Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.naic.edu/~tghosh/rev04/AN-rep2003.pdf Дата изменения: Thu Oct 7 22:23:28 2004 Дата индексирования: Sun Apr 10 05:07:26 2016 Кодировка: Поисковые слова: arp 220

Annual Report of Academic Activity of Tapasi Ghosh (Mar03 - Feb04)

1. Summary of Research and Scientific Activities In this section, I describe the astronomical areas covered by the pro jects that I have worked on in the past one year. Many of these are on-going. I report the progress made in each of these in the appropriate sections. In addition, I am also involved with other pro jects which are yet to be brought to completion. As these were not worked on during the period of this report, they remained un-mentioned here. (i) Atomic and molecular gas in AGN host: CSS/GPS Sources: Collaborators: Drs C.J. Salter, D.J. Saikia (NCRA, India), and Jeyakumar and Stutzki (U Cologne) Observations for an Arecibo and GMRT study/search HI absorption and OH emission/absorption in Compact Steep Spectrum (CSS) and GigaHertz Peaked Spectrum (GPS) radio sources was completed in March 2004. This has made use of the Double Position Switching technique developed by ourselves over recent years. The results include a first detection of deep HI absorption within the CSS galaxy, 3C258 (z = 0.165), and confirmation of a number of HI absorption detections by other telescopes, usually with better signal-to-noise. Upper limits are also placed on OH spectral lines for the sample. A global VLBI proposal to image the HI absorption in 3C258 is awaiting scheduling. ARP 220: As a "Hands-On Experiment" for 4 students at the 2nd NAIC/NRAO School on "Single-Dish Radio Astronomy", held in Green Bank in Aug 2003, C. Salter and I supervised observations of HI and all 4 OH lines in the prototype starburst galaxy, Arp 220. The aim of the experiment was to illustrate the problems of baseline ripple due to standing waves when the source observed has significant continuum emission, and how this can be corrected by Double Position Switching. This end was well achieved by the students, but we had an added surprise in that the profiles measured for both satellite lines of OH were completely different to the previously published profiles of Baan and Haschick (1987). Our profiles contain velocity ranges where both emission and absorption are present. We believe that Baan & Haschick probably removed the absorption components in the spectra via their baseline fitting. The new profiles are now being written up for publication, including the four summer students among the authors. To interpret these complex OH satellite line profiles, we have recently applied for global VLBI time to image both of the satellite lines at milliarcsecond resolution. PKS 1413+113: Collaborators: Nissim Kanekar (U.Groningen, NL), Jayaram Chengalur (GMRT,Inida) We have detected the two 18cm OH satellite lines from the z 0.247 source PKS1413+135; the 1720 MHz line in emission and the 1612 MHz line in absorption. The 1720 MHz luminosity is LOH 354L , more than an order of magnitude larger than that of any other known 1720 MHz maser. The profiles of the two satellite lines are conjugate, implying that they arise in the same gas. This allows us to test for any changes in the values of fundamental constants, without being affected by systematic uncertainties arising from relative motions between the gas clouds in which the different lines arise. Our data constrain changes in G gp [2 /y ]1.849 , where y me /mp , and are consistent with the different constants remaining unchanged 1


from z 0.247 to today. If gp and me /mp are assumed to not vary, we obtain / = 0.6 ± 1.0 в 10 over the range 0 < z < 0.247. Search for Water Vapour Masers in High-redshift AGNs: Collaborators: Smita Mathur (Ohio State Univ), and C. J. Salter

