Large-Scale Structure in the DEEP2
Galaxy Redshift Survey
Jeffrey Newman
Lawrence Berkeley National Laboratory
And
The DEEP2 Team
UCSC - August, 2004
Large-Scale Structure of the DEEP2
team
The DEEP2 Galaxy Redshift Survey, which uses the DEIMOS
spectrograph on the Keck II telescope, is studying both galaxy
properties and large-scale structure at z=1.
U.C. Berkeley
U.C. Santa Cruz
JPL
M. Davis (PI)
A. Coil
M. Cooper
B. Gerke
R. Yan
C. Conroy
S. Faber (Co-PI)
D. Koo
P. Guhathakurta
D. Phillips
C. Willmer
B. Weiner
R. Schiavon
K. Noeske
A. Metevier
L. Lin
N. Konidaris
G. Graves
P. Eisenhardt
LBNL
J. Newman
U. Hawaii
N. Kaiser
Princeton
D. Finkbeiner
U. Pitt.
A. Connolly
K survey (Caltech)
K. Bundy
C. Conselice
R. Ellis
LSS provides the link between galaxies
and their cosmological context
Nearly Normal(?) Galaxies
LCDM
LSS
Universe
UCSC - August, 2004
Outline
I.
The DEEP2 Redshift Survey
II.
Clustering of Galaxies in DEEP2
III. DEEP2 galaxies and their environments
IV. Galaxy groups in DEEP2
V.
Voids in DEEP2
UCSC - August, 2004
Scientific Goals of the
DEEP2 Galaxy Redshift Survey
1. Characterize the properties of galaxies (colors, sizes,
linewidths, luminosities, etc.) at z~1 for comparison to z~0
2.
Study the clustering statistics (2- and 3-pt. correlations) of
galaxies as a function of their properties, illuminating the nature
of the galaxy bias
3.
Determine N(s,z) of groups and clusters at high redshift,
providing constraints on m and w
4. Measure the small-scale “thermal” motions of galaxies at z~1,
providing a measure of the mass of the halos the galaxies are
within
UCSC - August, 2004
Comparison with Local Surveys
DEEP2 was designed to have comparable size and density to
the previous generation local redshift surveys and is
>50 times larger than past surveys at z~0.3-1.
1.00E+06
Number of Galaxies
SDSS
2dF
1.00E+05
DEEP2 is similar
to LCRS in sample
size, but at z~1
LCRS
DEEP2
1.00E+04
1.00E+03
1.00E+05
CFA+
SSRS
z~0
z~1
PSCZ
1.00E+06
1.00E+07
1.00E+08
Volume (h -3 Mpc3)
UCSC - August, 2004
DEEP2 has been made possible by
DEIMOS, a new instrument on Keck II
DEIMOS (PI: Faber)
and Keck provide a
unique combination
of wide-field
multiplexing (up to
160 slitlets over a
16’x4’ field), high
resolution (R~5000),
spectral range
(~2600 Å at highest
resolution), and
telescope size.
UCSC - August, 2004
A Redshift Survey at z~1
Observational details:
• 3 sq. degrees over 4 fields
• primary z~0.75-1.4 (preselected using BRI photometry)
• ~5·106 h-3 Mpc3 volume
• lookback 6 - 8.5Gyr
• >400 1-hour exposures
• >40,000 z’s to RAB=24.1
• 1200 l/mm: ~6500-9200 Å
• 1.0” slit: FWHM 68 km/s
Color cut used in 3 of 4
DEEP2 fields
UCSC - August, 2004
Redshift Distribution of Data: z~0.7-1.4
Our color cuts are very
successful! ~90% of our
targets are at z>0.75 and
we miss only 3% of high-z
objects.
Status:
- Designed as a
three-year survey
- Began summer 2002
- 80 night UC time
allocation is now complete
-Finished 3 of 4 fields, 4th
>75% done (will complete
in S06)
UCSC - August, 2004
Coordinated observations of
the Extended Groth Strip
(EGS)
Background: 2 x 2 deg
from POSS
Spitzer MIPS, IRAC
DEEP2 spectra
and Caltech / JPL
Ks imaging
HST/ACS
V,I (Cycle 13)
DEEP2/CFHT
B,R,I
GALEX NUV+FUV
Chandra & XMM:
Past coverage
Awarded (1.4Ms)
Plus VLA (6 & 21
cm), SCUBA, etc….
