arXiv subjects

Bianca M. Poggianti

Publications and source records attributed to Bianca M. Poggianti.

At least 55 records · Page 3Linked to original sources

arXiv2020

GASP XXIX -- Unwinding the arms of spiral galaxies via ram-pressure stripping

We present the first study of the effect of ram-pressure "unwinding" the spiral arms of cluster galaxies. We study 11 ram-pressure stripped galaxies from GASP (GAs Stripping Phenomena in galaxies) in which, in addition to more commonly observed "jellyfish" features, dislodged material also appears to retain the original structure of the spiral arms. Gravitational influence from neighbours is ruled out and we compare the sample with a control group of undisturbed spiral galaxies and simulated stripped galaxies. We first confirm the unwinding nature, finding the spiral arm pitch angle increases radially in 10 stripped galaxies and also simulated face-on and edge-on stripped galaxies. We find only younger stars in the unwound component, while older stars in the disc remain undisturbed. We compare the morphology and kinematics with simulated ram-pressure stripping galaxies, taking into account the estimated inclination with respect to the intracluster medium and find that in edge-on stripping, unwinding can occur due to differential ram-pressure caused by the disc rotation, causing stripped material to slow and "pile-up". In face-on cases, gas removed from the outer edges falls to higher orbits, appearing to "unwind". The pattern is fairly short-lived (<0.5Gyr) in the stripping process, occurring during first infall and eventually washed out by the ICM wind into the tail of the jellyfish galaxy. By comparing simulations with the observed sample, we find a combination of face-on and edge-on "unwinding" effects are likely to be occurring in our galaxies as they experience stripping with different inclinations with respect to the ICM.

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arXiv2020

The GOGREEN and GCLASS Surveys: First Data Release

We present the first public data release of the GOGREEN and GCLASS surveys of galaxies in dense environments, spanning a redshift range $0.8<z<1.5$. The surveys consist of deep, multiwavelength photometry and extensive Gemini GMOS spectroscopy of galaxies in 26 overdense systems ranging in halo mass from small groups to the most massive clusters. The objective of both projects was primarily to understand how the evolution of galaxies is affected by their environment, and to determine the physical processes that lead to the quenching of star formation. There was an emphasis on obtaining unbiased spectroscopy over a wide stellar mass range ($M\gtrsim 2\times 10^{10}~\mathrm{M}_\odot$), throughout and beyond the cluster virialized regions. The final spectroscopic sample includes 2771 unique objects, of which 2257 have reliable spectroscopic redshifts. Of these, 1704 have redshifts in the range $0.8<z<1.5$, and nearly 800 are confirmed cluster members. Imaging spans the full optical and near-infrared wavelength range, at depths comparable to the UltraVISTA survey, and includes \textit{HST}/WFC3 F160W (GOGREEN) and F140W (GCLASS). This data release includes fully reduced images and spectra, with catalogues of advanced data products including redshifts, line strengths, star formation rates, stellar masses and rest-frame colours. Here we present an overview of the data, including an analysis of the spectroscopic completeness and redshift quality.

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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

The role of environment on quenching, star formation and AGN activity

Galaxies undergoing ram pressure stripping in clusters are an excellent opportunity to study the effects of environment on both the AGN and the star formation activity. We report here on the most recent results from the GASP survey. We discuss the AGN-ram pressure stripping connection and some evidence for AGN feedback in stripped galaxies. We then focus on the star formation activity, both in the disks and the tails of these galaxies, and conclude drawing a picture of the relation between multi-phase gas and star formation.

