High Altitude Molecular Clouds

A population of molecular clouds with a significantly greater scale height than that of Giant Molecular Clouds has been identified by examining maps of the latitude distribution of the $^{12}CO(1-0)$ emission in the first quadrant of the Galaxy. These clouds are found by identifying emission more than 2.6 times the scale-height away from the galactic midplane (centroid of CO emission) at the tangent points. Since the distance to the tangent points is known, we know the height and the sizes of these clouds. They are smaller and fainter than the GMCs and do not seem to be gravitationally bound. These clouds have properties similar to the high latitude clouds in the solar neighborhood. Although they lie outside the molecular cloud layer, the high altitude clouds are well within the HI layer in the Galaxy and coincide with distinct peaks in the HI distribution. These clouds represent a galaxy wide population of small molecular clouds having a larger scale height. They may be clouds in transition between molecular and atomic phases.Comment: 13 pages, 20 figures, uses AAS LaTeX aaspp.sty macro, PostScript figures available through anonymous ftp (to astro.princeton.edu and change directory to san/HAC) or on request. Submitted for publication in the Astrophysical Journal. Princeton Observatory Preprint POP-55

The Volume Fraction of Ionized Intergalactic Gas at Redshift z=6.5

The observed number density of Lyman-alpha sources implies a minimum volume of the inter-galactic medium that must be ionized, in order to allow the Lyman-alpha photons to escape attenuation. We estimate this volume by assigning to each Lyman-alpha emitter the minimum Stromgren sphere that would allow half its Lyman-alpha photons to escape. This implies a lower limit to ionized gas volume fraction of 20-50% at redshift z=6.5. This is a lower limit in two ways: First, we conservatively assume that the Lyman-alpha sources seen (at a relatively bright flux limit) are the only ones present; and second, we assume the smallest Stromgren sphere volume that will allow the photons to escape. This limit is completely independent of what ionizing photon sources produced the bubbles. Deeper Lyman-alpha surveys are possible with present technology, and can strengthen these limits by detecting a higher density of Lyman-alpha galaxies.Comment: Submitted to ApJ Letter

Infrared Counterpart of the Gravitational Lens 1938+66.6

We report the detection of a very red source coincident with the gravitational lens 1938+66.6 (Patnaik et al. 1992) in K' (2.12 micron), H (1.6 micron), J (1.25 micron), and Thuan-Gunn r (0.65 micron) bands. 1938+66.6 has previously been detected as a partial radio ring indicating lensing. We find K'=17.1 +- 0.1 and r = 23.9 +- 0.2, making it a very red source with (r-K')=6.8 +- 0.25. We also observed in Thuan-Gunn g band (0.49 micron) and found g>24.5 at the 90% confidence level. We interpret our observations as a reddened gravitational lens on the basis of its optical-IR color and positional coincidence with the radio source.Comment: 8 pages, one PostScript figure; uses AAS LaTeX macros. Accepted for publication in The Astronomical Journa

Luminosity functions of Lyman-alpha emitters at z=6.5, and z=5.7: evidence against reionization at z=6

Lyman-alpha emission from galaxies should be suppressed completely or partially at redshifts beyond reionization. Without knowing the instrinsic properties of galaxies at z = 6.5, this attenuation is hard to infer in any one source, but can be infered from a comparison of luminosity functions of lyman-alpha emitters at redshifts just before and after reionization. We combine published surveys of widely varying depths and areas to construct luminosity functions at z=6.5 and 5.7, where the characteristic luminosity L_star and density phi_star are well constrained while the faint-end slope of the luminosity function is essentially unconstrained. Excellent consistency is seen in all but one published result. We then calculate the likelihood of obtaining the z=6.5 observations given the z=5.7 luminosity function with (A) no evolution and (B) an attenuation of a factor of three. Hypothesis (A) gives an acceptable likelihood while (B) does not. This indicates that the z=6.5 lyman-alpha lines are not strongly suppressed by a neutral intergalactic medium and that reionization was largely complete at z = 6.5.Comment: Submitted to Astrophysical Journal Letter

