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)