arXiv subjects

Daniela Bettoni

Publications and source records attributed to Daniela Bettoni.

At least 19 recordsLinked to original sources

arXiv2024

Identification of ram pressure stripping features in galaxies using citizen science

Ram pressure stripped galaxies are rare cases of environmental evolution in action. However, our ability to understand these galaxies is limited by the small number of identified galaxies experiencing ram pressure stripping (RPS). Our aim is to explore the efficacy of citizen science classifications in identifying ram pressure stripped galaxies, and use this to aid in motivating new samples of ram pressure stripped candidates. We compile a sample of over 200 known ram pressure stripped galaxies from existing literature, with morphological classifications obtained from Galaxy Zoo. We compare these galaxies with magnitude and redshift-matched comparison cluster and field galaxies. Additionally, we create a sample of SDSS cluster galaxies, with morphological classifications similar to known ram pressure stripped galaxies, and compare the fraction of potential new RPS candidates against control samples. We find that ram pressure stripped galaxies exhibit a higher proportion of odd and irregular morphological classifications compared to field and cluster comparison samples. This trend is particularly pronounced in galaxies displaying strong optical ram pressure stripping features, but absent from galaxies with only radio tails. We find that SDSS galaxies with Galaxy Zoo classifications consistent with the known RPS galaxies have a higher fraction of visible ram pressure stripping features ($19\%$) compared with other cluster galaxies ($12\%$) when classified by experts. We identify 101 new ram pressure stripping candidate galaxies through these expert classifications. We demonstrate that indirect morphological classifications from citizen science projects can increase the efficiency in which new stripping candidates are found. Projects such as Galaxy Zoo can aid in the identification of ram pressure stripped galaxies that are key to understanding galaxy evolution in clusters.

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arXiv2023

The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation

WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366$-$959\,nm at $R\sim5000$, or two shorter ranges at $R\sim20\,000$. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for $\sim$3 million stars and detailed abundances for $\sim1.5$ million brighter field and open-cluster stars; (ii) survey $\sim0.4$ million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey $\sim400$ neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in $z<0.5$ cluster galaxies; (vi) survey stellar populations and kinematics in $\sim25\,000$ field galaxies at $0.3\lesssim z \lesssim 0.7$; (vii) study the cosmic evolution of accretion and star formation using $>1$ million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at $z>2$. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.

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arXiv2023

The relation between morphology, star formation history, and environment in local universe galaxies

The observed properties of galaxies are strongly dependent on both their total stellar mass and their morphology. Furthermore, the environment is known to play a strong role in shaping them. The galaxy population in the local universe that is located in virialized clusters is found to be red, poorly star-forming, and mostly composed of early morphological types. Towards a holistic understanding of the mechanisms that drive galaxy evolution, we exploit the spectrophotometric data from the WINGS and OmegaWINGS local galaxy cluster surveys, and study the role of both the local and the large-scale environments. We attempt to disentangle their effects from the intrinsic characteristics of the galaxies, in shaping the star formation activity at fixed morphological type and stellar mass. Using a sample of field galaxies from the same surveys for comparison, we analyse the effects of the environment, embodied by the local density, clustercentric distance, and close neighbours, respectively, on the star formation histories of cluster galaxies. We find that local effects have a more relevant impact on galaxy stellar properties than the large-scale environment, and that morphology needs to be taken into account to pinpoint the mechanisms that are driving the influence of clusters in galaxy evolution.

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arXiv2023

UV and H$α$ HST observations of 6 GASP jellyfish galaxies

Star-forming, H$α$-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 Hα 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.

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arXiv2022

Morphology driven evolution of barred galaxies in OMEGAWINGS Clusters

We present a study of barred galaxies in the cluster environment, exploiting a sample of galaxies drawn from the extended WIde-field Nearby Galaxy-cluster Survey (OmegaWINGS) that covers up to the outer regions of 32 local X-ray selected clusters. Barred galaxies are identified through a semi-automatic analysis of ellipticity and position angle profiles. We find, in agreement with previous studies, a strong co-dependence of the bar fraction with the galaxy stellar mass and morphological type, being maximum for massive late-type galaxies. The fraction of barred galaxies decreases with increasing cluster mass and with decreasing clustercentric distance, a dependence that vanishes once we control for morphological type, which indicates that the likelihood of a galaxy hosting a bar in the cluster environment is determined by its morphological transformation. At large clustercentric distances, we detect a dependence on the distance to the nearest neighbor galaxy, suggesting that tidal forces with close companions are able to suppress the formation of bars or even destroy them. Barred galaxies in our sample are either early-type, star forming galaxies located within the virial radii of the clusters or late-type quenched galaxies found beyond the virial radii of the clusters. We propose a scenario in which already quenched barred galaxies that fall into the clusters are centrally rejuvenated by the interplay of the perturbed gas by ram-pressure and the bar, in galaxies that are undergoing a morphological transformation.

