The brightest galaxies at cosmic dawn Mason, Charlotte A; Trenti, Michele; Treu, Tommaso
Monthly notices of the Royal Astronomical Society,
03/2023, Letnik:
521, Številka:
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Journal Article
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ABSTRACT
Recent JWST observations suggest an excess of z ≳ 10 galaxy candidates above most theoretical models. Here, we explore how the interplay between halo formation time-scales, star formation ...efficiency, and dust attenuation affects the properties and number densities of galaxies observed in the early Universe. To guide intuition, we calculate the theoretical upper limit on the UV luminosity function (LF), assuming star formation is 100 per cent efficient and all gas in haloes is converted into stars, and that galaxies are at the peak age for UV emission (∼10 Myr). This upper limit is ∼4 orders of magnitude greater than current observations, implying no formal tension with star formation in Lambda cold dark matter cosmology. In a more realistic model, we use the distribution of halo formation time-scales derived from extended Press–Schechter theory as a proxy for star formation rate (SFR). We predict that the galaxies observed so far at z ≳ 10 are dominated by those with the fastest formation time-scales, and thus most extreme SFRs and young ages. These galaxies can be upscattered by ∼1.5 mag compared to the median UV magnitude versus halo mass relation. This likely introduces a selection effect at high redshift whereby only the youngest (≲10 Myr), most highly star-forming galaxies (specific SFR$\gtrsim 30\, \mathrm{Gyr}^{-1}$) have been detected so far. Furthermore, our modelling suggests that redshift evolution at the bright end of the UV LF is substantially affected by the build-up of dust attenuation. We predict that deeper JWST observations (reaching m ∼ 30) will reveal more typical galaxies with relatively older ages (∼100 Myr) and less extreme specific SFRs ($\sim 10\, \mathrm{Gyr}^{-1}$ for a MUV ∼ −20 galaxy at z ∼ 10).
ABSTRACT We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the ...assumption of a mass-dependent, but redshift-independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at z > 10 (lookback time 500 Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations (0 z 10). The significant drop in luminosity density of currently detectable galaxies beyond z ∼ 8 is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth fully consistent with the latest Planck measurement, implying that the universe is fully reionized at In addition, our model naturally produces smoothly rising star formation histories for galaxies with L L* in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at z > 10 we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope ( ∼ −3.5 at z ∼ 16). Finally, we construct forecasts for surveys with James Webb Space Telescope (JWST) and Wide-field Infrared Survey Telescope (WFIRST) and predict that galaxies out to z ∼ 14 will be observed. Galaxies at z > 15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.
ABSTRACT
Identifying and characterizing reionized bubbles enables us to track both their size distribution, which depends on the primary ionizing sources, and the relationship between reionization ...and galaxy evolution. We demonstrate that spectrally resolved z ≳ 6 Lyman-alpha (Lyα) emission can constrain properties of reionized regions. Specifically, the distance from a source to a neutral region sets the minimum observable Lyα velocity offset from systemic. Detection of flux on the blue side of the Lyα resonance implies the source resides in a large, sufficiently ionized region that photons can escape without significant resonant absorption, and thus constrains both the sizes of and the residual neutral fractions within ionized bubbles. We estimate the extent of the region around galaxies which is optically thin to blue Lyα photons, analogous to quasar proximity zones, as a function of the source’s ionizing photon output and surrounding gas density. This optically thin region is typically ≲ 0.3 pMpc in radius (allowing transmission of flux ≳ −250 km s−1), ≲ 20 per cent of the distance to the neutral region. In a proof-of-concept, we demonstrate the z ≈ 6.6 galaxy COLA1 – with a blue Lyα peak – likely resides in an ionized region >0.7 pMpc, with residual neutral fraction <10−5.5. To ionize its own proximity zone we infer COLA1 has a high ionizing photon escape fraction (fesc > 0.50), relatively steep UV slope (β < −1.79), and low line-of-sight gas density (∼0.5 times the cosmic mean), suggesting it is a rare, underdense line-of-sight.
