arXiv subjects

N. H. M. Crighton

Publications and source records attributed to N. H. M. Crighton.

10 recordsLinked to original sources

arXiv2017

Probing the intra-group medium of a z = 0.28 galaxy group

We present new MUSE observations of a galaxy group probed by a background quasar. The quasar sightline passes between multiple $z=0.28$ galaxies, whilst showing at the same redshift low ionised metal line species, including Ca II, Mg I, Mg II and Fe II. Based on the galaxy redshifts measured from the MUSE data, we estimate the galaxies to be part of a small galaxy group with a halo mass of $\approx6\times10^{12}$ M$_{\odot}$. We use the MUSE data to reveal the two dimensional dynamical properties of the gas and stars in the group galaxies, and relate these to the absorber kinematics. With these data we consider a number of scenarios for the nature of the gas probed by the sightline absorbers: a co-rotating gas halo associated with a single galaxy within the group; outflowing material from a single group member powered by recent star-formation; and cool dense gas associated with an intra-group medium. We find that the dynamics, galaxy impact parameters, star-formation rates, and the absorber strength suggest the cool gas can not be clearly associated with any single galaxy within the group. Instead we find that the observations are consistent with a superposition of cool gas clouds originating with the observed galaxies as they fall into the group potential, and are now likely in the process of forming the intra-group medium.

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arXiv2016

The VLT LBG Redshift Survey - VI. Mapping HI in the proximity of $z\sim3$ LBGs with X-Shooter

We present an analysis of the spatial distribution of gas and galaxies using new X-Shooter observations of $z\sim3-4$ quasars. Adding the X-Shooter data to an existing dataset of high resolution quasar spectroscopy, we use a total sample of 29 quasars alongside $\sim1700$ Lyman Break Galaxies in the redshift range $2<z<3.5$. Analysing the Ly$α$ forest auto-correlation function using the full quasar sample, we find $s_0=0.081\pm0.006h^{-1}$Mpc. We then investigate the clustering and dynamics of Ly$α$ forest absorbers around $z\sim3$ LBGs. From the redshift-space cross-correlation, we find $s_0=0.27\pm0.14h^{-1}$Mpc, with power-law slope $γ=1.1\pm0.2$. We make a first analysis of the dependence of this clustering length on absorber strength based on cuts in the sightline transmitted flux, finding a clear preference for stronger absorption features to be more strongly clustered around the galaxy population than weaker absorption features. Further, we calculate the projected correlation function, finding $r_0=0.24\pm0.04h^{-1}$Mpc (assuming a fixed slope $γ=1.1$). Taking this as the underlying real-space clustering, we fit the 2D cross-correlation function with a dynamical model incorporating the infall parameter and the peculiar velocity, finding $β_{\rm F}=1.02\pm0.22$ and $240\pm60$ km s$^{-1}$ respectively. This result shows a significant detection of gas infall relative to the galaxy population, whilst the measured velocity dispersion is consistent with the velocity uncertainties on the galaxy redshifts. We evaluate the Cauchy-Schwarz inequality between the galaxy-galaxy, absorber-absorber, and galaxy-absorber correlation functions, finding a result significantly less than unity: $ξ_{\rm ag}^2/(ξ_{\rm gg}ξ_{\rm aa})=0.25\pm0.14$, implying that galaxies and Ly$α$ absorbers do not linearly trace the underlying dark matter distribution in the same way.

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arXiv2016

The VLT LBG Redshift Survey - V. Characterising the z = 3.1 Lyman Alpha Emitter Population

We present a survey of $z\sim3$ Ly$α$ emitters (LAEs) within the fields of the VLT LBG Redshift Survey. The data encompasses 5 independent survey fields co-spatial with spectroscopic LBG data and covering a larger total area than previously analysed for LAE number counts and clustering. This affords an improved analysis over previous work by minimising the effects of cosmic variance and allowing the cross-clustering analysis of LAEs and LBGs. Our photometric sample consists of $\approx600$ LAE candidates, over an area of 1.07~deg$^2$, with equivalent widths of $\gtrsim65$~Å and a flux limit of $\approx2\times10^{-17}$~erg~cm$^{-2}$~s$^{-1}$. From spectroscopic follow-up, we measured a success rate of $78\pm18\%$. We find the $R$-band continuum luminosity function to be $\sim10\times$ lower than the luminosity function of LBGs at this redshift, consistent with previous studies. Exploiting the large area of the survey, we estimate the LAE auto-correlation function and find a clustering length of $r_0=2.86\pm0.33~h^{-1}$~Mpc, low compared to the $z\sim3$ LBG population, but somewhat higher than previous LAE measurements. This corresponds to a median halo mass of $M_{\rm DM}=10^{11.0\pm0.3}~h^{-1}~$M$_{\odot}$. We present an analysis of clustering length versus continuum magnitude and find that the measurements for LAEs and LBGs are consistent at faint magnitudes. Our combined dataset of LAEs and LBGs allows us to measure, for the first time, the LBG-LAE cross-correlation, finding a clustering length of $r_0=3.29\pm0.57~h^{-1}$~Mpc and a LAE halo mass of $10^{11.1\pm0.4}~h^{-1}$~M$_{\odot}$. Overall, we conclude that LAEs inhabit primarily low mass halos, but form a relatively small proportion of the galaxy population found in such halos.

