Transcript Star-Forming Galaxies in a Nearby Group: Abell 634. Reverte-Payá1, D.; Vílchez1, J.

Star-Forming Galaxies in a Nearby Group: Abell 634.
Reverte-Payá1, D.; Vílchez1, J. M. & Iglesias-Páramo2, J.
1Instituto
de Astrofísica de Andalucía-CSIC
2Laboratoire
d’Astrophysique de Marseille
A two-fold effect acting on gas rich
disk galaxies :
Motivations
• Environmental effects on Star Formation in Galaxies:
 The study of the population of emission line galaxies in nearby clusters is a
necessary step towards our understanding of the evolution of galaxies in dense
environments and earlier epochs.
- We report here on the study of star-forming galaxies detected in a
nearby northern cluster specially interesting.
 We aim to build up a firm local basis to compare with observations of clusters
of galaxies in a wide range of properties (density,..):
- We have selected one of the known nearby cluster.
1.- Inhibition of “standard” SF activity in disks
in very high density environments:
-Ram pressure stripping, gas removal, Harassment, [especially in clusters]. All of
these effects may take place in a galaxy cluster in a high probability.
2.- Enhancement in central parts or in tidal tips
Starburst .
-Galaxy Mergers, Close Encounters, Harassment. Cited article is a clear example
of enhancement in tidal tail and central part because of Intracluster gas pressure.
The Object
Big Group or Poor cluster?
• low X-ray luminosity;
• Dispersion of velocities similar to
Abell 779 but noticeable lower than
any other; and
• 30 objects knowns.
Name
Abell 634
Right Asc.(1)
8h 14m 33.7s
(1)
Declinat.(1)
+58o 02' 52"
Vel(1)
7945
Redshift(1)
0.0265
Data taken from NASA Extragalactic Database.(2) Data taken from White, Jones & Forman (1997).
Observation
Lx(bol)(2)
sv (km/s)
391
0.006:
(3)
BM type(1)
III
Abell(3) Radius
66
Data taken from Abell, Corwin & Olowin (1989).
X ray contour from
ROSAT overplotted on
DSS (40’x 40’) image of
Abell 634.
Wide Field Camera attached to 2.5 m Isaac Newton Telescope has been
the instrument used to these observations.
It can be seen that
there is not a central
source of emission,
indeed the distribution
doesn’t show a clear
pattern. The fact is: it
looks like normal noise
emission
from
background.
Four Pointings with a small overlapping with a central frame which
assembles the others, provide 1 degree square observed field.
Detection
We don’t ignore that pixel size in ROSAT image is higher than some galaxies but
we think it’s a good guide to see we talk about.
One degree square have been imaged
for the cluster with a depth of one hour
exposure. That grant us we will be able
to reach a low limit in bright as 21 H
magnitud.
Preliminary Analysis
We have maken extensive use of IRAF
tasks in order to reduce the images
and SExtrator to detect.
Emission-line sources can be separated in extended
and unresolved emitters. For the second group,
using the file provided by SExtractor, a small pipeline
is needed (because of the size of FOV) to find all
possible members which have an H excess.
Example image of 6’x10’ with SExtractor
detections contour.
Atlas and Table of Objects
Name
SBS0807+580B
SBS0808+581B
SBS0808+581A
SBS0807+581
SBS0810+581
SBS0809+582
CGCG 287-053
h
RA
m
s
08
08
08
08
08
08
08
12
12
12
11
14
13
13
08.74
34.75
16.80
53.52
38.79
47.06
17.89
º
Dec
‘
+57
+57
+57
+57
+58
+58
+58
54
57
58
57
01
04
00
Redshift
“
Vel.
Km/s
28.82
36.79
30.65
07.47
23.79
49.35
38.57
7795
X
X
8364
7885
8232
7821
0.02601
X
X
0.02790
0.02630
0.02746
0.02609
Left hand figure.
Each frame represented in the figure is 6’x7’ (h’xw’). On the left column
H emission is shown. Center: narrow continuum. Right column is
calculated as the difference between previous.
If background color for all frames aren’t the same is because to adjust
contrast in brightest galaxies must expand color bar-scale.
Next step absolute calibration.
A statistical analysis of unresolved sources is in progress to
decontaminate from background objects. Some red and
blue are spurious.
Work in progress
• Fine Structure of the H flux in each emitting galaxy.
• Statistical analysis of point sources. Decontamination. Probably
needed auxiliar spectra.
• Morphological classification.
In extended sources group, we have found just one case of
interlopers emission. Note that just viewing it cannot be possible
distinguish of the others.
• H Luminosity Function (Parameters of Schechter fit).
• Spatial distribution of H emission galaxies across the cluster.