Miguel Querejeta

Galactic bars are thought to play a critical role in the secular evolution of their hosts by, for example, reorganising the interstellar medium (ISM). We used a sample of 57 star-forming disc galaxies observed with JWST at 3 and 7.7 µm to probe how the spatial distribution of polycyclic aromatic hydrocarbon (PAH) emission as a structural marker of the cold ISM might depend on galaxy stellar mass and the presence of a bar. We find evidence for a ’watershed’ at a stellar mass of 10 ¹⁰ M _⊙ , marking a fundamental transition in the bar-driven distribution of PAH emission. This confirms trends previously predicted by numerical simulations and observed via ionised gas or UV light. While lower-mass galaxies exhibit a disordered and clumpy distribution of PAH emission regardless of bar presence, higher-mass barred hosts display well-structured dynamical features traced by PAH emission with significant gas reservoirs (e.g., discs and rings) within the central 15% of the bar radius (R _b ). Furthermore, we observed a systematic depletion of PAH emission within the [0.2–0.8] R _b range in barred systems with stellar masses above 10 ¹⁰ M _⊙ . Such central discs, rings, and associated radial dips (‘bar deserts’) appear to be a mass-dependent phenomenon as they are ubiquitous in massive galaxies but mostly absent in their lower-mass counterparts. In contrast to the structured features in massive hosts, the disorganised ISM in lower-mass galaxies masks the commonly observed bar-driven signatures. This suggests that tracer selection and dust obscuration may significantly bias observed bar fractions. Our study underlines the existence of two regimes of secular evolution, with different impacts and observability of bar-driven processes, and it reaffirms the role of bars as the primary drivers of rapid secular evolution in galaxies above 10 ¹⁰ M _⊙ , while the impact of bars is significantly reduced or delayed below this threshold. Our results further underscore the need to critically account for these processes when modelling galaxy evolution in cosmological simulations.

Multiple mechanisms are proposed for the formation of giant molecular clouds (GMCs) – from gravitational free-fall caused by self-gravity, to stellar feedback-driven gas compression. Both the galactic environment and galaxy conditions could play an additional role in enhancing the formation via their gas surface density and star formation activity. In this paper, we make use of a catalog of 108 466 GMCs identified by F770W PHANGS-JWST imaging across 66 galaxies at a homogenized resolution of 30 pc. We measure the mass spectra in various galactic regions, whose power-law slopes vary from −1.2 to −2.0. We then estimate the formation time of each cloud using a model in which GMCs form by multiple feedback compression, and find that clouds with masses ≤10 ⁵ M _⊙ form in 20 Myr on average, and more massive clouds (∼10 ^6 − 7 M _⊙ ) take up to 100 Myr. We also find that cloud formation proceeds most rapidly in the central regions of galaxies, with formation timescales that are typically shorter by ∼5 − 10 Myr compared to galactic disks. This effect is most pronounced in central molecular zones with enhanced star formation. This highlights the role of intense massive star formation, high molecular gas surface densities, and strong supersonic compressions in accelerating cloud formation. However, star formation is generally inefficient as the cloud lifetime is ∼1% of the molecular depletion time. The formation time of clouds is ∼0.1 dex longer than the free-fall time. This hints that magnetic fields, stellar feedback, or other mechanisms may prolong their formation instead of immediate free-fall collapse. This indicates a longevity of massive GMCs. The GMC ages also show only limited variation with galactocentric radius in both spiral and disk galaxies, suggesting that cloud formation proceeds similarly in these galaxy types.

Context. Molecular clouds form stars from the interstellar medium via gravitational collapse, following a sequence from low-density gas to high-density cores and eventually the formation of stars. In classical density wave theory, gas clouds orbiting the galaxy experience gas compression and triggered star formation, while encountering the gravitational well of spiral arms. Aims. We aim to trace these different phases of the molecular cloud life cycle via tracers of molecular gas (CO), dense molecular gas (HCN), and star formation (H α , 24 μm) within the spiral arms of two grand-design spiral galaxies: NGC 4321 and M51 (NGC 5194). Methods. In the spiral arms of these galaxies, we investigate the relation between molecular gas, dense gas, and star formation (CO-HCN-SFR) at matched physical resolutions of 270 pc and 125 pc in NGC 4321 and M51, respectively. We employed spiral arm masks for these galaxies and investigate trends of HCN/CO and SFR/HCN (SFR/CO), which serve as proxies for the dense gas fraction and dense (molecular) gas star formation efficiency, perpendicular to the spiral arm spines. Results. We find that HCN/CO, SFR/CO, and SFR/HCN increase from the upstream towards the downstream side of both spiral arms of NGC 4321, while their trends are less prominent in M51. Conclusions. Our results indicate that large-scale galactic dynamics (e.g. density waves) can induce a sequence of gas density and star formation-to-gas density variations perpendicular to the spiral arms. This sequence contributes to the increased scatter seen among spectroscopic ratios such as HCN/CO and SFR/HCN at sub-kiloparsec scales.

