HI Imaging in Abell 1367:
A subclump merging with the main cluster?
Héctor Bravo-Alfaro(1), E. Brinks(2) & I. Plauchu(1)
(1)Dept. de Astronomia, Universidad de Guanajuato. Mexico
(2) Centre for Astrophysics Research, University of Hertfordshire. UK
Introduction
High density environments represent the
ideal laboratory to study global and local
environment on individual galaxies. HI
imaging has proved to be a powerful
tool for testing environmental effects on
galaxies in groups and clusters.
The atomic hydrogen component, being
more extended than the stellar disk, is
the perfect target to study the prints left
by both gravitational tidal interactions,
and
hydrodynamical
interactions
between the intra cluster medium and
the interstellar medium. This issue is
part of the old debate usually known as
Nature or Nurture, summarized in Table
1. In environmental mechanisms we give
few examples of both gravitational and
hydrodynamic mechanisms affecting
galaxy evolution.
CGCG 160-058 (Bravo-Alfaro 2001)
Table 11
Table
Evolutionof
of galaxies:
galaxies:
Evolution
Natureor
or Nurture?
Nurture?
Nature
Environmental
Environmental
Mechanisms:
Mechanisms:
Initial
Conditions:
•Mass
•Angular momentum
Gravitational
Gravitational
Mergings
•• Mergings
Tidalinteractions
interactions
•• Tidal
Galaxycannibalism
cannibalism
•• Galaxy
Galaxyharassment
harassment
•• Galaxy
Hydrodynamic
Hydrodynamic
•Ram-pressurestripping
stripping
•Ram-pressure
stripping
••Viscous
Viscous stripping
•Evaporation
•Evaporation
So far, few clusters have been imaged in HI
with the aim to study environmental effects on
individual galaxies, like in Virgo (Cayatte et al.
1990, see Fig. 1). Furthermore, the dynamical
state of the cluster itself can be probed. Some
evidence has been found for groups of HI-rich
galaxies to be falling towards the main cluster
body in systems like Coma (Bravo-Alfaro
2000, 2001, Fig.2), Hydra (McMahon 1993),
and Abell 2670 (van Gorkom 1996).
Table 2 gives few data about clusters already
imaged in HI, either with the VLA or the
WSRT. Figs. 2 and 3 show two examples of
composite plots of HI, in Virgo and Coma.
Table 2: clusters imaged in HI
ID
Virgo
Hydra
A 262
Hercules
Coma
UMa
A 1367
Velocity
(km/s)
1026
3600
4704
11000
7000
800
6595
S:S0:E
LX
DefHI
(erg/s)
46:39:15
43.0
47:32:21
51:35:14
18:47:35
44.0
43.9
44.9
43:40:17
43.5
Ref.(HI)
0.56 Cayatte et al. 1990, 1994
McMahon 1993
0.48 Bravo-Alfaro et al. 1997
0.21 Dickey 1997
0.77 Bravo-Alfaro et al. 2000, 01
Verheijen 2001
0.42 Bravo-Alfaro et al. in prep.
Coming soon:
A 2670
A 85
A 754
A 2029
A 2192
24000
16500
16700
22800
56100
44.4
45.0
44.6
45.2
44.6
van Gorkom et al. in prep.
“
“
“
“
Fig. 1
VLA-HI imaging
in Virgo
Cayatte et al. (1990)
Fig. 2
HI and X-ray in Coma
(Bravo-Alfaro et al. 2000)
Abell 1367 (NW zone)
Morph. type: Irr
Vcum= 6595 kms-1
z = 0.02
∆v = 900 km s-1
A1367 is a nearby system
with a high fraction of both,
blue galaxies, and spiral
galaxies. These features,
being associated with
distant clusters, make of
A1367 a key system to link
nearby and distant clusters.
II. Observations and preliminary results
VLA - HI (21cm) imaging in Abell 1367
D - configuration (~45”)
2 observed data cubes (see Fig. 3):
A (7500km/s) “periphery”
B (6500km/s) “center”
Fig. 3
(a) Results: individual galaxies
In the follow we show very preliminary results of this HI
survey of the NW region of A1367, which not only show
evidence of environmental effects due to the ICM on
individual spirals, but also discovered an intriguing
sample of five HI-rich low-mass systems, likely
associated with the spirals Zw097-068/072/079/087/091.
These systems have been extensively studied in optical
and radio continuum emission (e.g. Gavazzi et al. 1995).
