My name is Jakob Helton and I am a fourth-year doctoral student at the University of Arizona pursuing an M.S. and Ph.D. in Astronomy. I spend most of my time thinking about the formation and evolution of galaxies and galaxy clusters in the early Universe. In the coming years, I will be working with the James Webb Space Telescope (JWST) on the JWST Advanced Deep Extragalactic Survey (JADES) with the Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) Science Teams to investigate the properties of the earliest observable galaxies. In addition to my research, I am also a visual artist. I focus on photography and painting, but I have recently started creating digital images and movies. In the coming years, I am hoping to publish a photography book and get my work featured in an art exhibition. You can take a look at my CV here.
I was recently part of a series of blog posts and press releases highlighting the discovery of JADES-GS-z14-0: NASA, UofA, Harvard, Cambridge, UCSC, DAWN, and JADES. These blog posts and press releases were subsequently picked up by major news networks: Astronomy Magazine, BBC, BBC Sky at Night Magazine, CBS News, Forbes, London Evening Standard, Reuters, Scientific American, Space.com, and Yahoo! News. I also helped explain how a distant galaxy like JADES-GS-z14-0 can be observed, despite the extreme distance: Space.com. JADES-GS-z14-0 fly-through visualization. JADES-GS-z14-0 interview with the UofA.
JWST/MIRI photometric detection at 7.7 microns of the stellar continuum and nebular emission in a galaxy at z > 14
Abstract: The James Webb Space Telescope (JWST) has spectroscopically confirmed numerous galaxies at z > 10. While weak rest-ultraviolet emission lines have only been seen in a handful of sources, the stronger rest-optical emission lines are highly diagnostic and accessible at mid-infrared wavelengths with the Mid-Infrared Instrument (MIRI) of JWST. We report the photometric detection of the most distant spectroscopically confirmed galaxy JADES-GS-z14-0 at z = 14.32+0.08−0.20 with MIRI at 7.7 μm. The most plausible solution for the stellar population properties is that this galaxy contains half a billion solar masses in stars with a strong burst of star formation in the most recent few million years. For this model, at least one-third of the flux at 7.7 μm comes from the rest-optical emission lines Hβ and/or [OIII]λλ4959,5007. The inferred properties of JADES-GS-z14-0 suggest rapid mass assembly and metal enrichment during the earliest phases of galaxy formation. ADS Link. arXiv Link.
Identification of High-Redshift Galaxy Overdensities in GOODS-N and GOODS-S
Abstract: We conduct a systematic search for high-redshift galaxy overdensities at 4.9 < zspec < 8.9 in both the GOODS-N and GOODS-S fields using JWST/NIRCam imaging from JADES and JEMS in addition to JWST/NIRCam wide field slitless spectroscopy from FRESCO. High-redshift galaxy candidates are identified using HST+JWST photometry spanning λ = 0.4−5.0 μm. We confirmed the redshifts for roughly a third of these galaxies using JWST/FRESCO spectroscopy over λ = 3.9−5.0 μm through identification of either Hα or [OIII]λ5008 around the best-fit photometric redshift. The rest-UV magnitudes and continuum slopes of these galaxies were inferred from the photometry: the brightest and reddest objects appear in more dense environments and thus are surrounded by more galaxy neighbors than their fainter and bluer counterparts, suggesting accelerated galaxy evolution within overdense environments. We find 17 significant (δgal ≥ 3.04, Ngal ≥ 4) galaxy overdensities across both fields (7 in GOODS-N and 10 in GOODS-S), including the two highest redshift spectroscopically confirmed galaxy overdensities to date at ⟨zspec⟩ = 7.955 and ⟨zspec⟩ = 8.222 (representing densities around ≈ 6 and ≈ 12 times that of a random volume). We estimate the total halo mass of these large-scale structures to be 11.5 ≤ log(Mhalo/M⊙) ≤ 13.4 using an empirical stellar mass to halo mass relation, which are likely underestimates as a result of incompleteness. These protocluster candidates are expected to evolve into massive galaxy clusters with log(Mhalo/M⊙) ≥ 14 by z = 0. ADS Link. arXiv Link.