Context. Active Galactic Nuclei (AGN) are intertwined with galaxy evolution, injecting energy into the interstellar medium (ISM) and possibly regulating star formation as a galaxy evolves. However, the phenomena through which we observe AGN are multiphase and multiscale, which can lead to conflicting results for how significantly and to what extent AGN influence the ISM. Aims. M51 is a perfect case study of the boundary between where AGN feedback and star formation feedback dominate the ISM, hosting a low-luminosity type II Seyfert nucleus with a well-defined molecular and ionized outflow. We endeavor to characterize the spatial extent and dominant modes of AGN feedback in M51 utilizing multiple phases of the ISM. Methods. Using integral field spectroscopy observations from VENGA of the central 3 kpc, we identified regions dominated by AGN ionization using an emission line ratio (ELR) function. We then combined this information with new observations of the dense molecular ISM in M51 from SWAN, including cloud-scale mapping of HCN(1–0), HNC(1–0), HCO ⁺ (1–0), and N ₂ H ⁺ (1–0). Both datasets allowed us to achieve ∼180 pc resolution, allowing for a clear demarcation of where AGN feedback dominates the ISM. We then tested how the ELR compares to other tracers of AGN activity, using both millimeter emission line ratios as well as X-ray observations from Chandra to assess the dominant mode of feedback. Results. If we assume that N ₂ H ⁺ (1–0) is the best tracer of dense, cold gas in SWAN, then AGN-dominated regions defined by the ELR all have greater emission in (1–0) transitions in HCN, HNC, and HCO ⁺ than would be expected if they traced dense gas alone, implying excitation of these lines from AGN feedback. The ELR is better at selecting these regions compared to molecular tracers of AGN activity, such as HCN(1–0)/HCO ⁺ (1–0), which are heightened for a greater extent in M51. Some of the highest ELR values are also associated with fast shocks evident in the optical, which are concurrent with large HNCO(4–3)/CO(1–0) values that point to slow shocks near the nucleus. The presence of shocks and heightened N ₂ H ⁺ (1–0) near the nucleus indicate a potential dense molecular outflow, meaning heightened dense tracer emission could be partly due to larger abundance rather than excitation alone in this limited region. Conclusions. All tracers of AGN activity point to a “two-stage” feedback scenario, whereby mechanical feedback from the jet-ISM interaction spurs soft X-ray emission that excites molecules such as HCN. Dense gas entrenched in a molecular outflow may also lead to a greater chemical abundance of multiple tracers measured with SWAN, but to a lesser extent than excitation from AGN feedback.

We present a multiwavelength catalog of mid-infrared-selected compact sources in 19 nearby galaxies, combining JWST NIRCam/MIRI, Hubble Space Telescope UV–optical broadband, H α narrowband, and Atacama Large Millimeter/submillimeter Array CO observations. We detect 24,945 compact sources at 21 μ m and 55,581 at 10 μ m. Artificial star tests show 50% completeness limits of ∼5 μ Jy for the 10 μ m catalog, and ∼24 μ Jy for the 21 μ m catalog. We find that 21 μ m compact sources contribute ∼20% of the total galaxy emission in that band, but only contribute 5% at 10 μ m. We classify sources using stellar evolution and population synthesis models combined with empirical classifications derived from the literature. Our classifications include H α -bright and dust-embedded optically faint clusters, red supergiants, oxygen-rich and carbon-rich asymptotic giant branch stars, and a range of rarer stellar types. In sampling a broad range of star-forming environments with a uniform, well-characterized selection, this catalog enables analyses of infrared-bright stellar populations. We find that H α -faint sources account for only 10% of dusty (likely young) clusters, implying that the infrared-bright, optically faint phase of cluster evolution is short compared to the H α -bright stage. The luminosity functions of 10 and 21 μ m sources follow power-law distributions, with the 21 μ m slope (−1.7 ± 0.1) similar to that of giant molecular cloud mass functions and ultraviolet bright star-forming complexes, while the 10 μ m slope (−2.0 ± 0.1) is closer to that of young stellar clusters.

Polycyclic aromatic hydrocarbon (PAH) emission is widely used to trace the distribution of molecular gas in the interstellar medium, exhibiting a tight correlation with CO(2–1) emission across nearby galaxies. Using PHANGS-JWST and PHANGS-Atacama Large Millimeter/submillimeter Array (ALMA) data, we identify localized regions where this correlation fails, with CO flux exceeding that predicted from 7.7 μ m PAH emission by more than an order of magnitude. These outlier regions are found in 20 out of 70 galaxies and are located in galaxy centers and bars, without signs of massive star formation. We explore two scenarios to explain the elevated CO-to-PAH ratios, which can either be due to suppressed PAH emission or enhanced CO emissivity. We examine PAH emission in other bands (3.3 and 11.3 μ m) and the dust-continuum-dominated bands (10 and 21 μ m), finding consistently high CO-to-PAH (or CO-to-dust continuum) emission ratios, suggesting that 7.7 μ m PAH emission is not particularly suppressed. In some outlier regions, PAH sizes and spectral energy distribution of the radiation differ slightly from nearby control regions with normal CO-to-PAH ratios, though without a consistent trend. We find that the outlier regions show higher CO velocity dispersions (Δ v _CO ). This increase in Δ v _CO lowers CO optical depth and raises its emissivity for a given gas mass. Our results favor a scenario where shear along the bar lanes and shocks at the bar ends elevate CO emissivity, leading to the breakdown of the CO–PAH correlation. Future JWST spectroscopy and deep ALMA observations of CO isotopologues will provide critical tests of this scenario.

