Spectroscopic Indicators of Galaxy Evolution:

Early-type Galaxies in Cl0024+16 at z~0.4

Sean MoranGe/Ay 132

Large Scale Surveys of Cl0024+17 (z~0.39) and MS0451-03 (Z~0.54)

• Cl0024: – 39 sparsely sampled

WFPC2 images, to 5 Mpc– Spectra of over 200

members

• MS0451: – Full coverage with 40 ACS

pointings; in progress– Complimentary cluster: ~8x

LX of Cl0024

Morphology-Densityand Environmental Processes

• Mix of galaxy types depends on where you look

• More Ellipticals in cluster centers

• Clusters: laboratories to study galaxies over a large range of Σ

• Chicken or Egg:– initial conditions (E/S0 form

in initially denser regions)– environmental processes

(galaxies are transformed by environment as they fall into denser regions.) Treu et al. (2003)

Environmental Processes• Spectral Properties as fn

of radius to disentangle these processes

• First results on Cl0024: look at Early type galaxies: [OII], [OIII], Hγ, Hδ

• Are there abrupt and/or gradual changes in galaxy properties?

[OII]• Emission from [OII] 3726,

3729Å can indicate ongoing star formation (HII regions near O, B stars)

• Transitions from: 2D3/2->4S3/2

2D5/2->4S3/2

• Also prominent in AGN

(Osterbrock 1989)

[OIII]• Emission from [OIII]

4959Å , 5007Å can also indicate star formation

• Transitions from: 1D2->3P2

1D2->3P1

• Additional transition at 4363A too weak at these distances (1S0->1D2)

• Also in AGN

(Osterbrock 1989)

Hγ, Hδ

• Hydrogen Balmer absorption may indicate recent star formation:– A and F stars relatively short-lived, but exhibit

strong Balmer lines• Balmer emission may indicate either AGN

activity or more HII regions from O, B stars.

• Line ratios help distinguish

• AGN show emission in Hγ, sometimes in Hδ• For non-AGN, EW of lines increases w/ radius• Population of early types shows some star formation at

edge of cluster

Conclusions

• Via [OII], [OIII], we identify AGN within a narrow range in cluster radius

• [OII], Hγ, Hδ EWs increase outward: some early types undergo ‘gentle’ interaction with cluster environment

• Will want to see if the trends in spectral features of spiral galaxies are as abrupt as we see for early types.