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64 65 66<!-- For all browsers --> 67<link rel="stylesheet" href="/assets/css/main.css"> 68<link rel="preload" href="https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@latest/css/all.min.css" as="style" onload="this.onload=null;this.rel='stylesheet'"> 69<noscript><link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@latest/css/all.min.css"></noscript> 70 71 72 73 <!-- start custom head snippets --> 74 75<!-- insert favicons. use https://realfavicongenerator.net/ --> 76 77<!-- end custom head snippets --> 78 79<!-- favicons --> 80 81 82 </head> 83 84 <body class="layout--splash wide-figures" dir="ltr"> 85 <nav class="skip-links"> 86 <ul> 87 <li><a href="#site-nav" class="screen-reader-shortcut">Skip to primary navigation</a></li> 88 <li><a href="#main" class="screen-reader-shortcut">Skip to content</a></li> 89 <li><a href="#footer" class="screen-reader-shortcut">Skip to footer</a></li> 90 </ul> 91</nav> 92 93 94 95<div class="masthead"> 96 <div class="masthead__inner-wrap"> 97 <div class="masthead__menu"> 98 <nav id="site-nav" class="greedy-nav"> 99 100 <a class="site-title" href="/"> 101 102 103 </a> 104 <ul class="visible-links"><li class="masthead__menu-item"> 105 <a 106 href="/" 107 108 109 >Home</a> 110 </li><li class="masthead__menu-item"> 111 <a 112 href="/assets/cv.pdf" 113 114 115 >CV</a> 116 </li><li class="masthead__menu-item"> 117 <a 118 href="/research/" 119 120 121 >Research</a> 122 </li><li class="masthead__menu-item"> 123 <a 124 href="/code/" 125 126 127 >Code</a> 128 </li><li class="masthead__menu-item"> 129 <a 130 href="/moments/" 131 132 133 >Photos</a> 134 </li></ul> 135 136 <button class="greedy-nav__toggle hidden" type="button"> 137 <span class="visually-hidden">Toggle menu</span> 138 <div class="navicon"></div> 139 </button> 140 <ul class="hidden-links hidden"></ul> 141 </nav> 142 </div> 143 </div> 144</div> 145 146 147 <div class="initial-content"> 148 149 150<div id="main" role="main"> 151 <article class="splash" itemscope itemtype="https://schema.org/CreativeWork"> 152 <meta itemprop="headline" content="Research"> 153 154 155 156 157 <section class="page__content" itemprop="text"> 158 <h2 id="an-earliest-overdensity-structure-at-cosmic-dawn">An Earliest Overdensity Structure at Cosmic Dawn</h2> 159 160<div class="entry-row"> 161 <div class="entry-text"> 162 163 <p>Wu et al. (2026) <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ae7723"><em>The Astrophysical Journal</em>, 1006, 18</a></p> 164 165 <p>We discover a candidate galaxy overdensity at <em>z â 10.5</em>, only 500 Myr after the Big Bang: 18 galaxies with consistent photometric redshifts within 8 comoving Mpc, at four times the field density. The structure hosts 30% of the bright galaxies and 50% of the star formation at <em>10 < z < 12</em> in JADES GOODS-S, which suggests that early luminous galaxies assemble preferentially in overdense environments. Its abundance significantly exceeds the expectation from cosmological simulations such as TNG100, pointing to more efficient galaxy and structure formation than current models predict.</p> 166 167 <p>We have been approved for a JWST/NIRSpec program in Cycle 5 to confirm the structure spectroscopically and to probe its ionized bubble through Lyα emission, and for an ALMA program in Cycle 13 to constrain the halo mass and the gas properties of its members.</p> 168 169 </div> 170 171 <div class="entry-fig"> 172 173 <figure class=""><img src="/assets/fig/overdensity.webp" alt="image" /><figcaption> 174 Galaxy candidates at 10 < z_phot < 12 in the JADES/NIRCam GOODSâS footprint, color-coded by photometric redshift. Large circles are bright sources (F356W > 8 nJy); contours trace the density field from the mean to 4Ï above it. The overdensity sits on the west side of the field, peaking above four times the mean. North is up, east is to the left. 175 176 </figcaption></figure> 177 178 </div> 179</div> 180 181<h2 id="extreme-deep-observation-of-a-galaxy-at-z14">
