Search

The properties of galaxies in low-density regions of the universe suggest an interplay between galaxy formation and environment. However, the specific reason why this particular large-scale environment influences the evolution of galaxies remains unclear. This paper examines the properties and evolutionary paths of galaxies within cosmic voids using the Illustris TNG300 simulation. The population of void galaxies at z = 0 has a higher star formation rate, a smaller stellar-to-halo-mass ratio, higher gas metallicity, and lower stellar metallicity in comparison with non-void galaxies at fixed stellar mass. Our analysis shows that these differences are mainly due to the characteristics of galaxies classified as satellites, for which the largest differences between void and non-void samples are found. Although the mean number of mergers is similar between void and non-void samples at a fixed stellar mass, void galaxies tend to experience mergers at later times, resulting in a more recent accumulation of accreted stellar mass. While the mean net accreted mass is comparable for high-mass galaxies, low-mass void galaxies tend to exhibit higher fractions of accreted stars than non-void galaxies. This finding challenges the common notion that void galaxies predominantly experience growth with infrequent mergers or interactions. With this paper, we also publicly release our void catalogue as part of the IllustrisTNG project. [ABSTRACT FROM AUTHOR]

We use a complete sample of 211 nearby (⁠|$z< 0.08$|⁠), dwarf (10 |$^{8}$|  M |$_{\odot }$| < |$M_{\rm {\star }}$| < 10 |$^{9.5}$|  M |$_{\odot }$|⁠) galaxies in low-density environments, to study their structural properties: effective radii (⁠|$R_{\rm e }$|⁠), effective surface brightnesses (⁠|$\langle \mu \rangle _{\rm e}$|⁠), and colour gradients. We explore these properties as a function of stellar mass and the three principal dwarf morphological types identified in a companion paper – early-type galaxies (ETGs), late-type galaxies (LTGs), and featureless systems. The median |$R_{\rm e }$| of LTGs and featureless galaxies are factors of |$\sim$| 2 and |$\sim$| 1.2 larger than the ETGs. While the median |$\langle \mu \rangle _{\rm e}$| of the ETGs and LTGs is similar, the featureless class is |$\sim$| 1 mag arcsec |$^{-2}$| fainter. Although they have similar median |$R_{\rm e }$|⁠ , the featureless and ETG classes differ significantly in their median |$\langle \mu \rangle _{\rm e}$|⁠ , suggesting that their evolution is different and that the featureless galaxies are not a subset of the ETGs. While massive ETGs typically exhibit negative or flat colour gradients, dwarf ETGs generally show positive colour gradients (bluer centres). The growth of ETGs therefore changes from being 'outside-in' to 'inside-out' as we move from the dwarf to the massive regime. The colour gradients of dwarf and massive LTGs are, however, similar. Around 46 per cent of dwarf ETGs show prominent, visually identifiable blue cores which extend out to |$\sim$| 1.5 |$R_{\rm e}$|⁠. Finally, compared to their non-interacting counterparts, interacting dwarfs are larger, bluer at all radii and exhibit similar median |$\langle \mu \rangle _{\rm e}$|⁠ , indicating that interactions typically enhance star formation across the entire galaxy. [ABSTRACT FROM AUTHOR]

The mass assembly history (MAH) of dark matter haloes plays a crucial role in shaping the formation and evolution of galaxies. MAHs are used extensively in semi-analytic and empirical models of galaxy formation, yet current analytic methods to generate them are inaccurate and unable to capture their relationship with the halo internal structure and large-scale environment. This paper introduces florah (FLOw-based Recurrent model for Assembly Histories), a machine-learning framework for generating assembly histories of ensembles of dark matter haloes. We train florah on the assembly histories from the Gadget at Ultra-high Redshift with Extra Fine Time-steps and vsmdpl N -body simulations and demonstrate its ability to recover key properties such as the time evolution of mass and concentration. We obtain similar results for the galaxy stellar mass versus halo mass relation and its residuals when we run the Santa Cruz semi-analytic model on florah -generated assembly histories and halo formation histories extracted from an N -body simulation. We further show that florah also reproduces the dependence of clustering on properties other than mass (assembly bias), which is not captured by other analytic methods. By combining multiple networks trained on a suite of simulations with different redshift ranges and mass resolutions, we are able to construct accurate main progenitor branches with a wide dynamic mass range from |$z=0$| up to an ultra-high redshift |$z \approx 20$|⁠ , currently far beyond that of a single N -body simulation. florah is the first step towards a machine learning-based framework for planting full merger trees; this will enable the exploration of different galaxy formation scenarios with great computational efficiency at unprecedented accuracy. [ABSTRACT FROM AUTHOR]

