| 1. |
- Binggeli, Christian, et al.
(author)
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A puzzling non-detection of [O III] and [C II] from a z ≈ 7.7 galaxy observed with ALMA
- 2021
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 646
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Journal article (peer-reviewed)abstract
- Context. Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, there have been very few observations at the very highest redshifts to date. Aims. In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-α emitting galaxy z7_GSD_3811 at z = 7.664 with bands 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We target the far-infrared [O iii] 88 µm and [C ii] 158 µm emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object and compare the results to those of earlier studies that observed [O iii] and [C ii] emission in high-redshift galaxies. Results. The [O iii] 88 µm and [C ii] 158 µm emission lines are undetected at the position of z7_GSD_3811, with 3σ upper limits of 1.6 × 108 L and 4.0 × 107 L, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continua are 26 and 9.9 µJy beam−1, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C ii] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O iii] line luminosity is lower than the previously observed [O iii] lines in high-redshift galaxies with similar UV luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O iii] and [C ii] lines could indicate that z7_GSD_3811 has a low metallicity (Z. 0.1 Z).
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| 2. |
- Binggeli, Christian, et al.
(author)
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Balmer breaks in simulated galaxies at z > 6
- 2019
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In: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 489:3, s. 3827-3835
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Journal article (peer-reviewed)abstract
- Photometric observations of the spectroscopically confirmed z approximate to 9.1 galaxy MACS1149-JD1 have indicated the presence of a prominent Balmer break in its spectral energy distribution, which may be interpreted as due to very large fluctuations in its past star formation activity. In this paper, we investigate to what extent contemporary simulations of high-redshift galaxies produce star formation rate variations sufficiently large to reproduce the observed Balmer break of MACS1149-JD1. We find that several independent galaxy simulations are unable to account for Balmer breaks of the inferred size, suggesting that MACS1149-JD1 either must be a very rare type of object or that our simulations are missing some key ingredient. We present predictions of spectroscopic Balmer break strength distributions for z approximate to 7-9 galaxies that may be tested through observations with the upcoming James Webb Space Telescope and also discuss the impact that various assumptions on dust reddening, Lyman continuum leakage, and deviations from a standard stellar initial mass function would have on the results.
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| 3. |
- Binggeli, Christian, 1989-
(author)
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Galaxies in the epoch of reionization : Investigating the high-redshift galaxy population through simulations and observations
- 2021
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Doctoral thesis (other academic/artistic)abstract
- The cosmic reionization is the last major gas phase transition in cosmic history, yet it remains poorly understood. Current constraints indicate that early star-forming galaxies drove the reionization process through producing and releasing large numbers of ionizing photons into the intergalactic medium. However, our understanding of the ionizing escape fraction (fesc) and the general properties of high-redshift galaxies is still limited.In this thesis, simulated galaxies and observations are used to investigate epoch-of-reionization galaxies and to explore methods that can aid future investigations of such objects. Using simulations, we have shown that it may be possible to constrain fesc in epoch-of-reionization galaxies using quite simple diagnostics that should be observable with the upcoming James Webb Space Telescope (JWST). We also show that variations in star formation activity larger than those predicted in our simulations may lead to a possible degeneracy with high fesc. However, auxiliary information obtained with the JWST may allow us to disentangle variations in the star formation activity from high fesc.We compare galaxies from several simulations to the recently spectroscopically confirmed z=9.1096 galaxy MACS1149-JD1. We find that none of the simulations are able to reproduce the large Balmer break observed in MACS1149-JD1, and argue that unless it represents an outlier in the high-redshift galaxy population, this may indicate that the simulations fail to capture some key physics. Finally, we present ALMA observations of the z=7.6637 galaxy z7_GSD_3811. This object remains undetected in several commonly detected FIR emission lines and FIR dust emission. Using SED-fitting and by comparing our observations to models and low-redshift observations, we show that our non-detections could indicate that the object is poor in metals and dust.Our findings could help future observers to further constrain the nature of high-redshift galaxies and their role in reionization.
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| 4. |
- Binggeli, Christian, et al.
(author)
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Lyman continuum leakage versus quenching with the James Webb Space Telescope : the spectral signatures of quenched star formation activity in reionization-epoch galaxies
- 2018
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 479:1, s. 368-376
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Journal article (peer-reviewed)abstract
- In this paper, we study the effects of a recent drop in star formation rate (SFR) on the spectra of epoch of reionization (EoR) galaxies, and the resulting degeneracy with the spectral features produced by extreme Lyman continuum leakage. In order to study these effects in the wavelength range relevant for the upcoming James Webb Space Telescope (JWST), we utilize synthetic spectra of simulated EoR galaxies from cosmological simulations together with synthetic spectra of partially quenched mock galaxies. We find that rapid declines in the SFR of EoR galaxies could seriously affect the applicability of methods that utilize the equivalent width of Balmer lines and the ultraviolet spectral slope to assess the escape fraction of EoR galaxies. In order to determine if the aforementioned degeneracy can be avoided by using the overall shape of the spectrum, we generate mock NIRCam observations and utilize a classification algorithm to identify galaxies that have undergone quenching. We find that while there are problematic cases, JWST/NIRCam or NIRSpec should be able to reliably identify galaxies with redshifts z similar to 7 that have experienced a significant decrease in the SFR (by a factor of 10-100) in the past 50-100 Myr with a success rate greater than or similar to 85 per cent. We also find that uncertainties in the dust-reddening effects on EoR galaxies significantly affect the performance of the results of the classification algorithm. We argue that studies that aim to characterize the dust extinction law most representative in the EoR would be extremely useful.
