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
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
Determining which between projected local density and distance from the cluster center plays a major role in regulating morphological fractions in clusters is a longstanding debate. Reaching ...a definitive answer will shed light on the main physical mechanisms at play in the most extreme environments. Here we make use of the data from the OmegaWINGS survey, currently the largest survey of clusters in the local universe extending beyond 2 virial radii from the cluster cores, to extend the previous analysis outside the virial radius. Local density and clustercentric distance seems to play different roles for galaxies of different morphology: the fraction of elliptical galaxies mainly depends on local density, suggesting that their formation was linked to the primordial densities, which now correspond to the cluster cores. Only the fraction of low-mass ellipticals shows an anticorrelation with clustercentric distance, suggesting a different origin for these objects. Excluding elliptical galaxies, the relative fraction of S0s and spirals instead depends on local density only far from the cluster cores, while within the virial radius their proportion is regulated by distance, suggesting that cluster-specific processes halt the star formation and transform Sp galaxies into S0s. This interpretation is supported by literature results on the kinematical analysis of early- and late-type galaxies, according to which fast and slow rotators have distinct dependencies on halo mass and local density.
Abstract
Based on results by recent surveys, the number of bright quasars at redshifts
z
> 3 is being constantly revised upward. The current consensus is that at bright magnitudes (
M
1450
≤ −27) the ...number densities of such sources could have been underestimated by a factor of 30%–40%. In the framework of the QUBRICS survey, we identified 58 bright QSOs at 3.6 ≤
z
≤ 4.2, with magnitudes
i
psf
≤ 18, in an area of 12400 deg
2
. The uniqueness of our survey is underlined by the fact that it allows us, for the first time, to extend the sampled absolute magnitude range up to
M
1450
= −29.5. We derived a bright-end slope of
β
= −4.025 and a space density at 〈
M
1450
〉 = −28.75 of 2.61 × 10
−10
Mpc
−3
comoving, after taking into account the estimated incompleteness of our observations. Taking into account the results of fainter surveys, active galactic nuclei (AGNs) brighter than
M
1450
= −23 could produce at least half of the ionizing emissivity at
z
∼ 4. Considering a mean escape fraction of 0.7 for the QSO and AGN population, combined with a mean free path of 41.3 proper Mpc at
z
= 3.9, we derive a photoionization rate of
, produced by AGNs at
M
1450
< −18, that is, ∼100% of the measured ionizing background at
z
∼ 4.
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.
GASP. I. Gas Stripping Phenomena in Galaxies with MUSE Poggianti, Bianca M.; Moretti, Alessia; Gullieuszik, Marco ...
Astrophysical journal/The Astrophysical journal,
07/2017, Letnik:
844, Številka:
1
Journal Article
Recenzirano
Odprti dostop
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.
When a supermassive black hole at the centre of a galaxy accretes matter, it gives rise to a highly energetic phenomenon: an active galactic nucleus. Numerous physical processes have been proposed to ...account for the funnelling of gas towards the galactic centre to feed the black hole. There are also several physical processes that can remove gas from a galaxy, one of which is ram-pressure stripping by the hot gas that fills the space between galaxies in galaxy clusters. Here we report that six out of a sample of seven 'jellyfish' galaxies-galaxies with long 'tentacles' of material that extend for dozens of kiloparsecs beyond the galactic disks-host an active nucleus, and two of them also have galactic-scale ionization cones. The high incidence of nuclear activity among heavily stripped jellyfish galaxies may be due to ram pressure causing gas to flow towards the centre and triggering the activity, or to an enhancement of the stripping caused by energy injection from the active nucleus, or both. Our analysis of the galactic position and velocity relative to the cluster strongly supports the first hypothesis, and puts forward ram pressure as another possible mechanism for feeding the central supermassive black hole with gas.
Abstract
In the cores of galaxy clusters there is a population of lows-mass stellar systems such as dwarf Early-type galaxies, ultra-compact dwarf galaxies (UCDs) and ultra diffuse dwarf galaxies. We ...present here the photometric and morphological characterization of this population of objects using deep CFHT images of a sample of clusters belonging to the WINGS survey (0.04 <
z
< 0.06). We study only galaxies that are spectroscopically confirmed members of the cluster. The population of dwarfs ranges from
∽
30% for the more rich clusters to
∽
5-6% for the less rich ones.
Using MUSE observations from the GASP survey, we study 54 galaxies undergoing ram pressure stripping (RPS) and 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 SFR observed in the stripped tails, once we take into account the fact that the star formation efficiency in the tails is a factor of ∼5 lower than in the galaxy disk, in agreement with GASP ongoing H i and CO observations. Finally, we 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 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 ∼4 × 109 M☉ of stars formed in the tails of RPS galaxies since z ∼ 1.
Abstract
Ram pressure stripping has been proven to be effective in shaping galaxy properties in dense environments at low redshift. The availability of Multi Unit Spectroscopic Explorer (MUSE) ...observations of a sample of distant (
z
∼ 0.3–0.5) clusters has allowed one to search for galaxies subject to this phenomenon at significant lookback times. In this paper we describe how we discovered and characterized 13 ram-pressure-stripped galaxies in the central regions of two intermediate redshift (
z
∼ 0.3–0.4) clusters, A2744 and A370, using the MUSE spectrograph. Emission-line properties as well as stellar features have been analyzed to infer the presence of this gas-only stripping mechanism, that produces spectacular ionized gas tails (H
α
and even more astonishing O
ii
(3727, 3729)) departing from the main galaxy body. The inner regions of these two clusters reveal the predominance of such galaxies among blue star-forming cluster members, suggesting that ram pressure stripping was even more effective at intermediate redshift than in today’s universe. Interestingly, the resolved O
ii
/H
α
line ratio in the stripped tails is exceptionally high compared to that in the disks of these galaxies, (which is comparable to that in normal low-
z
galaxies), suggesting lower gas densities and/or an interaction with the hot surrounding intracluster medium.
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