The JWST Advanced Deep Extragalactic Survey: Discovery of an Extreme Galaxy Overdensity at z = 5.4 with JWST/NIRCam in GOODS-S
Abstract: We report the discovery of an extreme galaxy overdensity at z = 5.4 in the GOODS-S field using JWST/NIRCam imaging from JADES and JEMS alongside JWST/NIRCam wide field slitless spectroscopy from FRESCO. We identified potential members of the overdensity using HST+JWST photometry spanning λ = 0.4−5.0 μm. These data provide accurate and well-constrained photometric redshifts down to m ≈ 29−30 mag. We subsequently confirmed N = 81 potential members of the overdensity using JWST slitless spectroscopy over λ = 3.9−5.0 μm through a targeted line search for Hα around the best-fit photometric redshift. We verified that N = 42 galaxies reside in the field at z = 5.2−5.5 while N = 39 galaxies reside in an overdensity at z = 5.4 around ≈ 10 times that of a random volume. Stellar populations for these galaxies were inferred from the photometry and used to construct the star-forming main sequence, where protocluster members appeared more massive and exhibited earlier star formation (and thus older stellar populations) when compared to their field galaxy counterparts. We estimate the total halo mass of this large-scale structure to be 12.6 < log(Mhalo/M⊙) < 12.8 using an empirical stellar mass to halo mass relation, although this is likely an underestimate as a result of incompleteness. Our discovery demonstrates the power of JWST at constraining dark matter halo assembly and galaxy formation at very early cosmic times. ADS Link. arXiv Link.
The nebular properties of star-forming galaxies at intermediate redshift from the Large Early Galaxy Astrophysics Census
Abstract: We present a detailed study of the partial rest-optical (λobs ≈ 3600-5600 Å) spectra of N = 328 star-forming galaxies at 0.6 < z < 1.0 from the Large Early Galaxy Astrophysics Census (LEGA-C). We compare this sample with low-redshift (z = 0) galaxies from the Sloan Digital Sky Survey (SDSS), intermediate-redshift (z = 1.6) galaxies from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS Survey, and high-redshift (z = 2) galaxies from the Keck Baryonic Structure Survey (KBSS). At a lookback time of 6-8 Gyr, galaxies with stellar masses 10.25 < log(M*/M⊙) < 11.00 appear remarkably similar to z = 0 galaxies in terms of their nebular excitation, as measured using [OIII]λ5008/Hβ. There is some evidence that 0.6 < z < 1.0 galaxies with lower M* have higher [OIII]λ5008/Hβ than z = 0 galaxies and are more similar to less evolved z = 1.6 and z = 2 galaxies, which are offset from the z = 0 locus at all M*. We explore the impact selection effects, contributions from active galactic nuclei, and variations in physical conditions (ionization parameter and gas-phase oxygen abundance) have on the apparent distribution of [OIII]λ5008/Hβ and find somewhat higher ionization and lower enrichment in 0.6 < z < 1.0 galaxies with lower M* relative to z = 0 galaxies. We use new near-infrared spectroscopic observations of N = 53 LEGA-C galaxies to investigate other probes of enrichment and excitation. Our analysis demonstrates the importance of obtaining complete rest-optical spectra of galaxies in order to disentangle these effects. ADS Link. arXiv Link.
