‘GoldenEye’ in action: Mapping the Galaxy with GALFA Snežana Stanimirović (UW-Madison)

At the end of “GoldenEye”James Bond goes to Puerto Rico searching for a gigantic satellite dish…

“GoldenEye” (1995):the 17th James

Bond movie

…And he finds the 305-m Arecibo radiotelescope, the largest radio telescope in the world!

Built in 1963 but still lots of exciting scientific capabilities….

“The Arecibo Observatory is part of the National Astronomy and Ionosphere Center (NAIC), a national research center operated by Cornell University under a cooperative agreement with the National Science Foundation (NSF).”

In this talk: What do we know and don’t know about the Galactic Halo How do we study Galactic Halo GALFA survey in a nutshell: Why? How? Science Highlights: 1. Cloudy transition region bw the Galactic disk and the halo 2. The tip of the Magellanic Stream 3. Some really fast clouds out there

What do we know and don’t know about the Galactic

Halo?

Disk/Halo Interface

orTransition

h~650 ly

h~5000 ly

A more schematic view of dramatic “links” btw the Galactic disk and halo

Hot Galactic Halo, or corona

Galactic disk

@200,000 ly

Most of the Galactic gas is in the form of atomic hydrogen (or HI) and can be

mapped by radio telescopes

Most of this gas belongs to the Galaxy. However…

Leiden/Argentine/Bonn survey36 arcmin resolution

~40% of sky is covered by “clouds” that do not take part in Galactic rotation High Velocity Clouds (HVCs)

Wa

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, UW

Ma

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MagellanicClouds

Magellanic Stream

We don’t know where HVCs come from, but we know that:

Supernovae blow large holes in the Galactic disk

Some gas is being grabbed from “outside”….

The Galaxy has a large hot corona through which HVCs move

-> Disk & Halo must be talking to each other, but HOW?

McClure-Griffiths et al. (2006)

These questions are important for the Galaxy but for far-away galaxies as well!

Need: large-area surveys with high angular resolution to zoom in on the disk-halo interactions!

• How do Galactic disk and halo exchange matter? • What’s the internal structure of the Galactic Halo?• What determines the size and morphology of HVCs?• Can we trace outflowing gas from the disk into the halo?• Can we trace infalling gas from the halo into the disk?

What we want to find out:

… and that’s what GALFA is about ! GALFA = Galactic Science with ALFA International collaboration (~80 members) @www.naic.edu/alfa/galfa/

Luckily James Bond saved the GoldenEye. In fact, the GoldenEye is more powerful than ever because of

ALFA...

ALFA andwhat do we measure with a

radio telescope?

ALFA = Arecibo L-band Feed Array

… To survey the sky much faster!

Cosmos: The Swinburne Astronomy Online Encyclopedia

The 21-cm line of atomic hydrogen

Hydrogen atom

every107 years

Measuring Motions: Spectral Line Maps Spectral Line Observations

Modified from Alyssa Goodman

Velocity from Spectroscopy

1.5

1.0

0.5

0.0

-0.5

Inte

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400350300250200150100

"Velocity"

Observed Spectrum

All thanks to Doppler,Radio astronomers work with CUBES instead of images

Telescope Spectrometer

Modified from Alyssa Goodman

Radial Velocity in km/sec

GALFA’s “art”: covering the whole sky visible from Arecibo

Effective integration time per pointing

Why is Arecibo + ALFA so special for Galactic science ?

A very unique combination:

1. Large bucket, or “Sensitivity”

2. Big dish, or “Good resolution (3’)”

3. A single big dish, or “Full spatial frequency coverage”

AC0 HVC -- LDSAC0 HVC -- GALFA

What do we find?

The Galactic disk has a blanket of small clouds, seen for the first time

l= 34degb= 15degV=-15 km/s

Spectacular examples of small,compact low-velocity HI clouds above the Galactic disk

Clouds “follow” the disk, but fall behind in velocity

Too small to be

seen in low-res.

surveys…

Previous surveys

Stanimirovic et al. (2006)

• Numerous, small, discrete, cold (400 K = 260 F) HI clouds, found at various locations above the Galactic disk.

• Typical cloud properties: 300-600 ly above the Galactic disk cloud size is ~10 ly

cloud mass is a few x M(Sun)

• We study cloud properties and motion and compare those with theoretical predictions.

What do we know about these clouds?

1.Galactic Fountain (Shapiro & Field 1976, Houck & Bregman 1990).

2.Final stage of the infalling material

(Maller & Bullock 2004

Kaufmann et al. 2005)

What mechanisms produce & maintain a very clumpy disk/Halo

interface ?

1. Galactic Fountain & ‘cannonball’ clouds Galactic Fountain

HOTCOLD

Idea: Clouds condense at higher altitudes and are now falling down, like little cannons, back onto the disk.

Cloud properties are telling us how effective fountain flows are in various places in the Galaxy.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

density temperature

2. New ideas of how galaxies form: Anisotropic cloud infall

and clumpy outer disks ?

Kaufmann et al. (2005)

h~650 ly

The disk/halo transition region is very clumpy, not

smooth as previously thought.

Hot Galactic Halo, like Solar corona

Galactic disk

@200,000 ly

What we still don’t know: what role these clouds have in the transfer of

matter & energy btw the disk and the Halo.

Putman et al. (2003)Observations with the ParkesTelescope in Australia

The Magellanic Streama huge starless tail of gas trailing behind the Magellanic Clouds

LMC

SMC

GALFA

What is the tip of the Stream telling us?

• Still highly controversial: how was the Stream formed? where did the Stream gas come from? how far away is the Stream?• Main suspects: gravitational vs gas dynamic forces.• Models are increasingly complex..• The tip = the formation point of the Stream.• Multiple streams at the tip give support to gravitational models as those are the only one that are able to produce such structure.• Morphology and clumpiness of different streams tells us they were not drawn from the same source or at the same time.

Stanimirovic et al. (2007)

Details of Cloud/Halo Interaction (Peek et al. 2006:

HVCs that move extremely fast

• Torn-off ‘condensations’are being de-accelerated.

• Differential drag: n(halo)xD = F[observed params]

• Such level of detail and disruption has not been seen before.

Summary:

GALFA is surveying the Galaxy with high angular and velocity resolution. Completion date = mid 2011.

Diverse and rich science case + legacy products for the astronomy community at large.

Already revising our Galactic knowledge:

- The transition region bw the disk and the halo is not smooth but made up of lots of small, cannon-like HI clouds.

- The tip of the Magellanic Stream consists of four distinct filaments, most likely produced by gravitational interactions bw the Magellanic Clouds and the Galaxy.

Thank you !