The «social life» of galaxies on the
outskirts of the Virgo cluster from
an HI perspective
JOSEP MARIA SOLANES (UB, Spain)
EDUARD SALVADOR-SOLÉ (UB, Spain)
GARY MAMON (IAP, France)
TERESA SANCHIS (UB, Spain)
JENAM 2004
EVOLUTION OF GALAXY PROPERTIES WITH ENVIRONMENT
Tomotsugu et al., MNRAS, 346, 601 (2003)
JENAM 2004
Gomez et al., ApJ, 584, 210 (2003)
EVOLUTION OF GALAXY PROPERTIES WITH ENVIRONMENT
Balogh et al., ApJ, 504, L75 (1998)
CNOC clusters
Solanes et al., ApJ, 548, 97 (2001)
z~0 clusters
JENAM 2004
IMPORTANT QUESTIONS
1. How far can galaxies bounce out of clusters?
2. Is the segregation of galaxy properties with
local density seen outside high density regions
also consistent with the evolutionary scenario?
Answers provided from the study of the HI content
of galaxies in the Virgo cluster region.
JENAM 2004
2D MAP OF THE VIRGO CLUSTER AT VARIOUS WAVELENGTHS
Solanes et al., AJ, 124, 2440 (2002)
161 S’s with HI content
and homogenized (from
8 catalogs) TF distance
measurements.
Contour map of the
distance-independent
HI-deficiency parameter
derived from 287 S’s
extracted from the
Arecibo General Catalog
(Giovanelli & Haynes):
DEF = 〈 log ∑ HI (T )〉 − log ∑ HI .
X-ray image from
ROSAT All-Sky Survey
in the hard (0.4−2.4 keV)
band.
JENAM 2004
3D DISTRIBUTION OF HI DEFICIENCY IN THE VIC REGION
Solanes et al., AJ, 124, 2440 (2002)
Sanchis et al., ApJ, 580, 164 (2002)
JENAM 2004
MAXIMUM REBOUND RADIUS IN A ΛCDM UNIVERSE
Mamon et al., A&A, 414, 445 (2004)
N-body replicas of the Virgo cluster:
Isolated massive halos at z = 0
extracted from the GALICS hybrid Nbody/semi-analytical model of
hierarchical galaxy formation (Ninin
1999; Hatton et al. 2003).
Simulation run for a ΛCDM model with
Ω0 =1-ΩΛ =1/3, h =2/3, and σ8 =0.88.
3D radial phase space plots show that
DM particles crossing through the core
of a cluster cannot bounce out beyond
~2 virial radii. DM halos (particle
condensations) reach even shorter
distances. Simulations of LSC by
Klypin et al. (2003) produce similar
results.
In the Virgo region (r100 = 1.65 Mpc)
galaxies passing through the
cluster cannot move away more
than ~4 Mpc from M87!
JENAM 2004
VELOCITY-DISTANCE RELATION AROUND M87
Sanchis et al., A&A, 418, 393 (2004)
Scaling equations:
D = Dsim
v = u sim
Vir
r100
sim
r100
Vir
v100
+ H 0 D.
sim
v100
Adopted values:
No error in distance
r100 = 1.65 Mpc,
v100 = 780 km s-1,
M100 = 2.3x1014 M.
The distance to the LG is
scaled by assuming DVir = DM87
= 16.8 Mpc, which gives Vsys =
998 ± 155 km/s in good
agreement with the 900-1000
km/s range found in the
literature.
20% relative distance errors
JENAM 2004
MAIN CANDIDATES TO PERIPHERAL HI-DEFICIENT SPIRALS
There are 13 VIC galaxies with HI DEF > 3σ satisfying D < 13 Mpc or D > 22 Mpc and/or θ/θ100 > 1 (▲).
Possible explanations:
¾ Errors in HI deficiency estimation: e.g., arising from type misclassification (highly unlikely).
¾ Incorrect distances: e.g., arising from underestimation of maximum rotation velocities (unlikely, but cannot be
discarded for some of the objects at dlos ~10 Mpc given their negative velocities with respect to the LG!). The
case of M90 is puzzling.
¾ Tidal perturbations/mergers (likely for 3 of the foreground objects with probable close companions; M90 is
not one of them).
¾ Grup membership (quite plausible for the 3 objects at ~28 Mpc).
JENAM 2004
SUMMARY OF RESULTS
• On a concordant ΛCDM universe rich cluster members cannot bounce out beyond
~2rvir from its center, in agreement with observational estimates of the radial extent of
the cluster influence. Most members of Virgo (@ ~17 Mpc) must be located between
~13-21 Mpc from us.
• ~20% 1σ-errors on z-independent distances produce an apparent elongation of the
VIC region along LOS, with distortions of ~1:3 for the central cluster.
• Up to 13 outlying HI-deficient spirals have been identified that are difficult to explain as
cluster members. Errors in distance less than 10% (0.2 mag) and sensitive VLA maps
(column densities ~1020 cm-2) are required to establish the origin of the gas-poor spirals
on Virgo’s suburbia.
• S’s with neutral gas deficiencies as important as those found in the cluster core are
detected on the far side of Virgo (~25−30 Mpc from us) for which the most plausible
explanation would be that they lie in a background concentration of newcomers. (Disk)
galaxies can enjoy an intense «social life» within groups: future cluster members fall in
preprocessed!
• In the Virgo region, the HI content of galaxies might not be a straightforward indicator
of cluster membership!
JENAM 2004
QUESTIONS
L. VERDES-MONTENEGRO: I wonder if there are HI maps of the HI-deficient
galaxies located on the outskirts of the Virgo cluster? This could help to
identify the origin of their neutral gas deficiency.
J.M. SOLANES: You are right, the 2D distribution of the HI for these gasdeficient galaxies should be a very valuable piece of information in order to
identify the mechanism(s) responsible for the observed HI deficiency.
Regrettably, there are only maps for a couple of them (one is M90). But this
situation will soon change. Currently, a large, targeted survey of HI in Virgo
cluster galaxies is being conducted with the VLA by Jeff Kenney and
collaborators that includes the mapping of 6 of the 13 HI-poor galaxies that
we have identified on Virgo’s suburbia.
JENAM 2004