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Patricia Novais Seminário de Extragaláctica 09/06/16
Overview
Understand how the stellar counter-rotating components in the galaxy were formed, through the study of their kinematics and properties.
2
Counter-rotating discs in galaxies! 3
For a review: Corsini et al. 2014 For a review:
Corsini et al. 2014 For a review: Corsini et al. 2014 For a review:
Corsini et al. 2014 For a review: Corsini et al. 2014
For a review: Corsini et al. 2014
I. Gas vs. stars (NGC4546)
II. Stars vs. stars (NGC4550)
III. Gas vs. gas (NGC7332)
Counter-rotating discs in galaxies! 4
For a review: Corsini et al. 2014 For a review:
Corsini et al. 2014 For a review: Corsini et al. 2014 For a review:
Corsini et al. 2014 For a review: Corsini et al. 2014
For a review: Corsini et al. 2014
I. retrograde acquisition of external gas and subsequent star formation
II. assembly of the counter-rotating stellar component from mergers
III. or internal instabilities.
Scenarios
NGC 4191
Ø S0 isolated galaxy at D = 42.4 Mpc Ø Stellar velocity field reveals an irregular structure with little rotation Ø Stellar velocity dispersion field shows two symmetric peaks Ø VIRUS-W IFU Spectrograph Ø Low resolution mode, 4340Å-6040Å 5
Analysis 6
I. Kinematics
II. Photometry
III. Stellar Populations
Kinematics
Line-of-sight velocity distribution (LOSVD) with double peak
Clear bimodal structure
7
Photometry
▹ 2D image-fitting with IMFIT: a Sérsic bulge + 2 exponential discs. ▹ Residual map: spiral-arm pattern? Faint spiral arm?
8
Photometry 9
In fact, 3 components is a good choice to describe the surface brightness radial profile.
Kinematics 10
Main V = 70 km/s σ= 120 km/s
Secondary V = 130 km/s σ= 90 km/s
Gas V = 150 km/s σ= from 60km/s to 30km/s
Stellar Populations 11
▹ Hβ, MG b, Fe5270, Fe5335 for both components: ▹ Properties very similar… ▹ Age radial profile: negative gradients.
Stellar Populations
▹ α elements and metallicity: no significant radial gradients
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Main: Age: ~12Gyr to ~6Gyr
Secondary: Age: ~12Gyr to ~3Gyr
Gas
▹ A elongated ring-like structure (or spiral arms) with 3 blobs within 25 ▹ Similar spiral-like structure in the residual maps
13
Possible scenario
▹ 2 components: bulge and disk + disk ▹ 2nd component more faster than the 1st. ▹ Properties of stellar populations very similar ▹ α elements and metallicity: no radial significant grandients ▹ Negative age radial gradient: inside-out formation ▹ Δage(main-sec) ~ 2Gyr
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I - Accretion scenario is better than merger scenario…
Conclusion 15
▹ Galaxy w/ 2 components rotating in opposite directions ▹ Inside-out formation for the 2nd component ▹ Accretion scenario ▹ Faint spiral-like structure
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THANKS!
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