GASP XIII. Star formation in gas outside galaxies Poggianti, Bianca M; Gullieuszik, Marco; Tonnesen, Stephanie ...
Monthly notices of the Royal Astronomical Society,
02/2019, Letnik:
482, Številka:
4
Journal Article
Abstract
It is well known that galaxies falling into clusters can experience gas stripping due to ram pressure by the intra-cluster medium. 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 versus 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 cluster-centric 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.
With MUSE, Chandra, VLA, ALMA, and UVIT data from the GASP program, we study the multiphase baryonic components in a jellyfish galaxy (JW100) with a stellar mass 3.2 × 1011 M hosting an active ...galactic nucleus (AGN). We present its spectacular extraplanar tails of ionized and molecular gas, UV stellar light, and 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 AGNs. We analyze the physical origin of the emission at different wavelengths in the tail, in particular in situ star formation (related to H , 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 (1 kpc) is due to different stages of the star formation process. We present the relation H -X-ray surface brightness, which is steeper for star-forming regions than for diffuse ionized gas regions with a high O i/H 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, observed O i excess, and 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 pointlike ultraluminous X-ray source commonly originating in a binary stellar system powered by either an intermediate-mass black hole or a magnetized neutron star.
Abstract
X-ray studies of jellyfish galaxies play a crucial role in understanding the interactions between the interstellar medium (ISM) and the intracluster medium (ICM). In this paper, we focused ...on the jellyfish galaxy JO201. By combining archival Chandra observations, Multi Unit Spectroscopic Explorer H
α
cubes, and maps of the emission fraction of the diffuse ionized gas, we investigated both its high-energy spectral properties and the spatial correlation between its X-ray and optical emissions. The X-ray emission of JO201 is provided by both the Compton-thick active galactic nucleus (
L
= 2.7 · 10
41
erg s
−1
, not corrected for intrinsic absorption) and an extended component (
L
1.9–4.5 · 10
41
erg s
−1
) produced by a warm plasma (
kT
keV), whose luminosity is higher than expected from the observed star formation (
L
3.8 · 10
40
erg s
−1
). The spectral analysis showed that the X-ray emission is consistent with the thermal cooling of hot plasma. These properties are similar to the ones found in other jellyfish galaxies showing extended X-ray emission. A point-to-point analysis revealed that this X-ray emission closely follows the ISM distribution, whereas
CLOUDY
simulations proved that the ionization triggered by this warm plasma would be able to reproduce the O
i
/H
α
excess observed in JO201. We conclude that the galactic X-ray emitting plasma originates on the surface of the ISM as a result of the ICM–ISM interplay. This process would entail the cooling and accretion of the ICM onto the galaxy, which could additionally fuel the star formation, and the emergence of O
i
/H
α
excess in the optical spectrum.
Abstract
We characterize the morphological properties of a statistically relevant sample of H
α
and UV young star-forming clumps and optical complexes, observed with the Hubble Space Telescope in six ...galaxies of the GASP sample undergoing ram pressure stripping. The catalogs comprise 2406 (323 in the tails) H
α
clumps, 3750 (899) UV clumps, and 424 tail optical complexes. About 15%–20% of the clumps and 50% of the complexes are resolved in size. We find that more than half of the complexes contain no H
α
clumps, while most of them contain at least one UV clump. The clump number and size increase with the complex size, while the median complex filling factor is larger for UV clumps (0.27) than that for H
α
clumps (0.10) and does not correlate with almost any morphological property. This suggests that the clumps' number and size grow with the complex keeping the filling factor constant. When studying the position of the clumps inside their complexes, H
α
clumps, and UV clumps to a lesser extent, show a displacement from the complex center of 0.1–1 kpc, and in ∼60% of the cases, they are displaced away from the galactic disk. This is in accordance with the fireball configuration, already observed in the tails of stripped galaxies. Finally, the filling factor and the clump radius increase with the distance from the galactic disk, suggesting that the reciprocal displacement of the different stellar generations increases as a consequence of the velocity gradient caused by ram pressure.
Abstract
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/Hubble Space Telescope (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 broadband (UV to I) filters and a narrowband H
α
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 and the universality of the star formation process, and to verify whether a disk is irrelevant, as hinted at by results from jellyfish galaxies. This paper presents the observations, data reduction strategy, and some general results based on the preliminary data analysis. The high spatial resolution of UVIS gives an unprecedentedly 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 and we did not detect a significant number of star-forming clumps in regions where MUSE did not detect any. The paper finally presents the development plan for the project.
