Galaxy Ecology

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



Field

Field

Field



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


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?


Bulge LuminosityFunctions (at fixeddensity)

Bulge Creation or Disk Bulge Creation or Disk Destruction?Destruction?


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


z=0.2899

B/T = 0.42

Wo (OII)=3.5 2.7 Wo (H)=4.9 1.3

[OII]

H

3” HST Image


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


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?

Galaxy Ecology

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