Monthly Notices of the Royal Astronomical Society

Published by Oxford University Press (OUP)
Online ISSN: 0035-8711
Publications
Article
High-resolution OH 1612-MHz spectra are presented of the supergiant OH–IR sources VY CMa, VX Sgr, IRC 10420 and NML Cyg. The spectra have a resolution of 300 Hz. Narrow components in the spectra have linewidths as small as 550 Hz (0.1 km s–1) but there is no evidence for components narrower than this. These results are in accord with present understanding of maser line-narrowing and of the physical conditions in the OH maser regions. Many of the narrow components have an appreciable degree of circular polarization which is not apparent at the lower frequency resolutions usually employed. The circular polarization indicates the presence of magnetic fields of $\sim{1}\text{mG}$ in the circumstellar envelopes, at distances of $\sim{3}\times {10}^{16}\text{cm}$ from the central stars. These fields are strong enough to influence the outflow from the stars, and may help to explain some of the asymmetries which are seen in their circumstellar envelopes.
 
Article
Based on laboratory work involving the ternary association reaction of HS+ and H2 at 80 K, we have estimated the rate of the analogous radiative association reaction under interstellar conditions. Both the ternary and radiative association reactions appear to occur via a mechanism in which the electronic spin of the H3S+ complex changes before the complex is stabilized. Although this spin change is of low probability, it leads to a radiative association rate coefficient at 80 K of $7\times10^{-16}\enspace \text {cm}^3 \enspace \text s^{-1}$ if radiative stabilization occurs at a rate of 103 s−1. This value of the radiative association rate coefficient at 80 K is large enough to lead to the observed abundance of H2S in the ambient ridge source in Orion.
 
Article
We describe an image analysis supervised learning algorithm that can automatically classify galaxy images. The algorithm is first trained using a manually classified images of elliptical, spiral, and edge-on galaxies. A large set of image features is extracted from each image, and the most informative features are selected using Fisher scores. Test images can then be classified using a simple Weighted Nearest Neighbor rule such that the Fisher scores are used as the feature weights. Experimental results show that galaxy images from Galaxy Zoo can be classified automatically to spiral, elliptical and edge-on galaxies with accuracy of ~90% compared to classifications carried out by the author. Full compilable source code of the algorithm is available for free download, and its general-purpose nature makes it suitable for other uses that involve automatic image analysis of celestial objects.
 
Integrated flux density of the OH 1612-(upper panel) and 1667-MHz (lower panel) spectra of OH127 as a function of time. The uncertainties of the measurements are comparable with the symbol sizes. The blue line shows the model light curve. The arrow marks the date of the MERLIN polarimetric observation.
Measured and derived parameters for OH127.8+0.0.
Mean and median values of the polarization parameters for the brightest OH features derived from the multi-epoch data.
Article
OH 1612- and 1667-MHz masers from the well-known object OH127.8+0.0 were monitored in full polarization mode over a period of 6.5 yr and mapped with MERLIN at one epoch. The OH variability pattern of the star is typical of extremely long-period asymptotic giant branch stars. The distance determined from the 1612-MHz light curve and a new measurement of the angular radius is 3.87 ± 0.28 kpc. At both frequencies, the flux of polarized emission tightly follows the total flux variations while, the degrees of circular and linear polarization are constant within measurement accuracy. There is net polarization at both lines. The magnetic field strength estimated from a likely Zeeman pair is −0.6 mG at the distance of 5400 au from the star. At the near and far sides of the envelope, the polarization vectors are well aligned implying a regular structure of the magnetic field. The polarization characteristics of the OH maser emission suggest a radial magnetic field which is frozen in the stellar wind.
 
