S. J. Curran

CN and HNC line emission in IR luminous galaxies

We have observed HNC 1{0, CN 1{0 & 2{1 line emission in a sample of 13 IR luminous (LIRGs, LIR > 10 11 L) starburst and Seyfert galaxies. HNC 1{0 is detected in 9, CN 1{0 is detected in 10 and CN 2{1 in 7 of the galaxies and all are new detections. We also report the rst detection of HC3N (10{9) emission in Arp 220. The excitation of HNC and CN emission requires densities n> 10 4 cm 3 . We compare their intensities to that of the usual high density tracer HCN. The I(HCN) I(HNC) 1{0 and I(HCN) I(CN) 1{0 line intensity ratios vary signicantly, from 0.5 to >6, among the galaxies. This implies that the actual properties of the dense gas is varying among galaxies who otherwise have similar I(CO) I(HCN) line intensity ratios. We suggest that the HNC emission is not a reliable tracer of cold (10 K) gas at the center of LIR galaxies, as it often is in the disk of the Milky Way. Instead, the HNC abundance may remain substantial, despite high gas temperatures, because the emission is emerging from regions where the HCN and HNC formation and destruction processes are dominated by ion-neutral reactions which are not strongly dependent on kinetic temperature. We nd ve galaxies (Mrk 231, NGC 7469, NGC 7130, IC 694 and NGC 2623) where the I(HCN) I(HNC) intensity ratio is close to unity. Four are classied as active galaxies and one as a starburst. In other active galaxies, however, the I (HCN) I(HNC) is >4. The CN emission is on average a factor of two fainter than the HCN for the luminous IR galaxies, but the variation is large and there seems to be a trend of reduced relative CN luminosity with increasing IR luminosity. This trend is discussed in terms of other PDR tracers such as the (C II) 158 m line emission. One object, NGC 3690, has a CN luminosity twice that of HCN and its ISM is thus strongly aected by UV radiation. We discuss the I(HCN) I(HNC) and I(HCN) I(CN) line ratios as indicators of starburst evolution. However, faint HNC emission is expected both in a shock dominated ISM as well as for a cloud ensemble dominated by dense warm gas in the very early stages of a starburst. Additional information will help resolve the dichotomy.

Molecules at z = 0.89 - A 4-mm-rest-frame absorption-line survey toward PKS 1830−211

We present the results of a 7 mm spectral survey of molecular absorption lines originating in the disk of a z = 0.89 spiral galaxy located in front of the quasar PKS 1830-211. Our survey was performed with the Australia Telescope Compact Array and covers the frequency interval 30-50 GHz, corresponding to the rest-frame frequency interval 57-94 GHz. A total of 28 different species, plus 8 isotopic variants, were detected toward the south-west absorption region, located about 2 kpc from the center of the z = 0.89 galaxy, which therefore has the largest number of detected molecular species of any extragalactic object so far. The results of our rotation diagram analysis show that the rotation temperatures are close to the cosmic microwave background temperature of 5.14 K that we expect to measure at z = 0.89, whereas the kinetic temperature is one order of magnitude higher, indicating that the gas is subthermally excited. The molecular fractional abundances are found to be in-between those in typical Galactic diffuse and translucent clouds, and clearly deviate from those observed in the dark cloud TMC 1 or in the Galactic center giant molecular cloud Sgr B2. The isotopic ratios of carbon, nitrogen, oxygen, and silicon deviate significantly from the solar values, which can be linked to the young age of the z = 0.89 galaxy and a release of nucleosynthesis products dominated by massive stars. Toward the north-east absorption region, where the extinction and column density of gas is roughly one order of magnitude lower than toward the SW absorption region, only a handful of molecules are detected. Their relative abundances are comparable to those in Galactic diffuse clouds. We also report the discovery of several new absorption components, with velocities spanning between -300 and +170 km s(-1). Finally, the line centroids of several species (e. g., CH3OH, NH3) are found to be significantly offset from the average velocity. If caused by a variation in the proton-to-electron mass ratio mu with redshift, these offsets yield an upper limit vertical bar Delta mu/mu vertical bar \textless 4x10(-6), which takes into account the kinematical noise produced by the velocity dispersion measured from a large number of molecular species.

