Jayaram N. Chengalur

New OH/IR stars from color-selected IRAS sources. 3: A complete survey

We present the results of 1612 MHz observations conducted at the Arecibo Observatory of 571 color-selected sources from the IRAS Point Source Catalog. Of these sources we detect 132, 113 for the first time. This is the third part of an Arecibo survey of color-selected IRAS sources. The earlier two parts together detected a total of 268 sources of 1612 MHz emission. An analysis of the properties of the OH/IR stars detected in all three parts of the survey is included. In particular we compute the limiting 1612 MHz peak flux of the entire survey to be approximately ˜40 mJy. The correlation between the IRAS infrared fluxes and the 1612 MHz flux of the 132 sources detected in part III of the survey is smaller than that found in the earlier parts of the survey. This is to be expected from the intrinsic variability of OH/IR stars and the longer time gap between the 1612 MHz observations and the IRAS measurements. We identify a subset of 54 stars as being near the tangent point of the galactic rotation curve. Using the kinematical distances to these stars we find that the efficiency of momentum transfer varies exponentially with the (25-12) micrometer color, consistent with the stellar outflow being driven by radiation pressure. Further the IR pump efficiency increases with increasing optical depth of the circumstellar shell, as expected for radiative pumping. The bolometric luminosity function is found to decrease sharply above L Bol =5600 L solar luminosity, and the 1612 MHz luminosity function shows a corresponding falloff above L 1612 =1.8 × 10 −8 solar luminosity. We also find direct confirmation of the expectation that sources with large expansion velocity are more luminous than sources with small expansion velocity.

Very Wide Galaxy Pairs of the Northern and Southern Sky

We present highly accurate observations of the 21 cm line of hydrogen in galaxies made at the Arecibo and Parkes Observatories. The galaxies observed have been identified, through rigorous selection criteria applied to the CfA and SSRS catalogs, as being members of pairs with projected separations of up to 1.5 Mpc (H0 = 75 km s-1 Mpc-1). These observations form the completion of the Chengalur-Nordgren galaxy pair sample with data previously published by Chengalur, Nordgren and colleagues. The new selection criteria used in this paper are an extension to larger projected separations of the criteria used previously. Forty-nine new galaxies are observed, while H I is detected in 41 of them. With the addition of these galaxies, the completed sample has highly accurate H I velocities for a total of 219 galaxies.

H i 21 cm emission as a tracer of gas during the evolution from protoplanetary to debris disks

We present radiative transfer models for the H I 21 cm emission from circumstellar disks and use them to convert observed upper limits on the H I 21 cm flux to limits on the total disk gas mass. We also present fresh upper limits for the H I 21 cm emission of the disks around HD 135344, LkCa 15, and HD 163296, obtained with the Giant Meterwave Radio Telescope. Our observations and models span a range of disk types, from young protoplanetary disks to old debris disks. The models self-consistently calculate the gas chemistry (H/H2 balance) and the thermal structure of UV irradiated disks. Atomic hydrogen production is dominated by UV irradiation in transition phase objects as well as debris disks, but for very young disks, H I production by stellar X-rays is important. This irradiation produces H I 21 cm at the surface of the disks. In massive protoplanetary disks, UV produced H I constitutes less than 0.5% of the total disk mass, while X-rays clearly dominate the chemistry and thus the H I production. In debris disks, hydrogen is mainly molecular, since the high dust-to-gas mass ratio leads to warmer disks. The 21 cm flux cannot be detected with currently available radio telescopes in such disks. The strongest 21 cm fluxes are predicted for transition phase disks at distances of 100 pc. The expected H I fluxes in such disks are close to current detection limits. A telescope with about ~10% the area of the SKA will be able to detect the H I 21 cm emission from such disks, while the full SKA will provide resolved images. Such observations will probe the kinematics of disks, as well as the effects of irradiation and evaporation at their surface layer.

The Ooty Wide Field Array

We describe here an ongoing upgrade to the legacy Ooty Radio Telescope (ORT). The ORT is a cylindrical parabolic cylinder 530 m × 30 m in size operating at a frequency of 326.5 (or z∼3.35 for the HI 21-cm line). The telescope has been constructed on a North–South hill slope whose gradient is equal to the latitude of the hill, making it effectively equatorially mounted. The feed consists of an array of 1056 dipoles. The key feature of this upgrade is the digitization and cross-correlation of the signals of every set of 4-dipoles. This converts the ORT into a 264 element interferometer with a field-of-view of 2∘×27.4∘cos(δ). This upgraded instrument is called the Ooty Wide Field Array (OWFA). This paper briefly describes the salient features of the upgrade, as well as its main science drivers. There are three main science drivers viz. (1) observations of the large scale distribution of HI in the post-reionization era, (2) studies of the propagation of plasma irregularities through the inner heliosphere and (3) blind surveys for transient sources. More details on the upgrade, as well as on the expected science uses can be found in other papers in this special issue.

