Nissim Kanekar

A deep search for 21-cm absorption in high redshift damped Lyman-alpha systems

We present deep GMRT 21-cm absorption spectra of 10 damped Lyman- systems (DLAs), of which 8 are at redshifts z> 1:3. HI absorption was detected in only one DLA, the z= 0:5318 absorber toward PKS 1629+12. This absorber has been identified with a luminous spiral galaxy; the spin temperature limit (Ts 310 K) derived from our observations continues the trend of DLAs associated with bright spirals having low spin temperatures. In seven of the remaining 9 systems, the observations place strong lower limits on the spin temperature of the HI gas. We combine this sample with data taken from the literature to study the properties of all known DLAs with 21-cm absorption studies. The sample of DLAs which have been searched for 21-cm absorption now consists of 31 systems, with Ts estimates available in 24 cases; of these, 16 are at z 2, with 11 (all at z 1000 K) have been identified either with LSBs or dwarfs. Further, we find no correlation between impact parameter and spin temperature; it is thus unlikely that the high measured Ts values for DLAs arise from lines of sight passing through the outskirts of large disk galaxies. Instead, the spin temperature of DLAs appears to correlate with the host galaxy type. The trend (noted earlier by Chengalur & Kanekar 2000) that low z DLAs exhibit both high and low Ts values while high redshift (z> 3) DLAs only show high spin temperatures is present in this expanded data set. Based on this dierence in spin temperatures, the Gehan test rules out the hypothesis that DLAs at z> 2 and DLAs at z 3. For local spirals, fCNM 0:5; in contrast, we find that fCNM< 0: 3i n all 7h ighz absorbers, and fCNM< 0: 1i n 5o f the 7c ases.

A high-velocity narrow absorption line outflow in the quasar J212329.46 − 005052.9

We report on the discovery of a high-velocity narrow absorption line outflow in the redshift 2.3 quasar J212329.46-005052.9.Five distinct outflow systems are detected with velocity shifts from 9710 to 14,050 km s 1 and Civ ��1548,1551 line widths of FWHM � 62 to 164 km s 1 . This outflow is remarkable for having high speeds and a degree of ionization similar to broad absorption line (BAL) flows, but line widths roughly 100 times narrower than BALs and no apparent X-ray absorption. This is also, to our knowledge, the highest-velocity narrow absorption line system confirmed to be in a quasar outflow by all three indicators of line variability, smooth super-thermal line profiles and doublet ratios that require partial covering of the quasar continuum source. All five systems have stronger absorption in Ovi ��1032,1038 than Civ with no lower ionization metal lines detected. Their line variabilities also appear coordinated, with each system showing larger changes in Civ than Ovi and line strength variations accompanied by nearly commensurate changes in the absorber covering fractions. The metallicity is approximately twice solar. These data require five distinct outflow structures with similar kinematics, physical conditions and characteristic sizes of order 0.01-0.02 pc (based on partial covering). The coordinated line variations, occurring on time scales 60.63 yr (quasar frame), are best explained by global changes in the outflow ionization caused by changes in the quasar’s ionizing flux. An upper limit on the acceleration, .3 km s 1 yr 1 , is consistent with blobs of gas that are gravitationally unbound and coasting freely &5 pc from the central black hole. Additional constraints from the variability time indicate that the full range of plausible distances is 5 . R . 1100 pc. However, if these small absorbing structures were created in the inner flow, they should be near the �5 pc minimum radius because they can travel just a few pc before dissipating (without external confinement). An apparent double line-lock in Civ suggests that the flow was radiatively accelerated and its present trajectory is within �16 o of the radial (line-ofsight) direction. The absence of strong X-ray absorption shows that radiative shielding in the far-UV and X-rays is not needed to maintain moderate BAL-like ionizations and therefore, apparently, it is not needed to facilitate the radiative acceleration to high speeds. We argue that the ionization is moderated, instead, by high gas densities in small outflow sub-structures. Finally, we estimate that the kinetic energy yield from this outflow is at least two orders of magnitude too low to be important for feedback to the host galaxy’s evolution.

