N RADIO A O Newsletter Issue 103 · April 2005 Newsletter Issue 103 ALMA Progress Update ... In electronics labs around the world, engineers are ... receiver cartridge builders around

NATIONAL RADIO ASTRONOMY OBSERVATORY

NewsletterNewsletterApril 2005 Issue 103

ALMA Progress Update

The GBT and VLBA Observe the Huygens Probe Descent to Titan

Heating the Hot Gas in Galaxy Clusters by Energetic Radio Jets

Also in this Issue:

North American ALMA Science Center (NAASC)

Japanese Film Crew documents Space VLBIResearch in Green Bank

A Large Gas Disk Around a Small Galaxy

Molecular Gas in the First Galaxies

A Pulsar Jackpot in Terzan 5 with the GBT

VLA Investigates Radio Emission from Brown Dwarfs

AOC

Green BankNAASC & HQ

Antafagasta

Atacama Large Millimeter Array (ALMA)

Robert C. Byrd Green Bank Telescope (GBT)

Very Long Baseline Array (VLBA)

Very Large Array (VLA)

JAO

TABLE OF CONTENTS

ATACAMA LARGE MILLIMETER ARRAY (ALMA)

ALMA NewsALMA Test FacilityNorth American ALMA Science Center (NAASC)

GREEN BANK

The Green Bank Telescope

SOCORRO

VLA/VLBA Large Proposal Deadline and Policy ChangeVLBI Global Network Call for Proposals

IN GENERAL

The GBT and VLBA Observe the Huygens Probe Decent to TitanGBT Student Support Program: Announcement of AwardsJapanese Film Crew documents Space VLBI Research in Green Bank

NEW RESULTS

A Large Gas Disk Around a Small GalaxyHeating the Hot Gas in Galaxy Clusters by Energetic Radio JetsA Pulsar Jackpot in Terzan 5 with the GBTVLA Investigates Radio Emission from Brown DwarfsMolecular Gas in the First Galaxies

The NRAO Graphics Department will be happy to assist you in the production of images for your article as well asfor you research papers. Contact Patricia Smiley ([email protected]) with your request.

If you have an interesting new result obtained using NRAO telescopes that could be featured in the NRAONewsletter, please contact Jim Condon at [email protected]. We particularly encourage Ph.D. students to describetheir thesis work.

Editor: Mark T. Adams ([email protected]); Science Editor: Jim Condon ([email protected]);Assistant Editor: Sheila Marks; Layout and Design: Patricia Smiley

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Cover Image: Map showing NRAO telescope sites and other major locations: the Array Operations Center (AOC) in Socorro, NM;the Green Bank, WV site; the North American ALMA Science Center (NAASC) and NRAO Headquarters (HQ) in Charlottesville, VA;Antafagasta, Chile and the Joint ALMA Office (JAO) location in Chile. The Atacama Large Millimeter Array (ALMA) is an internationalastronomy facility. ALMA is an partnership between Europe, North America, and Japan in cooperation with the Republic of Chile.

The map used in this image is courtesy of the SeaWiFS Project NASA/GSFC and ORBIMAGE.

April 2005 ALMA Issue 103

ATACAMA LARGE MILLIMETER ARRAY (ALMA)

Page 1Page 1

ALMA construction continues at sites worldwide.U.S. President Bush signed the FY2005 budget, whichallocates $49.30M to ALMA construction, the fourthyear of full ALMA construction funding and, includingthe design and development phase, the seventh year ofALMA funding. The FY06 request seeks full fundingfor the fifth year of construction, at $49.24M. At theend of January, the ALMA-Japan partner announcedsignature of a contract to build three 12m antennas tobe incorporated into the ALMA Compact Array.Contracts for the balance of the antennas are immi-nent.

An ALMA Town Meeting was held on January 11, 2005(Tuesday) during the 205th AAS Meeting in San Diego,CA. The meeting was an outstanding success, withdiscussion continuing afterward such that the room hadto be cleared so that the next session could begin. Atthe meeting, an ALMA booth was staffed by ALMApersonnel to answer questions. Booths are planned forthe upcoming AAS meeting in Minneapolis May 29-June 2 and also at the CASCA meeting in MontrealMay 15-17. ALMA will also be discussed at the 2005IEEE International Conference on Acoustics, Speech,and Signal Processing, held March 18-23, 2005 inPhiladelphia, as one element in a special sessionentitled “Towards A New Generation of RadioAstronomical Instruments: Signal Processing for LargeDistributed Arrays”.

Phil Myers left the ALMA Science Advisory Committee(ASAC). Andrew Blain of Caltech was nominatedby NSF and confirmed by the ALMA Board at itsJanuary 27, 2005 telecon. Jean Turner is currentlyChairperson of the ASAC. Jim Crocker of LockheedMartin has replaced Dominick Tenerelli as aNorth American ALMA Management AdvisoryCommittee member.

In electronics labs around the world, engineers areassembling ALMA components into functioning unitsand measuring performance against specifications. In

Tucson, the Local Oscillator (LO) system is undergo-ing phase drift measurements; the prototype of the LOPhotonics Line Length Corrector and Second LaserSynthesizer are under test. At the Array OperationsCenter (AOC) in Socorro, tests focus on elements ofthe backend, including data transmission system, pro-totype correlator, samplers, and digitizers. ALMAComputing in North America is also carried out inSocorro. At the NRAO Technology Center (NTC) inCharlottesville, assembly of the first quadrant of theALMA correlator is nearing completion. The multipliers(tunerless!) have been assembled and delivered toreceiver cartridge builders around the world. In theNTC, the first Band 6 (1.3mm) cartridge has beenassembled and tested; others are in an advanced state

ALMA News

Completed Band 6 receiver.


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of assembly. Soon, these elements will be broughttogether at the Antenna Test Facility and assembled intoa one-baseline forerunner of ALMA for prototypesystem integration and astronomical testing.

As ALMA construction has led to realization of itsvarious elements, from prototype antennas throughsamplers and correlators to front ends, the project hasevolved from the baseline set down at the outset ofconstruction. Over the winter, the project has engagedin using the information gleaned from construction ofthe elements of ALMA to rebaseline the project as it iscurrently envisioned. This process has been informedby the realization last fall of an integrated projectschedule, which defines critical paths through themany parts of ALMA. The rebaselined project will bediscussed with the ALMA Board, itself consulting withits scientific and management advisory committees(ASAC and AMAC respectively) before being finalized.

Any task of this magnitude requires a fully-staffedJoint ALMA Office. Only one remaining JAO position,that of the ALMA Project Scientist, remains to be filled.Advertisements have been placed with a goal ofspeedily identifying and hiring the most qualifiedcandidate.

At the ALMA Camp adjacent to the site of theOperations Support Facility (OSF) near San Pedro deAtacama, the focus is on support of the imminenteffort to construct the ALMA facilities at both the OSFand at the Array Operations Site on the Chajnantorplateau. To this end, the road between the two sites isbeing finished, and the ALMA Camp and theConstruction Camp are being enlarged.

H. A. Wootten

ALMA Test Facility

Since the turn of the year, activity has ramped up at theALMA Test Facility (ATF) located at the Very LargeArray site. All bids received for production antennaswere based on the prototype antennas located at theATF. The Antenna Evaluation Group (AEG) performeda number of tests on these antennas aimed at demon-

strating their performance relative to the technicalspecifications for the antennas. Owing to a numberof factors—antenna delivery schedule, weather at theVLA site, and poor optical seeing at the ATF amongthem—the data sets earlier produced by the AEG leftinterpretation of the performance relative to specifica-tions open to question.