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arXiv2020

GASP XXXII. Measuring the diffuse ionized gas fraction in ram-pressure stripped galaxies

The diffuse ionized gas (DIG) is an important component of the interstellar medium and it can be affected by many physical processes in galaxies. Measuring its distribution and contribution in emission allows us to properly study both its ionization and star formation in galaxies. Here, we measure for the first time the DIG emission in 38 gas-stripped galaxies in local clusters drawn from the GAs Stripping Phenomena in galaxies with MUSE survey (GASP). These galaxies are at different stages of stripping. We also compare the DIG properties to those of 33 normal galaxies from the same survey. To estimate the DIG fraction (C$_{DIG}$) and derive its maps, we combine attenuation corrected H$α$ surface brightness with $\rm [SII]/Hα$ line ratio. Our results indicate that we cannot use neither a single H$α$ or $\rm [SII]/Hα$ value, nor a threshold in equivalent width of H$α$ emission line to separate spaxels dominated by DIG and non-DIG emission. Assuming a constant surface brightness of the DIG across galaxies underestimates C$_{DIG}$. Contrasting stripped and non-stripped galaxies, we find no clear differences in C$_{DIG}$. The DIG emission contributes between 20\% and 90\% of the total integrated flux, and does not correlate with the galactic stellar mass and star-formation rate (SFR). The C$_{DIG}$ anti-correlates with the specific SFR, which may indicate an older ($>10^8$ yr) stellar population as ionizing source of the DIG. The DIG fraction shows anti-correlations with the SFR surface density, which could be used for a robust estimation of integrated C$_{DIG}$ in galaxies.

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arXiv2020

Low-redshift quasars in the SDSS Stripe 82 II: associated companion galaxies and signature of star formation

We present optical spectroscopy of the close companions of 22 low redshift (z<0.5) quasars (QSO) selected from a larger sample of QSO in the SDSS Stripe82 region for which both the host galaxy and the large scale environments have been investigated in our previous work. The new observations extend the number of QSO studied in our previous paper on close companion galaxies of 12 quasars. Our analysis here covers all 34 quasars from both this work and the previously published paper. We find that half of them (15 QSO; $\sim$44%) have at least one associated galaxy. Many (12 galaxies; $\sim$67%) of the associated companions exhibit [OII] 3727 A emission line as signature of recent star formation. The star formation rate (SFR) of these galaxies is modest (median SFR $\sim$ 4.3 M$_{\odot}$ yr$^{-1}$). For 8 QSO we are also able to detect the starlight of the host galaxy from which 3 have a typical spectrum of a post-starburst galaxy. Our results suggest that quasars do not have a strong influence on the star formation of their companion galaxies.

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arXiv2020

GASP XXI. Star formation rates in the tails of galaxies undergoing ram-pressure stripping

Using MUSE observations from the GASP survey, we study 54 galaxies undergoing ram-pressure stripping (RPS) spanning a wide range in galaxy mass and host cluster mass. We use this rich sample to study how the star formation rate (SFR) in the tails of stripped gas depends on the properties of the galaxy and its host cluster. We show that the interplay between all the parameters involved is complex and that there is not a single, dominant one in shaping the observed amount of SFR. Hence, we develop a simple analytical approach to describe the mass fraction of stripped gas and the SFR in the tail, as a function of the cluster velocity dispersion, galaxy stellar mass, clustercentric distance and speed in the intracluster medium. Our model provides a good description of the observed gas truncation radius and of the fraction of star-formation rate (SFR) observed in the stripped tails, once we take into account the fact that the star formation efficiency in the tails is a factor $\sim 5$ lower than in the galaxy disc, in agreement with GASP ongoing HI and CO observations. We finally estimate the contribution of RPS to the intracluster light (ICL) and find that the average SFR in the tails of ram-pressure stripped gas is $\sim 0.22 M_{\odot}\,\mathrm{yr}^{-1} $ per cluster. By extrapolating this result to evaluate the contribution to the ICL at different epochs, we compute an integrated average value per cluster of $\sim 4 \times 10^9 M_\odot$ of stars formed in the tails of RPS galaxies since $z\sim 1$.

