Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~tghosh/AN-rep2006.pdf Äàòà èçìåíåíèÿ: Thu Feb 11 01:48:01 2010 Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 00:29:36 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

Annual Rep ort of Academic Activity of Tapasi Ghosh (Mar06 - Feb07)

1. Summary of Research and Scientific Activities : In this section, I describ e 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 am also involved in other pro jects. As these were not worked on during the p erio d of this rep ort, they remained un-mentioned here. Variation of Fundamental Constants:(Collab orators: N. Kanekar (NRAO), J. Chengalur (NCRA, India) The two 18-cm OH satellite lines in the BLLac ob ject PKS1413+135, at z 0.247 were first detected in 2002 using the WSRT. The 1720-MHz line is seen in emission while the 1612-MHz line is in absorption. 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 physical constants, without b eing affected by systematic uncertainties arising from relative motions b etween the gas clouds in which the different lines arise. While not as yet statistically significant, the WSRT result p oints towards a change in one (or more) of , µ or gp , with cosmological time. Variations of g p with time are exp ected to b e small relative to those of µ and (e.g. Flambaum et al. 2004, PRD, 69, 115006). The present WSRT result is thus consistent with either a lower value of or a larger value of µ (or b oth) at earlier ep o chs. If we assume that µ is unchanged, we obtain / = (-0.6 ± 0.34) â 10 -5 , while assuming is constant yields µ/µ = (+1.2 ± 0.68) â 10 -5 . We are currently attempting to confirm the WSRT results with deep Arecib o sp ectra in the 18cm lines (prop osal No: A2123). Between February and July 2006, we had 40 hours of observations (at AO) on these lines. I have analyzed all these fully. The analysis pro cess led to the finding that the dopplar correction software for the WAPP and the IC did not include relativistic formula for velo city addition. This was subsequently rectified by Mikael Lerner for the WAPP, and in a separate investigation, Chris, Mayra and I checked the validity of those using b oth Galactic and Extragalactic sources. For my own pro ject (A2123), Chris and I develop ed an IDL-based correction program, which was used on the entire data set. With the visit of one of my collab orators, N. kanekar during Octob er2006, this pro ject was taken to the final stages of data analysis. Results will b e published so on. The 6 GHz OH lines in PKS 1413+135:(Collab orators: N. Kanekar (NRAO), J. Chengalur (NCRA, India) The conjugate 18cm satellite OH lines only allow one to measure changes in a combination of and µ (assuming gp to b e constant); one cannot measure changes in and µ separately. A detection of the higher-order excited-state OH lines would break this degeneracy, enabling a measurement of changes in and µ indep endently (Kanekar & Chengalur 2004); unfortunately, these lines have never b efore b een discovered at cosmological distances. However, the 1720 MHz inversion (and the 1612 MHz anti-inversion) arises due to an over-p opulation of the F = 2 level of the ground state relative to the F = 1 level, as transitions from the F = 3 level of the J = 5/2 state to the latter level are forbidden. This should also give rise to an over-p opulation of the ab ove F = 3 level, relative to the J = 5/2, F = 2 level by 50 % (Guib ert et al. 1978, A&A, 66, 395), causing masing to o ccur in the corresp onding satellite lines of the J = 5/2 excited state (at rest frequencies of 6049 MHz and 6016 MHz). A 48-hour integration using the WSRT in the redshifted 6016 MHz line (redshifted 1


