Browsing by Author "Cai, Zheng"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- ItemDiscovery of an Enormous Lyalpha Nebula in a Massive Galaxy Overdensity at z=2.3(2017) Cai, Zheng; Fan, Xiaohui; Yang, Yujin; Bian, Fuyan; Prochaska, J. Xavier; Zabludoff, Ann; McGreer, Ian; Zheng, Zhen-Ya; Green, Richard; Cantalupo, Sebastiano; Frye, Brenda; Hamden, Erika; Jiang, Linhua; Kashikawa, Nobunari; Wang, RanEnormous Ly alpha nebulae (ELANe), unique tracers of galaxy density peaks, are predicted to lie at the nodes and intersections of cosmic filamentary structures. Previous successful searches for ELANe have focused on wide-field narrowband surveys or have targeted known sources such as ultraluminous quasi-stellar objects (QSOs) or radio galaxies. Utilizing groups of coherently strong Ly alpha absorptions, we have developed a new method to identify high-redshift galaxy overdensities and have identified an extremely massive overdensity, BOSS1441, at z = 2-3. In its density peak, we discover an ELAN that is associated with a relatively faint continuum. To date, this object has the highest diffuse Ly alpha nebular luminosity of L-nebula = 5.1 +/- 0.1 x 10(44) erg s(-1). Above the 2 sigma surface brightness limit of SBLy alpha = 4.8 x 10(-18) erg s(-1) cm(-2) arcsec(-2), this nebula has an end-to-end spatial extent of 442 kpc. This radio-quiet source also has extended C IV lambda 1549 and He II lambda 1640 emission on greater than or similar to 30 kpc scales. Note that the Ly alpha, He II, and C IV emissions all have double-peaked line profiles. Each velocity component has an FWHM of approximate to 700-1000 km s(-1). We argue that this Lya nebula could be powered by shocks due to an active galactic nucleus-driven outflow or photoionization by a strongly obscured source.
- ItemLy alpha EMITTER GALAXIES AT z similar to 2.8 IN THE EXTENDED CHANDRA DEEP FIELD SOUTH. I. TRACING THE LARGE-SCALE STRUCTURE VIA Ly alpha IMAGING(IOP PUBLISHING LTD, 2016) Zheng, Zhen Ya; Malhotra, Sangeeta; Rhoads, James E.; Finkelstein, Steven L.; Wang, Jun Xian; Jiang, Chun Yan; Cai, ZhengWe present a narrowband survey with three adjacent filters for z - 2.8-2.9 Lyman alpha (Ly alpha) emitter (LAE) galaxies in the Extended Chandra Deep Field South (ECDFS), along with spectroscopic follow-up. With a complete sample of 96 LAE candidates in the narrowband NB466, we confirm the large-scale structure at z similar to 2.8 suggested by previous spectroscopic surveys. Compared to the blank field detected with the other two narrowband filters NB470 and NB475, the LAE-density excess in NB466 (900 arcmin(2)) is similar to 6.0 +/- 0.8 times the standard deviation expected at z similar to 2.8, assuming a linear bias of 2. The overdense large-scale structure in NB466 can be decomposed into four protoclusters, whose overdensities (each within an equivalent comoving volume 15(3) Mpc(3)) relative to the blank field (NB470+NB475) are in the range of 4.6-6.6. These four protoclusters are expected to evolve into a Coma-like cluster (M >= 10(15) M-circle dot) at z similar to 0. We also investigate the various properties of LAEs at z = 2.8-2.9 and their dependence on the environment. The average star formation rates derived from the Lya, rest-frame UV, and X-ray bands are similar to 4, 10, and < 16 M-circle dot yr(-1), respectively, implying a Ly alpha escape fraction of 25% less than or similar to f(ESC)(Ly alpha) less than or similar to 40% and a UV continuum escape fraction of f(ESC)(UV,cont) greater than or similar to 62% for LAEs at z similar to 2.8. The Ly alpha photon density calculated from the integrated Ly alpha luminosity function in the overdense field (NB466) is similar to 50% higher than that in the blank field (NB470+NB475), and more bright LAEs are found in the overdense field. The three brightest LAEs, including a quasar at z = 2.81, are all detected in the X-ray band and in NB466. These three LAE-active galactic nuclei contribute an extra 20%-30% Lya photon density compared to other LAE galaxies. Furthermore, we find that LAEs in overdense regions have larger equivalent width values, bluer U-B and V-R (similar to 2-3 sigma) colors compared with those in lower density regions, indicating that LAEs in overdense regions are younger and possible less dusty. We conclude that the structure at z similar to 2.8 in the ECDFS field is a very significant and rare density peak similar to the SSA22 protocluster, and narrowband imaging is an efficient method of detecting and studying such structures in the high-z universe.
