Table Of ContentI. Saviane V.D. Ivanov J. Borissova (Eds.)
Groups of Galaxies
in the Nearby Universe
Proceedings
of the ESO Workshop held
at Santiago de Chile, December 5-9, 2005
ABC
VolumeEditors
IvoSaviane JordankaBorissova
ValentinD.Ivanov UniversidaddeValparaiso
ESO Av.GranBretana1111
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Santiago,Chile Valparaiso,Chile
SeriesEditor
BrunoLeibundgut
EuropeanSouthernObservatory
Karl-Schwarzschild-Str.2
85748Garching
Germany
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Preface
This volume contains the proceeding of an international conference held in
Santiago, Chile, in December 2005. The meeting was attended by nearly a
hundred active researchers in the field. The following is the reproduction of
an article that appeared in the March 2006 issue of the ESO Messenger.
Groups of Galaxies in the Nearby Universe
For every galaxy in the field or in clusters, there are about three galaxies in
groups.Therefore,theevolutionofmostgalaxiesactuallyhappensingroups.
TheMilky Wayresidesinagroup,andgroupscanbefoundathighredshift.
The current generation of 10-m class telescopes and space facilities allows to
studymembersofnearbygroupswithexquisitedetailandtheirpropertiescan
be correlated with the global properties of their host group. Finally, groups
arerelevantforcosmology,sincetheytracelarge-scalestructuresbetterthan
clusters, and the evolution of groups and clusters may be related.
Strangely, there are three times less papers on groups of galaxies than on
clustersofgalaxies,asrevealedbyanADSsearch.Organizingthisconference
wasawaytofocustheattentionofthecommunityonthegalaxygroups.We
alsowantedtoofferavenuewherepeoplecomingfromvariousresearchfields
couldmeetanddiscussgroupsfromdifferentperspectives.Allthishappened
in a friendly atmosphere created by hotel Torremayor in Santiago.
The discussion was organized in seven sessions, introduced by invited
reviews: Eva Grebel (Local Group vs. Nearby Groups), Vince Eke (Groups
SearchesandSurveys),ChrisConselice(TheEvolutionofGalaxiesinGroups
– Observations), Gary Mamon (The Evolution of Galaxies in Groups – The-
ory), Ann Zabludoff (Evolution of Groups as Systems), Trevor Ponman (In-
terstellar Medium and Intragroup medium), Stefano Borgani (Groups in a
Cosmological context), and finally Ken Freeman (Conference Summary).
There were almost 50 contributed talks and 30 posters. In the following text
we give a short summary of the main conference ideas, mostly based on the
invited reviews.
All You Wanted To Know About Groups (But You Were Afraid To Ask)
Groups are bound structures with masses in the range m = 1012−14M(cid:1)
(Eke), containing less than 50 galaxies (Conselice), and with typical sizes of
VI Preface
a few Mpc. Groups detected in X-rays have luminosities of L = 1041−43
X
ergsec−1 and gas temperatures of kT = 0.1 − 3keV (Ponman). Most of
the stellar mass in the present universe is in groups similar to the Local
Group with masses 2×1012M(cid:1) and only 2% is in clusters with m >5 ×
1014M(cid:1) (Eke). Groups were already present at redshifts z > 1 (Conselice).
Cosmological simulations predict a much larger number of galaxy satellites
than observed, and HI high velocity clouds cannot fill in this gap (Pisano).
Groupsfollow afundamental plane(Muriel)andthemostmassiveoneshave
an X-ray halo with an extended component (Zabludoff).
A special class of groups are the so-called ‘fossil groups’ – isolated ellip-
ticals with properties similar to a group, which could be the final stage of a
collapsed group. However, most isolated ellipticals are not collapsed groups
(Forbes). There are only 15 fossil groups known to date.
The evolution of low velocity dispersion groups is dominated by mergers,
which could explain the bimodal mass function of the X-ray faint groups
(X-ray faint groups tend to have low velocity dispersion and vice versa),
if intermediate-mass members merge to build the largest group members
(Raychaudhury). The bimodal mass function, similar to that of clusters, is
confirmed in compact groups (Bomans). Compared to compact groups, the
loose ones tend to have fewer low-mass members.
Theresultspresentedherewereobtainedthankstolargeobservationalef-
forts(Table1).Historically,thefirstgroupcatalogswerebiasedtowardcom-
pact groups, which are the easiest to identify from imaging surveys. Modern
redshiftsurveysallowselectionsincludingrecessionvelocities,andfindingal-
gorithms can be tested on mock catalogs generated with dark matter (DM)
simulations (Eke).