to 4825 MHz), shows 4 absorption feature in the sp ectrum at a velo city of -11 km/s, very close to the p eak of the 1612 MHz absorption. In June 2006, we prop osed to use the Arecib o 5 GHz receiver to confirm the feature and to simultaneously obtain deep sp ectra in the other J = 5/2 lines from PKS 1413+135. It would b e extremely interesting if this feature were indeed real, b oth from the astrophysical p ersp ective (as it would b e the first known redshifted 6 GHz OH megamaser) and due to the p ossibility of measuring changes in and µ indep endently. In Octob er 06, we have taken 10 hours of Areicb o data for this pro ject. Preliminary analysis do esn't show any line at more than 3 level. Implications of this observation are b eing worked on at present. HI and OH in 2-Jy IRAS-NVSS sample of ULIRGs: (Collab orators: E. Momjian, C.J. Salter, Maria Ximena Fernandez (Vassar & Dartmouth), With Emmanuel Momjian and Chris Salter, Arecib o HI and OH observations have b een made of a sample that will eventually numb er ab out 580 Ultra Luminous Infra-Red Galaxies (ULIRGs) drawn from the 2-Jy IRAS-NVSS sample, with z < 0.2 . Measurements of 84 galaxies in this list have b een completed, the data analysis b eing p erformed together with summer student Maria Ximena. Essentially all the targets are detected in HI emission and/or absorption, with 16 new detections. The ma jority of these galaxies exhibit distorted features indicating galaxies in interacting/merging systems. Eight of the galaxies have also b een found to display OH main-line absorption or megamaser emission, of which 4 are new detections. The results of this survey are b eing used to, 1) investigate the differences in the physical characteristics (velo city widths, HI mass, etc.) for sources with AGNs and those with pure starbursts, 2) study the OH gas prop erties, including inferences from non-detection of the OH satellite lines, and 3) to lo ok for signs of galactic evolution out to z = 0.2. This will form Ximena's Senior Thesis. A New OH-megamaser in the ULIRG IRAS 23327+2913: During the ab ove survey of 84 galaxies from the 2 Jy IRAS-NVSS Sample with far-IR luminosities greater than 109 L , this new OH megamaser was detected. This ULIRG is a system of two galaxies separated by ab out 20 kp c and at an early stage of interaction. Details of the line characteristics show that IRAS 23327+2913 do es not fit into the commonly accepted scenario for ULIRGS of a merger b etween two disk galaxies, where the two progenitors of the merger are strongly disturb ed during the interacting phase, and the final merger pro duct resembles an elliptical galaxy. The Fate of Co oling Flow Gas: An Arecib o 21-cm Absorption Survey: (Collab orators: C.J. Salter, E. Momjian, H. Hernandez) Recent Chandra and XMM-Newton observations (Peterson et al., 2003, ApJ, 590, 207) have cast serious doubts over the classic co oling flow (CF) mo dels for rich, X-ray bright clusters of galaxies. Earlier generation X-ray satellites (EXOSAT and the Einstein Observatory) had established that X-ray surface brightness distributions in many X-ray bright clusters are centrally p eaked, with temp erature profiles that decrease (typically by an order of magnitude) towards the cluster center (e.g. Jones & Forman, 1984, ApJ 276, 38). Traditionally, these observations were explained by assuming that the hot intra-cluster medium loses most of its energy via thermal bremsstrahlung at X-rays. In order to maintain hydrostatic equilibrium in the presence of the gravitational p otential 2


of the cluster, the co oled gas then flows towards the center, providing the necessary pressure to supp ort the weight of the overlaying gas (Fabian, 1994, ARAA, 32, 277 and references therein). However, direct detection of the co oling flow (CF) gas has only b een partially successful. The detection of HI absorption against the radio continuum emission from galaxy clusters has b een successful only for a small numb er of clusters, (e.g. Ab ell 2125, Dwarakanath & Owen 2001; Ab ell 780, Dwarakanath et al. 1994, ApJ, 432, 469; the Perseus cluster, Crane et al, 1982, IAUS, 97, 307). While this HI may represent cold gas in a CF, there is also evidence for galaxy cannibalism in the central regions of clusters (e.g. Perseus; Momjian et al. 2003, ApJ, 566, 195). Both may contribute to the formation of a central cD galaxy. Clearly, each new case is the sub ject of interest, esp ecially when in a CF cluster. Using the Arecib o telescop e, we have recently detected strong HI 21-cm absorption against the complex continuum emission from the rich galaxy cluster, Ab ell 2390. This cluster contains one of the strongest known co oling flows. Following this discovery we have searched for cold neutral hydrogen in absorption against strong radio emitters within 85 rich Ab ell clusters using the Arecib o telescop e. HI emission was detected in 6 of our targets, while absorption lines are seen in 8 (with 2 other candidates). A collage of these sp ectra is shown in Fig. 1. We notice that while all HI emissions are seen in clusters with a lack of X-ray emissions HI absorption features are seen only in X-Ray rich clusters. Follow up mapping with connected-element interferometers (e.g. MERLIN, WSRT, GMRT and VLA) or VLBI (dep ending up on the resolution requirement for a particular cluster) will b e pursued. This will help us delineate whether the cold neutral hydrogen is in the co oling flows or represents the remnants of galactic cannibalism in the central regions of clusters. For Ab ell 2390, b oth WSRT and GMRT observations have recently b een obtained, and data analysis is underway. A cm-wavelength sp ectral line Census of ARP 220: (Collab orators: B. Catinella, M. Lebron, M. Lerner, R. Minchin, E. Momjian, C.J. Salter) Together with a ma jority of the Arecib o radio astronomy group I am participating in a pro ject to make a sp ectral scan of the prototyp e ULIRG, Arp 220. This pro ject uses the L-band Wide receiver, plus all Arecib o receivers covering the 3 - 10 GHz band. The newly commissioned (see b elow) 800MHz mo de of the WAPP sp ectrometer is b eing employed. The aim of the study is to investigate the various atomic/molecular line transitions detectable from the ob ject. The large numb er of radio recombination lines present will b etter constrain RRL emission mo dels, while the molecular census will improve our understanding of how starbursts o ccur, and how the star formation rate is regulated. As well as "shaking down" the new WAPP mo de, this pro ject will investigate the frequency range over which the Double Position Switching (DPS) mo de of observing is a necessity. An initial two nights observing to ok place very recently and, apart from detecting the absorption lines of excited OH and the known formaldehyde maser emission, candidate emission lines of other molecules are apparent and need confirmation. Continuum Survey with ALFA: (Collab orators: The GALFACTS Team) I am an active memb er of the GALFA Continuum Transit Survey (GALFACTS) consortium which aims to make a full-Stokes, "all-sky" continuum survey using the 7-b eam Arecib o L-band Feed Array (ALFA). The survey is exp ected to b egin in the summer of 2007, following the successful completion of precursor observations in 2005 and 2006 (see NAIC Newsletter No. 39, June 2006). One of the ma jor goals of this survey is to understand the 3-d microstructure of the magneto-ionic interstellar medium of our Galaxy via rotation-measure tomography. 3