Lyman-Alpha Comes of Age

The Lyman-alpha (Ly) line is the strongest recombination line of hydrogen, which constitutes the dominant share of normal matter in the Universe. Fifty-one years ago, it was predicted that Ly emission should appear prominently in the spectra of young primordial galaxies. For the next 30 years, this prediction was tested by many surveys, but none found the predicted galaxies at the predicted luminosities. The blame for these non-detections was squarely cast on the resonant nature of the Ly line, which requires Ly photons to scatter off many hydrogen atoms before escaping from a galaxy. This can hugely increase the path that they traverse, and consequently also the probability that they will be absorbed by dust. This remained the dominant explanation of the missing high-redshift lines for decades, despite some dissenting opinions about the effect of dust. The spectra of nearby galaxies from the International Ultraviolet Explorer are inconclusive about what allows galaxies to be Ly emitters. The missing lines were finally detected 20 years ago, at flux levels much below the original predictions - a difference that we understand to be predominantly due to the hierarchical growth of galaxies, such that star-forming objects at high redshift are much less massive than anticipated in the original prediction. The discovery and study of Ly galaxies has blossomed into an invaluable method for understanding the youngest stages of galaxy formation, the circumgalactic medium, and ultimately the epoch of reionization. The high equivalent widths of Ly galaxies from the earliest high-redshift surveys show that they are low-mass galaxies dominated by young stellar populations. The Sakura CLAW workshop (which used the Twitter hashtag #SakuraCLAW) gathered more than 110 participants (Fig. 1) who showcased progress that pushed the frontiers of Ly galaxy science in sample size, sensitivity, redshifts and physical understanding.

Lyman Alpha Emitters at Redshift z=5.7

Lyman alpha galaxies at high redshifts offer a powerful probe of both the formation of galaxies and the reionization of the intergalactic medium. Lyman alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in systems with young stars and little or no dust-- properties expected in galaxies undergoing their first burst of star-formation. Lyman alpha galaxies also provide a robust test of the reionization epoch that is independent of Gunn-Peterson trough observations in quasar spectra and is better able to distinguish line center optical depths tau=5 from tau=10^5. This is because neutral gas scatters Lyman alpha photons, dramatically ``blurring'' images of Lyman alpha galaxies embedded in a neutral intergalactic medium and rendering them undetectable. We present a photometrically selected sample of z=5.7 Lyman alpha emitters derived from the Large Area Lyman Alpha survey. The presence of these low-luminosity Lyman alpha sources at z=5.7 immediately implies that the reionization redshift was > 5.7. Comparing these objects to our earlier z=4.5 sample, we find that the number of z=5.7 emitters at fixed line luminosity marginally exceeds the no-evolution expectation, but falls well short of published model predictions. The equivalent width distribution is similar at the two redshifts. The large equivalent widths of the Lyman alpha line indicate young galaxies undergoing their first star formation.Comment: 10 pages, uses AASTeX macros; revised version, accepted by ApJ Letter

Assessing the pros and cons of vaginal birth after caesarean relative to elective repeat caesarean section

Background: Recent years have witnessed a rise in rate of primary caesarean section (CS). No. of women reporting with a previous CS scar is also increasing. Judicious trial of labor in such patients can prevent repeat caesarean section. Aim of this study was to assessing the safety and success rate of vaginal birth after caesarean (VBAC) in selected cases of patients who have undergone previous lower segment CS (LSCS) is the main aim of this study.Methods: In this prospective observational study carried out in a tertiary care teaching hospital over a period of 1 year. 375 pregnant women with a history of one previous LSCS for non-recurrent indications were enrolled. The statistical technique of t-test was administered for relative comparison with respect to maternal and neonatal complications across the two groups, i.e. repeat LSCS and vaginal delivery.Results: Out of 375 patients 187 patients (49.9%) underwent elective LSCS for recurrent indication and for non-recurrent indication associated with some complicating factor. Trial of labor in 188 (50.10%) was given out of which 59.3% had spontaneous vaginal delivery,7.20% had instrumental delivery and 33.50% landed into emergency CS. Commonest cause of Em. LSCS being Fetal distress. As regards maternal complications, no statistically significant difference was found between the Repeat LSCS and Vaginal delivery groups (t = 0.779, p > 0.05). On similar lines, there was no statistically significant difference across both groups as regards neonatal complications (t = 0.632, p > 0.05).Conclusions: Taking into account the increased trend of primary CS, trial of VBAC in selected cases is very important. It can be concluded that VBAC has chances of success in cases with previous one LSCS but it must be carefully investigated and monitored