Imaging Dust in Starburst Outflows with GALEX

Imaging Dust in Starburst Outflows with GALEX

Charles Hoopes Tim Heckman

Dave Stricklandand the GALEX Science Team

March 7, 2005Galactic Flows: The Galaxy/IGM Ecosystem

Galactic Flows: The Galaxy/IGM Ecosystem


Cool gas in starburst outflows

M82, from Strickland et al. 2004Blue: 0.2-3.0 keV ChandraRed: H-alphaGreen: R-band continuum

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)



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



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



The M81 System



The M82 outflow

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. 2005Gold: Near-UV (2300 Å)Blue: Far-UV (1500 Å)Image is 21’ (22.0 kpc) across

“cap”



Multiwavelength comparison

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)

cap



NGC 253

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

GALEX image of NGC 253, from Hoopes et al. 2005Gold: Near-UV (2300 Å)Blue: Far-UV (1500 Å)Image is 30’ (22.7 kpc) across



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



Halo comparison

NGC 253 M82

L(Hα) Halo 1.5х1039 (4%) 1.3х1040 (21%)

L(NUV) Halo 3.1х1040 (7%) 1.5х1041 (43%)

L(FUV) Halo 2.1х1040 (10%) 7.1х1040 (65%)

L(starburst) 7.8х1043 2.0х1044

Numbers in parentheses are fractions of total (disk+halo) luminosityLuminosities are in units erg s-1



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



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



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



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



Polarization Polarized Hα seen in

M82 (Scarrott et al. 1991)

Polarization pattern suggests illumination by central source

From Scarrott et al. 2000Note that the emission inthis figure extends ~1.2 kpc from the disk, while UV extends to >5 kpc



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. 2000survey of local starbursts



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



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)



NGC 891 in UV and Hα



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

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