Cosmology and Dark Energy with the DEEP2 Galaxy Redshift Survey

Transcription

1 Cosmology and Dark Energy with the DEEP2 Galaxy Redshift Survey Marc Davis University of California, Berkeley And The DEEP2 Team

2 The DEEP2 Collaboration 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 M. Davis (PI) A. Coil M. Cooper B. Gerke R. Yan C. Conroy LBNL J. Newman U. Hawaii N. Kaiser U.C. Santa Cruz 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 JPL P. Eisenhardt Princeton D. Finkbeiner U. Pitt. A. Connolly K survey (Caltech) K. Bundy C. Conselice R. Ellis

3 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(σ,z) of groups and clusters at high redshift, providing constraints on Ω m and w 4. Measure the small-scale thermal motions of galaxies at z~1, providing a mass scale for halo models (measuring Ω m and bias, in the paradigm when DEEP2 was designed)

4 Comparison with Other Surveys DEEP2 was designed to have comparable size and density to previous generation local redshift surveys and is >50 times larger than previous surveys at z~ Number of Galaxies 1.00E E E E+03 CFA+ SSRS PSC Z LCRS 2dF DEEP2 1.00E E E E+08 Volume ( h -3 Mpc 3 ) SDSS z~0 z~1 DEEP2 is similar to LCRS in sample size but at z=1 - with a very different geometry: ~ h -3 Mpc 3 per field (LCDM)

5 A Redshift Survey at z=1: Studying Evolution: Age of the Universe = 13.7 Gyr z=0.7 - ~6.0 Gyr ago z=1.0 - ~7.5 Gyr ago z=1.4 - ~8.5 Gyr ago Within DEEP2 we are surveying 2.5 Gyr or ~20% of the history of the Universe, and SDSS/2dF comparisons give ~3x this baseline Observational details: 3 sq. degrees 4 fields (0.5 o x <2 o ) primary z~ (preselected using BRI photometry) >40,000 redshifts ~ h -3 Mpc 3 80 Keck nights One-hour exposures R AB = l/mm: ~ Å 1.0 slit: FWHM 68 km/s

6 Coordinated observations of the Extended Groth Strip (EGS) Spitzer MIPS, IRAC DEEP2 spectra and Caltech / JPL K s 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. Background: 2 x 2 deg from POSS

7 The Extended Groth Strip is ~78% finished The Extended Groth Strip has become a magnet for multiwavelength studies, including wide-field coverage by HST, Spitzer, GALEX, the VLA, CFHT Legacy, etc. We plan to complete this critical field in 2006.

8 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 collecting area.

9 DEEP2 slitmask spectroscopy λ position Using custom-milled slitmasks with DEIMOS we are obtaining spectra of ~150 targets at a time. A total of 400 slitmasks will be required for the survey; we can tilt slits up to 30 degrees to obtain rotation curves.

10 Pre-selection of high-z targets with using colors Plotted are the colors of some galaxies with known redshifts in our fields; those at low redshift are plotted as blue, those at high redshift as red. We use a simple color cut defined by three line segments to select galaxies at z>0.75. We do not apply these color cuts in the EGS!

11 Redshift Distribution of Data: z~ 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 currently >90% complete - finished 3 of 4 fields now, will finish EGS next Spring

12 Completeness of Fields 2,3,4. These fields were all observed With.7< z <1.4

13 LSS in DEEP2 vs. local surveys Structure seen in DEEP2 7 Gyr ago looks similar to that in SDSS (rescaling by cosmic expansion); another sign that we live in a Universe with low Ω m. We are studying LSS using 2-point correlation functions, local density (environment) measures, and a group finder.

14 Redshift Maps in 4 Fields: z= Cone diagram of 1/12 of the full DEEP2 sample

15 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. Group in early DEEP2 data In particular, we are using the Voronoi- Delaunay 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.)

16 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(σ,z)/dzdσ, provides a useful test of the dark energy equation of state. Here we plot the expected 95% error contours for ΛCDM from combining DEEP2 with SDSS results, including systematics. Tests with mocks indicate we can use groups with σ>350 km/sec for this.