These five HI detections correspond to non-previously
catalogued objects, probably being LSB galaxies, as no
obvious optical counterpart is seen in DSS.
In Figs. 4 to 12, we show individual HI maps (overlaid on
DSS optical images) and spectral profiles compared,
when available, with those previously obtained with
Arecibo. Some observational information for every
galaxy is given in each figure. Other indications, such as
the distance and direction to the cluster center, are also
indicated.
Fig. 4 CGCG 097-068’s companion (Cube B)
T. Morph: Sbc
MHI = 9 x 108 Mo
∆V = 170 kms-1
Vc = 6,560 kms-1
¾No big asimmetries or
perturbations
¾Low continuum
emission
Center
Dcntr= 0.63Mpc
Fig. 5 VLA-HI profile
HI-maximuum position
(Chincarini et al. 1983)
6000
6100
6200
Fig. 6 CGCG 097-072 and a companion (Cube B)
CGCG 097-072 (Sa)
MHI = 1.2 x 109 Mo
∆V = 280 kms-1
Vc = 6,332 kms-1
DefHI = 0.11
(~20%)
Companion
MHI = 4 x 108 Mo
∆V = 130 kms-1
Vc = 6,288 kms-1
¾No asymmetry
¾Low continuum emission
Center
Dcntr= 0.51Mpc
Fig. 7 CGCG 097-073 (Cube A)
Blue galaxy (SAcd pec)
MHI = 4 x 108 Mo
∆V = 130 kms-1
Vc = 7,333 kms-1
¾ Slight shift in position
¾Continuum emission:
16.5mJy
Center
Dcntr= 0.45Mpc
SFR = 2.6 Mo/yr
Fig. 8 CGCG 097-079’s companion (Cube A)
Blue galaxy (Irr)
MHI = 3 x 108 Mo
∆V = 170 kms-1
Vc = 7,550 kms-1
¾Asymmetry and shift in
position
¾Continuum emission:
5.3mJy
SFR = 0.78 Mo/yr
Center
Dcntr= 0.39Mpc
Fig. 9 HI profil: CGCG 097-079 and neighbour
Fig. 10 CGCG 097-087 (Blue Irr galaxy, Cube A)
B
Companion
MHI = 4 x 108 Mo
∆V = 130 kms-1
Vc = 7,450 kms-1
A
¾Continuum emission:
66 mJy
SFR = 8.97 Mo/yr !!!
Center
Dcntr= 0.23Mpc
Fig. 11 HI profile of CGCG 097-087
Non observed zone
Fig. 12 CGCG 097-091 (Sa, Cube A)
First peak: CGCG097-091
Vc = 7600 kms-1
∆V = 260 kms-1
Center
Dcntr= 0.37Mpc
Second peak: neighbour
Vc = 7820 kms-1
∆V = 110 kms-1
Center
Dcntr= 0.37Mpc
(b) Results: a composed view
Fig. 13 shows a composite HI-Xray-Optical plot of
A1367. Large scale contours draw X-ray from ROSAT,
and short scale contours are the HI, overlaid on DSS
optical images. Detected galaxies are plotted at their
correct position but are scaled by a factor of four.
Red crosses indicate the two X-ray maximums, and
the blue cross indicates the position center of the
cluster. The red circle draws the center of the VLA
field of view.
Those spiral galaxies projected closer to the cluster
center, share similar properties: high radio
continuum emission, blue colors, and high star
formation rates. They are spread over a region (in
projection) of about 0.3 Mpc in diameter, and present
a very high velocity dispersion, some 800 km s-1. This
could be a second group of galaxies infalling to the
core of A1367, after the compact group reported by
Sakai et al. (2002) and Gavazzi et al. (2003).
Fig. 13
Global view of A1367: HI-Xray-optical
Preliminary conclusions
9
First HI imaging for 9 objects in A1367
9
Among them, 5 non-catalogued HI detections with no clear optical
counterpart: are they LSB dwarf galaxies or HI clouds?
9
HI physical parameters such as MHI, DefHI , ∆V , Vc evidence the
environmental effects exerted by the ICM
9
20cm radio flux enable to estimate SFR and compare with those
obtained from NIR and Hα observations.
9
Are we witnessing a subclump merging with A 1367?
∆v ≥ 800kms-1 and ∆dproy ~ 300 kpc
9
In any case, we test the dynamical state of the cluster and
can conclude that A1367 is a dynamically young system
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