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Paper   IPM / Astronomy / 11732
School of Astronomy
  Title:   Ultraviolet tails and trails in cluster galaxies: a sample of candidate gaseous stripping events in Coma
1.  Russell Smith
2.  John Lucey
3.  Derek Hammer
4.  Ann E. Hornschemeier
5.  David Carter
6.  Mike Hudson
7.  Ron Marzke
8.  Mustapha Mouhcine
9.  Sareh Eftekharzadeh
10.  Phil.. James
11.  Habib Gharar Khosroshahi
12.  Ehsan Kourkchi
13.  Arna Karick
  Status:   Published
  Journal: MNRAS
  Vol.:  408
  Year:  2010
  Pages:   1417-1432
  Publisher(s):   Monthly Notices of the Royal Astronomical Society
  Supported by:            IPM IPM
We have used new deep observations of the Coma cluster from Galaxy Evolution Explorer to visually identify 13 star-forming galaxies with asymmetric morphologies in the ultraviolet (UV). Aided by wide-field optical broad-band and H #945; imaging, we interpret the asymmetric features as being due to star formation within gas stripped from the galaxies by interaction with the cluster environment. The selected objects display a range of structures from broad fan-shaped systems of filaments and knots (`jellyfish') to narrower and smoother tails extending up to 100kpc in length. Some of the features have been discussed previously in the literature, while others are newly identified here. We assess the ensemble properties of the sample. The candidate stripping events are located closer to the cluster centre than other star-forming galaxies; their radial distribution is more similar to that of all cluster members, dominated by passive galaxies. The fraction of blue galaxies which are undergoing stripping falls from 40per cent in the central 500kpc to less than 5per cent beyond 1Mpc. We find that tails pointing away from (i.e. galaxies moving towards) the cluster centre are strongly favoured (11/13 cases). From the small number of `outgoing' galaxies with stripping signatures, we conclude that the stripping events occur primarily on first passage towards the cluster centre, and are short-lived compared to the cluster crossing time. Using galaxy infall trajectories extracted from a cosmological simulation, we find that the observed fraction of blue galaxies undergoing stripping can be reproduced if the events are triggered at a threshold radius of  1Mpc and detectable for  500Myr. Hubble Space Telescope images are available for two galaxies from our sample and reveal compact blue knots coincident with UV and H #945; emission, apparently forming stars within the stripped material. Our results confirm that stripping of gas from infalling galaxies, and associated star formation in the stripped material, is a widespread phenomenon in rich clusters. Deep UV imaging of additional clusters is a promising route to constructing a statistically powerful sample of stripping events and constraining models for the truncation of star formation in clusters.

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