ALFA Galactic Studies


Observer Information
GALFA Consortium
Survey Groups
Data Availability
Science Highlights


Radio observations of the Milky Way are of vital importance for understanding what really occurs within galaxies. The unique sensitivity of Arecibo's 305m dish is now enhanced 7-fold with ALFA to provide an unprecedented new tool for the investigation of star formation and evolution, the recycling of material between stars and the interstellar medium (ISM), the large-scale transfer of energy among the different components of the ISM, and the evolution of elemental abundances over cosmic timescales. These phenomena can be observed with ALFA over the portion of the Galactic sky between declinations of -1.33 and +38.03 degrees, marked below in red.

[The Galactic Sky Visible from Arecibo]

The background image is 21cm line emission from neutral atomic hydrogen (H I). The line peak brightness is shown to emphasize high-latitude features. This all-sky map is from Kalberla et al. (2005), who combined 25m and 30m telescope observations from Dwingeloo and Argentina. Arecibo can observe about 32% of this area, but with 10 times the angular resolution and 5 times the velocity resolution in the H I line!

The ALFA sky coverage nicely complements the CGPS, VGPS, and SGPS components of the International Galactic Plane Survey shown in the map. ALFA can observe the Galactic disk in both the inner and outer Galaxy in the first and third quadrants, supplementing the superior IGPS angular resolution in the plane with better sensitivity and spectral resolution. And unlike the IGPS, Galactic ALFA surveys will also cover a large, continuous area off the plane, where isolated clouds and disk-halo energy exchanges can be studied.

General Observer Information

ALFA is open to all telescope users through the normal proposal process. A consortium was formed in 2003 to conduct large surveys of the Galactic ISM with ALFA. The consortium is open to new members, but membership is not required to use ALFA. However, telescope users are encouraged to consult the documentation assembled by the consortium for general use.

One particular strength of ALFA is commensal observing, in which multiple backends can be used in parallel, enabling different science projects to use the same telescope pointing simultaneously. Commensal observing is especially powerful for sky surveys. A number of ALFA surveys are being observed commensally with each other to maximize the scientific return per hour of telescope time. The same option exists for smaller proposals.

The GALFA Consortium

* Organization

To exploit the full mapping power of ALFA for Galactic ISM studies, the Galactic ALFA (GALFA) Consortium was formed in 2003. A set of guidelines governs the functioning of this consortium. Various tasks are assigned to working groups and coordinated via an adopted organizational scheme. The different types of observations and science that the Consortium plans to address are described in the following section on survey groups.

* Membership

Membership in the GALFA Consortium is open to all interested parties irrespective of institutional affiliation, career level, expertise or scientific background. Individuals wishing to use ALFA for Galactic studies are not required to be members of the GALFA Consortium. However, anyone who wishes to contribute is encouraged to join. Most consortium members are associated with a particular survey group, as indicated in the current membership list. If you wish to join a GALFA project team (see list), please contact the relevant Principal Investigator.

* Meetings

The GALFA Consortium has held 3 organizational meetings. The links below include presentations and other materials generated for each meeting.

* GALFA-1: 2003 March 21-23, Arecibo Observatory
* GALFA-2: 2003 June 18, Boston University
* GALFA-3: 2004 August 29, Arecibo Observatory

In addition to these general consortium meetings, the various GALFA sub-consortia concerned with specific surveys have regular teleconferences and occasional face-to-face meetings to discuss survey technical details, logistics, and science. For further information about these sub-consortia, please see the following section on survey groups.

* Data Products and Availability

All GALFA Consortium data have a proprietary period of 18 months. The Consortium is responsible for subsequent production of finished data products of the completed surveys. These data products will be made publicly available through the National Virtual Observatory.

GALFA Survey Groups

The GALFA White Paper (PDF) outlines the ISM science that the Consortium plans to pursue. This science will be addressed by three separate sub-consortia, each focused on a particular observational tracer of interstellar matter and processes. Brief descriptions of each group are given below. Please follow the links for further information.

* I 21cm Line Emission and Absorption (GALFA - H I)

ALFA's unprecedented combination of sensitivity and mapping speed enables a unique H I sky survey, one that will serve as a standard Galactic astronomy reference for many years to come. The science case for GALFA - H I studies is rich and diverse. A few areas of special interest are: (1) the formation and lifetimes of molecular clouds; (2) disk-halo interaction energetics and structures; (3) high-velocity clouds in the Galactic halo; (4) the cold neutral medium in emission and self-absorption; (5) forbidden-velocity line wings from hidden stellar sources; and (6) turbulent energy injection and cascades in different Galactic environments. GALFA - H I observations are planned to cover the entire Arecibo sky but will be carried out in a series of smaller projects to enable more rapid scientific yields. These ``jigsaw puzzle'' pieces will be combined at the end to form a single, seamless survey.

