arXiv subjects

Junxian Wang

Publications and source records attributed to Junxian Wang.

At least 55 records · Page 3Linked to original sources

arXiv2021

Correlations between H$α$ Equivalent Width and Galaxy Properties at $z = 0.47$: Physical or Selection-driven?

The H$α$ equivalent width (EW) is an observational proxy for specific star formation rate (sSFR) and a tracer of episodic star-formation activity. Previous assessments show that EW strongly anti-correlates with stellar mass as $M^{-0.25}$ similar to the sSFR -- stellar mass relation. However, such a correlation may be driven/formed by selection effects. In this study, we investigate how H$α$ EWs correlate with galaxy properties and how selection biases could alter such correlations using a $z = 0.47$ narrowband-selected sample of 1572 H$α$ emitters from the Ly$α$ Galaxies in the Epoch of Reionization (LAGER) survey. The sample covers 3 deg$^2$ of COSMOS and $1.1\times10^5$ cMpc$^3$. We assume an intrinsic EW distribution to form mock samples of H$α$ emitters (HAEs) and propagate the selection criteria to match observations, giving us control on how selection biases can affect the underlying results. We find EW intrinsically correlates with stellar mass as $W_0 \propto M^{-0.16\pm0.03}$ and decreases by a factor of $\sim 3$ from $10^{7}$ to $10^{10}$ M$_\odot$. We find low-mass HAEs to be $\sim 320$ times more likely to have rest-frame EW$ > 200$Åcompared to high-mass HAEs. Combining the intrinsic EW -- stellar mass correlation with an observed SMF correctly reproduces the observed H$α$ LF, while not correcting for selection effects underestimates the number of bright HAEs. This suggests that the intrinsic EW -- stellar mass correlation is physically significant and reproduces three statistical distributions of galaxy populations (LF, SMF, EW distribution). At lower masses, we find there are more high-EW outliers compared to high masses, even after taking into account selection effects. Our results suggest that high sSFR outliers indicative of bursty SF activity are intrinsically more prevalent in low-mass HAEs and not a byproduct of selection effects.

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arXiv2021

A Lyman-α protocluster at redshift 6.9

Protoclusters, the progenitors of the most massive structures in the Universe, have been identified at redshifts of up to 6.6. Besides exploring early structure formation, searching for protoclusters at even higher redshifts is particularly useful to probe the reionization. Here we report the discovery of the protocluster LAGER-z7OD1 at a redshift of 6.93, when the Universe was only 770 million years old and could be experiencing rapid evolution of the neutral hydrogen fraction in the intergalactic medium. The protocluster is identified by an overdensity of 6 times the average galaxy density, and with 21 narrowband selected Lyman-$α$ galaxies, among which 16 have been spectroscopically confirmed. At redshifts similar to or above this record, smaller protogroups with fewer members have been reported. LAGER-z7OD1 shows an elongated shape and consists of two subprotoclusters, which would have merged into one massive cluster with a present-day mass of $3.7 \times 10^{15}$ solar masses. The total volume of the ionized bubbles generated by its member galaxies is found to be comparable to the volume of the protocluster itself, indicating that we are witnessing the merging of the individual bubbles and that the intergalactic medium within the protocluster is almost fully ionized. LAGER-z7OD1 thus provides a unique natural laboratory to investigate the reionization process.

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arXiv2020

Modeling Quasar UV/Optical Variability with the Corona-heated Accretion-disk Reprocessing (CHAR) Model

The rest-frame UV/optical variability of the quasars in the Sloan Digital Sky Survey (SDSS) Stripe 82 is used to test the Corona-Heated Accretion-disk Reprocessing (CHAR) model of Sun et al. 2020. We adopt our CHAR model and the observed black-hole masses ($M_{\mathrm{BH}}$) and luminosities ($L$) to generate mock light curves that share the same measurement noise and sampling as the real observations. Without any fine-tuning, our CHAR model can satisfactorily reproduce the observed ensemble structure functions for different $M_{\mathrm{BH}}$, $L$, and rest-frame wavelengths. Our analyses reveal that a luminosity-dependent bolometric correction is disfavored over the constant bolometric correction for UV/optical luminosities. Our work demonstrates the possibility of extracting quasar properties (e.g., the bolometric correction or the dimensionless viscosity parameter) by comparing the physical CHAR model with quasar light curves.

