CO Emission from Low-Redshift QSO Absorption Line Systems

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Session 113 -- Early Universe and Cosmic Microwave background
Oral presentation, Thursday, 12, 1995, 10:00am - 11:30am

[113.05] CO Emission from Low-Redshift QSO Absorption Line Systems

C.E.Walker, J.Bechtold, J.H.Black (Steward Observatory, U.Arizona)

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By studying the physical conditions in galaxies at different redshifts, we can begin to understand the evolutionary process of starformation from early epochs to the present. Such studies have been performed at optical and centimeter wavelengths for a number of years. Due to advances in receiver and telescope technology at millimeter and submillimeter wavelengths, molecular line studies have recently been performed toward high redshift absorption line systems. Observations of the mm/submm CO lines in these very young galaxies provide a way to investigate abundances of and conditions in potential starforming material. CO provides some of the strongest emission lines associated with star formation in nearby disk galaxies. Here we report the detection of CO in emission toward 4 galaxies at redshifts of 0.02 to 0.40. From these observations we are able to compute the molecular mass of the starforming material. Studies of starformation in galaxies at low to mid-redshift ranges are important, because these systems represent a transitional phase between starformation at early epochs and the present.

Our recent detections of CO emission indicate total molecular masses in three of the galaxies to be a few $\times 10^9 M_{\odot}$, using the ``standard conversion factor'' for molecular hydrogen column density to integrated CO intensity ratio (N(H$_2$)/I$_{co}$) and an H$_o$=75km/s/Mpc and q$_o$= 0.5. The fourth system, the z=0.40 21 cm absorber toward PKS 1229-021, has a molecular mass of $\sim 10^{11}$ M$_\odot$h$^{-2}$. Together with data at other wavelengths, the z=0.40 absorber may be a in pre-starburst phase. All four of our sources were selected to be metal line systems (with high HI column densities) and possess strong FIR fluxes detected by IRAS at 60 and/or 100$\rm {\mu m}$. The source possessing the brightest FIR emission among the four is the z=0.05 21 cm absorber toward S4 0248+43. The total observed FIR luminosity for this source is L$_{FIR}$ =3.0x10E11 L$_{\odot}$. Taking into account its luminosity and the additional correction for the integrated flux from 0.01-100 $\rm {\mu m}$ (Sanders et al 1988), this object can be classified as a transition object between a normal luminous galaxy and an ultraluminous IR galaxy. This absorber galaxy may be the only known starburst in front of a quasar.

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