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Abstract:

Distant quasars (QSOs) in galaxy overdensities are considered key actors in the evolution of the early Universe. In this work, we performed an analysis of the kinematic and physical properties of the BR1202-0725 system at z ∼ 4.7, one of the most overdense fields known in the early Universe, consisting of a QSO, a sub-millimetre galaxy (SMG), and three Lyman- α emitters. We used data from the JWST/NIRSpec integral field unit to analyse the rest-frame optical emission of each source in the system. Based on the continuum and Balmer line emission, we estimated a bolometric luminosity of log( L bol /[erg s −1 ]) = 47.2 ± 0.4 and a black hole mass of log( M BH / M ⊙ ) = 10.1 ± 0.5 for the QSO, which are consistent with previous measurements obtained with ground-based observations. The NIRSpec spectra of the SMG revealed, instead, unexpected [O  III ] and H α +[N  II ] profiles. The overall [O  III ] line profile is blueshifted by more than 700 km s −1 relative to the systemic velocity of the galaxy. Additionally, both the [O  III ] and H α +[N  II ] lines show prominent broad (∼1300 km s −1 ), blueshifted wings associated with outflowing ionized gas. The analysis of NIRSpec and X-ray observations indicates that the SMG likely hosts an accreting supermassive black hole, which is supported by the following results: (i) the excitation diagnostic diagram is consistent with ionization from an active galactic nucleus (AGN); (ii) the X-ray luminosity is higher than 10 44 erg s −1 ; and (iii) it hosts a fast outflow ( v out ∼ 5000 km s −1 ), comparable to the ones observed in luminous QSOs. Therefore, the QSO-SMG pair of BR1202-0725 represents one of the highest-redshift double AGNs found to date, with a projected separation of 24 kpc. Finally, we investigated the environment of this system and found four new galaxies, detected in both [O  III ] and H α emission, at the same redshift of the QSO and within a projected distance of 5 kpc from it. This overdense system includes at least ten galaxies in a field of view of only 980 kpc 2 .

Abstract:

Context. CO isotopologues are common tracers of the bulk molecular gas in extragalactic studies, providing insights into the physical and chemical conditions of the cold molecular gas, a reservoir for star formation. Aims. Since star formation occurs within molecular clouds, mapping CO isotopologues on the scale of clouds is important to understanding the processes driving star formation. However, achieving this mapping at such scales is challenging and time-intensive. The Surveying the Whirlpool Galaxy at Arcseconds with NOEMA (SWAN) survey addresses this by using the Institut de radioastronomie millimétrique (IRAM) NOrthern Extended Millimeter Array (NOEMA) to map the 13 CO(1−0) and C 18 O(1−0) isotopologues, alongside several dense gas tracers, in the nearby star-forming galaxy M51 at high sensitivity and spatial resolution (≈125 pc). Methods. We examine the 13 CO(1−0) to C 18 O(1−0) line emission ratio as a function of galactocentric radius and star formation rate surface density to infer how different chemical and physical processes affect this ratio at cloud scales across different galactic environments: nuclear bar, molecular ring, and northern and southern spiral arms. Results. In line with previous studies conducted at kiloparsec scales for nearby star-forming galaxies, we find a moderate positive correlation with galactocentric radius and a moderate negative correlation with star formation rate surface density across the field of view (FoV), with slight variations depending on the galactic environment. Conclusions. We propose that selective nucleosynthesis and changes in the opacity of the gas are the primary drivers of the observed variations in the ratio.

Abstract:

Tracing dense molecular gas, the fuel for star formation, is essential for understanding the evolution of molecular clouds and star-formation processes. We compared the emission of HCN (1–0), HNC (1–0), and HCO + (1–0) with the emission of N 2 H + (1–0) at cloud scales (125 pc) across the central 5 × 7 kpc of the Whirlpool galaxy, M51a, from “Surveying the Whirlpool galaxy at Arcseconds with NOEMA” (SWAN). We find that the integrated intensities of HCN, HNC, and HCO + are more steeply correlated with N 2 H + emission compared to the bulk molecular gas tracer CO, and we find variations in this relation across the center, molecular ring, northern, and southern disk of M51. Compared to HCN and HNC emission, the HCO + emission follows the N 2 H + emission more closely across the environments and physical conditions, such as the surface densities of molecular gas, stellar mass, star-formation rate, dynamical equilibrium pressure, and radius. Under the assumption that N 2 H + is a fair tracer of dense gas at these scales, this makes HCO + a more favorable dense gas tracer than HCN within the inner disk of M51. In all environments within our field of view, even when the central 2 kpc are removed, the ratio HCN/CO, which is commonly used to trace average cloud density, is only weakly dependent on molecular gas mass surface density. While ratios of other dense gas lines to CO show a steeper dependence on the surface density of molecular gas, this relation is still shallow in comparison to other nearby star-forming disk galaxies. One reason might be physical conditions in M51, which are different from other normal star-forming galaxies. Increased ionization rates, increased dynamical equilibrium pressure in the central few kiloparsecs, and the impact of the dwarf companion galaxy NGC 5195 are proposed mechanisms that might enhance HCN and HNC emission over HCO + and N 2 H + emission at larger-scale environments and cloud scales.

Abstract:

Stars in galactic centres are occasionally scattered so close to the central supermassive black hole that they are completely disrupted by tidal forces, initiating a transient accretion event. The aftermath of such a tidal disruption event (TDE) produces a bright-and-blue accretion flow that is known to persist for at least a decade (observationally) and can in principle produce ionizing radiation for hundreds of years. TDEs are known (observationally) to be overrepresented in galaxies that show extended emission-line regions (EELRs), with no pre-TDE classical active galactic nucleus activity, and to produce transient ‘coronal lines’, such as [Fe x] and [Fe xiv]. Using coupled cloudy-TDE disc simulations we show that TDE discs produce a sufficient ionizing radiation flux over their lifetimes to power both EELR of radial extents of light years, and coronal lines. EELRs are produced when the ionizing radiation interacts with low-density () clouds on galactic scales, while coronal lines are produced by high-density () clouds near the galactic centre. High-density gas in galactic centres will also result in the rapid switching on of narrow-line features in post-TDE galaxies, and also various high-ionization lines, which may be observed throughout the infrared with James Webb Space Telescope. Galaxies with a higher intrinsic rate of TDEs will be more likely to show macroscopic EELRs, which can be traced to originate from the previous TDE in that galaxy.