Discovery and origins of giant optical nebulae surrounding quasar PKS 0454-22
Abstract: We report optical integral-field spectroscopy in the field of one of the most luminous quasars in the z < 1 Universe, PKS 0454-22, with the Multi-Unit Spectroscopic Explorer. These data enable the discovery of three large ionized nebulae emitting in [OII], Hβ, and [OIII] with projected areas of 1720, 1520, and 130 pkpc2, which we refer to as N1, N2, and N3, respectively. N1 spatially and kinematically surrounds the quasar host and five nearby galaxies. The morphology and kinematics of N1 are most consistent with stripped interstellar medium resulting from ongoing interactions. Its ionization properties can be explained by quasar photoionization. N2 spatially and kinematically surrounds two galaxies that are at projected distances of d ≈ 90 pkpc and line-of-sight velocities of δv ≈ +1410 km s-1 from the quasar. The morphology and kinematics of N2 are also consistent with stripped interstellar medium. However, its ionization state requires additional ionization sources beyond the quasar, likely from fast shocks as it moves through the hot halo associated with a galaxy overdensity around the quasar. N3 is not coincident with any galaxies with secure redshifts, and may arise from a cool gas structure in the intragroup medium or a dwarf galaxy. These large ionized nebulae demonstrate that interactions can produce cool gas structures on halo scales, while also possibly facilitating quasar fueling. The growing availability of wide-area integral field spectroscopic data will continue to reveal the morphologies, kinematics, and conditions of the gas flows, which may fuel galaxy and black hole growth. ADS Link. arXiv Link.
Brown Dwarf Candidates in the JADES and CEERS Extragalactic Surveys
Abstract: By combining the JWST/NIRCam JADES and CEERS extragalactic datasets, we have uncovered a sample of twenty-one T and Y brown dwarf candidates at best-fit distances between 0.1-4.2 kpc. These sources were selected by targeting the blue 1.0μm-2.5μm colors and red 3.0μm-4.5μm colors that arise from molecular absorption in the atmospheres of Teff < 1300 K brown dwarfs. We fit these sources using multiple models of low-mass stellar atmospheres and present the resulting fluxes, sizes, effective temperatures and other derived properties for the sample. If confirmed, these fits place the majority of the sources in the Milky Way thick disk and halo. We observe proper motion for seven of the candidate brown dwarfs with directions in agreement with the plane of our galaxy, providing evidence that they are not extragalactic in nature. We demonstrate how the colors of these sources differ from selected high-redshift galaxies, and explore the selection of these sources in planned large-area JWST NIRCam surveys. Deep imaging with JWST/NIRCam presents an an excellent opportunity for finding and understanding these very cold low-mass stars at kpc distances. ADS Link. arXiv Link.
JADES: Resolving the Stellar Component and Filamentary Overdense Environment of HST-Dark Submillimeter Galaxy HDF850.1 at z = 5.18
Abstract: HDF850.1 is the brightest submillimeter galaxy (SMG) in the Hubble Deep Field. It is known as a heavily dust-obscured star-forming galaxy embedded in an overdense environment at z = 5.18. With nine-band NIRCam images at 0.8−5.0 μm obtained through the JWST Advanced Deep Extragalactic Survey (JADES), we detect and resolve the rest-frame UV-optical counterpart of HDF850.1, which splits into two components because of heavy dust obscuration in the center. The southern component leaks UV and Hα photons, bringing the galaxy ≈ 100 times above the empirical relation between infrared excess and UV continuum slope (IRX-βUV). The northern component is higher in dust attenuation and thus fainter in UV and Hα surface brightness. We construct a spatially resolved dust attenuation map from the NIRCam images, well matched with the dust continuum emission obtained through millimeter interferometry. The whole system hosts a stellar mass of 1010.8±0.1 M⊙ and star-formation rate of 102.8±0.2 M⊙/yr, placing the galaxy at the massive end of the star-forming main sequence at this epoch. We further confirm that HDF850.1 resides in a complex overdense environment at z = 5.17−5.30, which hosts another luminous SMG at z = 5.30 (GN10). The filamentary structures of the overdensity are characterized by 109 Hα-emitting galaxies confirmed through NIRCam slitless spectroscopy at 3.9−5.0 μm, of which only eight were known before the JWST observations. Given the existence of a similar galaxy overdensity in the GOODS-S field, our results suggest that 50±20% of the cosmic star formation at z = 5.1−5.5 occur in protocluster environments. ADS Link. arXiv Link.
