission as either non-existent, coincident, projected
spatial offset, or extended with respect to the observed 2D UV continuum
emission. The line emitters in our sample are classified as ~45% coincident,
~24% extended and ~11% offset emitters. For galaxies with detected UV
continuum, we show that extended Ly$\alpha$ emitters (LAEs) correspond to the
highest equivalent width galaxies (with an average
$W_\mathrm{Ly\alpha}\sim-22${\AA}). This means that this class of objects is
the most common in narrow-band selected samples, which usually select high
equivalent width LAEs, $<-20${\AA}. Extended Ly$\alpha$ emitters are found to
be less massive, less star-forming, with lower dust content, and smaller UV
continuum sizes ($r_{50}\sim0.9$kpc) of all the classes considered here. We
also find that galaxies with larger UV-sizes have lower fractions of Ly$\alpha$
emitters. By stacking the spectra per emitter class we find that the weaker
Ly$\alpha$ emitters have stronger low ionization inter-stellar medium (ISM)
absorption lines. Interestingly, we find that galaxies with Ly$\alpha$ offset
emission (median separation of $1.1_{-0.8}^{+1.3}$kpc from UV continuum) show
similar velocity offsets in the ISM as those with no visible emission (and
different from other Ly$\alpha$ emitting classes). This class of objects may
hint at episodes of gas accretion, bright offset clumps, or on-going merging
activity into the larger galaxies.
The Lya line in the UV and the CII line in the FIR are widely used tools to identify galaxies and to obtain insights into ISM properties in the early Universe. By combining data obtained with ALMA in ...band 7 at ~ 320 GHz as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE) with spectroscopic data from DEIMOS at Keck, VIMOS and FORS2 at the VLT, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4 < z < 6 in which we detect both the Lya line and the CII. We used CII, observed with ALMA, as a tracer of the systemic velocity of the galaxies, and we find that 90% of the selected objects have Lya-CII velocity offsets in the range 0 < Dv_Lya-CII < 400 km/s, in line with the few measurements available so far in the early Universe, and significantly smaller than those observed at lower z. We observe ISM-CII offsets in the range -500 < Dv_ISM-CII < 0 km/s, in line with values at all redshifts. We find significant anticorrelations between Dv_Lya-CII and the Lya rest-frame equivalent width EW0(Lya) (or equivalently, the Lya escape fraction f_esc(Lya)). According to available models for the radiative transfer of Lya photons, the escape of Lya photons would be favored in galaxies with high outflow velocities, in agreement with our observations. The uniform shell model would also predict that the Lya escape in galaxies with slow outflows (0 < v_out < 300 km/s) is mainly determined by the neutral hydrogen column density (NHI), while the alternative model by Steidel+10 would favor a combination of NHI and covering fraction as driver of the Lya escape. We suggest that the observed increase in Lya escape that is observed between z~2 and z~6 is not due to a higher incidence of fast outflows at high redshift, but rather to a decrease in average NHI along the line of sight, or alternatively, a decrease in HI covering fraction. abridged
Star formation rate (SFR) measurements at z>4 have relied mostly on rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on IRX-\(\beta\) relation are highly ...uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate CII at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4<z<5.9. We use stacks of continuum images to measure average infrared (IR) luminosities taking into account both detected and undetected sources. Based on these measurements, we measure the position of the main sequence of star-forming galaxies and the specific SFR (sSFR) at \(z\sim4.5\) and \(z\sim5.5\). We find that the main sequence and sSFR do not evolve significantly between \(z\sim4.5\) and \(z\sim5.5\), as opposed to lower redshifts. We develop a method to derive the obscured SFR density (SFRD) using the stellar masses or FUV-magnitudes as a proxy of FIR fluxes measured on the stacks and combining them with the galaxy stellar mass functions and FUV luminosity functions from the literature. We obtain consistent results independent of the chosen proxy. We find that the obscured fraction of SFRD is decreasing with increasing redshift but even at \(z\sim5.5\) it constitutes around 61\% of the total SFRD.
The ALPINE-ALMA large program targets the CII 158 \(\mu\)m line and the far-infrared continuum in 118 spectroscopically confirmed star-forming galaxies between z=4.4 and z=5.9. It represents the ...first large CII statistical sample built in this redshift range. We present details of the data processing and the construction of the catalogs. We detected 23 of our targets in the continuum. To derive accurate infrared luminosities and obscured star formation rates, we measured the conversion factor from the ALMA 158 \(\mu\)m rest-frame dust continuum luminosity to the total infrared luminosity (L\(_{\rm IR}\)) after constraining the dust spectral energy distribution by stacking a photometric sample similar to ALPINE in ancillary single-dish far-infrared data. We found that our continuum detections have a median L\(_{\rm IR}\) of 4.4\(\times 10^{11}\) L\(_\odot\). We also detected 57 additional continuum sources in our ALMA pointings. They are at lower redshift than the ALPINE targets, with a mean photometric redshift of 2.5\(\pm\)0.2. We measured the 850 \(\mu\)m number counts between 0.35 and 3.5 mJy, improving the current interferometric constraints in this flux density range. We found a slope break in the number counts around 3 mJy with a shallower slope below this value. More than 40 % of the cosmic infrared background is emitted by sources brighter than 0.35 mJy. Finally, we detected the CII line in 75 of our targets. Their median CII luminosity is 4.8\(\times\)10\(^8\) L\(_\odot\) and their median full width at half maximum is 252 km/s. After measuring the mean obscured SFR in various CII luminosity bins by stacking ALPINE continuum data, we find a good agreement between our data and the local and predicted SFR-L\(_{\rm CII}\) relations of De Looze et al. (2014) and Lagache et al. (2018).