The amount of power contained in the variations in galaxy star-formation histories (SFHs) across a range of time-scales encodes key information about the physical processes which modulate star formation. Modelling the SFHs of galaxies as stochastic processes allows the relative importance of different time-scales to be quantified via the power spectral density (PSD). In this paper, we build upon the PSD framework and develop a physically motivated, 'stochastic' prior for non-parametric SFHs in the spectral energy distribution (SED)-modelling code prospector. We test this prior in two different regimes: (1) massive, |$z = 0.7$| galaxies with both photometry and spectra, analogous to those observed with the LEGA-C survey, and (2) |$z = 8$| galaxies with photometry only, analogous to those observed with NIRCam on JWST. We find that it is able to recover key galaxy parameters (e.g. stellar mass, stellar metallicity) to the same level of fidelity as the commonly used continuity prior. Furthermore, the realistic variability information incorporated by the stochastic SFH model allows it to fit the SFHs of galaxies more accurately and precisely than traditional non-parametric models. In fact, the stochastic prior is |$\gtrsim 2\times$| more accurate than the continuity prior in measuring the recent star-formation rates (log SFR |$_{100}$| and log SFR |$_{10}$|⁠) of both the |$z = 0.7$| and |$z = 8$| mock systems. While the PSD parameters of individual galaxies are difficult to constrain, the stochastic prior implementation presented in this work allows for the development of hierarchical models in the future, i.e. simultaneous SED-modelling of an ensemble of galaxies to measure their underlying PSD. [ABSTRACT FROM AUTHOR]

Using deep imaging from the CANDELS and HFF surveys, we present bulge+disc decompositions with galfitm for |$\sim$| 17 000 galaxies over |$0.2 \le z\le 1.5$|⁠. We use various model parameters to select reliable samples of discs and bulges, and derive their stellar masses using an empirically calibrated relation between mass-to-light ratio and colour. Across our entire redshift range, we show that discs follow stellar mass–size relations that are consistent with those of star-forming galaxies, suggesting that discs primarily evolve via star formation. In contrast, the stellar mass–size relations of bulges are mass-independent. Our novel data set further enables us to separate components into star-forming and quiescent based on their specific star formation rates. We find that both star-forming discs and star-forming bulges lie on stellar mass–size relations that are similar to those of star-forming galaxies, while quiescent discs are typically smaller than star-forming discs and lie on steeper relations, implying distinct evolutionary mechanisms. Similar to quiescent galaxies, quiescent bulges show a flattening in the stellar mass–size relation at |$\sim 10^{10}$|  M |$_\odot$|⁠ , below which they show little mass dependence. However, their best-fitting relations have lower normalizations, indicating that at a given mass, bulges are smaller than quiescent galaxies. Finally, we obtain rest-frame colours for individual components, showing that bulges typically have redder colours than discs, as expected. We visually derive UVJ criteria to separate star-forming and quiescent components and show that this separation agrees well with component colour. HFF bulge+disc decomposition catalogues used for these analyses are publicly released with this paper. [ABSTRACT FROM AUTHOR]