JADES: Spectroscopic Confirmation and Proper Motion for a T-Dwarf at 2 Kiloparsecs
Abstract: Large area observations of extragalactic deep fields with the James Webb Space Telescope (JWST) have provided a wealth of candidate low-mass L- and T-class brown dwarfs. The existence of these sources, which are at derived distances of hundreds of parsecs to several kiloparsecs from the Sun, has strong implications for the low-mass end of the stellar initial mass function, and the link between stars and planets at low metallicities. In this letter, we present a JWST/NIRSpec PRISM spectrum of brown dwarf JADES-GS-BD-9, confirming its photometric selection from observations taken as part of the JWST Advanced Deep Extragalactic Survey (JADES) program. Fits to this spectrum indicate that the brown dwarf has an effective temperature of 800-900K (T5 - T6) at a distance of 1.8−2.3kpc from the Sun, with evidence of the source being at low metallicity ([M/H] ≤ −0.5). Finally, because of the cadence of JADES NIRCam observations of this source, we additionally uncover a proper motion between the 2022 and 2023 centroids, and we measure a proper motion of 20±4 mas/yr (a transverse velocity of 214 km/s at 2.25 kpc). At this predicted metallicity, distance, and transverse velocity, it is likely that this source belongs either to the edge of the Milky Way thick disk or the galactic halo. This spectral confirmation demonstrates the efficacy of photometric selection of these important sources across deep extragalactic JWST imaging. ADS Link. arXiv Link.
SMILES Initial Data Release: Unveiling the Obscured Universe with MIRI Multi-band Imaging
Abstract: The James Webb Space Telescope (JWST) is revolutionizing our view of the Universe through unprecedented sensitivity and resolution in the infrared, with some of the largest gains realized at its longest wavelengths. We present the Systematic Mid-infrared Instrument (MIRI) Legacy Extragalactic Survey (SMILES), an eight-band MIRI survey with Near-Infrared Spectrograph (NIRSpec) spectroscopic follow-up in the GOODS-S/HUDF region. SMILES takes full advantage of MIRI's continuous coverage from 5.6−25.5μm over a ≈ 34 square arcminutes area to greatly expand our understanding of the obscured Universe up to cosmic noon and beyond. This work, together with a companion paper by Rieke et al., covers the SMILES science drivers and technical design, early results with SMILES, data reduction, photometric catalog creation, and the first data release. As part of the discussion on early results, we additionally present a high-level science demonstration on how MIRI's wavelength coverage and resolution will advance our understanding of cosmic dust using the full range of polycyclic aromatic hydrocarbon (PAH) emission features from 3.3−18μm. Using custom background subtraction, we produce robust reductions of the MIRI imaging that maximize the depths reached with our modest exposure times (≈ 0.6−2.2ks per filter). Included in our initial data release are (1) eight MIRI imaging mosaics reaching depths of 0.2−18μJy (5σ) and (2) a 5−25.5μm photometric catalog with over 3,000 sources. Building upon the rich legacy of extensive photometric and spectroscopy coverage of GOODS-S/HUDF from the X-ray to the radio, SMILES greatly expands our investigative power in understanding the obscured Universe. ADS Link. arXiv Link.
A shining cosmic dawn: spectroscopic confirmation of two luminous galaxies at z ≈ 14
Abstract: The discovery by JWST of an abundance of luminous galaxies in the very early Universe suggests that galaxies developed rapidly, in apparent tension with many standard models. However, most of these galaxies lack spectroscopic confirmation, so their distances and properties are uncertain. We present JADES JWST/NIRSpec spectroscopic confirmation of two luminous galaxies at redshifts of z = 14.32+0.08−0.20 and z = 13.90±0.17. The spectra reveal ultraviolet continua with prominent Lyman-α breaks but no detected emission lines. This discovery proves that luminous galaxies were already in place 300 million years after the Big Bang and are more common than what was expected before JWST. The most distant of the two galaxies is unexpectedly luminous (MUV = −20.81±0.16) and is spatially resolved with a radius of 260 parsecs. Considering also the steep ultraviolet slope of the second galaxy (βUV = −2.71±0.19), we conclude that both are dominated by stellar continuum emission, showing that the excess of luminous galaxies in the early Universe cannot be entirely explained by accretion onto black holes. Galaxy formation models will need to address the existence of such large and luminous galaxies so early in cosmic history. ADS Link. arXiv Link.
