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

“GoldenEye” (1995): the 17th James Bond movie At the end of “GoldenEye” James Bond goes to Puerto Rico searching for a gigantic satellite dish…

…And he finds the 305-m Arecibo radio telescope, the largest radio telescope in the world! “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).” Built in 1963 but still lots of exciting scientific capabilities….

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?

A more schematic view of dramatic “links” btw the Galactic disk and halo Disk/Halo Interface or Transition Galactic disk h~650 ly h~5000 ly Hot Galactic Halo, or corona @200,000 ly

Most of the Galactic gas is in the form of atomic hydrogen (or HI) and can be mapped by radio telescopes Leiden/Argentine/Bonn survey 36 arcmin resolution Most of this gas belongs to the Galaxy. However…

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

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)

What we want to find out: 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? 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! … 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 Luckily James Bond saved the GoldenEye. In fact, the GoldenEye is more powerful than ever because of ALFA...

ALFA and what do we measure with a radio telescope?

ALFA = Arecibo L-band Feed Array … To survey the sky much faster!

The 21-cm line of atomic hydrogen every 107 years Cosmos: The Swinburne Astronomy Online Encyclopedia Hydrogen atom

Measuring Motions: Spectral Line Maps Modified from Alyssa Goodman

Velocity from Spectroscopy Observed Spectrum Telescope  Spectrometer 1.5 1.0 Intensity 0.5 All thanks to Doppler, Radio astronomers work with CUBES instead of images 0.0 Radial Velocity in km/sec -0.5 100 150 200 250 300 350 400 Modified from Alyssa Goodman "Velocity"

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: Large bucket, or “Sensitivity” Big dish, or “Good resolution (3’)” A single big dish, or “Full spatial frequency coverage” AC0 HVC -- LDS AC0 HVC -- GALFA

What do we find?

The Galactic disk has a blanket of small clouds, seen for the first time l= 34deg b= 15deg V=-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 Previous surveys Too small to be seen in low-res. surveys… Stanimirovic et al. (2006)

What do we know about these clouds? 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 mechanisms produce & maintain a very clumpy disk/Halo interface ? Galactic Fountain (Shapiro & Field 1976, Houck & Bregman 1990). 2.Final stage of the infalling material (Maller & Bullock 2004 Kaufmann et al. 2005)

1. Galactic Fountain & ‘cannonball’ clouds COLD HOT 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.

2. New ideas of how galaxies form: Anisotropic cloud infall and clumpy outer disks ? Kaufmann et al. (2005) density temperature

The disk/halo transition region is very clumpy, not smooth as previously thought. Galactic disk h~650 ly Hot Galactic Halo, like Solar corona What we still don’t know: what role these clouds have in the transfer of matter & energy btw the disk and the Halo. @200,000 ly

The Magellanic Stream a huge starless tail of gas trailing behind the Magellanic Clouds GALFA LMC SMC Putman et al. (2003) Observations with the Parkes Telescope in Australia

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)

HVCs that move extremely fast 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 !