Abstract
Ly
α
emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly
α
in the intergalactic medium ...(IGM) and the line profile emitted by the galaxy. Large shifts of Ly
α
redward of systemic due to scattering in the interstellar medium can boost Ly
α
transmission in the IGM during reionization. The relationship between the Ly
α
velocity offset from systemic and other galaxy properties is not well established at high redshift or low luminosities, due to the difficulty of observing emission lines which trace the systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding Ly
α
at
z
> 3. We present a sample of 12 UV-faint galaxies (−20 ≲
M
UV
≲ −16) at 3 ≲
z
≲ 6, with Ly
α
velocity offsets, Δ
v
Ly
α
, measured from the Very Large Telescope/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find a median Δ
v
Ly
α
of 205 km s
−1
and standard deviation of 75 km s
−1
, compared to 320 and 170 km s
−1
, respectively, for
M
UV
< −20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly
α
velocity offset with decreasing UV luminosity and optical line velocity dispersion, which extends to
M
UV
≳ −20, consistent with a picture where the Ly
α
profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly
α
from UV-faint galaxies will be preferentially attenuated, but that detecting Ly
α
with low Δ
v
Ly
α
can be an indicator of large ionized bubbles.
ABSTRACT
We present a Bayesian inference on the neutral hydrogen fraction of the intergalactic medium (IGM), $\overline{x}_{\small HI}$, at z ∼ 6–8 using the properties of Lyman break galaxies (LBGs) ...during the epoch of reionization. We use large samples of LBG candidates at 5.5 ≤ z ≤ 8.2 with spectroscopy from Keck/DEIMOS and Keck/MOSFIRE. For each galaxy, we incorporate either the Lyman-α (Lyα) equivalent width (EW) for detections or the EW limit spectrum for non-detections to parametrize the EW distribution at various ultraviolet brightnesses for a given redshift. Using our reference sample of galaxy candidates from the ionized universe at z ∼ 6.0, we are able to infer $\overline{x}_{\small HI}$ at two redshifts: z ∼ 6.7 and z ∼ 7.6. This work includes intrinsically faint, gravitationally lensed galaxies at z ∼ 6.0 in order to constrain the intrinsic faint-end Lyα EW distribution and provide a comparable population of galaxies to counterparts in our sample that are at higher redshift. The inclusion of faint galaxy candidates, in addition to a more sophisticated modelling framework, allows us to better isolate effects of the interstellar medium and circumgalactic medium on the observed Lyα distribution from those of the IGM. We infer an upper limit of $\overline{x}_{\small HI}$ ≤ 0.25 (0.44) at z = 6.7 ± 0.2 and a neutral fraction of $\overline{x}_{\small HI}$ = $0.83^{+0.08}_{-0.11}$ (0.83$^{+0.11}_{-0.21}$) at z = 7.6 ± 0.6, both within 68 per cent (95 per cent) uncertainty, results that favour a moderately late and fairly rapid reionization.
ABSTRACT We present a study on stellar properties of Lyman-alpha (Ly α) emitters at 5 < z < 8.2. We use 247 photometrically selected, lensed, high-redshift, low-luminosity galaxy candidates with ...spectroscopic follow-up. Of these, 38 are confirmed spectroscopically to be between 5 < z < 8.2 via detection of Ly α. For each galaxy and candidate, we estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age with spectral energy distribution fitting. We also measure the UV β slope and luminosity using values from photometry. We find no strong correlation between Ly α equivalent width and any of these properties, as well as no significant difference between the physical properties of Ly α emitters and candidates without Ly α detected. This lack of expected trends may be explained by a combination of the evolving opacity of the intergalactic medium at these redshifts as well as the unique phase space probed by our lensed sample. Via tests on other galaxy samples which show varying strengths of correlations, we conclude that if there exist any relationships between Ly α equivalent width and physical properties in the underlying population of faint galaxies, they are weak correlations. We also present the results of a spectroscopic search for C iii emission in confirmed Ly α emitters at z ∼ 7, finding no C iii detections, but putting constraints on strong active galactic nuclei activity and extreme nebular emission.
