Download Why Does Star Formation Stop?

Galaxy Ecology
The role of galaxy environment in determining
the star formation history of the universe
Michael Balogh
ICC, University of Durham
Galaxy Ecology
1. Motivation: cosmological context of observations
2. The local universe: 2dF and Sloan surveys
3. Low mass clusters and groups at intermediate redshift
4. Clusters and groups at z~1 and beyond
Galaxy Ecology
1. Motivation: cosmological context of observations
2. The local universe: 2dF and Sloan surveys
Bob Nichol, Chris Miller, Percy Gomez (CMU), Ann Zabludoff (Arizona),
Tomo Goto (CMU, Tokyo), Vince Eke, Richard Bower (Durham),
Ian Lewis (Oxford) and many others…
3. Low mass clusters and groups at intermediate redshift
4. Clusters and groups at z~1 and beyond
Galaxy Ecology
1. Motivation: cosmological context of observations
2. The local universe: 2dF and Sloan surveys
3. Low mass clusters and groups at intermediate redshift
Richard Bower, Roger Davies, Ian Smail, Simon Morris,
Dave Wilman (Durham), John Mulchaey, Gus Oemler (Carnegie)
4. Clusters and groups at z~1 and beyond
Galaxy Ecology
1. Motivation: cosmological context of observations
2. The local universe: 2dF and Sloan surveys
3. Low mass clusters and groups at intermediate redshift
4. Clusters and groups at z~1 and beyond
Fumiaki Nakata, Ian Smail, Richard Bower (Durham)
Taddy Kodama, Ichi Tanaka, Toru Yamada (NAOJ)
Motivation:
Two questions: 1. Why does star formation decline?
2. What physical mechanisms operate
in dense environments?
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
Galaxy clusters:
the end of star formation?
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
CNOC: Galaxy populations
Measurements of [OII]
emission line for galaxies
in 15 clusters and the
surrounding field at z~0.3
[OII] closely related to star
formation rate (SFR)
Showed that average SFR
within the virialised regions
of clusters is much lower
than in lower density
regions
Balogh et al. 1997, ApJ 488, L75
Ha in Rich Clusters at z~0.3
LDSS++ with nod
and shuffle sky
subtraction, on
AAT
(Field)
Star formation
rate is low in all
clusters observed
Couch et al. 2001
ApJ 549, 820
Balogh et al. 2002
MNRAS, 335, 110
Tying star formation to
structure growth
Press-Schechter plot of
dark matter mass
evolution
Groups
Clusters
Normalised to 1011 Mo
Clusters are negligible; but
groups dominate and
evolve strongly
Thus, can environmental
processes be responsible
for SFR evolution?
Additional physics?
1. Ram-pressure stripping (Gunn & Gott 1972)
2. Collisions / harassment (Moore et al. 1995)
3. “Strangulation” (Larson et al. 1980; Balogh et al. 2000)
Additional physics?
1. Ram-pressure stripping (Gunn & Gott 1972)
2.
Collisions / harassment (Moore et al. 1995)
3.
“Strangulation” (Larson et al. 1980; Balogh et al. 2000)
short timescale
Quilis, Moore & Bower 2000
Additional physics?
1.
Ram-pressure stripping (Gunn & Gott 1972)
2. Collisions / harassment (Moore et al. 1995)
3.
“Strangulation” (Larson et al. 1980; Balogh et al. 2000)
important in
groups?
Additional physics?
1.
Ram-pressure stripping (Gunn & Gott 1972)
2.
Collisions / harassment (Moore et al. 1995)
3. “Strangulation” (Larson et al. 1980; Balogh et al. 2000)
long timescale
Timescales
Numerical model of
infall rate + assumed decay
rate of star formation =>
radial gradient in SFR
Radial gradients in CNOC
clusters suggest t ~2 Gyr
Suppressed star formation
within several Mpc of cluster
centre! What environment is
responsible?
