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
Imaging Dust in Starburst Outflows with GALEX
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)
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
The M81 System
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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”
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
Halo comparisonNGC 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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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)
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
NGC 891 in UV and Hα
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
Galactic Flows: The Galaxy/IGM Ecosystem
Imaging Dust in Starburst Outflows with GALEX
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