Spatial distribution of far infrared emission in spiral galaxies I. Relation with radio continuum emission

We use high resolution IRAS and 20 cm radio continuum (RC) images of a sample of 22 spiral galaxies to study the correlation between the far infra-red (FIR) and RC emissions within the galactic disks. A combination of exponential and gaussian profiles rather than a single exponential profile is found to be a better representation of the observed intensity profiles in the two bands. The gaussian component, which we show is not due to the effects of limited beam-resolution, contains more than 60% of the total flux in majority of the galaxies. The dominance of the gaussian component suggests that the nuclear star forming regions and the bulge stars are more important contributors to the emission in the two bands, rather than the outer exponential stellar disks. The RC profile is flatter compared to the FIR profile, resulting in a decrease of their ratio, Q60, away from the center. However, the Q60 increases in the extreme outer parts, where the dispersion in the FIR and RC correlation is also higher than in the central regions. The global Q60 and its dispersion match those in the inner parts of the galaxies. These results imply that the observed tight correlation in the global quantities reflects processes in the inner regions only where OB stars and the associated Type II supernovae control the FIR and RC emission. In the outer parts heating of very small dust grains by the old disk stars provides a secondary component in the FIR emission, without associated RC emission. The edge-on galaxy NGC3079 shows extended FIR and RC emissions along its minor axis, probably associated with the nuclear starburst activity.Comment: Uses aas2pp4.sty and epsfig.sty, 21 pages. Figure 1 is spread over 22 pages and is available at http://www.inaoep.mx/~ydm/preprint.html To appear in Astronomical Journal, September 199

Spatial distribution of Far infrared emission in spiral galaxies II. Heating sources and gas-to-dust ratio

We study the radial distribution of the temperature of the warm dust and gas-to-dust mass ratios in a sample of 22 spiral galaxies. The heating capabilities of the diffuse interstellar radiation field (ISRF), based on Desert et al. model, are investigated in 13 of the sample galaxies. In general, the temperature of the warm dust decreases away from the center, reaches a minimum value at the mid-disk and increases again in the outer parts of galaxies. Heating a mixture of small and big grains by the ISRF is able to explain the observed behavior qualitatively. However, ultraviolet photons from recent star formation events are necessary for a detailed matching of the warm dust temperature profiles. Very small grains contribute typically more than 50% to the observed flux at 60 micron beyond half the disk radius in galaxies. Optical depth profiles, derived from the observed 60 micron and warm dust temperature profiles, peak at or close to the galactic center. In 13 of the galaxies, where dust temperature profiles are modeled, we obtain gas-to-dust mass ratio profiles, after correction for the contaminating effects of very small grains. The gas-to-dust mass ratio decreases by a factor of 8 from the center to the optical isophotal radius, where the value approaches the local galactic value. We demonstrate that the observed steep gradient is a result of the over-estimation of the molecular mass, and can be flattened out to within a factor of 2, if the molecular hydrogen mass (H2) is recomputed assuming a metallicity dependent conversion factor from CO intensity to H2 column density. The flattened radial profiles indicate a global gas-to-dust ratio of around 300, which is within a factor of two of the local galactic value.Comment: Uses aas2pp4.sty and epsfig.sty, 27 pages. To appear in Astronomical Journal, September 199

A new polychaete of the family Pilargidae from Palk Bay, South India

The family Pilargidae consists of the following seven genera : Ancistrosyllis Mc Intosh, Cabira Webster, Loandalia Monro, Otopsis Ditlevsen, Pilargis St. Joseph, Talehsapia Fauvel and Ancistargis Jones. However, Hartman (1947) has suggested that the genus Cabira, which is represented by only one species, might best be dropped from literature. Kitamori (I960) has described Pilargis matsunagaensis (= Ancistargis matsunagaensis), a new species from Matsunaga Bay, Hiroshima Prefecture, which combines the characters of both the genera Ancistrosyllis and Pilargis. It has a pair of antennae in the prostomium and the epitheUal papillae are scattered over most of the body. In addition, it has an acicular hook in notopodia, a character typical of the genus Ancistrosyllis. As pointed out by Jones (1961) P. matsunagaensis should belong to the genus Ancistargis. At present this genus is represented by two species, papillosus and matsunagaen

Maturity and spawning of the snapper, Lutianus kasmira (Forskal) from the Andaman sea

Lutianus kasmira of the Andaman Sea spawns only once in a year but the spawning period is likely to be spread over a period of four or five months from November to March. The occurrence of mature fish over a prolonged period and high gonadosomatic index during a number of months lend additional evidence for the prolonged spawning season of the fish. The minimum size at first maturity was about 170 mm and fifty per cent maturity was attained when the fish grew to a length of 200 mm. Fecundity was found to fluctuate very widely from 42,100 to 332,620. The sexes were found to be disproportionate in the catches, the males outnumbering the females, which suggests that differential fishing could occur in Lutianus kasmira

Radio continuum and far-infrared emission of spiral galaxies: Implications of correlations

Researchers present a study extending the correlation seen between radio continuum and far-infrared emissions from spiral galaxies to a lower frequency of 408 MHz and also as a function of radio spectral index. The tight correlation seen between the two luminosities is then used to constrain several parameters governing the emissions such as the changes in star formation rate and mass function, frequency of supernovae that are parents of the interstellar electrons and factors governing synchrotron radio emission

Evaluation of sensor, environment and operational factors impacting the use of multiple sensor constellations for long term resource monitoring

Moderate resolution remote sensing data offers the potential to monitor the long and short term trends in the condition of the Earth’s resources at finer spatial scales and over longer time periods. While improved calibration (radiometric and geometric), free access (Landsat, Sentinel, CBERS), and higher level products in reflectance units have made it easier for the science community to derive the biophysical parameters from these remotely sensed data, a number of issues still affect the analysis of multi-temporal datasets. These are primarily due to sources that are inherent in the process of imaging from single or multiple sensors. Some of these undesired or uncompensated sources of variation include variation in the view angles, illumination angles, atmospheric effects, and sensor effects such as Relative Spectral Response (RSR) variation between different sensors. The complex interaction of these sources of variation would make their study extremely difficult if not impossible with real data, and therefore, a simulated analysis approach is used in this study. A synthetic forest canopy is produced using the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model and its measured BRDFs are modeled using the RossLi canopy BRDF model. The simulated BRDF matches the real data to within 2% of the reflectance in the red and the NIR spectral bands studied. The BRDF modeling process is extended to model and characterize the defoliation of a forest, which is used in factor sensitivity studies to estimate the effect of each factor for varying environment and sensor conditions. Finally, a factorial experiment is designed to understand the significance of the sources of variation, and regression based analysis are performed to understand the relative importance of the factors. The design of experiment and the sensitivity analysis conclude that the atmospheric attenuation and variations due to the illumination angles are the dominant sources impacting the at-sensor radiance

On the occurrence of Malacanthus hoedtii Bleeker (Fam: Malacanthidae) in the Andaman sea.

The occurrence of Malacanthus hoedtii Bleeker is reported for the first time from the Andaman Sea. The various body measurements of M. hoedtii are compared with those of M. latovittatus and the range of distribution of the two species in the tropical Indo-Pacific Ocean is discussed

Criteria for site selection for mussel farms

In recent years considerable progress has been made in cultivating mussels in India. Mussel culture forms an important programme in the mariculture activities of countries like F:cance, Spain, Italy, Neilherlands and North -America. Hany countries in Asia like Singapore, Philippines, Thailand, Indonesia, etc., have also taken up mussel culture in recent years in view of its high production potentia