Download 3.1 Radio Astronomy Research Results For much of PY 2010, radio

3.1 Radio Astronomy Research Results
For much of PY 2010, radio astronomy operations at Arecibo were heavily impacted by the structural problem discovered
in early February 2010. Indeed, for about 9 months the zenith angle coverage of the telescope was limited to observations
within 3.5° < Z.A. < 12°. Nevertheless, a full astronomical program has been achieved, although this has had to be tailored
to fit the available declination coverage and tracking time.
During PY 2010, the Mock Spectrometer was routinely employed both for the GALFACTS, AUDS and PALFA multi-beam Lband surveys, and for a range of single-pixel projects, as described below. The temporary freeing up of the spectral region
between 700–800 MHz from mid-2009 by the federally-mandated requirement that US TV stations transmitting analog
signals move to digital operations using new frequency allocations was exploited at Arecibo during PY 2010. This littleexplored segment of the radio spectrum has been opened up to astronomers at Arecibo via a receiver produced and
commissioned in short order. Broadcast services that will eventually move into this band have not yet made this transition
in Puerto Rico, and for now Arecibo users continue to exploit the chance to make pulsar studies, and search for molecular
or redshifted neutral hydrogen (HI) lines within this band.
Arecibo has also made major moves towards the complete upgrade of its VLBI capabilities during PY 2010. Most apparent
is the acquisition and assembly of a 12-m diameter antenna on a hill-top within the Observatory grounds to act as a phasereference telescope for VLBI observations, as well as for a number of other applications towards scientific operations,
education and public outreach (see Section x). In addition, a pair of RDBEs (digital VLBI backends) have been ordered
from NRAO, with delivery expected late in 2010. Further, a pair of Mark-5C VLBI recorders have been delivered to Arecibo,
and are currently being equipped with the latest software. This matched pair of VLBI backends can be used separately on
the 12-m and 305-m antennas, or together on either of the two antennas to provide recording at double the data rate.
The distribution of observing time devoted to the ALFA and major single-feed surveys in PY 2010 was 2488 hours, a total
that excludes the time reused by commensal surveys. The total number of commensal observing hours, excluding
SETI@home, was 1379. The ability, unique to Arecibo, to execute several surveys simultaneously greatly increases the
efficiency of telescope usage.
3.1.1 Surveys
Approximately 60% of the telescope time devoted to radio astronomical observations in PY 2010 was allocated to ongoing ALFA and single-pixel surveys. Fig. 3.1 shows both the primary surveys and those that observe commensally with
them, followed by a description of the surveys that will continue into PY 2011. The 300-MHz bandwidth (BW) Mock
spectrometers continued to serve as the spctrometer of choice in PY 2010 for GALFACTS, AUDS and PALFA. Becoming a
standard data-taking mode in PY 2010, PALFA now runs commensally with (a) the Zone of Avoidance HI survey (ZoA) of
that part of the Universe obscured by our own Galaxy, and (b) the survey of Radio Recombination Lines (RRL) from the
Galactic plane. The primary surveys and their “commensal partners” are:
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Pulsar Search: PALFA Survey, and commensal partners ZoA & RRL.
Extragalactic 21-cm HI: ALFALFA, AGES, AUDS, and commensal partner GALFA-TOGS..
Continuum: GALFACTS (Full-Stokes), and commensal partners ZoA and GALFA-TOGS2.
Single-Pixel Surveys: (a) Zeeman-effect survey of magnetic fields in ULIRGS, (b) GASS (GALEX-Arecibo- SDSS) survey of
HI in 1000 massive galaxies, and (c) the 327-MHz drift-scan pulsar survey..
PY 2010 saw the continuation of these “primary” surveys. It is to be noted that the primary surveys of the GALFA, Galactic
HI, consortium were completed in PY 2009, although the GALFA commensal all-Arecibo sky HI survey, TOGS/TOGS2 , is
on-going.
The ALFA Galactic Plane Survey for Pulsars (PALFA): A deep search of the Galactic Plane for pulsars and transients is
being conducted by the Pulsar Consortium, PALFA, concentrating its activities in PY 2010 to latitudes within 5° of the
Galactic plane for the longitude sector available to Arecibo in the Galactic center quadrant. Its follow-up projects for
timing its discoveries routinely acquire full-Stokes arrival-times. Many of the stronger discoveries are also being timed at the
GBT, Jodrell Bank, Nançay, Parkes and Westerbork. In PY 2010, PALFA continued to acquire its data with the Mock
spectrometers, which provides a bandwidth of 300 MHz with robust response to the presence of radio-frequency
interference. PALFA now use longer observations (9 min instead of 4.5 min) for Galactic longitudes between ~30° and 45°
to expand the effective search volume. In PY 2010, PALFA continued processing data via the Einstein@Home community,
which was originally developed to process LIGO data for coherent gravitational wave signals. E@H now devotes 1/3 of its
processing resources to PALFA data to search for very compact binary pulsars in circular orbits. A total of ~200k clients
around the world have signed on to E@H, of which some fraction is active at any epoch: 1/3 of the active clients receive
PALFA data. Data taken with the 100-MHz BW WAPP spectrometers from 2005 to 2009 have been 90% processed with
the Cornell code (non-acceleration search), 50% processed with the PRESTO-based code (acceleration search), and a few
% processed with Einstein@Home (full circular-orbit search). Six graduate students work with PALFA. On the outreach
side, Arecibo Remote Control Center (ARCC) students from the University of Texas at Brownsville continue their
involvement in PALFA. PALFA has ZoA, RRL and SETI as commensal partners.
PALFA accumulated 262 hours observing in PY 2010. To date, it has blindly detected about 170 pulsars of which 54 are
new (found in the periodicity analysis, the single-pulse analysis or both). It has now discovered seven millisecond pulsars,
all of which are objects of potential utility for the pulsar timing array for gravitational wave detection. Einstein@Home
made its first two discoveries in 2010, both in PALFA data. PSR J2007+27 is a disrupted recycled pulsar with a very wide
double-peaked profile, indicating that its rotational and magnetic axes are nearly aligned. PSR J1952+26 is a recycled
pulsar in a 9.4-hour binary with a massive companion and is an excellent candidate for the measurement of relativistic
effects in the system via consistent timing observations over the coming year.
The first PALFA msec pulsar was J1903+0327. This is in an eccentric (e=0.44) 95-day orbit with an ~1 M⊙ companion.