Galaxies in Groups
Galaxies in groups can be affected by processes like ram pressure stripping,
interactions and harassment, mergers, group tidal field, gas loss and sup-
pressed star formation (also known as strangulation or suffocation). Merging
isthemostimportantofthesebecauseofthelowrelativevelocitiesofgalaxies
in groups in comparison with the galaxies in clusters. Simulations show that
mergers induce an intense and brief (of the order of a hundred Myr) surge
of star formation before the final coalescence into a spheroid, which evolves
passively afterwards. Simultaneously, mergers transfer momentum from the
interacting galaxies to the group as a whole, thereby increasing the group
velocity dispersion. Indeed, observations show that there are more spheroids
in groups with higher velocity dispersion (Zabludoff).
Eventually, the feedback from the residual black-hole and active galactic
nucleus(AGN)reducesthestarformationbyafactoroftenormore.Atleast
50%ofgalaxiesincompactgroupsarelow-luminosityAGNs(Martinez),while
the field fraction is only 30%. Moreover, the cores of X-ray groups are often
disturbed,whichcouldbeadditionalevidenceforAGNfeedback(O’Sullivan).
Preface VII
Theselectivesuppressionofstarformationinlargergroupmemberscouldex-
plainthedownsizingphenomenon–thedecreaseofthemaximumluminosity
of star-forming galaxies at lower redshifts. Mergers occur mostly at redshifts
z > 1, for example at z = 2.5 about 50% of bright galaxies are undergoing
mergers,whiletodayonly2%ofgalaxiesmergeperGyr(Conselice).Mostof
the stars in group members also formed between redshifts z =2.5 and 1.
Locally, environmental effects can be traced directly by reconstructing
star formation histories of individual galaxies. For example, the fraction of
intermediate-age stars of Milky Way dwarf satellites depends on their dis-
tance from the Galaxy. On the contrary, this fraction is constant in M81
satellites (Da Costa) probably due to the compactness of the M81 group,
where multiple close encounters have homogenized their star formation his-
tories.
The Evolution of Groups
The origin of groups is probably related to large-scale gaseous filaments at
high redshift. Before virialization, smooth accretion, super novae and AGN
activity enhance the entropy, and the metal-enriched gas cannot be retained
by the shallow potential of pre-collapse groups (Ponman, Borgani). During
the virialization, the central spheroidals grow via mergers. Early-type stars
and enriched gas become part of the intragroup environment. Eventually, a
common dark matter and a hot (X-ray) gas halos are formed (Zabludoff).
The X-ray emission increases, and the X-ray halo becomes more and more
regular. Later, the diffuse DM distribution will reduce the merger rate and
moderatetheevolutionofgroups.Atleastafractionofgroupsendtheirlives
as fossil groups.
Mostlow-redshiftgroupsarejustdetachingfromtheHubbleflow,assug-
gested by the time evolution of the virial mass to light ratio (Mamon). In
particular, the detachment for the Local Group occurred at z < 0.7 (Free-
man).Themass-temperatureandmass-luminositydistributionsintheX-rays
forclustersandgroupscanconstrainthecosmologicalparameters(Borgani).
To summarize, as a group evolves, the dwarf-to-giant ratio, early-type
galaxy fraction, intragroup starlight and metallicity, the velocity dispersion,
and the mass of the central giant elliptical grow. The metallicity of the in-
tragroup medium also increases thanks to the intragroup stars, whose ejecta
do not have to overcome galactic potential wells (Zabludoff).
Observations are consistent with this scenario. As mentioned above,
groups with higher velocity dispersions have higher fractions of early type
galaxies.Andtheintragroupmediumcanberesponsibleforstripping,e.g.of
NGC2276intheNGC2300group(Ponman).Inturn,strippingenhancesthe
fraction of passive galaxies in groups. Further observational support for this
evolutionary scheme are the constant radial profiles of velocity dispersion,
which point to a common DM halo. Next, if the early enrichment history of
theintragroupgasisdominatedbytypeIIsupernovae,andthelatehistoryby
VIII Preface
typeIasupernovae,thenthiscouldexplaintheobserveddecreaseoftheover-
all metallicity toward the outskirts of the group and the alpha-enhancement
in the outer parts of groups (Rasmussen) because the early ejecta had time
to spread across the group.
Groups and Clusters of Galaxies
It was realized during the conference that groups are important for the evo-
lution of clusters as well. Clusters may grow by accretion of groups, as ex-
emplified by the Eridanus Super-group infalling toward Fornax (Brough).
