Speaker: Dave Wilman MPE

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The influence of the group environment since
z0.5 Morphologies and Star Formation
Speaker Dave Wilman (MPE) Collaborators Mike
Balogh (Waterloo), George Hau, Richard Bower
(Durham) John Mulchaey, Gus Oemler (Carnegie)
Ray Carlberg (Toronto)
Groups at 0.3 z 0.55
Wilman, Balogh, Bower et al., March 2005, MNRAS,
Paper I Group Properties Paper II Evolution
to z0
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Observing the Cosmic History of Star Formation...
By z 0, 50 of galaxies in groups. (Eke et
al., 2004)

• ?CDM cosmology
• Dust corrected

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Tying star formation to structure growth
Press-Schechter plot of dark matter mass
evolution Normalised to 1011 Mo Clusters are
negligible but groups dominate and evolve
strongly Thus, can environmental processes be
responsible for SFR evolution?
Groups
Clusters
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Evolution and Environment

• Decline in Cosmic SFR
• Increase in fraction of S0 galaxies in clusters
  (Dressler et al., 1997)
• Development of the red and dead population
• Cosmic Downsizing
• Environmental Trends preserved and even enhanced
  during hierarchical assembly
• understanding the group environment is
  critical.

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CNOC2 Groups at 0.3z0.55

• Kinematically selected from the CNOC2 redshift
  survey. Group detection described in Carlberg et
  al. (2001)

• Follow-up spectroscopy
• LDSS2 on Magellan (to RC 22)
• FORS2 on the VLT (to RC 23.2 June 05)
• redshifts (greater depth completeness)
• Infer presence of star-formation using the OII
  emission line
• HST ACS imaging (recent)
• Morphological classification
• GALEX UV imaging (current)
• Non-obscured star formation
• NIR imaging SOFI scheduled,
• MIR GTO Spitzer
• Chandra and XMM observations scheduled

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Spectroscopy

• With Magellan Extended spectroscopic sample to
  RC22.0
• Combined sample contains
• 282 0.3 z 0.55 group members in 26 groups.
• 334 0.3 z 0.55 serendipitous field galaxies
  to the same depth
• ( everything in Magellan FOV targetted
  groups)
• Selection function is well understood and sample
  is representative. (see Paper I)
• OII emission infers presence of star formation
  (EW5?).
• SED fitting -gt rest-frame luminosities.
• Groups range in sv from lt100km/s to 800km/s
  (poor cluster)
• To come gt400 new redshifts down to Rc23.2 from
  FORS2 including 13 groups.

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HST ACS data

• Observations of 20 groups for 1 orbit each in
  F775W filter.
• Morphological classification possible to R23.9
  (c.f. MORPHS WFPC2)
• Preliminary results for 16 ACS fields
• Visual classification by Gus Oemler of all
  galaxies with spectroscopic redshifts 0.3 z
  0.55 in the 16 fields
• 158 classified group galaxies 124 classified
  field galaxies.
• Classified according to the MORPHS scheme.

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The CNOC2 Sample
95ile k-correction at magnitude limit
0ile
r0
100ile
z
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Colours - Bimodal Fitting
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Colours - Bimodal Fitting
Dotted line SDSS (z0)
mean µ
(u-r)0
r0
Stdev s
r0
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Colours - Bimodal Fitting
Local SDSS fred(r0)
fred
r0
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Colours - Bimodal Fitting
CNOC2 Group galaxies only
fred
r0
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Downsizing
SDSS Transision mass 3x1010Mo for full range of
M/L
group
field
(u-r)0
(3.6µm) luminosity (IRAC Band 1)
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Observations fp vs z
fp fraction(EWOIIlt5?)
2dFGRS
BJ -19.65
CNOC1
Cluster cores
groups
Postmann 00, Van Dokkum 01 clusters
CNOC2
field
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Morphological Composition
Ellipticals
S0s
29 group S0s 7 field S0s
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Morphology-Density at z0.5
Dressler et al., 1997
MORPHS clusters
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Colour - Magnitude
SDSS (u-r)0
SDSS r0
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Intermediate Colour Galaxies

