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Register a new userKeck/Palomar Cosmic Web Imagers (KCWI/PCWI) Reveal an Enormous Ly$alpha$ Nebula in an Extremely Overdense QSO Pair Field at $z=2.45$
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Enormous Ly$alpha$ nebulae (ELANe) represent the extrema of Ly$alpha$ nebulosities. They have detected extents of $>200$ kpc in Ly$alpha$ and Ly$alpha$ luminosities $>10^{44}$ erg s$^{-1}$. The ELAN population is an ideal laboratory to study the interactions between galaxies and the intergalactic/circumgalactic medium (IGM/CGM) given their brightness and sizes. The current sample size of ELANe is still very small, and the few $zapprox2$ ELANe discovered to date are all associated with local overdensities of active galactic nuclei (AGNs). Inspired by these results, we have initiated a survey of ELANe associated with QSO pairs using the Palomar and Keck Cosmic Web Imagers (PCWI/KCWI). In this letter, we present our first result: the discovery of ELAN0101+0201 associated with a QSO pair at $z=2.45$. Our PCWI discovery data shows that, above a 2-$sigma$ surface brightness of $1.2times10^{-17}$ sbunit, the end-to-end size of ELAN0101+0201 is $gtrsim 232$ kpc. We have conducted follow-up observations using KCWI, resolving multiple Ly$alpha$ emitting sources within the rectangular field-of-view of $approx 130times165$ projected kpc$^2$, and obtaining their emission line profiles at high signal-to-noise ratios. Combining both KCWI and PCWI, our observations confirm that ELAN0101+0201 resides in an extremely overdense environment. Our observations further support that a large amount of cool ($Tsim10^4$K) gas could exist in massive halos (M$gtrsim10^{13}$M$_odot$) at $zapprox2$. Future observations on a larger sample of similar systems will provide statistics of how cool gas is distributed in massive overdensities at high-redshift and strongly constrain the evolution of the intracluster medium (ICM).
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We report on the results of deep and wide-field (1.1 deg$^2$) narrow-band observations with Subaru/Hyper Suprime-Cam (HSC) of a field around a hyperluminous QSO (HLQSO), HS1549+1919, residing in a protocluster at $z=2.84$, to map the large-scale structure of Ly$alpha$ emitters (LAEs). One HSC pointing enables us to detect 3490 LAEs and 76 extended Ly$alpha$ blobs (LABs), probing diverse environments from voids to protoclusters. The HLQSO is found to be near the center of the protocluster, which corresponds to the intersection of $sim$100 cMpc-scale structures of LAEs. LABs are basically distributed along the large-scale structure, with larger ones particularly clustered around the HLQSO, confirming a previously noted tendency of LABs to prefer denser environments. Moreover, the shapes of LABs near the HLQSO appear to be aligned with the large-scale structure. Finally, a deep Ly$alpha$ image reveals a diffuse Ly$alpha$ nebula along a filamentary structure with no luminous UV/sub-mm counterpart. We suggest that the diffuse nebula is due to a cold filament with high clumping factor illuminated by the QSO, with a required high clumpiness provided by unresolved residing halos of mass $leq 10^{9-10}M_odot$.
Context. Searching for high-redshift galaxies is a field of intense activity in modern observational cosmology that will continue to grow with future ground-based and sky observatories. Over the last few years, a lot has been learned about the high-z Universe. Aims. Despite extensive Ly-alpha Blobs (LAB) surveys from low to high redshifts, giant LABs over 100 kpc have been found mostly at z~2-4. This redshift range is coincident with the transition epoch of galactic gas-circulation processes from inflows to outflows at z~2.5-3. This suggests that the formation of giant LABs may be related to a combination of gas inflows and outflows. Their extreme youth makes them interesting objects in the study of galaxy formation as they provide insight into some of the youngest known highly star forming galaxies, with only modest time investments using ground-based telescopes. Methods. Systematic narrow-band Ly-alpha nebula surveys are ongoing, but they are limited in their covered redshift range and their comoving volume. This poses a significant problem when searching for such rare sources. To address this problem, we developed a systematic searching tool, ATACAMA (A Tool for seArChing for lArge LyMan Alpha nebulae) designed to find large Ly-alpha nebulae at any redshift within deep multi-wavelength broad-band imaging. Results. We identified a Ly-alpha nebula candidate at zphot~3.3 covering an isophotal area of 29.4sq.arcsec. Its morphology shows a bright core and a faint core which coincides with the morphology of previously known Ly-alpha blobs. A first estimation of the Ly-alpha equivalent width and line flux agree with the values from the study led by several groups.