Constraints on Changes in Fundamental Constants from a Cosmologically Distant OH Absorber or Emitter

We have detected the four 18 cm OH lines from the z approximaetely 0.765 gravitational lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the z approximately 0.765 absorber and the z approximately 0.685 lens toward B0218 + 357 to place stringent constraints on changes in F triple-bond g(p)[alpha(2)/mu](1.57). We obtain [DeltaF/F] = (0.44 +/- 0.36(stat) +/- 1.0(sys)t) x 10(-5), consistent with no evolution over the redshift range 0 < z < or = 0.7. The measurements have a 2sigma sensitivity of [Deltaalpha/alpha] < 6.7 x 10(-6) or [Deltamu/mu] < 1.4 x 10(-5) to fractional changes in alpha and mu over a period of approximately 6.5 G yr, half the age of the Universe. These are among the most sensitive constraints on changes in mu.

The spin temperature of high-redshift damped Lyman α systems

We report results from a programme aimed at investigating the temperature of neutral gas in high-redshift damped Lyman α absorbers (DLAs). This involved (1) H I 21 cm absorption studies of a large sample of DLAs towards radio-loud quasars, (2) very long baseline interferometric studies to measure the low-frequency quasar core fractions, and (3) optical/ultraviolet spectroscopy to determine DLA metallicities and the velocity widths of low-ionization metal lines. Including literature data, our sample consists of 37 DLAs with estimates of the harmonic mean spin temperature Ts. We find a statistically significant (4σ) difference between the Ts distributions in the high-z (z > 2.4) and low-z (z 1.7 have Ts values indicating CNM fractions >20 per cent, comparable to the median value (≈27 per cent) in the Galaxy. We tested whether the H I column density measured towards the optical quasar might be systematically different from that towards the radio core by comparing the H I column densities inferred from H I 21 cm emission studies at different spatial resolutions (≈15 pc-1 kpc) in the Large Magellanic Cloud. The high-resolution NH I values are, on average, larger than the smoothed ones for NH I > 1021 cm-2, but lower than the smoothed NH I estimates for NH I 1. Since all DLAs at z > 1 have angular diameter distances comparable to or larger than those of their background quasars, they have similar efficiency in covering the quasars. We conclude that low covering factors in high-z DLAs cannot account for the observed redshift evolution in spin temperatures.

CONSTRAINING CHANGES IN THE PROTON-ELECTRON MASS RATIO WITH INVERSION AND ROTATIONAL LINES

We report deep Green Bank Telescope spectroscopy in the redshifted NH3 (1,1), CS 1-0, and H2CO 000-101 lines from the z ~ 0.685 absorber toward B0218+357. The inversion (NH3) and rotational (CS, H2CO) line frequencies have different dependences on the proton-electron mass ratio μ, implying that a comparison between the line redshifts is sensitive to changes in μ. A joint three-component fit to the NH3, CS, and H2CO lines yields [Δμ/μ] = (–3.5 ± 1.2) × 10–7, from z ~ 0.685 to today, where the error includes systematic effects from comparing lines from different species and possible frequency-dependent source morphology. Two additional sources of systematic error remain, due to time variability in the source morphology and velocity offsets between nitrogen-bearing and carbon-bearing species. We find no statistically significant (≥3σ) evidence for changes in μ and obtain the stringent 3σ constraint, [Δμ/μ] < 3.6 × 10–7, over 6.2 Gyr; this is the best present limit on temporal changes in μ from any technique, and for any look-back time, by a factor 5.

A HIGH-FREQUENCY SEARCH FOR PULSARS WITHIN THE CENTRAL PARSEC OF Sgr A

We report results from a deep high-frequency search for pulsars within the central parsec of Sgr A* using the Green Bank Telescope. The observing frequency of 15 GHz was chosen to maximize the likelihood of detecting normal pulsars (i.e., with periods of ~500 ms and spectral indices of ~–1.7) close to Sgr A* that might be used as probes of gravity in the strong-field regime; this is the highest frequency used for such pulsar searches of the Galactic center (GC) to date. No convincing candidate was detected in the survey, with a 10σ detection threshold of ~10 μJy achieved in two separate observing sessions. This survey represents a significant improvement over previous searches for pulsars at the GC and would have detected a significant fraction (≳5%) of the pulsars around Sgr A*, if they had properties similar to those of the known population. Using our best current knowledge of the properties of the Galactic pulsar population and the scattering material toward Sgr A*, we estimate an upper limit of 90 normal pulsars in orbit within the central parsec of Sgr A*.

HI 21 cm absorption in low

We report Giant Metrewave Radio Telescope (GMRT) 21 cm observations of two confirmed and one candidate low redshift damped Lyman- α systems (DLAS). HI absorption was detected in the two confirmed systems, at

\vec z

z = 0.2378

damped Lyman-

and

\alpha

z = 0.5247