arXiv subjects

Eric Giunchi

Publications and source records attributed to Eric Giunchi.

11 recordsLinked to original sources

arXiv2026

With arms wide open: a VLT/MUSE view of the mechanisms driving unwinding spiral arms in cluster galaxies

The environmental mechanisms driving unwinding spiral arms in cluster galaxies remain debated. While earlier studies attributed it mainly to gravitational interactions, recent works suggest that RPS alone can induce unwinding. We present a VLT/MUSE spatially resolved analysis to investigate the mechanisms responsible for spiral-arm unwinding in two galaxies, UG101 and UG103, drawn from a larger sample. They are selected as tidal and RPS-driven candidates, respectively, based on the proximity of close neighbors. We estimate the galactocentric radius at which tidal forces, from a companion or the cluster potential, become relevant ($R_{\mathrm{tid}}$). We examine gas and stellar kinematics, exploiting their different responses to gravitational and hydrodynamical perturbations. SINOPSIS is used to map stellar populations in age bins and constrain unwinding timescales. For UG101, we find $R_{\mathrm{tid}} \sim 1.5 R_e$, while the unwound features extend beyond this radius. UG101 shows irregular stellar and gas kinematics; its rotation curve indicates similar motions, although the gas is truncated on one side and extended on the other. For UG103, neither the closest companion nor the cluster appear capable of triggering unwinding. UG103 displays regular stellar but disturbed gas kinematics, with truncation on the disk side likely facing the ICM wind and gas extended in the opposite direction. Stellar population maps show the emergence and unwinding of the spiral arms in UG103 on timescales consistent with its cluster infall time ($\sim 1.6$ Gyr). We conclude that unwinding in UG101 and UG103 is primarily driven by tidal interactions and RPS, respectively, although a combined effect cannot be excluded for UG101. Our methodology provides a framework to identify the mechanisms driving unwinding in cluster galaxies from spatially resolved properties.

astro-ph.GA↗

arXiv2026

Great Balls of Fire: Star Formation in Gas Clouds Accelerated by a Hot Wind

Satellite galaxies undergo ram pressure stripping, in which their gas is directly removed by a hydrodynamical interaction with the surrounding host halo gas. In clusters, ram pressure stripped tails of gas have been observed to be multiphase, even forming stars within the stripped material. Some observations find a specific age gradient along the tail, with old stars closer to the galaxy disk, and a ``fireball'' toy model has been proposed in which a gas cloud being accelerated away from a galaxy continuously forms stars. In this paper, we simulate individual gas clouds (with masses of ~10$^6$ M$_\odot$ and radii of a few-100 pc) interacting with an intracluster medium wind, and include star formation. We find that our accelerating clouds do generally produce a stellar age gradient with younger stars formed farther along the wind direction and with higher velocities. However, our simulations are more physically accurate than an empirical model of monolithic cloud acceleration, leading to strongly nonmonotonic age gradients. First, the evolution of the gas cloud, both from cloud compression and collapse as well as from the shredding of cloud material into downwind filaments, can lead to stars formed simultaneously at a range of heights and velocities. Second, the gravity from the gas and stars of the cloud can lead to velocity evolution of newly-formed stars. We conclude that the most distinct fireball stellar age gradients are formed from star-forming clouds that are rapidly accelerated and shredded by their surroundings.

astro-ph.GA↗

arXiv2025

Death by Impact: Evidence for Merger-Driven Quenching in a Collisional Ring Galaxy at Cosmic Noon