Mass-loss rate as a function of time for the 7.5 M ⊙ Z=0.0001 with low-T fixed (red) and low-T variable (black) composition molecular opacities.
Temperature at the base of the convective envelope as a function of total stellar mass for the 7.5 M ⊙ Z=0.0001 models with VW93 mass-loss rate with fixed (red) and variable (black) molecular low temperature opacities.
Article
We present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z = 0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal-rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of 4He, 13C, 14N and 27Al as well as the heavy magnesium isotopes 25Mg and 26Mg. There is a transition in yield trends at metallicity Z ≈ 0.001, below which we find positive yields of 12C, 16O, 15N and 28Si, which is not the case for higher metallicities. We explore the large uncertainties derived from wind prescriptions in super-AGB stars, finding ≈2 orders of magnitude difference in yields of 22Ne, 23Na, 24, 25, 26Mg, 27Al and our s-process proxy isotope g. We find inclusion of variable composition low-temperature molecular opacities is only critical for super-AGB stars of metallicities below Z ≈ 0.001. We analyse our results, and those in the literature, to address the question: Are super-AGB stars the polluters responsible for extreme population in the globular cluster NGC 2808? Our results, as well as those from previous studies, seem unable to satisfactorily match the extreme population in this globular cluster.
 
Surface abundances (in logarithm of mole fraction Y) of selected isotopes as a function of time for the 8.5 M ⊙ Z=0.02 model. The time axis has been offset with the zero at the time of first thermal pulse.
Surface abundances of the number ratio C/O for our standard VW93 mass-loss rates cases. The horizontal dashed line represents the divide between M stars (O-rich) and the C stars (C-rich). The time axis has been offset with the zero at the time of first thermal pulse.
Mass-loss rate in M ⊙ yr −1 as a function of time during the thermally pulsing super AGB phase for the set of 8.5 M ⊙ Z=0.02 models.
26 Al surface abundance in log mole fraction Y as a function of time for the series of 8.5 M ⊙ Z=0.02 stellar model test cases.
Difference between standard yield production factors and those which include the effects of extrapolated pulses for VW93 (top panel) and VW-M (bottom panel) models. Colors and symbols as per Figure 4. The error bars on the 8.5 M ⊙ Z=0.02 model encompass the range of values found for the test cases.
Article
We have computed detailed evolution and nucleosynthesis models for super and massive asymptotic giant branch (AGB) stars over the mass range 6.5–9.0 M⊙ in divisions of 0.5 M⊙ with metallicities Z = 0.02, 0.008 and 0.004. These calculations, in which we find third dredge-up and hot bottom burning, fill the gap between existing low- and intermediate-mass AGB star models and high-mass star models that become supernovae. For the considered metallicities, the composition of the yields is largely dominated by the thermodynamic conditions at the base of the convective envelope rather than by the pollution arising from third dredge-up. We investigate the effects of various uncertainties, related to the mass-loss rate, mixing length parameter, and the treatment of evolution after the envelope instability that develops near the end of the (super)AGB phase. Varying these parameters alters the yields mainly because of their impact on the amount of third dredge-up enrichment, and to a lesser extent on the hot bottom burning conditions. Our models produce significant amounts of 4He, 7Li (depending on the mass-loss formulation) 13C, 14N, 17O, 23Na, 25Mg, as well the radioactive isotope 26Al in agreement with previous investigation. In addition, our results show enrichment of 22Ne, 26Mg and 60Fe, as well as a substantial increase in our proxy neutron capture species representing all species heavier than iron. These stars may provide important contributions to the Galaxy's inventory of the heavier Mg isotopes, 14N, 7Li and 27Al.
 
Article
We present an all-sky catalogue of 395 nearby galaxy groups revealed in the Local Supercluster and its surroundings. The groups and their associations are identified among 10 914 galaxies at |b| > 15° with radial velocities VLG < 3500 km s−1. Our group-finding algorithm requires the group members to be located inside their zero-velocity surface. Hereby, we assume that individual galaxy masses are proportional to their total K-band luminosities, M/LK= 6 M⊙/L⊙. The sample of our groups, where each group has n≥ 4 members, is characterized by the following medians: mean projected radius 〈R〉= 268 kpc, radial velocity dispersion σV= 74 km s−1, K-band luminosity LK= 1.2 × 1011 L⊙, virial and projected masses Mvir= 2.4 × 1012 and Mp= 3.3 × 1012 M⊙, respectively. Accounting for measurement error reduces the median masses by 30 per cent. For 97 per cent of identified groups the crossing time does not exceed the cosmic time, 13.7 Gyr, with the median at 3.8 Gyr. We examine different properties of the groups, in particular of the known nearby groups and clusters in Virgo and Fornax. About a quarter of our groups can be classified as fossil groups where the dominant galaxy is at least 10 times brighter than the other group members. In total, our algorithm identifies 54 per cent of galaxies to be members of groups. Together with triple systems and pairs they gather 82 per cent of the K-band light in the local Universe. We have obtained the local value of matter density to be Ωm= 0.08 ± 0.02 within a distance of ∼40 Mpc assuming H0= 73 km s−1 Mpc−1. It is significantly smaller than the cosmic value, 0.28, in the standard ΛCDM model. The discrepancy between the global and local quantities of Ωm may be caused by the existence of a dark matter component unrelated to the virial masses of the galaxy systems.
 