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arXiv2020

Corona-Heated Accretion-disk Reprocessing (CHAR): A Physical Model to Decipher the Melody of AGN UV/optical Twinkling

Active galactic nuclei (AGNs) have long been observed to "twinkle" (i.e., their brightness varies with time) on timescales from days to years in the UV/optical bands. Such AGN UV/optical variability is essential for probing the physics of supermassive black holes (SMBHs), the accretion disk, and the broad-line region. Here we show that the temperature fluctuations of an AGN accretion disk, which is magnetically coupled with the corona, can account for observed high-quality AGN optical light curves. We calculate the temperature fluctuations by considering the gas physics of the accreted matter near the SMBH. We find that the resulting simulated AGN UV/optical light curves share the same statistical properties as the observed ones as long as the dimensionless viscosity parameter $α$, which is widely believed to be controlled by magnetohydrodynamic (MHD) turbulence in the accretion disk, is about $0.01$---$0.2$. Moreover, our model can simultaneously explain the larger-than-expected accretion disk sizes and the dependence of UV/optical variability upon wavelength for NGC 5548. Our model also has the potential to explain some other observational facts of AGN UV/optical variability, including the timescale-dependent bluer-when-brighter color variability and the dependence of UV/optical variability on AGN luminosity and black hole mass. Our results also demonstrate a promising way to infer the black-hole mass, the accretion rate, and the radiative efficiency, thereby facilitating understanding of the gas physics and MHD turbulence near the SMBH and its cosmic mass growth history by fitting the AGN UV/optical light curves in the era of time-domain astronomy.

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arXiv2020

Adaptive-Multilevel BDDC algorithm for three-dimensional plane wave Helmholtz systems

In this paper, we are concerned with the weighted plane wave least-squares (PWLS) method for three-dimensional Helmholtz equations, and develop the multi-level adaptive BDDC algorithms for solving the resulting discrete system. In order to form the adaptive coarse components, the local generalized eigenvalue problems for each common face and each common edge are carefully designed. The condition number of the two-level adaptive BDDC preconditioned system is proved to be bounded above by a user-defined tolerance and a constant which is dependent on the maximum number of faces and edges per subdomain and the number of subdomains sharing a common edge. The efficiency of these algorithms is illustrated on a benchmark problem. The numerical results show the robustness of our two-level adaptive BDDC algorithms with respect to the wave number, the number of subdomains and the mesh size, and illustrate that our multi-level adaptive BDDC algorithm can reduce the scale of the coarse problem and can be used to solve large wave number problems efficiently.

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arXiv2020

A comprehensive study of H$α$ emitters at $z \sim$ 0.62 in the DAWN survey: the need for deep and wide regions

We present new estimates of the luminosity function (LF) and star formation rate density (SFRD) for an H$α$ selected sample at $z\sim0.62$ from the Deep And Wide Narrow-band (DAWN) survey. Our results are based on a new H$α$ sample in the extended COSMOS region (compared to Coughlin et al. 2018) with the inclusion of flanking fields, resulting in a total area coverage of $\sim$1.5 deg$^2$. A total of 241 H$α$ emitters were selected based on robust selection criteria using spectro-photometric redshifts and broadband color-color classification. We explore the effect of different dust correction prescriptions by calculating the LF and SFRD using a constant dust extinction correction, A{$_{\textrm{H}α}=1$} mag, a luminosity-dependent correction, and a stellar-mass dependent correction. The resulting H$α$ LFs are well fitted using Schechter functions with best-fit parameters: L$^*=10^{42.24}$ erg s$^{-1}$, $ϕ^*=10^{-2.85}$ Mpc$^{-3}$, $α= -1.62$ for constant dust correction, L$^*=10^{42.31}$ erg s$^{-1}$, $ϕ^*=10^{-2.8}$ Mpc$^{-3}$, $α=-1.39$ for luminosity-dependent dust correction, and L$^*=10^{42.36}$ erg s$^{-1}$, $ϕ^*=10^{-2.91}$ Mpc$^{-3}$, $α= -1.48$, for stellar mass-dependent dust correction. The deep and wide nature of the DAWN survey effectively samples H$α$ emitters over a wide range of luminosities, thereby providing better constraints on both the faint and bright end of the LF. Also, the SFRD estimates $ρ_{\textrm{SFR}}=10^{-1.39}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (constant dust correction), $ρ_{\textrm{SFR}}=10^{-1.47}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (luminosity-dependent dust correction), and $ρ_{\textrm{SFR}}=10^{-1.49}$ M$_{\odot}$yr$^{-1}$Mpc$^{-3}$ (stellar mass-dependent dust correction) are in good agreement with the evolution of SFRD across redshifts ($0 < z < 2$) seen from previous H$α$ surveys.

