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157
result(s) for
"Boselli, Alessandro"
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On the origin of the faint-end of the red sequence in high-density environments
With the advent of the new generation wide-field cameras it became possible to survey in an unbiased mode galaxies spanning a variety of local densities, from the core of rich clusters, to compact and loose groups, down to filaments and voids. The sensitivity reached by these instruments allowed to extend the observation to dwarf galaxies, the most “fragile” objects in the universe. At the same time models and simulations have been tailored to quantify the different effects of the environment on the evolution of galaxies. Simulations, models, and observations consistently indicate that star-forming dwarf galaxies entering high-density environments for the first time can be rapidly stripped from their interstellar medium. The lack of gas quenches the activity of star formation, producing on timescales of
∼
1 Gyr quiescent galaxies with spectro-photometric, chemical, structural, and kinematical properties similar to those observed in dwarf early-type galaxies inhabiting rich clusters and loose groups. Simulations and observations consistently identify ram pressure stripping as the major effect responsible for the quenching of the star-formation activity in rich clusters. Gravitational interactions (galaxy harassment) can also be important in groups or in clusters whenever galaxies have been members since early epochs. The observation of clusters at different redshifts combined with the present high infalling rate of galaxies onto clusters indicate that the quenching of the star-formation activity in dwarf systems and the formation of the faint end of the red sequence is a very recent phenomenon.
Journal Article
A universal correlation between warm and hot gas in the stripped tails of cluster galaxies
The impact of ram pressure stripping on galaxy evolution is well known (for example, ref.
1
). Recent multi-wavelength data have revealed many examples of galaxies undergoing stripping, often accompanied with multi-phase tails
2
–
13
. As energy transfer in the multi-phase medium is an outstanding question in astrophysics, galaxies in stripping are great objects to study. Despite the recent burst of observational evidence, the relationship between gas in different phases in the tails is poorly known. Here we report a strong linear correlation between the X-ray surface brightness and the Hα surface brightness of the diffuse gas in the stripped tails at ~10–40 kpc scales, with a slope of ~3.5. This discovery provides evidence for the mixing of the stripped interstellar medium with the hot intra-cluster medium as the origin of the multi-phase tails. The established relation in stripped tails, also in comparison with the probably related correlations in similar environments such as galactic winds and X-ray cool cores, provides an important test for models of energy transfer in the multi-phase gas. It also indicates the importance of the Hα data to study clumping and turbulence in the intra-cluster medium.
The authors report the linear correlation of X-ray and Hα surface brightnesses in the material stripped from a galaxy, providing evidence for the mixing of galactic interstellar and hot intra-cluster medium as the origin of the multi-phase stripped tails observed previously.
Journal Article
VERTICO II: How H i-identified Environmental Mechanisms Affect the Molecular Gas in Cluster Galaxies
In this VERTICO early science paper we explore in detail how environmental mechanisms, identified in H i, affect the resolved properties of molecular gas reservoirs in cluster galaxies. The molecular gas is probed using ALMA ACA (+TP) observations of 12CO(2–1) in 51 spiral galaxies in the Virgo cluster (of which 49 are detected), all of which are included in the VIVA H i survey. The sample spans a stellar mass range of 9≤logM⋆/M⊙≤11 . We study molecular gas radial profiles, isodensity radii, and surface densities as a function of galaxy H i deficiency and morphology. There is a weak correlation between global H i and H2 deficiencies, and resolved properties of molecular gas correlate with H i deficiency: galaxies that have large H i deficiencies have relatively steep and truncated molecular gas radial profiles, which is due to the removal of low-surface-density molecular gas on the outskirts. Therefore, while the environmental mechanisms observed in H i also affect molecular gas reservoirs, there is only a moderate reduction of the total amount of molecular gas.