It is crucial for a deeper understanding of the formation and evolution of galaxies in the Universe to study stellar mass (M *) and star formation rate (SFR). Traditionally, astronomers infer the properties of galaxies from spectra, which are highly informative, but expensive and hard to be obtained. Fortunately, modern sky surveys obtained a vast amount of high-spatial-resolution photometric images. The photometric images are obtained relatively economically than spectra, and it is very helpful for related studies if M * and SFR can be estimated from photometric images. Therefore, this paper conducted some preliminary researches and explorations on this regard. We constructed a deep learning model named Galaxy Efficient Network (GalEffNet) for estimating integrated M * and specific star formation rate (sSFR) from Dark Energy Spectroscopic Instrument galaxy images. The GalEffNet primarily consists of a general feature extraction module and a parameter feature extractor. The research results indicate that the proposed GalEffNet exhibits good performance in estimating M * and sSFR, with σ reaching 0.218 and 0.410 dex. To further assess the robustness of the network, prediction uncertainty was performed. The results show that our model maintains good consistency within a reasonable bias range. We also compared the performance of various network architectures and further tested the proposed scheme using image sets with various resolutions and wavelength bands. Furthermore, we conducted applicability analysis on galaxies of various sizes, redshifts, and morphological types. The results indicate that our model performs well across galaxies with various characteristics and indicate its potentials of broad applicability. [ABSTRACT FROM AUTHOR]

Modern cosmological hydrodynamical galaxy simulations provide tens of thousands of reasonably realistic synthetic galaxies across cosmic time. However, quantitatively assessing the level of realism of simulated universes in comparison to the real one is difficult. In this paper of the Extracting Reality from Galaxy Observables with Machine Learning series, we utilize contrastive learning to directly compare a large sample of simulated and observed galaxies based on their stellar-light images. This eliminates the need to specify summary statistics and allows to exploit the whole information content of the observations. We produce survey-realistic galaxy mock data sets resembling real Hyper Suprime-Cam (HSC) observations using the cosmological simulations TNG50 and TNG100. Our focus is on galaxies with stellar masses between 109 and 1012 M⊙ at z  = 0.1–0.4. This allows us to evaluate the realism of the simulated TNG galaxies in comparison to actual HSC observations. We apply the self-supervised contrastive learning method Nearest Neighbour Contrastive Learning to the images from both simulated and observed data sets (g -, r -, i -bands). This results in a 256-dimensional representation space, encoding all relevant observable galaxy properties. First, this allows us to identify simulated galaxies that closely resemble real ones by seeking similar images in this multidimensional space. Even more powerful, we quantify the alignment between the representations of these two image sets, finding that the majority (≳ 70 per cent) of the TNG galaxies align well with observed HSC images. However, a subset of simulated galaxies with larger sizes, steeper Sérsic profiles, smaller Sérsic ellipticities, and larger asymmetries appears unrealistic. We also demonstrate the utility of our derived image representations by inferring properties of real HSC galaxies using simulated TNG galaxies as the ground truth. [ABSTRACT FROM AUTHOR]

We present the 'Cosmological Jellyfish' project – a citizen-science classification program to identify jellyfish (JF) galaxies within the IllustrisTNG cosmological simulations. JF are satellite galaxies that exhibit long trailing gas features – 'tails' – extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of |$\sim 80\, 000$| satellite galaxies spanning an unprecedented range of stellar masses, |$10^{8.3}{-}10^{12.3}\, \mathrm{M_\odot }$|⁠ , and host masses, |$M_\mathrm{200,c}=10^{10.4}{-}10^{14.6}\, \mathrm{M_\odot }$| back to z  = 2. Based on this sample, |$\sim 90\, 000$| galaxy images were presented to volunteers in the citizen-science Zooniverse platform, who were asked to determine whether the galaxy image resembles a JF. Based on volunteer votes, each galaxy received a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a data set of 5307 visually identified JF galaxies. We find that JF is common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of |$M_\mathrm{200,c}\sim 10^{11.5}{-}10^{13}\, \mathrm{M_\odot }$|⁠ , radial positions within hosts exceeding the virial radius R 200, c, and at high redshift up to z  = 2. The full data set of our JF scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations. [ABSTRACT FROM AUTHOR]

The current properties of globular cluster systems (GCSs) in the nearby Universe are a consequence of an evolutionary history ruled by accretion and disruption processes. The analysis of scaling relations for GCSs is crucial for understanding the relevance of different physical processes involved in their origin and subsequent survival. In this work, radial profiles are calculated for a sample of GCSs associated with nearby massive galaxies. This is supplemented with results from our previous papers, achieving a total sample of 53 GCSs with radial profiles homogeneously calculated, and spanning more than two orders of magnitude in stellar mass of the host galaxy. Scaling relations involving different parameters of the GCSs are obtained for the entire sample, and their significance in terms of different scenarios is considered. Finally, the results are analysed in the literature context. [ABSTRACT FROM AUTHOR]

