Jonathan Braine

We used narrow-band Hα+ ∋i imaging data gathered during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) survey, a blind survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope, to identify $ erg s$^ regions in 385 galaxies showing ionised gas emission. After excluding objects where the emission is not associated with star formation and edge-on systems, we identified 76,645 regions in 322 star-forming galaxies and studied their physical properties for those above the completeness limit of the survey (L(Hα) ≥ 10 37 -1 , 34,358 regions). The present work is focused on perturbed cluster galaxies, identified as those having a reduced amount of atomic hydrogen when compared to similar objects in the field. We derived composite luminosity functions, diameter and electron density distributions, and several scaling relations, and we compare them to those already derived for unperturbed gas-rich systems identified during the VESTIGE survey. Our analysis shows that the statistical and physical properties of gas-deficient cluster galaxies are different from those of unperturbed systems, with perturbed objects having a steeper faint-end slope and a brighter characteristic Hα luminosity than gas-rich galaxies. The difference in the two distributions comes principally from the outer disc (outside the effective radius). Perturbed and unperturbed systems share a similar size distribution, while gas-poor objects host higher electron density regions than systems. The analysis of the scaling relations indicates that perturbed objects have, on average, a lower number of regions per unit stellar mass and disc surface than unperturbed systems, with differences increasing with the parameter, principally in the outer disc where regions are less present in gas-poor systems. This systematic difference is also observed in the Hα luminosity of the first ranked and first three ranked regions, which is reduced in systems with respect to gas-rich objects. All of these differences can be explained in the framework of galaxy evolution in rich environments, where their hydrodynamic interaction with the surrounding intracluster medium (ram pressure) removes the gas from the outside in, quenching the star formation activity in the outer disc once the atomic hydrogen is removed.

We characterize kinematic processes in the G012.80 protocluster. We primarily focused on the N_2H+$(1-0) emission to trace the dense and cold gas. Additionally, we used complementary lines such as DCN(3-2), H41α, C^18O(2-1), and SiO(5-4), as well as continuum maps. We performed a N_2H^+ hyperfine spectral line fitting to analyze multiple velocity components and extract spectral parameters. We estimated velocity gradients, column densities, and line-mass profiles for the two main filaments in G012, which we named R1 and R2. The line-mass profiles follow łambda(ω),=,5660,M_⊙,pc^-1(ω/pc)^0.30 for R1 and łambda(ω),=,6943,M_⊙,pc^-1(ω/pc)^0.20 for R2. This is much larger than profiles of typical low-mass filaments. R1 and R2 show disparate position-velocity (PV) features. R1 exhibits a transverse velocity gradient of 10.4,km,s^-1,pc^-1 and a few dense cores. This velocity gradient is interpreted with a simple rotation toy model when combined with the line-mass profile, and it corresponds to a rotational timescale of ∼,0.1,Myr. In contrast, R2 exhibits compact velocity structures (ΔV < 2,km,s^-1), likely due to collapse, as evidenced by the comparatively large number of massive cores and protostellar outflows. R2 is forming prestellar and protostellar cores at a rate of ∼ 55.3,M_⊙,Myr^-1, with an efficiency similar to the Orion integral shaped filament (ISF). The R1 filament, in contrast, lacks protostellar cores and only contains a few prestellar cores, resulting in an estimated star formation rate of ∼ -1 , which is lower by more than an order of magnitude than that of R2. Combining gas kinematics, core incidence, and the line-mass profiles, we suggest that R1 is younger and still rotates, while R2 has evolved to collapse with a higher star formation rate. G012 thus hosts filaments at different evolutionary stages.

In this work, we investigate whether dwarf galaxies differ from spirals and whether star formation produces radio and far-infrared (FIR) emission in the same way as it does for spiral galaxies. Radio, FIR, and CO emission depend on gas density, temperature, magnetic field strength, and metallicity. The radio-FIR correlation and Schmidt-Kennicutt relation characterize the links for Milky Way-like galaxies. However, in this work, we want to investigate whether they also hold for smaller objects with different morphologies. Here, we extend our previous work on the IR, line, and radio emission of local and high- z galaxies to local star-forming low-mass and dwarf galaxies. The calculation of the cosmic ray (CR) densities were improved compared to the previous version of the model. The CR ionization rate we found for the different galaxy samples is higher by a factor of 3 than the rate determined for the solar neighborhood. This means that the mean yield of low-energy CR particles is three times higher in external galaxies than what was observed by Voyager I. The dependence of the N (H ₂ )/ I _CO factor on the metallicity and stellar mass are calculated by the model. The weaker CO emission from low-metallicity galaxies is due to the large amount of (CO-dark) H ₂ surrounding the regions where CO is not photodissociated. Within our model framework, star-forming low-mass and dwarf galaxies follow the radio-IR correlation.