The role of interactions and mergers in the rapid quenching of massive galaxies in the early Universe remains uncertain, largely due to the difficulty of directly linking mergers to quenching. Collisional ring galaxies provide a unique opportunity, as their morphology allows precise dating of the interaction, which can then be compared to quenching timescales inferred from star formation histories. We study a gravitationally bound system at $z=1.61$ in the UDS field, composed of a Host galaxy ($M_\star = 10^{11.4} M_\odot$) with a collisional ring and an X-ray AGN, and the Bullet galaxy ($M_\star = 10^{11.2} M_\odot$), located at a projected distance of $\sim 8$ kpc. Combining JWST and HST imaging with Keck/MOSFIRE spectroscopy, we find compelling evidence for an ongoing starburst in the Host concurrent with rapid quenching in the Bullet. The ring, $\sim 20$ kpc in diameter, is expanding at $127^{+72}_{-29}$ km s$^{-1}$, implying the galaxies first collided 47--96 Myr ago. This timeline is consistent with the Host's current starburst and the Bullet's sudden quenching, strongly suggesting both phenomena were triggered by the interaction. Crucially, the Bullet shows no evidence of a preceding starburst, ruling out rapid gas consumption as the primary quenching channel. Instead, we suggest that merger-driven processes -- such as enhanced turbulence and disk instabilities -- may have suppressed star formation. An additional possibility, which we term the ``Dragon Effect,'' is that AGN-driven outflows from the Host disrupted the Bullet's low-density molecular gas, thereby preventing efficient star formation and accelerating quenching.

astro-ph.GA↗

arXiv2025

The dynamical evolution of the stellar clumps in the Sparkler galaxy

Recent JWST observations detected stellar clumps around the z=1.4 gravitationally lensed Sparkler galaxy (of stellar mass $M_*\sim 10^9\,\mathrm{M_\odot}$), with ages and metallicities compatible with globular clusters (GCs). However, most of their masses ($>10^6\,\mathrm{M_\odot}$) and sizes (>30 pc) are about 10 times those of GCs in the local Universe. To assess whether these clumps can evolve into GCs, we performed N-body simulations of their dynamical evolution from z=1.4 to z=0 (9.23 Gyr), under the effect of dynamical friction and tidal stripping. Dynamical friction is studied performing multiple runs of a clump system in a Sparkler-like spherical halo of mass $M_{200}\simeq 5\times 10^{11}\,\mathrm{M_\odot}$ (from the stellar-to-halo mass relation). For the tidal stripping, we simulated resolved clumps, orbiting in an external, static gravitational potential including the same halo as in the dynamical friction simulations and also a Sparkler-like stellar disk. Dynamical friction causes the clumps with mass $>10^7\,\mathrm{M_\odot}$ to sink into the galaxy central regions, possibly contributing to the bulge growth. In absence of tidal stripping, the mass distribution of the surviving clumps (40%) peaks at $5\times 10^6\,\mathrm{M_\odot}$, implying the presence of uncommonly over-massive clumps at z=0. Tidal shocks by the stellar disk strip considerable mass from low-mass clumps, even though their sizes remain larger than those of present-day GCs. When the surviving clumps are corrected for tidal stripping, their mass distribution peak shifts to $2\times 10^6\,\mathrm{M_\odot}$, compatible with massive GCs. Our simulations suggest that a fraction of the Sparkler clumps is expected to fall into the central regions, where they might become bulge fossil fragments or contribute to form a nuclear star cluster. The remaining clumps are too large in size to be progenitors of GCs.

astro-ph.GA↗

arXiv2025

What goes around comes around: the fate of stars in stripped tails of gas

We conduct high-resolution wind-tunnel simulations to study in-situ star formation in the stripped tails of two massive ($M_\text{star}=10^{11}M_\odot$) galaxies undergoing time-evolving ram-pressure stripping: one is stripped face-on (W0) and the other is subject to an angled wind (W45). We find that the majority of stars in the tail are formed close to the galaxy disc at the beginning of stripping. Most stars have ages that reflect outside-in stripping -- older stars are found at larger radii than younger stars. The velocities and metallicities of stars indicate that ICM mixing both increases the velocity and decreases the metallicity of star-forming gas, leading to faster, lower metallicity stars at larger distances from the galaxies. However, not all stars follow this simple model, even in the case of face-on stripping. Indeed, a considerable number (15--25 per cent) of tail stars are formed with negative velocities, indicating the fallback of star-forming gas on to the galaxy. Almost all of the tail stars formed within 20 kpc from the disc will eventually fall back on to the galaxy, and their contribution to the intracluster light is negligible. The orbits of the stars formed in the tail result in an extended (and asymmetric in the case of W45) stellar distribution around the disc. Mock UV images reveal that the observed vertical distribution of its stars is not significantly broader than in an undisturbed galaxy, indicating that more stars would need to form in the stripped tail than we find in our simulations to observably impact the UV disc width of ram pressure stripped galaxies.