Spin temperatures and covering factors for Hi 21-cm absorption in damped Lyman α systems

We investigate the practice of assigning high spin temperatures to damped Lyman a absorption systems (DLAs) not detected in H 121-cm absorption. In particular, Kanekar & Chengalur have attributed the mix of 21-cm detections and non-detections in low-redshift (z abs ≤ 2.04) DLAs to a mix of spin temperatures, while the non-detections at high redshift were attributed to high spin temperatures. Below z abs = 0.9, where some of the DLA host galaxy morphologies are known, we find that 21-cm absorption is normally detected towards large radio sources when the absorber is known to be associated with a large intermediate (spiral) galaxy. Furthermore, at these redshifts, only one of the six 21-cm non-detections has an optical identification and these DLAs tend to lie along the sight-lines to the largest background radio continuum sources. For these and many of the high-redshift DLAs occulting large radio continua, we therefore expect covering factors of less than the assumed/estimated value of unity. This would have the effect of introducing a range of spin temperatures considerably narrower than the current range of ΔT s ≥ 9000 K, while still supporting the hypothesis that the high-redshift DLA sample comprises a larger proportion of compact galaxies than the low-redshift sample.

A search for propylene oxide and glycine in Sagittarius B2 (LMH) and Orion

We have used the Mopra Telescope to search for glycine and the simple chiral molecule propylene oxide in the Sgr B2 (LMH) and Orion KL, in the 3-mm band. We have not detected either species, but have been able to put sensitive upper limits on the abundances of both molecules. The 3 sigma upper limits derived for glycine conformer I are 3.7 x 10(14) cm(-2) in both Orion-KL and Sgr B2 ( LMH), comparable to the reported detections of conformer I by Kuan et al. However, as our values are 3s upper limits rather than detections we conclude that this weighs against confirming the detection of Kuan et al. We find upper limits for the glycine II column density of 7.7 x 10(12) cm(-2) in both Orion-KL and Sgr B2 ( LMH), in agreement with the results of Combes et al. The results presented here show that glycine conformer II is not present in the extended gas at the levels detected by Kuan et al. for conformer I. Our ATCA results have ruled out the detection of glycine ( both conformers I and II) in the compact hot core of the LMH at the levels reported, so we conclude that it is unlikely that Kuan et al. have detected glycine in either Sgr B2 or Orion-KL. We find upper limits for propylene oxide abundance of 3.0 x 10(14) cm(-2) in Orion-KL and 6.7 x 10(14) cm(-2) in Sgr B2 (LMH). We have detected fourteen features in Sgr B2 and four features in Orion-KL which have not previously been reported in the interstellar medium, but have not been able to plausibly assign these transitions to any carrier.

Limits on variations in fundamental constants from 21-cm and ultraviolet quasar absorption lines

Quasar absorption spectra at 21-cm and UV rest wavelengths are used to estimate the time variation of x [triple-bond] alpha(2)g(p)mu, where alpha is the fine structure constant, g(p) the proton g factor, and m(e)/m(p) [triple-bond] mu the electron/proton mass ratio. Over a redshift range 0.24 < or = zeta(abs) < or = 2.04, (Deltax/x)(weighted)(total) = (1.17 +/- 1.01) x 10(-5). A linear fit gives x/x = (-1.43 +/- 1.27) x 10(-15) yr(-1). Two previous results on varying alpha yield the strong limits Deltamu/mu = (2.31 +/- 1.03) x 10(-5) and Deltamu/mu=(1.29 +/- 1.01) x10(-5). Our sample, 8 x larger than any previous, provides the first direct estimate of the intrinsic 21-cm and UV velocity differences 6 km s(-1).

The connection between metallicity and metal-line kinematics in (sub-)damped Lyα systems

A correlation between the metallicity, [M/H], and rest-frame Mg II equivalent width, W λ2796 r , is found from 49 damped Lyα absorbers (DLAs) and strong sub-DLAs drawn from the literature over the redshift range 0.2 0.7 A, the correlation remains at >3σ significance. Since the Mg II λ2796 transition is predominantly saturated in DLAs (which always have W λ2796 r greater than 0.3 A), W λ2796 r

A survey for redshifted molecular and atomic absorption lines – II. Associated H i, OH and millimetre lines in the z≳ 3 Parkes quarter-Jansky flat-spectrum sample