Article
Deep measurements are presented of four rich clusters of galaxies: Abell 1367 (z=0.022), Abell 2199 (z=0.030), Abell 1795 (z=0.063), and Abell 1146 (z=0.141). All clusters have an excess of galaxies at faint magnitudes above blank sky fields. We correct for background contamination and measure the luminosity function of these galaxies in each cluster, and then combine these luminosity functions to get better statistics. The resultant combined luminosity function is rising at faint magnitudes, with a logarithmic slope -1.5 < \alpha < -1.2 for -18 < M_B < -13 and -19 < M_R < -15. This is similar to what has been observed independently in the Coma cluster. The colours of these faint galaxies suggest that they are dwarf spheroidals.
 
Article
We report the discovery of quasi-periodic oscillations (QPOs) at 0.02 Hz in a transient high-mass X-ray binary pulsar KS 1947+300 using the RXTE Proportional Counter Array (PCA). The QPOs were detected during 2001 May–June, at the end of a long outburst. This is the ninth transient accretion-powered high magnetic field X-ray pulsar in which QPOs have been detected, and the QPO frequency of this source is lowest in this class of sources. The unusual feature of this source is that though the outburst lasted for more than 100 days, the QPOs were detected only during the last few days of the outburst when the X-ray intensity had decayed to 1.6 per cent of the peak intensity. The rms value of the QPO is large, ∼15.4 ± 1.0 per cent with a slight positive correlation with energy. The detection of QPOs and strong pulsations at a low luminosity level suggests that the magnetic field strength of the neutron star is not as high as was predicted earlier on the basis of a correlation between the spin-up torque and the X-ray luminosity.
 
Article
We present a new grid of ionizing fluxes for O and Wolf—Rayet (W—R) stars for use with evolutionary synthesis codes and single-star H ii region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z⊙) using the wm-basic code of Pauldrach, Hoffmann & Lennon for O stars and the cmfgen code of Hillier & Miller for W—R stars. The stellar wind parameters are scaled with metallicity for both O and W—R stars. We compare the ionizing fluxes of the new models with the CoStar models of Schaerer & de Koter and the pure helium W—R models of Schmutz, Leitherer & Gruenwald. We find significant differences, particularly above 54 eV, where the emergent flux is determined by the wind density as a function of metallicity. The new models have lower ionizing fluxes in the He i continuum with important implications for nebular line ratios. We incorporate the new models into the evolutionary synthesis code starburst99 and compare the ionizing outputs for an instantaneous burst and continuous star formation with the work of Schaerer & Vacca (SV98), and Leitherer et al. The changes in the output ionizing fluxes as a function of age are dramatic. We find that, in contrast to previous studies, nebular He iiλ4686 will be at, or just below, the detection limit in low metallicity starbursts during the W—R phase. The new models have lower fluxes in the He i continuum for Z≥ 0.4 Z⊙ and ages ≤7 Myr because of the increased line blanketing. We test the accuracy of the new model atmosphere grid by constructing photoionization models for simple H ii regions, and assessing the impact of the new ionizing fluxes on important nebular diagnostic line ratios. For the case of an H ii region where the ionizing flux is given by the WM-basic dwarf O star grid, we show that He iλ5786/Hβ decreases between 1 and 2 Z⊙ in a similar manner to observations. We find that this decline is caused by the increased effect of line blanketing above solar metallicity. We therefore suggest that a lowering of the upper mass limit at high abundances is not required to explain the diminishing strength of He iλ5786/Hβ, as has been suggested in the past. For an H ii region where the ionizing flux is provided by an instantaneous burst of total mass 10⁶ M⊙, we plot the softness parameter η′ against the abundance indicator R23 for ages of 1–5 Myr. The new models are coincident with the observational data of Bresolin et al., particularly during the W—R phase, unlike the previous models of SV98 which generally over-predict the hardness of the ionizing radiation. The new model grid and updated starburst99 code can be downloaded from http://www.star.ucl.ac.uk/starburst.
 
