mos scientific applications michael balogh university of durham
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MOS Scientific Applications
Michael BaloghUniversity of Durham
MOS Scientific Applications(mostly galaxy clusters)
Michael BaloghUniversity of Durham
Outline1. Galaxy Clusters: scientific motivation
2. Canadian Network for Observational Cosmology (CNOC)
3. More clusters and groups with MOS
4. Ultra-plex spectroscopy: H spectroscopy of 4 clusters at z~0.4
5. Future considerations
Why Clusters?
Why clusters?
1. Very rare objects, in the tail of the mass distribution. So very sensitive to cosmology
2. Largest structures just virialising today, so we can study the process of structure formation
3. Extreme environments can affect galaxy properties
University of Durham
Institute for Computational Cosmology
150 Mpc/h
dalla Vechia, Jenkins & Frenk
Renormalised relative to 1011 M☼
A Press-Schechter plot showing the growth of the mass structure of the universe
LCDM cosmologyRapid growth of structure
Groups
Clusters
Steidel et al. 1999
Why Does Star Formation Stop?Why Does Star Formation Stop?
Cluster environments inhibit star formation (Balogh et al. 1997; 1998)
Can the growth in the abundance of clusters explain the global decline of star formation?
Or is it related to internal galaxy properties?
Why MOS?
Clusters are ideal targets for MOS because:
1. high density of galaxies
2. close in velocity space, so can use narrow wavelength range to increase multiplex
3. Learn about cluster dynamics and galaxy properties from the same set of spectra
CNOC: Cluster masses
CNOC: GoalsSample: 15 X-ray luminous clusters from EMSS,
0.2<z<0.55
Goal to obtain 50-200 member redshifts per cluster, for a total of ~1500 (r~22)
Observations over large fields (~0.5 degree) to sample virialised region
Carlberg, Yee, Ellingson 1996 ApJS 102, 269
CNOC: Survey StrategyMOS on CFHT
1. 4 band-limiting filters to sample rest-frame ~3500Å – 4300 Å, at 4 redshift slices
2. Obtain ~30 spectra per 9′ field of view; 2-3 masks per field, 1-5 fields per cluster
3. Real-time operations:• Imaging, mask design, mask cutting, and
spectroscopy all done at the telescope
Carlberg, Yee, Ellingson 1996 ApJS 102, 269
CNOC: Survey Strategy
Carlberg, Yee, Ellingson 1996 ApJS 102, 269
CNOC: Results
1. Dynamical measurement of m
2. Mass profiles of clusters
3. Cluster galaxy properties
Dynamical measurement of m
1. From velocity and spatial distribution, determine cluster mass M and virial radius, R
2. Calculate mass-to-light ratio M/LCarlberg et al. 1996 ApJ 462, 32
Dynamical measurement of m
1. Assume average galaxy M/L is the same in clusters and in the field
2. Use the field sample from same survey to measure (M/L)crit = crit/j, where j is the luminosity density of the Universe
3. This calculation yields m~0.3; the most convincing evidence for low m at the time.
Carlberg et al. 1996 ApJ 462, 32
CNOC: Average mass profiles
Carlberg et al. 1997 ApJ 478, 462Carlberg et al. 1997 ApJ 485, L13
Dynamically determined average mass profile of the most massive clusters
In good agreement with predictions from simulations (Navarro, Frenk & White 1996)
CNOC: Galaxy populations
Balogh et al. 1997, ApJ 488, L75
Measurements of [OII] emission line for galaxies in 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
CNOC: Galaxy populations
Balogh et al. 1998, ApJ 504, L75
Showed presence of strong radial gradient in SFR. Always lower than the field
Gradient much steeper than expected from morphology-density relation
Observed relation
Morph-density relation
Field
CNOC: Galaxy populations
Balogh, Navarro & Morris 2000
Use numerical model ofinfall to estimate timescalefor disruption of SFR
Radial gradients in CNOCclusters suggest ~2 Gyr
CNOC: Remaining Questions
1. Are X-ray luminous clusters unusual?
2. Dust-obscured starburts? Is [OII] a good enough SFR indicator? Are data complete enough to rule out a small fraction of intense, cluster-induced starbursts?
