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The systematic targeting of extended Ly$\alpha$ emission around high-redshift quasars resulted in the discovery of rare and bright Enormous Ly$\alpha$ Nebulae (ELANe) associated with multiple active galactic nuclei (AGN). We here initiate "a multiwavelength study of ELAN environments" (AMUSE$^2$) focusing on the ELAN around the $z\sim3$ quasar SDSS J1040+1020, a.k.a. the Fabulous ELAN. We report on VLT/HAWK-I, APEX/LABOCA, JCMT/SCUBA-2, SMA/850$\mu$m, ALMA/CO(5-4) and 2mm observations and compare them to previously published VLT/MUSE data. The continuum and line detections enable a first estimate of the star-formation rates, dust, stellar and molecular gas masses in four objects associated with the ELAN (three AGNs and one Ly$\alpha$ emitter), confirming that the quasar host is the most star-forming (${\rm SFR}\sim500$ M$_\odot$ yr$^{-1}$) and massive galaxy ($M_{\rm star}\sim10^{11}$ M$_{\odot}$) in the system, and thus can be assumed as central. All four embedded objects have similar molecular gas reservoirs ($M_{\rm H_2}\sim10^{10}$ M$_{\odot}$), resulting in short depletion time scales. This fact together with the estimated total dark-matter halo mass, $M_{\rm DM}=(0.8-2)\times10^{13}$ M$_{\odot}$, implies that this ELAN will evolve into a giant elliptical galaxy. Consistently, the constraint on the baryonic mass budget for the whole system indicates that the majority of baryons should reside in a massive warm-hot reservoir (up to $10^{12}$ M$_{\odot}$), needed to complete the baryons count. Additionally, we discuss signatures of gas infall on the compact objects as traced by Ly$\alpha$ radiative transfer effects and the evidence for the alignment between the satellites' spins and their directions to the central., Comment: 26 pages, 19 figures, 4 appendix; submitted to ApJ

Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old

Radio galaxies are ideal sites to scrutinize AGN feedback physics, as they are massive galaxies with jets that interact with the surrounding ISM. I will present a detailed analysis of the recent star formation history and conditions of a starbursting, massive radio galaxy at z = 2.6, PKS 0529-549. In the 8.5-hour VLT/X-Shooter spectrum, we detect unambiguous signatures of stellar photospheric absorption lines originating from OB-stars. Comparison with model spectra shows that more than one burst took place in its recent past: the most recent one at 4 − 7 Myr, and another aged ⩾20 Myr. ALMA observations of the [CI] atomic carbon emission line indicates that it has a low molecular gas fraction (∼13%) and short depletion time (∼40 Myr). Most intriguing is the modest velocity dispersion (⩽50 km/s) of these photospheric lines and the ALMA [CI] cold gas. We attribute its efficient star formation to compressive gas motions, induced by radio jets and/or interaction. Star formation works in concert with the AGN to remove any residual molecular gas and eventually leads to quenching.

A key outstanding issue in galaxy evolution studies is how galaxies quench their star formation. I will present new results from our VLT/X-Shooter, ALMA and VLA campaign of a pilot sample of lensed quiescent massive galaxies at z > 1.5. Lensing magnification enables us to spatially resolve the stellar structure and kinematics of these compact galaxies, that are otherwise barely resolvable even with HST. Our deep X-Shooter spectra provided multiple absorption lines enabling strong constraints on their stellar populations, namely their star formation rates, ages, dispersions, and in some cases metallicities. Our complementary ALMA+VLA programme probes their molecular gas content through CO emission. All these observations provide unparalleled constraints on their quenching mechanisms. Our results indicate that quiescent galaxies at z ∼ 2 (1) have short star formation timescales of a few hundred Myrs; (2) have a variety of stellar morphology from exponential disks to bulges; (3) are devoid of molecular gas; and (4) host low-luminosity active galactic nuclei which may be responsible for suppressing star formation. In addition to discussing the insights gained on quenching, I will highlight how these findings bring about new questions that can be addressed with future JWST and ALMA studies.

The role of galaxy mergers in the evolution of massive galaxies remains debated. While deep near-infrared surveys have enabled several independent merger rate measurements out to z~3, they are limited to small samples and results are discrepant at z=2–3. In Man et al., we use the UltraVISTA and CANDELS surveys to obtain the largest sample of photometric galaxy pairs at z>1 for measuring the galaxy merger fraction and rate of massive galaxies. We find that the discrepancy of previous studies is due to selection effect. Defining galaxy pairs by stellar mass ratio leads to a flat z-evolution of the merger fraction, while defining by flux ratio leads to an increasing trend. The implications on the evolution of massive galaxies are summarized here.

In this work I investigate the redshift evolution of pair fraction of a sample of 196 massive galaxies from z = 0 to 3, selected from the COSMOS field. We find that on average a massive galaxy undergoes ~ 1.1 \pm 0.5 major merger since z = 3. I will review the current limitations of using the pair fraction as a probe for quantifying the impact of mergers on galaxy evolution. This work is based on the paper Man et al. (2011)., 4 pages; to appear on the Conference Proceedings for "Galaxy Mergers in an Evolving Universe", held in Hualien, Taiwan (October 2011)