ABSTRACT
Galaxies forming in low-mass haloes are thought to be primarily responsible for reionizing the Universe during the first billion years after the big bang. Yet, these haloes are extremely ...inefficient at forming stars in the nearby Universe. In this work, we address this apparent tension, and ask whether a physically motivated model of galaxy formation that reproduces the observed abundance of faint galaxies in the nearby Universe is also consistent with available observational constraints on the reionization history. By interfacing the Santa Cruz semi-analytic model for galaxy formation with an analytic reionization model, we constructed a computationally efficient pipeline that connects ‘ground-level’ galaxy formation physics to ‘top-level’ cosmological-scale observables. Based on photometric properties of the galaxy populations predicted up to z = 15, we compute the reionization history of intergalactic hydrogen. We quantify the three degenerate quantities that influence the total ionizing photon budget, including the abundance of galaxies, the intrinsic production rate of ionizing photons, and the LyC escape fraction. We explore covariances between these quantities using a Markov chain Monte Carlo method. We find that our locally calibrated model is consistent with all currently available constraints on the reionization history, under reasonable assumptions about the LyC escape fraction. We quantify the fraction of ionizing photons produced by galaxies of different luminosities and find that the galaxies expected to be detected in James Webb Space Telescope Near-Infrared Camera (NIRCam) wide and deep surveys are responsible for producing ∼40–80 per cent of ionizing photons throughout the Epoch of Reionization. All results presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.
ABSTRACT
The long anticipated James Webb Space Telescope (JWST) will be able to directly detect large samples of galaxies at very high redshift. Using the well-established, computationally efficient ...Santa Cruz semi-analytic model, with recently implemented multiphase gas partitioning, and H2-based star formation recipes, we make predictions for a wide variety of galaxy properties for galaxy populations at z = 4–10. In this work, we provide forecasts for the physical properties of high-redshift galaxies and links to their photometric properties. With physical parameters calibrated only to z ∼ 0 observations, our model predictions are in good agreement with current observational constraints on stellar mass and star formation rate distribution functions up to z ∼ 8. We also provide predictions representing wide, deep, and lensed JWST survey configurations. We study the redshift evolution of key galaxy properties and the scaling relations among them. Taking advantage of our models’ high computational efficiency, we study the impact of systematically varying the model parameters. All distribution functions and scaling relations presented in this work are available at https://www.simonsfoundation.org/semi-analytic-forecasts-for-jwst/.
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
Abstract
We present the results from a spectroscopic survey using the MOSFIRE near-infrared spectrograph on the 10 m Keck telescope to search for Ly
α
emission from candidate galaxies at
z
∼ 9–10 in ...four of the CANDELS fields (GOODS-N, EGS, UDS, and COSMOS). We observed 11 target galaxies, detecting Ly
α
from one object in ∼8.1 hr of integration, at
z
= 8.665 ± 0.001 with an integrated signal-to-noise ratio > 7. This galaxy is in the CANDELS Extended Groth Strip (EGS) field and lies physically close (3.5 physical Mpc pMpc) to another confirmed galaxy in this field with Ly
α
detected at
z
= 8.683. The detection of Ly
α
suggests the existence of large (∼1 pMpc) ionized bubbles fairly early in the reionization process. We explore the ionizing output needed to create bubbles of this size at this epoch and find that such a bubble requires more than the ionizing power provided by the full expected population of galaxies (by integrating the UV luminosity function down to
M
UV
= −13). The Ly
α
we detect would be able to escape the predominantly neutral intergalactic medium at this epoch if our detected galaxy is inhabiting an overdensity, which would be consistent with the photometric overdensity previously identified in this region by Finkelstein et al. This implies that the CANDELS EGS field is hosting an overdensity at
z
= 8.7 that is powering one or more ionized bubbles, a hypothesis that will be imminently testable with forthcoming James Webb Space Telescope observations in this field.
