Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/research/LVmeeting/magsys_pres/Mag_07_Madsen.pdf Äàòà èçìåíåíèÿ: Sun Aug 5 03:42:55 2007 Äàòà èíäåêñèðîâàíèÿ: Sun Dec 23 11:03:30 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: spacecraft

Ionized Gas in the Magellanic Stream

Greg Madsen
University of Sydney and University of Wisconsin

J. Bland-Hawthorn (AAO), M. Putman (Mich.), L.M. Haffner, S. Stanimirovic, R.J. Reynolds (Wisc.)


The Magellanic Stream
HI Map · HI filament extends 100º `behind' the LMC/SMC, no stars · ~ 500 km/s velocity gradient · Provides detailed view of present-day galaxy formation/evolution · Probe of low-density Galactic halo · Origin remains debated: · tidal? (
Gardinier & Noguchi 96, Connors et al, 06, Bekki)

· ram-pressure?
96, Mastropietro)

(Weiner & Williams

· LMC blowout? · How large is it?
Nidever et al 2007

(Nidever et al 07)

· What is the total gas content?


Ionized Gas
· Traced by diagnostic emission lines (e.g., H, [NII]6584,
[SII]6716, [OI]6300, [OIII]5007)

LMC in H, [SII], [OIII]

· Probe of temperature, density, excitation mechanism, metallicity, ionization fraction · Line widths of different ions used to quantify non-thermal motions ·H emission toward ~ 10 sightlines in the Stream (Weiner
Williams 1996, Putman et al 2003) &

· brighter than other HVCs, not photoionized? · shocks? · New WHAM data on northern tip, ~ 20 sightlines
MCELS, C. Smith et al 2006 / NOAO


Wisconsin H-Alpha Mapper
·15 cm, dual etalon Fabry-Perot on a dedicated 60 cm telescope located at Kitt Peak and remotely operated · designed to study ionized gas in Galactic interstellar medium · 1.º0 diameter beam on sky · 12 km s-1 velocity resolution (R ~ 25,000) · 200 km s-1 spectral window can be centered between 4800å and 7300å · High sensitivity (EM~0.1 in 30 s) · Provides high throughput and high spectral resolution · Moving to southern hemisphere (late 2008)
Haffner et al. 2003

http://www.astro.wisc.edu/wham/


H Observations
· 22 sightlines in/around northern tip using `ON-OFF' technique · Surface brightness I
H

= 0.03 - 0.6 Rayleigh (EM ~ 0.01 - 0.2 cm-6 pc )

· Strong correlation in H- velocity centroids, line widths ~ 40 km/s · No correlation between IH and NHI

H

HI


H toward the Magellanic Stream


HVC Complex A: Testing Photoionization Model
HI Velocity Map
Prediction

Wakker (2001)

Observations · 4 < D < 8 kpc (Wakker 2001) · Several HI bright `cores' ·H emission is faint, increases with increasing latitude -> consistent with model · Need to consider cloud geometry!


[NII], [SII], and [OIII] in the Stream
· `MS II' brightest sightline in H · Weiner: 1.3 R (7' FOV) · WHAM: 0.65 R (60' FOV) · [NII]/H traces temperature · [SII]/[NII] traces ionization state · [NII]/H = 0.20, [SII]/H = 0.34 · If Z = Z
Sun

:

· T = 6,000 K, S+/S = 1 · If Z = 0.1 ZSun · T = 30,000 K, S+/S = 0.2 · [OIII]/H < 0.06


[OI] toward MS II: Ionization Fraction


High Resolution HI with Arecibo
HI Column Density · GALFA: Galactic Science with ALFA · Northern tip observed with 3.5' resolution · Very compact clouds (6') at -360 km/s · Continuous velocity gradient · HI spectra show multi-phase structure
LAB Survey

· narrow core, broad wings (7 km/s, 25 km/s) · Some compact clouds have cold core/warm envelope structure

Stanimirovic et al 2007, in prep


High Resolution HI with Arecibo
HI Column Density
Arecibo

· GALFA: Galactic Science with ALFA · Northern tip observed with 3.5' resolution · Very compact clouds (6') at -360 km/s · Continuous velocity gradient · HI spectra show multi-phase structure · narrow core, broad wings (7 km/s, 25 km/s) · Some compact clouds have cold core/warm envelope structure

Stanimirovic et al 2007, in prep


High Resolution HI with Arecibo
HI Velocity Field
Arecibo

· GALFA: Galactic Science with ALFA · Northern tip observed with 3.5' resolution · Very compact clouds (6') at -360 km/s · Continuous velocity gradient · HI spectra show multi-phase structure · narrow core, broad wings (7 km/s, 25 km/s) · Some compact clouds have cold core/warm envelope structure

Stanimirovic et al 2007, in prep


Summary
· Emission lines from ionized gas in the Stream provide important constraints on

physical conditions · H is bright, has significant structure on ~arcmin scales · Line widths ~ 40 km/s, weak evidence for velocity offset from HI · [SII]/[NII] is unusually bright, no [OIII] -> low ionization state? · H+/H is > 50% · Small-scale, multi-phase structure (pressure confinement?) · Look for He I/H; traces shape of ionizing spectrum · Need models that account for ionized gas, predict line strengths/ratios · What is full extent of the Stream? Signatures detected outside NHI~1018 contours HI: Lockman et al (2002), Braun & Thilker (2005) Mg I: Gibson et al (2000) OVI: Sembach et al (2003)


Complex A
HI Velocity Map
· 4 < D < 8 kpc (Wakker 2001) · Extends ~ 4 kpc above plane · Metallicity uncertain · < 0.4 solar (Wakker 2001) · Several HI bright `cores' · ~ 80 km/s velocity gradient · 21 sightlines observed with WHAM, 17 H detections ·H emission is faint, increases with increasing latitude -> consistent with models

Wakker (2001)