Since the performance of prototypes relative to thetechnical specifications was a key issue in bid evalua-tion, a Joint Antenna Technical Group consisting ofexperts in antenna design and testing was assembled atthe ATF to conduct a new series of tests aimed atresolving issues remaining from the report of theAntenna Evaluation Group. These tests have been runduring January through the beginning of March 2005.Tests included holography using a transmitter on anearby tower, photogrammetry of the antennas over arange of elevations, out-of-focus beam maps and out-of-focus holography of astronomical sources, pointingwith the optical pointing telescope, and radiometry ofastronomical sources. While still under scrutiny, itappears that these tests have resolved most remainingquestions. The testing concludes with a period often-second fast-switching cycles on the antennas. Thisinvolves continuously fast-switching the antennas forabout 100,000 cycles: 24 hours per day for about14 days or 42 eight-hour shifts.

A nighttime photograph of the AEC prototype antenna, taken asfinal preparations are made for photogrammetic measurements.(Photograph by Fred Schwab)


At the conclusion of this round of tests, the project willcontract for the production antennas armed with a morecomplete understanding of the performance of theprototype antennas.

Independent of the testing of the two antennas suppliedby the ALMA bilateral partners, a Japanese prototypehas also been tested at the ATF. Based on these testsand an independent bidding process, Japan selectedMitsubishi to produce three 12m antennas which willbe included in the Atacama Compact Array and signeda three-year contract with them on January 31, 2005.

H. A. Wootten

North American ALMA Science Center

The North American ALMA Science Center (NAASC)will be the main interface between the North Americanuser community and the Joint ALMA observatory. Inaddition to hosting a complete copy of the ALMA archive,the NAASC will provide North American astronomerssupport with proposal submission, observing scheduling,data reduction, and outreach activities such as workshopsand Summer Schools. More information can be foundat the NAASC website at: http://www.cv.nrao.edu/naasc/.

The NAASC is poised to occupy its new offices inthe addition to the NRAO Edgemont Road Building,located on the grounds of the University of Virginia inCharlottesville, Virginia. The move is expected to becomplete by early April. Initially, the Science Centerwill be located in a suite of offices on the third floor,above the office of the North American ALMA(Construction) Project. Others moving into the newspace include NRAO Administration and HumanResources. Renovation of the Library, Auditorium,and common spaces will provide excellent facilities forvisitors to the NAASC and for ALMA workshops.

The ALMA North American Science AdvisoryCommittee (ANASAC) provides scientific adviceon the operation of the NAASC to NRAO as represen-tatives of the wider North American astronomicalcommunity. The ANASAC welcomed new membersfor a three-year term at its meeting on February 18, 2005:Andrew Baker (Jansky Fellow, U. Maryland), John Bally(U. Colorado), Crystal Brogan (JCMT Fellow,U. Hawaii), Paul Ho (CfA, Harvard), Jonathan Williams(U. Hawaii), and Mel Wright (U. C. - Berkeley).Members continuing for two years are: Andrew Blain(Caltech), Xiaohui Fan (U. Arizona), Doug Johnstone(HIA/DAO, Victoria), Lee Mundy (U. Maryland),Jean Turner (U. C. L. A.), and Christine Wilson

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Vertex antenna (foreground) being fitted with photogrammetrytargets at the ATF. Mitsubishi antenna shown in background.(Photograph by Fred Schwab)

A model of the Observatory’s expanded Edgemont Road facility thatwill house the North American ALMA Science Center (NAASC)located in Charlottesville, VA.

April 2005 Green Bank Issue 103

(McMaster U.); and for one year: Chris Carilli (NRAO),Richard Crutcher (U. Illinois), Jason Glenn(U. Colorado), Mark Gurwell (CfA, Harvard),Joan Najita (NOAO), and Min Yun (U. Mass.).Special thanks go to members completing their serviceon the ANASAC: Phil Myers (CfA, Harvard),

Dave Hollenbach (NASA - Ames), Dan Jaffe(U. Texas - Austin), Luis Rodriguez (UNAM),Dave Sanders (U. Hawaii), and Dick Plambeck(U. C. - Berkeley).

P. A. Vanden Bout

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GREEN BANK

The Green Bank Telescope

This winter, the Robert C. Byrd Green Bank Telescope(GBT) has successfully moved into long millimeterwave observing with commissioning of the Ka-band(26- 40 GHz) receiver and production use of the Q-band(40-50 GHz) receiver. We have made significantprogress on several other initiatives, including the newIDL data-reduction package, the Precision TelescopeControl System (PTCS) project for 3mm observing,the Penn bolometer camera, the Caltech Continuumbackend, and GBT Spectrometer upgrades. Resultsfrom the December engineering review of the GBTAzimuth Track project are described, as well as notablescience results, including follow-up pulsar observationsof the Terzan 5 globular cluster and important contribu-tions to the Cassini-Huygens mission to Titan.

The new Ka-band receiver is a two-beam, dual-polarization, pseudo-correlation receiver and is thefirst of its type on the GBT. It is capable of kHz-rateswitching between the two beams and is designed togive wide-bandwidth continuum noise performancethat approaches radiometer-equation predictions, i.e.,with 1/f noise greatly minimized. It also has sensitivespectral-line performance. This receiver will be usedfor a number of significant science projects includinghigh-redshift molecular line searches and sensitivecontinuum observations, particularly for foregroundpoint-source correction of cosmic background radiationfields. Two of four spectral channels have beensuccessfully commissioned and were released forinitial science projects in March. An upgrade will be

made this summer to bring all channels into operationand to allow for integration with a future cross-correlation wideband spectrometer.

The Q-band receiver was modified last summer toimprove its gain stability. The receiver has performedvery well in several observing runs this winter, and inparticular has yielded very flat spectral baselines forwideband high-redshift line searches. The useful tun-ing band for this receiver is presently ~ 42- 48 GHz.Work is planned this summer to investigate broadeningthe band back to its original specification of 40 -50 GHz.

The software and science groups have been working todevelop a set of single-dish data reduction modulesusing IDL, known as GBTIDL. The new systemcombines the best capabilities of the old Unipopspackage with some useful features from aips++/dish.The design and features of GBTIDL are heavilyinfluenced by successful systems developed by T. Baniaand others, and cleanly separates the data from thealgorithms ensuring that the package will supportGBT’s current and future observing modes. The pack-age imports and exports data from the SDFITS formatand will be available for real-time use at the GBT aswell as for post-observing run processing. Although weintend to provide a package with all the basic featuresfor observing at single positions on the sky, it will beaccessible for expansion and enhancements by others.For example, users who wish to perform customcalibration will be able to easily plug in the modules

April 2005 Green Bank Issue 103

they write themselves and use them within the contextof existing GBTIDL capabilities. The package is alsoserving as the exploratory platform for developing ascience data model for the GBT, which is critical forthe development of next-generation data-reductionsystems which are aligned with Observatory-wideefforts. The GBTIDL package is presently being testedinternally and by a small group of external users whiledevelopment continues. Plans include a public releaseby June of this year.

The PTCS project has concentrated on “out-of-focus”holography measurements, precision pointing systemdesign, and investigations of a new-generation lasermetrology system. The out-of-focus holographymeasurements have been plagued by poor weather onscheduled test nights this winter. In one session withgood weather, maps were made, and surface correc-tions were computed and input into the active-surfacecontrollers. Observations made alternately with thenew and old surface figures showed that the new figureproduced significant improvements in Q-band apertureefficiency. Work will continue through the winter andspring with hopes for better luck with the weather.The project team has also spent considerable timedeveloping a system design to achieve the requiredpointing accuracy of ~1 arcsec. Simulations and erroranalyses of the concepts are promising. Work alsoproceeds on the development and prototyping of next-generation metrology instrumentation.

The Penn Array bolometer camera, a 64-pixel full-sampling array for the 90 GHz band, continues toproceed well in the labs at the University ofPennsylvania and at Goddard Space Flight Center.Present plans call for integration tests on the GBT thissummer and first commissioning observations thisfall. The first season will be devoted to engineeringshakedown, initial astronomical characterization, andcontinued development. The Penn camera is a jointproject of UPenn, GSFC, NIST, U. Cardiff, and NRAO,and is supported by the NRAO’s university-builtinstrumentation program.