3. How far does the cluster’s influence extend?
4. Is star formation sensitive to local effects (i.e. density) or global ones (i.e. clusters vs. groups)
1. Low Lx Clusters
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
Low Lx Clusters at z~0.25
Multiobject spectroscopy with MOSCA (Calar Alto) and LDSS2 (WHT)
No band-limiting filter, to allow measurement of H in some cases
Star Formation in Low-Lx Star Formation in Low-Lx ClustersClusters
Balogh et al. 1997
Spectroscopy for 172 cluster members Mr< -19 (h=1)
SFR from [OII] emission line
Identical to more massive clusters
Balogh, et al. 2002, MNRAS 337, 256
2. Dust-obscured starbursts?
300
200
100
0-1
00-2
00-3
00
-200 -100 0 100 200Dec
RA
AC114 (z=0.31)
Butcher-Oemler effect?
Does star formation takeplace in clusters at z>0 ?
Couch et al. 2001, ApJ 549, 820
Nod & Shuffle: LDSS++ Nod & Shuffle: LDSS++ (AAT)(AAT)
Band-limiting filter +microslit = ~800 galaxies per 7’ field
Nod & Shuffle: LDSS++ Nod & Shuffle: LDSS++ (AAT)(AAT)
Advantages:
1. Perfect sky subtraction. Allows observation of Hat z=0.31 (8600 Å)
2. Short slits = maximum multiplex
3. Trivial data reduction
Disadvantages:
1. Lose 2/3 of detector, unless you use an oversized CCD
2. Need √2 more exposure time, unless you nod along the slit
HH in Rich Clusters at z~0.3 in Rich Clusters at z~0.3
Couch et al. 2001 ApJ 549, 820 Balogh et al. 2002 MNRAS, 335, 110
LDSS++ with nod and shuffle sky subtraction, on AAT
No evidence for enhanced star formation
(Field)
3. Cluster sphere of influence
Cluster sphere of influence
Fibre based wide field surveys:
1. 2dF galaxy redshift survey • H in 11000 galaxies within 20 Mpc of 17 clusters,
down to MB=-19 (Lewis et al. 2002, MNRAS 334, 673)
2. Sloan digital sky survey• Volume-limited sample of 8600 galaxies from the
EDR, MR<-20.5 (Gomez et al. 2003, ApJ 584, 210)
SFR-Environment Relation in SFR-Environment Relation in the 2dFGRSthe 2dFGRS
Lewis et al. 2002MNRAS 334, 673
4. Galaxy Groups
The CNOC2 Field survey
1. Similar strategy to cluster survey, using MOS on CFHT to study field galaxies out to z~0.6
• Yee et al. (2000) ApJS 129, 475
2. Main goal to measure evolution of correlation function and star formation rates
• Carlberg et al. (2000) ApJ 542, 57• Lin et al. (1999) ApJ 518, 533
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~0.45CNOC2 Groups at z~0.45
LDSS2 on Magellan
CNOC2 Groups at z~0.45CNOC2 Groups at z~0.45
Combined with CNOC2 multicolour photometry and spectroscopy, we can determine group structure, dynamics, stellar mass, and star formation history
CNOC2 Groups at z=0.45CNOC2 Groups at z=0.45[OII] [OII]
CNOC2 Groups at z~0.45CNOC2 Groups at z~0.45[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
The Future: Clusters 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 H and [OIII] at z=2.3 • GMOS/FORS2 narrow band filter + grism H and
[OII] spectroscopy at z=1.4, 1.47, 2.3
Lynx clusters: z=1.2Lynx clusters: z=1.2Subaru VRi’z’
INGRID JKs
Identified 7 groupsaround the clustersfrom photometricredshifts.
GMOS spectroscopy pending
X (arcmin)
Y (
arcm
in)
Nakata et al. (2002)
Overdensities around HizRGOverdensities around HizRG
Best et al. 2003
z=1.59z=1.44
Conclusions
1. Clusters and groups have a large impact on galaxy star formation rates at the present day
2. Need to understand how cluster populations evolve to disentangle internal and external effects
3. MOS at high redshift essential. Nod-and-shuffle required to work at red wavelengths, but need full field of view.