JADES: Primeval Lyman-α emitting galaxies reveal early sites of reionisation out to redshift z ≈ 9
Abstract: Given the sensitivity of the resonant Lyman-α (Lyα) transition to absorption by neutral hydrogen, observations of Lyα emitting galaxies (LAEs) have been widely used to probe the ionising capabilities of reionisation-era galaxies and their impact on the intergalactic medium (IGM). However, prior to JWST our understanding of the contribution of fainter sources and of ionised "bubbles" at earlier stages of reionisation remained uncertain. Here, we present the characterisation of three exceptionally distant LAEs at z > 8, newly discovered by JWST/NIRSpec in the JADES survey. These three similarly bright (MUV ≈ −20 mag) LAEs exhibit small Lyα velocity offsets from the systemic redshift, αvLyα < 200 km/s, yet span a range of Lyα equivalent widths (15 Å, 31 Å, and 132 Å). The former two show moderate Lyα escape fractions (fesc,Lyα ≈ 10%), whereas Lyαescapes remarkably efficiently from the third (fesc,Lyα ≈ 71%), which moreover is very compact (half-light radius of 90±10 pc). We find these LAEs are low-mass galaxies dominated by very recent, vigorous bursts of star formation accompanied by strong nebular emission from metal-poor gas. We infer the two LAEs with modest fesc,Lyα, one of which reveals evidence for ionisation by an active galactic nucleus, may have reasonably produced small ionised bubbles preventing complete IGM absorption of Lyα. The third, however, requires a ≈ 3 physical Mpc bubble, indicating faint galaxies have contributed significantly. The most distant LAEs thus continue to be powerful observational probes into the earlier stages of reionisation. ADS Link. arXiv Link.
The FLAMINGO simulation view of cluster progenitors observed in the epoch of reionization with JWST
Abstract: Motivated by the recent JWST discovery of galaxy overdensities during the Epoch of Reionzation, we examine the physical properties of high-z protoclusters and their evolution using the FLAMINGO simulation suite. We investigate the impact of the apertures used to define protoclusters, because the heterogeneous apertures used in the literature have limited our understanding of the population. Our results are insensitive to the uncertainties of the subgrid models at a given resolution, whereas further investigation into the dependence on numerical resolution is needed. When considering galaxies more massive than log(M*/M⊙) ≈ 8.0, the FLAMINGO simulations predict a dominant contribution from progenitors similar to those of the Coma cluster to the cosmic star-formation rate density during the reionization epoch. Our results indicate the onset of suppression of star formation in the protocluster environments as early as z ≈ 5. The galaxy number density profiles are similar to NFW at z < 1 while showing a steeper slope at earlier times before the formation of the core. Different from most previous simulations, the predicted star-formation history for individual protoclusters is in good agreement with observations. We demonstrate that, depending on the aperture, the integrated physical properties including the total (dark matter and baryonic) mass can be biased by a factor of 2 to 5 at z = 5.5-7.0, and by an order of magnitude at z < 4. This correction suffices to remove the ≈ 3σ tensions with the number density of structures found in recent JWST observations. ADS Link. arXiv Link.