ABSTRACT We report on a $\rm {CII}_{158\mu \rm {m}}$ search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed Ly α emitting galaxies at z ∼ 7. Our targets are ...ultraviolet (UV) faint systems with stellar masses on the order of M* ∼ 109 M⊙. We detect a single C ii line emission (4σ) from the brightest (L ∼ 2.4 × 1010L⊙) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (zC ii = 6.3151 ± 0.0005) for MACS0454-1251 and measure a Ly α velocity offset of $\Delta v \approx 300 \pm 70 \rm {km\, s}^{-1}$. The remaining two galaxies we detect no C ii but provide 3σ upper limits on their C ii line luminosities which we use to investigate the $L_{\textrm {CII}} - \rm {SFR}$ relation. Overall our single C ii detection shows agreement with the relation for local dwarf galaxies. Our C ii deficient galaxies could potentially be exhibiting low metallicities (Z < Z⊙). Another possible explanation for weaker C ii emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of $T_{d}=35 \rm {K}$ dust masses (Mdust) range from <4.8 × 107 M⊙ to 2.3 × 108 M⊙. Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing C ii emission.
The Epoch of Reionization marks the period following the Dark Ages, the era beginning 400,000 years after the Big Bang in which neutral hydrogen permeated the Universe. Reionization is defined as the ...period of cosmic history in which this hydrogen went from being neutral to ionized, ending at around redshift z ∼ 6, or about 1 billion years after the Big Bang. This period marks the last major phase change of hydrogen in the intergalactic medium. It was also a time of significant galaxy and structure formation, when the first sources of light emerged. These nascent galaxies were likely major contributors to reionization, emitting large amounts of high energy photons which escaped into the intergalactic medium and began to ionize the vast sea of neutral hydrogen. However, beyond these facts, there are still many open questions surrounding the Epoch of Reionization. Some of the remaining uncertainties concern how quickly the transition occurred, what the key drivers were in the process, and what their physical properties are. This dissertation aims to address some of these lingering questions. In this work, I use a large sample of characteristically faint, gravitationally lensed, high-redshift galaxies in order to constrain both the timeline of reionization and the physical properties of the ionizing sources. The galaxies used in this sample have deep photometric data in multiple bands from the Hubble Space Telescope and Spitzer Space Telescope, as well as followup spectroscopy from the Keck Observatory. The high quality of photometric data provides good constraints on the redshift and physical properties of galaxies in our sample, even if they lack spectroscopic confirmation. The sample is comprised of ∼ 250 Lyman Break galaxy candidates within the redshift range 5 < z < 8.2, spanning the heart and tail ends of the reionization era. Galaxy candidates for spectroscopic follow-up were chosen after multiband photometric observations were completed. These were selected via the Lyman Break technique and using constraints on the redshift probability distribution created from each galaxy’s photometry. Follow-up spectroscopic observations resulted in 38 spectroscopically confirmed galaxies via detection of the Lyman-α (Lyα , 1216˚A) line, and constraints on Lyα strength for the rest of the sample. For all analyses done in this dissertation, I use these ∼ 250 galaxies lying in the redshift range 5 < z < 8.2 in order to constrain both the timeline of reionization and the stellar and UV properties of galaxies in this epoch.I begin in Chapter 2 with a study on the timeline of reionization using Lyα emission properties from galaxies during and directly after the process was complete. In this work, I compare the prevalence and strength of Lyα emission from galaxies within the Epoch of Reionization (z ∼ 6.7 and z ∼ 7.6) and when reionization was mostly, if not entirely, complete (z ∼ 6). I compare the UV luminosities and β slopes of the samples at the different redshifts and show that the distributions are similar for both properties. As the galaxies all have similar UV properties, and therefore are likely at similar states of interstellar medium evolution, we attribute any difference in the Lyα equivalent width distributions to the evolving opacity of hydrogen in the intergalactic medium. The results of this study, which are consistent with other works, suggest a rapid and fairly late reionization scenario. This work is published in the Monthly Notices of the Royal Astronomical Society, (Bolan et al., 2022).In Chapter 3, I present an analysis of the physical properties of the galaxy sample as well as the results of a search for CIII emission in confirmed Lyα emitters, which can provide systemic redshifts as well as a basis on which to infer metallicities and ionization parameters. For each of the galaxies, I calculate UV luminosity and β slope, the slope in the UV spectrum of a galaxy redward of Lyα emission, from photometry as well as estimate stellar mass, star formation rate, specific star formation rate, and mass-weighted age via spectral energy density fitting. For galaxies with Lyα emission, I look at the equivalent width (EW) of the emission line as a function of all of these properties to see if there are any correlations. I also compare the distributions of each of