Geometrically Thick Dust Layer in Edge-on Galaxies

Transcription

1 Geometrically Thick Dust Layer in Edge-on Galaxies A Case Study of NGC 891! Kwang-Il Seon 1, Adolf N. Witt 2, Jong-Ho Shinn 1, & Il-Joong Kim 1!! 1 Korea Astronomy and Space Science Institute! 2 University of Toledo, USA

2 Dust Distribution: Geometrically Thin Disk Most of dust is concentrated in the galactic midplane scaleheight ~.2 kpc Xilouris et al. (1999)

3 Dust Mass: Central Face-on Optical Depth NGC 891: Optical/near-IR observations: Xilouris et al. (1998) central face-on optical depth ~.9 at B-band Far-IR/sub-mm observations: The spectral energy distribution (SED) in Far-IR/submm requires at least a dust mass twice, up to four times, as large as estimated from the radiative transfer model of optical/near-ir images. central face-on optical depth ~ 2.6: (Bianchi 28) central face-on optical depth ~ 4.: (Popescu et al. 2; Bianchi & Xilouris 211) λ F λ [ erg cm 2 s 1 ] this work Bianchi (28) Popescu et al. (211) Herschel SPIRE Planck HFI 1 1 λ [ µm ] ig. 2. The integrated FIR-submm SED Bianchi of NGC & 891. Xilouris (211)

4 Extraplanar Dust Additional dust component that exists in a form different from the geometrically thin disk. In fact, filamentary dust structures above the galactic plane is observed using the unsharp-mask technique of high-resolution optical images. Unsharp masked image = original image / smoothed image. These highly structured dust-bearing clouds are viewed in absorption against the background stellar light of the galaxy.

5 Extraplanar Dust Clouds - NGC 891 The dusty structures are traceable to heights z ~ 2 kpc from the midplane. They have a visual extinction of > 1. About 1-2% of total dust mass Howk & Savage (2)

6 Extraplanar Dust Clouds - NGC 4217 Thompson et al. (24)

7 Diffuse Extraplanar Dust? The filamentary features, however, were traced in absorption against the background starlight, implying preferentially dense dust features visible only to heights limited by the vertical extent of the background starlight. Therefore, diffuse dust component above the galactic plane were not traceable in the studies.

8 UV Reflection Nebula? The diffuse dust should appear as a faint extended reflection nebula illuminated by starlight. The scattered light would not be easily distinguished from direct starlight when the scale height of the light source is greater than or comparable to that of the extra planar dust. Therefore, UV observation of edge-on galaxies can provide the best method for detecting the scattered light from the diffuse extra planar dust, because OB stars, the main source of the UV continuum, have a scale height <.2 kpc and have no bulge or halo component.

9 GALEX observation of NGC 891

10 GALEX UV Observations NGC 891 NGC 413 NGC 4217 NGC 432 NGC 46 NGC 97 Shinn et al. (in preparation)

11 1 HODGES-KLUCK & BREGMAN Swift/GALEX UV Observations RGB images with three Swift UV bands. Figure 6. Hodges-Kluck Halo emission fluxes and& SEDs Bregman for Scd spiral galaxies (214, in ourarxiv, sample continued. submitted)

12 Geometrically Thick Dust Disk in NGC 891 Asymmetry between NE (left) and SW (right) sides. The average vertical profile is composed of a core and an extended tail and the profile is well fitted with two exponential function FUV 2 h 22 m 4 s h 23 m s 2 h 22 m 2 s Radial profile ( 3 CU) FUV Radial profile Vertical profile (CU) FUV Vertical profile NUV 2 h 22 m 4 s h 23 m s 2 h 22 m 2 s Radial profile ( 3 CU) NUV Vertical profile (CU) NUV -1-1 Seon et al. (214)

13 Radiative Transfer Model The core + extended tail suggests two exponential dust disks: geometrical thin + dust disks. Two exponential dust disks!! ( κ(r, z) = κ thin exp r + κ exp h thin d ( z ) zd thin r z h d An exponential stellar disk z d ) central face-on optical depth: τ = τ thin + τ = 2κ thin en by ( ) zd thin +2κ zd I(r, z) = I exp ( r z ) h s z s

14 Assumptions:!!! Optical/near-IR observations: Approach central face-on optical depth (of thin disk) ~.9 at B-band Far-IR/sub-mm observations: The SED in Far-IR/submm requires at least a dust mass twice, up to four times, as large as estimated from the optical/near-ir images. (total) central face-on optical depth ~ 2.6 or 4.! was assumed to have the h thin d = h d = 8kpc. e = 89 8andadista d = d inclination angle θ = GC distance 891 (van = 9. der Mpc Kruit & Searl

15 Three model types: Type 1: optical depth of thin disk =.9 at B-band (Xilouris 1998, 199) Type 2: total (thin+) optical depth = 2.6 (Bianchi 28) Type 3: total (thin+) optical depth = 4. (Popescu et al. 2; Bianchi & Xilouris 211) We varied the optical depth of the dust disk from.1 to 1.2 in steps of. or.1. The best-fit values of other parameters were obtained for each optical depth of the disk.!!