When a galaxy falls into a cluster, its outermost parts are the most affected by the environment. In this paper, we are interested in studying the influence of a dense environment on different galaxy's components to better understand how this affects the evolution of galaxies. We use, as laboratory for this study, the Hydra cluster which is close to virialization; yet it still shows evidence of substructures. We present a multiwavelength bulge–disc decomposition performed simultaneously in 12 bands from S-PLUS (Southern Photometric Local Universe Survey) data for 52 galaxies brighter than mr  = 16. We model the galaxies with a Sérsic profile for the bulge and an exponential profile for the disc. We find that the smaller, more compact, and bulge-dominated galaxies tend to exhibit a redder colour at a fixed stellar mass. This suggests that the same mechanisms (ram-pressure and tidal stripping) that are causing the compaction in these galaxies are also causing them to stop forming stars. The bulge size is unrelated to the galaxy's stellar mass, while the disc size increases with greater stellar mass, indicating the dominant role of the disc in the overall galaxy mass–size relation found. Furthermore, our analysis of the environment unveils that quenched galaxies are prevalent in regions likely associated with substructures. However, these areas also harbour a minority of star-forming galaxies, primarily resulting from galaxy interactions. Lastly, we find that ∼37 per cent of the galaxies exhibit bulges that are bluer than their discs, indicative of an outside-in quenching process in this type of dense environments. [ABSTRACT FROM AUTHOR]

We present results from the JWST First Reionization Epoch Spectroscopically Complete Observations survey on the star-forming sequence (SFS) of galaxies at 1.0 < z < 1.7, around the peak of the cosmic star formation history. Star formation rates (SFRs) are measured from the redshifted, relatively dust-insensitive Paschen- α emission line, and stellar mass measurements include the F444W (4.4 μ m; rest-frame H) band. We find SFRs of galaxies with log(M */ M ⊙) > 9.5 that are lower than found in many earlier studies by up to 0.6 dex, but in good agreement with recent results obtained with the Prospector fitting framework. The difference (log(SFR(Pa α)-SFR(Prospector)) is −0.09 ± 0.04 dex at 1010−11 M ⊙. We also measure the empirical relation between Paschen- α luminosity and rest-frame H- band magnitude and find that the scatter is only 0.04 dex lower than that of the SFR– M * relation and is much lower than the systematic differences among relations in the literature due to various methods of converting observed measurements to physical properties. We additionally identify examples of sources—that, with standard cutoffs via the UVJ diagram, would be deemed quiescent—with significant (log(sSFR)> −11 yr−1), typically extended, Paschen- α emission. Our results may be indicative of the potential unification of methods used to derive the SFS with careful selection of star-forming galaxies and independent SFR and stellar mass indicators. [ABSTRACT FROM AUTHOR]

We present the galaxy stellar mass–size relation in the rest-frame near-IR (1.5 μ m) and its evolution with redshift up to z = 2.5. Sérsic profiles are measured for ∼26,000 galaxies with stellar masses M ⋆ > 109 M ⊙ from JWST/NIRCam F277W and F444W imaging provided by the COSMOS-WEB and PRIMER surveys using coordinates, redshifts, colors, and stellar mass estimates from the COSMOS2020 catalog. The new rest-frame near-IR effective radii are generally smaller than previously measured rest-frame optical sizes, on average by 0.14 dex, with no significant dependence on redshift. For quiescent galaxies, this size offset does not depend on stellar mass, but for star-forming galaxies, the offset increases from −0.1 dex at M ⋆ = 109.5 M ⊙ to −0.25 dex at M ⋆ > 1011 M ⊙. That is, we find that the near-IR stellar mass–size relation for star-forming galaxies is flatter in the rest-frame near-IR than in the rest-frame optical at all redshifts 0.5 < z < 2.5. The general pace of size evolution is the same in the near-IR as previously demonstrated in the optical, with slower evolution (R e ∝ (1 + z)−0.7) for L * star-forming galaxies and faster evolution (R e ∝ (1 + z)−1.3) for L * quiescent galaxies. Massive (M ⋆ > 1011 M ⊙) star-forming galaxies evolve in size almost as fast as quiescent galaxies. Low-mass (M ⋆ < 1010 M ⊙) quiescent galaxies evolve as slow as star-forming galaxies. Our main conclusion is that the size evolution narrative as it has emerged over the past two decades does not radically change when accessing the rest-frame near-IR with JWST, a better proxy of the underlying stellar mass distribution. [ABSTRACT FROM AUTHOR]