UCSC - August, 2004
LSS in DEEP2 vs. local surveys
Structure seen in
DEEP2 7 Gyr ago
looks similar to that
in SDSS (rescaling
by the cosmic
expansion); another
sign that we live in
a Universe with low
Om. Detailed studies
can test Dark
Energy models and
galaxy formation
scenarios.
UCSC - August, 2004
DEEP2 sees the same color
bimodality as SDSS, COMBO-17, etc.
to z~1.4
Willmer et al. 2005
Our R-band magnitude limit corresponds to ~4000Å rest-frame at
z=0.7, ~2800 Å at z=1.4 . As redshift increases, red galaxies of a
given luminosity fall out before blue ones. Nevertheless,
bimodality appears to persist to the limits of the survey, and is a
vital tool for many of our analyses.
UCSC - August, 2004
Galaxy Clustering in DEEP2
(for L>=L*, z=0.7-1.0, preliminary:)
red: r0=5.09 (0.11) g=1.95 (0.05)
blue: r0=3.56 (0.07) g=1.74 (0.05)
We are now performing
a second generation of
studies of the galaxy
correlation function
using volume-limited
samples and a much
larger dataset. Locally,
x(r) is roughly a powerlaw: (r0/r)g with r0~5
Mpc/h and g~1.8. Local
trends of correlation vs.
color persist at z~1.
Coil et al. 2005, in prep.
UCSC - August, 2004
x(rp,p) depends strongly on color
Red galaxies not only have a larger correlation length, but also
larger velocity dispersion/fingers of god: they
reside in more clustered / denser environments.
We detect coherent infall on large scales for both blue and red galaxies.
Coil et al. 2005, in prep.
UCSC - August, 2004
Clustering vs. Luminosity in DEEP2
We are starting to
measure correlation
statistics of galaxies as a
function of many other
properties: luminosity,
linewidth/velocity
dispersion, stellar mass,
morphology, etc. Many
comparisons to models
will soon be possible.
As at low z, brighter galaxies
cluster more strongly in DEEP2.
Coil et al. 2005, in prep.
UCSC - August, 2004
Galaxy Properties and Environment
SDSS
(Blanton et al. 2004)
color red
Cooper et al. 2005, in prep.
blue
DEEP2
blue
color
log overdensity
linear overdensity
We measure galaxy environments using projected 3rd-nearest neighbor
distance, shown to be near-optimal in Cooper et al. 2005 (accepted).
As at z~0, there is a strong trend of galaxy density with restframe
color. [OII] trends are weaker and explained by color.
red
UCSC - August, 2004
Environment over the CMD
SDSS, z~0.1
DEEP2, 0.75<z<1.05
redder
brighter
Basic trends from z~0 studies persist at z~1: e.g., the reddest and
brightest galaxies are preferentially found in dense environments.
Cooper et al. 2005, in prep.
UCSC - August, 2004
Environment over the CMD, II
Red galaxies
denser
Blue galaxies
brighter
However, unlike locally, red and blue galaxies have very similar trends
of environment vs. luminosity at z~1. Suggestive that the bright blue
galaxies we see at z~1 will be part of the red population at z~0.
Cooper et al. 2005, in prep.
UCSC - August, 2004
Galaxy groups in DEEP2
We can focus on galaxy populations in the densest regions by studying
groups of galaxies. We identify groups in DEEP2 by finding
overdensities in the galaxy distribution in redshift space using the VDM
algorithm of Marinoni et al. (2002).
position
l, z
Group in early DEEP2 data
s~250 km/sec
We are identifying groups in
DEEP2 not only to study
galaxy evolution, but also
because their apparent
abundance provides a test of
dark energy models. (N.B.
For our purposes, “clusters”
are just especially massive
groups.)
UCSC - August, 2004
Evolution of blue fraction in groups
We define the blue fraction using
galaxies to the left of a limit shown
by the dashed line in the CMDs
below (to which we are complete at
all z), dividing at the dotted line.
Blue fraction is lower in groups
than the field, but appears to be
converging at z~1.1.
Gerke et al. 2005, in prep. (SEE POSTER!)
UCSC - August, 2004
Group & galaxy correlation functions
We can also use correlation
statistics to study the
relationship between galaxies
and groups. The group-galaxy
cross-correlation shows how
galaxies are clustered within
and around groups. Red
galaxies are preferentially
found near the centers of
DEEP2 groups, while blue
galaxies actively avoid them.
