We present the first rest-frame optical size-luminosity relation of galaxies at $z>7$, using the NIRCam imaging data obtained by the GLASS James Webb Space Telescope Early Release Science (GLASS-JWST-ERS) program, providing the deepest extragalactic data of the ERS campaign. Our sample consist of 19 photometrically selected bright galaxies with $m_\text{F444W}\leq27.8$ at $77$. Given the limited sample size and magnitude range, we first fix the slope to that observed for larger samples in rest-frame UV using HST samples. The median size $r_0$ at the reference luminosity $M=-21$ decreases slightly from rest-frame optical ($600\pm80$ pc) to UV ($450\pm130$ pc). We then re-fit the size-luminosity relation allowing the slope to vary. The slope is consistent with $\beta\sim0.2$ for all bands except F150W, where we find a marginally steeper slope of $\beta=0.53\pm0.15$. The steep UV slope is mainly driven by the smallest and faintest galaxies. If confirmed by larger samples, it implies that the UV size-luminosity relation breaks toward the faint end as suggested by lensing studies.
We discuss spatially resolved emission line spectroscopy secured for a total sample of 15 gravitationally lensed star-forming galaxies at a mean redshift of $z\simeq2$ based on Keck laser-assisted adaptive optics observations undertaken with the recently-improved OSIRIS integral field unit (IFU) spectrograph. By exploiting gravitationally lensed sources drawn primarily from the CASSOWARY survey, we sample these sub-L$^{\ast}$ galaxies with source-plane resolutions of a few hundred parsecs ensuring well-sampled 2-D velocity data and resolved variations in the gas-phase metallicity. Such high spatial resolution data offers a critical check on the structural properties of larger samples derived with coarser sampling using multiple-IFU instruments. We demonstrate how serious errors of interpretation can only be revealed through better sampling. Although we include four sources from our earlier work, the present study provides a more representative sample unbiased with respect to emission line strength. Contrary to earlier suggestions, our data indicates a more diverse range of kinematic and metal gradient behavior inconsistent with a simple picture of well-ordered rotation developing concurrently with established steep metal gradients in all but merging systems. Comparing our observations with the predictions of hydrodynamical simulations suggests that strong feedback plays a key role in flattening metal gradients in early star-forming galaxies.
The distribution and properties of the first galaxies and quasars are critical pieces of the puzzle in understanding galaxy evolution and cosmic reionization. Previous studies have often excluded unresolved sources as potential low redshift interlopers. We combine broadband color and photometric redshift analysis with morphological selections to identify a robust sample of candidates consistent with unresolved point sources at redshift $z\sim8$ using deep Hubble Space Telescope images. We also examine G141 grism spectroscopic data to identify and eliminate dwarf star contaminants. From these analyses, we identify three, bright ($M_{UV}\lesssim-22$ ABmag) dropout point sources at $7.5
ABSTRACT The JWST has discovered a surprising abundance of bright galaxy candidates in the very early universe (≤500 Myr after the Big Bang), calling into question current galaxy formation models. Spectroscopy is needed to confirm the primeval nature of these candidates, as well as to understand how the first galaxies form stars and grow. Here we present deep spectroscopic and continuum ALMA observations towards GHZ2/GLASS-z12, one of the brightest and most robust candidates at z > 10, identified in the GLASS-JWST Early Release Science Program. We detect a 5.8σ line, offset 0${_{.}^{\prime\prime}}$5 from the JWST position of GHZ2/GLASS-z12, that associating it with the [O iii] 88 $\mu {\rm m}$ transition, implies a spectroscopic redshift of z = 12.117 ± 0.001. We verify the detection using extensive statistical tests. The oxygen line luminosity places GHZ2/GLASS-z12 above the [O iii]-SFR relation for metal-poor galaxies, implying an enhancement of [O iii] emission in this system while the JWST-observed emission is likely a lower-metallicity region. The lack of dust emission seen by these observations is consistent with the blue UV slope observed by JWST, which suggest little dust attenuation in galaxies at this early epoch. Further observations will unambiguously confirm the redshift and shed light on the origins of the wide and offset line and physical properties of this early galaxy. This work illustrates the synergy between JWST and ALMA, and paves the way for future spectroscopic surveys of z > 10 galaxy candidates.