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arXiv2020

GASP XXVII: Gas-phase metallicity scaling relations in disk galaxies with and without ram-pressure stripping

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we study the gas-phase metallicity scaling relations of a sample of 29 cluster galaxies undergoing ram-pressure stripping and of a reference sample of (16 cluster and 16 field) galaxies with no significant signs of gas disturbance. We adopt the PYQZ code to infer the mean gas metallicity at the effective radius and achieve a well-defined mass-metallicity relation (MZR) in the stellar mass range $10^{9.25}\le M_\star \le 10^{11.5}\,{\rm M_\odot}$ with a scatter of 0.12 dex. At any given mass, reference cluster and stripping galaxies have similar metallicities, while the field galaxies with $M_\star < 10^{10.25}\,{\rm M_\odot}$ show on average lower gas metallicity than galaxies in clusters. Our results indicate that at the effective radius the chemical properties of the stripping galaxies are independent of the ram-pressure stripping mechanism. Nonetheless, at the lowest masses we detect 4 stripping galaxies well above the common MZR that suggest a more complex scenario. Overall, we find signs of an anti-correlation between the metallicity and both the star formation rate and the galaxy size, in agreement with previous studies. No significant trends are instead found with the halo mass, clustercentric distance and local galaxy density in clusters. In conclusion, we advise a more detailed analysis of the spatially resolved gas metallicity maps of the galaxies, able to highlight effects of gas redistribution inside the disk due to the ram-pressure stripping.

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arXiv2020

GASP XXV: Neutral Hydrogen gas in the striking Jellyfish Galaxy JO204

We present JVLA-C observations of the HI gas in JO204, one of the most striking jellyfish galaxies from the GASP survey. JO204 is a massive galaxy in the low-mass cluster Abell 957 at z=0.04243. The HI map reveals an extended 90 kpc long ram-pressure stripped tail of neutral gas, stretching beyond the 30 kpc long ionized gas tail and pointing away from the cluster center. The HI mass seen in emission is (1.32 $ \pm 0.13) \times 10^{9} \rm M_{\odot}$, mostly located in the tail. The northern part of the galaxy disk has retained some HI gas, while the southern part has already been completely stripped and displaced into an extended unilateral tail. Comparing the distribution and kinematics of the neutral and ionized gas in the tail indicates a highly turbulent medium. Moreover, we observe associated HI absorption against the 11 mJy central radio continuum source with an estimated HI absorption column density of 3.2 $\times 10^{20}$ cm$^{-2}$. The absorption profile is significantly asymmetric with a wing towards higher velocities. We modelled the HI absorption by assuming that the HI and ionized gas disks have the same kinematics in front of the central continuum source, and deduced a wider absorption profile than observed. The observed asymmetric absorption profile can therefore be explained by a clumpy, rotating HI gas disk seen partially in front of the central continuum source, or by ram-pressure pushing the neutral gas towards the center of the continuum source, triggering the AGN activity.

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arXiv2020

Passive spirals and shock influenced star formation in the merging cluster A3376

We present a detailed analysis of star formation properties of galaxies in a nearby ($z\sim0.046$) young ($\sim$0.6 Gyr) post-merger cluster system A3376, with a moderate shock front ( $v_{s}\sim$1630 km/s) observed as symmetric radio relics. Exploiting the spectroscopic data from the wide-field OmegaWINGS survey and the associated photometric information, our investigations reveal the plausible effects of the dynamic post-merger environment differing from the putative pre-merger cluster environment. The remnants of the pre-merger relaxed cluster environment are realised through the existence of passive spiral galaxies located in the central regions of the cluster between the two BCGs. We discover A3376 to contain a population of massive $(M_{*}/M_{\odot})>10$) blue regular star-forming spirals in regions of maximum merger shock influence but exhibiting star formation rates similar to those in relaxed clusters at similar epoch. We further discover low-mass (Log $(M_{*}/M_{\odot})\leq 10$) late-type blue PSBs which could either be formed as a result of rapid quenching of low-mass spirals following the shock-induced star formation or due to the intense surge in the ICM pressures at the beginning of the merger. With the possibility of the merger shock affecting high- and low-mass spirals differently, our results bridge the seemingly contradictory results observed in known merging cluster systems so far and establish that different environmental effects are at play right from pre- to post-merger stage.