ABSTRACT
It is often stated that the removal of gas by ram-pressure stripping of a galaxy disc is not a common process in galaxy groups. In this study, with the aid of an observational classification ...of galaxies and a simple physical model, we show that this may not be true. We examined and identified 45 ram-pressure-stripped galaxy candidates from a sample of 1311 galaxy group members within 125 spectroscopically selected galaxy groups. Of these, 13 galaxies are the most secure candidates with multiple distinct features. These candidate ram-pressure-stripped galaxies have similar properties to those found in clusters – they occur at a range of stellar masses, are largely blue and star-forming, and have phase-space distributions consistent with being first infallers into their groups. The only stand-out feature of these candidates is they exist not in clusters, but in groups, with a median halo mass of 1013.5 M⊙. Although this may seem surprising, we employ an analytic model of the expected ram-pressure stripping force in groups and find that reasonable estimates of the relevant infall speeds and intragroup medium content would result in ram-pressure-stripped galaxies at these halo masses. Finally, given the considerable uncertainty on the lifetime of the ram-pressure phase, this physical mechanism could be the dominant quenching mechanism in galaxy groups, if our ram-pressure-stripped candidates can be confirmed.
GAs Stripping Phenomena in galaxies with MUSE (GASP) is a new integral-field spectroscopic survey with MUSE at the VLT aimed 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 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 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 ( ) in a low-mass cluster ( ) at a small projected clustercentric radius and a high relative velocity, with ≥90 kpc long tentacles of ionized gas stripped away by ram pressure. We present the spatially resolved kinematics and physical properties of the gas and stars and depict the evolutionary history of this galaxy.
The so-called jellyfish galaxies are objects exhibiting disturbed morphology, mostly in the form of tails of gas stripped from the main body of the galaxy. Several works have strongly suggested ram ...pressure stripping to be the mechanism driving this phenomenon. Here, we focus on one of these objects, drawn from a sample of optically selected jellyfish galaxies, and use it to validate sinopsis, the spectral fitting code that will be used for the analysis of the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and study the spatial distribution and physical properties of the gas and stellar populations in this galaxy. We compare the model spectra to those obtained with gandalf, a code with similar features widely used to interpret the kinematics of stars and gas in galaxies from IFU data. We find that sinopsis can reproduce the pixel-by-pixel spectra of this galaxy at least as well as gandalf does, providing reliable estimates of the underlying stellar absorption to properly correct the nebular gas emission. Using these results, we find strong evidences of a double effect of ram pressure exerted by the intracluster medium onto the gas of the galaxy. A moderate burst of star formation, dating between 20 and 500 Myr ago and involving the outer parts of the galaxy more strongly than the inner regions, was likely induced by a first interaction of the galaxy with the intracluster medium. Stripping by ram pressure, plus probable gas depletion due to star formation, contributed to create a truncated ionized gas disk. The presence of an extended stellar tail on only one side of the disk points instead to another kind of process, likely gravitational interaction by a fly-by or a close encounter with another galaxy in the cluster.
Abstract
Ram pressure stripping is one of the most efficient mechanisms able to affect the gas reservoir in cluster galaxies, and in the last decades many studies have characterized the properties of ...stripped galaxies. A definite census of the importance of this process in local clusters is still missing, though. Here, we characterize the fraction of galaxies showing signs of stripping at optical wavelengths, using the data of 66 clusters from the WINGS and OMEGAWINGS surveys. We focus on the infalling galaxy population, and hence only consider blue, bright (
B
< 18.2), late-type, spectroscopically confirmed cluster members within two virial radii. In addition to “traditional” stripping candidates (SC)—i.e., galaxies showing unilateral debris and tails—we also consider unwinding galaxies (UG) as potentially stripped galaxies. Recent work has indeed unveiled a connection between unwinding features and ram pressure stripping, and even though only integral field studies can inform on how often these features are indeed due to ram pressure, it is important to include them in the global census. We performed a visual inspection of
B
-band images, and here we release a catalog of 143 UG. SC and UG each represent ∼15%–20% of the inspected sample. If we make the assumption that they both are undergoing ram pressure stripping, we can conclude that, at any given time in the low-z universe, about 35% of the infalling cluster population show signs of stripping in their morphology at optical wavelengths. These fractions depend on color, mass, and morphology, and little on clustercentric distance. Making some rough assumptions regarding the duration of the tail visibility and the time that cluster galaxies can maintain blue colors, we infer that almost all bright blue late-type cluster galaxies undergo a stripping phase during their life, boosting the importance of ram pressure stripping in cluster galaxy evolution.
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