Many GALFA - H I projects have been pursued since 2004. The largest of these currently underway is the Turn On GALFA Survey (TOGS), which runs commensally during E-ALFA observations for the ALFALFA and AGES projects. Another project with multiple commensal partners is the I-GALFA survey of the inner parts of the Galactic disk. All GALFA - H I observations use the specially-designed GALSPECT backend, covering a 1413 km/s range with 7679 channels, each 0.184 km/s wide. A considerable body of information on GALFA-H I observing, data processing software, and science is available on the GALFA documentation page. Specific information on the current H I reduction software and how to use it can be found on the GSR version page. The GALFA - H I project coordinator is Snezana Stanimirovic.

* Full-Stokes Radio Continuum Emission (GALFA - CON)

The radio continuum sky has been surveyed at many frequencies and angular resolutions. However, ALFA will provide critical new data for a wide range of cutting-edge continuum science. Areas of investigation include: (1) polarimetric constraints on the large-scale Galactic magnetic field, including the disk-halo interface; (2) magnetic field studies of supernova remnants (SNRs), molecular clouds, and H II regions; (3) 3-D Faraday tomography of the ambient magneto-ionic medium, including turbulent cascades; (4) high-resolution, total-intensity imaging of Galactic loops and spurs, low-surface-brightness SNRs, H II regions, and the general interstellar medium, with separation into thermal and nonthermal components by multiwavelength analysis; (5) an extremely sensitive point-source catalog, including polarimetry and variability constraints; and (6) characterization of the ``true'' Galactic synchrotron foreground, which is essential for CMB studies at higher frequencies. All of these topics will be addressed by the G-ALFA Continuum Transit Survey (GALFACTS), a 5-year effort to map the entire Arecibo continuum sky in all four Stokes parameters at the highest possible sensitivity.

GALFACTS pilot observations were carried out in project a1947 to test observing and data processing techniques. The full GALFACTS survey (project a2130) awaits a new backend, currently being commissioned, that will cover 300 MHz in over 1000 channels to eliminate contamination by RFI and ``unwrap'' frequency-dependent Faraday rotation effects. Further information can be found at the University of Calgary GALFACTS website and in several GALFA science documents. The GALFACTS Principle Investigator is Russ Taylor.

* Radio Recombination Line Emission (GALFA - RRL)

ALFA will allow ISM studies using radio recombination lines of hydrogen and even helium and carbon for localized sources. Numerous galactic continuum thermal sources can be mapped in one or more recombination lines of hydrogen, from large H II regions to compact galactic objects, including planetary nebulae. RRLs will provide critical probes of physical conditions in the warm diffuse medium. In addition, Galactic structure can be investigated from H II region kinematics, Galactic chemical evolution can be studied via H II region abundances, and photodissociation region physics can be explored via carbon recombination lines. The combination of GALFA-RRL and other surveys (e.g., MSX, ISO, 2MASS, NVSS, GALFACTS, GALFA-H I) offers a powerful multiwavelength probe of the Galactic ISM.

Precursor observations were made as part of project a1943. A 2000-hour RRL survey of the inner Galaxy for |b| < 5 deg is planned (project a2064), and may be observed commensally with P-ALFA. A new, specialized backend spectrometer is being designed for this undertaking. For further details on the survey and RRL science, please see the 2005 RRL White Paper and 2003 GALFA White Paper. The GALFA-RRL Principle Investigator is Yervant Terzian.

Data Availability

As noted above, all GALFA data will be made publicly available after an 18-month proprietary period. This period is counted from the time that final data products are generated. Preliminary data products are for internal consortium use only. Exceptions may be made in the case of external collaborations approved by the relevant sub-consortium, with the proviso that the external parties are clearly aware that the data are not in their final state and are subject to change as pipeline processing is refined.

For specific details on data availability, potential users are encouraged to contact one of the following individuals:

* Galactic H I Line Data : Steven Gibson
* Full-Stokes Continuum Data : Russ Taylor
* Recombination-Line Data : Yervant Terzian

Science Highlights

[first image by the ALFA Galactic H I survey]

Although GALFA surveys are only just beginning, a number of exciting results have already emerged. The image above shows the first GALFA H I map. The links below give more details on this and several other results.