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arXiv2020

Anisotropic infall in the outskirts of OmegaWINGS galaxy clusters

We study the effects of the environment on galaxy quenching in the outskirts of clusters at $0.04 < z < 0.08$. We use a subsample of 14 WINGS and OmegaWINGS clusters that are linked to other groups/clusters by filaments and study separately galaxies located in two regions in the outskirts of these clusters according to whether they are located towards the filaments' directions or not. We also use samples of galaxies in clusters and field as comparison. Filamentary structures linking galaxy groups/clusters were identified over the Six Degree Field Galaxy Redshift Survey Data Release 3. We find a fraction of passive galaxies in the outskirts of clusters intermediate between that of the clusters and the field's. We find evidence of a more effective quenching in the direction of the filaments. We also analyse the abundance of post-starburst galaxies in the outskirts of clusters focusing our study on two extreme sets of galaxies according to their phase-space position: backsplash and true infallers. We find that up to $\sim70\%$ of post-starburst galaxies in the direction of filaments are likely backsplash, while this number drops to $\sim40\%$ in the isotropic infall region. The presence of this small fraction of galaxies in filaments that are falling into clusters for the first time and have been recently quenched, supports a scenario in which a significant number of filament galaxies have been quenched long time ago.

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arXiv2019

GASP XXIII: A jellyfish galaxy as an astrophysical laboratory of the baryonic cycle

With MUSE, Chandra, VLA, ALMA and UVIT data from the GASP programme we study the multiphase baryonic components in a jellyfish galaxy (JW100) with a stellar mass 3.2 X 10^{11} M_sun hosting an AGN. We present its spectacular extraplanar tails of ionized and molecular gas, UV stellar light, X-ray and radio continuum emission. This galaxy represents an excellent laboratory to study the interplay between different gas phases and star formation, and the influence of gas stripping, gas heating, and AGN. We analyze the physical origin of the emission at different wavelengths in the tail, in particular in-situ star formation (related to Halpha, CO and UV emission), synchrotron emission from relativistic electrons (producing the radio continuum) and heating of the stripped interstellar medium (ISM) (responsible for the X-ray emission). We show the similarities and differences of the spatial distributions of ionized gas, molecular gas and UV light, and argue that the mismatch on small scales (1kpc) is due to different stages of the star formation process. We present the relation Halpha--X-ray surface brightness, which is steeper for star-forming regions than for diffuse ionised gas regions with high [OI]/Halpha ratio. We propose that ISM heating due to interaction with the intracluster medium (either for mixing, thermal conduction or shocks) is responsible for the X-ray tail, the observed [OI]-excess and the lack of star formation in the northern part of the tail. We also report the tentative discovery in the tail of the most distant (and among the brightest) currently known ULX, a point-like ultraluminous X-ray source commonly originating in a binary stellar system powered either by an intermediate-mass black hole or a magnetized neutron star.

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arXiv2019

GASP. XX. From the loose spatially-resolved to the tight global SFR-Mass relation in local spiral galaxies

Exploiting the sample of 30 local star-forming, undisturbed late-type galaxies in different environments drawn from the GAs Stripping Phenomena in galaxies with MUSE (GASP), we investigate the spatially resolved Star Formation Rate-Mass (ΣSFR-Σ_star) relation. Our analysis includes also the galaxy outskirts (up to >4 effective radii, re), a regime poorly explored by other Integral Field Spectrograph surveys. Our observational strategy allows us to detect Hα out to more than 2.7re for 75% of the sample. Considering all galaxies together, the correlation between the ΣSFR and Σ_star is quite broad, with a scatter of 0.3 dex. It gets steeper and shifts to higher Σ_star values when external spaxels are excluded and moving from less to more massive galaxies. The broadness of the overall relation suggests galaxy-by-galaxy variations. Indeed, each object is characterized by a distinct ΣSFR-Σ_star relation and in some cases the correlation is very loose. The scatter of the relation mainly arises from the existence of bright off-center star-forming knots whose ΣSFR-Σ_star relation is systematically broader than that of the diffuse component. The ΣSFR-Σtot gas (total gas surface density) relation is as broad as the ΣSFR-Σ_star relation, indicating that the surface gas density is not a primary driver of the relation. Even though a large galaxy-by-galaxy variation exists, mean ΣSFR and Σ_star values vary of at most 0.7 dex across galaxies. We investigate the relationship between the local and global SFR-M_star relation, finding that the latter is driven by the existence of the size-mass relation.