To high redshift and low mass: exploring the emergence of quenched galaxies and their environments at 3 < z < 6 in the ultra-deep JADES MIRI F770W parallel
Abstract: We present the robust selection of quiescent (QG) and post-starburst (PSB) galaxies using ultra-deep NIRCam and MIRI imaging from the JWST Advanced Deep Extragalactic Survey (JADES). Key to this is MIRI 7.7 μm imaging which breaks the degeneracy between old stellar populations and dust attenuation at 3 < z < 6 by providing rest-frame J-band. Using this, we identify 23 passively evolving galaxies in UVJ color space in a mass-limited (log(M*/M⊙) > 8.5) sample over 8.8 square arcminutes. Evaluation of this selection with and without 7.7 μm shows that dense wavelength coverage with NIRCam (8−11 bands including 1−4 medium-bands) can compensate for lacking the J−band anchor, meaning that robust selection of high-redshift QGs is possible with NIRCam alone. Our sample is characterized by rapid quenching timescales (≈ 100−600 Myr) with formation redshifts zf < 8.5 and includes a potential record-holding massive QG at zphot = 5.33+0.16-0.17 and two QGs with evidence for significant residual dust content (AV ≈ 1−2). In addition, we present a large sample of 12 log(M*/M⊙) = 8.5-9.5 PSBs, demonstrating that UVJ selection can be extended to low mass. Analysis of the environment of our sample reveals that the group known as the Cosmic Rose contains a massive QG and a dust-obscured star-forming galaxy (a so-called Jekyll and Hyde pair) plus three additional QGs within ≈ 20 kpc. Moreover, the Cosmic Rose is part of a larger overdensity at z ≈ 3.7 which contains 7/12 of our low-mass PSBs. Another 4 low-mass PSBs are members of an overdensity at z ≈ 3.4; this result strongly indicates low-mass PSBs are preferentially associated with overdense environments at z > 3. ADS Link. arXiv Link.
JADES: deep spectroscopy of a low-mass galaxy at redshift 2.3 quenched by environment
Abstract: We report the discovery of a quiescent galaxy at z = 2.34 with a stellar mass of only M* ≈ 9.5 × 108 M⊙, based on deep JWST/NIRSpec spectroscopy. This is the least massive quiescent galaxy found so far at high redshift. We use a Bayesian approach to model the spectrum and photometry, and find the target to have been quiescent for 0.6 Gyr with a mass-weighted average stellar age of 0.8-1.7 Gyr (dominated by systematics). The galaxy displays an inverse colour gradient with radius, consistent with environment-driven quenching. Based on a combination of spectroscopic and robust (medium- and broad-band) photometric redshifts, we identify a galaxy overdensity near the location of the target (5σ above the background level at this redshift). We stress that had we been specifically targetting galaxies within overdensities, the main target would not have been selected on photometry alone; therefore, environment studies based on photometric redshifts are biased against low-mass quiescent galaxies. The overdensity contains three spectroscopically confirmed, massive, old galaxies (M* = 8−17 × 1010 M⊙). The presence of these evolved systems points to accelerated galaxy evolution in overdensities at redshifts z > 2, in agreement with previous works. In projection, our target lies only 35 pkpc away from the most massive galaxy in this overdensity (spectroscopic redshift z = 2.349) which is located close to overdensity's centre. This suggests the low-mass galaxy was quenched by environment, making it possibly the earliest evidence for environment-driven quenching to date. ADS Link. arXiv Link.
Evolution of Gas Flows along the Starburst to Post-Starburst to Quiescent Galaxy Sequence
Abstract: We measure velocity offsets in the NaI λλ5890,5896 (Na D) interstellar medium absorption lines to track how neutral galactic winds change as their host galaxies evolve. Our sample of ∼80,000 SDSS spectra at 0.010 < z < 0.325 includes starburst, post-starburst, and quiescent galaxies, forming an evolutionary sequence of declining star formation rate (SFR). We detect bulk flows across this sequence, mostly at higher host stellar masses (log[M*/M⊙] > 10). Along this sequence, the fraction of outflows decreases (76±2% to 65±4% to a 3σ upper limit of 34%), and the mean velocity offset changes from outflowing to inflowing (−84.6±5.9 to −71.6±11.4 to 76.6±2.3 km/s). Even within the post-starburst sample, wind speed decreases with time elapsed since the starburst ended. These results reveal that outflows diminish as galaxies age. For post-starbursts, there is evidence for an AGN contribution, especially to the speediest outflows: 1) SFR declines faster in time than outflow velocity, a decoupling arguing against massive stellar feedback; 2) of the few outflows strong enough to escape the interstellar medium (9/105), three of the four hosts with measured emission lines are Seyfert galaxies. For disky starburst galaxies, however, the trends suggest flows out of the stellar disk plane (with outflow 1/2-opening angle > 45 degrees) instead of from the nucleus: the wind velocity decreases as the disk becomes more edge-on, and the outflow fraction, constant at ≈ 90% for disk inclinations i < 45 degrees, steadily decreases from ≈ 90% to 20% for i > 45 degrees. ADS Link. arXiv Link.