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arXiv2020

A large, deep 3 deg$^2$ survey of H$α$, [OIII], and [OII] emitters from LAGER: constraining luminosity functions

We present our measurements of the H$α$, [OIII], and [OII] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 $z = 0.47$ H$α$-, 3933 $z = 0.93$ [OIII]-, and 5367 $z = 1.59$ [OII]-selected emission line galaxies in a single 3 deg$^2$ CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5$σ$ depths of $8.2\times10^{-18}$ erg s$^{-1}$ cm$^{-2}$ and comoving volumes of $(1-7)\times10^{5}$ Mpc$^3$ making our survey one of the deepest narrowband surveys. We measure the observed luminosity functions and find best-fits of $ϕ^\star = 10^{-3.16\pm0.09}$ Mpc$^{-3}$ and $L^\star = 10^{41.72\pm0.09}$ erg s$^{-1}$ for H$α$, $ϕ^\star = 10^{-2.16^{+0.10}_{-0.12}}$ Mpc$^{-3}$ and $L^\star = 10^{41.38^{+0.07}_{-0.06}}$ erg s$^{-1}$ for [OIII], and $ϕ^\star = 10^{-1.97^{+0.07}_{-0.07}}$ Mpc$^{-3}$ and $L^\star = 10^{41.66\pm0.03}$ erg s$^{-1}$ for [OII], with $α$ fixed to $-1.75$, $-1.6$, and $-1.3$, respectively. An excess of bright $> 10^{42}$ erg s$^{-1}$ [OIII] emitters is observed and may be due to AGN contamination. Dust corrections are applied assuming $A_{\rm{H}α} = 1$ mag. We also design our own empirical rest-frame $g - r$ calibration using SDSS DR12 data, test it against our $z = 0.47$ H$α$ emitters with $z$COSMOS $1$D spectra, and calibrate it for $(g - r)$ between $-0.8$ and $1.3$ mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as $\log_{10}ρ_{\rm{SFR}}/(\rm{M}_\odot\ \rm{yr}^{-1}\ \rm{Mpc}^{-3}) = -1.63\pm0.04$, $-1.07\pm0.06$, and $-0.90\pm0.10$ for H$α$, [OIII], and [OII], respectively. We find our [OIII] and [OII] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multi-wavelength SFRDs, while the H$α$ sample traces $\sim 70$ percent of the total $z = 0.47$ SFRD.

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arXiv2019

The Ly$α$ Luminosity Function and Cosmic Reionization at $z \sim$ 7.0: a Tale of Two LAGER Fields

We present the largest-ever sample of 79 Ly$α$ emitters (LAEs) at $z\sim$ 7.0 selected in the COSMOS and CDFS fields of the LAGER project (the Lyman Alpha Galaxies in the Epoch of Reionization). Our newly amassed ultradeep narrowband exposure and deeper/wider broadband images have more than doubled the number of LAEs in COSMOS, and we have selected 30 LAEs in the second field CDFS. We detect two large-scale LAE-overdense regions in the COSMOS that are likely protoclusters at the highest redshift to date. We perform injection and recovery simulations to derive the sample incompleteness. We show significant incompleteness comes from blending with foreground sources, which however has not been corrected in LAE luminosity functions in {the} literature. The bright end bump in the Ly$α$ luminosity function in COSMOS is confirmed with 6 (2 newly selected) luminous LAEs (L$_{Lyα}$ $>$ 10$^{43.3}$ erg s$^{-1}$). Interestingly, the bump is absent in CDFS, in which only one luminous LAE is detected. Meanwhile, the faint end luminosity functions from the two fields well agree with each other. The 6 luminous LAEs in COSMOS coincide with 2 LAE-overdense regions, while such regions are not seen in CDFS. The bright-end luminosity function bump could be attributed to ionized bubbles in a patchy reionization. It appears associated with cosmic overdensities, thus supports an inside-out reionization topology at $z$ $\sim$ 7.0, i.e., the high density peaks were ionized earlier compared to the voids. An average neutral hydrogen fraction of $x_{HI}$ $\sim$ 0.2 -- 0.4 is derived at $z\sim$ 7.0 based on the cosmic evolution of the Ly$α$ luminosity function.

