Galaxy formation and evolution

Abstract:

Hydrocarbons play a key role in shaping the chemistry of the interstellar medium, but their enrichment and relation with carbonaceous grains and polycyclic aromatic hydrocarbons still lack clear observational constraints. Here we report on JWST NIRSpec + MIRI/MRS infrared observations (~3–28 μm) of the local ultra-luminous infrared galaxy (ULIRG) IRAS 07251−0248, which revealed the extragalactic detection of small gas-phase hydrocarbons, such as benzene (C₆H₆), triacetylene (C₆H₂), diacetylene (C₄H₂), acetylene (C₂H₂), methane (CH₄) and methyl radical (CH₃), as well as deep amorphous C–H absorptions in the solid phase. The unexpectedly high abundance of these molecules indicates an extremely rich hydrocarbon chemistry not explained by high-temperature gas-phase chemistry, ice desorption or oxygen depletion. Instead, the most plausible explanation is the erosion and fragmentation of carbonaceous grains and polycyclic aromatic hydrocarbons. This scenario is supported by the correlation between the abundance of one of their main fragmentation products, C₂H₂, and the cosmic-ray ionization rate for a sample of local ULIRGs. These hydrocarbons are outflowing at ~160 km s⁻¹, which may represent a potential formation pathway for hydrogenated amorphous grains. Our results indicate that IRAS 07251−0248 might not be unique but represents an extreme example of the commonly rich hydrocarbon chemistry prevalent in deeply obscured galactic nuclei.

Abstract:

We use the full-disk Very Large Telescope/MUSE mosaic of NGC 253 to identify 2492 H ii regions and study their resolved structure. With an average physical resolution of 17 pc, this is one of the largest samples of highly resolved spectrally mapped extragalactic H ii regions. Regions of all luminosities exhibit a characteristic emission profile described by a double Gaussian with a marginally resolved or unresolved core with radius < 10 pc surrounded by a more extended halo of emission with radius = 20–30 pc. Approximately 80% of the emission of a region originates from the halo component. As a result of this compact structure, the luminosity–radius relations for core and effective radii of H ii regions depend sensitively on the adopted methodology. Only the isophotal radius yields a robust relationship in NGC 253, but this measurement has an ambiguous physical meaning. We invert the measured emission profiles to infer density profiles and find central densities of ne ≈ 10–100 cm−3. In the brightest regions, these agree well with densities inferred from the [S ii] λλ6716, 6730 doublet. The central density of H ii regions correlates well with the surface brightness within the effective radius. We show that this same scaling relation applies to the recent MUSE + Hubble Space Telescope catalog for 19 nearby galaxies. We also discuss potential limitations, including completeness, impacts of background subtraction and spatial resolution, and the generality of our results when applied to other galaxies.

Abstract:

Current spatially resolved kinematic measurements of supermassive black hole (SMBH) masses are largely confined to the local Universe (distances Mpc). We investigate the potential of the Extremely Large Telescope’s (ELT) first-light instruments, MICADO and HARMONI, to extend these dynamical measurements to galaxies at redshift . We select a sample of five bright, massive, quiescent galaxies at these redshifts, adopting their Sérsic profiles, from HST photometry, as their intrinsic surface brightness distributions. Based on these intrinsic models, we generate mock MICADO images using SimCADO and mock HARMONI integral-field spectroscopic data cubes using hsim. The HARMONI simulations utilize input stellar kinematics derived from Jeans Anisotropic Models (JAM). We then process these mock observations: the simulated MICADO images are fitted with Multi-Gaussian Expansion (MGE) to derive stellar mass models, and stellar kinematics are extracted from mock HARMONI cubes with pPXF. Finally, these derived stellar mass models and kinematics are used to constrain JAM dynamical models within a Bayesian framework. Our analysis demonstrates that SMBH masses can be recovered with an accuracy of 10 per cent. We find that MICADO can provide detailed stellar mass models with 1 hour of on-source exposure. HARMONI requires longer minimum integrations for reliable stellar kinematic measurements of SMBHs. The required on-source time scales with apparent brightness, ranging from 5–7.5 hours for galaxies at (F814W, 20–20.5 mag) to 5 hours for galaxies at (F160W, 20.8 mag). These findings highlight the ELT’s capability to push the frontier of SMBH mass measurements to , enabling crucial tests of SMBH-galaxy co-evolution at the top end of the galaxies mass function.