Large high-quality samples of H II regions and their parent giant molecular clouds (GMCs) are now available for local galaxies. It is therefore possible to investigate the links between the CO and H α luminosity functions and whether massive stars form in GMCs of all masses. The CO luminosity functions, representing the distribution of GMC masses, are consistently steeper than the H α luminosity functions. The CO luminosity function invariably steepens in the outer disk, where fewer massive GMCs are present beyond the median cloud galactocentric distance. The H α luminosity function also steepens in the outer disk for most of the galaxies examined. Using Salpeter, Kroupa, and Chabrier initial mass functions (IMFs) along with stellar mass-luminosity-radius relations, we calculate the bolometric luminosity and H α emission from young star clusters. The cluster masses are linked to the GMC mass by assuming that the cluster mass is a constant fraction (3%) of the parent cloud mass. In particular, results for a fully stochastic IMF are compared to suggestions that very massive stars only form in massive clusters or clouds. Within the limits of the observations - no small molecular clouds or low-luminosity H II regions can be detected at the typical ∼10 Mpc distance of the sample galaxies - we find no evidence for a maximum stellar mass that varies with cloud or cluster mass.

Determining the Hubble constant tension requires alternative strategies, and multiply imaged quasars, with their intermediate redshifts, can potentially be used in this regard. We provide a currently complete catalogue of spectroscopically confirmed lensed quasars with ESA/ Gaia astrometry and photometry, as well as redshifts and time delays when available. In addition to the improved astrometry, the catalogue increases the number of lensed quasars by a factor of 1.5 (now 364, of which 277 are doubles and 87 are quads or triples) and significantly increases the number of lensing galaxies detected (now 218), which represents a major step forward. Redshifts are provided for 347 quasars and 188 deflectors. A completely new table of time delays, required for estimates of H ₀ , is presented, with 195 time delays from 73 systems. Gaia absolute astrometry is sub-milliarcsecond and covers the entire sky. Future Gaia data releases will provide long-term photometry, which should provide many more time delays. The catalogues as presented here enable machine-learning techniques to be trained and tested and subsequently applied to the Gaia data releases. Finally, we derive simple but homogeneous models of the 18 quadruply imaged quasars for which images of all four components are presented in Gaia DR3.

Context. Galaxies fly inside galaxy clusters and ram pressure by the intracluster medium (ICM) can remove a large amount of the interstellar medium (ISM) from the galaxy, and deposit the gas in the ICM. The ISM decoupled from the host galaxy leaves a long trail following the moving galaxy. Such long trails track galaxy motions and they can be detected with sensitive data in H α . Aims. We study the H α tail trailing NGC 4569 in the Virgo cluster. Methods. The initial discovery was made with the deep H α imaging data with CFHT from the VESTIGE project. The follow-up spectroscopic observations were carried out with APO / DIS , MMT / Binospec , and CFHT / SITELLE . Results. Aside from the known 80 kpc H α tail downstream of NGC 4569, the deep H α imaging data allow the H α tail detected to at least 230 kpc from the galaxy. More importantly, we confirmed the H α clumps implied from the imaging data with spectroscopic data. The H α clumps show a smooth radial velocity gradient across ∼1300 km/s, eventually reaching the velocity of the cluster. Conclusions. For the first time, this discovery offers a view of the full deceleration process of the stripped ISM. This discovery also showcases the potential with wide-field H α survey on galaxy clusters to discover intracluster optical emission-line clouds originated from cluster galaxies. These clouds provide kinematic tracers to the infall history of cluster galaxies and the turbulence in the ICM. They also serve as excellent multi-phase objects for studying the classical cloud-crushing problem and other important physical processes.