181Extreme Deep Observation of a Galaxy at z=14</h2> 182 183<div class="entry-row"> 184 <div class="entry-text"> 185 186 <p>Wu et al. (2025) <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ae01a1"><em>The Astrophysical Journal</em>, 992, 212</a></p> 187 188 <p>We lead the analysis of ultra-deep JWST observations of JADES-GS-z14-1 (<em>z = 13.86</em>), one of the two most distant galaxies known and by far the fainter of them. We found that it falls in a small overlap of JADES MIRI pointings and so carries a fortuitous 70-hour exposure, the deepest MIRI observation of any high-redshift galaxy. With 56 new hours of NIRSpec/PRISM spectroscopy and 16-band NIRCam imaging, the dataset probes a sub-luminous galaxy in the early Universe at a depth normally reserved for the brightest ones.</p> 189 190 <p>Working at this signal-to-noise required new machinery: exposure-level model-fitting photometry for NIRCam and MIRI, and a covariance-aware treatment of the PRISM spectra. The galaxy shows only weak metal lines, unlike the luminous <em>z > 10</em> population, and departs from the expected sizeâline strength relation. The most natural reading is low metallicity together with a high escape fraction â which would make faint galaxies like this one efficient contributors to reionization while still early in their chemical enrichment.</p> 191 192 </div> 193 <div class="entry-fig"> 194 195 <figure class=""><img src="/assets/fig/mosaic.jpg" alt="image" /><figcaption> 196 NIRCam and MIRI/F770W imaging of JADES-GS-z14-1, unresolved in every band. The 70-hour F770W exposure gives a rest-frame optical flux density of 7.9 ± 2.6 nJy (29.2 mag). 197 198 </figcaption></figure> 199 200 <figure class=""><img src="/assets/fig/spectrum.webp" alt="spectrum" /><figcaption> 201 NIRSpec/PRISM spectrum of JADES-GS-z14-1. The 56-hour exposure shows no emission lines, but a tentative â and puzzling â absorption feature at 2µm. 202 203 </figcaption></figure> 204 205 </div> 206</div> 207 208<h2 id="detection-of-oxygen-emission-from-a-galaxy-at-z14">Detection of Oxygen Emission from a Galaxy at z=14</h2> 209 210<div class="entry-row"> 211 <div class="entry-text"> 212 213 <p>Helton et al. (2025) <a href="https://www.nature.com/articles/s41550-025-02503-z">Nature Astronomy, 1-12</a></p> 214 215 <p>The MIRI/F770W detection of JADES-GS-z14-0 (<em>z = 14</em>) is blended with a bright foreground galaxy, so the measurement that anchors its rest-frame optical emission is also the hardest one to make. We developed a forward-modeling approach that uses the high-resolution NIRCam imaging to model the source and the contaminant together, then performs exposure-level forced photometry with full propagation of uncertainties and covariances. This yields the F770W flux for the most luminous galaxy known at <em>z</em> > 14. This method can be applied to any MIRI photometry limited by blending.</p> 216 217 </div> 218 <div class="entry-fig"> 219 220 <figure class=""><img src="/assets/fig/GS-z14-0.webp" alt="miri" /><figcaption> 221 MIRI/F770W imaging of JADES-GS-z14-0. The foreground galaxy 183349 severely contaminates the measurement. 222 223 </figcaption></figure> 224 225 </div> 226</div> 227 228<h2 id="subtraction-of-scattered-light-artifacts-in-jwst-imaging">Subtraction of Scattered-light Artifacts in JWST Imaging</h2> 229 230<div class="entry-row"> 231 <div class="entry-text"> 232 233 <p>Wu et al. (2026) <a href="https://iopscience.iop.org/article/10.3847/1538-3881/ae8254"><em>The Astronomical Journal</em>, 172, 105</a></p> 234 235 <p>Wisps are among the most severe scattered-light artifacts in JWST/NIRCam, contaminating nearly a quarter of the area in certain detectors, and their morphology changes from exposure to exposure. Therefore, subtraction with a single fixed template may leave noticeable residuals. We developed a data-driven method that models each wisp as a combination of components learned from the data by non-negative matrix factorization (NMF), which captures the morphological variation of wisps. This method is part of the JADES data reduction pipeline and is released as the <a href="/code/">NMFwisp</a> package.