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| 5. |
- Giri, Sambit K., et al.
(author)
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Constraining Lyman continuum escape using Machine Learning
- 2018
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In: Peering towards Cosmic Dawn. - : Cambridge University Press. - 9781107192461 ; , s. 254-258
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Conference paper (peer-reviewed)abstract
- The James Webb Space Telescope (JWST) will observe the rest-frame ultraviolet/optical spectra of galaxies from the epoch of reionization (EoR) in unprecedented detail. While escaping into the intergalactic medium, hydrogen-ionizing (Lyman continuum; LyC) photons from the galaxies will contribute to the bluer end of the UV slope and make nebular emission lines less prominent. We present a method to constrain leakage of the LyC photons using the spectra of high redshift (z greater than or similar to 6) galaxies. We simulate JWST/NIRSpec observations of galaxies at z = 6-9 by matching the fluxes of galaxies observed in the Frontier Fields observations of galaxy cluster MACS-J0416. Our method predicts the escape fraction f(esc) with a mean absolute error Delta f(esc) approximate to 0.14. The method also predicts the redshifts of the galaxies with an error approximate to 0.0003.
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| 6. |
- Giri, Sambit K., et al.
(author)
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Identifying reionization-epoch galaxies with extreme levels of Lyman continuum leakage in James Webb Space Telescope surveys
- 2020
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In: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 491:4, s. 5277-5286
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Journal article (peer-reviewed)abstract
- The James Webb Space Telescope (JWST) NIRSpec instrument will allow rest-frame ultraviolet/optical spectroscopy of galaxies in the epoch of reionization (EoR). Some galaxies may exhibit significant leakage of hydrogen-ionizing photons into the intergalactic medium, resulting in faint nebular emission lines. We present a machine learning framework for identifying cases of very high hydrogen-ionizing photon escape from galaxies based on the data quality expected from potential NIRSpec observations of EoR galaxies in lensed fields. We train our algorithm on mock samples of JWST/NIRSpec data for galaxies at redshifts z = 6-10. To make the samples more realistic, we combine synthetic galaxy spectra based on cosmological galaxy simulations with observational noise relevant for z greater than or similar to 6 objects of a brightness similar to EoR galaxy candidates uncovered in Frontier Fields observations of galaxy cluster Abell-2744 and MACS-J0416. We find that ionizing escape fractions (f(esc)) of galaxies brighter than m(AB,1500) approximate to 27 mag may be retrieved with mean absolute error Delta f(esc) approximate to 0.09(0.12) for 24 h (1.5 h) JWST/NIRSpec exposures at resolution R = 100. For 24 h exposure time, even fainter galaxies (m(AB,1500) < 28.5 mag) can be processed with Delta f(esc) approximate to 0.14. This framework simultaneously estimates the redshift of these galaxies with a relative error less than 0.03 for both 24 (m(AB,1500) < 28.5 mag) and 1.5 h (m(AB,1500) < 27 mag) exposure times. We also consider scenarios where just a minor fraction of galaxies attain high f(esc) and present the conditions required for detecting a subpopulation of high-f(esc) galaxies within the data set.
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| 7. |
- Hsiao, Tiger Yu-Yang, et al.
(author)
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JWST Reveals a Possible z similar to 11 Galaxy Merger in Triply Lensed MACS0647-JD
- 2023
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 949:2
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
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| 9. |
- Rubensson, Jan-Erik, et al.
(author)
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Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
- 2015
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 114:13
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Journal article (peer-reviewed)abstract
- Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
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| 10. |
- Sugahara, Yuma, et al.
(author)
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Big Three Dragons : A [N ii] 122 μm Constraint and New Dust-continuum Detection of a z = 7.15 Bright Lyman-break Galaxy with ALMA
- 2021
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In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 923:1
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Journal article (peer-reviewed)abstract
- We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman-break galaxy at z = 7.15, B14-65666 ("Big Three Dragons"), which is an object detected in [O iii] 88 μm, [C ii] 158 μm, and dust continuum emission during the epoch of reionization. Our targets are the [N ii] 122 μm fine-structure emission line and the underlying 120 μm dust continuum. The dust continuum is detected with a ∼19σ significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 μm, we obtain a best-fit dust temperature of 40 K (79 K) and an infrared luminosity of (12.1) at the emissivity index β = 2.0 (1.0). The [N ii] 122 μm line is not detected. The 3σ upper limit of the [N ii] luminosity is 8.1 × 107 L⊙. From the [N ii], [O iii], and [C ii] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high (Z > 0.4 Z⊙), the ionization parameter and hydrogen density are and nH ≃ 50–250 cm−3, respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, N/O, is constrained to be subsolar. At Z < 0.4 Z⊙, the allowed U drastically increases as the assumed metallicity decreases. For high ionization parameters, the N/O constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.
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