Article
We determine the low-redshift field galaxy stellar mass function (GSMF) using an area of 143 deg2 from the first three years of the Galaxy And Mass Assembly (GAMA) survey. The magnitude limits of this redshift survey are r < 19.4 mag over two-thirds and 19.8 mag over one-third of the area. The GSMF is determined from a sample of 5210 galaxies using a density-corrected maximum volume method. This efficiently overcomes the issue of fluctuations in the number density versus redshift. With H0= 70 km s−1 Mpc−1, the GSMF is well described between 108 and 1011.5 M⊙ using a double Schechter function with , , α1=−0.35, and α2=−1.47. This result is more robust to uncertainties in the flow-model corrected redshifts than from the shallower Sloan Digital Sky Survey main sample (r < 17.8 mag). The upturn in the GSMF is also seen directly in the i-band and K-band galaxy luminosity functions. Accurately measuring the GSMF below 108 M⊙ is possible within the GAMA survey volume but as expected requires deeper imaging data to address the contribution from low surface-brightness galaxies.
 
Scatter plot showing the colour-magnitude (CM) distribution of galaxies in the SubS (blue circles) and OptS (black- grey circles). The division between Red Sequence and Blue Cloud defined in the text is shown as the black solid line. 
Article
We present two large, nearby (0.013$\le$z$\le$0.06) samples of Early-Type Galaxies (ETGs): a visually classified sample of 220 ETGs, created using source-matched data from the Galaxy and Mass Assembly (GAMA) database with FIR/sub-mm detections from $Herschel$-ATLAS; and a visually classified sample of 551 ETGs which are undetected with $Herschel$-ATLAS. Active galactic nuclei (AGN) are removed from our samples using optical emission line diagnostics. These samples are scrutinised to determine characteristics of sub-mm detected versus undetected ETGs. We find similarities in the stellar mass distributions of the two ETG samples but testing other properties uncovers significant differences. The sub-mm detected sample is shown to have lower concentration and S\'ersic indices than those in the undetected sample - a result which may be linked to the presence of dust in the former. Optical and UV-optical colours are also shown to be much bluer, indicating that the dust is linked with recent star formation. The intrinsic effective radii are on average 1.5 times larger for the sub-mm detected ETGs. Surface densities and groups data from the GAMA database are examined for the two samples, leading to the conclusion that dusty ETGs inhabit sparser environments than non-dusty ETGs in the nearby universe, although environments of the brightest ETGs are shown to differ the least. Modified Planck functions are fit to the H-ATLAS detected PACS and SPIRE fluxes for ETGs with sub-mm flux densities of at least 3$\sigma$ in the 350$\mu$m SPIRE band, giving a resultant mean cold dust temperature of T$_{d}$=22.1K, with a range of 9-30K. The corresponding mean dust mass is 1.8$\times10^{7}$M$_{\odot}$, with a range of (0.08-35.0)$\times10^{7}$M$_{\odot}$. The dust masses calculated from these fits, normalised by stellar mass, are shown to increase with decreasing stellar mass and bluer colours.
 
Article
We consider the physical conditions and origin of the z= 0.0777 absorption system observed in C iii, C ii, Si iii, C iv, O vi and H i absorption along the line of sight towards the quasar PHL 1811. We analysed the Hubble Space Telescope/Space Telescope Imaging Spectrograph and Far Ultraviolet Spectroscopic Explorer spectra of this quasar and compared the results to cloudy photoionization and collisional ionization models in order to derive densities, temperatures and metallicities of the absorbing gas. The absorption can be explained by two C iii clouds, offset by 35 km s−1 in velocity, with metallicities of approximately one-tenth the solar value. One cloud has a density of the order of nH= 1.2+0.9−0.5× 10−3 cm−3 (thickness 0.4+0.3−0.2 kpc) and produces the observed C ii and Si iii absorption, while the other has a density of the order of nH= 1.2+0.9−0.5× 10−5 cm−3 (thickness 80+70−40 kpc) and gives rise to the observed weak C iv absorption. Cloud temperatures are ∼14 000+3000−2000 K and ∼34 000+2000−4000 K for photoionized models. Although collisionally ionized clouds with T∼ 70 000 K are possible, they are less likely because of the short cooling time-scales involved. Previous studies revealed no luminous galaxy at the absorber's redshift, so it is probably related to tidal debris, ejected material, a dwarf galaxy or other halo material in a galaxy group. Our models also indicate that one of the two clouds would produce detectable weak Mg ii absorption if spectral coverage of that transition existed. We predict what the system would look like at z∼ 1 when the ionizing background radiation was more intense. We find that at z∼ 1 the denser component resembles a C iv absorber. The second C iii cloud in this z= 0.0777 absorber may be analogous to a subset of the more diffuse O vi absorbers at higher redshift.
 
