arXiv subjects

F. -Y. Liu

Publications and source records attributed to F. -Y. Liu.

4 recordsLinked to original sources

arXiv2026

A search for the first galaxies across $>0.6$ deg$^2$ of JWST imaging: new evidence for a rapid decline in star-formation activity at $z>12$

We present a new determination of the evolving galaxy UV luminosity function (LF) over the extreme redshift range $12.5 $0.6 deg$^2$ of JWST NIRCam imaging containing $>150$ independent sight-lines. We find evidence for an accelerated decline in the UV LF, and hence inferred star-formation rate density ($ρ_{\rm SFR}$), over the $\simeq100\rm{Myr}$ cosmic time interval between $z=11$ and $z=13.5$. Moreover, based on a notable lack of galaxy candidates at $z>14.5$, we find evidence for an even more rapid descent in star-formation activity towards earlier times, with our new measurement of $ρ_{\rm SFR}$ at $z\simeq15.5$ lying significantly below an extrapolation of the log-linear $ρ_{\rm SFR}(\rm z)$ relation inferred from early JWST LF studies. Instead, we find that the evolution in $ρ_{\rm SFR}(\rm z)$ at these very early times is better described by a piece-wise log-linear relation, in which the decline in $ρ_{\rm SFR} (\rm z)$ at $z>12$ is $\simeq4$ times steeper than at redshifts $z < 12$. Our observational results are consistent with a number of theoretical models of galaxy evolution which have incorporated a range of treatments in an attempt to explain the prevalence of UV-bright galaxies at least out to $z \simeq 12$ (e.g., increased star-formation efficiency, stochastic star-formation histories, an evolving stellar initial mass function and/or a shift towards attenuation-free stellar populations). However, our results are also entirely consistent with a relatively simple galaxy evolution model with no such adjustments, in which the rapid evolution of the dark-matter halo mass function at early times is for a while partially masked by progressively younger stellar ages, with the inferred epoch of first galaxy formation lying at $z\simeq15$.

astro-ph.GA↗

arXiv2024

JWST PRIMER: A new multi-field determination of the evolving galaxy UV luminosity function at redshifts $\mathbf{z \simeq 9-15}$

We present a new determination of the evolving galaxy UV luminosity function (LF) over the redshift range $8.5 8.5)>0.05$) to undertake a statistical calculation of the UV LF. Our new measurements span $\simeq4$ magnitudes in UV luminosity at $z=9-12.5$, placing new constraints on both the shape and evolution of the LF at early times. Our measurements yield a new estimate of the early evolution of cosmic star-formation rate density ($ρ_{\rm{SFR}}$) confirming the gradual decline deduced from early JWST studies, at least out to $z \simeq 12$. Finally we show that the observed early evolution of the galaxy UV LF (and $ρ_{\rm{SFR}}$) can be reproduced in a ${\rm Λ}$CDM Universe, with no change in dust properties or star-formation efficiency required out to $z \simeq 12$. Instead, a progressive trend towards younger stellar population ages can reproduce the observations, and the typical ages required at $z \simeq$ 8, 9, 10, and 11 all converge on $\simeq 380-330$ Myr after the Big Bang, indicative of a rapid emergence of early galaxies at $z \simeq 12 - 13$. This is consistent with the first indications of a steeper drop-off in $ρ_{\rm{SFR}}$ we find beyond $z \simeq 13$, possibly reflecting the rapid evolution of the halo mass function at earlier times.

astro-ph.GA↗

arXiv2024

The NIRVANDELS Survey: the stellar and gas-phase mass-metallicity relations of star-forming galaxies at z = 3.5

We present determinations of the gas-phase and stellar metallicities of a sample of 65 star-forming galaxies at $z \simeq 3.5$ using rest-frame far-ultraviolet (FUV) spectroscopy from the VANDELS survey in combination with follow-up rest-frame optical spectroscopy from VLT/KMOS and Keck/MOSFIRE. We infer gas-phase oxygen abundances ($Z_{\mathrm{g}}$; tracing O/H) via strong optical nebular lines and stellar iron abundances ($Z_{\star}$; tracing Fe/H) from full spectral fitting to the FUV continuum. Our sample spans the stellar mass range $8.5 < \mathrm{log}(M_{\star}/\mathrm{M}_{\odot}) < 10.5$ and shows clear evidence for both a stellar and gas-phase mass-metallicity relation (MZR). We find that our O and Fe abundance estimates both exhibit a similar mass-dependence, such that $\mathrm{Fe/H}\propto M_{\star}^{0.30\pm0.11}$ and $\mathrm{O/H}\propto M_{\star}^{0.32\pm0.09}$. At fixed $M_{\star}$ we find that, relative to their solar values, O abundances are systematically larger than Fe abundances (i.e., $α$-enhancement).We estimate an average enhancement of $\mathrm{(O/Fe)} = 2.65 \pm 0.16 \times \mathrm{(O/Fe)_\odot}$ which appears to be independent of $M_{\star}$. We employ analytic chemical evolution models to place a constraint on the strength of galactic-level outflows via the mass-outflow factor ($η$). We show that outflow efficiencies that scale as $η\propto M_{\star}^{-0.32}$ can simultaneously explain the functional form of of the stellar and gas-phase MZR, as well as the degree of $α$-enhancement at fixed Fe/H. Our results add further evidence to support a picture in which $α$-enhanced abundance ratios are ubiquitous in high-redshift star-forming galaxies, as expected for young systems whose interstellar medium is primarily enriched by core-collapse supernovae.

astro-ph.GA↗

arXiv2022

Machine learning spectral functions in lattice QCD

We study the inverse problem of reconstructing spectral functions from Euclidean correlation functions via machine learning. We propose a novel neural network, SVAE, which is based on the variational autoencoder (VAE) and can be naturally applied to the inverse problem. The prominent feature of the SVAE is that a Shannon-Jaynes entropy term having the ground truth values of spectral functions as prior information is included in the loss function to be minimized. We train the network with general spectral functions produced from a Gaussian mixture model. As a test, we use correlators generated from four different types of physically motivated spectral functions made of one resonance peak, a continuum term and perturbative spectral function obtained using non-relativistic QCD. From the mock data test we find that the SVAE in most cases is comparable to the maximum entropy method (MEM) in the quality of reconstructing spectral functions and even outperforms the MEM in the case where the spectral function has sharp peaks with insufficient number of data points in the correlator. By applying to temporal correlation functions of charmonium in the pseudoscalar channel obtained in the quenched lattice QCD at 0.75 $T_c$ on $128^3\times96$ lattices and $1.5$ $T_c$ on $128^3\times48$ lattices, we find that the resonance peak of $η_c$ extracted from both the SVAE and MEM has a substantial dependence on the number of points in the temporal direction ($N_τ$) adopted in the lattice simulation and $N_τ$ larger than 48 is needed to resolve the fate of $η_c$ at 1.5 $T_c$.

hep-lat↗