Abstract Galaxy evolution is thought to be driven in large part by the flow of gas between galaxies and the circumgalactic medium (CGM), a halo of metal-enriched gas extending out to ≳100 kpc from each galaxy. Studying the spatial structure of the CGM holds promise for understanding these gas flow mechanisms; however, the common method of using background quasar sight lines provides minimal spatial information. Recent works have shown the utility of extended background sources such as giant gravitationally lensed arcs. Using background lensed arcs from the CSWA 38 lens system, we continuously probed, at a resolution element of about 15 kpc 2 , the spatial and kinematic distribution of Mg ii absorption in a star-forming galaxy at z = 0.77 (stellar mass ≈10 9.7 M ⊙ , star formation rate ≈10 M ⊙ yr −1 ) at impact parameters D ≃ 5–30 kpc. Our results present an anisotropic, optically thick medium whose absorption strength decreases with increasing impact parameter, in agreement with the statistics toward quasars and other gravitational arcs. Furthermore, we find generally low line-of-sight velocities in comparison to the relatively high velocity dispersion in the Mg ii gas (with typical σ ≈ 50 km s −1 ). While the galaxy itself exhibits a clear outflow (with Mg ii velocities up to ∼500 km s −1 ) in the down-the-barrel spectrum, the outflow component is subdominant and only weakly detected at larger impact parameters probed by the background arcs. Our results provide evidence of mainly dispersion-supported, metal-enriched gas recycling through the CGM.
We use spectroscopic observations to investigate galaxies from the age of reionization to the peak of star formation, and the local universe. This thesis presents three projects to better understand characteristics of galactic feedback, i.e., how it regulates galactic gas flows. We used deep absorption line spectroscopy to estimate the escape fractions fesc of star-forming gravitationally-lensed galaxies at z ≃ 5. The approach is to measure the covering fraction of neutral hydrogen in a galaxy from the amount of non-ionizing UV radiation absorbed by low-ionization metal species. With the boost of signal by gravitational lensing, we observed four 4 Spatially resolved spectroscopic observations of galaxies at the peak era of star-formation activities are effective in providing insight into the primitive disks. Specifically, we used metallicity gradients to provide constraints on the amount and extent of feedback produced in star-forming galaxies. We observed 15 star-forming galaxies at z ~ 2 with OSIRIS to obtain their kinematic properties and gas-phase metallicity gradients. With helps from AO correction and gravitational lensing, the typical spatial resolution in our study is less than a half-light radius of a typical L* galaxies at z ≃ 2. Combining with the sample in Jones et al., 2013, we approximately tripled the existing metallicity gradient measurements. We found a lower fraction of rotationally-supported systems than reported from larger kinematic surveys with coarser spatial resolution, which might be partially due to a our improved spatial resolution. We demonstrated that a high spatial resolution is crucial for an accurate diagnosis of the kinematic properties and dynamical maturity of z ≃ 2 galaxies. As for metallicity gradients, we found a much higher fraction of z ≃ 2 galaxies having weak or flat metallicity gradients than in previous studies. We correlated the metallicity gradient with the total metallicity and found that all galaxies with low total metallicities have flat gradients ( 0.1), there is a divergence between isolated or rotationally-supported and dynamically-immature systems with the latter showing zero gradients irrespective of the integrated metallicity. The results indicate that relatively strong feedback (e.g. high mass loading factors or high SN energy output) is required in order to explain the majority of the observed flat gradients. In the second part of the thesis, we observed quiescent galaxies at z Lastly, we measured magnesium (Mg) abundances and extended the observed redshift to z ~ 0.55. We found that while the mass-[Fe/H] relation evolves significantly over the observed redshift range, the mass-[Mg/H] relation does not. This is due to the shorter star formation histories of quiescent galaxies at higher redshifts. Fe is mainly produced in Type Ia SN. It has a longer recycling time than Mg, which is mainly produced in core-collapse SN. Using core-collapse SN elements as a metal indicator lessens the complication of delayed recycling time and allows us to effectively use galactic chemical models with instantaneous recycling to quantify average outflows that these galaxies experience over their lifetime. We found that the average mass-loading factor η is a power-law function of galaxy stellar mass, η ∝ M*-0.21±0.09, consistent with the results of other observational methods and with the predictions where outflow is caused by star formation feedback in turbulent disks.