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Strong 22-GHz water-vapor masers have so far been detected in about 20 nearby AGNs. These "megamaser" sources are mostly associated with Seyfert 2 and LINER galaxies whose active nuclei are hidden by a large column density of optically obscuring, X-ray absorbing gas. Detailed studies of H 2 O masers with VLBI imaging and spectral monitoring have become important tools for probing dense gas near the central engines of these sources, investigating the properties of their accretion disks and measuring the masses of their (supermassive) black holes. Such studies have also been employed to estimate geometrical distances completely independent of the rungs of the extragalactic distance ladder. However, so far most of the detections of extragalactic H2 O masers have been in relatively nearby ob jects (with systemic velocities less than 7500 km s-1 ), and (hence) in low-luminosity AGNs. To date, two searches of high-z water masers have been initiated using the 100-m Effelsberg telescope and the VLBA using the U, X, C and L-band receivers at those telescopes. Their observations are sensitive to flux densities of 20 and 40 ­ 50 mJy respectively. No detection has yet been reported. We notice that one of the selection criteria for these studies has been detectable X-ray flux in their targets. X-ray emission is an ubiquitous property of quasars, and indeed, according to models of X-rays are responsible for keeping the molecular gas "warm" enough for maser production. However, direct exposure to X-rays tend to make the gas too hot to form molecules, and the necessary condition for making the environment conducive for maser production appears to be substantial shielding from the X-ray source. Indeed al l the nearby maser sources, observed in X-rays, show large absorption in soft X-rays Thus, the appropriate selection criterion appears to be "soft X-ray absorption" instead of "detectable X-ray flux" which may, in fact, select against obscured sources. Hence, we have undertaken a H2 O-maser search in the redshift ranges 1.22 ­ 1.78 and 2.70 ­ 4.55 using the X and C-band receivers of the 305-m telescope in 35 AGNs either with soft-X-ray absorption or other indirect evidence of obscuring torus such as compact steep spectrum double radio structures. Two sessions of observations have already been carried out in September and November 03 (A1785) covering about 25 % of our sample. During this time, the characteristics of the X-band receiver has improved by about 60 %. We are looking forward to completing this pro ject in the near future. (ii) HI in High-z DLAs: Collaborators: Nissim Kanekar (U.Groningen, NL), Jayaram Chengalur (GMRT,Inida) Using the low-frequency capability of Arecibo 305-m telescope, we are searching for HI absorption in a high redshift (z 3.38) Damped Lyman- absorber (DLA) toward PKS 0201+113, and two other candidate DLAs at z 2.4 seen toward two radio loud quasars. Our observations are sensitive to 10 4 K gas in the z = 3.38 absorber providing the first possibility of detecting warm neutral medium at high redshifts. For the two z 2.4 DLAs, the observations, when completed will be sensitive to spin temperatures of 1000 K, a value typical of that in most damped systems. The observations will test an emerging trend that high-z DLAs predominantly contain the warm phase of HI, while both cold and warm HI are seen in low-z systems. The search also include OH absorption in two lower redshift absorbers at z 0.24 using the L-wide receiver to study chemical evolution of DLAs.

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(iii) Unbiased search for Damp ed Lyman-alpha Absorb ers at radio wavelengths: With Drs. C.J. Salter, and K. O'Neil (NRAO), I am applying the recently developed technique of DoublePosition 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. An initial epoch of this observation took place in Nov 03, and Feb 04. We have successfully used the WAPP to acquire 400-MHz spectra, its first use in this mode and have developed an IDL-based analysis pathway using a FITS-reader and codes developed by Erick Meuller, and ourselves. A regorous RFIdetection/flagging/excision method is also being developed to identify real signature of DLA systems in these spectra. The observations have already detected two DLA lines in a test run, both already known, but demonstrating the robustness of the approach. (iv) VLBI survey of faint FIRST sources: With Drs. Porcas, Alef (MPIfR, Bonn) & Salter, I am beginning 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 50ob jects down to m(V) 24 mag. Thus redshifts of many ob jects 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. (v) Hosts of GRBs With Pihlstrom, Taylor (NRAO), Momjian and Salter, an urgent proposal in Oct 2003 led to a search for HI and OH (main lines, plus the 1720-MHz satellite line) absorption/emission associated with the host galaxy of the Gamma Ray Burster, GRB 030329, at z = 0.1685. HI absorption against the afterglow of the GRB was the primary target. Neither absorption nor emission was detected for any of lines, and implications of the results will be combined with results of recent VLBI on the source by Taylor. (vi) North Pp olar Spur: With Dr Salter , the first wide-area continuum imaging with the upgraded Arecibo telescope was made in 2000. This mapped an area of 6 deg x 6 deg at 430 MHz within the North Polar Spur (Loop I), where a semi-circular emission arc is superposed on the larger feature. This arc may represent the remnant of a second-generation supernova resulting from star formation within the compressed shell of Loop I, and is a promising candidate for the "reheating event" often invoked to explain the X-ray emission of Loop I. It is hoped that these high-resolution total-power observations will aid understanding of the nature of the arc, and its relation to Loop I. Analysis of the data proved to be complicated due to the lack of many header parameters in the data format available at the epoch of observation. However, the reduction of the images was undertaken in the summer of 2003, in conjunction with REU student, Kit Reilly. Considerable progress had been made when Kit was killed in a tragic hiking accident. Dr Salter and I returned to the data later in the year, and produced a first map of the region which were presented at the Atlanta AAS meeting. It now remains to optimise these maps and to basket-weave the orthogonal coverages to produce 3


a final image. (vi) Rotation Measure tomography at 327-MHz for the ISM With Deshpande and Salter, a modest feasibility study was proposed and observed during 2003. This took drift-scan data at 327 and 1400 MHz with the 305-m telescope to investigate the feasibility of studying the magneto-ionic component of the ISM of our Galaxy via polarization mapping, and associated Faraday tomography. The data were acquired in Aug 2003, and initial data reduction has taken place. Full data analysis will be paralleled by the pilot study for a GALFA Continuum Transit study, for which data is currently being taken (see below). (vii) Continuum Surveys with ALFA: With a number of members of the GALFA Continuum science subconsortium, Taylor (Calgary), Deshpande, Salter and Freire, a pilot survey towards a GALFA Continuum Survey is being made. This uses the L-wide receiver, and is exploring the effectiveness of the meridian NODding observing technique proposed for the full GALFA Continuum Transit Survey (GALFACTS). Two fields will eventually be mapped with Nyquist sampling, the first of these being now about 80analysis pipeline being developed for this study will serve as the proptype for the full GALFACTS survey. To acquire the data for this survey, a new data taking mode for meridian nodding scans was added to the CIMA user interface by Jeff Hagen.