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arXiv2014

The VLT LBG Redshift Survey - IV. Gas and galaxies at z ~ 3 in observations and simulations

We use observations and simulation to study the relationship between star-forming galaxies and the intergalactic medium at z~3. The observed galaxy sample is based on spectroscopic redshift data from a combination of the VLT LBG Redshift Survey and Keck observations in fields centred on bright z>3 QSOs, whilst the simulation data is taken from GIMIC. In the simulation, we find that the dominant peculiar velocities are in the form of large-scale coherent motions of gas and galaxies. Gravitational infall of galaxies towards one another is also seen. At smaller scales, the peculiar velocities in the simulation over-predict the difference between the simulated real- and z-space galaxy correlation functions. Peculiar velocity pairs separated by <1Mpc/h have a smaller dispersion and explain the z-space correlation function better. The Lyα auto- and cross-correlation functions in the GIMIC simulation show infall smaller than implied by previous work. This reduced infall may be due to the galaxy wide outflows implemented in the simulation. The main challenge in comparing these simulated results with the observed correlation functions comes from the presence of velocity errors for the observed LBGs which dominate at ~1Mpc/h scales. When these are taken into account, the observed LBG correlation function is well matched by a simulated $M_*>10^9M_\odot$ galaxy sample. The simulated cross-correlation shows similar neutral gas densities around galaxies as are seen in the observations. The simulated and observed Lyα z-space autocorrelation functions agree well with each other. Our overall conclusion is that gas and galaxy peculiar velocities are towards the low end of expectation. Finally, little direct evidence is seen in either simulation or observations for high transmission near galaxies due to feedback. (Abridged)

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arXiv2013

The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z ~ 3

We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Visible Multi-Object Spectrograph (VIMOS), giving a mean redshift of z=2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. From the semiprojected correlation function, wp(σ) we find that the results are well fit with a single power-law model, with clustering scale lengths of r0=3.46+-0.41 and 3.83+-0.24 Mpc/h, respectively. We note that the corresponding combined ξ(r) slope is flatter than for local galaxies at γ = 1.5-1.6 rather than γ=1.8. This flat slope is confirmed by the z-space correlation function, ξ(s), and in the range 10<s<100 Mpc/h the VLRS shows ~2.5σ excess over the Λ cold dark matter. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z~1. We then analyse the LBG z-space distortions using the 2D correlation function, ξ(σ, π), finding for the combined sample a large-scale infall parameter of $β$ = 0.38+-0.19 and a velocity dispersion of 420km/s. Based on our measured β, we are able to determine the gravitational growth rate, finding a value of f(z = 3)=0.99+-0.50 (or fσ8 = 0.26+-0.13), which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with ΛCDM. Finally, we constrain the mean halo mass for the LBG population, finding that the VLRS and combined sample suggest mean halo masses of log(MDM/Msun) = 11.57+-0.15 and 11.73+-0.07, respectively.

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arXiv2011

The VLT LBG Redshift Survey I: Clustering and Dynamics of ~1000 Galaxies at z~3

We present the initial imaging and spectroscopic data acquired as part of the VLT VIMOS Lyman-break galaxy Survey. UBR (or UBVI) imaging covers five 36'x36' fields centred on bright z>3 QSOs, allowing ~21,000 2 2 LBGs and 10 z>2 QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a 625+-510 km/s velocity offset between the ISM absorption and Ly-alpha emission line redshifts. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at z~3. In the photometric case, the angular correlation function, w(theta), is well fit by a double power-law with clustering scale-length, r_0 = 3.19+0.32-0.54 Mpc/h for r < 1 Mpc/h and r_0 = 4.59+0.31-0.33 Mpc/h at larger scales. Using the redshift sample we estimate the semi-projected correlation function, w_p(sigma) and find r_0 = 3.67+0.23-0.24 Mpc/h for the VLT sample and r_0 = 3.98+0.14-0.15 Mpc/h for a combined VLT+Keck sample. From the z-space correlation functions and assuming the above xi(r) models, we find that the combined VLT and Keck surveys require a galaxy velocity dispersion, ^1/2 ~ 700 km/s, higher than the ~400 km/s found by previous authors. We also measure a value for the gravitational growth rate parameter of beta(z=3) = 0.48+-0.17, implying a low value for the bias of b = 2.06+1.1-0.5. This value is consistent with the galaxy clustering amplitude which gives b = 2.22+-0.16, assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. We have compared our LBG clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift L* spirals for simple 'long-lived' galaxy models.