The Cosmos in its Infancy: JADES Galaxy Candidates at z > 8 in GOODS-S and GOODS-N
Abstract: We present a catalog of 717 candidate galaxies at z > 8 selected from 125 square arcminutes of NIRCam imaging as part of the JWST Advanced Deep Extragalactic Survey (JADES). We combine the full JADES imaging dataset with data from the JEMS and FRESCO JWST surveys along with extremely deep existing observations from HST/ACS for a final filter set that includes fifteen JWST/NIRCam filters and five HST/ACS filters. The high-redshift galaxy candidates were selected from their estimated photometric redshifts calculated using a template fitting approach, followed by visual inspection from seven independent reviewers. We explore these candidates in detail, highlighting interesting resolved or extended sources, sources with very red long-wavelength slopes, and our highest redshift candidates, which extend to zphot = 18. Over 93% of the sources are newly identified from our deep JADES imaging, including 31 new galaxy candidates at zphot > 12. We also investigate potential contamination by stellar objects, and do not find strong evidence from SED fitting that these faint high-redshift galaxy candidates are low-mass stars. Using 42 sources in our sample with measured spectroscopic redshifts from NIRSpec and FRESCO, we find excellent agreement to our photometric redshift estimates, with no catastrophic outliers and an average difference of ⟨δz = zphot − zspec⟩ = 0.26. These sources comprise one of the most robust samples for probing the early buildup of galaxies within the first few hundred million years of the Universe's history. ADS Link. arXiv Link.
Inside the bubble: exploring the environments of reionisation-era Lyman-α emitting galaxies with JADES and FRESCO
Abstract: We present a study of the environments of 16 Lyman-α emitting galaxies (LAEs) in the reionisation era (5.8 < z < 8.0) identified by JWST/NIRSpec as part of the JWST Advanced Deep Extragalactic Survey (JADES). Unless situated in sufficiently (re)ionised regions, Lyman-α emission from these galaxies would be strongly absorbed by neutral gas in the intergalactic medium (IGM). We conservatively estimate sizes of the ionised regions required to reconcile the relatively low Lyman-α velocity offsets (δvesc, Ly-α < 300 km/s) with moderately high Lyman-α escape fractions (fesc, Ly-α > 5%) observed in our sample of LAEs, indicating the presence of ionised "bubbles" with physical sizes of the order of 0.1 < Rion/pMpc > 1.0 in a patchy reionisation scenario where the bubbles are embedded in a fully neutral IGM. Around half of the LAEs in our sample are found to coincide with large-scale galaxy overdensities seen in FRESCO at z ≈ 5.8-5.9 and z ≈ 7.3, suggesting Lyman-α transmission is strongly enhanced in such overdense regions, and underlining the importance of LAEs as tracers of the first large-scale ionised bubbles. Considering only spectroscopically confirmed galaxies, we find our sample of UV-faint LAEs (MUV > −20 mag) and their direct neighbours are generally not able to produce the required ionised regions based on the Lyman-α transmission properties, suggesting lower-luminosity sources likely play an important role in carving out these bubbles. These observations demonstrate the combined power of JWST multi-object and slitless spectroscopy in acquiring a unique view of the early stages of Cosmic Reionisation via the most distant LAEs. ADS Link. arXiv Link.