FIGGS Faint Irregular Galaxies GMRT Survey

The Faint Irregular Galaxies GMRT Survey (FIGGS) is a large program aimed at providing a comprehensive and statistically robust characterisation of the neutral ISM properties of faint (M_B > -14.5), nearby, gas rich, dwarf irregular galaxies using the Giant Metrewave Radio Telescope (GMRT). Here we briefly describe the survey and discuss some of the science that we anticipate can be done with this data set.

Gas Rich Galaxies from the FIGGS Survey

The FIGGS (Faint Irregular Galaxy GMRT Survey) is aimed at creating a multi-wavelength observational data base for a volume limited sample of the faintest gas rich galaxies. In this paper we discuss two very gas rich galaxies that were observed as part of the FIGGS survey, viz. NGC 3741 and And IV. These galaxies are unusual in that they have extremely extended gas disks and very high ratios of dark to luminous matter. The very extended HI disks provide an unique opportunity to trace the extended distribution of dark matter around faint galaxies. We compare the baryon fraction of these galaxies with a sample of galaxies with well measured rotation curves and discuss whether extremely gas rich dwarf galaxies have abnormally small baryon fractions.

Polarimetric images with the GMRT

We present the first set of polarimetric images made with the GMRT. These were obtained as part of the program to commission the polarization mode at the telescope. We find that the instrumental polarization leakage at the GMRT varies with frequency. It is hence necessary to solve for the leakage as a function of spectral channel. Once this is done however, it is possible to calibrate these terms to better than 1% accuracy, making it feasible to study sources that are polarized at the few percent level. We present 610 MHz polarization images of two extended FR-II radio galaxies, viz. 3C 79 and 3C 265. These were selected from the sample of sources for which the total polarization fraction at 610 MHz is known from the survey of Conway & Strom (1984). We present high resolution polarization images of these two sources and also find that the polarization fractions of the two sources as seen at the GMRT are consistent with those reported by Conway & Strom (1984).

The 1.0 Megaparsec Galaxy Pair Sample in Low-Density Regions

Using complete redshift catalogs, we have compiled a list of galaxy pairs based solely on a pairs pro- jected separation, and velocity diUerence, *V. We have made high-velocity precision H I observations r p , of each galaxy in the sample and have reported these in the literature. Due to the nature of the redshift catalogs, we are able to quantitatively evaluate the eUects of isolation and number density of surround- ing galaxies on each pair in the sample. For the close galaxy pairs kpc), the degree of isolation (r p 100 (a measure of the number of near neighbors) has little eUect on the median *V. This median is about 55 km s~1 for the 25 close pairs (if medium-density close pairs are omitted *V is even smaller, but the diUerence is not statistically signi—cant). The eUect of isolation is strong for the entire sample of galaxy pairs with separations as large as 1.0 Mpc. For these larger separation pairs, relaxation of strict isolation requirements introduces small groups into the sample, which dramatically increases the median *V.W e —nd little evidence of an increase in the median *V with decreasing nor with increasing total lumi- r p , nosity. For our isolated pairs in low-density regions, the overall median *V is only 30 km s~1. For similar separations and isolation criteria, galaxy satellites with larger luminosity ratios (i.e., less dynami- cal friction) in higher density regions have *V approximately twice as large. We conjecture that our orbits are highly eccentric, so that the indirect eUect of dynamical friction leads to predominantly small *V. However, the halos of our galaxies may also be of low density (although highly extended). Subject headings: galaxies: clusters: generalgalaxies: distances and redshiftsgalaxies: interactions

Phased array observations with infield phasing

We present results from pulsar observations using the Giant Metrewave Radio Telescope (GMRT) as a phased array with infield phasing. The antennas were kept in phase throughout the observation by applying antenna based phase corrections derived from visibilities that were obtained in parallel with the phased array beam data, and which were flagged and calibrated in real time using a model for the continuum emission in the target field. We find that, as expected, the signal to noise ratio (SNR) does not degrade with time. In contrast observations in which the phasing is done only at the start of the observation show a clear degradation of the SNR with time. We find that this degradation is well fit by a function of the form SNR(τ)=α+βe−(τ/τ0)5/3

H i in extremely metal deficient galaxies – III. Giant Metrewave Radio Telescope observations of blue compact galaxy HS 0822+3542

(tau ) = alpha + beta e^{-(tau /tau _{0})^{5/3}}