Three years of intensive timing of this pulsar have yielded a pulsar mass of 1.667±0.021 M⊙ , clearly above the
Chandrasekhar limit and ruling out some equations of state for super-dense matter. Its mass is also consistent with spin-up
of the pulsar by mass accretion. Optical spectroscopy shows the companion to be a main sequence star, implying that it is
not the star that recycled the pulsar. It is suggested that the neutron star was originally in a tight orbit with another main
sequence star and accreted matter as that companion evolved, forming a MSP. This donor star would then have
disappeared due to either a 3-body interaction with the present (then outer) companion as its orbit evolved, or through
ablation/accretion by the newly-formed MSP. Two of the other MSP discoveries are also in binaries, while the third is
isolated. A young, high-(dE/dt) pulsar, J1856+0245, is a likely counterpart to a TeV-ray source detected by HESS that is
most likely a pulsar wind nebula. Timing of the young relativistic binary J1906+0746 will continue because the secular
changes in its pulse shape from geodetic precession allow the pulsar’s beam shape to be sampled. Timing will also allow
PALFA to determine the masses and to test the orbital period decay against GR to reasonably high precision.
Pulsars have long been known to be intermittent through the appearance of bursts of pulses, pulse nulling and other
modulations. Recent work has only underscored intermittency, including the discovery of rotating radio transients”
(RRATs; McLaughlin et al. 2006, Nature, 439, 817). It is not yet clear to what extent RRATs represent a new physical class of
radio pulsar as opposed to being merely an empirical extreme, where some objects are missed in standard periodicity
searches but emit atypically strong pulses detectable in single-pulse analyses. The PALFA survey will yield good statistics
on this empirical class. Of the previously known pulsars found blindly in the periodicity search analysis, 63% are detected
in the single-pulse (SP) analysis, somewhat surprising if one assumes pulse amplitudes are fairly steady in the data streams
that typically contain more than 100 pulse periods. Obviously, pulse amplitudes are highly modulated, with RRATs being
extreme cases. So far, PALFA has found 8 objects through the Cornell single-pulse analysis that were missed in the
periodicity analysis. Five RRATs have been confirmed through re-observation. Arecibo REU student, Deborah Schmidt,
extracted pulse arrival times from multi-frequency data on RRAT J0627+16, the object with the lowest known duty cycle of
pulsars and RRATs, and a partial timing solution was obtained allowing narrowing down of its position. Counterparts have
been looked for in other surveys, but nothing found within the error box.
The 327-MHz Drift-Scan Pulsar Survey: Well suited to using telescope time under the temporary restrictions caused by the
recent platform problem, the Arecibo Drift-Scan Pulsar Survey at 327 MHz acquired considerable amounts of data during
PY 2010. The data reduction effort is being spearheaded by the University of West Virginia, and began in earnest in
October 2010. From UWV, the project is being worked on by a team of professors, and graduate, undergraduate and
high-school students. Already a number of known pulsars have been redetected, and a first excellent pulsar candidate
(Fig. 3.2) awaits confirmation.
Extragalactic H I Studies – EALFA: The EALFA Consortium explores the extragalactic Universe via observation of the
neutral hydrogen line (HI) at 21cm. Their strategy calls for a classic ‘wedding cake’ design, comprising three separate
survey depths, each prosecuted by a different sub-consortium. ALFALFA conducts the large-area, shallow survey that aims
to greatly improve on the small number statistics afflicting previous surveys. It plans to cover 7000 square degrees of sky,
and expects to detect more than 30,000 HI sources. AGES is the mid-level sensitivity survey, which aims to investigate the
HI content of the periphery of nearby galaxies, groups and clusters, but with less sky coverage. The last two sub-consortia
are AUDS (the Arecibo Ultra Deep Survey), which will carry out a high sensitivity pencil beam exploration to z ~ 0.25, and
the commensal survey, ZoA (Zone of Avoidance), which will identify galaxies near the Galactic plane. Both ZoA and
AUDS were initiated in PY 2009, as they needed the 300-MHz BW of the Mock spectrometers, whereas ALFALFA and
AGES were already well under way using the 100-MHz BW WAPP spectrometers.
The Arecibo Legacy Fast ALFA Survey (ALFALFA): ALFALFA is a two-pass, drift-scan, HI survey of the high Galactic latitude
sky visible from Arecibo, and is conducting a census of 7000 deg2 of sky out to a redshift z~0.06 with 5 km s-1 resolution.
Now in its 6th year, ALFALFA aims to obtain a census of HI-bearing objects over a cosmologically significant volume of the
local universe. With nearly 90% of the main survey observed, the fully analyzed dataset currently covers some 40% of the
final survey area, yielding HI masses, systemic velocities and HI line widths from about 16,000 extragalactic objects. While
some investigations will require completion of the full survey, 2010 has brought the first opportunity to explore the
cosmological questions which ALFALFA is intended to addressed. Fig. 3.3 shows a Spanhauer diagram of the distribution
with distance from us of the HI masses of galaxies detected by ALFALFA and illustrates the richness of the ALFALFA
catalog in comparison with the previous HIPASS survey which was conducted over only a 64-MHz bandpass meaning that
it did not sample distances to the right of the vertical dashed line. The blue and red curves illustrate the HIPASS
completeness (blue) and detection (red) thresholds. Clearly, ALFALFA has delivered on its design promise to increase
greatly our census of the HI-rich present day universe.
The derivation of the first global HI mass function from ALFALFA, based on the 40% catalog, was recently published
(Martin et al., 2010, ApJ 723, 1359). Fig. 3.4 compares the HI mass functions derived by ALFALFA (solid blue curve) and
HIPASS (dashed red curve: Zwaan et al. 2005 MNRAS 359, L30). Also evident from Fig. 3.3, ALFALFA samples HI masses
over a significantly larger dynamic range and a much larger volume, thereby placing the derived HI mass function on
much more robust ground. As designed, ALFALFA detects hundreds of galaxies with masses < 10 8 M⊙. It also detects a
substantial population of very massive HI disks with masses > 1010 M⊙, the present day counterparts of the galaxies at high
redshift that will be detected by the Square Kilometre Array. Integration of the ALFALFA result yields a present day
contribution of HI to the cosmic density that is 16% larger than that measured by HIPASS. At the highest masses, ALFALFA
finds many more galaxies than predicted previously, suggesting an upward adjustment of the estimated detection rate for
future large-scale HI surveys with the SKA.
Cornell graduate students Ann Martin and Manolis Papastergis are working on using the ALFALFA 40% catalog to derive
other relevant cosmological parameters, the HI correlation function and the disk galaxy velocity function, while Jayce
Dowell, who has recently completed his Ph.D. at Indiana University, has used ALFALFA to derive the HI diameter function.
Future work on the possible dependence of these functions on local environment awaits completion of the full ALFALFA
survey.
