1. Photoz
z=0.8
z=0.6
z=0.4
z=0.2
IAB<25
1.4Mio
galaxies
X-ray
contours

2. X-ray galaxy groups in zCOSMOS
Alexis Finoguenov
MPE/UMBC
+zCOSMOS team

3. View on baryons from COSMOS
X-ray+red sequence: 278
Xray+spectroscopy:
195
z< /175 91%
0.8<z<1 37/50 74%
z> / %
N(z)=>2
Alexis Finoguenov
View on baryons from COSMOS

4. View on baryons from COSMOS
X-ray only groups
Alexis Finoguenov
View on baryons from COSMOS

5. How X-ray groups are different from spectroscopic groups?
Spec. completeness
is better at low z
But drops faster with redshift

6. Comparison of a group definition
X-ray only
Spec-z groups with X-rays
Spec-z 3 member groups, no X-rays: stacked X-ray
@z>0.8 X-rays (`a 6.e-16 cgs) are more
sensitive group tracer
compared to IAB<22.5 galaxies
Inside dense LSS
Fraction of X-ray groups
increases by a factor of 2
Alexis Finoguenov
View on baryons from COSMOS

7. Stacked X-ray detection of Knobel groups
Redshift
Flux (cgs)
Lx ( keV)
M200
Msun
kT (keV)
1.6e-16
2.e42
1.7e13
0.7
9.e-17
1.e42
1.1e13
0.6
4.e-17
6.e40
0.4e13
0.3
0.37
1.e-16
4.e-16
8.e40
1.6e41
0.3e13 0.5e13
0.4
Alexis Finoguenov
View on baryons from COSMOS

8. Stacked detection
of spectro-z groups

9. View on baryons from COSMOS
Lx-sigma relation
Alexis Finoguenov
View on baryons from COSMOS

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

11. Resolving LSS with X-ray groups
Alexis Finoguenov
View on baryons from COSMOS

12. Simulations… Fraction of matter resolved in groups
Alexis Finoguenov
A. Faltenbacher, AF, N. Drory 2010 ApJ

13. Environmental dependence of galaxy mass function
Alexis Finoguenov
View on baryons from COSMOS

14. View on baryons from COSMOS
No change in HOD!
Alexis Finoguenov
View on baryons from COSMOS

15. Bump in galaxy mass function: centrals vs sattelites
Alexis Finoguenov
View on baryons from COSMOS

16. View on baryons from COSMOS
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.
Alexis Finoguenov
View on baryons from COSMOS

17. View on baryons from COSMOS
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!)
Alexis Finoguenov
View on baryons from COSMOS