Abstract We present a comprehensive search and analysis of high-redshift galaxies in a suite of nine public JWST extragalactic fields taken in Cycle 1, covering a total effective search area of ∼358arcmin2 . Through conservative (8 σ ) photometric selection, we identify 341 galaxies at 5 < z < 14, with 109 having spectroscopic redshift measurements from the literature, including recent JWST NIRSpec observations. Our regression analysis reveals that the rest-frame UV size–stellar mass relation follows Reff∝M*0.19±0.03 , similar to that of star-forming galaxies at z ∼ 3, but scaled down in size by ∼0.7 dex. We find a much slower rate for the average size evolution over the redshift range, R eff ∝ (1 + z ) −0.4±0.2 , than that derived in the literature. A fraction (∼13%) of our sample galaxies are marginally resolved even in the NIRCam imaging (≲100 pc), located at ≳1.5 σ below the derived size–mass slope. These compact sources exhibit a high star formation surface density Σ SFR > 10 M ⊙ yr −1 kpc −2 , a range in which only <0.01% of the local star-forming galaxy sample is found. For those with available NIRSpec data, no evidence of ongoing supermassive black hole accretion is observed. A potential explanation for the observed high [O iii ]-to-H β ratios could be high shock velocities, likely originating within intense star-forming regions characterized by high Σ SFR . Lastly, we find that the rest-frame UV and optical sizes of our sample are comparable. Our results are consistent with these early galaxies building up their structures inside out and being yet to exhibit the strong color gradient seen at lower redshift.
Abstract We present deep JWST NIRSpec observations in the sight line of MACS J1149.5+2223, a massive cluster of galaxies at z = 0.54. We report the spectroscopic redshift of 28 sources at 3 < z < 9.1, including nine sources with the detection of the OIIIλ4363 auroral line. Combining these with 16 OIIIλ4363 -detected sources from publicly available JWST data, our sample consists of 25 galaxies with robust gas-phase metallicity measurements via the direct method. We observe a positive correlation between stellar mass and metallicity, with an ∼0.5 dex offset down below the local relation. Interestingly, we find a larger-than-expected scatter of ∼0.3 dex around the relation, which cannot be explained by redshift evolution among our sample or other third parameters. The scatter increases at higher redshift, and we tentatively attribute this to the enrichment process having higher stochasticity, due to shallower potential wells, more intense feedback processes, and a higher galaxy merger rate. Despite reaching a considerably low-mass regime ( logM*/M⊙∼7.3 ), our samples have metallicity of log(O/H) +12 ≳ 7, i.e., comparable to the most metal-poor galaxies in the local Universe. The search for primordial galaxies may be accomplished by extending toward a lower mass and/or by investigating inhomogeneities at smaller spatial scales. Lastly, we investigate potential systematics caused by the limitation of JWST’s Micro-Shutter Assembly observations. Caution is warranted when the target exceeds the slit size, as this situation could allow an overestimation of global metallicity, especially under the presence of a strong negative metallicity gradient.
ABSTRACT The fraction of ionizing photons escaping from high-redshift star-forming galaxies is a key obstacle in evaluating whether galaxies were the primary agents of cosmic reionization. We previously proposed using the covering fraction of low-ionization gas, measured via deep absorption-line spectroscopy, as a proxy. We now present a significant update, sampling seven gravitationally lensed sources at 4 < z < 5. We show that the absorbing gas in our sources is spatially inhomogeneous, with a median covering fraction of 66%. Correcting for reddening according to a dust-in-cloud model, this implies an estimated absolute escape fraction of ≃19% ± 6%. With possible biases and uncertainties, collectively we find that the average escape fraction could be reduced to no less than 11%, excluding the effect of spatial variations. For one of our lensed sources, we have sufficient signal-to-noise ratio to demonstrate the presence of such spatial variations and scatter in its dependence on the Ly α equivalent width, consistent with recent simulations. If this source is typical, our lower limit to the escape fraction could be reduced by a further factor ≃2. Across our sample, we find a modest anticorrelation between the inferred escape fraction and the local star formation rate, consistent with a time delay between a burst and leaking Lyman continuum photons. Our analysis demonstrates considerable variations in the escape fraction, consistent with being governed by the small-scale behavior of star-forming regions, whose activities fluctuate over short timescales. This supports the suggestion that the escape fraction may increase toward the reionization era when star formation becomes more energetic and burst-like.