The Arecibo Galactic Environment Survey (AGES): AGES observes a variety of nearby galactic environments, and the
volumes behind them. It reaches a lower noise level (~0.7 mJy) than the 2.2 mJy of ALFALFA, and so searches for lower
mass and column density HI objects. In PY 2010, AGES used 224 hr of telescope time and, to date, has completed 41% of
the requested survey area of 200 deg2. Four of the proposed fields are now complete to full depth (NGC1156, NGC7332,
VC2, UGC2082). AGES is specifically designed to quantify how the evolution of atomic hydrogen differs in various
environments in the local Universe, and its results already suggest that large-scale structure needs to be described
differently for galaxies selected at 21 cm as compared to those selected optically.
Previously collected AGES data has led to a number of publications this year. A paper has been published on the fields
around NGC7332 and NGC1156 (Minchin et al.,2010, AJ, 140, 1093), while Scott et al. (2010, MNRAS, 403, 1175) used
AGES data in their study of environmental effects in the cluster A1367. Davies et al. have just submitted a paper (MNRAS)
on the NGC7448 group and the first AGES determination of the HI mass function. Rhys Taylor completed his PhD on the
AGES Virgo cluster data, and is taking up a post-doctoral position at Arecibo. An NSF REU student, Tim Taber, will present
his work on UGC2082 at the winter AAS.
An AGES objective is to investigate the number of low mass gas rich dwarf galaxies that reside around isolated galaxies
and within galaxy groups, as hierarchical models of galaxy formation predict hundreds of dwarf companions for each
giant galaxy. AGES typically finds only one or two new dwarf galaxies, at odds with the theory. In the NGC7448 data ( Fig.
3.5) three of the five newly discovered dwarf galaxies are not group members, but may reside in the filament local to the
NGC7448 group. In the central regions of this group AGES confirm the existence of intra-group HI and measure there to
be about 2.5 times more HI external to the main galaxies than within them, demonstrating the strength of tidal effects in
the group environment.
Over a typical volume, AGES (rms=0.7 mJy) detects about 95% and 50% more galaxies than the other blind surveys,
HIPASS (rms=13 mJy) and ALFALFA (rms=2.2 mJy) respectively. About 80% of the HI detections are new. Combining the
data for all AGES fields has yielded a first estimate of its HI mass function ( Fig 3.6). This gives a total cosmic density of HI in
good agreement with that obtained by ALFALFA, but with a low mass slope steeper than both ALFALFA and HIPASS (a
slope of ~-1.5 compared to -1.3). The reasons for this difference are being investigated. The AGES value for the cosmic
density of HI is ΩHI=8.6±0.8 x 10-4 h72-1.
The AGES ‘global’ HI mass function has been compared with that from AGES observations of the Virgo and A1367 clusters
(Fig 3.6). In particular, the Virgo cluster mass function appears peaked, lacking both high and low mass galaxies when
compared to the global function. This is a further indication of the effect of the environment on galaxy evolution.
During PY 2011, AGES hope to finish the N7448, Virgo Cluster 1, A1367, NGC3193 and M33/PP fields.
The Arecibo Ultra Deep Survey (AUDS): AUDS is the most sensitive of the Arecibo blind 21-cm line surveys, and is
searching for HI line emission for 0 < z < 0. 16. AUDS uses the Mock spectrometer to cover the full ALFA frequency range
of 1225 to 1525 MHz. Its main goals are to investigate the evolution of HI gas in the Universe and to explore the lowdensity gas around the edges of galaxies with unprecedented sensitivity. To this end, two regions are observed in “driftand-chase” mode, where the telescope is positioned at the start of the region and fixed at that Azimuth and Elevation
whilst the sky drifts past for 230 sec. This yields excellent bandpass stability as the spillover radiation from the ground is
essentially constant. The scientific goals require a sensitivity of ~50 µJy at a velocity resolution of 20 km s -1, or ~100 µJy at
the full spectral resolution of 5 km s -1. AUDS began operations with the commissioning of the Mock spectrometers in PY
2009. In PY 2010 it accumulated ~187 hr of its 1100-hour time request.
ALFA Zone of Avoidance (ZoA): The obscuration due to dust and the high stellar density in our Galaxy varies from place to
place within the Milky Way. Overall, it blocks ~20% of the extragalactic Universe at optical wavelengths and a smaller
fraction at infrared. This Zone of Avoidance (ZoA) does not pose a problem for the study of galaxies themselves, as there is
no reason to believe that the population of obscured galaxies should differ from those in optically unobscured regions.
Yet, an accurate knowledge of the mass distribution within our neighborhood is essential if we are to understand the
dynamical evolution of the Local Group from kinematic studies. In addition, the discovery of previously unknown nearby
galaxies furthers efforts to understand the local velocity field, while mapping more distant, hidden galaxies allows us to
explore the connectivity of large-scale structure across the Galactic plane.
The ALFA ZoA survey is a combination of two separate commensal projects: (1) a mapping of the Arecibo sky in the
Galactic longitude range 30° - 75° and Galactic latitudes < 10° (Inner Galaxy region), where the primary project for this
program was I-GALFA, and (2) a deeper mapping at Galactic latitudes < 5°, beginning in the Inner Galaxy region, where
the primary project is PALFA. Both of these projects reach farther north than the extant Parkes ZoA survey, as well as
providing higher spatial and velocity resolution. The second project also provides higher sensitivity and deeper redshift
coverage.
The shallower ZoA survey of the entire inner Galaxy region began in May 2008, and was completed in 2009.
Extrapolating from the precursor observations, the resulting catalog will contain ~500 galaxies. Most of these will be new
detections, as only 1/10th of Inner Galaxy detections from the precursor survey had 2MASS counterparts in its extendedsource catalog. In addition to many conference proceedings and abstracts, the team has a refereed publication on this
phase of the survey (Henning et al., 2010, AJ, 139, 2130). Data reduction is ongoing, concentrating first on the summer
2009 data taken with the Mock spectrometers. Data from 2008, commensal with GALFACTS, will be reduced in turn, as
the detailed routines for handling its use of “winking” calibration signals has slowed the immediate processing of these
data. Graduate student Travis McIntyre (U. New Mexico) is working on ZoA data for his dissertation. In the coming year,
the project will produce the catalog of HI detections, investigate any multi-wavelength counterparts, and study lowlatitude large-scale structure, which feeds into our understanding of the local density field and the mass-dipole.
Deeper commensal ZoA observations with PALFA (b < 5°) using the Mock spectrometers began in July 2009 and
continued through PY 2010. The ZoA team has developed IDL routines to handle the data reduction, and observations
are now fully commensal, with appropriate ON - OFF pointings taken by PALFA for the ZoA and RRL projects. These
observations are quite deep, 1 mJy rms or better, allowing the tracing of distant large-scale structure, and the detection of
very low-mass local galaxies, over a wide angle of the sky. In addition to tracing obscured mass, these observations will be
used to study the HI properties of galaxies in a sensitive survey, and the HIMF. Observations will continue next year, and
beyond, the completion date being mainly determined by time allocation on the telescope.