these properties for Lyα emitters against nonemitters to see if there are significant physical differences between these groups of galaxies. I find no statistically significant relationships between Lyα EW and any physical properties, nor any significant difference between the sample of Lyα emitters and nonemitters.In Chapter 4, I provide a summary. Using a sample of gravitationally lensed, intrinsically faint, high-redshift galaxies, I infer a timeline of cosmic reionziation and characterize the physical properties of typical galaxies from the era. These analyses are especially important as we enter an era of massive space and ground based observatories, such as the James Webb Space Telescope, the European Extremely Large Telescope, the Thirty Meter Telescope, and the Giant Magellan Telescope. The work done in this dissertation improves the of knowledge on high-redshift galaxies to guide future observations and surveys. With deep data on large samples of early galaxies from these observatories, a detailed timeline of reionization can be even further constrained, as well as the properties of the main drivers of the process.
Abstract
MACS0647–JD is a triply lensed
z
∼ 11 galaxy originally discovered with the Hubble Space Telescope. The three lensed images are magnified by factors of ∼8, 5, and 2 to AB mag 25.1, 25.6, and ...26.6 at 3.5
μ
m. The brightest is over a magnitude brighter than other galaxies recently discovered at similar redshifts
z
> 10 with JWST. Here, we report new JWST imaging that clearly resolves MACS0647–JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. The brighter larger component “A” is intrinsically very blue (
β
∼ −2.6 ± 0.1), likely due to very recent star formation and no dust, and is spatially extended with an effective radius ∼70 ± 24 pc. The smaller component “B” (
r
∼ 20
−
5
+
8
pc) appears redder (
β
∼ −2 ± 0.2), likely because it is older (100–200 Myr) with mild dust extinction (
A
V
∼ 0.1 mag). With an estimated stellar mass ratio of roughly 2:1 and physical projected separation ∼400 pc, we may be witnessing a galaxy merger 430 million years after the Big Bang. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be dissimilar, which is also suggested by the spectral energy distribution fitting, suggesting they formed further apart. We also identify a candidate companion galaxy “C” ∼3 kpc away, likely destined to merge with A and B. Upcoming JWST Near Infrared Spectrograph observations planned for 2023 January will deliver spectroscopic redshifts and more physical properties for these tiny magnified distant galaxies observed in the early universe.
We report the discovery of a spectroscopically confirmed strong Lyαemitter atz=7.0281±0.0003, observed as part of the Reionization Lensing Cluster Survey(RELICS). This galaxy, dubbed“Dichromatic ...Primeval Galaxy”atz∼7(DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet(UV)luminosity(~L0.3UV*,whereLUV*is the characteristic luminosity), DP7 has one of the highest observed Lyαequivalent widths(EWs)amongLyαemitters atz>6(>200Åin the rest frame). The strong Lyαemission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slopeβof the galaxy as a whole is redder than typical star-forming galaxies at these redshifts,−1.13±0.84, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measureβfor the two components separately, however, we find evidence of differing UVcolors, suggesting two separate stellar populations. Also, we find that Lyαis spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyαhalo. Rejuvenation or merging events could explain these results.Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured active galactic nucleus. DP7, with its low UV luminosity and high LyαEW, represents the typical galaxies that are thought to be the major contribution to the reionization of the universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope
MACS0647-JD is a triply lensed z similar to 11 galaxy originally discovered with the Hubble Space Telescope. The three lensed images are magnified by factors of similar to 8, 5, and 2 to AB mag 25.1, ...25.6, and 26.6 at 3.5 mu m. The brightest is over a magnitude brighter than other galaxies recently discovered at similar redshifts z > 10 with JWST. Here, we report new JWST imaging that clearly resolves MACS0647-JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. The brighter larger component "A" is intrinsically very blue (ss similar to-2.6 +/- 0.1), likely due to very recent star formation and no dust, and is spatially extended with an effective radius similar to 70 +/- 24 pc. The smaller component "B" (r similar to 20-+ 58 pc) appears redder (ss similar to-2 +/- 0.2), likely because it is older (100-200 Myr) with mild dust extinction (AV similar to 0.1 mag). With an estimated stellar mass ratio of roughly 2:1 and physical projected separation similar to 400 pc, we may be witnessing a galaxy merger 430 million years after the Big Bang. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be dissimilar, which is also suggested by the spectral energy distribution fitting, suggesting they formed further apart. We also identify a candidate companion galaxy "C" similar to 3 kpc away, likely destined to merge with A and B. Upcoming JWST Near Infrared Spectrograph observations planned for 2023 January will deliver spectroscopic redshifts and more physical properties for these tiny magnified distant galaxies observed in the early universe.