We’re testing the same thing
in many ways…
Coil et al. 2005, submitted, astro-ph/0507647
UCSC - August, 2004
Group-based correlations are sensitive
to relationship between galaxies & halos
Mock catalogs which match early DEEP2 x(r) predict very different
clustering of group galaxies or field galaxies than observed.
Coil et al. 2005, submitted, astro-ph/0507647
UCSC - August, 2004
Void statistics at z~1 and z~0
We have studied the Void Probability Function (VPF) - the
probability that a sphere of radius R centered at a random point
contains no galaxies - using both DEEP2 and SDSS data.
The VPF can be described by an
infinite sum of higher-order
correlation functions and potentially
contains a wealth of information on
biasing, etc. However, a simple
“negative binomial” ansatz predicts
the observed VPF very well, given
only the two-point correlation
function and the number density of
the tracer used.
Conroy et al. 2005, submitted, astro-ph this week
UCSC - August, 2004
Measuring the VPF
DEEP2
“Negative binomial” model
matches VPF for dark matter halo
centers (not mass points) in
simulations - insensitive to halo
model parameters.
Conroy et al. 2005, submitted
Voids are larger for brighter /
redder / less common galaxies.
“Negative binomial” ansatz
works fairly well for both
DEEP2 & SDSS data, for all
subsamples and scales probed.
SDSS
UCSC - August, 2004
ITo understand the evolution of galaxies, we need to
know not just how things change… but where!
DEEP2 is opening many new windows
on galaxies by allowing us to study them
within their LSS context over a >7
billion year span. Many more analyses
still to come!
UCSC - August, 2004
Other recent and upcoming papers include:
•
•
•
•
•
•
•
•
•
•
•
Angular clustering of galaxies: Coil et al., 2004, ApJ, 617, 765
DEEP2 survey strategy & dark energy: Davis et al.,astro-ph/0408344
Evolution of close-pairs/merger rates: Lin et al., 2004, ApJ, 617, 9
DEEP2 Group catalog: Gerke et al., 2005, ApJ, 625, 6
Satellite galaxy kinematics: Conroy et al., astro-ph/0409305
Environment in deep redshift surveys: Cooper et al., acc. (0506518)
DETF white paper: Davis et al., astro-ph/0507555
Luminosity function: Willmer et al. & Faber et al., submitted
Metallicities of DEEP2 galaxies: Shapley et al., submitted
K+A galaxies in DEEP2 : Yan et al., in prep. (SEE POSTER!)
Test for evolution in fine structure constant: Newman et al., in prep.
First semester’s data is now public:
http://deep.berkeley.edu/DR1
UCSC - August, 2004
Color vs. Equivalent Width of [OII]
Red galaxies have low [OII] equivalent width, while blue galaxies
span a wide range. It appears that the scatter in this relation is most
likely not due to environment. Color correlates better with
environment than [OII] EW; there is little residual trend when env.
vs. color trend is removed (diamonds).
UCSC - August, 2004
Why search for groups in DEEP2?
In Newman et al. (2002) we
showed that the apparent
abundance of groups as a
function of redshift and
velocity dispersion,
dN(s,z)/dzds, provides a
useful test of the dark energy
equation of state. For
modest-mass groups, this is
dominated by differences in
the volume element (which
varies by 3x between w=0 and
w=-1), though affected by the
growth factor as well.
Changes to constraint estimates
We have recently added
completely-covariant (i.e.
pessimistic) systematic errors
to our constraint estimates, and
fixed an error in our growth
factor calculations noticed by
Eric Linder.
Here we plot the new 95%
error contours for a LCDM
model resulting from
combining DEEP2 with SDSS
results, including systematic
errors but assuming s8 is
Tests with mocks indicate we can use
known.
groups with s>350 km/sec reliably.
Constraints for w=-0.7
As for most
techniques,
constraints are a bit
stronger for w=-0.7
models than w=-1.
We are beginning to measure w…
N(s) from 314 groups
are plotted. Even
ignoring redshift
information, the
sensitivity to w is clear.
However, the group
abundance also depends
on other parameters we
need to tie down…
Furthermore, we are
still checking
systematics!!
Gerke et al. 2005
UCSC - August, 2004
s8 Dependence of N(s)
The normalization of the
Power Spectrum, s8, can
strongly influence the
abundance of groups, as if
s8 is greater, fluctuations
are larger and groups are
more common.