Journal Article
Constraining Star Formation in M87 Using Deep Hubble Space Telescope UV Data
We analyzed the deepest Hubble Space Telescope F275W ultraviolet (UV) imaging of M87 to obtain the most robust constraints on its star formation rate (SFR) and star formation history (SFH). After removing the galaxy continuum and globular clusters, we detected an excess of UV point sources near the center. By comparing their colors to young stellar source (YSS) colors generated by stochastically simulated star formation (SF) for various SFRs and SFHs, we ruled out their origin as a UV-upturn population and identified them as YSS. We found an extremely low SFR of ∼2 × 10−5 M⊙ yr−1 in M87, with evidence of a weak starburst ∼125 Myr ago that formed ∼1000 M⊙ of stars. Unlike other cool-core clusters where SF is stronger and directly linked to cooling gas, we found no spatial correlation between YSS and Hα filaments. Comparing SF activity with M87’s active galactic nucleus (AGN) outburst history suggests that recent AGN feedback events (≲12 Myr ago) neither triggered nor were associated with any detectable SF; however, earlier outbursts may have triggered weak starbursts. We detected UV filaments cospatial with Hα filaments with similar lengths and widths, though they are obscured by dust near the center. These filaments are likely powered by metal-line emission from collisional ionization, suggesting ongoing low-level precipitation of the intracluster medium. Our results indicate that AGN feedback has quenched SF significantly in M87 for at least 200 Myr, even though some precipitation persists. Additionally, we identified a hotspot created by the counterjet, with the spectral index also constrained.
Journal Article
Deep Galaxy Stellar Mass Functions As a Function of Star Formation Rate in the Virgo Cluster Environment
We analyze deep (M* ≳ 107 M⊙) galaxy stellar mass functions (SMFs) of the Virgo cluster using stellar masses derived as part of the Next Generation Virgo Survey. The total SMF has a slope of α=−1.35−0.02+0.02 , which is similar to or steeper than typical field values. Using deep Hα data from the Virgo Environmental Survey Tracing Ionised Gas Emission we separate out star-forming galaxies, quiescent galaxies with no ongoing star formation, and low star formation rate (SFR) galaxies that are intermediate between these two populations. For each of these populations, the shape of the SMF is found to be universal throughout the cluster, from the core to the outskirts. The star-forming and quiescent SMFs show stark differences with values seen in field galaxies. The relative fraction of quiescent galaxies is highest in the core of the cluster, with low-SFR and star-forming galaxies more significant in the outer regions of the cluster. At low stellar masses (M* ≲ 109 M⊙), the quiescent fraction in the main cluster is significantly higher than that of the field and even satellites of massive groups. At high stellar masses, the quiescent fraction is similar to other studies of cluster galaxies. We model the quiescent population in the infall region of the cluster as a combination of backsplash and field quiescent galaxies, and find that the backsplash fractions needed to explain the observed population are unrealistically high. This suggests the existence of a third population of low-mass galaxies that are preprocessed outside the virial radius of the cluster, possibly in groups prior to infall.
Journal Article
VERTICO. VII. Environmental Quenching Caused by the Suppression of Molecular Gas Content and Star Formation Efficiency in Virgo Cluster Galaxies
We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 pc scales. We present the resolved star-forming main sequence for cluster galaxies, dividing the sample based on their global H i properties and comparing to a control sample of field galaxies. H i–poor cluster galaxies have reduced star formation rate (SFR) surface densities with respect to both H i–normal cluster and field galaxies (∼0.5 dex), suggesting that mechanisms regulating the global H i content are responsible for quenching local star formation. We demonstrate that the observed quenching in H i–poor galaxies is caused by environmental processes such as ram pressure stripping (RPS), simultaneously reducing the molecular gas surface density and star formation efficiency (SFE) compared to regions in H i–normal systems (by 0.38 and 0.22 dex, respectively). We observe systematically elevated SFRs that are driven by increased molecular gas surface densities at fixed stellar mass surface density in the outskirts of early stage RPS galaxies, while SFE remains unchanged with respect to the field sample. We quantify how RPS and starvation affect the star formation cycle of inner and outer galaxy disks as they are processed by the cluster. We show both are effective quenching mechanisms, with the key difference being that RPS acts upon the galaxy outskirts while starvation regulates the star formation cycle throughout disk, including within the truncation radius. For both processes, the quenching is caused by a simultaneous reduction in the molecular gas surface densities and SFE at fixed stellar mass surface density.