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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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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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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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arXiv2018

GASP. XII. The variety of physical processes occurring in a single galaxy group in formation

GAs Stripping Phenomena in galaxies with MUSE (GASP) is a program aimed at studying gas removal processes in nearby galaxies in different environments. We present the study of four galaxies that are part of the same group (z= 0.06359) and highlight the multitude of mechanisms affecting the spatially resolved properties of the group members. One galaxy is passive and shows a regular stellar kinematics. The analysis of its star formation history indicates that the quenching process lasted for a few Gyr and that the star formation declined throughout the disk in a similar way, consistent with strangulation. Another galaxy is characterised by a two-component stellar disk with an extended gas disk that formed a few 10^8 yr ago, most likely as a consequence of gas accretion. The third member is a spiral galaxy at the edges of the group, but embedded in a filament. We hypothesise that the compression exerted by the sparse intergalactic medium on the dense circumgalactic gas switches on star formation in a number of clouds surrounding the galaxy ("cosmic web enhancement"). Alternatively, also ram pressure stripping might be effective. Finally, the fourth galaxy is a spiral with a truncated ionised gas disk and an undisturbed stellar kinematics. An analytical model of the galaxy's restoring pressure, and its location and velocity within the cluster, suggest ram pressure is the most likely physical mechanism in action. This is the first optical evidence for stripping in groups.

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arXiv2018

GASP IX. Jellyfish galaxies in phase-space: an orbital study of intense ram-pressure stripping in clusters

It is well known that galaxies falling into clusters can experience gas stripping due to ram-pressure by the intra-cluster medium (ICM). The most spectacular examples are galaxies with extended tails of optically-bright stripped material known as "jellyfish". We use the first large homogeneous compilation of jellyfish galaxies in clusters from the WINGS and OmegaWINGS surveys, and follow-up MUSE observations from the GASP MUSE programme to investigate the orbital histories of jellyfish galaxies in clusters and reconstruct their stripping history through position vs. velocity phase- space diagrams. We construct analytic models to define the regions in phase-space where ram-pressure stripping is at play. We then study the distribution of cluster galaxies in phase-space and find that jellyfish galaxies have on average higher peculiar velocities (and higher cluster velocity dispersion) than the overall population of cluster galaxies at all clustercentric radii, which is indicative of recent infall into the cluster and radial orbits. In particular, the jellyfish galaxies with the longest gas tails reside very near the cluster cores (in projection) and are moving at very high speeds, which coincides with the conditions of the most intense ram-pressure. We conclude that many of the jellyfish galaxies seen in clusters likely formed via fast (~1- 2 Gyr), incremental, outside-in ram-pressure stripping during first infall into the cluster in highly radial orbits.

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arXiv2017

GASP VIII: Capturing the birth of a Tidal Dwarf Galaxy in a merging system at z~0.05

Within the GAs Stripping Phenomena in galaxies with MUSE (GASP) sample, we identified an ongoing 1:1 merger between two galaxies and the consequent formation of a tidal dwarf galaxy (TDG). The system is observed at z = 0.05043 and is part of a poor group. Exploiting the exquisite quality of the MUSE/VLT data, we present the spatially resolved kinematics and physical properties of gas and stars of this object and describe its evolutionary history. An old (luminosity weighted age ~2x10^9yr), gas poor, early-type-like galaxy is merging with a younger (luminosity weighted age ~2.5x10^8 yr), gas rich, late-type galaxy . The system has a quite strong metallicity gradient, indicative of an early-stage phase. Comparing the spatial extension of the star formation at different epochs, we date the beginning of the merger between ~10^7 yr<t<5.7x10^8 yr ago. The gas kinematic pattern reflects that of the late-type object and is distorted in correspondence to the location of the impact. The stellar kinematic instead is more chaotic, as expected for mergers. The gas redistribution in the system induces high levels of star formation between the two components, where we indeed detect the birth of the TDG. This stellar structure has a mass of ~6x10^9 M_sun, a radius of ~2 kpc and, even though it has already accreted large quantities of gas and stars, it is still located within the disk of the progenitor, is characterized by a high velocity dispersion, indicating that it is still forming, is dusty and has high levels of star formation SFR~0.3 M_sun/yr). This TDG is originated in an early-stage merger, while these structures usually form in more evolved systems.

