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Enormous Ly$alpha$ nebulae, extending over 300-500,kpc around quasars, represent the pinnacle of galaxy and cluster formation. Here we present IRAM Plateau de Bure Interferometer observations of the enormous Ly$alpha$ nebulae `Slug ($z$=$2.282$) and `Jackpot ($z$=$2.041$). Our data reveal bright, synchrotron emission associated with the two radio-loud AGN embedded in the targeted nebulae, as well as molecular gas, as traced via the CO(3-2) line, in three galaxies (two sources in the Slug, and one in the Jackpot). All of the CO emission is associated with galaxies detected in their rest-frame UV stellar emission. The total mass in molecular gas of these three galaxies [$sim (3-5)times10^{10}$ M$_odot$] is comparable with the total ionized gas mass responsible for the diffuse nebular emission. Our observations place limits on the molecular gas emission in the nebulae: The molecular gas surface density is $Sigma_{rm H2}<12-25$ M$_odot$ pc$^{-2}$ for the Slug nebula and $Sigma_{rm H2}<34-68$ M$_odot$ pc$^{-2}$ for the Jackpot nebula. These are consistent with the expected molecular gas surface densities, as predicted via photoionization models of the rest-frame UV line emission in the nebulae, and via Ly$alpha$ absorption in the Jackpot nebula. Compared to other radio--loud quasars at $z>1$, and high-redshift radio--loud galaxies, we do not find any strong trends relating the molecular gas reservoirs, the radio power, and the Ly$alpha$ luminosities of these systems. The significant step in sensitivity required to achieve a detection of the molecular gas from the nebulae, if present, will require a substantial time investment with JVLA, NOEMA, or ALMA.
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Star-forming galaxies (SFGs) with stellar masses below $10^{10},M_odot$ make up the bulk of the galaxy population at $z>2$. The properties of the cold gas in these galaxies can only be probed in very deep ALMA observations or by targeting strongly lensed galaxies. Here we report the results of a pilot survey using the Atacama Compact Array (ACA) of molecular gas in the most strongly magnified galaxies selected as giant arcs in optical data. The selection in rest-frame UV wavelengths ensures that sources are regular star forming galaxies, without a priori indications of intense dusty starburst activity. We conducted Band 4 and Band 7 observations to detect mid-$J$ CO, [C I] and thermal continuum as molecular gas tracers from four strongly lensed systems at $zapprox2-3$: our targets are SGAS J1226651.3+215220 (A and B), SGAS J003341.5+024217 and the Sunburst Arc. The measured molecular mass is then projected onto the source plane with detailed lens models developed from high resolution HST observations. Multiwavelength photometry is then used to obtain the intrinsic stellar mass and star formation rate via SED fitting. In only one of the sources are the three tracers robustly detected, while in the others they are either undetected or detected in continuum only. The implied molecular gass masses range from $4times 10^{9},M_odot$ in the detected source to an upper limit of $lesssim 10^9,M_odot$ in the most magnified source. The inferred gas fraction and gas depletion timescale are found to lie approximately 0.5 to 1.0 dex below the established scaling relations based on previous studies of unlensed massive galaxies. Our results indicate that the cold gas content of intermediate to low mass galaxies should not be extrapolated from the trends seen in more massive high-$z$ galaxies. (Abridged abstract)
We present first results from Multi Unit Spectroscopic Explorer (MUSE) observations at the Very Large Telescope in the MUSE Ultra Deep Field (MUDF), a $approx 1.2times 1.4$ arcmin$^2$ region for which we are collecting $approx$200 hours of integral field spectroscopy. The $approx 40$-hour observation completed to date reveals the presence of a group of three Ly$alpha$ nebulae associated with a bright quasar pair at $zsimeq3.23$ with projected separation of $approx 500rm~kpc$. Two of the nebulae are physically associated with the quasars which are likely powering the Ly$alpha$ emission, and extend for $gtrsim 100~rm kpc$ at a surface brightness level of $approx 6times 10^{-19}~rm erg~s^{-1}~cm^{-2}~arcsec^{-2}$. A third smaller ($approx$35 kpc) nebula lies at a velocity offset of $approx 1550$ km s$^{-1}$. Despite their clustered nature, the two large nebulae have properties similar to those observed in isolated quasars and exhibit no sharp decline in flux at the current depth, suggesting an even more extended distribution of gas around the quasars. We interpret the shape and the alignment of the two brighter nebulae as suggestive of the presence of an extended structure connecting the two quasar host galaxies, as seen for massive galaxies forming within gas-rich filaments in cosmological simulations.