astro-ph.GA↗

arXiv2025

Stripped and Enriched: The Role of Ram-Pressure in Shaping Chemical Enrichment of Galaxies at Intermediate Redshift

The chemical evolution of galaxies is shaped by their star formation histories and the exchange of gas with their environments. Metallicity provides key insights into these processes, reflecting the interplay between star formation and gas flows. A fundamental aspect of this evolution is the mass-metallicity relation, which captures the strong correlation between a galaxy stellar mass ($M_\star$) and its gas-phase oxygen abundance. In this study, we use MUSE observations to analyze star-forming disc galaxies in 12 clusters within the redshift range $0.3 < z < 0.5$. Galaxies were classified into three groups: ram-pressure stripping (RPS), control cluster, and control field. For the first time, we investigate the impact of RPS on gas-phase metallicities across a wide mass range of galaxies at intermediate redshift, comparing RPS galaxies to counterparts in both cluster and field environments. By analyzing the integrated flux within galactic disks, our results reveal that, on average, RPS induces a metallicity enhancement of 0.2 dex over non-stripped galaxies. Contrary to the prevailing view that cluster membership alone drives metallicity enrichment, we find that control cluster galaxies exhibit metallicities comparable to field galaxies at a given $M_\star$, with only RPS galaxies displaying significantly higher metal content, highlighting the unique role of RPS in shaping the chemical properties of galaxies. These differences become more pronounced at lower $M_\star$, indicating that environmental influences play a more critical role in shaping the chemical evolution of lower-mass galaxies. Our findings suggest that both enhanced star formation rates and suppressed gas inflows -- consequences of ram pressure stripping -- drive the elevated metallicity observed in RPS galaxies.

astro-ph.GA↗

arXiv2025

Clump formation in ram-pressure stripped galaxies: evidence from mass function

The mass function (MF) of young ($\mathrm{age\lesssim 200}$ Myr) stellar clumps is an indicator of the mechanism driving the collapse of the interstellar medium (ISM) into giant molecular clouds. Typically, the clump MF in main-sequence galaxies is described by a power law ($dN/dM_*\propto M_*^{-\alpha}$) with slope $\alpha=2$, hinting a turbulence-driven collapse. To understand whether the local environment affects star formation, we have modelled the clump MF of six cluster galaxies from the GASP survey, undergoing strong ram-pressure stripping. This process, exerted by the hot and high-pressure intra-cluster medium (ICM), has produced long tails of stripped ISM where clumps form far away from the galactic disk and surrounded by the ICM itself. Clumps were selected from HST-UVIS/WFC3 images, covering from near-UV to red-optical bands and including H$\alpha$-line maps. The catalogue comprises 398 H$\alpha$ (188 in tails, 210 in disk outskirts, the so-called extraplanar region) and 1270 UV clumps (593 tail, 677 extraplanar). Using mock images, we quantified the mass completeness and bias of our sample. Accounting for these two effects, we adopted a Bayesian approach to fit the clump mass catalogue to a chosen function. The resulting MFs are steeper than expected. In the tails, the H$\alpha$ clumps have slope $\alpha=2.31\pm0.12$, while the UV slope is larger ($2.60\pm0.09$), in agreement with ageing effects. Similar results are found in the extraplanar region, with H$\alpha$ slope $\alpha=2.45^{+0.20}_{-0.16}$ and UV slope $\alpha=2.63^{+0.20}_{-0.18}$, even if they are consistent within uncertainties. We suggest that the steepening results from the higher-than-usual turbulent environment, arising from the interaction between ISM and ICM. As shown by recent works, this process can favour the fragmentation of the largest ISM clouds, inhibiting the formation of very massive clumps.

astro-ph.GA↗

arXiv2024

Investigating the intracluster medium viscosity using the tails of GASP jellyfish galaxies