To be able to constrain w,
we need an accurate
measurement of s8 . New
SDSS studies are now
making this possible (e.g..
Seljak et al. 2004).
UCSC - August, 2004
M Dependence of N(s)
The number of highredshift groups is
sensitive to M .
However, given a value
of s8, the z~0 SDSS
cluster abundance will
tie down M very
tightly (Newman et al.
2002).
Velocity bias and N(s)
A final degenerate
parameter is the “velocity
bias”, bv. This is the
factor by which the
velocity dispersion of
galaxies in a cluster
differs from the dark
matter dispersion. Some
simulations currently
favor bv=1.1, others 0.9.
In the end, our results
match bv~1.1, M ~0.4,
s8~1, or w ~-1.25.
UCSC - August, 2004
Some conclusions
• Our results are consistent with no evolution in the fine
structure constant from z~0 to z~0.7.
• Large surveys can make possible many kinds of
scientific discoveries, and go far beyond whatever topics
and fields are thought to be interesting when the survey is
designed.
•Future baryonic oscillation surveys may be able to do
very well at constraining evolution in , if they have the
resolution and right wavelength coverage; they will have
large samples of bright, star-forming galaxies at z~1.
100x larger samples may be feasible.
UCSC - August, 2004
Looking for changes from z=0
Start with the
simplest thing:
combine all
data with z>0.6
into one bin,
and measure
<D2>.
UCSC - August, 2004
Results - exploring d/dt
UCSC - August, 2004
Redshift Maps in 4 Fields: z=0.7-1.3
Cone diagram of 1/12 of the full DEEP2 sample
UCSC - August, 2004
Finding groups in DEEP2
We find groups using the locations of galaxies in redshift space - no
photometric information is used, just the overdensity in the 3d galaxy
distribution.
position
l
Group in early DEEP2 data
In particular, we are
using the VoronoiDelaunay Method of
Marinoni et al. (2002),
which has been optimized
for use at high z and
performs well. (For our
purposes, “clusters” are
just especially massive
groups.)
UCSC - August, 2004
Why search for groups in DEEP2?
In Newman et al. (2002) we
showed that the apparent
abundance of groups as a
function of redshift and
velocity dispersion,
dN(s,z)/dzds, provides a
useful test of the dark energy
equation of state. Here we
plot the expected 95% error
contours for LCDM from
combining DEEP2 with SDSS
results, including systematics.
Tests with mocks indicate we
can use groups with s>350
km/sec for this.
First DEEP2 Group Catalog
We currently have group catalogs for 3 fields
Gerke et al. 2005, astro-ph/0410721
UCSC - August, 2004
Group Richness Distribution
Ngroups
(s>200 km/s)
group richness
Most groups have N=2-3 within our sample
(but we are sampling ~L* galaxies - there are many more fainter galaxies
in these groups)
Gerke et al. 2005, astro-ph/0410721
UCSC - August, 2004
Galaxy properties in groups
We are using the group
catalog to study galaxy
properties within
groups. We find that
redder, early-type
galaxies are
preferentially found in
groups at z~1, similar to
local trends.
Gerke et al. 2005
0.7<z<0.9
UCSC - August, 2004
The Voronoi-Delaunay Method
Group-Finder (VDM)
• We use the Voronoi cell volume
to find dense regions: potential
‘group seeds’.
• Then we use the Delaunay
mesh, its geometric dual, to
estimate density of group core.
• Then we search adaptively for
group members based on
central density estimate.
• We have been testing VDM
extensively using realistic
DEEP2 mock catalogs to
optimize the group-finder and
test our systematics.
UCSC - August, 2004
K+A Post-Starburst Galaxies
Have ~100 galaxies with
features of K stars (old,
elliptical-type spectra)
and A stars (youngish,
<1 Gyr) - K+A galaxies.
Yan et al. in prep
K+A galaxies show little on-going star-formation (lack of OII) but
strong Balmer features due to recent star-formation (within 1 Gry) ‘post-starburst galaxies’. These objects are rare, but we cover a
large enough volume to find a large statistical sample.
UCSC - August, 2004
K+A Post-Starburst Galaxies
These galaxies populate
the ‘gap’ in the color bimodality and lie on the
red sequence - they may
provide clues as to how
galaxies move onto the
red sequence. We are
currently estimating
evolution in the rate of
K+A galaxies from z=1
to z=0 and investigating
their morphologies and
environments.
Yan etUCSC
al. -in
prep
August, 2004