TAUP 2001

Evolution of clustering in Evolution of clustering in COSMOS: a progress reportCOSMOS: a progress report

Luigi Guzzo (INAF, Milano)

N. Scoville, O. Le Fevre, A. Pollo, B. Meneux, & COSMOS Team

Basic goal of COSMOS: Basic goal of COSMOS: measure the interplay measure the interplay between the growth of large-scale structure and between the growth of large-scale structure and the formation and evolution of galaxy properties the formation and evolution of galaxy properties within it (morphology, SED, size, luminosity, within it (morphology, SED, size, luminosity, presence of central black hole, …)presence of central black hole, …)

Quantify local structure via moments of the Quantify local structure via moments of the galaxy distribution: galaxy distribution: mean density, two-point mean density, two-point correlation function, higher-order momentscorrelation function, higher-order moments

Goal here: Measure two-point correlation Goal here: Measure two-point correlation function as a function of redshift from photo-z function as a function of redshift from photo-z COSMOS catalogueCOSMOS catalogue

Final goal: measure evolution of how clustering Final goal: measure evolution of how clustering depends on galaxy properties depends on galaxy properties

Redshift-space correlations simply destroyed by Redshift-space correlations simply destroyed by photo-z errorsphoto-z errorsSolution: treat redshift errors as (very large) Solution: treat redshift errors as (very large) redshift-space distortions and use projected function redshift-space distortions and use projected function in z slicesin z slices

Usual effect of real to redshift-space mapping (using mock survey):Usual effect of real to redshift-space mapping (using mock survey):

Destructive effect of the large photo-z errors on redshift-space Destructive effect of the large photo-z errors on redshift-space correlation function:correlation function:

Recover diluted signal by projecting Recover diluted signal by projecting (r(rpp,,) along the ) along the line of sight and fitting a power-law real-space line of sight and fitting a power-law real-space correlation function correlation function (r)=(r/r(r)=(r/r00))--

• IAB < 24

• 150.83 < RA < 149.4 & 1.5 < DEC < 2.9

• Use very thick redshift slices (>> photo-z error):

• 0.2 – 0.6 40515 galaxies

• 0.4 – 0.8 47222 galaxies

• 0.6 – 1.0 50097 galaxies

• 0.8 – 1.2 34480 galaxies

• Compute and project power back onto w and project power back onto wpp(r(rpp))

• Fit power-law Fit power-law (r) and recover amplitude and slope (r) and recover amplitude and slope at each redshiftat each redshift

Application to May 2005 COSMOS photo-z Application to May 2005 COSMOS photo-z catalogue:catalogue:

Montecarlo realization of catalogue maskMontecarlo realization of catalogue mask

Results (blue) and comparison to VVDS (red)Results (blue) and comparison to VVDS (red)

Old results from Nov 2004 catalogue version Old results from Nov 2004 catalogue version

• Encouraging result: the catalogue has improved! The recovered evolution of the correlation length r0 and slope of (r) is fully consistent with what is measured in the VVDS spectroscopic survey (Le Fevre et al. astro-ph/0409135)

• Remaining problems: stars with wrong z still in

• Further improvements:

• Improve mock samples, including more realistic photo-z errors (on new Millennium simulation)

• Next science steps:

• Most obvious: measure clustering of morphological classes (with Capak et al.)

Remarks and perspectives:Remarks and perspectives:

Test with mock COSMOS: degrade z’s as for Test with mock COSMOS: degrade z’s as for photo-zphoto-z

Compute rCompute r00 and and for increasing for increasing photo-z errorsphoto-z errors

ZZphph=Z=Zspsp+G(+G(zz))

Where G(Where G(zz) is a ) is a random deviate random deviate extracted from a extracted from a Gaussian with Gaussian with dispersiondispersion

zz= = 00 (1+z (1+zspsp))

Crude first approximationCrude first approximation

Comparison with VVDS Comparison with VVDS indicates then that average indicates then that average error should be error should be 00~0.01~0.01

In reality, errors have In reality, errors have more complex behaviour more complex behaviour and systematic effect play and systematic effect play major role (ongoing refined major role (ongoing refined analysis)analysis)