16 Best-fit Parameters black: type 1 (optical depth of thin dust disk =.9 at B-band) red : type 2 (total optical depth = 2.6 at B-band) blue : type 3 (total optical depth = 4. at B-band) scaleheight of dust disk scaleheight of thin dust disk/ stellar disk scalelength of stellar disk radial size of dust/stellar disk SFR or UV luminosity of stellar disk FUV (kpc) z d FUV τ B thin =.9 τ B tot = 2.6 τ B tot = 4. (kpc) and z s (kpc) z d thin τ B z d thin (line) z s (symbol) τ B h s (kpc) τ B R d (kpc) and R s (kpc) R d (line) R s (symbol) τ B SFR (M τ B NUV (kpc) z d NUV τ B thin =.9 τ B tot = 2.6 τ B tot = 4. (kpc) and z s (kpc) z d thin τ B z d thin (line) z s (symbol) τ B h s (kpc) τ B R d (kpc) and R s (kpc) R d (line) R s (symbol) τ B τ B

17 Best-fit Models (type 2) total optical depth = FUV data 1 - FUV model 1 - NUV data 1 - NUV model Intensity ( 3 CU) x <18 x <4 4< x <8 8< x < Intensity ( 3 CU) z <1 z <1. 1.< z <3 3< z < Intensity ( 3 CU) x <18 x <4 4< x <8 8< x < Intensity ( 3 CU) z <1 z <1. 1.< z <3 3< z <

18 Best-fit Models (type 3) total optical depth = FUV data 1 - FUV model 1 - NUV data 1 - NUV model Intensity ( 3 CU) x <18 x <4 4< x <8 8< x < Intensity ( 3 CU) z <1 z <1. 1.< z <3 3< z < Intensity ( 3 CU) x <18 x <4 4< x <8 8< x < Intensity ( 3 CU) z <1 z <1. 1.< z <3 3< z <

19 Vertical Far-IR Profile Comparison with Herschel/PACS observations Houghes et al. (214) Dashed curves: PSF Red curves: thin disk model, convolved with PSF Blue curves: observed profile Blue circles: adopted from Houghes et al. (214) Red line : best-fit model, convolved with PSF Solid line : thin + disks profile Dotted line : thin disk profile Dashed line: PACS PSF

20 Extended PAH emission? WISE W3 band (12µm; 8.6µm µm PAH)

21 GALEX Image of Sombrero

22 UV Halo Luminosity vs Galaxy Properties One of the promising scenarios for the origins of the extra planar dust would be expulsion of dust in the galactic plane via stellar radiation pressure and/or (magneto)hydrodyamic flows such as galactic fountains and chimneys

23 Transport of Dust Grains Transport of charged dust grains into the galactic halo Sergey Khoperskov Institute of Astronomy of the Russian Academy of Sciences, Pyatnitskaya st., 48, Moscow, Russia Sternberg AstronomicalInstitute, Moscow MV LomonosovState University, Universitetskij pr., 13, Moscow, Russia Yuri Shchekinov Southern Federal University, Sorge Str., Rostov-on-Don 3449, Russia We develop a 3D dynamical model of dust outflows from galactic discs. The outflows are initiated by multiple SN explosions in a magnetized interstellar medium (ISM) with a gravitationally stratified density distribution. Dust grains are treated as particles in cells interacting collisionally with gas, and forced by stellar radiation of the disc and Lorenz force. We show that magnetic field plays a crucial role in accelerating the charged dust grains and expelling them out of the disc: in 1 2 Myr they can be elevated at distances up to 1 kpc abovethegalacticplane.the dust-to-gas ratio in the outflowing medium varies in the range along the vertical stream. Overall the dust mass loss rate depends on the parameters of ISM and may reach up to M yr 1.

24 Summary Swift/GALEX data suggest the widespread existence of geometrically dust layer above the galactic plane in normal star-forming galaxies. NGC 891 We model the vertically extended FUV/NUV emissions in edge-on spiral NGC 891 as being due to dust-scattered starlight. Two exponential dust disks: one with a scale height of ~.2-.2 kpc and the other with a scale height of kpc. The central face-on optical depth of the geometrically disk is found to be ~.3-. at the B-band. The model is consistent with the vertical profile of the Herschel/PACS data. Origin of the geometrically dust disk Superbubble, Radiation pressure, etc Next Step Extend the modeling to other edge-on galaxies Oligochromatic Modeling?, SED