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Pota et al., 2015, A SLUGGS and Gemini/GMOS combined study of the elliptical galaxyM60: wide-field photometry and kinematics of the globular cluster system

by 펄서까투리 2021. 8. 23.

# 세줄 요약 #

  1. We present new wide-field photometry and spectroscopy of the globular clusters (GCs) around NGC 4649 (M60), the third brightest galaxy in the Virgo cluster.
  2. We confirm significant GC colour bimodality and find that the red GCs are more centrally concentrated, while the blue GCs are more spatially extended.
  3. We find that formation via a major merger between two gas-poor galaxies, followed by satellite accretion, can consistently reproduce the observations of NGC 4649 at different radii.

 

# 상세 리뷰 #

1. Photometric study of NGC4649

Fig 1. Subaru/Suprime-Cam gri colour image of NGC 4649 (left) and NGC 4647 (right). The projected separation between the two galaxies is 13 kpc. There are no clear signs of interaction between the two galaxies. [Pota et al., 2015]

  • HST/ACS, CFHT/MegaCam, Subaru/Suprime-Cam

Fig 2. . Overview of the observations. Shown is a Digitized Sky Survey image of NGC 4649 and surroundings. [Pota et al., 2015]

  • GC color bimodality
    • The red GCs: more centrally concentrated
    • The blue GCs: more spatially extended

Fig 3. GC surface density profiles. Blue and red GCs are colour coded accordingly. Open and filled circles are from HST/ACS and from groundbased photometry, respectively. The red GCs are more centrally concentrated than the blue GCs. [Pota et al., 2015]

  • color gradient
    • A negative GC color gradients in the innermost 20 kpc
    • A flat gradients out to large radii

Fig 4. Radial variation of GC colours. Grey and black small points are GC candidates from HST observations and from our ground-based imaging, respectively. The GC subpopulation colour gradients are steeper towards the galaxy centre. [Pota et al., 2015]

 

2. Spectroscopic study of NGC 4649

  • Keck/DEIMOS, Gemini/GMOS, MMT/Hectospec

Fig 5. Spectrum of a GC of NGC 4649 as seen from the three multi-object spectrographs used in this paper. Red is DEIMOS, blue is GMOS and green is Hectospec [Pota et al., 2015]

  • Confirmed 431 GCs catalog
    • A factor of 3.5 larger than previous data sets
    • A factor of 3 improvements in velocity precision.

Fig 6. Spatial distribution of the spectroscopically confirmed objects. NGC 4649 is at (0, 0). Top and right-hand axes show the comoving physical scale at the distance of NGC 4649. [Pota et al., 2015]

  • Spectroscopy result
    • Significant rotation at all radii
    • Counter-rotating Subgroups
    • Bumpy velocity dispersion
    • all result meaning -> major merger?

Fig 7. GC velocity distribution versus galactocentric radius. Shown are all 447 spectroscopically confirmed objects. Left-hand panel: observed radial velocities versus galactocentric distance R, shown in physical units on the top axis. Grey points are objects associated with NGC 4649; Green stars are Galactic stars. The ±3σ envelope of the NGC 4649 GCs (grey points only) is shown as a blue lines. Right-hand panel: velocity distribution histogram for GCs/UCDs belonging to NGC 4649 only (grey histogram), and Galactic stars (green histogram). [Pota et al., 2015]

 

3. Formation scenarios of NGC 4649

  • Stage 1. Dry major merger -> Stage 2. Satellite accretion
  • Spiral galaxy gas stripping -> Elliptical galaxy [S0 type]
    • but non-detection primordial disc
  • no strong evidence: interacting with neighboring NGC 4647

 

* Reference: Pota, V., “A SLUGGS and Gemini/GMOS combined study of the elliptical galaxy M60: wide-field photometry and kinematics of the globular cluster system”, [Monthly Notices of the Royal Astronomical Society], vol. 450, no. 2, pp. 1962–1983, 2015. doi:10.1093/mnras/stv677.

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