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arXiv2019

GASP. XVI. Does cosmic web enhancement turn on star formation in galaxies?

Galaxy filaments are a peculiar environment, and their impact on the galaxy properties is still controversial. Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP), we provide the first characterisation of the spatially resolved properties of galaxies embedded in filaments in the local Universe. The four galaxies we focus on show peculiar ionised gas distributions: Halpha clouds have been observed beyond four times the effective radius. The gas kinematics, metallicity map and the ratios of emission line fluxes confirm that they do belong to the galaxy gas disk, the analysis of their spectra shows that very weak stellar continuum is associated to them. Similarly, the star formation history and luminosity weighted age maps point to a recent formation of such clouds. The clouds are powered by star formation, and are characterised by intermediate values of dust absorption. We hypothesise a scenario in which the observed features are due to "Cosmic Web Enhancement": we are most likely witnessing galaxies passing through or flowing within filaments that assist the gas cooling and increase the extent of the star formation in the densest regions in the circumgalactic gas. Targeted simulations are mandatory to better understand this phenomenon.

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arXiv2019

GASP XIX: AGN and their outflows at the center of jellyfish galaxies

The GASP survey, based on MUSE data, is unveiling the properties of the gas in the so-called "jellyfish" galaxies: these are cluster galaxies with spectacular evidence of gas stripping by ram pressure. In a previous paper, we selected the seven GASP galaxies with the most extended tentacles of ionized gas, and based on individual diagnostic diagrams concluded that at least five of them present clear evidence for an Active Galactic Nucleus. Here we present a more detailed analysis of the emission lines properties in these galaxies. Our comparison of several emission line ratios with both AGN and shock models show that photoionization by the AGN is the dominant ionization mechanism. This conclusion is strengthened by the analysis of $\rm Hβ$ luminosities, the presence of nuclear iron coronal lines and extended ($>10$ kpc) emission line regions ionized by the AGN in some of these galaxies. From emission line profiles, we find the presence of outflows in four galaxies, and derive mass outflow rates, timescales and kinetic energy of the outflows.

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arXiv2018

GASP XIII. Star formation in gas outside galaxies

Based on MUSE data from the GASP survey, we study the Halpha-emitting extraplanar tails of 16 cluster galaxies at z~0.05 undergoing ram pressure stripping. We demonstrate that the dominating ionization mechanism of this gas (between 64% and 94% of the Halpha emission in the tails depending on the diagnostic diagram used) is photoionization by young massive stars due to ongoing star formation (SF) taking place in the stripped tails. This SF occurs in dynamically quite cold HII clumps with a median Halpha velocity dispersion sigma = 27 km s^-1. We study the characteristics of over 500 star-forming clumps in the tails and find median values of Halpha luminosity L_{Halpha} = 4 X 10^38 erg s^-1, dust extinction A_V=0.5 mag, star formation rate SFR=0.003 M_sun yr^-1, ionized gas density n_e =52 cm^-3, ionized gas mass M_gas = 4 X 10^4 Msun, and stellar mass M_{*} = 3 X 10^6 Msun. The tail clumps follow scaling relations (M_gas-M_{*}, L_{Halpha} -sigma, SFR-M_gas) similar to disk clumps, and their stellar masses are comparable to Ultra Compact Dwarfs and Globular Clusters.The diffuse gas component in the tails is ionized by a combination of SF and composite/LINER-like emission likely due to thermal conduction or turbulence. The stellar photoionization component of the diffuse gas can be due either to leakage of ionizing photons from the HII clumps with an average escape fraction of 18%, or lower luminosity HII regions that we cannot individually identify.

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arXiv2018

Enhanced star formation in both disks and ram pressure stripped tails of GASP jellyfish galaxies

Exploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) program, we compare the integrated Star Formation Rate- Mass relation (SFR-M_ast) relation of 42 cluster galaxies undergoing ram pressure stripping ("stripping galaxies") to that of 32 field and cluster undisturbed galaxies. Theoretical predictions have so far led to contradictory conclusions about whether ram pressure can enhance the star formation in the gas disks and tails or not and until now a statistically significant observed sample of stripping galaxies was lacking. We find that stripping galaxies occupy the upper envelope of the control sample SFR-M_ast relation, showing a systematic enhancement of the SFR at any given mass. The star formation enhancement occurs in the disk (0.2 dex), and additional star formation takes place in the tails. Our results suggest that strong ram pressure stripping events can moderately enhance the star formation also in the disk prior to gas removal.

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