Pitch Angles of Clustered Spiral Galaxies in the

Pitch Angles of Clustered Spiral Galaxies in the

Pitch Angles of Clustered Spiral
Galaxies in the Chandra Deep Field
Jazmin Berlanga Medina , Benjamin Davis ,
Daniel Kennefick




University of Arkansas-Fayetteville, 2Arkansas Center for Space & Planetary


We have examined a set of 125 spiral galaxies lying in the Chandra Deep Field South for which we
have redshifts & pitch angles from previous work. Upon cross-referencing this set with the larger &
comprehensive COMBO-17 survey, we found a cluster that is confirmed by recent literature. When
comparing the pitch angle of galaxies in & out of clustered regions, there seems to be little to no
difference, suggesting no environmental effect of clusters on pitch angle.


What is pitch

tightness of spiral
Smaller pitch
angle means
tighter arm
structure & vice

astronomers working
in the Arkansas
Center for Space &
Planetary Sciences.
Found relation
between pitch angle
& black hole mass of
spiral galaxies1.

BUTNot yet understood how
environmental factors (i.e., galaxy
harassment, dark matter concentration)
affect spiral arm structureincluding
pitch angle. Need to know that pitch
angle estimate of black hole mass is
reliable across different

So why
Concentrations of
galaxies & other celestial

objects/matter in the sky
Identified by optical, X-ray &
microwave sources,
gravitational lensing
By definition, galaxies in
clusters more likely to
experience galaxy harassment,
effects of dark matter
Pressures affect morphology
of galaxiesand thus structure
& possibly intrinsic pitch angle
Clusters = Excellent testing
fields for galaxy evolution &

n Deep Field South

Patch of sky visible from

southern hemisphere
We have COMBO-17 survey
data of CDFS: 63,501 objects
with available photometric
BUTchosen due to lack of clustered
objects (obstructions) along our line of
sight in order to obtain deep, telescopic
Our working definition of cluster will
depend on galaxy density calculated from
optical data only (not strictly defined)
Have set of 125 galaxies with pitch angles
& photometric redshifts in CDFS from prev.
Looking for concentrations of 1000
galaxies or more within a radius of 10 Mpc3


Distinguishing false
Black line from
is 2-Dreal
distance ,
one of yellow lines is
actual distance
Embed galaxy in
middle (or corner) of
Pick radius of cylinderlength of cylinder
determined by a redshift range suitable to
experimental needs
If galaxy falls within the radius/diameter of
cylinder (apparent distance) but NOT within
redshift range, Wrote
false neighbor
Fortran program

to find number of actual neighbors in
1)Looked at our set of galaxies one at a

time, calculated distance to every object in
2) Counted number of objects within 10
Mpc radius
Literature: What is already known
3)Threw out false neighbors not within z
sourcesinon galaxy
morphology in clusters
2) All agree: Lenticular to spiral galaxy ratio
changes in favor of lenticular over time
(higher to lower redshift)
3)Speculations: Could spirals evolve with
tighter & tighter arms towards lenticulars?
Could cluster environment weed out/disturb
spirals all-together over time?

1) We found a cluster at
z~1.04. Seems to be the same one
found by Trevese et al. (z~0.96,

Figs. 1 & 2, Location vs. Redshift, Above:
The red dots are galaxies with >1000 galaxies in
their cylinders, collectively they make up a
cluster and lie at a higher z. The blue dots are
mostly outside the clustered region, with the
higher z galaxies on the fringe of the cluster.

2) No correlation between pitch angle
and clustering. Appears so far that
clustering has no environmental effect on
pitch angle.
Fig. 3, Neighbor
Count vs. Pitch
angle, Left: The red
line represents the
relationship between
number of neighbors
and pitch anglethe
slope is very nearly

Tbl. 1, Bins, Right:
When grouped into
statisticallyproportional groups, the
pitch angles in clustered
& non were nearly the

Further Work:

1) Determine more about cluster. Need exact
dimensions, map of galaxy density
(galaxies/volume), which of COMBO-17 galaxies
not in our set are part of cluster.
2) Careful comparison between Trevese et al.s
cluster & ours: Data, technique, etc.
3) Part of our original pitch angle vs. black hole
mass sample of galaxies is in the Hubble Deep
Field North. Will repeat procedure with this set.
References: [1] Seigar M. S., et al. (2008) ApJ., 678, 93-96.
[2] Wolf C. et al. (2004) Astro. and Astrophys., 421, 913-936. [3]
Berrier J. (2009) Private Communication. [4] Trevese D. et al.
(2009) AIP Conf. Proc., 1126, 125-127.
Acknowledgements: Id like to thank my mentor, Dr. Dan
Kennefick, & grad students Doug Shields & Ben Davis, for
enlightening many a concept, the Honors College at U of A for
the research grant, and my physics advisor Dr. Lin Oliver for all
the encouragement.

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