RESUMO
Galaxy mergers produce pairs of supermassive black holes (SMBHs), which may be witnessed as dual quasars if both SMBHs are rapidly accreting. The kiloparsec (kpc)-scale separation represents a physical regime sufficiently close for merger-induced effects to be important1 yet wide enough to be directly resolvable with the facilities currently available. Whereas many kpc-scale, dual active galactic nuclei-the low-luminosity counterparts of quasars-have been observed in low-redshift mergers2, no unambiguous dual quasar is known at cosmic noon (z ≈ 2), the peak of global star formation and quasar activity3,4. Here we report multiwavelength observations of Sloan Digital Sky Survey (SDSS) J0749 + 2255 as a kpc-scale, dual-quasar system hosted by a galaxy merger at cosmic noon (z = 2.17). We discover extended host galaxies associated with the much brighter compact quasar nuclei (separated by 0.46â³ or 3.8 kpc) and low-surface-brightness tidal features as evidence for galactic interactions. Unlike its low-redshift and low-luminosity counterparts, SDSS J0749 + 2255 is hosted by massive compact disk-dominated galaxies. The apparent lack of stellar bulges and the fact that SDSS J0749 + 2255 already follows the local SMBH mass-host stellar mass relation, suggest that at least some SMBHs may have formed before their host stellar bulges. While still at kpc-scale separations where the host-galaxy gravitational potential dominates, the two SMBHs may evolve into a gravitationally bound binary system in around 0.22 Gyr.
RESUMO
Ultraluminous infrared galaxies are among the most luminous objects in the local Universe and are thought to be powered by intense star formation. It has been shown that in these objects the rotational spectral lines of molecular hydrogen observed at mid-infrared wavelengths are not affected by dust obscuration, but left unresolved was the source of excitation for this emission. Here I report an analysis of archival Spitzer Space Telescope data on ultraluminous infrared galaxies and demonstrate that dust obscuration affects star formation indicators but not molecular hydrogen. I thereby establish that the emission of H(2) is not co-spatial with the buried starburst activity and originates outside the obscured regions. This is unexpected in light of the standard view that H(2) emission is directly associated with star-formation activity. I propose the alternative view that H(2) emission in these objects traces shocks in the surrounding material that are excited by interactions with nearby galaxies. Large-scale shocks cooling by means of H(2) emission may accordingly be more common than previously thought. In the early Universe, a boost in H(2) emission by this process may have accelerated the cooling of matter as it collapsed to form the first stars and galaxies, and would make these first structures more readily observable.
RESUMO
Quasar-driven outflows on galactic scales are a routinely invoked ingredient for galaxy formation models. We report the discovery of ionized gas nebulae surrounding three luminous red quasars at z ~ 0.4 from Gemini integral field unit observations. All these nebulae feature unprecedented pairs of "superbubbles" extending ~20 kpc in diameter, and the line-of-sight velocity difference between the red- and blueshifted bubbles reaches up to ~1200 km/s. Their spectacular dual-bubble morphology (in analogy to the galactic "Fermi bubbles") and their kinematics provide unambiguous evidence for galaxy-wide quasar-driven outflows, in parallel with the quasi-spherical outflows similar in size from luminous type 1 and type 2 quasars at concordant redshift. These bubble pairs manifest themselves as a signpost of the short-lived superbubble "break-out" phase, when the quasar wind drives the bubbles to escape the confinement from the dense environment and plunge into the galactic halo with a high-velocity expansion.