1. Galaxy evolution in group environments: The role of preprocessing
Gandhali Joshi
PhD Committee Meeting
6 July 2017

2. Introduction
Populations of galaxies in groups and clusters vs. field populations:
redder, reduced star formation rates,more elliptical morphologies
Trends present in lower mass groups => evidence for pre-processing?
Possible evolution mechanisms:
Local environment based :
Harassment, tidal stripping, mergers
Global environment based:
Starvation, ram pressure stripping
Different time scales involved, dependent on location within host group

3. Aim
Understand what are the various processes of galaxy evolution in groups with a focus on mass loss and star formation quenching
Establish the degree and importance of pre- processing

4. Dark Matter Simulation
N-body, dark matter simulation using ChaNGa [Jetley+ 2008,2010; Menon+2015]
(100 Mpc)3 comoving volume
10243 particles
mparticle = 3.7×107 Mʘ
200 snapshots, 68.9 Myr apart.
Halo finding using ROCKSTAR [Behroozi+ 2013a] and Consistent Trees [Behroozi+ 2013b]

5. Project 1: Selecting galaxy analogues
Mass      

6. Project 1: Mass segregation
Much noisier trend when considering only massive analogues
Significant trend in average mass within 0.5rvir
Nearly no trend outside 0.5rvir

7. Project 2: Mass Loss and Pre-processing
Mpeak ~ Mstellar
Strong radial trend of mass loss since peak within rvir

8. Project 2 : Total mass loss
Single galaxies retain more mass than grouped galaxies
Break separates backsplash galaxies

9. Project 2: Before & after accretion
Before crossing, grouped galaxies lose significantly more mass
After crossing, single galaxies lose more mass within rvir, “catch up” to the grouped galaxies

10. Project 2: Mass loss with time
Amount of mass lost is determined by time spent in dense environment
Before crossing
After crossing

11. Hydrodynamical Simulation
SPH hydrodynamical zoom-in simulation of a galaxy group using Gasoline [Wadsley+ 2004]
Group properties:
Mvir = 2.7×107 Mʘ
Rvir = kpc
High-res region:
mDM = 3.9×106 Mʘ
mbaryon = 7.2×105 Mʘ
87 snapshots, Myr apart.
Halo finding using ROCKSTAR [Behroozi+ 2013a] and Consistent Trees [Behroozi+ 2013b]

12. Project 3: Mass loss over time
Dark matter
Gas
Significant mass loss in dark matter and gas, but not stars
Mass
Stars
Time

13. Project 3: Gas mass loss and sSFR
Cold gas
sSFR
Time
Similar trends in cold and hot gas
Gradual decline in sSFR – faster for grouped galaxies
Hot gas
Mass
Time

14. Project 3: Radial trajectories
Dark matter
Single
Grouped
Distance from group
Mass
(Time)

15. Project 3: Radial trajectories
Stars
Single
Grouped
Distance from group
Mass
(Time)

16. Project 3: Dark matter vs. gas and the role of ram pressure
Single
Grouped
Mgas/MDM
Ram pressure
Distance from group

17. Project 3: Implications for galaxy properties
Similar gas fractions for all three categories
But higher stellar fractions for single galaxies, even higher for grouped galaxies – scatter in SMHM relation?
Mstar/Mtot
Mgas/Mtot
Mtot

18. Timeline Currently: Completing final science chapter
By July 14: Complete thesis draft
By July 21: Initiate defense process
By Aug 4: Submit thesis
Sep 15: Defense

19. Extra slides

20. Project 1: Mass segregation
Small Groups
Large Groups
Clusters
Segregation trends dominated by small and large groups
Nearly no trend seen in clusters

21. Single
Grouped
Distance from group
Mass