Observing Prop osals: · October 2003 deadline: "A Pilot Study for GALFA Continuum Transit Survey" (Taylor, Salter, Ghosh, Deshpande, Freire) · October 2003 Urgent Proposal: "Neutral Hydrogen Observations of GRB 030329" (Taylor, Pihlstrom, Momjian, Salter, Ghosh) · October 2003, Global VLBI; "Measuring apparent angular size of pulsars behind HII regions", R. Ramachandran, A. Deshpande, C. Gwinn, T. Ghosh · ALFA-precursor Observations: "Commissioning and Test Observations for a Full-Stokes ALFA Continuum Survey - GALFACTS", R. Taylor, C. Salter, A. Deshpande, T. Ghosh, etc.) · February 2004: "VLBI Imaging of Arp 220 ih the OH Satellite Lines", EVN, (Ghosh, Salter, Momjian) · February 2004: "The Physics of an OH Megamaser at z 0.25", Global Array, (Kanekar, Vermeulen, Chengalur, Ghosh) 2. List of Publications: Papers Published: (Conf. proceedings etc.) · Ghosh, T.; Kavars, D.W.; Robinson, P.E.; Saintonge, A.; Strasser, S.T.; Salter, C.J., 2003, "High Sensitivity Observations of the Satellite OH Lines of Arp 220", BAAS, 203, 115.08 4


· Reilly, K., Salter, C., Ghosh, T., 2003, "Continuum mapping of an Interaction Region within Loop I (The North Polar Spur)", BAAS, 203, 110.15 · Salter, C.J., Jeyakumar, S., Saikia, D.J., Ghosh, T., Stutzki, J., 2003, "HI Absorption towards Compact Steep Spectrum Radio Sources", BAAS, 202, 42.10 Papers Submitted: (Refered Journals) N. Kanekar, J. N. Chengalur, T. Ghosh, "Conjugate 18cm OH Satellite Lines at a Cosmological Distance", Submitted to Physical Review Letters, Feb 2004. 3. Other Academic Activities: · REU student: Kit Reilly (deceased) , New College, Fl., "Continuum Mapping of NPS" . · Helped in remote observing and data reduction for the NAIC/NRAO single dish summer school in Aug03. · Along with Dr. Salter, supervised Arecibo REU's Hands-on pro ject on continuum observations using 305-m telescope. · Arecibo Journal Club contribution in January-04, "The use of OH 'main' lines to constrain the variation of fundamental constants"- Kanekar and Chengalur, submitted to MNRAS. · Attended VLBI Technical Operations Workshop in Haystack in September 03 · Attended the AAS summer03 and winter04 meetings and presented Poster contributions. 4. Technical Activities: · User Friending - VLBI : During this period, with the help of Dr. Salter and (since October 03) E. Momjian I have carried out 17 VLBI runs. This involved checking/calibrating the equipment, help preparing schedules, running the observation, data tape handling, and reducing and providing calibration data to the users. · User Friending - Single Dish: I have helped 5 spectral line pro jects' P.I.s during this time as their "friend of the telescope". This involves providing varied level of assitance to the users to conduct their observing run and data reduction. · Friend of Receivers: Currently, I am the friend of the S-wide and S-high receivers. During the year, I had also been the friend of 610-MHz receiver. In this connection, I have developed the webpages for these two receivers. · Newsletter: I am the co-editor of the NAIC/AO Newsletter. · Other : I have provided various inputs to CIMA's functionality, particularly on the DPS mode of observing. Have also initiated and tested a new antenna control program written by Jeff Hagen to be used by the VLBI-software (PCFS).

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5. Adminstrative Activities: · I have been a member of the local organizing committee for the first GALFA meeting at Arecibo. Along with Mayra Lebron, I had prepared a webpage detailing the meeting report (as this was before Steve Torchinsky's joining the observatory). · I have given presentation to AUSAC meeting of 2003 on VLBI related topics. · I have been an active member of the Scientific Staff Policy Committee. 6. Education and Outreach: Participated in a NASA Sci file (for 11- 13 year olds) "The Case of the Galactic Vacation" which was aired on PBS in May 03.

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