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For refcode 1991A&A...251..431v:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1991A&A...251..431v A study of southern extreme IRAS galaxies III. CO (J = 1-0) line observations W. van Driel and A.C. van den Broek Astronomical Institute "Anton Pannekoek, University of Amsterdam, Kruislaan 403, NL- 1098 SJ Amsterdam, The Netherlands Received December 21, 1990; accepted April 8, 1991 Abstract. As part of a multi-wavelength study of an infrared-complete sample of some 50 extreme IRAS galaxies with a high far-infrared/blue luminosity ratio (L_FIR_/L^0^_B_ >~3), CO (J = 1-0) line observations were made of 19 of these galaxies with the SEST, and detections of five galaxies from our sample were taken from the literature. This total of 21 galaxies observed includes a distance-limited (V < 6000 km s^-1^) "statistical CO subsample" of 16 galaxies, 10 of which were detected, as well as 5 additional objects, all of which were detected. The 10 detected galaxies from the statistical CO subsample, which have L_FIR_S ranging from 7 10^9^ to 7 10^10^ L_sun_ (H_0_ = 75 km s^-1^ Mpc^- 1^), have estimated total H_2_ masses ranging from 0.5 to 7.5 10^9^M_sun_ (or about 0.2 to 2.5 times the mass of molecular gas in our Galaxy), and L_FIR_/M_H2_ ratios between 6 and 30 L_sun_M^-1^_sun_. This ratio, which is considered to be a measure of the "starformation efficiency", is on an average some 4 times higher in these galaxies than in spirals, and comparable to the ratios found for other samples of IRAS galaxies with moderate luminosities, and for "classical" starburst galaxies such as M 82. Of the three distinct subclasses in which we can divide our infrared- complete sample (dwarfs, barred spirals, and interacting/merging systems), we tend to find the least infrared-extreme objects in our statistical CO subsample due to the distance limit. The 8 dwarfs constitute half of the statistical CO subsample, but only two of them were detected, one of which is a rare, gas-rich star-forming S0-type galaxy. The dwarfs appear to have a mean star-formation efficiency which is (at least) as high as that of the two other subclasses. All 6 barred spirals were detected and they show a large spread in both L_FIR_ and the L_FIR_/M_H2_ ratio. The interacting systems and merger candidates appear to have the highest average L_FIR_ of the three subclasses in our sample, but have only average L_FIR_/M_H2_ ratios. The correlation of the L_FIR_/M_H2_ ratio with both the equivalent width of the H{alpha} line and the L_FIR_/L^0^_B_ ratio seems to imply that the magnitude of the starburst is related to the efficiency of the massive star-formation process. The estimated amount of gas converted during the entire starburst is much smaller than the estimated H_2_ masses, so the galaxies have an ample supply of gas to sustain the ongoing starburst. For our galaxies the estimated radiating H_2_ gas-to-dust mass ratios are of the order of 5000, if we use a single-temperature dust distribution. This high ratio can be brought into agreement with the canonical Galactic value of 150, if we adopt a two-component dust distribution with cool and warm dust of 18 and 60 K, respectively. The total galaxy masses estimated from the CO line widths, assuming undisturbed rotation in a flat disk coplanar with the stars, gives reasonable mass-to-light ratios. Two inclined noninteracting galaxies have Gaussian-shaped CO line profiles, probably indicating disturbed kinematics and/or distribution of the molecular gas. In some of the galaxies HI or OH emission and/or absorption was found by others. The H_2_/HI mass ratios are comparable to those of other IRAS galaxies. Two of our most infrared-luminous objects have OH megamasers. Key words: galaxies: general - interstellar matter: molecules - radio lines: molecules - stars: formation of
Retrieve 23 NED objects in this reference.
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