Three-Dimensional Distribution of the Interstellar Dust in the Milky Way Helong Guo (郭贺龙，helong_guo@mail.ynu.edu.cn) Supervisor: Xiaowei Liu，Bingqiu Chen Yunnan University

Introduction Dust makes up just about 1% of the interstellar medium (ISM), but plays important role in a number of physical and chemical processes. 2D map only give the total amount of extinction in a given direction integrated along the line-of-sight, So for, Several approaches are available to obtain information of distance and derive an extinction map in three dimensions (3D). Some efforts have already been made to model the structure of inter-stellar dust in the Milky Way. However the dust disk structure parameters of the Milky Way have not been well constrained.

3D extinction map Sale et al. (2014) Chen et al. (2019) Marshall et al.(2006) Chen et al. (2013) Schultheis et al. (2014) Chen et al. (2014) Sale et al. (2014) Chen et al. (2019) Green et al. (2015,2018,2019) Hanson et al. (2016)

The SkyMapper Southern Sky Survey (DR1) Location(s): SDO, Australia Wavelength: 325 - 969nm 6 bands: u,v,g,r,i,z The Shallow survey: median point source completeness limits in AB mag are (17.75, 17.5, 18, 18, 17.75, 17.5) for (u, v, g, r, i, z). Coverage: Dec < 0 deg Wolf el al. (2018)

Gaia (DR2) Gaia Collaboration et al., (2018)

Data   Data distribution l (deg) b(deg)  

METHOD   Berry et al. (2011)

Results: Integrated 2D maps Orion Vela Chamaeleon The map covers about 14,000 deg2 sky area of the Galactic Southern Sky with spanning distances ranging from 0 to ∼ 5 kpc. The angular resolution of 6.9 arcmin for Galactic latitudes −10◦ < b < 10◦ , 14 arcmin for −10◦ <b < −30◦ and 27 arcmin for b < −30◦ .

Results: 3D differential maps d < 0.4 kpc 0.4 < d < 0.8 kpc Orion Chamaeleon Vela 0.8 < d < 1.6 kpc 1.6 < d < 5.0 kpc

Extinction values of the individual stars compared with previous work

3D extinction maps compared with previous work Ours minus those of Chen et al (2019), from top to bottom, 400, 1000, 1600, 2200, 3000 and 5000pc Ours minus those of Green et al (2018), from top to bottom, 1.0, 2.0, 3.0, and 5.0kpc.

The all-sky 3D extinction map d < 0.4kpc Our this work: b < -10° Chen et al. (2019): |b| < 10° Green et al. (2018): δ > -30° 0.4<d <0.8kpc 0.8<d <1.6kpc

The dust disk of the Milky Way Averaged δE(B-V ) (in unit of mag/kpc) distribution in R and Z space. The bin size is 100 pc × 100 pc. Distribution of the cumulative extinction in magnitudes of E(B − V ) out to distance of 5 kpc. The maps use a Galactic Mollweide projection, with the l = 0◦ in the middle of the map. Regions shaded grey are not covered by our maps.

The dust disk of the Milky Way Model:We divided the all-sky 3D extinction map into 9 bins of different R ranges, from 6.3 kpc to 10.8 kpc with bin-size of 0.5 kpc. For each bin, the vertical distribution of the Galactic dust is described by sech2 functions, similar as the Galactic stellar disk model, Two models: single disk model (N =1) two disks model (N =2). parameter: ρ0,j Hj ZΘ C where ρ0,j and Hj are the dust density at the Galactic plane, C is an offset.

Model fitting Fitting the vertical dust distribution respectively with one-disk model (left panel) and two-disks model (right panel) in different R slices. The black dots and error bars are median and standard errors of the mean in Z bins of 0.025 kpc width. The curves of different colours are the fits.

Compare two models To discriminate between the two models, we introduce the Bayesian Information Criterion (BIC; Schwarz 1978), defined as, ∆BIC<2: barey worth mentioning 2<∆BIC<6: positive 6<∆BIC<10: strong ∆BIC>10: significantly In the inner disk (R < 8.3 kpc), the two-disk model is significantly preferred over the one-disk model, with ln(∆BIC ) of about 9.77. For the outer disk (R > 8.3 kpc), the two-disk model is also significantly preferred over the one-disk model, with ln(∆BIC ) of about 8.25.

Scale-height for each Rbin H=205.5±1.46 pc H2=224.6±0.72 pc H1=72.7±2. 2 pc H=205.5±1.46 pc Yuan et al. (in prep.) and Dobashi et al. (in prep.) H1=70 pc, H2=200 pc Resulted scale-heights Hj as functions of the radial distances R for respectively for the one-disk model (left panel) and two-disks model (right panel).

Summary  

Thanks for attention!