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Annual Report (2002) for Tapasi Ghosh
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A. CURRENT ASTRONOMICAL INTERESTS
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(1) Host galaxies of AGNs (Seyfert Galaxies and QSOs):

During the summer of 2002, Tapasi studied evolutionary Tracks of
12-micron sample of Seyfert Galaxies as seen via their 21-cm neutral
hydrigen spectra. Her collaborators in this project are Leslie Hunt
(Achetry, ITaly), Samantha Stevenson (NAIC funded summer student from
Weslyan College) and JoAnn Eder.

(2) VLBI survey of faint FIRST sources:

With Drs. Porcas, Alef (MPIfR, Bonn) & Salter, Tapasi is begining a
VLBI visibility survey of around 1000 faint (down to 1.4-GHz flux
density of 1 mJy) sources selected from the VLA-FIRST survey. This will
make use of the ultra-high sensitivity achievable with the Arecibo and
Effelsberg telescopes at 21~cm using VLBA4/MK4 recording. The selected
sources lie within the area of the Sloan Digital Sky Survey, and it is
expected that ~50% of FIRST sources will be identified with SDSS
objects down to m(V) ~ 24 mag. Thus redshifts of many objects in the
sample should eventually become available. Amongst other uses, our
survey will help identify the fraction of AGNs (as opposed to starburst
galaxies) in the faint source population, and the number of faint
targets existing for such future instruments as the high-resolution
options for the SKA.

(3) Unbiased search for Damped Lyman-alpha Absorbers at radio wavelengths:

With Drs. Salter, O'Neil, Tapasi will be applying the recently
developed technique of Double-Position Switching (DPS) to search for
low-redshift Damped Lyman-alpha (DLA) systems via 21-cm
absorption along the lines-of-sight to ~200 compact distant radio
sources. This will help improve both DLA statistics for 0 < z < 0.3,
and knowledge of the HI mass fraction at z~0. The detection
level for these low redshift systems will enhance the studies of
cosmological evolution of the nature and number density of DLAs, and
their interstellar media. In addition, as the source sample is radio
selected, dust obscuration will not bias the statistics.

(4) CSS Sources:

Tapasi is also a co-investigator (along with Drs. Saikia,
Jeyakumar, and Salter) of a pilot project with the 305-m telescope to
observe the HI and OH spectra of 8 Compact Steep Spectrum radio
Sources. The project aims to determine if the reason for the
compactness of this class of object is indeed denser ISM (likely to be
coupled to their younger age), as has been suggested in previous radio
depolarization studies. For detected sources, we also anticipate
follow-up searches for CO via the 30-m Pico Veleta telescope, and plan
to study the distribution of the gas through the distribution of the HI
absorption across the radio source using VLBI, including the Arecibo
telescope to obtain the high sensitivity required. These objects offer
the potential for investigating both the atomic and molecular gas at
different cosmological epochs.

(5) Continuum Surveys with ALFA:

In addition, Tapasi has also joined the consortium for making an all
stokes (Arecibo) sky, continuum survey using the up-coming L-band Feed
array system.


B. OBSERVING/REDUCTION TECHNIQUES :
-------------------------------------

Tapasi wrote an IDL-based routine to reduce a simple cross-scan record
(taken with the spectral-line correlator) on a continuum calibrator.
This will be invoked from the New GUI to provide a fast and easy way to
check the pointing error and system temperature. IT will also porvide
the user with the option of applying an on-the-spot pointing
correction.

Tapasi also wrote IDL code for analysing the Rader Interface data,
recording the SEFD values during any VLBI run and producing a
"gain-table" in the AIPS-readable format. This is used by the VLBI
observers to calibrate their data offline.

B. SERVICE WORK AT ARECIBO OBSERVATORY:
______________________________________

Tapasi, in collaboration from Jon Hagan, jeff Hagan and Chris
Salter provides all VLBI related support at the observatory.

In addition, Tapasi acted as the "Friend of the telescope" for
5 HI-spectral line observing program during this year.

C. LIST OF PUBLICATIONS
________________________________

(1) Ghosh, T., ``Spectrum Management'', ASP Conference Series;
"NAIC/NRAO School on Single-Dish Radio Astronomy: Techniques and
Applications", eds. S. Stanimirovic, D.A. Altschuler, P.F.
Goldsmith, C.J. Salter, (in press)

2. Ghosh, T., Salter, C.J., 2002, "Arecibo Spectral Baselines in the
Presence of Continuum Emission", ASP Conference Series; "NAIC/NRAO
School on Single-Dish Radio Astronomy: Techniques and Applications",
eds. S. Stanimirovic, D.A. Altschuler, P.F. Goldsmith, C.J. Salter,
(in press)

3. Molotov, I., Chuprikov, A., Likhachev, S., Salter, C.J., Ghosh, T.,
Ghigo, F., Dougherty, S., 2002, "First VLBI Observations with Arecibo
in an International S2 Ad-hoc Array", ASP Conference Series;
"NAIC/NRAO School on Single-Dish Radio Astronomy: Techniques and
Applications", eds. S. Stanimirovic, D.A. Altschuler, P.F.
Goldsmith, C.J. Salter, (in press).