Therefore, some cluster properties might be explained by groups, like the X-
ray medium, high dwarf to giant galaxy ratio, brightest cluster galaxies and
the early-types galaxy fraction (especially in more massive groups).
Likewise, the evolution of galaxies in clusters might be dominated by
group-scale environment, driving, e.g. the morphology-environment relation,
the Butcher-Oemler effect, and the brightest cluster galaxies formation. For
example, the intra-cluster light in Virgo probably originates in tidal inter-
actions inside group-size structures (Mihos), favoured by their low velocity
dispersion. Since tidal features are erased as clusters evolve, the presence
of such features would indicate that the cluster is dynamically young, still
’fragmented’ in groups.
Although mergers can happen both in clusters and groups, the high ve-
locity dispersion in clusters leads to less efficient orbital-decay-type mergers,
whilemoreefficient,directhead-onmergersarecommoningroups,especially
the evolved, X-ray bright ones (Mamon). This can explain the higher frac-
tion of early type galaxies in this class of groups compared to the field and
clusters.
These few paragraphs could only give a brief sense of the stimulating
discussion during the five days of the conference, and we hope that all par-
ticipants went away with fresh views on the current status of galaxy groups
studies. The entire proceedings of the symposium are presented in this vol-
ume.
We would like to express our gratitude to the members of the SOC, and
especially of the SOC Chair Duncan Forbes, for their efforts that made it
possible to organize this meeting. Last but not least, the success of the con-
ference would have been impossible without the excellent work of Maria Eu-
genia Go´mez, Paulina Jiron and Ismael Mart´ınez, and the financial support
of ESO.
Santiago de Chile Ivo Saviane
November 2006 Valentin D. Ivanov
Jordanka Borissova
Contents
Part I Local Group versus Nearby Groups
Local Group(s)
E.K. Grebel ................................................... 3
The Local Group Dwarfs Compared
E.D. Skillman .................................................. 21
Galaxy Groups in the Local Volume: An HI Perspective
B.S. Koribalski ................................................. 27
HI in Local Group Analogs: What does it Tell Us about
Galaxy Formation?
D.J. Pisano, D.G. Barnes, B.K. Gibson, L. Staveley-Smith,
K.C. Freeman and V.A. Kilborn .................................. 33
Stellar Metallicities and Ages in LeoI dSph
M. Gullieuszik, I. Saviane, E.V. Held and L. Rizzi ................. 39
Globular Clusters in M31 and the Local Group
S.C. Kim, M.G. Lee, D. Geisler, A. Sarajedini, W.E. Harris,
H.S. Park, H.S. Hwang and J.C. Seguel............................ 41
Properties of RR Lyrae Stars in the Inner Regions of the
Large Magellanic Cloud. II. The Extended Sample
J. Borissova, D. Minniti, M. Rejkuba and D. Alves.................. 45
Diffuse Ionized Gas in the Dwarf Galaxy DDO 53
N. Flores-Fajardo and A.M. Hidalgo-Ga´mez ........................ 47
Part II Groups Searches and Surveys
Galaxy Group Searches and Surveys
V. Eke ........................................................ 53
X Contents
Baryon Budget in 2keV Galaxy Groups
A. Hornstrup, A. Vikhlinin, R. Burenin, H. Ebeling, O. Kotov,
K. Pedersen, H. Quintana and J. Rasmussen ...................... 67
Isolated Compact Groups of Galaxies in the 2dF Galaxy
Redshift Survey
J. Saucedo-Morales and P. Loera-Gonz´alez ......................... 73
Environmental Effects on Galaxy Evolution Based on the
Sloan Digital Sky Survey
T. Goto ....................................................... 79
DPOSS II Compact Groups: The EMMI/NTT Survey
E. Pompei, A. Iovino and R.R. de Carvalho........................ 85
The Low-luminosity Galaxy Population
in the NGC 5044 Group
S.A. Cellone and A. Buzzoni ..................................... 91
The Galaxy Evolution Multi-wavelength Study (GEMS)
Project
D.A. Forbes .................................................... 97
A Search for Ultra-compact Dwarf Galaxies in the NGC
1023 Group of Galaxies
S. Mieske, M.J. West and C.M. de Oliveira ........................ 103
Dwarf Galaxies in the Antlia Cluster: First Results
A.V.S. Castelli, L.P. Bassino, S.A. Cellone, T. Richtler, B. Dirsch,
L. Infante, C. Aruta and M. G´omez .............................. 109
Compact Groups: A Statistical Analysis
E. D´ıaz, C. Ragone, H. Muriel ................................... 111
Study of Intracluster Diffuse Light within the Fornax Cluster
A.C. Ca´rdenas, S.A. Cellone and J.C. Forte ....................... 113
BVRI Photometric Analysis for the Galaxy Group NGC 4410
J.A.P. Grana, S.N. Kemp, A.C. Katsiyannis, E. de la Fuente,
A. Franco-Balderas and J. Meaburn ............................... 115
Photometric and Kinematical Study of Nearby Groups
of Galaxies Around IC 65 and NGC 6962
J. Vennik and E. Tago........................................... 119
Contents XI
Part III Evolution of Galaxies in Groups – Observational
The History of Galaxy Formation in Groups: An
Observational Perspective
C.J. Conselice .................................................. 123
Deep Optical Imaging of ESO 383–45: A Galaxy Undergoing
Ram-pressure Stripping, or a Tidal Merger Remnant?