We present the results of a z ≥ 2.9 survey for Hi 21-cm and molecular absorption in the hosts of radio quasars using the Giant Metrewave Radio Telescope and the Tidbinbilla 70-m telescope. Although the atomic gas has been searched to limits capable of detecting most known absorption systems, no HI was detected in any of the 10 sources. Previously published searches, which are overwhelmingly at redshifts of z ≤ 1, exhibit a 42 per cent detection rate (31 out of 73 sources), whereas the inclusion of our survey yields a 17 per cent detection rate (two out of 12 sources) at z > 2.5. We therefore believe that our high-redshift selection is responsible for our exclusive non-detections, and find that at ultraviolet (UV) luminosities of L UV ≥ 10 23 W Hz -1 , 21-cm absorption has never been detected. We also find this to not only apply to our targets, but also those at low redshift exhibiting similar luminosities, giving zero detections out of a total of 16 sources over z = 0.24 to 3.8. This is in contrast to the L UV ≤ 10 23 W Hz -1 sources where there is a near 50 per cent detection rate of 21-cm absorption. The mix of 21-cm detections and non-detections is currently attributed to orientation effects, where according to unified schemes of active galactic nuclei, 21-cm absorption is more likely to occur in sources designated as radio galaxies (type 2 objects, where the nucleus is viewed through dense obscuring circumnuclear gas) than in quasars (type 1 objects, where we have a direct view to the nucleus). However, due to the exclusively high UV luminosities of our targets it is not clear whether orientation effects alone can wholly account for the distribution, although there exists the possibility that the large luminosities are indicative of a changing demographic of galaxy types. We also find that below luminosities of L UV ∼ 10 23 W Hz -1 , both type 1 and type 2 objects have a 50 per cent likelihood of exhibiting 21-cm absorption. Finally, we do not detect molecular gas in any of the sources. The lack of H i absorption, combined with the results from Paper I, suggests these sources are not conducive to high molecular abundances.

The detectability of H i 21-cm absorption in damped Lyman α systems

In this paper we investigate the possible reasons why H I 21-cm absorption in damped Lyman-α systems (DLAs) has only been detected at low redshift: To date, no 21-cm absorption has yet been detected at zabs > 2.3 and at redshifts less than this, there is a mix of detections and non-detections in the DLAs searched. This has been attributed to the morphologies of the galaxies hosting the DLAs, where at low redshift the DLAs comprise of both large and compact galaxies, which are believed to have low and high spin temperatures, respectively. Likewise, at high redshift the DLA population is believed to consist exclusively of compact galaxies of high spin temperature (Chengalur & Kanekar 2000; Kanekar & Chengalur 2001, 2003). However, in a previous paper (Curran et al. 2005) we found that by not assuming or assigning an, often uncertain, value for the coverage of the radio continuum source by the 21cm absorbing gas, that there is generally no difference in th e spin temperature/covering factor ratio between the 21-cm detections and non-detections or between the low and high redshift samples. Furthermore, only one of the 18 non-detections has a known host morphology, thus making any link between morphology and 21-cm detectability highly speculative. We suggest that the lack of 21-cm absorption detections at high redshift arises from the fact that these DLAs are at similar angular diameter distances to the background quasars (i.e. the distance ratios are always close to unity): Above zabs � 1.6 the covering factor becomes largely independent of the DLA‐QSO distance, making the high redshift absorbers much less effective at covering the background continuum emission. At low redshift, small distance ratios are strongly favoured by the 21-cm detections, whereas large ratios are favoured by the non-detections. This mix of distance ratios gives the observed mix of detections and non-detections at zabs < 1.6. In addition to the predominance of large distance ratios an d non-detections at high redshift, this strongly suggests th at the observed distribution of 21-cm absorption in DLAs is dominated by geometric effects.

DOES THE FINE STRUCTURE CONSTANT VARY? A THIRD QUASAR ABSORPTION SAMPLE CONSISTENT WITH VARYING α

We report results from a third sample of quasar absorption line spectra from the Keck telescope which has been studied to search for any possible variation of the fine structure constant, α. This third sample, which is larger than the sum of the two previously published samples, shows the same effect, and also gives, as do the previous two samples, a significant result. The combined sample yields a highly significant effect, Δα = (αz - α0 )/α0 = -0.57 ± 0.10 × 10-5, averaged over the redshift range 0.2 < z < 3.7. We include a brief discussion of small-scale kinematic structure in quasar absorbing clouds. However, kinematics are unlikely to impact significantly on the averagednon-zeroΔα /α above, and we have so far been unable to identify any systematic effect which can explain it. New measurements of quasar spectra obtained using independent instrumentation and telescopes are required to properly check the Keck results.

Molecular gas conditions in NGC 4945 and the Circinus galaxy

We present results of a multi-transition study of the dense molecular gas in the central part of the hybrid star-burst/Seyfert galaxies NGC 4945 and the Circinus galaxy. From the results of radiative transfer calculations, we estimate in NGC 4945