The protagonists of the last great phase transition of the universe-cosmic reionization-remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and ...may have significant ionizing photon escape fractions ( ). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density ( at ). We generate an ionizing spectrum for each galaxy in our model and constrain by leveraging latest measurements of the reionization timeline (e.g., Ly damping of quasars and galaxies at z > 7). Assuming a constant across all sources at z > 6, we find < −13.5 galaxies need = to complete reionization. The inferred Intergalactic Medium neutral fraction is 0.9, 0.5, 0.1 at -that is, the bulk of reionization transpires rapidly in 300 Myr, driven by the z > 8 SFR and favored by high neutral fractions (∼60%-90%) measured at z ∼ 7-8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0-6.6 that overwhelmingly displays higher-than-average star-formation surface density ( ), we propose a physically motivated model relating to and find . Since falls by ∼2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on at lower redshifts and its required evolution to ∼ 0.2 at z > 6. Within this model, strikingly, <5% of galaxies with < −18 and log(M /M ) > 8 (the "oligarchs") account for 80% of the reionization budget-a stark departure from the canonical "democratic" reionization led by copious faint sources. In fact, faint sources ( > −16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7-8. Shallow faint-end slopes of the UV luminosity function ( > −2) and/or distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict that LyC leakers like COLA1 (z = 6.6, ∼ 30%, = −21.5) will become increasingly common toward z ∼ 6 and that the drivers of reionization do not lie hidden across the faint end of the luminosity function but are already known to us.
This book explains that the natural and only quite wholesome way of teaching is to let the child's desire for knowledge operate in the schoolboy and guide the teacher. This means that without ...foregoing discipline, nor cutting ourselves off from tradition, we must continue experiments already being started in our elementary schools. These are based on the chastening fact that children learn best before we adults begin to teach them at all: and hence that however uncongenial the task may be, we must conform our teaching methods to those of Nature. The attempt has often been made before. But in this book there is a rare combination of intuitive insight and practical sagacity. The author refused to believe that the collapse of the desire for knowledge between seven and seventeen years of age is inevitable.
Abstract
We present a new flexible Bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR,
z
∼ 6–10) from ...detections and non-detections of Lyman Alpha (Ly
α
) emission from Lyman Break galaxies (LBGs). Our framework combines sophisticated reionization simulations with empirical models of the interstellar medium (ISM) radiative transfer effects on Ly
α
. We assert that the Ly
α
line profile emerging from the ISM has an important impact on the resulting transmission of photons through the IGM, and that these line profiles depend on galaxy properties. We model this effect by considering the peak velocity offset of Ly
α
lines from host galaxies’ systemic redshifts, which are empirically correlated with UV luminosity and redshift (or halo mass at fixed redshift). We use our framework on the sample of LBGs presented in Pentericci et al. and infer a global neutral fraction at
z
∼ 7 of
, consistent with other robust probes of the EoR and confirming that reionization is ongoing ∼700 Myr after the Big Bang. We show that using the full distribution of Ly
α
equivalent width detections and upper limits from LBGs places tighter constraints on the evolving IGM than the standard Ly
α
emitter fraction, and that larger samples are within reach of deep spectroscopic surveys of gravitationally lensed fields and
James Webb Space Telescope
NIRSpec.
ABSTRACT
Modelling reionization often requires significant assumptions about the properties of ionizing sources. Here, we infer the total output of hydrogen-ionizing photons (the ionizing emissivity, ...$\dot{N}_\textrm {ion}$) at z = 4–14 from current reionization constraints, being maximally agnostic to the properties of ionizing sources. We use a Bayesian analysis to fit for a non-parametric form of $\dot{N}_\textrm {ion}$, allowing us to flexibly explore the entire prior volume. We infer a declining $\dot{N}_\textrm {ion}$ with redshift at z > 6, which can be used as a benchmark for reionization models. Model-independent reionization constraints from the cosmic microwave background (CMB) optical depth and Ly α and Ly β forest dark pixel fraction produce $\dot{N}_\textrm {ion}$ evolution ($\mathrm{ d}\log _{10}\dot{\mathbf {N}}_{\bf ion}/\mathrm{ d}z|_{z=6\rightarrow 8} = -0.31\pm 0.35$ dex) consistent with the declining UV luminosity density of galaxies, assuming constant ionizing photon escape fraction and efficiency. Including measurements from Ly α damping of galaxies and quasars produces a more rapid decline: $\mathrm{ d}\log _{10}\dot{\mathbf {N}}_{\bf ion}/\mathrm{ d}z|_{z=6\rightarrow 8} =-0.44\pm 0.22$ dex, steeper than the declining galaxy luminosity density (if extrapolated beyond $M_\rm{\small UV}\gtrsim -13$), and constrains the mid-point of reionization to z = 6.93 ± 0.14.