JADES Imaging of GN-z11: Revealing the Morphology and Environment of a Luminous Galaxy 430 Myr After the Big Bang
Abstract: We present JWST NIRCam nine-band near-infrared imaging of the luminous z = 10.6 galaxy GN-z11 from the JWST Advanced Deep Extragalactic Survey of the GOODS-N field. We find a spectral energy distribution (SED) entirely consistent with the expected form of a high-redshift galaxy: a clear blue continuum from 1.5 to 4.0 microns with a complete dropout in F115W. The core of GN-z11 is extremely compact in JWST imaging. We analyze the image with a two-component model, using a point source and a Sérsic profile that fits to a half-light radius of 200 pc and an index n = 0.9. We find a low-surface brightness haze about 0.4 arcseconds to the northeast of the galaxy, which is most likely a foreground object but might be a more extended component of GN-z11. At a spectroscopic redshift of 10.60 (Bunker et al. 2023), the comparison of the NIRCam F410M and F444W images spans the Balmer jump. From population synthesis modeling, here assuming no light from an active galactic nucleus, we reproduce the SED of GN-z11, finding a stellar mass of log(M*/M⊙) ≈ 9, a star-formation rate of ≈ 20 M⊙/yr and a young stellar age of ≈ 20 Myr. As massive galaxies at high redshift are likely to be highly clustered, we search for faint neighbors of GN-z11, finding nine galaxies out to ≈ 5 comoving Mpc transverse with photometric redshifts consistent with z = 10.6, and a 10th more tentative dropout only 3 arcseconds away. This is consistent with GN-z11 being hosted by a massive dark-matter halo (≈ 8 × 1010 M⊙), though lower halo masses cannot be ruled out. ADS Link. arXiv Link.
Identification and properties of intense star-forming galaxies at redshifts z > 10
Abstract: Surveys with the James Webb Space Telescope (JWST) have discovered candidate galaxies in the first 400 Myr of cosmic time. Preliminary indications have suggested these candidate galaxies may be more massive and abundant than previously thought. However, without confirmed distances, their inferred properties remain uncertain. Here we identify four galaxies located in the JWST Advanced Deep Extragalactic Survey Near-Infrared Camera imaging with photometric redshifts z of roughly 10-13. These galaxies include the first redshift z > 12 systems discovered with distances spectroscopically confirmed by JWST in a companion paper. Using stellar population modelling, we find the galaxies typically contain 100 million solar masses in stars, in stellar populations that are less than 100 million years old. The moderate star-formation rates and compact sizes suggest elevated star-formation rate surface densities, a key indicator of their formation pathways. Taken together, these measurements show that the first galaxies contributing to cosmic reionization formed rapidly and with intense internal radiation fields. ADS Link. arXiv Link.
The Atacama Cosmology Telescope: DR4 maps and cosmological parameters
Abstract: We present new arcminute-resolution maps of the Cosmic Microwave Background temperature and polarization anisotropy from the Atacama Cosmology Telescope, using data taken from 2013-2016 at 98 and 150 GHz. The maps cover more than 17,000 deg2, the deepest 600 deg2 with noise levels below 10μK-arcmin. We use the power spectrum derived from almost 6,000 deg2 of these maps to constrain cosmology. The ACT data enable a measurement of the angular scale of features in both the divergence-like polarization and the temperature anisotropy, tracing both the velocity and density at last-scattering. From these one can derive the distance to the last-scattering surface and thus infer the local expansion rate, H0. By combining ACT data with large-scale information from WMAP we measure H0 = 67.6 ± 1.1 km/s/Mpc, at 68% confidence, in excellent agreement with the independently-measured Planck satellite estimate (from ACT alone we find H0 = 67.9 ± 1.5 km/s/Mpc). The ΛCDM model provides a good fit to the ACT data, and we find no evidence for deviations: both the spatial curvature, and the departure from the standard lensing signal in the spectrum, are zero to within 1σ; the number of relativistic species, the primordial Helium fraction, and the running of the spectral index are consistent with ΛCDM predictions to within 1.5-2.2σ. We compare ACT, WMAP, and Planck at the parameter level and find good consistency; we investigate how the constraints on the correlated spectral index and baryon density parameters readjust when adding CMB large-scale information that ACT does not measure. The DR4 products presented here will be publicly released on the NASA Legacy Archive for Microwave Background Data Analysis. ADS Link. arXiv Link.
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