The Caltech Continuum backend, a collaborationbetween Caltech and NRAO, is also proceeding well.This backend will work in conjunction with the Ka-band

and future W-band (68-92 GHz) correlation receivers,and will allow the full continuum capability of thesereceivers to be exploited scientifically. The design andconstruction work is scheduled for completion by fall,with astronomical commissioning to proceed next falland winter.

The digital group has been working on two upgrades tothe GBT Spectrometer, a redesign of the long-termaccumulator (LTA) cards and development of a cross-correlation mode test fixture. The existing LTA cardshave been problematic and occasionally result incorrelation lag dropouts. Design of the new card,which should correct this problem, is complete andthe first prototype board has been received from thefabricator for testing. The cross-correlation test fixturewill allow the cross-correlation mode of the spectrometerto be verified and released for spectral-polarimetry andother cross-correlation observing needs. The design ofthe test fixture is complete, and it is presently underconstruction.

The GBT azimuth track engineering review panel metin Green Bank on December 7- 8, 2004. The panelwas again chaired by Karl Frank (U. Texas). The statusof the project, the results of the trial retrofit, and theresults of a number of classical and finite-element

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The Robert C. Byrd Green Bank Telescope (GBT). Photograph byAndrew Clegg.

April 2005 Green Bank and Socorro Issue 103

analyses were presented. Concepts for a full repair ofthe track were discussed in detail. These concepts arebased largely on the trial retrofit, which consists ofwelded base-plate joints and overlapping (staggered)wear plates with balanced joints. The panel was wellsatisfied with the analyses and results presented andthe overall concepts for the full repair. They recom-mended that we perform follow-up investigations ofthe effects of thicker, full-width wear plates, the attach-ment (bolting) scheme, and the benefits of replacingthe base plates rather than field-grinding the existingones. These investigations are underway and areexpected to conclude this spring. The major retrofitwork is not yet scheduled, but will likely be in thesummer of either 2006 or 2007.

GBT observers continue to produce interesting andsignificant science results. As described in a sciencearticle in this newsletter, the number of millisecond

pulsars detected in the Terzan 5 globular cluster is nowup to 26 (Ransom et al.). In addition, as described inthe accompanying article by Ghigo and Romney, theGBT and VLBA also provided major support to theCassini-Huygens mission, including the acquisition ofunique science data. Results from the GBT figuredprominently in lists of scientific highlights from 2004as chosen by several publications. These included thediscovery of potential leftover building blocks of theAndromeda Galaxy (Thilker et al.), listed among thetop astronomy results of 2004 by Science News, andthe detection of complex, biologically significantmolecules in the interstellar medium (Hollis et al.),included as one of the top 100 science stories of 2004by Discover magazine. The double binary pulsar,discovered at Parkes and studied in detail at the GBT,was listed as one of the top ten breakthroughs of theyear by Science.

P. R. Jewell

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SOCORRO

VLA/VLBA Large-Proposal Deadline and Policy Change

Prospective proposers are reminded that the next large-proposal deadline for the VLA and the VLBA will beon June 1, 2005. Large proposals should be sent inby the same process as normal proposals (e-mail [email protected]), using the same forms. Allproposals requesting more than 200 hours will beconsidered to be large proposals. The large proposalshave no page limit for the scientific justification, soproposers are strongly encouraged to provideinformation such as a data-reduction plan and evidencethat their proposal team is capable of making fulluse of the large amount of data acquired. Formore information on the large proposal process, seehttp://www.vla.nrao.edu/astro/prop/largeprop/.

A data-release plan is a mandatory part of the justifica-tion for any large proposal. We encourage proposers tothink carefully about data products that would be of the

most use to the community and to think about howtheir data products may be useful ultimately to theNational Virtual Observatory.

Previously, we have accepted VLBA large proposals atany normal VLA/VLBA proposal deadline. However,beginning on June 1, 2005, we will accept large VLBAproposals only at the same 16-month intervals as forthe VLA. Accepting individual large VLBA proposalsat random deadlines forces the Large Proposal ReviewCommittee to conduct ad-hoc meetings to considersingle proposals and also prevents them from evaluatingthese proposals in the overall context of the otherproposals seeking large amounts of observing time.Therefore, any large proposals received afterJune 1, 2005 will be held over until the October 2, 2006deadline.

J. S. Ulvestad

April 2005 Socorro Issue 103

GENERAL: Please use the most recent proposal cover-sheets, which can be retrieved at http://www.nrao.edu/administration/directors_office/tel-vla.shtml for theVLA and at http://www.nrao.edu/administration/directors_office/vlba-gvlbi.shtml for the VLBA.Proposals in Adobe Postscript format may be sent [email protected]. Please ensure that the Postscriptfiles request U.S. standard letter paper. Proposals mayalso be sent by paper mail, as described at the webaddresses given above. Fax submissions will not beaccepted. Finally, VLA/VLBA referee reports are nowdistributed to proposers by e-mail only, so please pro-vide current e-mail addresses for all proposal authorsvia the most recent LaTeX proposal coversheets.

VLA: The maximum antenna separations for the fourVLA configurations are A-36 km, B-11 km, C-3 km,and D-1 km. The BnA, CnB, and DnC configurationsare the hybrid configurations with the long north arm,which produce a circular beam for sources south ofabout -15 degree declination and for sources north ofabout 80 degree declination. Some types of VLAobservations are significantly more difficult in daytimethan at night. These include observations at 90 cm(solar and other interference; disturbed ionosphere,especially at dawn), deep 20 cm observations (solarinterference), line observations at 18 and 21 cm (solar

interference), polarization measurements at L-band(uncertainty in ionospheric rotation measure), andobservations at 2 cm and shorter wavelengths in B andA configurations (trophospheric phase variations,especially in summer). Proposers should defer suchobservations for a configuration cycle to avoid suchproblems. In 2005, the C configuration daytime willinvolve RAs between 06h and 12h; and the D configu-ration daytime will involve RAs between 13h and 19h.Current and past VLA schedules may be found athttp://www.vla.nrao.edu/astro/prop/schedules/old/.EVLA construction will continue to impact VLAobservers; please see the web page at http://www.aoc.nrao.edu/evla/archive/transition/impact.html.

Approximate VLA Configuration Schedule

Year Q1 Q2 Q3 Q42005 A,B B,C C D2006 A A,B B,C C2007 D D,A A A,B

VLBA: Time will be allocated for the VLBA on intervalsapproximately corresponding to the VLA configurations,from those proposals in-hand at the corresponding VLAproposal deadline. VLBA proposals requesting antennas

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Configuration Starting Date Ending Date Proposal Deadline

B 18 Feb2005 06 Jun 2005 1 Oct 2004CnB 17 Jun 2005 05 Jul 2005 1 Feb 2005C 08 Jul 2005 26 Sep 2005 1 Feb 2005DnC 07 Oct 2005 24 Oct 2005 1 Jun 2005D 28 Oct 2005 09 Jan 2006 1 Jun 2005

Large VLA/VLBA 27 Jan 2006 07 May 2007 1 Jun 2005A(+PT?) 27 Jan 2006 08 May 2006 3 Oct 2005

BnA 19May2006 05 Jun 2006 1 Feb 2006B 09 Jun 2006 11 Sep 2006 1 Feb 2006CnB 22 Sep 2006 09 Oct 2006 1 Jun 2006C 13 Oct 2006 08 Jan 2007 1 Jun 2006DnC 19 Jan 2007 05 Feb 2007 2 Oct 2006D 09 Feb 2007 07 May 2007 2 Oct 2006

VLA Configuration Schedule; VLA/VLBA Proposals

April 2005 Socorro Issue 103

beyond the 10-element VLBA must justify, quantita-tively, the benefits of the additional antennas. Anyproposal requesting a non-VLBA antenna is ineligiblefor dynamic scheduling, and fixed-date schedulingof the VLBA currently amounts to only about onequarter of observing time. Adverse weather increasesthe scheduling prospects for dynamics requestingfrequencies below about 10 GHz. See http://www.vlba.nrao.edu/astro/schedules/ for a list ofdynamic programs which are currently in the queue orwere recently observed. VLBA proposals requestingthe GBT, the VLA, and/or Arecibo need to be sent onlyto the NRAO. Note also the possibility to propose forthe High Sensitivity Array. Any proposal requestingNRAO antennas and antennas from two or moreinstitutions affiliated with the European VLBI Network(EVN) is a Global proposal, and must reach both theEVN scheduler and the NRAO on or before the pro-posal deadline. VLBA proposals requesting only oneEVN antenna, or requesting unaffiliated antennas, arehandled on a bilateral basis; the proposal should besent both to the NRAO and to the operating institutionof the other antenna requested. Coordination of obser-vations with non-NRAO antennas, other than membersof the EVN and the DSN, is the responsibility of theproposer.

