‘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 radio telescope, 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. The Magellanic Stream 2. “Bucky galaxy”

Artist: Ron Miller Artist: Jon Miller

h~650 ly A more schematic view of dramatic “links” btw the Galactic disk and halo Hot Galactic Halo, or corona Galactic disk ~130,00 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 survey 36 arcmin resolution

~40% of sky is covered by “clouds” that do not take part in Galactic rotation High Velocity Clouds (HVCs) Wakker, UW Madison Magellanic Clouds 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 our neighbors….  The Galaxy has a large hot corona through which HVCs move -> Disk & Halo must be talking to each other…. McClure-Griffiths et al. (2006)

Artist: Ron Miller Artist: Jon Miller the most spectacular example of disk-halo 60 kpc or 200,000 ly

Stream in HI: Parkes HI observations (15’ resolution) Stream Bridge Leading Arm SMC LMC Tip of The Stream b=-40deg b=-45deg Parkes radio telescope Australia Dish Diameter = 64 m

Stream in HI: Parkes HI observations (15’ resolution) Stream Bridge Leading Arm SMC LMC Tip of The Stream Putman et al. (2003) Mathewson & Ford (1984, IAU Symp. 108) Two double-helix filaments At Dec~0 deg chaotic network of filaments and clumps b=-40deg b=-45deg

These questions are important for our own 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? How do galaxies like the Milky Way harass their neighbors? How do galaxies like the Milky Way accrete gas ? 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

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!

Cosmos: The Swinburne Astronomy Online Encyclopedia The 21-cm line of atomic hydrogen Hydrogen atom every 10 7 years

Measuring Motions: Spectral Line Maps Modified from Alyssa Goodman

Velocity from Spectroscopy Intensity "Velocity" Observed Spectrum All thanks to Doppler. Hotter gas  faster motions of H atoms  Broader spectral line 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?

Stream in HI: Parkes HI observations (15’ resolution) Stream Bridge Leading Arm SMC LMC Tip of The Stream Putman et al. (2003) Mathewson & Ford (1984, IAU Symp. 108) Two double-helix filaments At Dec~0 deg chaotic network of filaments and clumps b=-40deg b=-45deg

The Magellanic Stream: Velocity Field: 400 (Clouds) to -400 (tip) km/s SMC Putman et al. (2003) GALFA-HI image: ~900 deg 2 3’ resolution,  N=3x10 18 cm -2 (3- ,  v=20 km/s) LMC b=-50 b=-25

“Secondary Streams”: Westmeier & Koribalski 08 How extended is the northern MS? 4 GALFA ‘filaments’ + 5 ‘filaments’ in HIPASS || to MS to LMC

Milky Way SMC LMC Connors et al. (2006)

SMC Bridge Leading arm Stream Main ‘stream’ bifurcated Very distant stream 2 younger streams Connors et al. (2006): detailed spatial structure of the Stream can be reproduced by gravitational interactions But, specific encounters needed!

Samantha’s catalog of ~180 clouds: N(HI), angular size, velocity profiles. Cross-correlated with catalogs of HVCs and mini- HVCs  “purely” MS sample Samantha Hoffman UW undergrad. student But there is all this clumpy structure….

Spatial and Velocity structure along the MS ram pressure old tidal new tidal  LMC X Putman03 ∆ GALFA We can compare velocity of Stream clouds with predictions from various models.  Gravity is doing ok, but need to think about additional processes

~15% of clouds have multi-phase (warm & cold gas) structure “Cold cores”: FWHM ~13 km/s (range 3 to ~20 km/s) “Warm envelopes”: FWHM ~25 km/s  Multi-phase medium Narrow line means cooler gas Broader line means warmer gas And all this happening 60 kpc away from us, deep in the Galactic halo Why is this interesting?

Challenges theoretical understanding of heating/cooling processes in the Milky Way halo

Summary :  Arecibo radio telescope is surveying the Galaxy with high angular and velocity resolution.  Diverse and rich science case + legacy products for the astronomy community at large.  Already revising our knowledge about interactions between the Galactic disk and halo.  The Magellanic Stream is more extended (& filamentary) than previously thought.  Our observations favors gravity for explaining new filaments, but new proper motions and/or additional mechanism needed.  Multi-phase medium at large distances requires reconsideration of Halo properties and phase conversion mechanisms.