Galactic Neutral Hydrogen (H I) Studies GALFA Consortium : The behavior of the ISM is affected by large-scale turbulence,
and by the presence of cosmic rays and magnetic fields, quite apart from the injection of energy from supernova
explosions, bursts of star formation, and sundry other denizens of the Galactic zoo (O-B stars, µ-quasars, the central black
hole, Galactic-ray and X-ray sources, etc.). Our Galaxy is much the best laboratory for these explorations, as it allows
better angular resolution, and the identification of many of the sources of energy injected into the ISM. Most HI studies of
our Galaxy depend on mapping surveys, so that the HI column density is determined as a function of position and
velocity. Arecibo, equipped with ALFA, is ideal for this, given its sensitivity, angular resolution, and complement of highresolution spectrometers.
The GALFA Consortium has been exploiting these capabilities. It has conducted several projects over recent years,
including a comprehensive HI mapping survey of the Inner Galaxy within ±10° of the Galactic Plane,
I-GALFA. GALFA is currently making a commensal survey (TOGS/TOGS2) that maps the sky covered by other ALFA
consortia, who serve as the primary observers. In addition to GALFA-HI, other GALFA subconsortia include GALFACTS,
which aims to investigate the large-scale Galactic magnetic field by tomographic inversion of full-Stokes spectra of the
continuum signal, and the radio-recombination line survey (RRL) which began commensal operations with PALFA in PY
2010.
The Inner Galaxy ALFA (I-GALFA) Low-Latitude HI Survey: In PY 2009, the I-GALFA survey completed mapping of the H I in
the Arecibo-accessible inner Galactic disk for lbl < 10° to investigate molecular cloud formation, shells and chimneys
related to massive star energetics, and the detailed structure of our Galaxy, among other topics. I-GALFA used the ALFA 7beam receiver with the narrow bandwidth GALSPECT spectrometer, to produce fully-sampled, 3.35’-resolution image
cubes with Trms ~ 0.25 K for 0.184 km s-1 width velocity channels, covering |vlsr| < 750 km s-1. Their blank-field sensitivity is
10 times better than either the Canadian or VLA Galactic Plane surveys, which have a 1’ beams, but only 0.824 km s -1
channels, with less latitude coverage. I-GALFA had two commensal partners, ZoA and GALFACTS2. Two PhD candidates,
Geumsook Park (Seoul National Univ.) and Vojtech Sidorin (Charles U., Prague), are using I-GALFA data.
I-GALFA’s public release scheme follows the standard NAIC 18-month proprietary period, counting from the earliest
availability of HI cubes of a particular region to the I-GALFA science team members. Fig. 3.7 shows an example of a little
known supershell from one of the processed iI-GALFA cubes.
The Turn on GALFA Survey (TOGS/TOGS2): TOGS has collected data commensally with ALFALFA since August 2005, and
with AGES since January 2006. The complementary TOGS2 survey has been running commensally with GALFACTS since
November 2008. The combined objective of these projects is to produce a fully-sampled HI survey of the full Arecibo sky to
be used for a diverse range of scientific endeavors. By the end of PY 2010, this objective is well advanced.
The Radio Recombination Line (RRL) Survey: Following lengthy discussions concerning observing procedures, PALFA has
adopted a reworked survey grid that provides the optimized ON-OFF strategy required by ts commensal partners, RRL and
ZoA. Observations using the new grid began in August 2010. This marked the effective commencement of the RRL
survey. The entire survey is expected to take several years to complete. However, data reduction and analysis can begin
almost immediately, dealing with the data as it is acquired. The RRL survey represents an intensive data reduction exercise
and requires a post doc (or at least a PhD student) to oversee data tracking, data reduction, and archiving. An NSF
proposal is being prepared to fund this person.
A baseline calibration program has been written for the RRL Survey using IDL. Still to be written is the program to
separately "stack" the α, β, γ, δ, etc. radio recombination lines to give individual spectra at a common velocity resolution for
each position where lines are detected. It has been discovered that two of the twelve α radio recombination lines in the
band lie at frequencies affected by RFI, and these will not be included in the stacking. Once the stacking program is
available, the rms for the RRL survey should be reduced to ~0.3 mJy, or somewhat deeper for the higher order lines as
there are successively more of these within the band.
The GALFA Continuum Transit Survey (GALFACTS): GALFACTS aims to survey the full-Stokes continuum emission from the
whole of the Arecibo sky using the full 300-MHz ALFA bandwidth. This is technically the most demanding ALFA survey. It
was delayed until the Mock spectrometers became available in PY 2009. During PY 2010, the Arecibo electronics team
solved a saturation recovery-time problem in the front-end that was present in the observations for the first eighth of the
survey. The second eighth of the survey was then completed between November 2009 and January 2010. Further
observations in 2010 were prevented by the telescope structural problem of February 2010, but the GALFACTS team look
forward to resuming the survey in 2011.
The radio continuum sky has been surveyed at many frequencies and angular resolutions but not with full polarization
information. GALFACTS 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 multi-wavelength 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; (7) relationship of full-Stokes images to other ISM
components (HI, dust, etc); (8) variability and radio transients. The GALFACTS sub-consortium has organized itself into a
number of sub-groups to accomplish these diverse aims.
The GALFACTS team has now considerably refined the image of both the first GALFACTS field mapped, and of the
observations of the Galactic center quadrant acquired commensally with the I-GALFA HI survey. The consortium continues
original work on “basket-weaving” the survey scans, correcting the leakage between the different Stokes parameters, and
the CLEANing of sidelobe contributions from the images. However, the quality of the GALFACTS data is already
spectacular. Rich polarization structure is ubiquitous in the Stokes-U image, and Fig. 3.8 displays the overall data quality.
The GALFACTS main data product will be full-Stokes data cubes. Science-quality cubes await only a few final elements to
complete the data reduction pipeline.
The GALEX Arecibo SDSS Survey (GASS): GASS is a large targeted survey designed to measure the HI content of ~1000
massive galaxies, uniformly selected from the SDSS spectroscopic and GALEX imaging surveys. Its principal goal is to
provide an unbiased view of the processes responsible for the transition between blue, star-forming spirals and red,
passively evolving ellipticals. The combination of SDSS, GALEX and Arecibo data will result in a unique, homogeneous
dataset of structural and physical parameters, star formation rates and gas properties of massive galaxies. This proposal
has requested 925 hours, of which approximately 470 (~50%) have been allocated to date. Already GASS has
demonstrated that it detects galaxies with gas fractions a factor of 10 lower than those typically found by ALFALFA,
whose detections are heavily biased towards blue, star-forming galaxies (ALFALFA only detects a small fraction of gas-rich,
green-valley objects). Six graduate students are working with GASS data.