J. M. Wrobel, B.G. [email protected]

VLBI Global Network Call for Proposals

Proposals for VLBI Global Network observing arehandled by the NRAO. There are three Global Networksessions per year, with up to three weeks allowed persession. The Global Network sessions currentlyplanned are:

Dates Proposals Due

02 Jun to 20 Jun 2005 01 Feb 200520 Oct to 10 Nov2005 01 Jun 2005

Any proposal requesting NRAO antennas and antennasfrom two or more institutions affiliated with theEuropean VLBI Network (EVN) is a Global proposal,and must reach both the EVN scheduler and theNRAO on or before the proposal deadline. Fax sub-missions of Global proposals will not be accepted. Afew EVN-only observations may be processed by theSocorro correlator if they require features of the EVNcorrelator at JIVE which are not yet implemented.Other proposals (not in EVN sessions) that request theuse of the Socorro correlator must be sent to NRAO,even if they do not request the use of NRAO antennas.Similarly, proposals that request the use of the EVNcorrelator at JIVE must be sent to the EVN, even ifthey do not request the use of any EVN antennas. Allrequests for use of the Bonn correlator must be sent tothe MPIfR.

Please use the most recent proposal coversheet, whichcan be retrieved at http://www.nrao.edu/administration/directors_office/vlba-gvlbi.shtml. Proposals may besubmitted electronically in Adobe Postscript format.For Global proposals, those to the EVN alone, or thoserequiring the Bonn correlator, send proposals [email protected]. For Globalproposals that include requests for NRAO resources,send proposals to [email protected]. Please ensurethat the Postscript files sent to the latter address requestU.S. standard letter paper. Proposals may also be sentby paper mail, as described at the web address given.Only black-and-white reproductions of proposal figureswill be forwarded to VLA/VLBA referees. Finally,VLA/VLBA referee reports are now distributed toproposers by e-mail only, so please provide currente-mail addresses for all proposal authors via the mostrecent LaTeX proposal coversheet.

J.M. Wrobel, B.G. [email protected]

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April 2005 In General Issue 103

On January 14, 2005 the NRAO participated in aunique and exciting event: the descent of the HuygensProbe through the atmosphere of Titan, the largest ofSaturn’s moons. This participation was organized in ajoint proposal from JIVE (Joint Institute for VLBI inEurope) and JPL (Jet Propulsion Laboratory) by a largecollaboration with co-investigators at many institutionsworldwide.

The event was observed with three different systems.One was a VLBI observation involving eight VLBAstations, the GBT, and several telescopes in Australia,Japan, and China, coordinated by JIVE. This part ofthe project was designed to measure the preciseangular position of Huygens using a variant of thephase-referenced astrometry commonly done on theVLBA. The remaining two systems aimed at detectingthe Doppler shift of the Huygens signal. Both usedspecialized JPL recording systems. PC-based recordingunits were installed temporarily at four of the VLBAstations involved, while a more specialized RadioScience Receiver (RSR), normally used at the NASADSN facilities, was stationed at the GBT. One majorchallenge of operating the multiple observing systemswas to use the VLBA scheduling system to set up allthe NRAO equipment required by all three systems,but to record only the VLBI signals.

While one might expect that the NASA DSN stationswould observe the probe’s descent, the 2040 MHz linkfrom Huygens to the Cassini “mother ship” was out-side the passbands of their receivers. Both the GBTand VLBA S-band receivers can observe quite well atthis frequency, however, although front-end bandpassfilters had to be removed temporarily at some of theVLBA stations. To minimize the impact of RFI on theobservation, a number of known interference sourceswere asked to minimize transmissions during theencounter at Titan.

Some extensions to standard VLBI phase-referencingtechniques were necessitated because the VLBI

observation was eavesdropping on the comparativelyshort-range Huygens-Cassini communications, in asidelobe of the Huygens telemetry antenna, andbecause Huygens was expected to be buffeted bywinds in Titan’s atmosphere. Both the weak signal andthe accelerations led JIVE to develop an extensivesoftware correlation technique for the Huygens signals,and this in turn required that these observations berecorded on Mark 5 VLBI recorders, which have aconvenient computer interface. Mark 5A units, fundedby ESA and NASA, were installed at the GBT and fiveVLBA stations.

Preparations for this event included test observingsessions in August and November involving the entireplanned network. Several VLBA-only tests were alsoperformed in December and January. In the Novembertest, a crew from JPL brought the NASA RSR toGreen Bank. The complex frequency-conversion andscheduling schemes were checked, the expected per-formance of the VLBA S-band systems at 2040 MHzwas confirmed, the RFI environments at that frequencywere explored at some stations, and interferometric use

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Figure 1. The happy JIVE and JPL scientists following detectionof the signal from Huygens at the GBT, from left to right:Max Avruch (JIVE), Sami Asmar (JPL), Kees van t'Klooster (ESA),Sergei Pogrebenko (JIVE), and Sue Finley (JPL).

IN GENERAL

The GBT and VLBA Observe the Huygens Probe Descent to Titan


of the new Mark 5 units was demonstrated. Theseshakedown sessions were well worth the effort, bring-ing to light a number of unanticipated problems. In theactual observation, all these systems worked flawlessly.

On the morning of the big event, the GBT controlroom was crowded, with not only the JIVE and NASAcrews, but also programmers, engineers, and telescopemaintenance people standing by to fix quickly anyproblem that might occur. A webcam system providedimages of this activity to the rather smaller number ofus monitoring the VLBA’s performance in the AOC.Bob Anderson, the GBT chief telescope engineer, wasprepared to bend the bad-weather shutdown rules, butfortunately the predicted blizzard did not materialize.Extremely cold temperatures overnight at the VLBANorth Liberty station left an azimuth brake frozen, butquick action by the site techs there resulted in only anegligible loss of observing time. North Liberty wasalso the only station where serious interference wasseen in the absence of the front-end filters. TheMauna Kea station experienced unusually strong windgusts throughout the run, which fortunately stayed justbelow the auto-stow limit except for a brief periodwhen the antenna was pointed directly into the wind.

There was much nervous anticipation until theHuygens signal appeared at just about the predictedtime. Those of us watching in Socorro saw everyonein the GBT control room suddenly congregate aroundone monitor and then break into cheers. Shortly after-ward, Green Bank personnel heard the cheers from theESA control center in Darmstadt over the speakerphone when Sami Asmar told them the GBT haddetected the signal.

The Huygens Probe’s power system outperformed itsspecifications; the probe was still transmitting as theend of scheduled observing approached on the VLBA.Huygens had set at all stations but Mauna Kea by thattime, but we were able to continue observing there foranother hour, until the start of the next scheduled pro-gram occurred with Huygens at a very low elevation.Indeed, Huygens continued to transmit for hours, andplans were made to observe at some European VLBINetwork stations if it continued until rising there. Anabrupt change in the Doppler shift, as Huygens finallylanded on the surface of Titan, was reported from theParkes radio telescope in Australia, and shortly after-wards the signal finally disappeared.

After the experiment, we learned that there had been areceiver failure on the Cassini orbiter, and all Dopplervelocity data had been lost. Thus, the ground-basedmeasurements, from Green Bank, the VLBA, and otherparticipating observatories, will be the only measure-ments of velocity during the probe’s descent throughthe atmosphere of Titan. The correlation and analysisof the 17-station VLBI data are in progress at JIVE.Fringes have been found from the phase-referencesource on most baselines, and the Huygens signal hasbeen seen in the autocorrelations. The work of extract-ing the correlated Huygens signal has begun.