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arXiv2010

VLT LBG Redshift Survey II: Interactions between galaxies and the IGM at z ~3

We have measured redshifts for 243 z ~3 quasars in nine VLT VIMOS LBG redshift survey areas, each of which is centred on a known bright quasar. Using spectra of these quasars, we measure the cross-correlation between neutral hydrogen gas causing the Lya forest and 1020 Lyman-break galaxies at z ~3. We find an increase in neutral hydrogen absorption within 5 h^-1 Mpc of a galaxy in agreement with the results of Adelberger et al. (2003, 2005). The Lya-LBG cross-correlation can be described by a power-law on scales larger than 3 h^-1 Mpc. When galaxy velocity dispersions are taken into account our results at smaller scales (<2 h^-1 Mpc) are also in good agreement with the results of Adelberger et al. (2005). There is little immediate indication of a region with a transmission spike above the mean IGM value which might indicate the presence of star-formation feedback. To measure the galaxy velocity dispersions, which include both intrinsic LBG velocity dispersion and redshift errors, we have used the LBG-LBG redshift space distortion measurements of Bielby et al. (2010). We find that the redshift-space transmission spike implied in the results of Adelberger et al. (2003) is too narrow to be physical in the presence of the likely LBG velocity dispersion and is likely to be a statistical fluke. Nevertheless, neither our nor previous data can rule out the presence of a narrow, real-space transmission spike, given the evidence of the increased Lya absorption surrounding LBGs which can mask the spike's presence when convolved with a realistic LBG velocity dispersion. Finally, we identify 176 CIV systems in the quasar spectra and find an LBG-CIV correlation strength on scales of 10 h^-1 Mpc consistent with the relation measured at ~Mpc scales.

astro-ph.CO↗

arXiv2007

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 3-sigma 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 (Jones et al.) 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 ISM, but have not be able to plausibly assign these transitions to any carrier.

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arXiv2005

A CH3CN and HCO+ survey towards southern methanol masers associated with star formation

We present the initial results of a 3-mm spectral line survey towards 83 methanol maser selected massive star-forming regions. Here we report observations of the J=5-4 and 6-5 rotational transitions of methyl cyanide (CH3CN) and the J=1-0 transition of HCO+and H13CO+. CH3CN emission is detected in 58 sources (70 %) of our sample). We estimate the temperature and column density for 37 of these using the rotational diagram method. The temperatures we derive range from 28-166 K, and are lower than previously reported temperatures, derived from higher J transitions. We find that CH3CN is brighter and more commonly detected towards ultra-compact HII (UCHII) regions than towards isolated maser sources. Detection of CH3CN towards isolated maser sources strongly suggests that these objects are internally heated and that CH3CN is excited prior to the UCHII phase of massive star-formation. HCO+ is detected towards 82 sources (99 % of our sample), many of which exhibit asymmetric line profiles compared to H13CO+. Skewed profiles are indicative of inward or outward motions, however, we find approximately equal numbers of red and blue-skewed profiles among all classes. Column densities are derived from an analysis of the HCO+ and H13CO+ line profiles. 80 sources have mid-infrared counterparts: 68 seen in emission and 12 seen in absorption as `dark clouds'. Seven of the twelve dark clouds exhibit asymmetric HCO+ profiles, six of which are skewed to the blue, indicating infalling motions. CH3CN is also common in dark clouds, where it has a 90 % detection rate.

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arXiv2004

D/H in a new Lyman limit quasar absorption system at z=3.256 towards PKS1937-1009

We have identified a new Lyman limit absorption system towards PKS1937-1009, with log N(HI)=18.25 +/- 0.02 at z=3.256. It is suitable for measuring D/H, and we find a 68.3% confidence range for D/H of 1.6^{+0.25}_{-0.30} \times 10^{-5}, and a 95.4% range of 1.6^{+0.5}_{-0.4} \times 10^{-5}. The metallicity of the cloud where D/H was measured is low, [Si/H] = -2.0 +/- 0.5. At these metallicities we expect that D/H will be close to the primordial value. Our D/H disagrees at a level of 99.4% with the predicted D/H using the baryon density calculated from the cosmic background radiation measured by WMAP, 2.60^{+0.19}_{-0.17} \times 10^{-5}. Our result also exacerbates the scatter in D/H values around the mean primordial D/H.

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