17 First DEEP2 Group Catalog Groups with σ>350 km/s We currently have group catalogs for 3 fields Gerke et al. 2005, astro-ph/

18 Group Richness Distribution N groups (σ>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/

19 What if we had 20x as much area? Future baryonicoscillation surveys could be used to make this same measurement if they are densely sampled. A 60 square degree survey could yield tight constraints on w - IF systematics are wellconstrained.

20 Constraints for w=-0.7 As for most techniques, constraints are a bit stronger for w=-0.7 models than w=-1.

21 Measurement of w in DEEP2 Survey N(σ) 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!!

22 σ 8 Dependence of N(σ) The normalization of the Power Spectrum, σ 8, can strongly influence the abundance of groups, as if σ 8 is greater, fluctuations are larger and groups are more common. To be able to constrain w, we need an accurate measurement of σ 8. New SDSS studies are now making this possible (e.g.. Seljak et al. 2004).

23 The number of highredshift groups is sensitive to Ω M. However, given a value of σ 8, the z=0 SDSS group abundance will tie down Ω M very tightly (Newman et al. 2002). Ω M Dependence of N(σ)

24 A final degenerate parameter is the velocity bias, b v. This is the factor by which the velocity dispersion of galaxies in a cluster differs from the dark matter dispersion. Some simulations currently favor b v =1.1, others 0.9. In the end, our results match b v ~1.1, Ω M ~0.4, σ 8 ~1, or w ~ Velocity bias and N(σ)

25 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 <z<0.9

26 Advantages of a high-dispersion survey The high resolution used for DEEP2 observations yields well-resolved linewidths for all objects, and rotation curves as a free byproduct for thousands. Shown are four 2d spectra exhibiting resolved [OII] emission and the derived circular velocity Vc(r). Cooper etnovember, al Kona, 2005

27 DEEP2 sees the same color bi-modality as SDSS, COMBO-17, etc. to z~1.4 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. Willmer et al. 2005

28 Galaxy Properties and Environment We measure galaxy environments using projected 3rd-nearest neighbor distance, shown to be near-optimal in Cooper et al (submitted). There are strong trends of galaxy density with restframe color and [OII] equivalent width (a proxy for star formation rate); the color trend can explain the [OII] one. log density blue color red Cooper et al [OII] equivalent width (SFR)

29 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. We are currently matching the DEEP2 colors and magnitudes to SDSS to look for evolution in environmental dependence between z=1 and z=0.

30 Environment over the CMD SDSS, z~0.1 DEEP2, 0.75<z<1.05 redder brighter Trends from z~0 studies persist at z~1: e.g. redder or brighter galaxies are preferentially found in dense environments. Cooper et al. 2005

31 Galaxy Clustering as a Function of Color We are now working on our second round of studies of the galaxy correlation function. Locally, ξ(r) is roughly a power-law: (r 0 /r) γ w/ r 0 ~5 Mpc/h and γ~1.8 (for L>=L*, z= , preliminary:) red: r 0 =5.09 (0.11) γ=1.95 (0.05) blue: r 0 =3.56 (0.07) γ=1.74 (0.05) Coil et al. 2005

32 ξ(r p,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.

33 Group-galaxy cross-correlation function 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. 2005a

34 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 Gyr) - post-starburst galaxies. These objects are rare, but we cover a large enough volume to find a large statistical sample.

35 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 et al. in prep

36 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/ Evolution of close-pairs/merger rates: Lin et al., 2004, ApJ, 617, 9 Satellite galaxy kinematics: Conroy et al., astro-ph/ Measuring environment in deep redshift surveys: Cooper et al., astro-ph/ Luminosity function: Willmer et al. & Faber et al., astroph/ , astro-ph/ Group correlation function: Coil et al., astro-ph/ K+A galaxies in the DEEP2 sample: Yan et al., in prep. Void statistics in the DEEP2 sample: Conroy et al., astro-ph/ Overview of the DEEP2 sample: Faber et al., in prep. Evolution of the Fine Structure Constant: Newman et al., in prep. First semester s data is now public: