1. The dust attenuation in the galaxy merger Mrk848
沈世银
上海天文台
袁方婷, Maria Argudo Fernandez

2. Introduction
Galaxy merging is important for galaxy formation and evolution
Gas inflow, star formation enhancement
Metallicity
Details of the interaction triggered star formation are not clear
Spatial extent
Quantitative study of the SF enhancement
Dust properties affected by the interaction

3. Multi-wavelength data
UV: GALEX (FUV, NUV)
Optical: SDSS
IR: Spitzer IRAC (3.6, 4.5, 5.8, 8 micron)
Match these bands by degrading all these images into GALEX NUV resolution (~6”)

4. IFS data from MaNGA Mapping Nearby Galaxies at APO
, one of the project of SDSS IV
SHAO, NAOC, NJU, TU
10,000 galaxies (largest IFS survey)
wavelength coverage
IFU size from 19 to 127 fibers, diameters from 12″ to 32″

5. IFS cover R3, R4 and R5, partly
R1, R2 and R5, R6 are tail regions
R3 and R4 are core regions

6. Spectra fitting of IFS data
Spectral fitting with pPXF(Penalized Pixel-Fitting)
BC03 SSP, metallicity [0.0001, 0.05], age [10Myr, 13Gyr]
Dust attenuation: as a parameter, assuming Calzetti Law

7. SED fitting of multi-wavelength data
SED fitting with CIGALE
BC03 SSP, two populations with exponentially decreasing SFHs
Attenuation: Calzetti Law
But E(B-V)old=0.5E(B-V)young
Dust emission is modeled using
the templates of Dale+2014
Old
SFR
Young t

9. Results: Dust attenuation
E(B-V)s from pPXF vs from CIGALE
E(B-V)[ppxf]=0.6E(B-V)[CIGALE]

10. Direct indicators without fitting
IRX: the FIR-to-UV ratio (Buat et al. 2005)
(AUV=10.23E(B-V)s)

11. IRX-beta
Cores
Cores follow the starburst law, tails are more similar to the quiescent galaxies

12. E(B-V) from Balmer decrement

13. Comparing with the color excess given by Balmer decrement
E(B-V)[SED UV-IR]
~ E(B-V)[gas]
~ 2E(B-V)[optical]

14. What happens? Two components of dust (model from Charlot&Fall 2000)
Young stars are embedded in the birth clouds and thus suffer from heavier attenuation
Similar results from higher redshifts (Kashino et al. 2013, Price et al. 2014, Puglisi et al. 2016)
Price et al. (2014)

15. Dust lane？ Grey extinction in UV-optical Emission in IR
E(B-V)[IR] > E(B-V)[UV-optical]
E(B-V)[UV] ~ E(B-V)[IR]

16. What effects?
Fit the spectra with the dust attenuation as a free parameter
First correct the spectra with the UV-to-IR derived dust attenuation, and then fit the spectra
Using two-component dust model:
E(B-V)[t<t_0]=2E(B-V)[t>t_0]
E(B-V)[t>t_0]: [0.05,0.3]
t_0:[10Myr, 500Myr]

17. Dust extinction as a free parameter
Correcting the spectra using SED derived dust extinction

18. Star formation history of Mrk848
Recent star burst happens 50M years ago
Merge time scale?
More recent star burst in central region(R4)
Gas inflow?

19. Conclusion
Even with the best photometry and spectroscopy data in hand, the break of the degeneracy between the stellar population and dust attenuation is a non-trivial task for (merge) galaxies.
For the case study of Mrk848, we find that the dust attenuation implied from different data set could only be explained by a two dust components model ?.
E(B-V)[UV-IR] ~ E(B-V)[gas] ~ 2E(B-V)[optical]