Galaxy EcologyThe role of galaxy environment in determining the star formation history of the universe
Michael BaloghICC, 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 EcologyThe role of galaxy environment in determining the star formation history of the universe
Michael BaloghICC, 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
B) External? Hierarchical build-up of structure inhibits star formation
A) Internal? i.e. gas consumption and “normal” aging
Steidel et al. 1999
SFR ~ (1+z)1.7
(Wilson, Cowie et al. 2002)
Why Does Star Formation Why Does Star Formation Stop?Stop?
Renormalised relative to 1011 Msol
A Press-Schechter plot showing the growth of the mass structure of the universe
LCDM cosmologyRapid growth of structure
Groups
Clusters
Galaxy clusters: the end of star Galaxy clusters: the end of star formation?formation?
Abell 2390 (z~0.23)Abell 2390 (z~0.23)3.6 arcmin R image from
CNOC survey(Yee et al. 1996)
Butcher-Oemler effect?
Does star formation takeplace in clusters at z>0 ?
HH in Abell 2390 in Abell 23903.6 arcmin
Balogh & Morris 2000
300
200
100
0-1
00-2
00-3
00
-200 -100 0 100 200Dec
RA
AC114 (z=0.31)
(Couch et al. 2001)
Nod & Shuffle: LDSS++ Nod & Shuffle: LDSS++ (AAT)(AAT)
band-limiting filter +microslit = ~800 galaxies per 7’ field
HH in Rich Clusters at z~0.3 in Rich Clusters at z~0.3
Balogh et al. 2002MNRAS, 335, 110
Couch et al. 2001ApJ 549, 820
LDSS++ with nod and shuffle sky subtraction, on AAT
(Field)
Fine for clusters – but what about groups?
Groups Clusters
MechanismsMechanisms
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
ICM
Gunn & Gott, 1972
Examples of galaxy collisionsin the real universe and in a simulation (Moore et al 1995)
Strangulation: removal of the gas halo
First suggested by Larson, Tinsley & Caldwell, 1984
Could occur in groups
Strangulation ?Strangulation ?
Use numerical model ofinfall to estimate timescalefor disruption of SFR
Radial gradients in CNOCclusters suggest ~2 Gyr
(Balogh, Navarro & Morris 2000)
Where do Where do environmental effects environmental effects become important?become important?
The Local UniverseThe Local Universe
2dFGRS (Lewis et al. 2002, MNRAS 334, 673)
– H in 11000 galaxies within 20 Mpc of 17 clusters, down to MB=-19
– SFR-density, SFR-radius relations in clusters with >400 km/s
SDSS (Gomez et al. 2003, ApJ 584, 210)
– 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
A1620
Rvir
(data extracted over ~7 deg field)
Data for 17 Abell-like clusters Covers velocity dispersions 500 km/s - 1100 km/s
Region out to > 20 Rvir extracted from the survey
Major advantages: ● Star formation rate measured from H
● Complete redshift information - no need to subtract background!
● Compare with surrounding field directly
1 degree
SFR-Environment Relation in SFR-Environment Relation in the 2dFGRSthe 2dFGRS
Lewis et al. 2002MNRAS 334, 673
SFR-Radius RelationField
Field
Field
SFR-Density Relation
SFR-Environment Relation in SFR-Environment Relation in the 2dFGRSthe 2dFGRS
Lewis et al. 2002MNRAS 334, 673
Field
Field
Field
SFR-Environment Relation in SFR-Environment Relation in the 2dFGRSthe 2dFGRS
Lewis et al. 2002MNRAS 334, 673
R>2 Rvirial
SFR-Density Relation
c.f. Morphology-Density Relation
Field
Field
Field
SFR-Environment relation in SFR-Environment relation in the SDSSthe SDSS
Sta
r F
orm
atio
n R
ate
(Mo/
yr)
Galaxy Surface Density (Mpc-2)
Median
75th percentile
Gomez et al. (2003)
Field 75th percentile
Field median
Groups at z=0.2-0.5Groups 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
spectroscopyCNOC2 groups at z=0.45
– Spectroscopy with LDSS-2 on Magellan 6.5-m– Goal is complete group membership to M*+1
Low LLow Lxx Clusters at z~0.25 Clusters at z~0.25
Cl0818z=0.27=630
Cl0819z=0.23=340
Cl0841z=0.24=390
Cl0849z=0.23=750
Cl1309z=0.29=640
Cl1444z=0.29=500
Cl1701z=0.24=590
Cl1702z=0.22=370
Lx ~ 1043 - 1044 ergs/s, ~ 10 X less massive than CNOC
Morphologies in Low-Lx Morphologies in Low-Lx Clusters at z~0.25Clusters at z~0.25
Disks
Bulges
Inte
rmed
iate
B/T<0.4
B/T>0.6
Balogh et al. 2002, ApJ 566, 123
Bulge/Total Fractions from GIM2D (Simard et al. 2002)
Low-LLow-Lxx Disk Fractions Disk Fractions
Balogh et al. 2002, ApJ 566, 123
High-Lx Clusters from the lensing sample of Smith et al. 2001
(from Medium Deep Survey)
Morphology-density relationMorphology-density relationat z~0.25at z~0.25
Balogh et al. 2002ApJ 566, 123
Disk LuminosityFunctions (at fixeddensity)
Bulge Creation or Disk Bulge Creation or Disk Destruction?Destruction?