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 report on the discovery of extended Ly-alpha nebulae at z~3.3 in the Hubble Ultra Deep Field (HUDF, ~ 40 kpc X 80 kpc) and behind the Hubble Frontier Fields galaxy cluster MACSJ0416 (~ 40kpc), spatially associated with groups of star-forming galaxies. VLT/MUSE integral field spectroscopy reveals a complex structure with a spatially-varying double peaked Ly-alpha emission. Overall, the spectral profiles of the two Ly-alpha nebulae are remarkably similar, both showing a prominent blue emission, more intense and slightly broader than the red peak. From the first nebula, located in the HUDF, no X-ray emission has been detected, disfavoring the possible presence of AGNs. Spectroscopic redshifts have been derived for 11 galaxies within two arcsec from the nebula and spanning the redshift range 1.037<z<5.97. The second nebula, behind MACSJ0416, shows three aligned star-forming galaxies plausibly associated to the emitting gas. In both systems, the associated galaxies reveal possible intense rest-frame-optical nebular emissions lines [OIII]4959-5007+Hbeta with equivalent widths as high as 1500A rest-frame and star formation rates ranging from a few to tens of solar masses per year. A possible scenario is that of a group of young, star-forming galaxies sources of escaping ionising radiation that induce Ly-alpha fluorescence, therefore revealing the kinematics of the surrounding gas. Also Ly-alpha powered by star-formation and/or cooling radiation may resemble the double peaked spectral properties and the morphology observed here. If the intense blue emission is associated with inflowing gas, then we may be witnessing an early phase of galaxy or a proto-cluster (or group) formation.
We investigate the potential for the emission lines OV] $lambdalambda$1213.8,1218.3 and HeII $lambda$1215.1 to contaminate flux measurements of Ly$alpha$ $lambda$1215.7 in the extended nebulae of quasars. We have computed a grid of photoionization models with a substantial range in the slope of the ionizing powerlaw (-1.5 $<$ $alpha$ $<$ -0.5), gas metallicity (0.01 $<$ $Z/Z_{odot}$ $<$ 3.0), gas density (1 $<$ $n_H$ $<$ 10$^4$ cm$^{-3}$), and ionization parameter (10$^{-5}$ $<$ U $<$ 1.0). We find the contribution from HeII $lambda$1215.1 to be negligible, i.e., $<$ 0.1 of Ly$alpha$ flux, across our entire model grid. The contribution from OV] $lambdalambda$1213.8,1218.3 is generally negligible when U is low (<10$^{-3}$) and/or when the gas metallicity is low ($Z/Z_{odot}$ < 0.1). However, at higher values of U and Z we find that OV] can significantly contaminate Ly$alpha$, in some circumstances accounting for more than half the total flux of the Ly$alpha$+HeII+OV] blend. We also provide means to estimate the fluxes of OV] $lambdalambda$1213.8,1218.3 and HeII $lambda$1215.1 by extrapolating from other lines. We estimate the fluxes of OV] and HeII for a sample of 107 Type 2 active galaxies at z$>$2, and find evidence for significant (>10%) contamination of Ly$alpha$ fluxes in the majority of cases (84%). We also discuss prospects for using OV] $lambdalambda$1213.8,1218.3 as a diagnostic for the presence of AGN activity in high-z Ly$alpha$ emitters, and caution that the presence of significant OV] emission could impact the apparent kinematics of Ly$alpha$, potentially mimicking the presence of high-velocity gas outflows.
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