NRAO personnel who participated in this excitingexperience included: Bob Anderson, Walter Brisken,Pete Chestnut, Chris Clark, Juan Cordova, John Ford,Doug Gerrard, Frank Ghigo, Don Haenichen,Phillip Hicks, Glen Langston, Dan Mertely, Greg Monk,Roger Norrod, Jim Ogle, Peggy Perley, Tony Perreault,Paul Rhodes, Jon Romney, Bob Simon, Craig Walker,Galen Watts, Tim Weadon, and Brian Willard.

F. Ghigo and J. Romney

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Figure 2. The signal as recorded by the RSR. The X-axis is about20 minutes of time, and the Y-axis is the deviation from the expectedfrequency of the signal. The flat line parts are the signal fromHuygens; the deviations occurred when the telescope was pointed toa nearby calibration source.


GBT Student Support Program:Announcement of Awards

Four awards were made in December as part of theGBT Student Support Program. This program isdesigned to support GBT research by graduate orundergraduate students at U.S. universities or colleges,thereby strengthening the proactive role of theObservatory in training new generations of telescopeusers.

The December awards were in conjunction withapproved observing proposals submitted at the Octoberdeadline. Awards were made for the following students:

New applications to the program may be submittedalong with new GBT observing proposals at anyproposal deadline. For full details, restrictions, andprocedures, select “GBT Student Support Program”from the GBT astronomers page. For a cumulativerecord of past awards under this program, select “GBTStudent Support Status” from the GBT astronomerspage.

K.E. Johnson (U Virginia), D.J. Nice (Princeton U),J.E. Hibbard, P.R. Jewell, F.J. Lockman, J.M. Wrobel

Japanese Film Crew Documents SpaceVLBI Research in Green Bank

On February 24 and 25, 2005 the Green Bank site wasturned into a movie set for the filming of a documen-tary of the Japanese Space Very Long BaselineInterferometer (VSOP) mission. This documentary,funded by the Japanese government, was shot at severallocations across the globe, with Green Bank beingchosen due to the prominent roles that the Green BankEarth Station and the 140 Foot Telescope played in thismission. The documentary will be used for scienceeducation in high schools throughout Japan.

Two scientists from the VSOP mission, Phil Edwardsand Yashuhiro Murata, along with three people fromImage Science (the film’s production company) arrivedin Green Bank on the night of February 23 just in timeto beat the arrival of a snowstorm. Filming proceededcontinually over the next two days. Filming highlightsincluded an interview of Ed Fomalont in front ofthe GBT, recreating a VSOP tele-conference (withToney Minter, Ed Fomalont and Galen Watts“participating” in Green Bank), and the Green BankEarth Station simulating a tracking pass. Many shotsof the site were also made after four-wheeling throughthe snow (without getting stuck) to get the right cameraangles on a gorgeous day after the snowstorm.

Filming the three-minute teleconference requiredalmost an hour of preparation. The film crew set upadditional lighting as a cloudy day failed to provideenough light for filming in the upstairs conferenceroom. For context, the Green Bank participants wereshown portions of the teleconference already shot andinto which the Green Bank sequences would be edited.The on-site sequences were then shot from two differ-ent angles, and the Green Bank participants improviseda short “technical” conversation regarding the OVLBItracking station. After the two days of filming, we havea new-found respect for those in the film industry.

Toney Minter, Galen Watts, Glen Langston

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Paul Demorest (UC Berkeley) in the amount of$33,000 for the proposal entitled “Precision Timingof Binary and Millisecond Pulsars”.

Laura Hainline (Caltech) in the amount of $31,600for the proposals entitled “Survey for CO(1-0) fromdusty submillimeter galaxies at known redshifts”,“Searching for cool molecular gas in high-z submil-limeter-bright QSOs from CO(1-0) at GBT”, and“Detecting CO(1-0) in representative high-redshiftdusty galaxies using giant gravitational lenses”.

Tim Robishaw (UC Berkeley) in the amount of$2,100 for the proposal entitled “Constraining theMagnetic Field in the Taurus Molecular Cloud”.

Tim Robishaw (UC Berkeley) in the amount of$3,000 for the proposal entitled “Threading theMagnetic Slinky: Mapping the Zeeman Effect in theEridanus/Orion Region”.

Neutral hydrogen (HI) observations with the Very LargeArray (VLA) have revealed an extensive gas diskaround the low-luminosity dwarf irregular galaxyUGC 5288 (van Zee 2004, AAS, 205, 9319). Whilemost gas-rich galaxies have HI disks up to twice thediameter of the stellar component, the gas disk associ-ated with UGC 5288 can be traced to a diameter morethan seven times larger than the optical system (Figure 1).The large gas disk may be a remnant of the nascentenvelope from which the galaxy collapsed. In addition,such a large gaseous envelope represents a reservoir forfuture star-formation activity in this low-mass galaxy.

The VLA observations of UGC 5288 were obtained aspart of a study of the connection between the neutralgas distribution and the kinematics, star-formationactivity, and metal enrichment of dwarf irregular galaxies(van Zee & Haynes, in preparation). UGC 5288 was

selected for this study because it appeared to be atypical dwarf irregular galaxy. UGC 5288 is a low-luminosity galaxy (MB = –14.44) with blue colors(B–V = 0.46±0.06) and a modest current star-formationrate (0.0083 solar masses per year). The stellarcomponent has an optical diameter of 1.8 ×1.2 kpc anda scale length of 0.23 kpc. Prior optical imaging andspectroscopy did not suggest that this galaxy wouldreside in a large reservoir of neutral hydrogen.

The VLA observations revealed that the HI disk has adiameter of 12.7× 8.7 kpc (i.e., it can be traced to morethan 27 optical scale lengths). The majority of the HI islocated outside the optical disk; less than 1/8 of the HIis coincident with the optical galaxy. The gas densitypeaks in two knots offset from the optical and kinematiccenters. The knot having the highest column density isspatially coincident with the bright ionized hydrogen

April 2005 New Results Issue 103

NEW RESULTS

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A Large Gas Disk Around a Small Galaxy

Figure 1: The HI disk of UGC 5288 is shown in blue in thisoptical/HI color composite image. The stellar component is confinedwithin the inner pink/white region. The HI image is from the VLA, andthe optical images were obtained with the KPNO 0.9m telescope.

Figure 2: The velocity field of the neutral hydrogen gas. Although aslight warp is present, the outer gas disk is undergoing organized,coherent rotation. Combined with the lack of known near neighbors,the ordered kinematics indicates that the extended gas may be aremnant of the nascent HI envelope rather than the result of tidalinteractions.

7'

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region in the northwest. The outer gas is distributedasymmetrically; a large clump of neutral gas is located150-170 arcsec to the southwest. Inspection of deepoptical images obtained with the WIYN 3.5m telescopeindicates that there is no optical emission associatedwith this clump to a surface-brightness level of27.5 mag arcsec-2 in the R band.

The gas kinematics (Figure 2) indicates that the extendedgas distribution has coherent ordered rotation along anaxis (PA = 74 deg) nearly perpendicular to the opticalaxis (PA = 145 deg). With a maximum rotation velocityof 68 km s-1 at a radius of 6.4 kpc, UGC 5288 has adynamical mass of 6.98×109 solar masses, which isa factor of 30 more than the mass of HI. Thus, likemost dwarf irregular galaxies, UGC 5288 is adark-matter-dominated galaxy.

