Pitch Angles of Clustered Spiral Galaxies in the Chandra Deep Field

SouthJazmin Berlanga Medina1, Benjamin Davis2, Daniel Kennefick1,2

1 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

Investigation

Results

What is pitch angle?•Measures tightness of spiral arms•Smaller pitch angle means tighter arm structure & vice versaAGES

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.

Chandra Deep Field South•Patch of sky visible from southern hemisphere•We have COMBO-17 survey data of CDFS: 63,501 objects with available photometric redshifts2

Programming: Wrote Fortran program to find number of actual neighbors in cylinder

Literature: What is already known about spiral galaxies in clusters? Are there known clusters in

So why clusters?Clusters: Concentrations of

galaxies & other celestial objects/matter in the skyIdentified by optical, X-ray & microwave sources, gravitational lensingBy 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 angleClusters = Excellent testing fields for galaxy evolution & morphology

•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

1)Looked at our set of galaxies one at a time, calculated distance to every object in COMBO-172) Counted number of objects within 10 Mpc radius3)Threw out false neighbors not within z range

1) We found a cluster at z~1.04. Seems 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 statistically- proportional groups, the pitch angles in clustered & non were nearly the same.

1)Found several sources on galaxy morphology in clusters2) 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?

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.

3-D in a 3-D in a Cylinder:Cylinder:Distinguishing false Distinguishing false neighbors from real neighbors from real onesones33

•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