In this paper we present a detailed study of the structures and morphologies of a sample of 1188 massive galaxies with M
* ≥ 1010 M between redshifts z = 1 and 3 within the Ultra Deep Survey (UDS) ...region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Using this sample we determine how galaxy structure and morphology evolve with time, and investigate the nature of galaxy structure at high redshift. We visually classify our sample into discs, ellipticals and peculiar systems and correct for redshift effects on these classifications through simulations. We find significant evolution in the fractions of galaxies at a given visual classification as a function of redshift. The peculiar population is dominant at z > 2 with a substantial spheroid population, and a negligible disc population. We compute the transition redshift, z
trans, where the combined fraction of spheroidal and disc galaxies is equal to that of the peculiar population, as z
trans = 1.86 ± 0.62 for galaxies in our stellar mass range. We find that this transition changes as a function of stellar mass, with Hubble-type galaxies becoming dominant at higher redshifts for higher mass galaxies (z
trans = 2.22 ± 0.82), than for the lower mass galaxies (z
trans = 1.73 ± 0.57). Higher mass galaxies become morphologically settled before their lower mass counterparts, a form of morphological downsizing. We furthermore compare our visual classifications with the Sérsic index, the concentration, asymmetry and clumpiness (CAS) parameters, star formation rate and rest-frame U − B colour. We find links between the colour of a galaxy, its star formation rate and how extended or peculiar it appears. Finally, we discuss the negligible z > 2 disc fraction based on visual morphologies and speculate that this is an effect of forming disc appearing peculiar through processes such as violent disc instabilities or mergers. We conclude that to properly define and measure high-redshift morphology and structure a new and more exact classification scheme is needed.
We examine a sample of 1495 galaxies in the CANDELS fields to determine the evolution of two-component galaxies, including bulges and discs, within massive galaxies at the epoch 1 < z < 3 when the ...Hubble sequence forms. We fit all of our galaxies’ light profiles with a single Sérsic fit, as well as with a combination of exponential and Sérsic profiles. The latter is done in order to describe a galaxy with an inner and an outer component, or bulge and disc component. We develop and use three classification methods (visual, F-test and the residual flux fraction) to separate our sample into one-component galaxies (disc/spheroids-like galaxies) and two-component galaxies (galaxies formed by an ‘inner part’ or bulge and an ‘outer part’ or disc). We then compare the results from using these three different ways to classify our galaxies. We find that the fraction of galaxies selected as two-component galaxies increases on average 50 per cent from the lowest mass bin to the most massive galaxies, and decreases with redshift by a factor of 4 from z = 1 to 3. We find that single Sérsic ‘disc-like’ galaxies have the highest relative number densities at all redshifts, and that two-component galaxies have the greatest increase and become at par with Sérsic discs by z = 1. We also find that the systems we classify as two-component galaxies have an increase in the sizes of their outer components, or ‘discs’, by about a factor of 3 from z = 3 to 1.5, while the inner components or ‘bulges’ stay roughly the same size. This suggests that these systems are growing from the inside out, whilst the bulges or protobulges are in place early in the history of these galaxies. This is also seen to a lesser degree in the growth of single ‘disc-like’ galaxies versus ‘spheroid-like’ galaxies over the same epoch.
We combine photometry from the Ultra Deep Survey (UDS), Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) UDS and CANDELS the Great Observatories Origins Deep Survey-South ...(GOODS-S) surveys to construct the galaxy stellar mass function probing both the low- and high-mass end accurately in the redshift range 0.3 < z < 3. The advantages of using a homogeneous concatenation of these data sets include meaningful measures of environment in the UDS, due to its large area (0.88 deg2), and the high-resolution deep imaging in CANDELS (H
160 > 26.0), affording us robust measures of structural parameters. We construct stellar mass functions for the entire sample as parametrized by the Schechter function, and find that there is a decline in the values of ϕ and of α with higher redshifts, and a nearly constant M* up to z ∼ 3. We divide the galaxy stellar mass function by colour, structure, and environment and explore the links between environmental overdensity, morphology, and the quenching of star formation. We find that a double Schechter function describes galaxies with high Sérsic index (n > 2.5), similar to galaxies which are red or passive. The low-mass end of the n > 2.5 stellar mass function is dominated by blue galaxies, whereas the high-mass end is dominated by red galaxies. This shows that there is a possible link between morphological evolution and star formation quenching in high mass galaxies, which is not seen in lower mass systems. This in turn suggests that there are strong mass-dependent quenching mechanisms. In addition, we find that the number density of high-mass systems is elevated in dense environments, suggesting that an environmental process is building up massive galaxies quicker in over densities than in lower densities.