- ItemMapping the Most Massive Overdensities through Hydrogen (MAMMOTH). II. Discovery of the Extremely Massive Overdensity BOSS1441 at z=2.32(IOP PUBLISHING LTD, 2017) Cai, Zheng; Fan, Xiaohui; Bian, Fuyan; Zabludoff, Ann; Yang, Yujin; Prochaska, J. Xavier; McGreer, Ian; Zheng, Zhen Ya; Kashikawa, Nobunari; Wang, Ran; Frye, Brenda; Green, Richard; Jiang, LinhuaCosmological simulations suggest a strong correlation between high optical-depth Lya absorbers, which arise from the intergalactic medium, and 3D mass overdensities on scales of 10-30 h(-1) comoving Mpc. By examining the absorption spectra of similar to 80,000 QSO sight lines over a volume of 0.1 Gpc(3) in the Sloan Digital Sky Survey III (SDSS-III), we have identified an extreme overdensity, BOSS1441, which contains a rare group of strong Lya absorbers at z = 2.32 +/- 0.02. This absorber group is associated with six QSOs at the same redshift on a 30 comoving Mpc scale. Using Mayall/MOSAIC narrowband and broadband imaging, we detect Lya emitters (LAEs) down to 0.7 x L-Ly alpha ' * a and reveal a large-scale structure of LAEs in this field. Our follow-up LBT observations have spectroscopically confirmed 20 galaxies in the density peak. We show that BOSS1441 has an LAE overdensity of 10.8 +/- 2.6 on a 15 comoving Mpc scale, which could collapse to a massive cluster with M greater than or similar to 10(15) M-circle dot at z similar to 0. This overdensity is among the most massive large-scale structures at z similar to 2 discovered to date.
- ItemThe Identification of a Dusty Multiarm Spiral Galaxy at z =3.06 with JWST and ALMA(2023) Wu, Yunjing; Cai, Zheng; Sun, Fengwu; Bian, Fuyan; Lin, Xiaojing; Li, Zihao; Li, Mingyu; Bauer, Franz E.; Egami, Eiichi; Fan, Xiaohui; Gonzalez-Lopez, Jorge; Li, Jianan; Wang, Feige; Yang, Jinyi; Zhang, Shiwu; Zou, SiweiSpiral arms serve crucial purposes in star formation and galaxy evolution. In this paper, we report the identification of "A2744-DSG-z3," a dusty, multiarm spiral galaxy at z = 3.059 using the James Webb Space Telescope (JWST) NIRISS imaging and grism spectroscopy. A2744-DSG-z3 was discovered as a gravitationally lensed submillimeter galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). This is the most distant stellar spiral structure seen thus far, consistent with cosmological simulations that suggest z approximate to 3 as the epoch when spirals emerge. Thanks to the gravitational lensing and excellent spatial resolution of JWST, the spiral arms are resolved with a spatial resolution of approximate to 290 pc. Based on spectral energy distribution fitting, the spiral galaxy has a delensed star formation rate of 85 +/- 30 M (circle dot) yr(-1), and a stellar mass of approximate to 10(10.6) M (circle dot), indicating that A2744-DSG-z3 is a main-sequence galaxy. After fitting the spiral arms, we find a stellar effective radius (R (e,star)) of 5.0 +/- 1.5 kpc. Combining with ALMA measurements, we find that the effective radii ratio between dust and stars is approximate to 0.4, similar to those of massive star-forming galaxies (SFGs) at z similar to 2, indicating a compact dusty core in A2744-DSG-z3. Moreover, this galaxy appears to be living in a group environment: including A2744-DSG-z3, at least three galaxies at z = 3.05-3.06 are spectroscopically confirmed by JWST/NIRISS and ALMA, residing within a lensing-corrected projected scale of approximate to 70 kpc. This, along with the asymmetric brightness profile, further suggests that the spiral arms may be triggered by minor-merger events at z greater than or similar to 3.