Extragalactic Absorption Lines Observed from Arecibo Chris Salter (National Astronomy & Ionosphere Center, Arecibo Observatory, Puerto Rico)

Principal Collaborators Tapasi Ghosh (NAIC, Arecibo) — Especially Emmanuel Momjian (NAIC, Arecibo) D.J. Saikia (NCRA, Pune, India) Neeraj Gupta (NCRA, Pune, Arecibo) Karen O’Neil (NRAO, Green Bank, WV)

The Arecibo 305-m Radio Telescope Diameter = 305m; Platform Height = 137 m; Frequency Range = 327 MHz – 10 GHz Pointing Accuracy ~ 5 arcsec (rms) Sensitivity ~ GHz, (1 Jy = W m -2 Hz -1 ) System Temperature ~ GHz

Observing with the 305-m Telescope Drive Configuration = Simple Azimuth/Elevation Highly Blocked Aperture (Platform, Support cables, Tie-downs, Dome, Dish centre panels, etc.) Accessible Zenith Angle Range  19.7 degrees Sky Coverage: 0 h  R.A.  24 h ; –1.4 deg  Dec  38.0 deg

Observing Complications Position Switching: Track ON (Target) for t min, then track OFF (Reference) position for same length of time, tracking over the same pattern in (Az, El), i.e. track the ‘footprint’ over the same path on the dish. (ON – OFF) subtracts out standing waves (if they are the same for ON and OFF), while OFF provides a reference bandpass. Thus, (ON – OFF) / OFF normally supplies a “standing-wave free”, bandpass-corrected, spectrum. HOWEVER, if the target radiates continuum emission, as well as spectral lines, the quantity (ON – OFF) does not at all cancel the standing waves due to that continuum emission, and the (ON – OFF)/OFF spectrum is degraded by a “baseline ripple”. If the path difference between the direct and reflected rays is 2D, then the baseline ripple across the spectrum has a repetition frequency of * c/2D MHz/cycle ~ 1 MHz for Arecibo.

Double Position Switching (DPS) The residual “baseline” ripple from a source’s continuum emission is proportional to the intensity (flux density) of the target. Hence, if we also observe an ON/OFF pattern on another continuum source of different redshift (Calibrator), tracking over a similar (Az, El) range to the Target source, then the quantity, (ON T – OFF T ) (ON C – OFF C ) cancels the standing-wave residual, leaving a baselined spectrum whose amplitude is proportional to the ratio of the flux densities of the Target and Calibrator sources. Zenith Angle (rising) (transit) (setting)

Double Position Switching II Integration time ~ 20 hr RMS noise = 350  Jy/beam In theory, simple Position Switching results in about a factor of two better SNR for a given integration time than DPS. In practice, for a source emitting continuum radiation, the SNR soon ceases to improve by  t, and DPS quickly surpasses it. DPS continues to integrate down as  t for at least 20 hr.

HI and OH Absorption in CSS/GPS Sources J (4C+31.04: HI) HI: N(HI) = 1.84  T s (K)   1420 (v) dv / f c cm -2 OH: N(OH) = 2.25  T ex (K)   1667 (v) dv / f c cm -2

HI and OH Absorption in CSS/GPS Sources II J (4C12.50: HI) J (Mrk 668: HI) J (3C459: HI) J (3C213.1)

HI and OH Absorption in CSS/GPS Sources III N(HI) = 5.0  cm -2, for T s = 100 K N(OH)  1.1  cm -2, for T ex = 10 K N(HI) / N(OH)  4.4  10 6 HST image of 3C258 (de Vries et al. 1997), overlaid by 5-GHzcontours (Akujor et al. (1991).

HI and OH Absorption in CSS/GPS Sources IV

HI and OH Absorption in CSS/GPS Sources V

Cooling Flow Cluster, Abell 2390

OH Satellite Lines in Arp 220 2MASS image of Arp 200 (3 x 3) 1420 MHz 1665/1667 MHz

OH Satellite Lines in Arp 220: II 1720 MHz 1612 MHz

Damped Ly-  Absorber Search