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arXiv2017

Ram pressure feeding super-massive black holes

When supermassive black holes at the center of galaxies accrete matter (usually gas), they give rise to highly energetic phenomena named Active Galactic Nuclei (AGN). A number of physical processes have been proposed to account for the funneling of gas towards the galaxy centers to feed the AGN. There are also several physical processes that can strip gas from a galaxy, and one of them is ram pressure stripping in galaxy clusters due to the hot and dense gas filling the space between galaxies. We report the discovery of a strong connection between severe ram pressure stripping and the presence of AGN activity. Searching in galaxy clusters at low redshift, we have selected the most extreme examples of jellyfish galaxies, which are galaxies with long tentacles of material extending for dozens of kpc beyond the galaxy disk. Using the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of the 7 galaxies of this sample host a central AGN, and two of them also have galactic-scale AGN ionization cones. The high incidence of AGN among the most striking jellyfishes may be due to ram pressure causing gas to flow towards the center and triggering the AGN activity, or to an enhancement of the stripping caused by AGN energy injection, or both. Our analysis of the galaxy position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another, yet unforeseen, possible mechanism for feeding the central supermassive black hole with gas.

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arXiv2017

GASP IV: A muse view of extreme ram-pressure stripping in the plane of the sky: the case of jellyfish galaxy JO204

In the context of the GAs Stripping Phenomena in galaxies with Muse (GASP) survey, we present the characterization of JO204, a jellyfish galaxy in A957, a relatively low-mass cluster with $M=4.4 \times10^{14}M_\odot$. This galaxy shows a tail of ionized gas that extends up to 30 kpc from the main body in the opposite direction of the cluster center. No gas emission is detected in the galaxy outer disk, suggesting that gas stripping is proceeding outside-in. The stellar component is distributed as a regular disk galaxy; the stellar kinematics shows a symmetric rotation curve with a maximum radial velocity of 200km/s out to 20 kpc from the galaxy center. The radial velocity of the gas component in the central part of the disk follows the distribution of the stellar component; the gas kinematics in the tail retains the rotation of the galaxy disk, indicating that JO204 is moving at high speed in the intracluster medium. Both the emission and radial velocity maps of the gas and stellar components indicate ram-pressure as the most likely primary mechanism for gas stripping, as expected given that JO204 is close to the cluster center and it is likely at the first infall in the cluster. The spatially resolved star formation history of JO204 provides evidence that the onset of ram-pressure stripping occurred in the last 500 Myr, quenching the star formation activity in the outer disk, where the gas has been already completely stripped. Our conclusions are supported by a set of hydrodynamic simulations.

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arXiv2017

GASP I: Gas stripping phenomena in galaxies with MUSE

GASP (GAs Stripping Phenomena in galaxies with MUSE) is a new integral-field spectroscopic survey with MUSE at the VLT aiming at studying gas removal processes in galaxies. We present an overview of the survey and show a first example of a galaxy undergoing strong gas stripping. GASP is obtaining deep MUSE data for 114 galaxies at z=0.04-0.07 with stellar masses in the range 10^9.2-10^11.5 M_sun in different environments (galaxy clusters and groups, over more than four orders of magnitude in halo mass). GASP targets galaxies with optical signatures of unilateral debris or tails reminiscent of gas stripping processes ("jellyfish galaxies"), as well as a control sample of disk galaxies with no morphological anomalies. GASP is the only existing Integral Field Unit (IFU) survey covering both the main galaxy body and the outskirts and surroundings, where the IFU data can reveal the presence and the origin of the outer gas. To demonstrate GASP's ability to probe the physics of gas and stars, we show the complete analysis of a textbook case of a "jellyfish" galaxy, JO206. This is a massive galaxy (9 x 10^10 M_sun in a low-mass cluster (sigma ~500 km/s), at a small projected clustercentric radius and a high relative velocity, with >=90kpc-long tentacles of ionized gas stripped away by ram pressure. We present the spatially resolved kinematics and physical properties of gas and stars, and depict the evolutionary history of this galaxy.

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