The survey was designed such that ALFALFA and GASS are maximally complementary. ALFALFA contributes the high HI
gas-fraction portion of the complete sample, while GASS observes a proportionate subset of ALFALFA non-detections (and
low S/N detections) to much deeper limits. The combination of GASS and ALFALFA enables complete samples of galaxies
with HI gas-fraction measurements down to 1.5% of the stellar mass of a galaxy. GASS aims to obtain HI measurements of
~1000 galaxies at redshift 0.025 < z < 0.05 with stellar masses M* > 10 10 M⊙. This range straddles the “transition mass” (M*
~ 3.1010 M⊙) above which galaxies show a marked decrease in their present to past-averaged star formation rates. By
observing these down to a low gas-mass limit, GASS seeks to obtain insight into the physical mechanisms that shape the
stellar mass function, regulate gas accretion, and quench further galaxy growth by conversion of gas into stars. GASS
complements on-going blind surveys, by measuring HI mass fractions of galaxies down to an order of magnitude lower
limit. This addresses three key groups of questions, namely (1) What fraction of massive galaxies possess reservoirs of cold
gas, but no active star formation; (2) Is this population distinguished by its environment, AGN activity and/or morphology,
and what implications does that have for their gas accretion history and star formation thresholds; (3) Which populations
are gas deficient (at fixed M*, and/or fixed SFR) with respect to the complete sample? Is it possible to identify a quenching
process, starvation or gas-removal process that explains this deficiency?
PY 2010 highlights from GASS include, 1) public availability of Data Release 1 containing 20-25% of the complete sample,
2) GASS paper II: a measurement of the star formation efficiency of massive galaxies, 3) GASS paper III: spectroscopic
follow-up of a GASS-discovered massive gas-rich disk galaxy in formation, 4) publication of an ALFALFA/GASS stacking
analysis of a massive galaxy sample, allowing detailed statistical analysis of fundamental galaxy scaling relations, 5) GASS
paper IV: on the inside-out formation of massive galaxy disks, 6) submission of the first COLD GASS paper from the IRAM
large survey program to detect CO in GASS galaxies (following a successful pilot program with IRAM), 7) observation of
160+ GASS galaxies as part of a large long-slit spectroscopy follow-up program being carried out at Apache Point
Observatory and the Multi-Mirror Telescope. In these six new papers, GASS has discovered new scaling relations relating
gas fraction to stellar mass surface density and star formation rate. These provide important new constraints for
cosmologically motivated galaxy formation and evolution models that have had to rely on indirect or poorly sampled
measurement of the gas content of galaxies in large cosmic volumes. GASS analyses also serve as a pathfinder for similar
studies with future deep and wide HI surveys.
With the release of DR1 and ~20-30% of the wished-for sample in hand, GASS has already demonstrated that it can
quantify the mean scaling relations between HI mass fraction and galaxy properties in one dimension. To answer 2ndorder questions, such as how the HI mass fraction depends on metallicity and environment at fixed stellar mass, GASS
needs the full sample. It has also been demonstrated that GASS can robustly and efficiently identify HI transition galaxies,
which are the galaxies with anomalous gas content given their optical/NUV colors as determined from GALEX, and
structural parameters determined from SDSS. Their sample of transition galaxies, particularly the HI deficient objects, is still
very small. The aim is to quantify the frequency with which different kinds of transition galaxies occur in the local Universe,
and how this depends on factors such as the local environment, possession of an of an AGN, etc.
Magnetic Fields in ULIRGS: This is a survey of all known OH megamasers in the Arecibo sky to determine magnetic field
strengths in their nuclei. With a final 75 observing hours in PY 2010, this program was effectively completed. Its rapid
completion was helped by its use of twilight observing time that no other survey besides PALFA wishes to use.
3.1.2 Non-survey Projects
The Massive Protostellar Object IRAS 18566+0408: In 2002, Arecibo observations showed IRAS18566+0408 to be the fifth
Galactic source known to show H2CO 6-cm emission. In 2010 the discovery of periodic H2CO maser flares were reported
in this object (Araya et al. 2010, ApJL, 717, 133). Based mostly on a long-term Arecibo monitoring, five H2CO maser flares
were registered between May 2006 and November 2009 ( Fig. 3.9). Additionally, the peak flux densities of both the flares
and the quiescent state show an exponential decay. Arecibo has also been used to monitor the 6.7-GHz CH3OH spectrum,
which shows at least 9 overlapping maser lines. One of these CH3OH maser components shows flares that are similar to
the H2CO outbursts, whereas the other components show aperiodic flares and/or flares that are delayed with respect to
the H2CO variability. (Fig. 3.10). This is the first detection of a CH3OH/H2CO periodic flare system. MERLIN observations
during a flare episode revealed that the H2CO and CH3OH maser components that exhibit simultaneous flares are not
spatially coincident, indicating that the flares must be triggered by a mechanism that is external to the maser regions.
Recently, it was found that the 6.035-GHz OH line in IRAS 18566+0408 also shows flaring maser emission. However, the
peaks of the OH flares are not simultaneous with those of the H 2CO masers, but may show a delay with respect to the
H2CO and CH3OH flares, or even be uncorrelated with them.
The Importance of Magnetic Fields in Star Formation: Interstellar (IS) magnetic fields likely play an important role in the
formation of molecular clouds and their evolution to star formation, and it is important to determine their effect on this
process. Do magnetic fields control molecular cloud evolution or only play a secondary role? The effect of magnetic fields
in IS clouds can be determined by measuring the mass-to-flux ratio, λ , a comparison of the gravitational and magnetic
energies within a cloud. If λ > 1, the cloud is magnetically supercritical and cannot be fully supported by the field. If λ <
1, it is magnetically subcritical and supported by the field regardless of external pressure. Thus far, studies have
concentrated on studying molecular cloud cores, where only a small fraction of the mass resides. These suggest that cores
are mildly supercritical and so not fully supported by the field. However, magnetic fields are expected to be important
throughout these clouds, and not just within their localized cores. Hence, the role of magnetic fields in the formation and
evolution of whole molecular clouds has yet to be determined. A first systematic study has been undertaken at Arecibo to
address this question via the Zeeman effect in OH absorption toward radio continuum sources lying behind molecular
clouds. Such sources are distributed at random, providing probes of the magnetic fields along random lines-of-sight
through molecular clouds without favoring dense cloud cores. To date, the Zeeman effect has been searched for toward
7 lines-of-sight through molecular clouds. A strong Zeeman detection of -54 ± 1.5 μ G has been made toward one
continuum source, PKS1944+251, a Galactic HII region ( Fig. 3.11). 3σ upper limits on the field of 15-36 μ G have been
set for 5 of the remaining 6 lines-of-sight. Preliminary determinations of λ indicate that in all cases λ ≫ 1, suggesting
that the sampled clouds are supercritical and not fully supported by the field. The Zeeman effect can only reveal the lineof-sight component of the field and thus this study is statistical in nature. To be confident that small observed values of B los
do not reflect much stronger fields lying nearly in the plane of the sky, additional lines-of-sight will be investigated to draw
conclusions about the nature of IS fields within molecular clouds as a whole.