Article
We present a detailed study of the QSO–galaxy pair [SDSS J163956.35+112758.7 (zq = 0.993) and SDSS J163956.38+112802.1 (zg = 0.079)] based on observations carried out using the Giant Metrewave Radio Telescope (GMRT), the Very Large Baseline Array (VLBA), the Sloan Digital Sky Survey and the ESO New Technology Telescope. We show that the interstellar medium of the galaxy probed by the QSO line of sight has near-solar metallicity [12+log(O/H) = 8.47 ± 0.25] and dust extinction [E(B − V) ∼ 0.83 ± 0.11] typical of what is usually seen in translucent clouds. We report the detection of absorption in the λ6284 diffuse interstellar band (DIB) with a rest equivalent width of 1.45 ± 0.20 Å. Our GMRT spectrum shows a strong 21-cm absorption at the redshift of the galaxy with an integrated optical depth of 15.70 ± 0.13 km s−1. Follow-up VLBA observations show that the background radio source is resolved into three components with a maximum projected separation of 89 pc at the redshift of the galaxy. One of these components is too weak to provide useful 21-cm H i information. The integrated H i optical depth towards the other two components are higher than that measured in our GMRT spectrum and differ by a factor 2. By comparing the GMRT and VLBA spectra we show the presence of structures in the 21-cm optical depth on parsec scales. We discuss the implications of such structures for the spin-temperature measurements in high-z damped Lyman α systems. The analysis presented here suggests that this QSO–galaxy pair is an ideal target for studying the DIBs and molecular species using future observations in optical and radio wavebands.
 
Article
We present the first detailed analysis of the mass and dynamical structure of a sample of six early-type lens galaxies, selected from the Sloan Lens ACS Survey, in the redshift range 0.08 < z < 0.33. Both Hubble Space Telescope (HST)/ACS high-resolution imaging and VLT VIMOS integral field spectroscopy are available for these systems. The galaxies are modelled - under the assumptions of axial symmetry and two-integral stellar distribution function - by making use of the CAULDRON code, which self-consistently combines gravitational lensing and stellar dynamics, and is fully embedded within the framework of Bayesian statistics. The principal results of this study are: (i) all galaxies in the sample are well described by a simple axisymmetric power-law profile for the total density, with a logarithmic slope gamma very close to isothermal ( = 1.98 +/- 0.05 and an intrinsic spread close to 5 per cent) showing no evidence of evolution over the probed range of redshift; (ii) the axial ratio of the total density distribution is rounder than 0.65 and in all cases, except for a fast rotator, does not deviate significantly from the flattening of the intrinsic stellar distribution; (iii) the dark matter fraction within the effective radius has a lower limit of about 15 to 30 per cent; (iv) the sample galaxies are only mildly anisotropic, with delta <= 0.16; (v) the physical distinction among slow and fast rotators, quantified by the v/sigma ratio and the intrinsic angular momentum, is already present at z > 0.1. Altogether, early-type galaxies at z = 0.08 - 0.33 are found to be markedly smooth and almost isothermal systems, structurally and dynamically very similar to their nearby counterparts. (Abridged)
 