The microphysics of the intracluster medium (ICM) in galaxy clusters is still poorly understood. Observational evidence suggests that the effective viscosity is suppressed by plasma instabilities that reduce the mean free path of particles. Measuring the effective viscosity of the ICM is crucial to understanding the processes that govern its physics on small scales. The trails of ionized interstellar medium left behind by the so-called jellyfish galaxies can trace the turbulent motions of the surrounding ICM and constrain its local viscosity. We present the results of a systematic analysis of the velocity structure function (VSF) of the H$\alpha$ line for ten galaxies from the GASP sample. The VSFs show a sub-linear power law scaling below 10 kpc which may result from turbulent cascading and extends to 1 kpc, below the supposed ICM dissipation scales of tens of kpc expected in a fluid described by Coulomb collisions. Our result constrains the local ICM viscosity to be 0.3-25$\%$ of the expected Spitzer value. Our findings demonstrate that either the ICM particles have a smaller mean free path than expected in a regime defined by Coulomb collisions, or that we are probing effects due to collisionless physics in the ICM turbulence.

astro-ph.CO↗

arXiv2023

The most stringent upper limit from dynamical models on the mass of a central black hole in 47 Tucanae

Globular clusters (GCs) were proposed as promising sites for discovering intermediate-mass black holes (IMBHs), possibly providing crucial insights into the formation and evolution of these elusive objects. The Galactic GC 47 Tucanae (also known as NGC 104) has been suggested as a potential IMBH host, but, previous studies have yielded conflicting results. We, therefore, present self-consistent dynamical models based on distribution functions (DFs) that depend on action integrals to assess the presence (or absence) of an IMBH in 47 Tucanae. Leveraging state-of-the-art Multi Unit Spectroscopic Explorer and Hubble Space Telescope data, we analyzed the three-dimensional (3D) kinematics of the cluster's central regions, fitting individual star velocities down to the sub-arcsec scale (approximately $10^{-2}$ pc). According to our analysis, the inner kinematics of 47 Tucanae is incompatible with a central BH more massive than 578 M$_\odot$ (at $3\sigma$). This is the most stringent upper limit on the mass of a putative IMBH in 47 Tucanae that has been put by any dynamical study.

astro-ph.GA↗

arXiv2023

HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxies

Exploiting broad- and narrow-band images of the Hubble Space Telescope from the near-UV to I-band rest frame, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong ram pressure stripping. Clumps are detected in H alpha and near-UV, tracing star formation on different timescales. We consider clumps located in galaxy disks and stripped tails and formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 H alpha-selected clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3745 UV-selected clumps (2021 disk, 825 extraplanar, and 899 tail clumps). Only 15 per cent of star-forming clumps are spatially resolved, meaning that most are smaller than 140 pc. We study the luminosity and size distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average LDF slope is 1.79 +/- 0.09, while the average SDF slope is 3.1 +/- 0.5. The results suggest that the star formation is turbulence-driven and scale-free, as in main-sequence alaxies. All of the clumps, whether they are in the disks or tails, have an enhanced H alpha luminosity at a given size, compared to the clumps in main-sequence galaxies. Indeed, their H alpha luminosity is closer to that of clumps in starburst galaxies, indicating that ram pressure is able to enhance the luminosity. No striking differences are found among disk and tail clumps, suggesting that the different environments in which they are embedded play a minor role in influencing the star formation.

astro-ph.GA↗

arXiv2023

UV and H$\alpha$ HST observations of 6 GASP jellyfish galaxies

Star-forming, H$\alpha$-emitting clumps are found embedded in the gaseous tails of galaxies undergoing intense ram-pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a unique opportunity to study star formation under extreme conditions, in the absence of an underlying disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination of broad-band filters and a narrow-band H{\alpha} filter. HST observations are needed to study the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will be used to study the clump scaling relations, the universality of the star formation process and verify whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis: the UVIS high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions of the galaxies and of the substructures in the galaxy disks; we found clear signatures of stripping in regions very close in projection to the galactic disk; the star-forming regions in the stripped tails are extremely bright and compact while we did not detect a significant number of star-forming clumps outside those detected by MUSE. The paper finally presents the development plan for the project.

astro-ph.GA↗