Brown Dwarf Pulsars: Arecibo observations of the broadband dynamic spectra of radio pulses from the M9 brown dwarf
TVLM 513-46546 have yielded the brightest pulse yet detected from an ultracool dwarf (T b > 1015 K.) The emission is
thought to arise in the same way as that from the auroral regions of magnetized planets in our solar system, i.e., by the
electron cyclotron maser instability. This produces radio emission at the electron cyclotron frequency which is proportional
to B, the magnetic field where the burst originates. Magnetic field strengths in the dwarf's magnetosphere of ~1650 G are
derived.
A number of other pulsing ultracool dwarfs have also now been observed at Arecibo, displaying similarities between the
pulses measured. Fig. 3.12 compares individual pulses from TVLM 513-46546, and the L0 dwarf, 2MASSW
J0746425+200032; similar frequency drifts and broadening towards higher frequencies are observed for both. The former
is probably a geometrical effect due to the narrow beaming of the pulsed emission, with the broadening being a
fundamental characteristic of the pulses from these dwarfs.
An observing campaign has investigated whether the auroral radio emission from TVLM 513-46546 is accompanied by
auroral emissions at other wavebands. Along with Arecibo observations, time-resolved optical spectroscopy of this star
were made using the ULTRASPEC high speed spectroscopic camera on the NTT 3.6-m telescope in Chile, revealing that
the Hα line and nearby continuum also vary periodically in phase and from the same location as the radio pulses. Further,
the [OI] line at 5577 Å, responsible for the green terrestrial aurora, also varies in phase with Hα and the optical continuum
confirming the presence of an auroral hot spot on the surface of TVLM 513-46546, and signaling a transition from stellar
to planet-like magnetic activity at the end of the main sequence. The emissions in all bands are driven by the presence of
powerful quasi-stable current systems within the dwarf's magnetosphere, analogous to the auroral emissions from Jupiter
where correlated variability is observed in the UV (Lyα and H2), optical (Hα) infrared (H3+) and radio. Of course, orders of
magnitude more powerful emissions are required for the behavior in TVLM 513-46546.
In March 2010, the brown dwarf system 2MASSW J0746425+200032 was detected via VLBI observations (sadly lacking
Arecibo involvement due to the problems with the suspended platform.) In particular, it was confirmed that the radio
emission is coming from the secondary component of the binary. A major VLBI campaign (including Arecibo) is now
planned for the next twelve months. The key goals are, (1) to establish the mass for each component through dynamical
mass measurement and, (2) to investigate the presence of a planet through detection of astrometric wobble.
HI Forbidden Velocity Wings: The majority of old Galactic supernova remnants (SNRs) remain unidentified via either radio
continuum or X-ray emission due to intrinsic faintness and background confusion. However, old SNRs are expected to
develop expanding HI shells. Kang & Koo have suggested that faint, wing-like, HI emission features extending to velocities
beyond those allowed by Galactic rotation (Forbidden Velocity Wings; FVWs) may represent HI gas accelerated by SN
explosions. To date they have identified ~90 FVWs from existing low resolution HI surveys. Most FVWs are not associated
with known objects, leaving their natures unclear. A number of FVWs have been observed at Arecibo, and more than
half appear to be partial expanding shells. These could indeed be old SNRs, too faint to be otherwise visible, but
revealed via their HI 21-cm emission. A typical FVW that shows apparent shell structure in the Arecibo survey is at
G39.0+4.0. In Fig. 3.13, the contour lines show the HI column density over the velocity range +80 to +135 kms -1, while the
overlaid colors split the data into smaller velocity ranges. Early-type stars and pulsars within the field are also marked.
Molecules in the Galactic Environment: Within our Galaxy, the proto-planetary nebula, CRL 618, was discovered to radiate
strong maser emission in the 4765-MHz satellite excited-OH line. Observations with the Mock spectrometer for a 700-800
MHz and 1-10 GHz spectral scan of the star-forming region, W51-IRS1, commenced in 2010, and will continue over 2011.
Already, a number of molecular lines, and a host of RRL's have been detected. Of note is the discovery of strong 4660-MHz
maser emission in the (J=1/2, Ω=1/2, F=0-1) excited-OH line.
Apparent Faster than Light Wave-Propagation in the ISM: Bound electrons on neutral hydrogen atoms in the ISM cause
the group velocity in the medium to be greater than light at frequencies near the 21-cm HI resonance line. This is due to
the phenomenon of "anomalous dispersion". To demonstrate this astronomically, PSR B1937+21 was observed looking at
frequencies near the HI line. Fig. 3.14 displays modelling of the expected forms of both HI absorption and the pulse "delay
spectrum" due to anomalous dispersion. The latter is effectively the pulse timing residual as a function of frequency after
removing the usual dispersion for free electrons in the ISM. Fig. 3.15 shows the spectra that resulted from the totality of
the measurements. Agreement between the model and measured spectra is excellent. The important thing is that the
delay spectrum holds different information to that contained in the absorption spectrum; the magnitude of the delay and
the magnitude of the absorption scale differently with the temperature and density of the HI clouds. Hence, using both
spectra, one can infer additional information about the intervening clouds to add to that available from an absorption
measurement alone.
Timing the Binary Pulsar, PSR B1913+16: The famous binary pulsar, B1913+16, whose discovery and timing led to the
award of the 1993 Nobel Prize for Physics, was timed at Arecibo for the first time since 2006 in this program year. A recent
publication on the Arecibo timing of this object (Weisberg et al., 2010, ApJ, 722, 1030) presents proper motion values for
the system of μ α =-1.43±0.13, μ δ =-0.70±0.13 mas yr-1. A small timing glitch of Δ f/f=3.7×10 -11 was seen in May 2003. A
relativistic solution for orbital parameters yields mass estimates for the pulsar and its companion of m1=1.4398±0.0002 M⊙
and m2=1.3886±0.0002 M⊙. The system's orbital period has been decreasing at a rate of 0.997±0.002 times that predicted
as a result of gravitational radiation damping in general relativity, conclusive evidence for the existence of gravitational
radiation as predicted by Einstein's theory. Current estimates indicate that the pulsar beam will precess out of our line-ofsught in about a decade, rendering it invisible.