Balogh, Navarro & Morris 2000
Diaferio et al. 2001
The local Universe:
Going beyond cluster cores…
The 2dFGRS and SDSS
1. 2dF Galaxy redshift survey:
•
•
spectra and redshifts for 220 000 nearby galaxies
only photographic plate photometry
2. Sloan digital sky survey:
•
•
goal is spectra for 1 million galaxies, with digital
photometry (ugriz)
First data release contains 186 240 galaxies
2dFGRS/SDSS Part I: 2dF clusters
A1620
Rvir
Data for 17 Abell-like clusters
Covers velocity dispersions
500 km/s - 1100 km/s
Region out to > 20 Rvir
extracted from the survey
Star formation rate measured
from Ha
1 degree
(data extracted over ~7 deg field)
Lewis, Balogh et al. 2002
MNRAS 334, 673
2dFGRS/SDSS Part I: 2dF clusters
Normalised star formation
rate measured from Ha in
17 nearby clusters
Field
Critical density:
~group scales
Identified a critical density
of ~1 Mpc-2, where
environmental effects
become important
This corresponds to low
density groups in the
infall regions of clusters
Lewis, Balogh et al. 2002
MNRAS 334, 673
2dFGRS/SDSS Part I: 2dF clusters
Field
SFR-Density Relation
Field
Field
Lewis et al. 2002
MNRAS 334, 673
2dFGRS/SDSS Part I: 2dF clusters
Field
SFR-Density Relation
c.f. Morphology-Density Relation
R>2 Rvirial
Field
Field
Lewis et al. 2002
MNRAS 334, 673
Star Formation Rate (Mo/yr)
2dFGRS/SDSS Part II: SDSS
Field 75th percentile
75th percentile
Median
Field median
Gomez et al. (2003)
Galaxy Surface Density
(Mpc-2)
2dFGRS/SDSS Part III: Groups
Compare groups with clusters and the field: does
the large-scale environment play any role?
2dFGRS/SDSS Part III: Groups
2dFgrs
Based on a friends-offriends algorithm
(Eke et al., in prep)
Effective at finding
small groups with
s«500 km/s
SDSS
Different algorithm,
includes colour
information (Miller et al.
in prep).
Effective at finding
more massive groups
2dFGRS/SDSS Part III: Groups
SFR of galaxies as a function of
group velocity dispersion
● 2dFGRS
● SDSS
Mean SFR appears to be
suppressed in all galaxy
associations at z=0!
There is a trend with group
mass, but this is due to the
different distributions of local
densities…
Balogh et al., in prep
Field
2dFGRS/SDSS Part III: Groups
75th %-tile
Field
Field
Median
Red hatched region: all galaxies (~30 000)
White lines: groups with indicated s
Balogh et al., in prep
Luminosity dependence
Balogh et al., in prep
Does any environment enhance
star formation?
Close pairs in the SDSS
ds~(Dv/250)2+(Dr/100)2
Dv~100 km/s
Dr~50 kpc
Balogh et al., in prep
Close pairs in SDSS groups
ds~(Dv/250)2+(Dr/100)2
Dv~100 km/s
Dr~50 kpc
Balogh et al., in prep
Groups at z~0.4
Outskirts of Clusters at z~0.4
Subaru image
Abell 851 at z=0.41
30 arcmin
Kodama et al. 2001
Outskirts of Clusters at z~0.4
Kodama et al. 2001
Critical density where
red sequence first
appears.
Scrit~4 Mpc-2
Corresponds to
density of infalling
groups, well outside of
cluster
Star formation in groups at z=0.2-0.5
1. Low-Lx Clusters at z=0.25
•
•
Factor ~10 less massive than CNOC clusters
HST imaging, extensive ground-based spectroscopy
2. 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
z=0.24
s=390
Cl0849
z=0.23
s=750
Cl1701
z=0.24
s=590
Cl1702
z=0.22
s=370
Cl0818
z=0.27
s=630
Cl0819
z=0.23
s=340
Cl1309
z=0.29
s=640
Cl1444
z=0.29
s=500
Lx ~ 1043 - 1044 ergs/s, ~ 10 X less massive than CNOC
Morphology-density relation
at z~0.25
Some evidence that disk
galaxies are more
common in groups than
clusters, for a given local
density.
Low Lx (groups)
The same is not true of
star formation rates,
however…
High Lx (clusters)
Balogh et al. 2002
ApJ 566, 123
Star Formation in Low-Lx
Clusters
Balogh et al.
1997
Spectroscopy for 172
cluster
members Mr< -19 (h=1)
SFR from [OII] emission
line
Distributions of massive
and low-mass clusters are
identical!