</p> 236 237 </div> 238 <div class="entry-fig"> 239 240 <figure class="align-center"><img src="/assets/fig/wisp_model.gif" alt="wisp" /><figcaption> 241 Wisp removal in JWST/NIRCam: the default STScI pipeline correction compared with the NMF-based method. 242 243 </figcaption></figure> 244 245 </div> 246</div> 247 248<h2 id="probing-wandering-imbhs-with-quasar-microlensing">Probing Wandering IMBHs with Quasar Microlensing</h2> 249 250<div class="entry-row"> 251 <div class="entry-text"> 252 253 <p>Wu & Ho (2025) <a href="https://iopscience.iop.org/article/10.3847/1538-4357/adcec3"><em>The Astrophysical Journal 985, 2</em></a></p> 254 255 <p>Wandering intermediate-mass black holes are essentially invisible on their own, which leaves their population almost unconstrained. We show that microlensing of background quasars offers a way to find them, and that the signal is within reach of the 10-year LSST survey, especially for IMBHs hosting compact star cluster
255s. The lensing magnifies only the emission from scales smaller than the broad-line region, so a lensed quasar should present as a high-Eddington, weak-line source; cosmological peculiar motions then drive slow variability whose amplitude is the same in the ultraviolet, optical, and X-ray. IMBHs embedded in companion clusters produce complex caustic networks and correspondingly distinctive light curves. Each of these signatures is testable against the survey data.</p> 256 257 </div> 258 <div class="entry-fig"> 259 260 <figure class=""><img src="/assets/fig/IMBH.webp" alt="imbh" /><figcaption> 261 Caustic network of a 1000â¯Mâ black hole at <em>z</em>â¯=â¯1, embedded in a stellar cluster of 30 stars pcâ»Â². 262 263 </figcaption></figure> 264 265 </div> 266</div> 267 268<h2 id="origin-of-agn-radio-jets-in-disk-galaxies">Origin of AGN Radio Jets in Disk Galaxies</h2> 269 270<div class="entry-row"> 271 <div class="entry-text"> 272 273 <p>Wu et al. (2022) <a href="https://iopscience.iop.org/article/10.3847/1538-4357/ac9cd5#back-to-top-target"><em>The Astrophysical Journal 941, 95</em></a></p> 274 275 <p>Large-scale radio jets are found almost exclusively in giant elliptical galaxies, and it has long been unclear whether morphology itself is what matters. We studied the rare disk galaxies that do host double radio lobes, drawn from the Gems of the Galaxy Zoos project, and found that the apparent preference for ellipticals is better explained as a mass bias: these radio-loud disks carry stellar masses an order of magnitude above typical disks, comparable to giant ellipticals. That two rare properties â extreme stellar mass and a powerful jet â coincide so consistently suggests jet formation is set by mass, and more fundamentally by black hole mass, rather than by the morphology of the host.</p> 276 277 </div> 278 <div class="entry-fig"> 279 280 <figure class=""><img src="/assets/fig/radio.webp" alt="radio" /><figcaption> 281 HST image of a radio galaxy with clear disk morphology; white contours show VLA synchrotron emission from the jets. 282 283 </figcaption></figure> 284 285 </div> 286</div> 287 288 </section> 289 </article> 290</div> 291 292 293 </div> 294 295 296 297 <div id="footer" class="page__footer"> 298 <footer> 299 <!-- start custom footer snippets --> 300 301<!-- end custom footer snippets --> 302 <!-- <div class="page__footer-follow"> 303 <ul class="social-icons"> 304 305 306 307 308 309 <li><a href="/feed.xml"><i class="fas fa-fw fa-rss-square" aria-hidden="true"></i> Feed</a></li> 310 311 </ul> 312</div> --> 313 314<div class="page__footer-copyright">© 2026 <a href="https://zihaowu-astro.github.io">Zihao Wu</a>. Powered by <a href="https://jekyllrb.com" rel="nofollow">Jekyll</a> & <a href="https://mademistakes.com/work/jekyll-themes/minimal-mistakes/" rel="nofollow">Minimal Mistakes</a>.</div> 315 316 </footer> 317 </div> 318 319 320
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