The geometry of the neutral gas in and around galaxies is a key regulator of the escape of ionizing photons. We present the first statistical study aimed at linking the neutral and ionized gas ...distributions to the Lyman continuum (LyC) escape fraction ( f esc LyC ) in a sample of 22 confirmed LyC leakers and non-leakers at z ≈ 0.35 using the Keck Cosmic Web Imager (Keck/KCWI) and the Low Resolution Spectrograph 2 (HET/LRS2). Our integral field unit data enable the detection of neutral and low-ionization gas, as traced by Mg II , and ionized gas, as traced by O II , extending beyond the stellar continuum for seven and ten objects, respectively. All but one object with extended Mg II emission also show extended O II emission; in this case, Mg II emission is always more extended than O II by a factor 1.2 on average. Most of the galaxies with extended emission are non or weak LyC leakers ( f esc LyC < 5%), but we find a large diversity of neutral and low-ionization gas configurations around these weakly LyC-emitting galaxies. Conversely, the strongest leakers ( f esc LyC > 5%) appear uniformly compact in both Mg II and O II with exponential scale lengths ≲1 kpc. Most are unresolved at the resolution of our data. We also find a trend between f esc LyC and the spatial offsets of the nebular gas and the stellar continuum emission. Moreover, we find significant anticorrelations between the spatial extent of the neutral and/or low-ionization gas and the O III /O II ratio, and H β equivalent width, as well as positive correlations with metallicity and UV size, suggesting that galaxies with more compact neutral and/or low-ionization gas sizes are more highly ionized. The observations suggest that strong LyC emitters do not have extended neutral and/or low-ionization gas halos and ionizing photons may be emitted in many directions. Combined with high ionization diagnostics, we propose that the Mg II , and potentially O II , spatial compactness are indirect indicators of LyC emitting galaxies at high redshift.
Abstract
We use the Illustris-1 simulation to explore the capabilities of the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) data to analyze the stellar populations in ...high-redshift galaxies, taking advantage of the combined depth, spatial resolution, and wavelength coverage. For that purpose, we use simulated broadband ACS, WFC3, and NIRCam data and two-dimensional stellar population synthesis (2D-SPS) to derive the integrated star formation history (SFH) of massive (
M
*
> 10
10
M
⊙
) simulated galaxies at 1 <
z
< 4 that evolve into a local
M
*
> 10
11
M
⊙
galaxy. In particular, we explore the potential of HST and JWST data sets reaching a depth similar to those of the CANDELS and ongoing CEERS observations, respectively, and concentrate on determining the capabilities of this data set for characterizing the first episodes in the SFH of local
M
*
> 10
11
M
⊙
galaxies by studying their progenitors at
z
> 1. The 2D-SPS method presented in this paper has been calibrated to robustly recover the cosmic times when the first star formation episodes occurred in massive galaxies, i.e., the first stages in their integrated SFHs. In particular, we discuss the times when the first 1%–50% of their total stellar mass formed in the simulation. We demonstrate that we can recover these ages with typical median systematic offset of less than 5% and scatter around 20%–30%. According to our measurements on Illustris data, we are able to recover that local
M
*
> 10
11
M
⊙
galaxies would have started their formation by
z
= 16, forming the first 5% of their stellar mass present at
z
∼ 1 by
z
= 4.5, 10% by
z
= 3.7, and 25% by
z
= 2.7.
PDF
![Linking Mg II and [O II] sp...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6361/small "Linking Mg II and [O II] spatial distribution to ionizing photon escape in confirmed LyC leakers and non-leakers")