The standard cosmological model ($Lambda$CDM) predicts the existence of the cosmic web: a distribution of matter into sheets and filaments connecting massive halos. However, observational evidence has been elusive due to the low surface brightness of the filaments. Recent deep MUSE/VLT data and upcoming observations offer a promising avenue for Ly$alpha$ detection, motivating the development of modern theoretical predictions. We use hydrodynamical cosmological simulations run with the AREPO code to investigate the potential detectability of large-scale filaments, excluding contributions from the halos embedded in them. We focus on filaments connecting massive ($M_{200c}sim(1-3)times10^{12} M_odot$) halos at z=3, and compare different simulation resolutions, feedback levels, and mock-image pixel sizes. We find increasing simulation resolution does not substantially improve detectability notwithstanding the intrinsic enhancement of internal filament structure. By contrast, for a MUSE integration of 31 hours, including feedback increases the detectable area by a factor of $simeq$5.5 on average compared with simulations without feedback, implying that even the non-bound components of the filaments have substantial sensitivity to feedback. Degrading the image resolution from the native MUSE scale of (0.2)$^2$ per pixel to (5.3)$^2$ apertures has the strongest effect, increasing the detectable area by a median factor of $simeq$200 and is most effective when the size of the pixel roughly matches the width of the filament. Finally, we find the majority of Ly$alpha$ emission is due to electron impact collisional excitations, as opposed to radiative recombination.
The MAMMOTH-I Nebula at redshift 2.3 is one of the largest known Ly-alpha nebulae in the Universe, spanning ~440 kpc. Enormous Ly-alpha nebulae like MAMMOTH-I typically trace the densest and most active regions of galaxy formation. Using sensitive low-surface-brightness observations of CO(1-0) with the Very Large Array, we trace the cold molecular gas in the inner 150 kpc of the MAMMOTH-I Nebula. CO is found in four regions that are associated with either galaxies or groups of galaxies that lie inside the nebula. In three of the regions, the CO stretches up to ~30 kpc into the circum-galactic medium (CGM). In the centermost region, the CO has a very low velocity dispersion (FWHM$_{rm CO}$ ~ 85 km/s), indicating that this gas is dynamically cold. This dynamically cold gas coincides with diffuse restframe optical light in the CGM around a central group of galaxies, as discovered with the Hubble Space Telescope. We argue that this likely represents cooling of settled and enriched gas in the center of MAMMOTH-I. This implies that the dynamically cold gas in the CGM, rather than the obscured AGN, marks the core of the potential well of this Ly-alpha nebula. In total, the CO in the MAMMOTH-I Nebula traces a molecular gas mass of M$_{rm H2}$ ~ 1.4 ($alpha_{rm CO}$/3.6) $times$ 10$^{11}$ M$_{odot}$, with roughly 50% of the CO(1-0) emission found in the CGM. Our results add to the increasing evidence that extended reservoirs of molecular gas exist in the CGM of massive high-z galaxies and proto-clusters.
We present an IGM HI tomography map in a survey volume of $16 times 19 times 131 h^{-3} {rm comoving Mpc}^{3}$ (cMpc$^3$) centered at MAMMOTH-1 nebula and three neighbouring quasars at $z=2.3$. MAMMOTH-1 nebula is an enormous Ly$alpha$ nebula (ELAN), hosted by a type-II quasar dubbed MAMMOTH1-QSO, that extends over $1 h^{-1}$ cMpc with not fully clear physical origin. Here we investigate the HI-gas distribution around MAMMOTH1-QSO with the ELAN and three neighbouring type-I quasars, making the IGM HI tomography map with a spatial resolution of $2.6 h^{-1}$ cMpc. Our HI tomography map is reconstructed with HI Ly$alpha$ forest absorption of bright background objects at $z=2.4-2.9$: one eBOSS quasar and 16 Keck/LRIS galaxy spectra. We estimate the radial profile of HI flux overdensity for MAMMOTH1-QSO, and find that MAMMOTH1-QSO resides in a volume with significantly weak HI absorption. This suggests that MAMMOTH1-QSO has a proximity zone where quasar illuminates and photo-ionizes the surrounding HI gas and suppresses HI absorption, and that the ELAN is probably a photo-ionized cloud embedded in the cosmic web. The HI radial profile of MAMMOTH1-QSO is very similar to those of three neighbouring type-I quasars at $z=2.3$, which is compatible with the AGN unification model. We compare the distributions of the HI absorption and star-forming galaxies in our survey volume, and identify a spatial offset between density peaks of star-forming galaxies and HI gas. This segregation may suggest anisotropic UV background radiation created by star-forming galaxy density fluctuations.
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