分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yu-Heng Lin
Claudia Scarlata
Hayley Williams
Wenlei Chen
Patrick Kelly
Danial Langeroodi
Jens Hjorth
John Chisholm
Anton M. Koekemoer
Adi Zitrin
Jose M. Diego
摘要： We present a new analysis of the rest-frame UV and optical spectra of a sample of three $z>8$ galaxies discovered behind the gravitational lensing cluster RX J2129.4+0009. We combine these observations with those of a sample of $z>7.5$ galaxies from the literature, for which similar measurements are available. As already pointed out in other studies, the high [OIII]$\lambda$5007/[OII]$\lambda$3727 ratios ($O_{32}$) and steep UV continuum slopes ( $\beta$ ) are consistent with the values observed for low redshift Lyman continuum emitters, suggesting that such galaxies contribute to the ionizing budget of the intergalactic medium. We construct a logistic regression model to estimate the probability of a galaxy being a Lyman continuum emitter based on the measured $M_{UV}$, $\beta$, and $O_{32}$ values. Using this probability together with the UV luminosity function, we construct an empirical model that estimates the contribution of high redshift galaxies to reionization based on these observable quantities. Our analysis shows that at $z\sim8$, the average escape fraction of the galaxy population (i.e., including both LyC emitters and non-emitters) varies with $M_{UV}$, with brighter galaxies having larger $f_{esc}$. For $M_{UV}$ $-16$. Galaxies with intermediate UV luminosity ($-19 <$ $M_{UV}$ $< -16$) contribute half of the ionizing photons. The relative contribution of faint versus bright galaxies depends on redshift, with UV bright galaxies ($-23 <$ $M_{UV}$ $< -19$) becoming more important over time and reaching $\approx 40\%$ at the end of reionization around $z=6$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Danial Langeroodi
Jens Hjorth
Wenlei Chen
Patrick L. Kelly
Hayley Williams
Yu-Heng Lin
Claudia Scarlata
Adi Zitrin
Tom Broadhurst
Jose M. Diego
Xiaosheng Huang
Alexei V. Filippenko
Ryan J. Foley
Saurabh Jha
Anton M. Koekemoer
Masamune Oguri
Ismael Perez-Fournon
Justin Pierel
Frederick Poidevin
Lou Strolger
摘要： A tight positive correlation between the stellar mass and the gas-phase metallicity of galaxies has been observed at low redshifts, with only $\sim 0.1$ dex scatter in metallicity. The shape and normalization of this correlation can set strong constraints on theories of galaxy evolution. In particular, its redshift evolution is thought to be determined by stellar and active galactic nucleus feedback-driven outflows, the redshift evolution of the stellar initial mass function or stellar yields, and broadly the star-formation histories of galaxies. The advent of \jwst\ allows probing the mass--metallicity relation at redshifts far beyond what was previously accessible. Here we report the discovery of two emission-line galaxies at redshift $z = 8.15$ and $z = 8.16$ in \jwst\ NIRCam imaging and NIRSpec spectroscopy of galaxies gravitationally lensed by the cluster RX\,J2129.4$+$0009. We measure their metallicities using the strong-line method and their stellar masses through spectral-energy-distribution fitting with a nonparametric star-formation history. We combine these with nine similarly re-analysed galaxies at $7.2 < z < 9.5$ to compile a sample of eleven galaxies at $z \approx 8$ (six with \jwst\ metallicities and five with ALMA metallicities). Based on this sample, we report the first quantitative statistical inference of the mass--metallicity relation at $z\approx8$ (median $z = 8.15$). We measure a $\sim 1.0$ dex redshift evolution in the normalization of the mass--metallicity relation from $z \approx 8$ to the local Universe; at fixed stellar mass, galaxies are 10 times less metal enriched at $z \approx 8$ compared to the present day (abridged).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Patrick L. Kelly
Wenlei Chen
Amruth Alfred
Thomas J. Broadhurst
Jose M. Diego
Najmeh Emami
Alexei V. Filippenko
Allison Keen
Sung Kei Li
Jeremy Lim
Ashish K. Meena
Masamune Oguri
Claudia Scarlata
Tommaso Treu
Hayley Williams
Liliya L. R. Williams
Rui Zhou
Adi Zitrin
Ryan J. Foley
Saurabh W. Jha
摘要： Once only accessible in nearby galaxies, we can now study individual stars across much of the observable universe aided by galaxy-cluster gravitational lenses. When a star, compact object, or multiple such objects in the foreground galaxy-cluster lens become aligned, they can magnify a background individual star, and the timescale of a magnification peak can limit its size to tens of AU. The number and frequency of microlensing events therefore opens a window into the population of stars and compact objects, as well as high-redshift stars. To assemble the first statistical sample of stars in order to constrain the initial mass function (IMF) of massive stars at redshift z=0.7-1.5, the abundance of primordial black holes in galaxy-cluster dark matter, and the IMF of the stars making up the intracluster light, we are carrying out a 192-orbit program with the Hubble Space Telescope called "Flashlights," which is now two-thirds complete owing to scheduling challenges. We use the ultrawide F200LP and F350LP long-pass WFC3 UVIS filters and conduct two 16-orbit visits separated by one year. Having an identical roll angle during both visits, while difficult to schedule, yields extremely clean subtraction. Here we report the discovery of more than a dozen bright microlensing events, including multiple examples in the famous "Dragon Arc" discovered in the 1980s, as well as the "Spocks" and "Warhol" arcs that have hosted already known supergiants. The ultradeep observer-frame ultraviolet-through-optical imaging is sensitive to hot stars, which will complement deep James Webb Space Telescope infrared imaging. We are also acquiring Large Binocular Telescope LUCI and Keck-I MOSFIRE near-infrared spectra of the highly magnified arcs to constrain their recent star-formation histories.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hayley Williams
Patrick L. Kelly
Wenlei Chen
Gabriel Brammer
Adi Zitrin
Tommaso Treu
Claudia Scarlata
Anton M. Koekemoer
Masamune Oguri
Yu-Heng Lin
Jose M. Diego
Mario Nonino
Jens Hjorth
Danial Langeroodi
Tom Broadhurst
Noah Rogers
Ismael Perez-Fournon
Ryan J. Foley
Saurabh Jha
Alexei V. Filippenko
摘要： Given their extremely faint apparent brightness, the nature of the first galaxies and how they reionized the Universe's gas are not yet understood. Here we report the discovery, in JWST imaging, of a highly magnified, low mass (log(Mstellar/Msun) = 7.63+0.22-0.24) galaxy visible when the Universe was only 510 Myr old, and follow-up JWST spectroscopy from Lyman alpha to [O III] 5007 A in its rest frame. We detect the [O III] 5007 A and H Beta emission lines with a respective signal-to-noies ratio of 40 and 7, and five additional lines with signal-to-noise greater than 3. The galaxy's magnification of approximately 20 allows us to measure a radius of 16.4+10.7-7.0 pc, which is a factor of 9.3+10.5-4.4 (3.5 sigma) smaller than galaxies with comparable luminosity at z = 6 - 8.
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