S.N. Kemp, E. de la Fuente, A. Franco-Balderas and J. Meaburn ..... 139
Morphologies and Star Formation in z ∼0.5 Group Galaxies
D.J. Wilman, M.L. Balogh, R.G. Bower, J.S. Mulchaey, A.
Oemler Jnr and R.G. Carlberg ................................... 145
Formation and Evolution of Early-type Galaxies
C. Chiosi and E. Merlin ........................................ 151
Dwarf Galaxies in Hickson Compact Groups
D.J. Bomans, E. Krusch, R.-J. Dettmar, V. Mu¨ller and C. Taylor ... 157
Low Luminosity Activity in Hickson Compact Groups
M.A. Martinez, A. del Olmo, J. Perea and R. Coziol ................ 163
Dwarf Elliptical Galaxies in Cen A Group
M. Rejkuba .................................................... 169
Stellar Populations in Compact Group Elliptical Galaxies
I.G. de la Rosa, R.R. de Carvalho, A. Vazdekis and B. Barbuy ....... 175
Spitzer 4.5 µm Luminosity-Metallicity and Mass-Metallicity
Relations for Nearby Dwarf Irregular Galaxies
H. Lee, E.D. Skillman, J.M. Cannon, D.C. Jackson, R.D. Gehrz,
E. Polomski and C.E. Woodward ................................. 181
Shapes and Galaxy Flows Around Clusters
and Groups of Galaxies
N. Padilla...................................................... 187
Infrared Surface Brightness Analysis
of Galaxies in Compact Groups
I. Plauchu-Frayn, R. Coziol and H. Bravo-Alfaro.................... 193
Size and Orientation of the ‘Z’ in ZRGs
C. Zier ........................................................ 195
XII Contents
IMF Model Sampling and the Emission Lines
in Star Forming Galaxies
G. Magris C., F. Molina and A. Parravano ........................ 197
Part IV Evolution of Galaxies in Groups – Theoretical
The Evolution of Galaxy Groups and of Galaxies Therein
G.A. Mamon ................................................... 203
Diffuse Starlight and the Evolution of Groups and Clusters
of Galaxies
J.C. Mihos..................................................... 221
Simulating Diffuse Light in Galaxy Clusters
C.S. Rudick, J.C. Mihos and C. McBride .......................... 227
Lensing by Groups
O. Mo¨ller, M. Kitzbichler, V.R. Eke and P. Natarajan............... 233
The Role of Tidal Interactions in Driving Galaxy Evolution
J. P´erez, P.B. Tissera, D.G. Lambas, C. Scannapieco and
M.E. De Rossi ................................................. 239
Chemical and Photometric Evolution of NGC 6822 in a
Cosmological Context
L. Carigi, P. Col´ın and M. Peimbert .............................. 241
Evolution of the Luminosity-Metallicity-Stellar Mass
Correlation in a Hierarchical Scenario
M.E. De Rossi, P.B. Tissera and C. Scannapieco ................... 243
Part V Evolution of Groups as Systems
Groups: The Rich, the Poor and the Destitute
A. Zabludoff.................................................... 249
The Eridanus Supergroup
S. Brough...................................................... 261
ClG J1205+4429, the Most Distant Fossil Group at z=0.59
F. Durret, M.P. Ulmer, C. Adami G. Covone and G.B. Lima Neto.... 267
Past and Future of CG J1720-67.8: Constraints from
Observations and Models
S. Temporin and W. Kapferer .................................... 273
