1

Photozz=0.8z=0.6z=0.4z=0.2

IAB<25

1.4Mio galaxies

X-raycontours

X-ray galaxy groups in zCOSMOS

Alexis FinoguenovAlexis FinoguenovMPE/UMBCMPE/UMBC

+zCOSMOS team+zCOSMOS team

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COSMOS 3

N(z)=>2

X-ray+red sequence: 278Xray+spectroscopy:195z<0.8 152/175 91%0.8<z<1 37/50 74%z>1 6/53 11%

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COSMOS 4

X-ray only groups

How X-ray groups are different from spectroscopic groups?

5

Spec. completeness is better at low zBut drops faster with redshift

Comparison of a group definition

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COSMOS 6

X-ray onlySpec-z groups with X-raysSpec-z 3 member groups, no X-rays: stacked X-ray signal @<2.e-16>@z>0.8 X-rays (`a 6.e-

16 cgs) are more sensitive group tracercompared to IAB<22.5 galaxies

Inside dense LSSFraction of X-ray groupsincreases by a factor of 2

Stacked X-ray detection of Knobel groups

Redshift Flux (cgs) Lx (0.1-2.4 keV)

M200Msun

kT (keV)

0.9-1.1 1.6e-16 2.e42 1.7e13 0.7

0.7-0.9 9.e-17 1.e42 1.1e13 0.6

0.4-0.7 4.e-17 6.e40 0.4e13 0.3

0.1-0.30.37

1.e-16 4.e-16

8.e40 1.6e41

0.3e13 0.5e13

0.30.4

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COSMOS 7

8

Stacked detectionof spectro-z groups

Lx-sigma relation

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COSMOS 9

10

LSS at 0.12, 0.22, 0.34, 0.37, 0.51, 0.73, 0.89(Optical groups:0.22,0.36,0.38)

K.Kovac

Resolving LSS with X-ray groups

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COSMOS 11

12A. Faltenbacher, AF, N. Drory 2010 ApJ

Fraction of matter resolved in groups

Simulations…

Alexis Finoguenov

Environmental dependence of galaxy mass function

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COSMOS 13

No change in HOD!

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COSMOS 14

Bump in galaxy mass function:centrals vs sattelites

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COSMOS 15

Conclusions

X-ray groups approach the status of being spectroscopically confirmed.

X-ray groups are not a subsample of spectroscopic groups

Groups are tracers of density field and can be used to overcome to sample variance.

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COSMOS 16

People involved Masayuki Tanaka – properties of galaxies in X-ray groups using

zCOSMOS Stefania Giodini – HOD of galaxies, galaxy mass function, fossil groups Alexie Leauthaud – properties of BCGs Berian James – conditional mass function – modeling Andreas Faltenbacher – conditional mass function – simulations Katarina Kovac – density fields Angela Iovino, Michol Bolzonella, Olga Cucciatti – properties of galaxies Viola Allevato (my PhD student) – clustering analysis Michael Ballogh – 10 groups at z~0.9 with Gemini Masayuki Tanaka – groups at z>1 with Subaru Mara Salvato – high-z clusters Simona Mei et al. FORS2 program – already 350 redshifts for groups

added (or 30% of total number) And likely you! (a number of on-going efforts!)

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COSMOS 17