Download Poster - Arkansas Center for Space and Planetary Sciences

Pitch Angles of Clustered Spiral Galaxies in
the Chandra Deep Field South
1
Medina ,
Jazmin Berlanga
Benjamin
1,2
Daniel Kennefick
1
2
Davis ,
University of Arkansas-Fayetteville, 2Arkansas Center for Space & Planetary Sciences
Introduction
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.
Background
What is pitch angle?
•Measures tightness
of spiral arms
•Smaller pitch angle
means tighter arm
structure & vice versa
AGES Research
•Collaboration of
astronomers working in
the Arkansas Center for
Space & Planetary
Sciences.
•Found relation between
pitch angle & black hole
mass of spiral galaxies1.
BUT…Not yet understood how environmental
factors (i.e., galaxy harassment, dark matter
concentration) affect spiral arm structure—
including pitch angle. Need to know that pitch
angle estimate of black hole mass is reliable
across different environments.
So why clusters?
Clusters: 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
galaxies—and thus structure & possibly
intrinsic pitch angle
Clusters = Excellent testing fields for
galaxy evolution & morphology
Investigation
Results
Chandra Deep Field South
1) We found a cluster at z~1.04. Seems
•Patch of sky visible from southern
hemisphere
•We have COMBO-17 survey data of
CDFS: 63,501 objects with available
photometric redshifts2
•BUT—chosen due to lack of clustered objects
(obstructions) along our line of sight in order to
obtain “deep,” telescopic look
•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. work1
•Looking for concentrations of 1000 galaxies or
more within a radius of 10 Mpc3
3-D in a Cylinder:
Distinguishing false
neighbors from real ones3
•Black line is 2-D
(apparent) distance , one
of yellow lines is actual
distance
•Embed galaxy in middle
(or corner) of cylinder
• Pick radius of cylinder—length 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 the redshift range,
false neighbor
Programming: Wrote Fortran program to find
number of actual neighbors in cylinder
1)
2)
3)
Looked at our set of galaxies one at a time,
calculated distance to every object in COMBO-17
Counted number of objects within 10 Mpc radius
Threw out false neighbors not within z range
Literature: What is already known about spiral
galaxies in clusters? Are there known clusters in
1)
2)
3)
Found several sources on galaxy morphology in
clusters
All agree: Lenticular to spiral galaxy ratio changes
in favor of lenticular over time (higher to lower
redshift)
Speculations: Could spirals evolve with tighter &
tighter arms towards lenticulars? Could cluster
environment weed out/disturb spirals all-together
over time?
to be the same one found by Trevese et al.
(z~0.96, 2009)4
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 angle—the slope is
very nearly zero.
Tbl. 1, Bins, Right: When
grouped into statisticallyproportional groups, the pitch
angles in clustered & non
were nearly the same.
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: I’d 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.