A Study of the “Partial Cone” Pulsars: When Lyne & Manchester produced their classification of pulsar profile shapes in
1988, some 20% did not fit into the scheme of core and (single and double) cone morphologies. These they dubbed
“partial cones”. This population has often raised caution regarding the core/conal model of pulsar emission beams. A fullStokes study of 39 of the 50 thus-classified stars has now been made with Arecibo and the GMRT and has been accepted
for publication. It is found that while these objects are “partial” in so far as the emission above different areas of their polar
caps can be highly
asymmetric, their overall emission geometries are identical to core/double cone structure with conal dimensions scaling
with polar cap size. Also found is that aberration-retardation seems to play a role in distorting the core/cone emissionbeam structure in rapidly rotating pulsars. Several examples of highly polarized pre- and post-cursor features have been
found that seem to arise at high altitude in the pulsar magnetosphere, far from the usual sites of core/conal radiation.
A Critical Test of TeVeS Theories: Binary pulsar PSR J1738+0333 has been timed at Arecibo since 2002.
From its observed rate of orbital decay due to gravitational wave emission, this has provided the most
constraining limits on dipolar gravitational wave emission ever.
In addition, the limits derived from
PSR J1738+0333 can exclude all the relativistic TeVeS (Tensor-Vector-Scalar gravity) theories proposed as
the relativistic version of MOND (MOdified Newtonian Dynamics; put forward to explain the rotation curves of
galaxies.) This result has great importance for cosmology and galactic dynamics, reaffirming our
understanding of gravity, even at scales where MOND supposedly operates, and also reaffirming that dark
matter exists.
Arecibo and Fermi/GLAST Pulsars: During the past year, Arecibo observers have continued to investigate -ray pulsars
and other compact objects discovered by the Fermi Gamma-Ray Space Telescope. The radio pulsar, PSR J2021+3651,
discovered at Arecibo in 2002 while searching positions from the earlier EGRET catalog, has not only been confirmed by
Fermi to be a gamma-ray pulsar, but to be one of the strongest emitters in the whole -ray sky.
The recently discovered radio pulsar PSR J1907+0602, connected with a Fermi -ray pulsar (period = 106.64 msec), has
been found to emit pulsed radio waves with the period of the Fermi pulsar, and has a 1400-MHz flux density of ~3 µJy, a
duty cycle of ~3%, and a DM of 80.5 cm-3pc. For the implied distance of 3 kpc, this makes PSR J1907+0602 the second
lowest luminosity radio pulsar yet detected.
Found in coincidence with an "unidentified" Fermi source by the GBT, Arecibo timing of the radio pulsar PSR J2214+3002
has contributed greatly to the recent detection of the object as a -ray pulsar by Fermi. PSR J2214+3002 has now also
been revealed to be a “black widow” binary. Also coincident with an "unidentified" Fermi object, and found as a radio
pulsar by a team at the Nançay telescope, PSR J2017+0603 has been observed at Arecibo and found to have a "supersharp" (presently unresolved in time) main pulse. As this is likely a normal MSP-WD binary, which are known to be very
stable systems, it would appear to be a promising candidate for inclusion in the pulsar ensemble being used by the
NANOGrav (North American Nanohertz Observatory for Gravitational Waves) Consortium to attempt detection of
gravitational waves via a precise timing network of radio pulsars.
The millisecond pulsar, PSR J2043+1710, was discovered at the Nançay radio telescope in a search for radio pulsations at
the position of Fermi LAT sources with no known associations (see Guillemot, Freire, Cognard, et al., in preparation).
However, because of strong intensity variations at L-band induced by scintillation, Nançay could only detect the pulsar
once in approximately 10 observations, making timing observations there very difficult. Subsequent Arecibo radio
observations at 327 MHz and 1.17 GHz yielded bright detections, allowing determination of rotational and orbital
parameters from just a few observations. These parameters were then used to phase-fold the data recorded by the Fermi
LAT, leading to the detection of the msec pulsar in -rays (see Fig. 3.16).
The Braking Index of PSR J1930+1852: Timing of PSR J1930+1852 (P = 0.136 sec), the young, energetic, radio/X-ray
pulsar at the center of the nonthermal supernova remnant, G54.1+0.3, is on-going. PSR J1930+1852 has not been
detected in -rays, which is odd given that it is so energetic. However, its braking index has been determined, placing it
among a select few objects. The braking index is formally determined to be 1.941 ± 0.001.
Continued Observations of the LMXB-MSP Transition Object, PSR J1023+0038: The 1.69-msec pulsar, PSR J1023+0038, is
the first object to be observed in transition between accretion from a low-mass companion star and being a millsecond
pulsar. Monitoring of this object at Arecibo (Archibald et al., 2009, Sci., 324, 1411) has shown it to be in a circular 0.2-day
orbit about an optically identified, 17mag, mid-G type companion, and it appears to be ending an X-ray binary phase and
becoming active as a radio pulsar. Its companion seems to have overflowed its Roche lobe in 2000-2001, but currently
shows only modest orbital variability due to heating of the side facing the pulsar. Currently, the parallax distance to this
system is being measured using the VLBA. This distance can be combined with optical color, brightness, and radial-
velocity measurements, plus the assumption that the companion fills its Roche lobe, to yield a pulsar mass measurement.
The parallax program depends on Arecibo timing for its pulsar gating, and will conclude in November/December 2010.
Results from 8 epochs to date are very promising, and it is expected to obtain a pulsar mass and distance with < 10% and <
3% uncertainty respectively.
Astronomy in the 700-800 MHz Band: The 700-800 MHz band has been temporarily opened up to radio astronomers by
the 2009 switch from analog to digital transmissions with new frequency allocations by US-TV stations. When aware of
this opportunity, the Arecibo Observatory prepared a suitable receiver, which is used In conjunction with the Mock
spectrometer. A special proposal call received a large number of worthy requests for observing time. Observations are
proceeding.
In a search for host-galaxy HI absorption and OH emission/absorption at redshifts near unity, HI absorption was soon
found against the “classic” radio galaxy, CTA21. The absorption depth is ~3.5% at z = 0.907, the detection being especially
interesting in light of the possibility that CTA 21 may be exhibiting multiple cycles of nuclear activity. The result was
published during PY 2010 (Salter et al., 2010, ApJL, 715, L117). In October 2010, HI host-galaxy absorption at the 2% level
was detected for the quasar, 4C+15.05. This object is an optically-faint, infra-red violently-variable source for which
controversy has long existed as to whether its optical faintness is due to host galaxy absorption or is intrinsic to the
synchrotron process in this quasar. There has also been a long-standing disagreement concerning this object's redshift
between values of z=0.405 and 0.833. Detection of its HI absorption resolves this in favor of z=0.833 (Fig. 3.17), allowing
reinterpretation of the best available optical/IR spectrum.
