Dwarf Galaxiesand Their Destruction...
Dwarf Galaxiesand Their Destruction...
Marla GehaCarnegie Observatories (OCIW)
Collaborators: P. Guhathakurta (UCSC), R. van der Marel (STScI)
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 GalaxiesDwarfs and the Build-up of Massive Galaxies
In studying M31, can resolve individual starswhile maintaining the ‘big’ picture.
M31: Evidence for Dwarf Galaxy AccretionM31: Evidence for Dwarf Galaxy Accretion
Ferguson et al. (2002)Ibata et al. (2001)
Giant StreamIbata et al (2004)Guhathakurta et al (2004)
N205 Stream?McConnachie et al (2004)
M31: Evidence for Dwarf Galaxy AccretionM31: Evidence for Dwarf Galaxy Accretion
NGC 205 Mv
= -16.5
Intermediate betweenLMC and Sag dSph.
NGC 205 provides a detailed view of a disrupting satellite.NGC 205 provides a detailed view of a disrupting satellite.
NGC 205: Evidence of Tidal Interactions 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.
Integrated-light spectroscopy cannot probe beyond half-light radius.
• 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 ObservationsNGC 205: Keck/DEIMOS Observations
NGC 205: Major-axis Velocity ProfileNGC 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’
NGC 205: Major-axis Velocity ProfileNGC 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’
NGC 205: Major-axis Velocity ProfileNGC 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.
NGC 205: 2-Body ModellingNGC 205: 2-Body Modelling
Orbital modeling will provide insight into role of distrupted satellites in halo formation.
NGC 205
Example #1Example #1
NGC 770
Example #2Example #2
Another Minor Merger System Another Minor Merger System
-- Survey of dwarf galaxies in groups.-- Isolated system, distance ~ 30 Mpc.
NGC 770Mv ~ -18.5
V-band Keck/ESI 2’x2’
Keck/ESI spectroscopy
A Counter-Rotating Core in NGC 770 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.
Keck/ESI spectroscopy
Gemini/GMOS IFU spectroscopy
A Counter-Rotating Core in NGC 770 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.
Keck/ESI spectroscopy
Gemini/GMOS IFU spectroscopy
A Counter-Rotating Core in NGC 770 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.
A Young Counter-Rotating Disk? 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.
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 exampleof dwarf-dwarf galaxy merging. If (1) then NGC 770 is an excellent exampleof dwarf-dwarf galaxy merging.
HI Gas near NGC 770 HI Gas near NGC 770 HI map suggest recent interactions ~100MyrHI map suggest recent interactions ~100Myr
VLA D-array map (Iyer & Simpson 2001)
HI column density HI velocity map
ConclusionsConclusions
NGC 205: On-going minor merger. Strong constraint on interaction history w/M31.
NGC 770: Example ofdwarf-dwarf galaxy merging. (astro-ph/0503370)