We present a study on stellar properties of Lyman-alpha (Ly$\alpha$) emitters
at 5 $< z <$ 8.2. We use 247 photometrically-selected, lensed, high-redshift,
low luminosity galaxy candidates with ...spectroscopic follow-up. Of these, 38 are
confirmed spectroscopically to be between 5 $< z <$ 8.2 via detection of
Ly$\alpha$. For each galaxy and candidate, we estimate stellar mass, star
formation rate, specific star formation rate, and mass-weighted age with
spectral energy distribution fitting. We also measure the UV $\beta$ slope and
luminosity using values from photometry. We find no strong correlation between
Ly$\alpha$ equivalent width and any of these properties, as well as no
significant difference between the physical properties of Ly$\alpha$ emitters
and candidates without Ly$\alpha$ detected. This lack of expected trends may be
explained by a combination of the evolving opacity of the IGM at these
redshifts as well as the unique phase space probed by our lensed sample. Via
tests on other galaxy samples which show varying strengths of correlations, we
conclude that if there exist any relationships between Ly$\alpha$ EW and
physical properties in the underlying population of faint galaxies, they are
weak correlations. We also present the results of a spectroscopic search for
CIII emission in confirmed Ly$\alpha$ emitters at $z \sim 7$, finding no CIII
detections, but putting constraints on strong AGN activity and extreme nebular
emission.
We report on a \(\rm{CII}_{158\mu\rm{m}}\) search using the Atacama Large Millimeter/submillimeter Array (ALMA) on three lensed, confirmed {\lya} emitting galaxies at \(z \sim 7\). Our targets are ...ultra-violet (UV) faint systems with stellar masses on the order of \(M_{*} \sim 10^{9} M_{\odot}\). We detect a single CII line emission (\(4\sigma\)) from the brightest (\(L \sim 2.4 \times 10^{10}L_{\odot}\)) galaxy in our sample, MACS0454-1251. We determine a systemic redshift (\(z_{\rm{CII}} = 6.3151 \pm 0.0005\)) for MACS0454-1251 and measure a {\lya} velocity offset of \(\Delta v \approx 300 \pm 70 \rm{km\,s}^{-1}\). The remaining two galaxies we detect no {\ct} but provide \(3 \sigma\) upper limits on their {\ct} line luminosities which we use to investigate the \(L_{\textrm{CII}} - \rm{SFR}\) relation. Overall our single {\ct} detection shows agreement with the relation for dwarf and local starburst galaxies. Our CII deficient galaxies could potentially be exhibiting low metallicities (\(Z<Z_{\odot}\)). Another possible explanation for weaker CII emission could be strong feedback from star formation disrupting molecular clouds. We do not detect continuum emission in any of the sources, placing upper limits on their dust masses. Assuming a single dust temperature of \(T_{d}=35 \rm{K}\) dust masses (\(M_{\rm{dust}}\)) range from \(< 4.8 \times 10^{7} M_{\odot} \) to \(2.3 \times 10^{8} M_{\odot}\). Collectively, our results suggest faint reionization era sources could be metal poor and/or could have strong feedback suppressing CII emission.
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