Observations have also been made at 700-800 MHz for pulsars in about 15 globular clusters, a number of which have not
been previously searched at any frequency. In preliminary analysis, six previously known pulsars have been detected in
M5, M13 and M15 (see the pulse profiles in Fig. 3.18). Initial candidates for new pulsars have been selected from the data,
and acceleration searches will be carried out to look for objects in tight binary systems. Follow-up observations are
awaited.
Studies of Luminous Infra-Red Galaxies (LIRGs): The highly successful Arecibo 1-10 GHz spectral scan of the prototypical
ULIRG, Arp 220, has been extended to look for lines from 20 other Arp 220-like LIRGS over a frequency range of 4.4 - 5.2
GHz. Two of these galaxies, IC860 and Zw049.057, have been found to show almost identical molecular-line spectra to
Arp 220 itself, including CH2NH in emission and HCN in absorption. A number of other molecules, plus radio
recombination lines, have also been detected in these and other LIRGs in the sample. Unexpected is the discovery of
variable excited-OH maser emission at 4750 and 4765 MHz in NGC 660.
A long-term survey aimed at providing HI spectra for all LIRGs in the 2 Jy IRAS-NVSS sample within the Arecibo sky is in its
final stages. This year, results were published for 85 targets in the 20 h < RA < 24h range, yielding 82 detections (Fernandez
et al., AJ, 139, 2066). Data were also acquired for the four ground-state lines of the OH molecule, with 7 galaxies being
detected. Various properties of the sub-sample were derived and reported on. In addition, observations have been
continuing to provide spectra on those sample LIRGs outside this RA range lacking either a HI spectrum at all, or one of
acceptable quality. Within the range 02h < RA < 10h, 78 of 85 targets have been observed yielding 72 detections. Of these,
6 display pure HI absorption, while 2 more show a mixture of HI emission and absorption. Observations over the
remaining 12 hours of RA have been impacted in 2010 by the telescope's structural problems. However, spectra have
been obtained for 49 of 140 targets. The observations for 00h < RA < 20h also recorded data to search for lines of HCN,
HCO+ and 18OH.
Search for Variability in an H2O Maser at z=2.64: The 6-GHz radio continuum and H2O maser emission in the type-1 quasar
MG J0414+0534 at z=2.639 has been monitored at Arecibo for about 15 months to shed light on the origin of the most
distant H2O maser known. The line profile is resolved into a complex of features with widths of 30-160 km/s (Fig. 3.19). A
further redshifted line was tentatively detected in Oct. 2008 at a velocity of +470 km/s. Both the overall appearance of the
main maser feature and the peak line flux density are surprisingly stable throughout the observing period, although the
integrated line intensity shows significant variations on monthly time scales, hinting at small changes in the line profile.
While also quite stable from epoch to epoch, the continuum flux density does vary smoothly on longer time scales.
Changes in the line intensity are not correlated with those of the continuum. An upper limit on the velocity drift of the line
peak of 2 km/s/yr has been set. The large linewidths of the individual components and the absence of a clear detection of
emission at systemic and redshifted velocities favors association of the maser with the relativistic jet(s) of the quasar. That
the H2O emission originates in an edge-on accretion disk is less likely, although it is not yet ruled out. The tentative
detection of the redshifted feature in the October 2008 spectrum favours the disk-maser hypothesis, although the density
of H2 molecules inferred from a simple disk model is too low to reach population inversion and, hence, to produce H2O
maser emission.
High Angular Resolution Science: EVN observations of parsec-scale radio cores in Seyfert galaxies have been made at 1.6
and 5 GHz. These galaxies are thought to be radio quiet, but the presence of a compact radio core seems to be essentially
ubiquitous when the sources are observed with high sensitivity. Arecibo is essential for this goal, and also provides the
long baselines needed to obtain the highest angular resolution.
The famous jet of the galaxy, M87, has been monitored on a number of occasions with eVLBI including Arecibo. These
observations have been made simultaneously with very high energy observations by VERITAS and other facilities. In
particular, the source has shown some activity in the TeV band, and by great good fortune a radio image (Fig. 3.20) was
obtained simultaneous with a high energy flare (Giroletti et al., Astronomer's Telegram, 2437). Again, Arecibo is very
important since it provides the high resolution needed to resolve the inner jet component and the sensitivity required to
reveal the weaker complex named HST-1 far down the jet (about 800 mas from the core). Remarkably, apparent
superluminal motion was found to be occurring there.
SKA Precursor Science: With its very large collecting area, Arecibo is a 10% Square Kilometer Array (SKA) and, hence, by far
the most capable existing telescope for carrying out mid-frequency SKA precursor science. The SKA key science projects as
listed by Carilli and Rawlings in “Science with the SKA” (New Astronomy Reviews, 48, 979-984, 2004) are; 1) The cradle of
life; 2) Strong field tests of gravity using pulsars and black holes; 3) The origin and evolution of cosmic magnetism; 4)
Galaxy evolution and cosmology, and; 5) Probing the dark ages. Current and planned surveys with Arecibo contribute to
many aspects of the first four key projects. The radar survey of the properties and orbits of near-Earth objects is
contributing significantly to our understanding of planetary system evolution, while the seti@home project is searching for
evidence of intelligent life. The survey for new pulsars is discovering objects that will elucidate the equation of state of
ultra-dense matter and objects that will be suitable additions to the global pulsar timing array aimed at detecting the
background energy density in gravitational waves at nanohertz frequencies. The GALFACTS survey aimed at studying
Galactic and extra-galactic magnetic fields via Faraday rotation measurements is a direct precursor for similar
measurements planned for the SKA. Finally, Arecibo surveys of HI in external galaxies out to redshifts of ~0.25 are
elucidating structure and galaxy evolution in the low redshift universe.
Apart from the expansion of our knowledge of the Universe, a very important aspect of the Arecibo work on most of the
key SKA science areas is the training of young researchers, including graduate and undergraduate students, in the science
areas and observational techniques that will be needed to fully exploit the SKA once it is completed. Investing in a very
expensive instrument without a trained and committed research community ready to exploit its capabilities makes little
sense. The Arecibo surveys involve dozens of researchers and graduate students who will be the future users of the SKA.
The NSF is supporting the undergraduate ALFALFA workshops, the most recent of which took place at Arecibo on
January 11–13, 2009, with the next to be held in November 2010 & January 2011.