Recently, the James Webb Space Telescope has revealed a new class of high-redshift (high-z, z > 4) compact galaxies that are red in the rest-frame optical and blue in the rest-frame UV with V-shaped spectral energy distributions (SEDs), referred to as “little red dots” (LRDs). It is very likely that LRDs host obscured broad-line active galactic nuclei (AGNs). In the meanwhile, Green Pea galaxies (GPs), which are compact dwarf galaxies at low redshift, share various similar properties with high-redshift star-forming galaxies. Here, we aim to find the connection between the LRDs and GPs hosting broad-line AGNs (BLGPs). With a sample of 19 BLGPs obtained from our previous work, we further identify seven GPs with V-shaped rest-frame UV-to-optical SEDs that are likely local analogs to LRDs. These V-shaped BLGPs exhibit faint UV absolute magnitudes and sub-Eddington rates similar to those of LRDs. Three of them occupy a similar region to LRDs in the Baldwin–Philips–Terlevich diagram, suggesting they have similar ionization conditions and gas-phase metallicities to LRDs. These similarities suggest that V-shaped BLGPs can be taken as local analogs of high-redshift LRDs. In addition, most (16/19) BLGPs, including six V-shaped BLGPs, host overmassive black holes (BHs) above the local M _BH–M _* relation, making it the first sample of galaxies hosting overmassive BHs at z < 0.4. These findings will help us learn more about the formation and coevolution of early galaxies and BHs.

Lyman continuum (LyC) emitters at z > 3 provide critical samples for studying the contribution of galaxies to the ionizing background in the epoch of reionization. We collect a sample of z > 3 LyC emitters, a dominant fraction (∼60%–70%) of which show spatial offsets between LyC emission and the nonionizing continuum. From this sample, especially, we find a case of an offset LyC emitter, CDFS-6664 (z = 3.797), which shows two components in the high-resolution Hubble Space Telescope and James Webb Space Telescope images. The exceptionally rich data set of CDFS-6664 enables us to extract the two components across multiple wavelengths and estimate their physical properties. We show that CDFS-6664 is consistent with a major merger system with boosted star formation in both components and that the offset LyC emission is most likely associated with the bluer and younger component in this merging system. Our result offers an example in which the offset can be caused by a merger. Future observations of more offset LyC emitters would elucidate the role that mergers play in the escape of LyC photons.

Understanding the ionizing photon escape from galaxies is essential for studying cosmic reionization. With a sample of 23 Lyman continuum (LyC) leakers (among which eight are high-confidence leakers) at 3 < z < 4.5 in the GOODS-S field, we investigate their morphologies using high-resolution data from the Hubble Space Telescope and the James Webb Space Telescope. We find that 20 of the 23 LyC leakers (seven out of eight high-confidence leakers) show merging signatures via visual inspection, while the remaining three are starbursts. The merger fraction of our sample is significantly higher than that of normal galaxies at similar or higher redshifts. Even when using the nonparametric method, which may miss some mergers in a sample, the merger fraction remains high, especially for the high-confidence leakers. Based on our previous finding that LyC leakers are not necessarily starbursts while some are in the star formation main sequence, we further find that those in the main sequence show merger signatures. Our results suggest that LyC leakers are either starbursts or mergers, both of which can facilitate the LyC photon escape, in addition to generating more LyC photons. Furthermore, we show that high-z LyC leakers are statistically more extended than those selected at low redshift, which exhibit a higher merger fraction as size increases. This is likely due to the observational bias that the spatial resolution limits the detection of high-z compact galaxies, while low redshift LyC leakers are more selected as compact starbursts.

We investigate the star-forming properties of 23 Lyman continuum (LyC) leakers at z > 3 in the Great Observatories Origins Deep Survey-South field based on a systematic review of LyC observations from the literature. Using data from the Hubble Space Telescope and the James Webb Space Telescope, we construct the spectral energy distributions for these LyC leakers, covering the spectrum from rest-frame ultraviolet to near-infrared. Through the application of a unified modeling approach, we measure the ultraviolet slope (β), star formation rate, and stellar mass for these LyC leakers in a consistent manner. These high-redshift LyC leakers demonstrate statistically blue UV-continuum slopes (β), which is consistent with their high escape fraction of LyC photons. We find that these high-redshift LyC leakers span a wide range of specific star formation rate ( log ( sSFR /yr) from −8.6 to −6.7). Ten of these LyC leakers are located on the star formation main sequence, instead of all being in the starburst mode. The results indicate that intense bursts of star formation are not necessarily required for the leakage of LyC photons for galaxies at z > 3.

Jets may have contributed to promoting the growth of seed black holes in the early Universe, and thus observations of radio-loud high-redshift quasars are crucial to understanding the growth and evolution of the early supermassive black holes. Here we report the radio properties of an X-ray bright z = 5.5 quasar, SRGE J170245.3+130104 (J1702+1301). Our high-resolution radio images reveal the radio counterpart at the optical position of J1702+1301, while another radio component is also detected at ∼23.5 arcsec to the south-west. Our analysis suggests that this south-west component is associated with a foreground galaxy at z ≈ 0.677, which is mixed with J1702+1301 in low-frequency low-resolution radio images. After removing the contamination from this foreground source, we recalculated the radio loudness of J1702+1301 to be R >1100, consistent with those of blazars. J1702+1301 exhibits a flat radio spectrum (α = −0.17 ± 0.05, S ∝ να) between 0.15 and 5 GHz; above 5 GHz, it shows a rising spectrum shape, and the spectral index $\alpha ^{8.2}_{4.7}$ appears to be correlated with the variation of the flux density: in burst states, $\alpha ^{8.2}_{4.7}$ becomes larger. J1702+1301 displays distinct radio variability on time-scales from weeks to years in the source’s rest frame. These radio properties, including high radio loudness, rising spectrum, and rapid variability, tend to support it as a blazar.

Although double-peaked narrow emission-line galaxies have been studied extensively in the past years, only a few are reported with the Green pea (GP) galaxies. Here we present our discovery of five GP galaxies with double-peaked narrow [O iii] emission lines, referred to as DPGPs, selected from the LAMOST and SDSS spectroscopic surveys. We find that these five DPGPs have blueshifted narrow components more prominent than the redshifted components, with velocity offsets of [O iii]λ5007Å ranging from 306 to 518 $\rm km\, s^{-1}$, and full widths at half maximums of individual components ranging from 263 to 441 $\rm km\, s^{-1}$. By analysing the spectra and the spectral energy distributions (SEDs), we find that they have larger metallicities and stellar masses compared with other GPs. The H α line width, emission-line diagnostic, mid-infrared colour, radio emission, and SED fitting provide evidence of the AGN activities in these DPGPs. They have the same spectral properties of type 2 quasars. Furthermore, we discuss the possible nature of the double-peaked narrow emission-line profiles of these DPGPs and find that they are more likely to be dual active galactic nuclei (AGNs). These DPGP galaxies are ideal laboratories for exploring the growth mode of AGNs in the extremely luminous emission-line galaxies, the co-evolution between AGNs and host galaxies, and the evolution of high-redshift galaxies in the early Universe.