Nuclear star clusters (NSC) are dense and compact stellar systems with sizes of a few parsecs located at galactic centers. Their properties and formation mechanisms seem to be tightly linked to the evolution of the host galaxy, with potentially different formation channels for late- and early-type galaxies (LTGs and ETGs). While most observations target ETGs, here we focus on the NSC in M 74 (NGC 628), a relatively massive and gas-rich star-forming spiral galaxy included in the PHANGS survey. We analyzed the central arc minute of the PHANGS-MUSE mosaic, in which the NSC is not spatially resolved. We analyzed the NSC stellar populations in a point spread function (PSF) aperture and compared it to the host galaxy. Within the PSF size, the NSC is contaminated by the host galaxy light. We performed a two-dimensional spectro-photometric decomposition of the MUSE cube, employing a modified version of the C2D code, to disentangle the NSC from its host. This method provided different data cubes for the NSC and the host galaxy, allowing for their comparison in a PSF aperture, as well as a spatially resolved analysis of the host. Our results show a very old and metal-poor NSC, in contrast to the surrounding regions. While similar properties have been found in NSCs hosted by galaxies of different masses and/or morphological types from M 74, they are somewhat unexpected for a relatively massive star-forming spiral galaxy. The spatially resolved stellar populations of the host galaxy display much younger (light-weighted) ages and higher metallicities, especially in the central region (∼500 pc) surrounding the NSC. This suggests that this NSC formed a long time ago and evolved passively until today without any further growth. No significant amounts of gas would have reached the very central region in the past 8 Gyr.

Context. Nearby galaxies exhibit a variety of structures, including so-called central or (circum-)nuclear rings that are similar to the Milky Way (MW) Central Molecular Zone (CMZ). These rings are common in barred galaxies and can be gas-rich and highly star-forming. Aims. We aim to study the molecular gas content and star formation rate of central rings within nearby galaxies and link them to global galaxy properties, especially the bar morphology. Methods. We utilized 1″(≲100 pc) resolution CO(2–1) observations from the PHANGS-ALMA survey, visually identifying 20 central rings and determine their properties. For 14 of these rings, MUSE observations tracing star formation rate (SFR) surface density were available. We derived the rings’ geometry, integrated molecular gas masses, SFRs, depletion times, and compared them to host galaxy and bar properties from the literature. Results. Molecular gas is an effective tracer for central rings. Previous studies have used ionized gas and dust tracers to identify central rings in galaxies of similar morphological types as the PHANGS galaxies (numerical Hubble type T ∼ −3 to T ∼ 9). In comparison, molecular gas yields similar fractions of galaxies hosting central rings and similar radii distributions. The gaseous central rings have typical radii of ∼ 400 ⁺²⁵⁰ ₋₁₅₀ pc, molecular gas masses of log( M / M _⊙ ) ∼ 8.1 ^+0.17 _−0.23 , and SFRs of ∼ 0.21 ^+0.15 _−0.16 M _⊙ /yr. As a result, they contribute 5.6 ^+4.5 _−2.1 % and 13 ⁺¹⁰ ₋₅ % to their host galaxies’ molecular gas mass and SFR, respectively. While the MW CMZ sits at the lower end of the radius, molecular gas mass, and SFR distribution, it matches well in terms of ring molecular gas mass and SFR fraction, and depletion time. Longer bars contain more massive molecular central rings, but there is no correlation between the classical bar strength parameters ( Q _b , ε _bar , A ₂ ^max ) and the ring’s molecular gas content. Conclusions. Although absolute central ring properties (ring radius, molecular gas mass, SFR) likely depend on host galaxy properties, the similarities between the MW CMZ and PHANGS central rings in relative parameters (molecular gas and SFR fraction, depletion time) suggest that the processes of gas inflow and star formation are similar for central rings across nearby galaxies.

This paper presents the first catalog of celestial and terrestrial globes, as well as armillary spheres and orreries, produced before 1900 and preserved in Spanish public institutions. Most globes have an English or French origin, predominantly from the late 18th or 19th centuries. We highlight a few outstanding examples, including an early metallic terrestrial globe, a mysterious blue celestial manuscript globe, the oldest preserved Spanish printed globe, and some interesting clockwork pieces. While Spain has not been a major producer of globes, it does preserve around 200 historical globes in public collections, including several remarkable pieces.