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arXiv2019

Lyman Alpha Galaxies in the Epoch of Reionization (LAGER): Spectroscopic Confirmation of Two Redshift ~ 7.0 Galaxies

We spectroscopically confirmed two narrow-band selected redshift 7.0 Ly$α$ galaxies and studied their restframe UV spectra. The Ly$α$ and other UV nebular lines are very useful to confirm the galactic redshifts and diagnose the different mechanisms driving the ionizing emission. We observed two narrowband-selected $z$=7.0 Ly$α$ candidates in the LAGER Chandra Deep Field South (CDFS) field with IMACS at Magellan telescope and confirmed they are Ly$α$ emitters at $z$=6.924 and 6.931. In one galaxy, we also obtained deep NIR spectroscopy, which yields non-detections of the high-ionization UV nebular lines. We measured upper-limits of the ratios of CIV$λ$1548/Ly$α$, HeII$λ$1640/Ly$α$, OIII]$λ$1660/Ly$α$, and CIII]$λ$1909/Ly$α$ from the NIR spectra. These upper-limits imply that the ionizing emission in this galaxy is dominated by normal star formation instead of AGN.

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arXiv2019

Design for the First Narrowband Filter for the Dark Energy Camera: Optimizing the LAGER Survey for z ~ 7 Galaxies

We present the design for the first narrowband filter NB964 for the Dark Energy Camera (DECam), which is operated on the 4m Blanco Telescope at the Cerro Tololo Inter-American Observatory. The NB964 filter profile is essentially defined by maximizing the power of searching for Lyman alpha emitting galaxies (LAEs) in the epoch of reionization, with the consideration of the night sky background in the near-infrared and the DECam quantum efficiency. The NB964 filter was manufactured by Materion in 2015. It has a central wavelength of 964.2 nm and a full width at half maximum (FWHM) of 9.2 nm. An NB964 survey named LAGER (Lyman Alpha Galaxies in the Epoch of Reionization) has been ongoing since December 2015. Here we report results of lab tests, on-site tests and observations with the NB964 filter. The excellent performances of this filter ensure that the LAGER project is able to detect LAEs at z~7 with a high efficiency.

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arXiv2019

A two-level overlapping Schwarz method with energy-minimizing multiscale coarse basis functions

A two-level overlapping Schwarz method is developed for second order elliptic problems with highly oscillatory and high contrast coefficients, for which it is known that the standard coarse problem fails to give a robust preconditioner. In this paper, we develop energy minimizing multiscale finite element functions to form a more robust coarse problem. First, a local spectral problem is solved in each non-overlapping coarse subdomain, and dominant eigenfunctions are selected as auxiliary functions, which are crucial for the high contrast case. The required multiscale basis functions are then obtained by minimizing an energy subject to some orthogonality conditions with respect to the auxiliary functions. Due to an exponential decay property, the minimization problem is solved locally on oversampling subdomains, that are unions of a few coarse subdomains. The coarse basis functions are therefore local and can be computed efficiently. The resulting preconditioner is shown to be robust with respect to the contrast in the coefficients as well as the overlapping width in the subdomain partition. Numerical results are presented to validate the theory and show the performance.

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arXiv2018

Evolution of quasar stochastic variability along its main sequence

We explore the evolution of the time variability (in the optical $g$-band and on timescales of weeks to years) of SDSS Stripe 82 quasars along the quasar main sequence. A parent sample of $1004$ quasars within $0.5\leq z \leq 0.89$ are used for our statistical studies, we then make subsamples from our parent sample: a subsample of $246$ quasars with similar luminosities, and a subsample of $399$ quasars with similar Rfe (i.e., the ratio of the equivalent width of FeII within $4435$--$4685\ \mathrmÅ$ to that of \Hbeta). We find the variability amplitude decreases with luminosity ($L_{\mathrm{bol}}$). The anti-correlation between the variability amplitude and Rfe is weak but statistically significant. The characteristic timescale, $τ$, correlates mostly with quasar luminosity, its dependence on Rfe is statistically insignificant. After controlling luminosity and Rfe, the high- and low-FWHM samples have similar structure functions. These results support the framework that Rfe is governed by Eddington ratio and FWHM of Hbeta is mostly determined by orientation. We then provide new empirical relations between variability parameters and quasar properties (i.e., luminosity and Rfe). Our new relations are consistent with the scenario that quasar variability is driven by the thermal fluctuations in the accretion disk, $τ$ seems to correspond to the thermal timescale. From our new relations, we find the short-term variability is mostly sensitive to $L_{\mathrm{bol}}$. Basing on this, we propose that quasar short-term (a few months) variability might be a new type of "Standard Candle" and can be adopted to probe cosmology.