The measurements of morphological indicators of galaxies are often influenced by a series of observational effects. In this study, we utilize a sample of 832 TNG50 simulated galaxies with log(M */ M ⊙)> 9 at 0.5 < z < 3 to investigate the differences in nonparametric morphological indicators (C, A, Gini, M 20, A O, and D O) derived from noise-free and high-resolution TNG50 images and mock images simulated to have the same observational conditions as JWST/NIRCam. We quantify the relationship between intrinsic and observed values of the morphological indicators and accordingly apply this calibration to 4733 galaxies in the same stellar mass and redshift ranges observed in JWST CEERS and JADES surveys. We find a significant evolution of morphological indicators with rest-frame wavelength (λ rf) at λ rf < 1 μ m, while essentially no obvious variations occur at λ rf > 1 μ m. The morphological indicators of star-forming galaxies (SFGs) and quiescent galaxies (QGs) are significantly different. The morphologies of QGs exhibit a higher sensitivity to rest-frame wavelength than SFGs. After analyzing the evolution of morphological indicators in the rest-frame V band (0.5–0.7 μ m) and rest-frame J band (1.1–1.4 μ m), we find that the morphologies of QGs evolve substantially with both redshift and stellar mass. For SFGs, the C, Gini, and M 20 show a rapid evolution with stellar mass at log(M */ M ⊙) ≥ 10.5, while the A O, D O, and A evolve with both redshift and stellar mass. Our comparison shows that TNG50 simulations effectively reproduce the morphological indicators we measured from JWST observations when the impact of dust attenuation is considered. [ABSTRACT FROM AUTHOR]

By using an ultradeep JWST/MIRI image at 5.6 μ m in the Hubble eXtreme Deep Field, we constrain the role of strong H α emitters (HAEs) during "cosmic reionization" at z ≃ 7–8. Our sample of HAEs is comprised of young (<35 Myr) galaxies, except for one single galaxy (≈300 Myr), with low stellar masses (≲109 M ⊙). These HAEs show a wide range of rest-frame UV continuum slopes (β), with a median value of β = −2.15 ± 0.21, which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency (ξ ion,0) of these sources (assuming f esc,LyC = 0%), which yields a median value log 10 (ξ ion , 0 / (Hz erg − 1)) = 25.50 − 0.12 + 0.10 . We show that ξ ion,0 positively correlates with H α equivalent width and specific star formation rate. Instead ξ ion,0 weakly anticorrelates with stellar mass and β. Based on the β values, we predict f esc , LyC = 4 % − 2 + 3 , which results in log 10 (ξ ion / (Hz erg − 1)) = 25.55 − 0.13 + 0.11 . Considering this and related findings from the literature, we find a mild evolution of ξ ion with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions (f esc,rel) of 6%–15% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ( N ̇ ion ) as N ̇ ion = 10 50.53 ± 0.45 s − 1 Mpc − 3 . When comparing their N ̇ ion with non-HAE galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during cosmic reionization. [ABSTRACT FROM AUTHOR]

