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					Galaxy Ecology
   The role of galaxy environment in determining
   the star formation history of the universe


           Michael Balogh
           ICC, University of Durham

    Plus: Richard Bower, Ian Smail, Simon Morris, Vince Eke (Durham)
         Ian Lewis and the 2df team
         Bob Nichol, Percy Gomez, Chris Miller, Tomo Goto (CMU)
         Ann Zabludoff (Arizona)
         John Mulchaey, Gus Oemler (Carnegie)
         Ray Carlberg (Toronto)
         Warrick Couch (UNSW)
Galaxy Ecology
   The role of galaxy environment in determining
   the star formation history of the universe


          Michael Balogh
          ICC, University of Durham

    Motivation: cosmological context of observations

    Clusters at intermediate redshift

    The local universe: 2dF galaxy redshift survey, and Sloan digital
    sky survey

    Low mass clusters and groups at intermediate redshift
    Why Does Star Formation Stop?

                                                   Steidel et al. 1999


                                                     SFR ~ (1+z)1.7
                                                 (Wilson, Cowie et al. 2002)




A) Internal? i.e. gas consumption and “normal” aging
B) External? Hierarchical build-up of structure inhibits star formation
A Press-Schechter plot showing the growth of the mass
structure of the universe

                                         LCDM cosmology
                                         Growth of structure still
                                        rapid
                                         But how should curves be
                                        normalised?




                                        Groups

                                                    Clusters


       Renormalised relative
       to 1011 Msol
Galaxy clusters: the end of star
          formation?
      30                                     AC114 (z=0.31)

                                            (Couch et al. 2001)
      200




                                           Butcher-Oemler effect?
      100




                                           Does star formation take
                                           place in clusters at z>0 ?
DRA
      0
      -100
      -200
      -300




             -200   -100   0   100   200
Abell 2390 (z~0.23)
  3.6 arcmin          R image from
                      CNOC survey
                      (Yee et al. 1996)
Ha in Abell 2390
               Balogh & Morris 2000
3.6 arcmin
Nod & Shuffle: LDSS++ (AAT)
                     band-limiting filter +
                     microslit = ~800
                     galaxies per 7’ field
Ha in Rich Clusters at z~0.3

                          LDSS++ with nod
                          and shuffle sky
                          subtraction, on
                          AAT
                (Field)




                          Couch et al. 2001
                          ApJ 549, 820

                          Balogh et al. 2002
                          MNRAS, 335, 110
Fine for clusters – but what about groups?




                      Groups     Clusters
                 Mechanisms
   Ram-pressure stripping
    – Needs dense ICM and high velocities - clusters
   Collisions / harassment
    – Groups are preferred place!
   "Strangulation"
    – Removal of the gas halo
    – Similar to ram-pressure stripping but much
      easier!
Ram pressure - simulations
from Quilis et al. 2000




      Gunn & Gott, 1972
Examples of galaxy
collisions
in the real universe and in a
simulation (Moore et al
1995)
Strangulation ?

             Use numerical model of
             infall to estimate timescale
             for disruption of SFR

             Radial gradients in CNOC
             clusters suggest t ~2 Gyr

             (Balogh, Navarro & Morris 2000)
Strangulation - removal of the gas halo


                                                             Could occur in
                                                                groups




                     First suggested by Larson, Tinsley & Caldwell, 1984
Where do environmental
   effects become
     important?
           The Local Universe

   2dFGRS (Lewis et al. 2002, MNRAS 334, 673)
    – Ha in 11000 galaxies within 20 Mpc of 17
      clusters, down to MB=-19
    – SFR-density, SFR-radius relations in clusters
      with s>400 km/s
   SDSS (Gomez et al. 2002, ApJ in press)
    – volume-limited sample of 8600 galaxies from
      the EDR, MR<-20.5
    – SFR-density relation independent of proximity
      to a cluster
Galaxy Transformation in the 2DF survey
                                     Data for 17 Abell-like clusters
                             A1620   Covers velocity dispersions
                                     500 km/s - 1100 km/s

                Rvir                  Region out to > 20 Rvir extracted from
                                     the survey

                                     Major advantages:
                                      ● Star formation rate measured from
                                     Ha

                                      ● Complete redshift information - no
                                     need to subtract background!

                                      ● Compare with surrounding field
                                     directly




           1 degree

(data extracted over ~7 deg field)
SFR-Environment Relation in the
           2dFGRS
 Field
                    SFR-Radius Relation



 Field




 Field




                           Lewis et al. 2002
                           MNRAS 334, 673
SFR-Environment Relation in the
           2dFGRS
 Field
                    SFR-Density Relation



 Field




 Field




                           Lewis et al. 2002
                           MNRAS 334, 673
SFR-Environment Relation in the
           2dFGRS
 Field
                     SFR-Density Relation
                    c.f. Morphology-Density Relation

                     R>2 Rvirial
 Field




 Field




                                Lewis et al. 2002
                                MNRAS 334, 673
SFR-Environment relation in the
           SDSS
    Star Formation Rate (Mo/yr)                                          Gomez et al. (2002)



                                                 Field 75th percentile




                                    75th percentile


                                        Median                           Field median




                                  Galaxy Surface Density (Mpc-2)
  What You Must Remember!