Abstract
The time frame in which hydrogen reionization occurred is highly uncertain, but can be constrained by observations of Lyman-alpha (Ly
α
) emission from distant sources. Neutral hydrogen in ...the intergalactic medium (IGM) attenuates Ly
α
photons emitted by galaxies. As reionization progressed the IGM opacity decreased, increasing Ly
α
visibility. The galaxy Ly
α
luminosity function (LF) is thus a useful tool to constrain the timeline of reionization. In this work, we model the Ly
α
LF as a function of redshift,
z
= 5–10, and average IGM neutral hydrogen fraction,
x
¯
Hɪ
. We combine the Ly
α
luminosity probability distribution obtained from inhomogeneous reionization simulations with a model for the UV LF to model the Ly
α
LF. As the neutral fraction increases, the average number density of Ly
α
emitting galaxies decreases, and are less luminous, though for
x
¯
Hɪ
≲
0.4
there is only a small decrease in the Ly
α
LF. We use our model to infer the IGM neutral fraction at
z
= 6.6, 7.0, and 7.3 from observed Ly
α
LFs. We conclude that there is a significant increase in the neutral fraction with increasing redshift:
x
¯
Hɪ
(
z
=
6.6
)
=
0.08
−
0.05
+
0.08
,
x
¯
Hɪ
(
z
=
7.0
)
=
0.28
±
0.05
and
x
¯
Hɪ
(
z
=
7.3
)
=
0.83
−
0.07
+
0.06
. We predict trends in the Ly
α
luminosity density and Schechter parameters as a function of redshift and the neutral fraction. We find that the Ly
α
luminosity density decreases as the universe becomes more neutral. Furthermore, as the neutral fraction increases, the faint-end slope of the Ly
α
LF steepens, and the characteristic Ly
α
luminosity shifts to lower values; hence, we conclude that the evolving shape of the Ly
α
LF—not just its integral—is an important tool to study reionization.
Drawing on traditional resource-based theory and its recent dynamic capabilities theory extensions, we examine both the possession of a market orientation and the marketing capabilities through which ...resources are deployed into the marketplace as drivers of firm performance in a cross-industry sample. Our findings indicate that market orientation and marketing capabilities are complementary assets that contribute to superior firm performance. We also find that market orientation has a direct effect on firms' return on assets (ROA), and that marketing capabilities directly impact both ROA and perceived firm performance.
Abstract
Detections and non-detections of Lyman alpha (Lyα) emission from z > 6 galaxies (<1 Gyr after the big bang) can be used to measure the timeline of cosmic reionization. Of key interest to ...measuring reionization’s mid-stages, but also increasing observational challenge, are observations at z > 7, where Lyα redshifts to near infra-red wavelengths. Here we present a search for z > 7.2 Lyα emission in 53 intrinsically faint Lyman Break Galaxy candidates, gravitationally lensed by massive galaxy clusters, in the KMOS Lens-Amplified Spectroscopic Survey (KLASS). With integration times of ∼7–10 h, we detect no Lyα emission with signal-to-noise ratio (S/N) > 5 in our sample. We determine our observations to be 80 per cent complete for 5σ spatially and spectrally unresolved emission lines with integrated line flux >5.7 × 10−18 erg s−1 cm−2. We define a photometrically selected sub-sample of 29 targets at z = 7.9 ± 0.6, with a median 5σ Lyα EW limit of 58 Å. We perform a Bayesian inference of the average intergalactic medium (IGM) neutral hydrogen fraction using their spectra. Our inference accounts for the wavelength sensitivity and incomplete redshift coverage of our observations, and the photometric redshift probability distribution of each target. These observations, combined with samples from the literature, enable us to place a lower limit on the average IGM neutral hydrogen fraction of $\gt 0.76 \,\, (68{{\ \rm per\ cent}}), \,\, \gt 0.46 \,\, (95{{\ \rm per\ cent}})$ at z ∼ 8, providing further evidence of rapid reionization at z ∼ 6–8. We show that this is consistent with reionization history models extending the galaxy luminosity function to $M_ \rm {\small UV}\lesssim -12$, with low ionizing photon escape fractions, $f_\textrm{esc} \lesssim 15{{\ \rm per\ cent}}$.
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