Possible origins of the diffuse gas disk aroundUGC 5288 include (1) the disk is the remnant of agalactic fountain (perhaps created after a past starburstepisode); (2) the disk is tidal debris created during arecent encounter; and (3) the disk is a remnant of thenascent material from which the galaxy collapsed.Possibilities (1) and (2) are unlikely since the distributionand kinematics of the extended gaseous disk aroundUGC 5288 indicate that the gas is relatively quiescentand is in stable orbits. For example, if the extendedgas were the result of infalling material raining downin the gravitational potential, one would expect highervelocity dispersions and less order to the velocity fieldthan observed. The disk does have a significant warp,which could be the result of a recent encounter.However, the nearest known galaxy at a similarredshift is another low-luminosity dwarf irregulargalaxy, IC 559, 220 kpc away. Thus, it is unlikely thatthe extended gas distribution is a remnant of a tidaltail, although a previous encounter may have beensufficient to warp the disk.

The HI envelope around UGC 5288 appears to bedynamically stable, which supports the hypothesis thatthe large gaseous disk is primordial in nature. In partic-ular, the surface density of the disk falls significantlybelow the Toomre instability threshold for star formationat all radii. In fact, the gas density of the outer gas

disk is more than a factor of 10 below the instabilitythreshold. Given the low gas density and apparentstability of the disk, it should not be surprising that thereis no significant star-formation activity in the outerdisk, despite the presence of a significant gas mass.

The existence of quiescent, extended gaseous disksaround a handful of dwarf irregular galaxies is puzzling.At present, there are no obvious unifying featuresamong the three isolated galaxies known to have largequiescent gas envelopes: UGC 5288, DDO 154, andNGC 2915. All three are gas-rich low-luminositygalaxies, but UGC 5288 and NGC 2915 are high-surface-brightness compact galaxies whereas DDO 154is a low-surface-brightness diffuse galaxy. DDO 154inhabits an over-dense region of the nearby universe,while UGC 5288 and NGC 2915 are relatively isolated.Further, since all of these extended gaseous disks werediscovered serendipitously, it is difficult to quantify thefraction of dwarf irregular galaxies that could host suchdisks. Clearly, such disks are relatively rare, but it isalso quite likely that additional extended gas disks willbe discovered as more galaxies are imaged in theneutral hydrogen line. Future detections of extended,quiescent gas disks will be necessary to quantify thefraction of galaxies with extended gas distributions andto enable a statistical examination of the host galaxies,their environments, morphologies, and the role of thegaseous disks in their evolution.

Liese van Zee (Indiana University)


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Radio jets emanating from the nuclei of galaxies arethe outward conduit for gravitational binding energyand momentum generated by accretion onto supermas-sive black holes. Jets transport energy and momentum over decades in distance from a region in the nucleusthe size of our solar system into the halo of the hostgalaxy. There the jet and its accompanying shock front interact with the surrounding matter causing gas clouds to glow in emission lines, and occasionally trigger starformation. But perhaps the most spectacular examplesof jet interactions are the giant X-ray cavity systemsthat NASA’s Chandra X-ray Observatory has discoveredin the hot halos of many galaxies, groups, and clustersof galaxies.

The cavities are usually about 10 kpc (about 30,000 lightyears) in diameter and are devoid of gas at ambienttemperatures. However, they are often filled withradio emission. Because the X-ray emissivity of thehot gas surrounding them is sensitive to the density and

temperature of the gas, the pressure p exerted by thehot gas on the cavities can be deduced. Diameters and,by geometry, the volumes V of cavities can be meas-ured to fairly high precision, yielding the work W = pVdone on the surrounding hot gas by the jets during theinflation phase of the cavities. This method gives adirect measurement of the jet energy and requires noknowledge of magnetic field strength or energy parti-tioning. Nor does it require a radio map.

Cavity systems in rich clusters, like jets, are usuallyfound in pairs with typical energies of 1059 erg. Theenthalpy of a cavity (free energy), the important quantityfor jet heating, ranges between ~2 pV– 4 pV, dependingon the state of the matter filling it. Knowledge of thisquantity is relevant to a variety of problems includingthe quenching of cooling flows, the growth of super-massive black holes, cluster and group “preheating,”the creation and dispersal of large-scale magneticfields, and the nature of radio sources themselves.

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Heating the Hot Gas in Galaxy Clusters by Energetic Radio Jets

Figure 1. The relationships among the X-ray, radio, and optical sources in MS0735.6+7421. The smoothed X-ray image (left) and opticalimage (right) are superposed on the 1.4 GHz radio contours. The 40 ksec X-ray image was obtained with the Chandra X-ray Observatory onDecember 1, 2003. The radio map, with 4 arcsec resolution, was made with the Very Large Array telescope in the C configuration. The X-raycavities are filled with radio emission. Each cavity is roughly an arcmin in diameter (200 kpc) centered approximately 125 kpc to the north-east and to the south-west of the cluster center. Each image is 250×250 arcsec (875×875 kpc) on a side.


My colleagues and I recently discovered anenormous pair of “supercavities” in the z = 0.22 clusterMS 0735.6+7421, each of which is nearly 200 kpc indiameter. Observations with the Very Large Array(VLA) show that the X-ray cavities are filled with radioemission at 1.4 GHz (Figure 1) and are surroundedby a weak (Mach 1.4) but powerful shock frontresembling a radio cocoon. The shock energy is anastonishing 6 ×1061 erg, which agrees with the cavityenthalpy to within the measurement error.

To put this figure in perspective, it represents thecombined energy of several hundred million supernovaexplosions and gamma-ray bursts. It’s enthalpy isroughly 250 times larger than the heralded cavitysystem in the Perseus cluster and is more than fourorders of magnitude larger than the cavity system in M87.Furthermore, the power generated by the jets over the100 Myr age of the shock front exceeds the cluster’sbolometric X-ray luminosity by 15 times. This outburstis having a significant impact on the entire gaseoushalo.

At the same time, the radio source is relatively weak inspite of its large size (550 kpc long). The shock energyexceeds the 1.4 GHz radio luminosity by more thanfive orders of magnitude! We know from the aggregateproperties of cavities that jet power can exceed the1.4 GHz luminosity by factors of 100-1000, but neverbefore have we seen such a powerful outburst accom-panied by such a feeble radio source.

The consequences of this discovery are far reaching.Periodic nuclear activity punctuated now and then bypowerful outbursts would supply enough energy to thehot gas to balance radiative cooling and reduce orquench a cooling flow. It now appears that coolingflows are governed by a feedback cycle in which thehot gas cools and accretes onto the central clustergalaxy, fueling star formation and the active galacticnucleus. (In fact the roughly one billion solar-massblack hole that created MS0735’s cavities must haveaccreted nearly one third of its mass during the out-burst.) The ensuing outburst heats the gas and stops theinflow until cooling can be reestablished, and the cycle

repeats. This is the prescription for galaxy formationgoverned by supermassive black holes.

Finally, powerful outbursts could be the key to under-standing the the long-standing “preheating” problemwith groups and clusters. The relationship between thetemperature and luminosity of the hot gas in thesesystems is steeper than expected from a collapsegoverned by gravity alone. The outburst inMS 0735.6+7421 has contributed ~1/3 kev per particleof heat to the surrounding gas, which is a significantfraction of the 1– 3 keV of preheating required steepenthe slope to the observed level. Evidently only severaloutbursts of this magnitude over a cluster’s lifetimewould do the job.

Although the most powerful outbursts must be relativelyrare, my colleagues and I have already found two othersystems with burst strengths that lie within an order ofmagnitude of MS 0735.6+7421. So it appears that thesupermassive black holes lurking at the centers ofgalaxy clusters play an important role in the develop-ment of the giant galaxies in which they reside and thevast halos of gas surrounding them.