The molecular gas content of normal galaxies at z>4 is poorly constrained, because the commonly used molecular gas tracers become hard to detect. We use the CII158um luminosity, recently proposed as ...a molecular gas tracer, to estimate the molecular gas content in a large sample of main-sequence star-forming galaxies at z=4.4-5.9, with a median stellar mass of 10^9.7 Msun, drawn from the ALMA Large Program to INvestigate CII at Early times (ALPINE) survey. The agreement between molecular gas masses derived from CII luminosity, dynamical mass, and rest-frame 850um luminosity, extrapolated from the rest-frame 158um continuum, supports CII as a reliable tracer of molecular gas in our sample. We find a continuous decline of the molecular gas depletion timescale from z=0 to z=5.9, which reaches a mean value of (4.6+/-0.8)x10^8 yr at z~5.5, only a factor of 2-3 shorter than in present-day galaxies. This suggests a mild enhancement of star formation efficiency toward high redshifts, unless the molecular gas fraction significantly increases. Our estimates show that the rise in molecular gas fraction as reported previously, flattens off above z~3.7 to achieve a mean value of 63%+/-3 over z=4.4-5.9. This redshift evolution of the gas fraction is in line with the one of the specific star formation rate. We use multi-epoch abundance matching to follow the gas fraction evolution over cosmic time of progenitors of z=0 Milky Way-like galaxies in 10^13 Msun halos and of more massive z=0 galaxies in 10^14 Msun halos. Interestingly, the former progenitors show a monotonic decrease of the gas fraction with cosmic time, while the latter show a constant gas fraction from z=5.9 to z~2 and a decrease at z<2. We discuss three possible effects, namely outflows, halt of gas supplying, and over-efficient star formation, which may jointly contribute to the gas fraction plateau of the latter massive galaxies.
We present a Bayesian full-spectral-fitting analysis of 75 massive (\(M_* > 10^{10.3} M_\odot\)) UVJ-selected galaxies at redshifts of \(1.0 < z < 1.3\), combining extremely deep rest-frame ...ultraviolet spectroscopy from VANDELS with multi-wavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the Bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We firstly constrain the stellar mass vs stellar age relationship, finding a steep trend towards earlier average formation with increasing stellar mass of \(1.48^{+0.34}_{-0.39}\) Gyr per decade in mass, although this shows signs of flattening at \(M_* > 10^{11} M_\odot\). We show that this is consistent with other spectroscopic studies from \(0 < z < 2\). This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by Simba and IllustrisTNG agree well with observations at \(z=0.1\), they are too shallow at \(z=1\), predicting an evolution of \(<0.5\) Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies (\(M_* \sim 10^{10.5} M_\odot\)) are consistent with formation in recent (\(z<2\)), intense starburst events, with timescales of \(\lesssim500\) Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by \(z=1\), they formed at \(z\sim5\) and quenched by \(z=3\). However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.
Many animals interact with the air-water interface during locomotion. Such location either involves moving through the water's surface or moving atop the water surface. This dissertation aims to ...investigate both of these forms of locomotion in frogs. First we quantified the kinematics of skittering, jumping on top the water's surface without sinking, in two species of frog, Acris crepitans and Euphlyctis cyanophlyctis. We found that what was described as "skittering" locomotion in Acris crepitans is actually more akin to porpoising. A. crepitans begins and ends each jump during their interfacial behavior under the water surface. These frogs may be unable to perform true skittering locomotion due to not being able to retract their hindlimbs fast enough. E. cyanophlyctis, however, does stay above the water surface during this mode of locomotion. We found that Euphlyctis is highly maneuverable during skittering locomotion compared to other inertial based water-surface traversing animals. Not only can they turn up to 80° between subsequent jumps, they also perform this behavior in close proximity to each other without collision. Next, we investigated control mechanisms used by frogs when jumping from water. Prior research has identified frogs of the genus Euphlyctis as high jumpers. But previous studies only considered their maximal performance. Here, we investigated how these frogs modulate propulsive force in order to control their jump height. We linked the frog limb kinematics to the jump force by modeling the added mass produced by the foot's motion.
Doctor of Philosophy
There are many animals that move across or through the water's surface. Most of them are very small and light and can thus be supported by surface tension. Larger animals instead must produce the force needed to stay afloat by moving quickly. Previous research has looked at the physics involved in running on the water surface in basilisk lizards and grebes. However, the ability of frogs to jump on the water surface (a behavior known as "skittering") has never been studied. In this dissertation, we examine the water-surface traversal of two frog species, Acris crepitans and Euphlyctis spp., using high-speed videography. Unlike previous human observations in the literature, we found that Acris does not stay atop the water's surface during its jumping behavior and instead begins and ends each jump under the water. This is similar to porpoising in animals like dolphins. Euphlyctis, however, does stay above the water during this jumping behavior. We found that these frogs can turn sharply between jumps which has not been observed in any other large water-runners. Additionally, we studied the ability of Euphlyctis to jump high in the air starting from floating on the water surface. These frogs are interesting to study because they can jump unusually high compared to other species of similar size and shape. We found that when shown insects at different heights, these frogs can control their jump height and only jump as high as necessary. By tracking the frogs' limbs during jumping we investigated several possible ways these frogs controlled their jump height.
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