Quiescent galaxies generally possess denser cores than star-forming galaxies with similar mass. As a measurement of the core density, the central stellar mass surface density within a radius of 1 kpc (Σ1) was thus suggested to be closely related to galaxy quenching. Massive star-forming galaxies with high Σ1 do not fit into this picture. To understand the origin of such galaxies, we compare the spatially resolved stellar population and star formation properties of massive (>1010.5 M ⊙) blue spiral galaxies with high and low Σ1, divided by Σ1 = 109.4 M ⊙ kpc−2, based on the final release of MaNGA integral field unit data. We find that both high-Σ1 and low-Σ1 blue spirals show large diversities in stellar population and star formation properties. Despite the diversities, high-Σ1 blue spirals are statistically different from the low-Σ1 ones. Specifically, the radial profiles of the luminosity-weighted age and Mgb/〈Fe〉 show that high-Σ1 blue spirals consist of a larger fraction of galaxies with younger and less α -element-enhanced centers than their low-Σ1 counterparts, ∼55% versus ∼30%. The galaxies with younger centers mostly have higher central specific star formation rates, which still follow the spaxel-based star formation main-sequence relation. Examinations of the H α velocity field and the optical structures suggest that galactic bars or galaxy interactions should be responsible for the rejuvenation of these galaxies. The remaining ∼45% of high-Σ1 blue spirals are consistent with the inside-out growth scenario. [ABSTRACT FROM AUTHOR]

The interaction between supermassive black hole (SMBH) feedback and the circumgalactic medium (CGM) continues to be an open question in galaxy evolution. In our study, we use smoothed particle hydrodynamics simulations to explore the impact of SMBH feedback on galactic metal retention and the motion of metals and gas into and through the CGM of L* galaxies. We examine 140 galaxies from the 25 Mpc cosmological volume Romulus25, with stellar masses between log(M */ M ⊙) = 9.5–11.5. We measure the fraction of metals remaining in the interstellar medium (ISM) and CGM of each galaxy and calculate the expected mass of each SMBH based on the M BH– σ relation (Kormendy & Ho 2013). The deviation of each SMBH from its expected mass, Δ M BH, is compared to the potential of its host via σ. We find that SMBHs with accreted mass above M BH– σ are more effective at removing metals from the ISM than undermassive SMBHs in star-forming galaxies. Overall, overmassive SMBHs suppress the total star formation of their host galaxies and more effectively move metals from the ISM into the CGM. However, we see little to no evacuation of gas from the CGM out of their halos, in contrast with other simulations. Finally, we predict that C iv column densities in the CGM of L* galaxies are unlikely to depend on host galaxy SMBH mass. Our results show that the scatter in the low-mass end of the M BH– σ relation may indicate how effective an SMBH is in the local redistribution of mass in its host galaxy. [ABSTRACT FROM AUTHOR]

The large-scale environment of the cosmic web is believed to impact galaxy evolution, but there is still no consensus regarding the mechanisms. We use a semi-analytic model (SAM) galaxy catalog to study the star formation and dust content of local galaxies in different cosmic environments of the cosmic web—namely voids, filaments, walls, and nodes. We find a strong impact of the environment only for galaxies with M stars ≲ 1010.8 M ⊙: the less dense the environment, the larger the star formation rate and dust content at fixed stellar mass. This is attributed to the fact that galaxies in less dense environments typically feature younger stellar populations, a slower evolution of their stellar mass, and delayed star formation compared to galaxies in denser environments. As for galaxies with M stars ≳ 1010.8 M ⊙, the differences among environments are milder, due to the disk-instability-driven supermassive black hole (SMBH) growth implemented in the SAM, which makes SMBH growth, and thus galaxy quenching, environment-insensitive. We qualitatively test our predictions against observations by identifying environments in Sloan Digital Sky Survey Data Release 16 using dust masses derived from the GAMA survey. The agreement is encouraging, particularly at log M stars / M ⊙ ≳ 10.5 – 11 , where the specific star formation rates and dust masses appear quite environment-insensitive. This result confirms the importance of in situ growth channels of SMBHs. [ABSTRACT FROM AUTHOR]

We present a multiple emission line study of ∼1300 H α emitters (HAEs) at z ∼ 2.3 in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE K s broadband data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [O iii ] λ λ 4959, 5007 and [O ii ] λ λ 3726, 3729. Our measurements demonstrate good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate, specific star formation rate, and ionization state (O32). We have identified a discrepancy between HAEs at z ∼ 2.3 and typical local star-forming galaxies observed in the Sloan Digital Sky Survey, suggesting the evolution of lower gas-phase metallicity (Z) and higher ionization parameters (U) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high EW[O iii ]. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters and Ly α emitters at z ≃ 2–3. Considering that these characteristics may indicate potential strong Lyman continuum leakage, higher-redshift analogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations of this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization. [ABSTRACT FROM AUTHOR]