Master’s Thesis DefenseAisha Mahmoud-PérezAdvisor: Dr. Bill Harris

Photometric Study of the Globular Cluster System of M49

Back to Basics: Globular Cluster Systems

- When globular clusters are considered as a system, it offers an open window into the galaxies history.

- Elliptical galaxies harbor more globular clusters than their spiral counterparts.

- This study focuses on giant elliptical galaxies.

M31 Globular Cluster System. Mark Peacock

Bimodality in Globular Clusters

metal-poormetal-rich

Figures: Harris et al. 2010

+ Metals

The Mass-Metallicity Relation

Figure: Strader et al. 2006

Metal-poor clusters tend to become redder as they become more massive

+ Mass

+ Metals

First observed in giant elliptical galaxies, but some spirals have also shown a MMR slope (Harris et al. (2006), Spitler et al. (2006)).

Usually observed for clusters of mass > 106M (Bailin & Harris 2009).

The Mass-Metallicity RelationCauses of the Mass-Metallicity Relation: Scenarios.

Cluster #1 Cluster #2

SNe

metals

metalsCluster

Metal-Rich cloud

Dwarf Galaxy

(1)MergersStrader & Brodie et al. (2008)

(2) Self-EnrichmentBailin & Harris (2009)

(3) Accretion in OrbitMaxwell et al. (2014)

Cluster

M49: Why are we interested in this galaxy?

Massive elliptical with no MMR slope (Strader et al. (2006), Mieske et al. (2007))

- Why?

- Type: Massive Elliptical

- Where: Virgo Cluster

- Distance: ~ 56 mly

- (m-M) ~ 31.29

I’m

the brig

htest

galaxy here!!

Obtaining Data

Observatory: Cerro Tololo Inter-American Observatory, ChileInstrument: Blanco 4m Telescope.Filters: R and C (red and blue)

R C

Object Detection and Photometry

Initial object selection conducted with IRAF. Matched frames: 23,540 objects. - How can we fine-tune this list?

Bad quadrant! Removed from sample.

Over-saturated center! Replaced with another dataset (Geisler 1996).

Object Detection and Photometry

Statistical cleaning and magnitude cuts. We are interested in objects R < 24.

Discard match!!

Results: MMR in M49

Cleaned CMD diagram.Total number of globular clusters: 2417

Strong bimodality! Well defined metal-poor and metal-rich populations.

How can we determine a MMR slope?

Results: MMR in M49

Locating Color Peaks: Gaussian Mixture Model (Muratov & Gnedin 2010).Peak locations: (C-R) = 1.32 and (C-R) = 1.81.

N ~ 17

18 objec

tsN ~

698 o

bjects

Results: MMR in M49Is there a MMR slope? No. Results agree with previous observations.

Sample was divided accoring to a limiting color, both populations have the same number contribution, (C-R) = 1.56 (shown in green)

Higher polynomial fitting (Least Squares Fit) to both populations yielded slopes (shown in blue and red).

(C-R) = -0.005R2+0.159R+0.197(C-R) = -0.009R2+0.421R-2.922

Results: MMR in M49, Magnitude Cuts

Is the lack of a MMR slope due to our splitting methods? No.

Splittings: (1) 1.1 < (C-R) < 2.1(2) 0.0 < (C-R) < 3.1

Similar conclusion reached: The data are consistent with a zero MMR slope.

Results: MMR in M49, ModelingMaxwell et al. (2014). Recreate accretion during orbit transit scenario.

Bondi & Hoyle Accretion

Metallicity estimate

Results: MMR in M49, Modeling

Final GC metallicity is plotted versus intial GC mass. Each lines represents a different cloud metallicity running from -3.0 to -0.3. The final metallicity is left as a free parameter. V ~ 25km/s.

Metal-RichMetal-Poor

Results: MMR in M49, ModelingIs there any degeneracy among the different parameters?

Metal-PoorHigher velocity, v~ 20km/s

Metal-PoorLower Density v ~ 25 km/s

Indeed, there is a degree of degeneracy among the parameters of this model, e.g, smaller velocities have similar effects as larger masses. Simulation shows that the initial mass and the velocity of the system are the most influential parameters in obtaining a MMR slope.

Results: MMR in M49, Fitting

Metal-Poor

Comparison to real data.

Results: Does our model work in MMR galaxies?

Strong MMR in NGC 4696. Our model works with both types of galaxies.

Metal-Poor

Summary

• Deep C and R photometry using the CTIO 4m telescope has been done in the massive elliptical galaxy, M49, located in the Virgo cluster.

• The GCS of M49 shows a very clear color-bimodality in its (C-T1) color distributions.

• The GCS of M49 does not exhibit a clear MMR slope.

• Self-enrichment is still a possible mechanism to produce a MMR slope.

• Using the Maxwell et al. (2014) approach, the mass of the cluster, the velocity and the metallicity of the surrounding gas are the most influential parameters in the accretion set up

Many thanks to my adviser Bill Harris for his outstanding mentoring and for sharing with me part of his boundless knowledge of astronomy. Without his precious help, this thesis would not have been possible. I want to thank my thesis committee, Dr. Laura Parker and Dr. Alison Sils for their insightful comments. Many, many thanks are due to the entire staff of the Department of Physics and Astronomy for the many kindness shown to me over the past two years.

I would also like to thank my officemates and ex-officemates, I appreciated every coffee break in their company.

Finally, I want to thank my parents, Mahmoud and Maria, who happened to visit during the busiest time of this whole project. Your presence was comforting and your cooking simply the best; thanks for your endless support.

awaiting revisions…