GONE WITH THE WIND Galaxy Transformation in Abell 2125

Galaxy Cluster Abell 2125 Among richest clusters in Abell catalog Redshift z=0.25, D=3 billion light-years 266 confirmed members Uniquely rich in radio sources Complex structure; assembly by infall? Underachieving in X-rays for a rich cluster Laboratory for active galaxy evolution

Trail of evidence Radio survey shows A2125 as special C153 among strongest radio emitters Redshift survey identifies cluster components Hubble imaging shows unusual structure Narrowband imaging reveals O + tail Spectra show gas and stars move differently Chandra shows soft X-ray tail

Frazer Owen and Mike Ledlow at Kitt Peak

Abell 2125 is unusual… A2125: X-ray clumps, many radio sources A2645: just as rich, X-rays smooth, few radio sources

Galaxy redshifts show multiple subgroups: C153

Hubble WFPC2 imagery Asymmetric “flying fish” structure Disturbed disk, chaotic dust lanes Star-forming blue knots “downstream”

Kitt Peak Mosaic images Narrow-band filter isolated [O II] emission Long ionized-gas trail stretching 200,000 ly Mass greater than 100 million solar masses

Gemini-N spectra Burst of star formation 100 million years ago (as galaxy entered cluster core?) involving several billion solar masses This fits with galaxy being ~7 times too bright for its gravitational mass Stars’ orbits not strongly disturbed Gas and stellar motions are completely different – which would not result from gravity during a tidal interaction

Gemini spectrum Best-fit model: (100 Myr burst on 10-Gyr basis)

Chandra X-ray results C153 shows a trail in soft X-rays (cooler gas than surrounding cluster material) Roughly matches optical gas trail

Galaxies in the eggbeater Known since Butcher/Oemler in 1978 that galaxy populations in rich clusters change with time (especially over last 5 Gyr) Hubble images show much of the action is in destruction/transformation of spirals Usually hard to distinguish roles of multiple processes in these busy environments

Coma million l.y. (Bothun/McGraw-Hill Obs.)

Abell 851 – 5 billion l.y. Hubble (Dressler/Morrison)

Coma cluster in X-rays U. Briel et al, XMM-Newton

Clusters themselves are dynamic Local redshift model implies Virgo growing Even rich “relaxed” clusters (Coma) show X-ray and redshift substructure Clusters as well as galaxies grow by merger and acquisition

Where have all the spirals gone? Most into elliptical and S0 galaxies Galaxy collisions/mergers Tidal forces from the cluster core Cumulative weak tides – “harassment” Stripping by ram pressure as galaxies move through hot cluster gas These would often happen together and are difficult to separate

An ongoing view of stripping C153 has an unusually high velocity within A2125 (at least 2000 km/s) It is the only large disk to have passed close to the dense gas of the cluster core Distinct star/gas responses tell us that its transformation is being dominated by gas stripping.

Summary We see all the signatures of ongoing stripping of gas from a spiral galaxy Previous detections have inferred this process from its aftermath, or seen more subtle effects from a single tracer Favorable circumstances of C153 allow this process to be seen very clearly Is this the Milky Way in 50 billion years?