B. R. McNamaraOhio University

References:

Bohringer, H. et al. 1993, MNRAS, 264, 25Carilli, C. L., Perley, R. A., & Harris, D. E. 1994,

MNRAS, 270, 173McNamara, B. R. et al. 2000, ApJ, 534, L135Fabian, A. C. et al. 2000, MNRAS, 318, 65Birzan, L. et al. 2004, ApJ, 607, 800McNamara, B.R., et al. 2005, Nature, 433, 45Forman et al. 2005, ApJ, in press, astro-ph/0312576Wu, K.K.S. et al. 2000, MNRAS, 318, 889Markevitch, M. 1998, ApJ, 504, 27

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For over 20 years astronomers have known that globularclusters over-produce millisecond pulsars (MSPs)compared to the Galactic disk per unit mass. Becausetiming observations of multiple MSPs in a clusterprovide unique probes into pulsar physics, clusterdynamics, and binary evolution (e.g. Freire et al. 2003,MNRAS, 340, 1359), and the fact that clusters can(theoretically) produce truly exotic objects (such asMSP-MSP or MSP-black hole binaries), several groupshave expended significant effort searching clustersdeeply for radio pulsars. One of the most promising,but previously disappointing, targets has been theglobular cluster Terzan 5 (Figure 1).

Terzan 5 is a dense, massive, and pre-core-collapseglobular cluster located near the center of our Galaxy(D~9 kpc, l=3.8 deg, b=1.7 deg) that has been predictedto contain tens or even hundreds of pulsars, more thanperhaps any other cluster (e.g. Kulkarni & Anderson,1996, IAUS, 174, 181). VLA imaging of Terzan 5(Fruchter & Goss, 2000, ApJ, 536, 865) supported thesepredictions by detecting steep-spectrum point sourcesand diffuse emission near the core, indicating thatperhaps 60-200 unresolved pulsars were contributingto the measured radio flux. However, deep pulsationsearches had only uncovered three pulsars.

With the Green Bank Telescope (GBT) and the newSpigot pulsar backend (produced by a collaborationbetween Caltech and NRAO), we observed Terzan 5for six hours in July 2004 at the higher-than-usualfrequency of 2 GHz where 600 MHz of relativelyinterference-free bandwidth is available. The large gainof the GBT, the wide observing bandwidth, and thedecreased scatter broadening and dispersive smearingcaused by observing at 2 GHz resulted in an observationthat was 5-20 times more sensitive than the best searchesof Terzan 5 conducted to date. As we began searchingthe data (using a tremendous number of CPU cycles atboth Green Bank and McGill University), new pulsarsbegan appearing in our candidate lists with a startlingregularity: we had hit the pulsar jackpot. From thatobservation alone, we uncovered 14 new MSPs, by farthe most pulsars ever discovered in a single pointing.

Additional GBT observations have resulted in at leastnine additional MSPs, bringing the total known inTerzan 5 to 26, the most of any globular cluster.47 Tucanae was the previous record holder with22 known pulsars. The spin periods of the pulsars inTerzan 5 (Figure 2) span a much wider range thanthose in 47 Tuc and appear to be drawn from a differ-ent underlying distribution, which may indicate differ-ent dynamical conditions in the cluster cores. In addi-tion, the four fastest MSPs known in any Galacticglobular cluster are in Terzan 5.

Fourteen of the new MSPs are members of binarysystems, several of which appear to be of significantscientific interest individually. Ter5E is in ~60 dayorbit, which is very long for a cluster pulsar and mayindicate that it resides in the relatively placid outskirtsof Terzan 5. Ter5N appears to have a Carbon-Oxygenwhite dwarf as its companion, the first such systemknown in a cluster. Ter5O and P are the third and

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A Pulsar Jackpot in Terzan 5 with the GBT

Figure 1. An I-band image of Terzan 5 taken with the NTT telescopeduring exceptional seeing conditions (~0.3"). Image courtesyS. Ortolani/ESO.

fourth fastest known MSPs and are also eclipsingsystems. Ter5O is a “Black Widow” system consumingits very low-mass companion (~0.04Mu), while theirregularly eclipsing Ter5P seems to have exchanged itsoriginal white-dwarf partner for a strange evolved starwith a mass of ~0.4 Mu.

The truly stand-out systems so far, though, are Ter5Iand J. These pulsars are both in compact (~30 hourorbital period) but highly eccentric (e~0.4) orbitsaround what are likely white-dwarf companions ofmass 0.3-0.4 Mu. We have measured the precession ofperiastron for both systems to be ~0.3 deg/yr, which ifdue to general relativity, indicates that the total massesof each of the systems are ~2.2 Mu. When combinedwith our knowledge of the mass functions, this impliesthat the pulsars are significantly more massive than anywell-measured pulsar to date: at 95 percent confidence,at least one of these pulsars has a mass >1.68 Mu. Ifproven correct over the next year or two by moredetailed timing observations, such high masses willrule out several “soft” equations of state for matter atnuclear densities.

Our ongoing timing observations will result in precisepositions for each of the pulsars by the end of thesummer (and thereafter possible infra-red or X-rayidentifications), and a wealth of science about the pul-sars and Terzan 5 itself will soon follow. In addition,new search algorithms, observations at different fre-quencies, and improvements to the Spigot make futuresearches very encouraging: our measurements of the fluxdensities of the currently known pulsars indicate thatperhaps one hundred more MSPs remain to be detectedin Terzan 5.

Note: Additional details of the observations, data analy-sis, and results can be found in Ransom et al. 2005,Science, 307, 892. Significant thanks go to the CanadaFoundation for Innovation for funding the Beowulfcluster at McGill University upon which we have beenhighly dependent.

Scott Ransom (NRAO), Jason Hessels (McGill Univ),Ingrid Stairs (UBC), Paulo Freire (Arecibo),

Fernando Camilo (Columbia), Victoria Kaspi (McGill Univ), David Kaplan (Caltech/MIT)


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Figure 2. Average pulse profiles and periods for the 26 currently known pulsars in Terzan 5. Asterisks indicate that the pulsar is in a binarysystem, and the length of the horizontal error bar (0.3 ms) is the effective system time resolution at a center frequency of 1950 MHz.

0 0.5 10 0.5 10 0.5 10 0.5 10 0.5 10 0.5 1 0 0.5 1

0 0.5 10 0.5 10 0.5 10 0.5 10 0.5 10 0.5 1 0 0.5 1

0 0.5 10 0.5 10 0.5 10 0.5 10 0.5 10 0.5 1 0 0.5 1

0 0.5 10 0.5 10 0.5 10 0.5 10 0.5 1

A*11.56 ms

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M*3.57 ms

N*8.67 ms

O*1.68 ms

P*1.73 ms

Q*2.81 ms

R5.03 ms

S6.12 ms

T7.08 ms

U*3.29 ms

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aa5.79 ms

Astronomers now suspect that radio emission frombrown dwarfs indicates magnetic activity on these sub-stellar objects, in possible agreement with magneticactivity signatures seen on higher-mass stars. Magneticfields are known to be important in producing bothpersistent and variable atmospheric heating in late-typestars, heating plasma to temperatures from 104–106 K(seen at optical, ultraviolet, and X-ray wavelengths),and accelerating the energetic particles which producenonthermal radio emission.

Many recent results give conflicting evidence about thesurvival of and nature of magnetic activity on extremelycool dwarfs. The decrease in the fraction of chromos-pherically active stars at spectral types later than M8suggests that magnetic activity is dying in ultracoolstellar objects (West et al. 2004). This has beenexplained theoretically as a temperature effect—theincreasingly neutral and dense cool atmospheres in lateM/early L objects have large resistivities and therebyprevent the buildup of magnetic stresses and subsequentmagnetic heating of their atmospheres (Mohanty et al.2002). While the bulk of ultracool dwarfs do notdemonstrate persistent magnetic activity, it is puzzlingthat any activity remains. There are lines of evidencewhich suggest that magnetic activity does survive insome form: the reports of dramatic Hα variability in

some ultracool dwarfs (Liebert et al.2003, Reid et al. 1999) which show noevidence for Hα emission outside offlares, frequent reports of sporadicX-ray flares with no detectable levels ofquiescent emission (Rutledge et al. 2000,Hambaryan et al. 2004), and detectionsat radio wavelengths (Berger et al. 2001,Berger 2002).

