| Description |
scientific abstract we propose to investigate star formation and the interstellar medium in normal galaxies, predominantly spirals but including important ellipticals and dwarfs. most of the luminous matter in the local universe is contained in normal galaxies, making their study crucial for understanding star formation in the local universe. normal galaxies also provide a template by which abnormal systems may be judged. we hope to determine how the morphology or environment of galaxies influence the star formation rate through lws grating studies of the far-infrared fine-structure lines, and the molecular lines of co, oh, h2o, and others covered in our full grating scans. our sample includes more than 40 galaxies. we have selected about a dozen (blue) dwarf and elliptical galaxies, and more than two dozen spiral galaxies. the spirals include both early and late types, interacting systems and barred and grand design galaxies. we have also selected a few nearby template objects for large scale, fully sampled mapping. these maps will enable us to discern the spatial origins of the line emission we observe, permitting detailed studies of the ism. the mapped galaxies will also provide standards by which the larger galaxy set may be compared. observation summary our top priority observations are the large scale lws01 maps of our template objects. these maps use lws aot01, fully spectrally sampled, and will acquire data over the full range of the instrument (for the stronger objects, however, we will not switch in the more sensitive longest wavelength, band lws4, detector). for an august launch this list of templates includes m51, m83 and ic342 in order of priority. for a spring launch the list also includes ngc 891 and m81. for m51 we will map the core in 4x4 points, and also do an undersampled, 16 point cross through the core; for the other templates the full grating scans will only be done in a cross through its center: a 16 point cross for m81 and ngc891 itself, and 26 point crosses for m83 and ic342. we are especially interested in measuring each of the 7 lines of oi, oiii, cii, nii and niii over large regions of the galaxies because this set of lines traces the gas temperature, density and abundances in the ionized, atomic and photodissociated molecular interstellar medium. in addition, the line ratios help to constrain the numbers and spectral types of stars in the galaxy. our extimates for line flux estimates were based on known kao cii measurements where available. as a basis for still undetected lines we used as a model scaling the fluxes as they are from ngc891 using the iras 60um continuum flux as the scaling reference. in the iso beam on ngc891 the values assumed for reference are: 64jy (continuum), 7e-15 w/m^2 (52um oiii), 2.5e-15 (57um niii), 10e-15w/m^2 (63um oi), 5e-15w/m^2 (88um oiii), 1.5e-15w/m^2 (122um nii), 0.5e-15w/m^2 (146um oi), and 10e-15w/m^2 (158um cii). for each of these galaxies, we calculated the integration times so that the signal to noise ratio at the nucleus is greater than 45 for all of the spectral lines except for the niii line, for which snr >= 20. in this way, we expect to have better than 5 sigma detections at the 10% of peak flux contour for each of the lines (except the niii line). at a lower priority we plan to do a 16 point map of the sc galaxy m33 in the three selected lines of oi,cii, nii. this set of lines trace densities and temperatures for the diffuse ionized, atomic and photodissociated molecular gas. line fluxes were estimated based on the 60 micron iras psc flux and scaled by the observed 60 micron continuum and cii line emission from ngc 891 as noted above. spacecraft time was determined by requiring a snr > 15 for each of these lines for an average place in our 16 pt map. in the autumn launch we will also do a full lws01 grating scan on the nucleus of m33. next priority are fully sampled lws01 grating scans of a set of 8/9 dwarf galaxies, 2/3 elliptical galaxies, and 5/7 spirals, both barred and unbarred, on their nuclei. for the dwarf/ellipticals, spacecraft times were chosen to ensure snr > 12 for the oi 63 micron line. each of the 7 lines of oi, oiii, cii, nii, niii (again, except niii) will also be detected with snr > 5. these deep integrations, which will measure the continuum as well as known and as yet undetected lines, will be used to model the evolutionary character of the interstellar medium in galaxies. the remaining lws01 galaxies are bright spirals for which we plan to integrate somewhat longer to achieve snr > 25 for each of the lines. we expect these deeper integrations to uncover some bright new molecular lines (e.g. h2o or co). the next priority is a set of various types of spirals for which we will obtain lws02 scans of the above 7 fine structure lines. the total integration time is chosen to yield snr > 15 for 6 of the lines, and snr > 5 for niii. our final priority is to detect the 3 lines oi, cii, nii in the remaining set of spirals listed, with an snr >= 15 on ea |