Galaxy Transformation does not occur in clusters!
       => ram-pressure stripping not important

 It occurs in groups
... these might then end up in clusters.
          Groups at z=0.2-0.5

   Low-Lx Clusters at z=0.25
    – Factor ~10 less massive than CNOC clusters
    – HST imaging, extensive ground-based
      spectroscopy
   CNOC2 groups at z=0.45
    – Spectroscopy with LDSS-2 on Magellan 6.5-m
    – Goal is complete group membership to M*+1
    Low Lx Clusters at z~0.25

Cl0841        Cl0849         Cl1701        Cl1702
z=0.24        z=0.23         z=0.24        z=0.22
s=390         s=750          s=590         s=370




Cl0818        Cl0819         Cl1309        Cl1444
z=0.27        z=0.23         z=0.29        z=0.29
s=630         s=340          s=640         s=500




Lx ~ 1043 - 1044 ergs/s, ~ 10 X less massive than CNOC
                 Morphologies in Low-Lx Clusters
                           at z~0.25
                    Bulge/Total Fractions from GIM2D (Simard et al. 2002)


Disks
B/T<0.4
  Intermediate




Bulges
B/T>0.6

                                                              Balogh et al. 2002, ApJ 566, 123
             Low-Lx Disk Fractions
                                   (from Medium Deep
                                   Survey)




                                                       High-Lx Clusters
                                                       from the lensing
                                                       sample of
                                                       Smith et al. 2001




Balogh et al. 2002, ApJ 566, 123
Morphology-density relation
        at z~0.25
                      Balogh et al. 2002
                      ApJ 566, 123
Bulge Creation or Disk
    Destruction?
                                Balogh et al. 2002,
                                ApJ 566, 123




          Disk Luminosity
          Functions (at fixed
          density)
Bulge Creation or Disk
    Destruction?
                                Balogh et al. 2002,
                                ApJ 566, 123




          Bulge Luminosity
          Functions (at fixed
          density)
Star Formation in Low-Lx
        Clusters
                           Spectroscopy for 172 cluster
                           members Mr< -19 (h=1)
           Balogh et al.
           1997
                           SFR from [OII] emission line

                           Balogh et al. (2002)
                           MNRAS, in press
                           astro-ph/0207360
  Disks Without Star Formation
Cl 1309 id=83                      [OII]
z=0.2934

B/T = 0.39

Wo (OII)=-2.64.0
                    3” HST Image
Wo (Hd)=3.8 2.1
  Disks Without Star Formation
                                   [OII]
Cl 1444 id=78
z=0.2899

B/T = 0.42

Wo (OII)=3.5 2.7   3” HST Image
Wo (Hd)=4.9 1.3
  Disks Without Star Formation
Cl 0818 id=58                       [OII]
z=0.2667

B/T = 0.19

Wo (OII)=-9.6 7.8
Wo (Ha)=22.1 11.6   3” HST Image
Wo (Hd)=2.0 3.6
                                            Ha
   Disks Without Star Formation
Cl 0841 id=20                       [OII]
z=0.2372

B/T = 0.42

Wo (OII)=-0.2 1.2
                     3” HST Image
Wo (Ha)=-1.4 0.6
Wo (Hd)=0.0 0.6
                                            Ha
     Low-Lx Clusters: Summary

 Bulge  formation may be more efficient in
    more massive clusters

    but star formation in disks is suppressed
    in all clusters
     The CNOC2 groups project
   The CNOC2 redshift survey was aimed at measuring
    correlation strengths and star formation rates in the
    z=0.5 universe.
   Group selection and inital look at properties described
    in Carlberg et al 2001
   Durham involvement: follow-up observations with
    Magellan to gain higher completeness confirming
    complete samples of group members using LDSS-2.
   Overall aim of comparing star formation rates in
    groups at z=0.5 and locally (Mulchaey & Zabludoff
    etc, 2dfgrs coming soon!)
                        Bower, Mulchaey, Oemler, Carlberg et al - in prep.
        CNOC2 Groups at z~0.45
Deep spectroscopy with LDSS-2             Infrared (Ks) images from INGRID
on Magellan 1




Combined with CNOC2 multicolour photometry and spectroscopy, we can
determine group structure, dynamics, stellar mass, and star formation history.
LDSS2 on Magellan
             [OII]   [OII]
         CNOC2 Groups at z~0.45

Preliminary results
based on only 12            Balogh et al.
                            1997
CNOC2 groups

Have observed >30
groups to date
                                                Putting it all together…
                                                                               Wilson et al. 2002

                            20
Mean EW [OII] (Angstroms)




                                                                                          ?
                            15                                CNOC2 Groups
                                     ?          CNOC1 Field

                            10
                                     SDSS Field

                                                       Low-Lx Clusters
                            5
                                     Clusters




                                                                CNOC1 Clusters
                                     SDSS




                                 0                         0.3           0.5                        1.0
                                                         Redshift
        Local Groups in the 2dFGRS
Based on friends-of-friends
catalogue (V. Eke)


Mean SFR appears to be
suppressed in all galaxy
associations at z=0!


So where is star formation
going on??
                                The Environmental-Madau plot
                                                                                       Wilson et al. 2002

                            20
Mean EW [OII] (Angstroms)




                                                                                                  ?
                            15                                        CNOC2 Groups
                                     ?                  CNOC1 Field

                            10
                                     SDSS Field

                                                               Low-Lx Clusters
                                     2dF Clusters




                            5                       ?
                                                                        CNOC1 Clusters

                                 0                                 0.3           0.5                        1.0
                                                                 Redshift
                  Summary
 2dFGRS and SDSS: SFR-density relation shows
  critical density at 1 Mpc-2
 SFR suppressed in all dense regions, in
  structures more massive than groups
 Lack of strong evolution in clusters + abundance
  of structure above the critical threshold suggests
  environmental processes are important to global
  evolution.

    BUT: Strong evolution in group SFRs?