The radio detections are importantbecause radio emission from late-typestars is traditionally ascribed to gyro-synchrotron emission from a populationof mildly relativistic electrons in mag-netic fields. If the interpretation of the

origin of radio emission from ultracool stars/browndwarfs is the same as that from active stars, then this isconfirmation that magnetic activity is indeed survivinginto the brown-dwarf regime. Radio observations canaddress magnetic activity in the brown-dwarf regime intwo ways: the first is to assess how common radioemission from brown dwarfs is, and the second is toexplore the nature of the radio emission via its spectraland polarization characteristics.

The first is being addressed by a volume-limited VLAsurvey of 65 late M, L, and T dwarfs closer than 13 pc.We observed at a frequency of 8 GHz to match thefrequencies where previous detections have been madeand to allow for a comparison of radio properties withnearby M dwarf stars. An NRAO summer student,Lynnae Quick, from the North Carolina Agriculturaland Technical State University, spent the summer of2004 reducing the first parts of the data set. She pre-sented her results at the 205th meeting of the AmericanAstronomical Society in San Diego, CA. Out of theten objects she studied, three (2 L dwarfs and a T dwarf)showed signs of being radio emitters. The reductionand analysis of this dataset is ongoing. The systematictrends of radio emission with spectral type, rotationrate, age, and mass (or internal structure), as well ascorrelations with other magnetic activity signatures,will be explored.


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VLA Investigates Radio Emission from Brown Dwarfs

Artist’s conception of, from left to right, the relative sizes of the Sun, an M dwarf, anL dwarf, a T dwarf, and Jupiter.


The second is being addressed by sensitive multi-frequency observations of radio-detected objects.While the survey is guaranteed to improve the statisticsof radio emission from brown dwarfs, it does notdetermine the origin of the emission. By studying thedetailed characteristics of the radio emission, notablyits spectral distribution and polarization, we cantest the gyrosynchrotron emission mechanism andexplore simple magnetic geometries. AstronomersR. A. Osten, T. Bastian (NRAO), and S. L. Hawley(U. of Washington) explored the radio emission fromthe M9 dwarf TVLM513–46546 in January 2004,using the VLA in its BnC configuration and observingat 20, 6, and 3.6 cm wavelengths. Detections at both3.6 and 6 cm provide spectral-index measurements of– 0.4±0.1 (flux decreases as frequency increases), andan upper limit at 20 cm suggests that the spectral peak

lies between 1.4 and 5 GHz. Upper limits of circularpolarization at 3.6 and 6 cm are <15 percent. Thesecharacteristics agree well with typical parameters forearly to mid-M dwarfs.

R. A. OstenReferences:Berger, E. et al. 2001 Nature, 410, 338Berger, E. 2002 ApJ, 572, 503Hambaryan, V. et al. 2004 A&A, 415, 265Liebert, J. et al. 2003 ApJ, 125, 343Mohanty, S., Basri, G., Shu, F., Allard, F., & Chabrier,

G. 2002 ApJ, 571, 469Reid, I. N., Kirkpatrick, J. D., Gizis, J. E., & Liebert, J.

1999 ApJ, 527, L105Rutledge, R. E. et al. 2000 ApJ, 538, L141West, A. A. et al. 2004 AJ, 128, 426

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Molecular Gas in the First Galaxies

Walter et al. (2004) recently presented high-resolutionVery Large Array (VLA) images of the carbon monoxide(CO) 3–2 emission from the quasistellar object (QSO)SDSS J1148+5251 at the highest known redshift: z = 6.42.These observations have pushed radio studies ofgalaxy formation into the epoch of cosmic reionizationwhen the first luminous sources (active galactic nucleiand stars) reionized the neutral intergalactic medium.

Also relevant to thesestudies of high-z QSOhost galaxies is the thenow well-establishedcorrelation betweenblack-hole mass and thevelocity dispersion ofthe stars in the hostspheroidal galaxy (the“Mbh–σv relation”).This correlation sug-gests a causal relationbetween the formationof supermassive blackholes (SMBH) andspheroidal galaxies(Gebhardt et al. 2000).

The low-resolution VLA image (left figure) revealsextended CO 3–2 emission on a scale of ~1", or 6 kpc(about 20,000 light years). The high-resolution VLAimage (right figure) shows two compact emissionfeatures separated by 0.3", with the compact componentscomprising about half the total CO luminosity. Walteret al. speculate that SDSS J1148+5251 is a merginggalaxy system havng extended tidal features and a

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CO 3-2 emission from SDSS J1148+5251 at z =6.42. Left: The VLA image at 0.3" resolution. Thebeamsize shown in the lower left implies that the source is clearly resolved. Right: The VLA image at0.15" resolution (Walter et al. 2003, 2004; Bertoldi et al. 2003). At this resolution the central sourcebreaks up into two peaks. The cross shows the SDSS position of the optical QSO (White et al. 2005).


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double nucleus, although the relative radio-opticalastrometric accuracy is insufficient to identifyunambiguously the optical QSO with either compactmolecular-gas component.

The intrinsic brightness temperature of the CO emissionin the compact components is about 20 K. This valueis similar the CO brightness temperatures in nearbystarburst nuclei (Downes & Solomon 1998). The hostgalaxy of SDSS J1148+5251 shows starburst character-istics in a number of other ways: (i) it follows theradio/far-infrared (FIR) correlation (Carilli et al. 2004),(ii) the CO excitation ladder up to CO 7–6 is similar tothat in the nucleus of the nearby starburst galaxyNGC 253 (Bertoldi et al. 2004), and (iii) the dust-to-gasratio is comparable with those of nearby starbursts. Ifthe FIR luminosity of SDSS J1148+5251 results fromstar formation, the implied star-formation rate is about1,000 solar masses per year.

The CO image also allows a rough estimate of thedynamical mass of the host galaxy. We note that theseobservations are the only method for determining sucha dynamical mass for the host galaxy of a high-z QSO.Walter et al. (2004) found that the host-galaxy dynamicalmass inside a radius of about 3 kpc is ~5×1010 solarmasses, which is comparable with the total molecular-gas mass derived from the CO luminosity. Thissuggests that the mass in the inner few kpc is baryondominated, as are nearby elliptical galaxies and ultra-luminous infrared galaxies, although for ellipticalgalaxies the mass is in stars, not molecular gas.Walter et al. also pointed out that the predictedspheroidal-galaxy mass based on the Mbh–σv relationis more than a factor of ten larger than the measureddynamical mass. This suggests a breakdown in theMbh–σv relation at the highest redshifts, with the impli-cation that the SMBH forms prior to the host galaxy.

Overall, the radio observations of the host galaxy ofthe z=6.42 QSO SDSS J1148+5251 suggest a massivestarburst coeval with the nuclear activity in a merginggalaxy system. The star-formation rate is sufficientto form a large spheroidal galaxy in a dynamicaltimescale, about 108 years. This conclusion is qualita-tively consistent with the coeval formation of SMBH

through Eddington-limited accretion and spheroidalgalaxies, although the VLA observations suggest thatthe SMBH may form prior to the main stellar compo-nent of the host galaxy. Formation of massive galaxiesin dramatic starbursts at high z is also consistent withthe recent “downsizing” scenario for galaxy formationin the context of ΛCDM structure-formation models(Bundy et al. 2005).

Pushing into the earliest epochs of galaxy formation isa major goal for the Atacama Large Millimeter Array(ALMA) and the Expanded Very Large Array (EVLA).The VLA results on SDSS J1148+5251 have presagedsuch studies by finding massive reservoirs of moleculargas, the necessary fuel for galaxy formation, even atthese extreme redshifts. Unfortunately, current radiotelescopes are able to study only exceptionally luminousgalaxies. The EVLA and ALMA will be able to detectrelatively normal galaxies at these epochs and henceprovide the necessary complement to future near-infrared telescopes such as the James Webb SpaceTelescope (JWST), with the near-infrared telescopesrevealing the stars and ionized gas while the EVLAand ALMA provide the unique capability to image themolecular gas, dust, and star-formation activity in thefirst galaxies. Hence, future facilties at radio throughnear-infrared wavelengths will provide a panchromaticview of the earliest galaxies, constraining all keyelements in galaxy formation.

C. Carilli (NRAO) and F. Walter (MPIA)

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