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arXiv2018

The Dawn Light of Blueberry Galaxies: Spectroscopic and Photometric Studies of two Starburst Dwarf Galaxies

A population of so-called "blueberry" starbursting dwarf galaxies with extremely blue colors, low-metallicities, and enormous ionization ratios, has recently been found by Yang et al. (2017). Yet we still do not know their detailed properties, such as morphologies, AGN occupations, massive star contents, infrared emission, dust properties, etc. As a pilot study of the blueberries, we investigate the spectroscopic and photometric properties of two blueberry candidates, RGG B and RGG 5, for which Hubble Space Telescope high-resolution images are available. We find that RGG B and RGG 5 perhaps are likely to be two merging dwarf galaxy systems. RGG B may have a close merging companion; yet the current evidence still cannot exclude the possibility that RGG B is just disturbed by in-situ star formation through, e.g., outflows, rather than undergoing a merger. RGG 5 presents stellar shells in the outskirt which can be the powerful evidence of galaxy merging. We also find that, all of the blueberries, including RGG B and RGG 5, are located close to the theoretical maximum-starburst-line in the BPT diagram, have very high ionization parameters, and relatively low hardness ionizing radiation fields, exhibit nitrogen overabundances, and show extremely red mid-IR colors, and reside in the so-called "ULIRGs/LINERs/Obscured AGN" region. The blueberry galaxies may not harbor AGN.

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arXiv2018

Adaptive BDDC algorithms for the system arising from plane wave discretization of Helmholtz equations

Balancing domain decomposition by constraints (BDDC) algorithms with adaptive primal constraints are developed in a concise variational framework for the weighted plane wave least-squares (PWLS) discritization of Helmholtz equations with high and various wave numbers. The unknowns to be solved in this preconditioned system are defined on elements rather than vertices or edges, which are different from the well-known discritizations such as the classical finite element method. Through choosing suitable "interface" and appropriate primal constraints with complex coefficients and introducing some local techniques, we developed a two-level adaptive BDDC algorithm for the PWLS discretization, and the condition number of the preconditioned system is proved to be bounded above by a user-defined tolerance and a constant which is only dependent on the maximum number of interfaces per subdomain. A multilevel algorithm is also attempted to resolve the bottleneck in large scale coarse problem. Numerical results are carried out to confirm the theoretical results and illustrate the efficiency of the proposed algorithms.

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arXiv2017

How far is quasar UV/optical variability from damped random walk at low frequency?

Studies have shown that UV/optical light curves of quasars can be described with the prevalent damped random walk (DRW, also known as Ornstein-Uhlenbeck process) model. A white noise power spectral density (PSD) is expected at low frequency in this model, however, direct observational constraint to the low frequency PSD slope is hard due to limited lengths of the light curves available. Meanwhile, quasars show too large scatter in their DRW parameters to be attributed to the uncertainties in the measurements and the dependence of variation to known physical factors. In this work we present simulations showing that, if the low frequency PSD deviates from DRW, the red noise leakage can naturally produce large scatter in variation parameters measured from simulated light curves. The steeper the low frequency PSD slope is, the larger scatter we expect. Based on the observations of SDSS Stripe 82 quasars, we find the low frequency PSD slope should be no steeper than -1.3. The actual slope could be flatter, which consequently requires that quasar variabilities should be influenced by other unknown factors. We speculate that magnetic field and/or metallicity could be such additional factors.

