Imaging Dust in Starburst Outflows with GALEX

1. Imaging Dust in Starburst Outflows with GALEX Charles Hoopes Tim Heckman Dave Strickland and the GALEX Science Team March 7, 2005 Galactic Flows: The Galaxy/IGM Ecosystem

2. Cool gas in starburst outflows • Current models require cool gas in outflows • X-ray emission arises at hot/cold interface (Strickland et al. 2002) • Metal content requires ISM (Martin et al. 2002) • Dusty cold gas necessary for radiation driven winds (Aguirre et al. 1999, Martin 2005) M82, from Strickland et al. 2004 Blue: 0.2-3.0 keV Chandra Red: H-alpha Green: R-band continuum Imaging Dust in Starburst Outflows with GALEX

3. Cool gas in starburst outflows • Current models require cool gas in outflows • X-ray emission arises at hot/cold interface (Strickland et al. 2002) • Metal content requires ISM (Martin et al. 2002) • Dusty cold gas necessary for radiation driven winds (Aguirre et al. 1999, Martin 2005) From Strickland et al. 2002 Imaging Dust in Starburst Outflows with GALEX

4. Probes of cool material • Absorption lines studies of Doppler-shifted Na D show cool gas in starburst outflows (Heckman et al. 2000, Rupke et al. 2002 Schwartz & Martin 2004, Martin 2005) Walter et al. 2002 CO map • CO streamers detected in M82 outflow to ~1.2 kpc (Walter et al. 2002) • 850 μm SCUBA emission from cold dust detected out to ~800 pc (Alton et al. 1999) Alton et al. 1999 SCUBA 850 μm Imaging Dust in Starburst Outflows with GALEX

5. The M81 System Imaging Dust in Starburst Outflows with GALEX

6. The M82 outflow “cap” • UV light extends several kiloparsecs into halo • Morphology consists of diffuse and filamentary components • Filament seen at 11 kpc above the plane GALEX image of M82, from Hoopes et al. 2005 Gold: Near-UV (2300 Å) Blue: Far-UV (1500 Å) Image is 21’ (22.0 kpc) across Imaging Dust in Starburst Outflows with GALEX

7. Multiwavelength comparison cap • High degree of similarity between UV, Hα, and X-rays • UV & Hα agree in terms of overall extent and individual features • Less contrast between filaments and diffuse light in UV than in Hα GALEX UV Ground-based Hα Chandra X-ray 0.3-2.0 keV (Strickland et al. 2004) Imaging Dust in Starburst Outflows with GALEX

8. Observed for 2 orbits (~3000s) in 2003, part of the Nearby Galaxy Survey UV light extends several kpc into halo Lacks filamentary structure seen in M82 NGC 253 GALEX image of NGC 253, from Hoopes et al. 2005 Gold: Near-UV (2300 Å) Blue: Far-UV (1500 Å) Image is 30’ (22.7 kpc) across Imaging Dust in Starburst Outflows with GALEX

9. Multiwavelength comparison • High degree of similarity between UV, Hα, and X-rays • UV, Hα, and X-rays fainter than M82 halo GALEX UV Ground-based Hα ROSAT X-ray Imaging Dust in Starburst Outflows with GALEX

10. Halo comparison Numbers in parentheses are fractions of total (disk+halo) luminosity Luminosities are in units erg s-1 Imaging Dust in Starburst Outflows with GALEX

11. Can nebular emission explain the UV? • Measured Hα/UV ratios in 30” square regions in halo, compared with model predictions • Models of emission from shock-heated gas • Mappings: Dopita & Sutherland 1996 • Shock velocity vs varied from 100 to 900 km s-1 • Balmer, bremsstrahlung, two-photon continua and line emission • Models of emission from photoionized gas • Cloudy: Ferland 1996 • Spherically symmetric cloud ionized by central source • Temp. of ionizing spectrum varied from 30,000 K to 50,000 K • Electron densities from 0.1 to 10 cm-3 • Solar metallicity for both shock and photo models Imaging Dust in Starburst Outflows with GALEX

12. Comparison with models • These processes cannot explain all of the UV light • These ratios are not corrected for internal extinction • Scattering responsible for ≥ 50% of UV light in Hα-bright regions (filaments) ≥ 90% of UV light in Hα-faint (diffuse) regions Hoopes et al. 2005 Imaging Dust in Starburst Outflows with GALEX

13. Comparison with models • UV colors alone do not rule out nebular emission • FUV/NUV colors agree with reddened starburst spectrum (Meurer et al. 1999) • UV/Hα ratios in many Hα-faint regions match the ratios seen local star-forming galaxies (Buat et al. 2002; blue arrows) • Suggests significant fraction of diffuse Hα in faintest regions may be scattered starlight • Most regions probably require nebular emission Imaging Dust in Starburst Outflows with GALEX

14. The M82 cap • Contains X-ray, Hα, and UV • Thought to be a collision between the hot wind fluid and tidal debris (Lehnert et al. 1999) • Cloud is dusty • Could lack of tidal debris near NGC 253 explain the lack of filaments? Hα (greyscale) and X-ray (contours) From Lehnert et al. 1999 Imaging Dust in Starburst Outflows with GALEX

15. Polarization • Polarized Hα seen in M82 (Scarrott et al. 1991) • Polarization pattern suggests illumination by central source From Scarrott et al. 2000 Note that the emission in this figure extends ~1.2 kpc from the disk, while UV extends to >5 kpc Imaging Dust in Starburst Outflows with GALEX

16. Line-of-sight reddening and line depth • Residual intensity of the blue-shifted Na D lines (I5890) is correlated with the line-of-sight reddening • Winds with more cold gas have more dust • This suggests dust is mixed with the cold gas in the outflow From Heckman et al. 2000 survey of local starbursts Imaging Dust in Starburst Outflows with GALEX

17. Putting it all together • UV/Ha ratio indicate that the UV halos are due to scattering by dust • Close morphological correspondence between dust and hotter phases of winds • Hotter material is known to be outflowing • This suggests that dust is outflowing in starburst winds (supported by absorption studies) • Consistent with the idea that cool gas and dust is entrained ISM or halo material Imaging Dust in Starburst Outflows with GALEX

18. What’s next? • GALEX will observe more starbursts: NGC 1482, NGC 2146, NGC 3079, NGC 3628 • Modeling the dust • Combine UV and optical (and IR?) to determine dust properties • Grain size distribution • Non-starburst galaxies • Radiation pressure does not require an outflow • Radiation driven dust efflux may be an important method of enriching the IGM (Aguirre et al. 1999) Imaging Dust in Starburst Outflows with GALEX

19. NGC 891 in UV and Hα Imaging Dust in Starburst Outflows with GALEX

20. Imaging Dust in Starburst Outflows with GALEX

21. Conclusions and Implications • GALEX images of M82 and NGC 253 reveal significant extraplanar UV light extending >5 kpc • The UV/Hα ratios indicate that the UV light is starlight from the disk scattered by dust in the halo • Dust is morphologically connected to hot and warm outflowing gas – suggests dust is outflowing as well (supported by absorption line studies) • We can directly image the cool material in starburst outflows • Dust is seen many kpc from disk – dust survives the journey • Dust may be ejected into the IGM Imaging Dust in Starburst Outflows with GALEX