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The Australia Telescope National Facility Colloquium
15:30-16:30 Wed 14 May 2008

ATNF Marsfield Lecture Theatre

Neeraj Gupta

(Australia Telescope National Facility)

GMRT survey of 21cm absorption in DLA candidates at intermediate redshift - Neeraj Gupta Colloquium

Damped Lyman-alpha absorbers (DLAs) seen in the spectra of high-z QSOs allow us to probe the physical conditions in protogalaxies. Our understanding of physical conditions in DLAs at high-z is primarily based on the absorption lines of H_2 molecules and fine-structure transitions. Another important way of probing the thermal state of interstellar medium in these systems is by studying the 21cm absorption in the spectra of background quasars. We are doing systematic searches for 21cm absorption in complete samples of
1) DLA candiates at intermediate redshifts (z ~ 1),
2) DLAs at z > 2, and
3) QSO-Galaxy pairs at low redshifts (z < 0.3).
In this talk I will present the main results of our GMRT survey to search for 21cm absorption in intermediate redshift DLA candidates. Our complete sample of 38 DLA candidates at 1.15 < z < 1.4 is mainly drawn from the QSO spectra from SDSS DR5. There are 2893 absorption line systems at 1.15 < z < 1.4 with W(MgII)>1 Angstrom. Using radio flux measurements from the literature we construct a complete sample of strong MgII systems in front of compact quasars and interpolated 610-MHz flux density in excess of 100mJy. Distribution of different equivalent width ratios (i.e. W(MgI)/W(MgII), W(FeII)/W(MgII) etc.) together with the distribution of W(MgII) in our sample is consistent with that observed for the DLAs. Observations of 37 out of 38 sources in our sample are completed and has resulted in 6 new and 2 tentaive detections of 21cm absorption. This has significantly increased the number of 21cm absorbers at z > 1 as only 4 21cm absorbers were known prior to our survey.

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