Stephan’s Quintet (SQ) is a local compact galaxy group system that exhibits significant star formation activity. A history of tidal interactions between its four member galaxies and a recent collision between an intruder galaxy and the original group are associated with active star formation, particularly in many shocked regions in the intragroup medium. Using an existing star cluster candidate (SCC) catalog constructed from Hubble Space Telescope (HST) UV/optical images, we integrate flux measurements from five near-infrared filters (F090W, F150W, F200W, F277W, and F356W) obtained from JWST NIRCam observations in 2022. Leveraging the extended photometric baseline from HST and JWST, spanning ∼300 to ∼3500 nm, we perform spectral energy distribution (SED) fitting using the C igale code to derive reliable estimates of age, mass, and extinction for the 1588 high-confidence SCCs. We confirm earlier results that very young SCCs (∼a few Myr) are predominantly located along previously identified shock regions near the merging galaxies, while older (>100 Myr) and globular clusters are more widely distributed. Our analysis shows that near-IR photometry helps break the age–extinction degeneracy, reclassifying many SCCs from older to younger, moderately dust-extincted clusters when added to HST-based SED fits. We also observe a strong spatial correlation between young clusters and CO-traced molecular gas, although active star formation is present in several regions with no detectable CO. We find that the two prominent epochs of star formation, around 5 and 200 Myr, correspond to the two major interaction events in SQ that gave rise to the observed extended tidal features.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

ALMA-IMF is a Large Program of the Atacama Large Millimeter/submillimeter Array (ALMA) that aims to determine the origin of the core mass function (CMF) of 15 massive Galactic protoclusters (~1.0–25.0 × 10³ M_⊙ within ~2.5 × 2.5 pc²) located toward the Galactic plane. In addition, the objective of the program is to obtain a thorough understanding of their physical and kinematic properties. Here we study the turbulence in these protoclusters with the C¹⁸O (2–1) emission line using the sonic Mach number analysis (M_s) and the size-linewidth relation. The probability distribution functions (PDFs) for M_s show a similar pattern, exhibiting no clear trend associated with evolutionary stage, peaking in the range between 4 and 7, and then extending to ~25. Such values of M_s indicate that the turbulence in the density regime traced by the C¹⁸O line inside the protoclusters is supersonic in nature. In addition, we compared the non-thermal velocity dispersions (σ_nth,C¹⁸O) obtained from the C¹⁸O (2–1) line with the non-thermal line widths (σ_{nth, DCN}) of the cores obtained from the DCN (3–2) line. We observed that, on average, the non-thermal linewidth in cores is half that of the gas surrounding them. This suggests that turbulence diminishes at smaller scales or dissipates at the periphery of the cores. Furthermore, we examined the size-linewidth relation for the structures we extracted from the position-position-velocity C¹⁸O (2–1) line emission cube with the dendrogram algorithm. The power-law index (p) obtained from the size-linewidth relation is between 0.41 and 0.64, steeper than the Kolmogorov law of turbulence, as expected for compressible media. In conclusion, this work is one of the first to carry out a statistical study of turbulence for embedded massive protoclusters.

We present new observational evidence supporting the hypothesis that SQ-A, a starburst in the intragroup medium (IGrM) of Stephan’s Quintet (SQ), is triggered by a high-speed collision between two gas systems, one associated with the IGrM (v ∼ 6900 km s⁻¹) and another with the intruder galaxy NGC 7318b (v ∼ 6000 km s⁻¹). The new CO(2–1) data set from the Atacama Large Millimeter/submillimeter Array has angular resolutions between 0 . ″ 2 and 7 . ″ 0 and the new Very Large Array H i data cube has an angular resolution of 6 . ″ 6 × 7 . ″ 9 . The CO maps show that the two gas systems are bridged by another system with an intermediate velocity of ∼6600 km s⁻¹, whereas the H i data show that the component of v ∼ 6600 km s⁻¹ fits well into a gap in the more extended v ∼ 6000 km s⁻¹ component, albeit with a displacement of ∼5 kpc. Both the bridge and the complementary distributions between different gas systems are common features of starbursts triggered by cloud–cloud collision. An analysis of clumps (sizes of 100–200 pc) reveals very diversified star formation (SF) activity in clumps belonging to different kinematic systems, with the molecular gas depletion time of the v ∼ 6900 km s⁻¹ clumps being more than 10 times longer than that of the v ∼ 6600 km s⁻¹ clumps. The results are consistent with a scenario in which the enhanced SF activity (and the starburst) in the system of v ∼ 6600 km s⁻¹ is due to gas compression generated in cloud–cloud collisions, whereas the suppression of SF in the v ∼ 6900 km s⁻¹ system is due to vortices (i.e. gas rotation) generated in more complex collisions involving dense clouds and diffuse intercloud gas associated with high-speed shocks.