Journal Article
MAUVE-MUSE: A Star-formation-driven Outflow Caught in the Act of Quenching the Stripped Virgo Galaxy NGC 4064
The rapid quenching of satellite galaxies in dense environments is often attributed to environmental processes such as ram pressure stripping. However, stripping alone cannot fully account for the removal of dense, star-forming gas in many satellites, particularly in their inner regions. Recent models and indirect observations have suggested that star-formation-driven outflows may play a critical role in expelling this remaining gas, yet direct evidence for such feedback-driven quenching remains limited. Here we report the discovery of an ionized gas outflow in NGC 4064, a Virgo cluster satellite that has already lost most of its cold gas through environmental stripping. MUSE observations from the Multiphase Astrophysics to Unveil the Virgo Environment survey reveal a bipolar outflow driven by residual, centrally concentrated star formation in NGC 4064—despite its current star formation rate being ∼0.4 dex below the star-forming main sequence due to prior interaction with the cluster environment. The outflow’s mass loading factor is ∼2, suggesting that stellar feedback could remove the remaining gas on timescales shorter than those required for depletion by star formation alone. These results demonstrate that even modest but centrally concentrated star formation can drive efficient feedback in stripped satellites, accelerating quenching in the final stages of their evolution.
Journal Article
ALMA-JELLY. I. High Resolution CO(2–1) Observations of Ongoing Ram Pressure Stripping in NGC 4858 Reveal Asymmetrical Gas Tail Formation and Fallback
We present new CO(2–1) observations (resolution ∼1″ = 460 pc) of the Coma cluster jellyfish galaxy NGC 4858 obtained from the ALMA-JELLY large program. Analyzing this data alongside complimentary Subaru Hα and Hubble Space Telescope (F600LP / F350LP) observations, we find numerous structural and kinematic features indicative of the effects from strong, inclined ram pressure, including an asymmetric inner gas tail. We estimate a highly inclined disk-wind angle of ϕDW=75−27+10 . By subtracting a simple circular velocity model, we find (1): gas clumps that are being accelerated by ram pressure, and (2): signatures of gas clumps that had been previously pushed out of the disk but are now falling inward. We also discuss head-tail morphologies in star complexes within the stellar disk that appear to be ram pressure stripping (RPS)-influenced. Lastly, we compare this galaxy to state-of-the-art galaxy “wind tunnel” simulations. We find that this galaxy is one of the best nearby examples of strong and inclined ram pressure gas stripping, and of gas that is perturbed by ram pressure but not fully stripped and falls back. We emphasize the importance of torques due to ram pressure in highly inclined interactions, which help drive gas inward on the side rotating against the wind, contributing to the formation of asymmetric inner RPS tails.
Journal Article
FAST-ASKAP Synergy: Quantifying Coexistent Tidal and Ram Pressure Strippings in the NGC 4636 Group
Combining new H i data from a synergetic survey of Australian Square Kilometre Array Pathfinder (ASKAP) Widefield ASKAP L-band Legacy All-sky Blind surveY and Five-hundred-meter Aperture Spherical radio Telescope with the Arecibo Legacy Fast ALFA data, we study the effect of ram pressure and tidal interactions in the NGC 4636 group. We develop two parameters to quantify and disentangle these two effects on gas stripping in H i-bearing galaxies: the strength of external forces at the optical-disk edge, and the outside-in extents of H i-disk stripping. We find that gas stripping is widespread in this group, affecting 80% of H i-detected nonmerging galaxies, and that 41% are experiencing both types of stripping. Among the galaxies experiencing both effects, the two types of strengths are independent, while two H i-stripping extents moderately anticorrelate with each other. Both strengths are correlated with H i-disk shrinkage. The tidal strength is related to a rather uniform reddening of low-mass galaxies (M * < 109 M ☉) when tidal stripping is the dominating effect. In contrast, ram pressure is not clearly linked to the color-changing patterns of galaxies in the group. Combining these two stripping extents, we estimate the total stripping extent, and put forward an empirical model that can describe the decrease of H i richness as galaxies fall toward the group center. The stripping timescale we derived decreases with distance to the center, from ∼1 Gyr beyond R 200 to ≲10 Myr near the center. Gas depletion happens ∼3 Gyr since crossing 2R 200 for H i-rich galaxies, but much quicker for H i-poor ones. Our results quantify in a physically motivated way the details and processes of environmental-effects-driven galaxy evolution, and might assist in analyzing hydrodynamic simulations in an observational way.
Journal Article