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 GHzPointing Accuracy ~ 5 arcsec (rms)Sensitivity ~ 11 K/Jy @ 1.4 GHz, (1 Jy = 10-26 W m-2 Hz-1)System Temperature ~ 25 K @ 1.4 GHz

Observing with the 305-m Telescope

Drive Configuration = Simple Azimuth/ElevationHighly Blocked Aperture (Platform, Support cables, Tie-downs, Dome, Dish centre panels, etc.)Accessible Zenith Angle Range 19.7 degreesSky Coverage: 0h R.A. 24h; –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 10-6 * 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,

(ONT – OFFT) ------------------- (ONC – OFFC)

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

18.80

15.90 (rising)

18.80

12.90 (transit)13.20

14.80 (setting)

17.30

Double Position Switching II

Integration time ~ 20 hrRMS 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

J0119+3210 (4C+31.04: HI)HI: N(HI) = 1.84 1018 Ts(K) 1420(v) dv / fc cm-2

OH: N(OH) = 2.25 1014 Tex(K) 1667(v) dv / fc cm-2

HI and OH Absorption in CSS/GPS Sources II

J1347+1217 (4C12.50: HI)

J1407+2827 (Mrk 668: HI)

J2316+0405 (3C459: HI)

J0901+2901 (3C213.1)

HI and OH Absorption in CSS/GPS Sources III

N(HI) = 5.0 1020 cm-2, for Ts = 100 K

N(OH) 1.1 1014 cm-2, for Tex = 10 K

N(HI) / N(OH) 4.4 106

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