Figure Figure 1: o Sp ectra showing HI emission, cold HI in absorption, and OH radical in absorption 1: Arecib HI and OH spectra of a subsample of Abell Clusters and combination of emission and absorption towards some of our cluster fields.

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A much larger GALFACTS precursor pro ject was p erformed this year. This pro ject verified the ability of GALFACTS to run commensally with the GALFA-HI group, and develop ed a drive program to do this. The pro ject with which these commensal op erations to ok place was "An HI Survey of the Perseus Molecular Cloud Complex", whose P.I.'s are Lewis Knee and James di Francesco (NRC, Canada). C. Salter and I ran the whole GALFACTS part of the commensal observing, and analyzed the data through its Stage-1 analysis which prepares the data for imaging, which is p erformed at Calgary. To augment the study of the "initial GALFACTS pilot region", with Wasim Ra ja, A. Deshpande (RRI), Russ Taylor (Calgary) and C. Salter, I am part of a prop osal submitted for the Arecib o February 2007 deadline to make 327-MHz full-Stokes continuum observations of that same region. My own area of interest in this survey is largely in the extragalactic opp ortunities that it op ens up. · Extragalactic Radio Sources: Covering the declination range, 37.8 > > -1.2 , the GALFACTS survey will span a celestial area of 4.0 Sr, with 300-MHz bandwidth, and with an rms noise of ab out 100 µJy/b eam (on cold sky). However, for Stokes-I this is well b elow the rms confusion level due to the p oint source background, (confusion) 2 mJy/b eam, implying weakest b elievable detections at S(min) 10 mJy/b eam. Standard 1.4-GHz source counts (e.g. Condon, 1984, ApJ 287, 461) lead us to exp ect that 230,000 discrete extragalactic sources with flux densities greater than 10 mJ y /b eam will b e detected by GALFACTS. At this flux density level, the extragalactic source p opulation will still b e dominated by p owerful AGNs. However, ab out a quarter of the sources are exp ected to b e normal and starburst galaxies, low luminosity AGNs (such as LINERs), and Seyfert galaxies. Most of these will have b een detected earlier by NVSS, although GALFACTS, with its 3-arcmin b eam, will b e more sensitive to low surface brightness features. Hence, we hop e to detect extended halos of nearby galaxies and clusters > of galaxies, as well as identifying a numb er of giant radio sources (size 1M pc) that could have b een considered to b e pairs of unconnected sources in NVSS. · Variability: With the planned observing strategy, each p oint in the sky will b e visited twice, with the interval b etween visits b eing uniformly distributed b etween 1 and 28 days. Thus, given the time interval uniformity, and the large numb er of (extragalactic) sources that will b e measured, extremely interesting statistics on the variability prop erties of sources at different timescales will b e obtained. The GALFACTS flux densities will also b e compared with those of NVSS to study variability over a time scale of ab out 10 yr. · Linear Polarization of Extragalactic Sources: The confusion level in linear p olarization will b e well b elow the total intensity value (in fact ab out two orders of magnitude less, 20 µJ y /b eam). Hence, we can certainly make a very sensitive, unconfused survey of the p olarization prop erties of radio sources. For unresolved sources, p olarization variability is exp ected to b e detected on b oth sub-monthly and 10 year (in comparison with the NVSS) time scales, the extremely active blazar (BL Lac and quasar) p opulation b eing known to show b oth p ercentage p olarization and p osition-angle variations on such time scales. GALFACTS will enhance the numb er of individual sources known to show such characteristics, and allow detailed, unbiased statistical studies of this phenomenon. · Rotation Measure Survey of Extragalactic Sources: The sensitivity of Arecib o, combined with the multiple channels across the 300-MHz bandwidth of ALFA, will p ermit a complete rotation measure (RM) survey of sources with detected linear p olarization. To emphasize the p ower of having a 300-MHz bandwidth available for p olarization measurements, the change of p osition angle across the band is =1.22âRM deg , (or one full 180 deg turn for an RM of 150 r ad/m2 ). 5