• Seeking the Transforming Population
• Colour transformation must last at least 0.75Gyr
  if SFR declines rapidly
• (Balogh et al, 05)

Hogg et al., 2005 SDSS ka galaxies have
preferentially intermediate colours.
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Passive Spirals

• Not seen in 2 massive groups sv gt 600km/s

Out of 67 group spirals and 68 field spirals

• Predominately brighter than MBj -20.0! (M)

• 3.2s excess wrt field for bright galaxies in
  smaller groups.

• Also see radial dependence

Normalised by rms distance of group galaxy from
group centre
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Colour - Magnitude
groups
SDSS (u-r)0
field
SDSS r0
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PAH emission at IRAC 8µ
Z0
Z0.3
Z0.48
Peeters et al., 2004 M81 (black) NGC 4945 (grey)
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IRAC colour (8µ-3.6µ) diagnostic
Large points S/N (8µ)gt2
EWOII
SDSS (u-r)0
IRAC colour
IRAC 3.6µm Luminosity
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Scatter in fp-s
fp
s (km/s)
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Morphological Properties of individual groups
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Evolutionary Type vs s
s (km/s)
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Segregation
Group 138
dec
RA
r0
dv (km/s)
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Segregation
Group 244
dec
RA
r0
dv (km/s)
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Segregation
Group 37
dec
RA
r0
dv (km/s)
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Segregation
Group 38
dec
RA
r0
dv (km/s)
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Conclusions

• Buildup of the red sequence is still in progress
• Across the luminosity range
• More advanced in groups
• Downsizing of mass for a typical star forming
  galaxy (but possibly no environmental dependence)
• Groups have excesses of faint Es and bright S0s,
  with similar morphological composition as
  irregular clusters at similar z.
• Most Groups are still evolving!!
• Transforming galaxies must have intermediate
  optical colours. Galaxies with intermediate
  optical colours are
• Often Spiral Galaxies
• Usually with low/no OII emission (passive
  spirals brighter than M these are
  particularly common in groups)
• Usually with strong PAH emission (!)
• Often with kA signatures
• If Spirals -gt S0s then the bulge luminosity must
  be enhanced -gt dusty central starbursts? The
  AGN connection? The importance of the group
  environment? Work to be done!

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The End!
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Tomo Goto
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Ignacio Garcia de la Rosa
Compact Group Ellipticals high S/N spectroscopy
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Ann Zabludoff
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Fundamental plane for groups also presented by
Hernan Muriel
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Somak Raychaudhury Miles et al. 2004
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Juan Cortes
IFU observations of Virgo spirals
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X-ray Selected Intermediate-Redshift Groups

• Tesla Jeltema
• John Mulchaey, Lori Lubin
• Chris Fassnacht, Piero Rosati, and Hans Böhringer

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Sample

• 9 groups selected from the ROSAT Deep Cluster
  Survey with z gt 0.2.
• Optical Observations
• Spectroscopy with Palomar and Las Campanas
• Additional spectroscopy for 7 with Keck and
  Gemini
• Imaging with WFPC2 on HST
• X-ray Observations
• XMM observations for 6 groups

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Spectroscopic Confirmation(From Palomar and Las
Campanas)

• z 0.23-0.59 from 4-20 group members.
• Velocity dispersions of 120-650 km/s.
• Early-type fractions of 0.27-0.94.

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Central Early-Type Galaxies
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Central Galaxies

• Like low-z groups, X-ray emission is peaked on a
  dominant early-type galaxy in 4 groups.
• In RXJ0329, BGG and X-ray emission align to
  within 20 degrees.

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Multiple Components in BGGs

• The BGGs in three groups show multiple
  components .

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Groups Without Central Galaxies

• At least 3 of 9 groups do not have a dominant,
  central early-type
• galaxy.

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Spirals in RXJ0210