Santiago Chile (5-9 Dec 2005) 1 “Groups of Galaxies in the nearby Universe” ESO 2005 workshop...

Santiago Chile(5-9 Dec 2005) 1

“Groups of Galaxies in the nearby Universe” ESO 2005

workshop

X-ray Properties of a Mass-X-ray Properties of a Mass-Selected Group CatalogSelected Group Catalog

P. Mazzotta

University of Roma “Tor Vergata”, Roma, ItalyAnd

Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA



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CollaboratorsCollaborators

M. Balogh M. Balogh R. BowerR. Bower A. Edge A. Edge V. Eke V. Eke T. PonmanT. Ponman T. TheunsT. Theuns

H. H. BohringerBohringer

C. CollinsC. Collins M. Colless M. Colless S. Maddox S. Maddox J. Peacock J. Peacock



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Overview of our projectOverview of our project The observed X-ray luminosities of groups are inconsistent The observed X-ray luminosities of groups are inconsistent

with a simple model of shock-heated ICM during the group with a simple model of shock-heated ICM during the group collapse:collapse:

the observed luminosities are much lower than the the observed luminosities are much lower than the predicted onespredicted ones

It is has been suggested that a combination of pre-heating, It is has been suggested that a combination of pre-heating, gas cooling and energy injection removes low entropy gas, gas cooling and energy injection removes low entropy gas, reducing the system's X-ray luminosity. reducing the system's X-ray luminosity.

The extent of this process is uncertain because all galaxy The extent of this process is uncertain because all galaxy group catalogues have been X-ray selected.group catalogues have been X-ray selected.

A proper analysis would require instead a mass-selected A proper analysis would require instead a mass-selected group catalogue group catalogue

Using the 2PIGG we built a mass-selected sub-sample and Using the 2PIGG we built a mass-selected sub-sample and we proposed for observation with both Chandra and XMM-we proposed for observation with both Chandra and XMM-Newton.Newton.



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What I am going to talk What I am going to talk aboutabout

Today I will describe our sub-Today I will describe our sub-sample sample

I will show some preliminary I will show some preliminary results of the X-ray properties of results of the X-ray properties of the sub-samplethe sub-sample

I will provide some clues that I will provide some clues that may allow you to figure out if may allow you to figure out if 2PIGG groups are well defined 2PIGG groups are well defined “objects” or not“objects” or not



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The 2 PIGG catalogThe 2 PIGG catalog

Eke et al. 2004, MNRAS, 355, 769

Has been derived from the 2dFGRS

Among the other, it provides:

Number of galaxy members

Group dispersion velocity ()

Estimate of the Group Mass (M=5.5 2 r/G )

From this we may estimate the Expected ICM X-ray temperature



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The Mass Selected The Mass Selected SampleSampleSelection Criteria

For this study, we selected all 2PIGG groups such as:

•z<0.1

•3·1014 <M/MO <6·1014

(1.5 keV <T< 3.5 keV)

• Number of galaxies Ng>10

•We get 18 groups



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The SampleThe Sample5 Chandra observations

11 XMM observations

No Observations approved for

two

3.1·1014Mo<M<5.6·1014Mo

1.6 keV <T<3.5 keV



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Groups in the Reflex Groups in the Reflex CatalogCatalog

C5799

= 700 km/s

T=2.7±1keV

C5797

= 590 km/s

T=4±0.7keV

C5798

= 580 km/s

T=1.7±0.2keV



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xmm2

T=??±?keV =680 km/s

xmm1

T=3.7±0.7 keV =580 km/s

xmm11

T=2.9±0.5keV = 540 km/s



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xmm6

T=5.64±0.2keV = 600 km/s

xmm8

No MOS

PN only

T=???? = 550 km/s

xmm7

T=3.5±0.5 keV = 620 km/s



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New Groups fainter than the New Groups fainter than the Reflex Catalog but detected in the Reflex Catalog but detected in the

RASSRASS

C4990

T=2.8±0.5 keV

= 530 km/s

xmm9

T=1.3±0.1keV

= 720 km/s

C4991

T= ??? keV

= 560 km/s



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New Groups fainter than the New Groups fainter than the Reflex Catalog but detected in the Reflex Catalog but detected in the

RASSRASS

xmm5

= 570 km/s

xmm4

= 700 km/s

xmm3

= 640 km/s



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Guess who game!!!!Guess who game!!!!Two galaxy groups at approx the same redshift and with approx the sameDispersion velocity. They both have a brighter central galaxy.

Which one is the X-ray emitting group?



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New Groups fainter than both the New Groups fainter than both the Reflex Catalog the RASSReflex Catalog the RASS

xmm10

= 730 km/s = 480 km/s = 710 km/s



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Sample X-ray Sample X-ray temperaturestemperatures

Affected by strong flares

Cluster



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Some “post-it like” Some “post-it like” statisticsstatistics

Out of 18 groups in the sample

13 show X-ray emission (72%)5 don’t (28%)

9 groups where already known from the Reflex survey.

We find 4 more X-ray emitting groups (44% more)

12 Groups provide enough X-ray photons to measure at least a single temperature.

8 out of this 12 allows to estimate a T profile in at least 4 radial bins.

For 5 groups we can also derive a T map



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ConclusionsConclusions Using the 2PIGG we build a mass-selected Using the 2PIGG we build a mass-selected

catalog of groups that we proposed for catalog of groups that we proposed for observation with both Chandra and XMM-observation with both Chandra and XMM-NewtonNewton

72% of the groups in our sample shows X-ray 72% of the groups in our sample shows X-ray emissionemission

The non X-ray emitting clusters tend to be the The non X-ray emitting clusters tend to be the ones with less galaxy membersones with less galaxy members

Because of low N_g, we think that the mass of Because of low N_g, we think that the mass of these systems may have been overestimatedthese systems may have been overestimated

The X-ray temperature of all groups (but one) The X-ray temperature of all groups (but one) is consistent with our selection criteriais consistent with our selection criteria



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The futureThe future

Stay tuned to see (hopefully Stay tuned to see (hopefully soon) Temperature, soon) Temperature,

Entropy, and Mass profiles Entropy, and Mass profiles of this (so far unique of his of this (so far unique of his kind) mass selected group kind) mass selected group

samplesample



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Santiago Chile (5-9 Dec 2005) 1 “Groups of Galaxies in the nearby Universe” ESO 2005 workshop...

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