* GALFACTS Team Ready to Go (Nov 15, 2007)
* The Many Streams of the Magellanic Stream (Nov 12, 2007)
* The Multi-Phase ISM in Perseus (Apr 19, 2007)
* GALFA Eye on Taurus (Dec 20, 2005)
* GALFA Studies Forbidden Velocity Line Wings (PDF) (Dec 19, 2005)
* GALFACTS Precursor Observations See Galactic Magnetic Field (Dec 18, 2005)
* First GALFA H I Map (Nov 29, 2004)
* First ``Wave'' for GALFA Observations (Sep 3, 2004)


GALFA publications are listed below in reverse-chronological order. Two AAS special sessions have been devoted to ALFA and GALFA presentations.

* Refereed Papers

* ``Velocity Spectrum for H I at High Latitudes'', Chepurnov, A., Lazarian, A., Stanimirovic, S., Peek, J. E. G., & Heiles, C., submitted [astro-ph/0611462]
* ``The Many Streams of the Magellanic Stream'', Stanimirovic, S., Hoffman, S., Heiles, C., Douglas, K. A., Putman, M., & Peek, J. E. G., 2008, ApJ, 680, 276 [arXiv:0802.1349]
* ``A New Technique for Heterodyne Spectroscopy: Least-Squares Frequency Switching (LSFS)'', Heiles, C. 2007, PASP, 119, 643 [arXiv:0707.2399]
* ``Reconstructing Deconstruction: High-Velocity Cloud Distance through Disruption Morphology'', Peek, J. E. G., Putman, M. E., McKee, C. F., Heiles, C., & Stanimirovic, S. 2006, ApJ, 656, 907 [astro-ph/0610429]
* ``First Results from the Arecibo Galactic H I Survey: The Disk/Halo Interface Region in the Outer Galaxy'', Stanimirovic, S., Putman, M., Heiles, C., Peek, J. E. G., Goldsmith, P. F., Koo, B.-C., Krco, M. Lee, J.-J., Mock, J., Muller, E., Pandian, J. D., Parsons, A., Tang, Y., Werthimer, D. 2006, ApJ, 653, 1210 [astro-ph/0609137]