Therefore, there must be a
population of diskdominated galaxies with
low SFR…
Balogh et al. (2002)
MNRAS, 337, 256
Disks Without Star Formation
Cl 1309 id=83
z=0.2934
[OII]
B/T = 0.39
Wo (OII)=-2.64.0
Wo (Hd)=3.8 2.1
3” HST Image
Disks Without Star Formation
[OII]
Cl 1444 id=78
z=0.2899
B/T = 0.42
Wo (OII)=3.5 2.7
Wo (Hd)=4.9 1.3
3” HST Image
Disks Without Star Formation
Cl 0818 id=58
z=0.2667
[OII]
B/T = 0.19
Wo (OII)=-9.6 7.8
Wo (Ha)=22.1 11.6
Wo (Hd)=2.0 3.6
3” HST Image
Ha
Disks Without Star Formation
Cl 0841 id=20
z=0.2372
[OII]
B/T = 0.42
Wo (OII)=-0.2 1.2
Wo (Ha)=-1.4 0.6
Wo (Hd)=0.0 0.6
3” HST Image
Ha
CNOC2 Groups
1. Identified a sample of groups from original
survey (Carlberg et al. 2001 ApJ 552, 427)
2. Properties of these groups can be directly
compared with low redshift counterparts from
2dFgrs and SDSS
3. Durham involvement: follow-up observations
with Magellan to gain higher completeness
confirming complete samples of group
members using LDSS-2
CNOC2 Groups at z~0.45
Deep spectroscopy with LDSS-2
on Magellan 1 (~30 groups)
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 Magellan
[OII]
[OII]
30
CNOC2 groups at z~0.45
20
10
15
Within ~1 Mpc of
group centre, galaxy
SFR is low relative
to surrounding field
5
Compare with z=0
data to establish
evolution of the
“critial” density
0
Mean EW [OII] (Å)
25
Preliminary result for
7 groups
0
0.5
1.0
1.5
2.0
2.5
Distance from centre (Mpc)
Wilman et al. in prep.
CNOC2 Groups at z~0.45
Preliminary results
based on only 12
CNOC2 groups
Have observed >30
groups to date
Preliminary results for 13
Balogh et
al.
groups show
excess
star
1997
formation in groups,
compared with rich
clusters.
But is this due to
differences in density
distributions?
Wilman et al. in prep
Implications?
Implications: SFR Evolution
Scrit (z~0) ~ 1 Mpc-2
(Lewis et al. 2002)
Scrit (z~0.4) ~ 4 Mpc-2
(Kodama et al. 2001, corrected)
Critical density
-0.6
0.6
1.6
Implications: SFR Evolution
Global SFR evolves as
(1+z)1.7
So increases by ~70%
between z=0 and z=0.4
This is consistent with an
unevolving SFR-density
correlation if most of the
mass in Universe at z~0.4
is below Scrit
However, nature of SF
must be different at z~1
Implications: SFR Evolution
Global SFR evolves as
(1+z)1.7
So increases by ~70%
between z=0 and z=0.4
70% increase?
This is consistent with an
unevolving SFR-density
correlation if most of the
mass in Universe at z~0.4
is below Scrit
However, nature of SF
must be different at z~1
Implications: Physical mechanisms
Ram-pressure stripping
Strangulation
Galaxy interactions
Implications: Physical mechanisms
not important
in groups
Ram-pressure stripping
Strangulation
Galaxy interactions
Implications: Physical mechanisms
Ram-pressure stripping
Strangulation no dependence
on s
Galaxy interactions
Clusters and Groups at z~1
Groups at z > 1
1. Deep multicolour (VRi′z′JKs) images of Lynx
and Q1335+28 (z=1.2).
2. Proposals to observe high redshift radio
galaxies and radio-loud quasars: known to
reside in dense environments
•
•
IRIS2 narrow band Ha and [OIII] at z=2.3
GMOS/FORS2 narrow band filter + grism Ha and
[OII] spectroscopy at z=1.4, 1.47, 2.3
Lynx clusters: z=1.2
Subaru VRi’z’
INGRID JKs
Y (arcmin)
Identified 7 groups
around the clusters
from photometric
redshifts.
GMOS spectroscopy
pending
X (arcmin)
Nakata et al. (2002)
Groups around the Lynx clusters
Group at z=1.27, ~3 Mpc from
main cluster
GR3
CMR is present, perhaps with more
scatter and fewer bright galaxies
CL1
CL2
Nakata et al. in prep
Groups around the Lynx clusters
M*clus ~ 20.13
M*group ~ 21.80
Nakata et al. in prep
Overdensities around HizRG
z=1.44
z=1.59
Best et al. 2003
Conclusions
1.
Clusters and groups have a large impact on galaxy
star formation rates at the present day
2.
Bright galaxies have little density dependence; trends
driven by faintest galaxies
3. Observations just consistent with explanation of global
SFR evolution to z~0.4 as due to growth of clustering
4. Most likely physical mechanism for transformation is
galaxy-galaxy interactions.