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arXiv2017

Blueberry galaxies: the lowest mass young starbursts

Searching for extreme emission line galaxies allows us to find low-mass metal-poor galaxies that are good analogs of high redshift Ly$α$ emitting galaxies. These low-mass extreme emission line galaxies are also potential Lyman-continuum leakers. Finding them at very low redshifts ($z\lesssim0.05$) allows us to be sensitive to even lower stellar masses and metallicities. We report on a sample of extreme emission line galaxies at $z\lesssim0.05$ (blueberry galaxies). We selected them from SDSS broadband images on the basis of their broad band colors, and studied their properties with MMT spectroscopy. From the whole SDSS DR12 photometric catalog, we found 51 photometric candidates. We spectroscopically confirm 40 as blueberry galaxies. (An additional 7 candidates are contaminants, and 4 remain without spectra.) These blueberries are dwarf starburst galaxies with very small sizes ($< 1\hbox{kpc}$), and very high ionization ([OIII]/[OII]$\sim10-60$). They also have some of the lowest stellar masses ($\log(\hbox{M}/\hbox{M}_{\odot})\sim6.5-7.5$) and lowest metallicities ($7.1<12+\log(\hbox{O/H})<7.8$) starburst galaxies. Thus they are small counterparts to green peas and high redshift Ly$α$ emitting galaxies.

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arXiv2017

First Spectroscopic Confirmations of z ~ 7.0 Lya Emitting Galaxies in the LAGER Survey

Narrowband imaging is a highly successful approach for finding large numbers of high redshift Lya emitting galaxies (LAEs) up to z~6.6. However, at z>~7 there are as yet only 3 narrowband selected LAEs with spectroscopic confirmations (two at z~6.9-7.0, one at z~7.3), which hinders extensive studies on cosmic reionization and galaxy evolution at this key epoch. We have selected 23 candidate z~6.9 LAEs in COSMOS field with the large area narrowband survey LAGER (Lyman-Alpha Galaxies at the End of Reionization). In this work we present spectroscopic followup observations of 12 candidates using IMACS on Magellan. For 9 of these, the observations are sufficiently deep to detect the expected lines. Lya emission lines are identified in six sources (yielding a success rate of 2/3), including 3 luminous LAEs with Lya luminosities of L(Lya) ~ 10^{43.5} erg/s, the highest among known spectroscopically confirmed galaxies at >~7.0. This triples the sample size of spectroscopically confirmed narrowband selected LAEs at z>~7, and confirms the bright end bump in the Lya luminosity function we previously derived based on the photometric sample, supporting a patchy reionization scenario. Two luminous LAEs appear physically linked with projected distance of 1.1 pMpc and velocity difference of ~ 170 km/s. They likely sit in a common ionized bubble produced by themselves or with close neighbors, which reduces the IGM attenuation of Lya. A tentative narrow NV$λ$1240 line is seen in one source, hinting at activity of a central massive black hole with metal rich line emitting gas.

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arXiv2017

Ly$α$ and UV Sizes of Green Pea Galaxies

Green Peas are nearby analogs of high-redshift Ly$α$-emitting galaxies. To probe their Ly$α$ escape, we study the spatial profiles of Ly$α$ and UV continuum emission of 24 Green Pea galaxies using the Cosmic Origins Spectrograph (COS) on Hubble Space Telescope (HST). We extract the spatial profiles of Ly$α$ emission from their 2D COS spectra, and of UV continuum from both the 2D spectra and NUV images. The Ly$α$ emission shows more extended spatial profiles than the UV continuum in most Green Peas. The deconvolved Full Width Half Maximum (FWHM) of the Ly$α$ spatial profile is about 2 to 4 times that of the UV continuum in most cases. Since Green Peas are analogs of high-z LAEs, it suggests that most high-z LAEs likely have larger Ly$α$ sizes than UV sizes. We also compare the spatial profiles of Ly$α$ photons at blueshifted and redshifted velocities in eight Green Peas with sufficient data quality, and find the blue wing of the Ly$α$ line has a larger spatial extent than the red wing in four Green Peas with comparatively weak blue Ly$α$ line wings. We show that Green Peas and MUSE $z=3-6$ LAEs have similar Ly$α$ and UV continuum sizes, which probably suggests starbursts in both low-z and high-z LAEs drive similar gas outflows illuminated by Ly$α$ light. Five Lyman continuum (LyC) leakers in this sample have similar Ly$α$ to UV continuum size ratios (~1.4-4.3) to the other Green Peas, indicating their LyC emission escape through ionized holes in the interstellar medium.

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