At low latitudes, a combination of GALFACTS RM estimates for SNRs and extragalactic sources seen through the galactic plane with those measured for pulsars will allow mo deling of the magnetic field distribution through the whole depth of the galactic disk (center and anticenter quadrants) visible from Arecib o. · Circular p olarization? We will also search the Stokes-V channel for evidence of significantly circularly p olarized sources such as pulsars, and flares stars. This serendipitous search for unexp ected circularly p olarized sources will b e a first. Observing Prop osals: · June 06 : N. Kanekar(NRAO), T. Ghosh and J. Chengalur (GMRT),"6-cm OH transition in PKS1413". · June 06: Arecib o; Momjian, E.A., Catinella, B., Ghosh, T., Lebron, M., Lerner, M., Minchin, R., Salter, C.J., "Probing the ISM of Arp 220 - A Cm-wavelength Sp ectral-line Census. · February 07: Arecib o; Ra ja, W., Deshpande, A.A., Taylor, A.R., Ghosh, T., Salter, C.J., "Full-Stokes 327-MHz Continuum Observations of the GALFACTS Pilot Region". 2. List of Publications: · Gupta, N., Salter, C.J., Saikia, D.J., Ghosh, T., Jeyakumar, S., "Probing Radio Source Environments via HI and OH Absorption", 2006, Mon. Not. R. astr. So c., 373, 972. · Momjian, E., Salter, C.J., Ghosh, T., Chengalur, J., Kanekar, N., Keeney, B.A., Sto cke, J.T. "Arecib o HI Observations of the Sub-DLA at z=0.0063 towards PG1216+069", 2006, American Astronomical So ciety Meeting Abstracts, 208, #15.03 · Fernandez, X.M., Momjian, E., Ghosh, T., Salter, C.J., "A Radio Sp ectral Line Study of the 2-Jy IRAS-NVSS Sample" , 2006, American Astronomical So ciety Meeting Abstracts, 209, 21705X · Hernandez, H., Ghosh, T., Salter, C.J., Momjian, E., "An Arecib o HI 21-com Absorption Survey of X-ray Rich Clusters", 2006, American Astronomical So ciety Meeting Abstracts, 209, 17219 3. Other Academic Activities: · REU student: I co-sup ervised REU student, Maria Ximena Fernandez (Vassar & Dartmouth) · I lectured on AGNs to the REU 06 students. · Along with Mayra Lebron and Chris Salter, I ran 3 sessions of hands-on observations with 4 students in each group. Title of the pro ject was, "A Search for Additional Molecular Line Detections in a Molecular Cloud at a Redshift of z 0.7". Last year, this was the only astronomy hands-on pro ject for the REU students. · With Chris Salter and Mayra Lebron, I have investigated p ossible small velo city inconsistencies within and b etween the Interim Correlator (ICOR) and the WAPPs (plus a large velo city offset that o ccurs for DPS observations with the ICOR!) We concluded that, while ICOR and WAPP sp ectra yield velo cities that are internally consistent, there are small, but significant, discrepancies b etween the velo city values from the two devices, b oth for zero redshift sources, 6


and increasingly for ob jects of higher redshift. Suggestions were made as to why this may b e. Suggestions were also made for fixing the ICOR DPS problem. Some of the problems app ear to lie in the software translation used to read the WAPP data into the IDL analysis package. A full rep ort has b een prepared, and made available to Mikael Lerner, Phil Perillat, and Murray Lewis, and we await developments to rectify problems. 4. Technical Activities: · VLBI: I am resp onsible for the general up-keep of the VLBI related equipment. I have up dated the software whenever necessary, and run tests to ensure successful observations. Along with Drs. C. J. Salter, E. Momjian and A. Venkatraman, I ran 3 eVLBI observations (including tests) during this p erio d, however, the network p erformance wasn't adequate to provide sustained data connectivity to JIVE. Efforts are now underway to improve this situation. · HSA/EVN/GLOBAL : Along with C. Salter and E. Momjian, we have observed 22 pro jects in this category. Post pro cessing of the SEFD monitoring data were also p erformed by myself for all these pro jects and provided to the users. Two of these were pulsar-baseband recording where a "new" observing mo de had to b e worked out. 5. Academic Activities not covered Ab ove: · I have attended the Chicago-I I meeting at Tucson. · I have co-edited the Decemb er issue of the NAIC/AO Newsletter. · I have gave presentations to b oth the AUSAC and the VC meetings in Januray and February 2006 on VLBI work at Arecib o. · I have participated in the AAS (remote, web-based) p oster sorting session as a volunteer.

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