Balogh et al. 2002, ApJ 566, 123
Bulge LuminosityFunctions (at fixeddensity)
Bulge Creation or Disk Bulge Creation or Disk Destruction?Destruction?
Balogh et al. 2002, ApJ 566, 123
Star Formation in Low-Lx Star Formation in Low-Lx ClustersClusters
Balogh et al. 1997
Spectroscopy for 172 clustermembers Mr< -19 (h=1)
SFR from [OII] emission line
Balogh et al. (2002)MNRAS, 337, 256
[OII]
3” HST Image
Disks Without Star Disks Without Star FormationFormationCl 1309 id=83
z=0.2934
B/T = 0.39
Wo (OII)=-2.64.0
Wo (H)=3.8 2.1
[OII]
3” HST Image
Disks Without Star Disks Without Star FormationFormationCl 1444 id=78
z=0.2899
B/T = 0.42
Wo (OII)=3.5 2.7 Wo (H)=4.9 1.3
[OII]
H
3” HST Image
Disks Without Star Disks Without Star FormationFormationCl 0818 id=58
z=0.2667
B/T = 0.19
Wo (OII)=-9.6 7.8 Wo (H)=22.1 11.6Wo (H)=2.0 3.6
[OII]
H
3” HST Image
Disks Without Star Disks Without Star FormationFormationCl 0841 id=20
z=0.2372
B/T = 0.42
Wo (OII)=-0.2 1.2 Wo (H)=-1.4 0.6Wo (H)=0.0 0.6
Low-Lx Clusters: SummaryLow-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 projectThe 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~0.45CNOC2 Groups at z~0.45Deep spectroscopy with LDSS-2 on Magellan 1
Infrared (Ks) images from INGRID
Combined with CNOC2 multicolour photometry and spectroscopy, we can determine group structure, dynamics, stellar mass, and star formation history.
LDSS2 on MagellanLDSS2 on Magellan[OII] [OII]
CNOC2 Groups at z~0.45CNOC2 Groups at z~0.45
Preliminary resultsbased on only 12 CNOC2 groups
Have observed >30groups to date
Balogh et al. 1997
Putting it all together…Putting it all together…
Redshift0 0.3 0.5
5
10
Mea
n E
W [
OII
] (A
ngst
rom
s)
CNOC1 Clusters
Low-Lx Clusters
SD
SS
C
lust
ers
15
20
1.0
Wilson et al. 2002
?CNOC2 Groups
SDSS Field
CNOC1 Field?
Local Groups in the 2dFGRSLocal Groups in the 2dFGRSBased 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??
Galaxy pairsGalaxy pairs
v < 100 km/s
The Environmental-Madau The Environmental-Madau plotplot
Redshift0 0.3 0.5
5
10
Mea
n E
W [
OII
] (A
ngst
rom
s)
CNOC1 Clusters
Low-Lx Clusters
2d
F C
lust
ers
15
20
1.0
Wilson et al. 2002
?CNOC2 Groups
SDSS Field
CNOC1 Field?
?
SummarySummary 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?
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