1. Dwarf Galaxies and Their Destruction... Marla Geha Carnegie Observatories (OCIW) Collaborators: P. Guhathakurta (UCSC), R. van der Marel (STScI)

2. In Milky Way-like environments, dwarf accretion is expected to contribute to build-up of stellar mass. Lacey & Cole (1993) NGC 205 Wechsler et al (2002), Helly et al. (2003) NGC 770 Dwarfs and the Build-up of Massive Galaxies

3. In studying M31, can resolve individual stars while maintaining the ‘big’ picture. M31: Evidence for Dwarf Galaxy Accretion

4. Ferguson et al. (2002) Ibata et al. (2001) Giant Stream Ibata et al (2004) Guhathakurta et al (2004) N205 Stream? McConnachie et al (2004) M31: Evidence for Dwarf Galaxy Accretion

5. NGC 205 M v = -16.5 Intermediate between LMC and Sag dSph. NGC 205 provides a detailed view of a disrupting satellite.

6. NGC 205: Evidence of Tidal Interactions Surface photometry of NGC205 consistent with early tidal disruption. Constrain interaction via kinematics of individual stars. ( Choi, Guhathakurta & Johnston 2003) Integrated-light spectroscopy cannot probe beyond half-light radius.

7. Targets chosen to be likely RBG stars Ca II triplet region (7800-9200A) Radial velocities for 725 RGB stars ( ~10 km/s). NGC 205: Keck/DEIMOS Observations

8. NGC 205: Major-axis Velocity Profile Keck/DEIMOS stars Simien & Prugniel (2000) Bender et al. (1990) -> dEs supported by anisotropic velocity dispersions. Half light radius = 2.5’ Tidal radius = 5’

9. NGC 205: Major-axis Velocity Profile Keck/DEIMOS stars Simien & Prugniel (2000) Inner rotation = 15 km s -1 Half light radius = 2.5’ Tidal radius = 5’

10. NGC 205: Major-axis Velocity Profile Half light radius = 2.5’ Tidal radius = 5’ Keck/DEIMOS stars Simien & Prugniel (2000) Inner rotation = 15 km s -1 Velocity turn-over beyond tidal radius strong constraint on interaction w/M31.

11. NGC 205: 2-Body Modelling Orbital modeling will provide insight into role of distrupted satellites in halo formation.

12. Lacey & Cole (1993) NGC 205 Example #1

13. Lacey & Cole (1993) NGC 770 Example #2

14. Another Minor Merger System -- Survey of dwarf galaxies in groups. -- Isolated system, distance ~ 30 Mpc. NGC 770 Mv ~ -18.5 V-band Keck/ESI 2’x2’

15. Keck/ESI spectroscopy A Counter-Rotating Core in NGC 770 Counter-rotating cores provide strong evidence of a past merging events. This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions. This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions.

16. Keck/ESI spectroscopy Gemini/GMOS IFU spectroscopy A Counter-Rotating Core in NGC 770 This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions. This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions.

17. Keck/ESI spectroscopy Gemini/GMOS IFU spectroscopy A Counter-Rotating Core in NGC 770 This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions. This counter-rotating core is unusual: - faintest known host galaxy. - region of on-going interactions.

18. A Young Counter-Rotating Disk? Photometric disk is co-spatial and aligned with counter-rotation. ~3% of total galaxy light. Comparison to stellar pop models suggests counter-rotating core ~ 3 Gyr. younger than main galaxy.

19. 1. Counter-rotating core formed during very minor merger with gas-rich dwarf galaxy (M ~ -14.) 2. Counter-rotating core formed during past interactions with primary galaxy -> gas accretion from primary. A Counter-Rotating Core in NGC 770 A Counter-Rotating Core in NGC 770 Lack of other galaxies in region limits formation scenarios: If (1) then NGC 770 is an excellent example of dwarf-dwarf galaxy merging. If (1) then NGC 770 is an excellent example of dwarf-dwarf galaxy merging.

20. HI Gas near NGC 770 HI Gas near NGC 770 HI map suggest recent interactions ~100Myr VLA D-array map (Iyer & Simpson 2001) HI column density HI velocity map

21. Conclusions NGC 205: On-going minor merger. Strong constraint on interaction history w/M31. NGC 770: Example of dwarf-dwarf galaxy merging. (astro-ph/0503370)