* Conference Proceedings

* ``Mapping Hydrogen in the Galaxy, Galactic Halo, and Local Group with ALFA: The GALFA-H I Survey Starting with TOGS'', Gibson, S. J., Douglas, K. A., Heiles, C., Korpela, E. J., Peek, J. E. G., Putman, M., & Stanimirovic, S. 2008, in The Evolution of Galaxies through the Neutral Hydrogen Window, at Arecibo Observatory, Puerto Rico, February 1-3; to be published in AIP conference proceedings, edited by R. Minchin & E. Momjian [arXiv:0805.0017v1]
* ``A Sharper View of MBM 53-55 in GALFA H I Emission'', Gibson, S. J., Korpela, E. J., Stanimirovic, S., Heiles, C., Douglas, K. A., Peek, J. E. G., & Putman, M. 2007, Bull. A.A.S., 39, 988 [#211, #139.18] [Electronic Poster]
* ``How Far Is the Tip of the Magellanic Stream?'', Stanimirovic, S., Hoffman, S., Heiles, C., Douglas, K., Putman, M., & Peek, J. 2007, Bull. A.A.S., 39, 988 [#211, #139.17]
* ``The Many Streams of the Magellanic Stream'', Hoffman, S. M., Stanimirovic, S., Heiles, C., Douglas, K. A., Putman, M., & Peek, J. E. G. 2007, Bull. A.A.S., 39, 985 [#211, #139.04]
* ``Halo Gas of M33'', Putman, M. E., Peek, J. E. G., Douglas, K. A., Heiles, C., Gibson, S. J., Korpela, E. J., & Stanimirovic, S., 2007, Bull. A.A.S., 40, ?? [#211, #095.34]
* ``H I in Local Group Dwarf Galaxies'', Grcevich, J., Putman, M., & Peek, J. E. G. 2007, Bull. A.A.S., 39, 895 [#211, #095.07]
* ``The Atomic Component of the Taurus Molecular Cloud Complex: Measurements and Implications'', Krco, M., Goldsmith, P. F., & Brown, R. L. 2007, Bull. A.A.S., 39, 780 [#211, #029.02]
* ``Hidden Galactic Accretion: The Discovery of Low-Velocity Halo Clouds'', Peek, J. E. G., Putman, M. Sommer-Larsen, J., Heiles, C., Stanimirovic, S., Douglas, K., Gibson, S., & Korpela, E. J., 2007, Bull. A.A.S., 39, 760 [#211, #014.08]
* ``Mapping the Galaxy in H I with GALFA'', Peek, J. E. G., Stanimirovic, S., Putman, M. E., Heiles, C., Douglas, K., Korpela, E., & Gibson, S. J., Mapping the Galaxy and Nearby Galaxies, Ishigaki Island, Okinawa, Japan, 2006 June 26-30
* ``Recent Results from GALFA: `GoldenEye' on Disk/Halo Interfaces'', Stanimirovic, S. 2006, Bull. A.A.S., 38, 110 [#208, #34.02]
* ``ALFA Surveys as Complements to Other Major Surveys'', Haynes, M. P. 2005, Bull. A.A.S., 37, 1489 [#207, #192.08], part of Special Session 192
* ``GALFACTS: A Full-Stokes Continuum Survey of the Arecibo Sky'', Gibson, S. J. 2005, Bull. A.A.S., 37, 1489 [#207, #192.07], part of Special Session 192
* ``GALFA-H I : The First 1000 Square Degrees'', Goldston, J. E., & GALFA-H I Consortium 2005, Bull. A.A.S., 37, 1489 [#207, #192.06], part of Special Session 192
* ``Optimized Mapping Modes and Algorithms for ALFA'', Goldston, J. 2004, Bull. A.A.S., 36, 1476 [#205, #78.08], part of Special Session 205
* ``GALFA Hardware and Calibration Techniques'', Heiles, C., Goldston, J., Mock, J., Parsons, A., Stanimirovic, S., & Werthimer, D. 2004, Bull. A.A.S., 36, 1476 [#205, #78.07], part of Special Session 205
* ``Arecibo Survey of Radio Recombination Lines'', Terzian, Y. 2004, Bull. A.A.S., 36, 1476 [#205, #78.06], part of Special Session 205
* ``A Full-Stokes ALFA Continuum Survey'', Taylor, A. R. 2004, Bull. A.A.S., 36, 1475 [#205, #78.05], part of Special Session 205
* ``ALFA and HVCs: If Jodie Foster Knew What She Could Discover Now . . .'', Putman, M. E. 2004, Bull. A.A.S., 36, 1475 [#205, #78.04], part of Special Session 205
* ``Using ALFA to Study H I and Molecular Clouds'', Arce, H. G., & GALFA-H I Consortium 2004, Bull. A.A.S., 36, 1475 [#205, #78.03], part of Special Session 205
* ``A New Era of Galactic H I Science with ALFA'', Stanimirovic, S., & GALFA-H I Collaboration 2004, Bull. A.A.S., 36, 1475 [#205, #78.02], part of Special Session 205
* ``Introduction to ALFA and the GALFA Consortium'', Goldsmith, P. F. 2004, Bull. A.A.S., 36, 1475 [#205, #78.01], part of Special Session 205


* GALFA Memos and Documents

* Science Documents, Observing Proposals, and Consortium Policy
* Observing Procedures and Data Processing Software
* Hardware Details (Spectrometer Backends, etc.)

* Other ALFA Memos and Documents

* General ALFA Technical Memos
* E-ALFA Memos and Documents
* P-ALFA Memos and Documents

* Other Arecibo Materials

* Arecibo Technical Memos
* Arecibo Observatory Astronomy Reference Pages
* Phil Perillat's Arecibo Resources
* Arecibo Observatory 305m Telescope Schedule
* Control Interface Module for Arecibo (CIMA; telescope control software)

* External Links

* U. Michigan - Turn On GALFA Survey (TOGS) website
* U. Calgary - Galactic ALFA Continuum Transit Survey (GALFACTS) website
* Arecibo Obs. - Inner Galaxy ALFA (I-GALFA) survey website

People to Contact for More Information

* Project Details

For more details on a specific survey project, please contact that project's Principal Investigator:

* GALFA - H I : see the GALFA - H I projects table
* GALFA - CON : Russ Taylor
* GALFA - RRL : Yervant Terzian

* General GALFA Information

For further information on GALFA generally, please contact Steven Gibson.