The spectral region containing Hα and the [N II] doublet. All three lines are consistent with the being unresolved at the instrumental FWHM. The relative strength of the doublet lines is consistent with that predicted from the electron transition probabilities. 
A comparison of the Balmer series emission lines in the GRB host galaxy, scaled by the appropriate line ratios for Case B H I recombination (T=10 4 K, low density, Osterbrock & Ferland 2006), such that in the absence of dust, all peaks would be expected to match Hβ in intensity. The line intensities are offset from zero for clarity. Even accounting for blending with the [N II] doublet, Hα still shows a relative excess, consistent with the blue-wards lines being attenuated by a dusty line of sight. 
Article
We present an analysis of the photometry and spectroscopy of the host galaxy of Swift-detected GRB 080517. From our optical spectroscopy, we identify a redshift of z = 0.089 ± 0.003, based on strong emission lines, making this a rare example of a very local, low-luminosity, long gamma-ray burst. The galaxy is detected in the radio with a flux density of S4.5 GHz = 0.22 ± 0.04 mJy – one of relatively few known gamma-ray bursts hosts with a securely measured radio flux. Both optical emission lines and a strong detection at 22 μm suggest that the host galaxy is forming stars rapidly, with an inferred star formation rate ∼16 M⊙ yr−1 and a high dust obscuration (E(B − V) > 1, based on sightlines to the nebular emission regions). The presence of a companion galaxy within a projected distance of 25 kpc, and almost identical in redshift, suggests that star formation may have been triggered by galaxy–galaxy interaction. However, fitting of the remarkably flat spectral energy distribution from the ultraviolet through to the infrared suggests that an older, 500 Myr post-starburst stellar population is present along with the ongoing star formation. We conclude that the host galaxy of GRB 080517 is a valuable addition to the still very small sample of well-studied local gamma-ray burst hosts.
 
Results of single component curve of growth analysis. The best fitted curve for the absorption from J = 2 and J = 3 levels are shown overlayed with data points. The ordinate errors are based on the measured equivalent width errors and the abscissa errors are due to column density errors from our COG analysis.
R-band image covering 1’ × 1’ centered around the QSO. The QSO and 5 galaxies close to the QSO in the angular scale are marked. Only galaxy G1 has the photometric redshift consistent with the z abs of the DLA. 
Article
We report the detection of H2 in a zabs = 0.0963 Damped Lyman α (DLA) system towards zem = 0.4716 QSO J1619+3342. This DLA has log N(H i) = 20.55 ± 0.10, 18.13 ≤ log N(H2) ≤ 18.40, [S/H] = −0.62 ± 0.13, [Fe/S] = −1.00 ± 0.17 and the molecular fraction − 2.11 ≤ log[f(H2)] ≤ −1.85. The inferred gas kinetic temperature using the rotational level population is in the range 95-132 K. We do not detect C i or C ii* absorption from this system. Using R- and V-band deep images, we identify a sub-L* galaxy at an impact parameter of 14 kpc from the line of sight, having consistent photometric redshift, as a possible host for the absorber. We use the photoionization code cloudy to get the physical conditions in the H2 component using the observational constrains from H2, C i, C ii* and Mg i. All the observations can be consistently explained if one or more of the following is true: (i) carbon is underabundant by more than 0.6 dex as seen in halo stars with Z ∼ 0.1 Z⊙, (ii) H i associated with H2 component is less than 50 per cent of the H i measured along the line of sight and (iii) the H2 formation rate on the dust grains is at least a factor of 2 higher than what is typically used in analytic calculations for Milky Way interstellar medium. Even when these are satisfied, the gas kinetic temperature in the models is much lower than what is inferred from the ortho-to-para ratio of the molecular hydrogen. Alternatively, the high kinetic temperature could be a consequence of contribution to the gas heating from non-radiative heating processes seen in hydrodynamical simulations.
 
Suzaku XIS1 image of CTB 37A in the 0.3–10 keV energy band. The spectral integration regions for the source (annular apertures) and the background are indicated by the solid blue and dashed black circles, respectively. The solid red circle represents the X-ray source (CXOU J171419.8–383023). The corner of the CCD chip illuminated by the 55Fe calibration source is excluded from the image as shown by the dashed red circle. The coordinates (RA and Dec.) refer to epoch J2000.
CTB 37A is displayed in the 0.3–10 keV energy band, with X-ray data obtained from the Suzaku XIS0 detector. The image is overlaid by 843-MHz radio isocontours logarithmically scaled (0.23, 0.36, 0.57, 0.90, 1.42, 2.23 and 3.51 mJy beam−1). Radio emission clearly shows two radio SNRs, CTB 37A and G348.5–0.0. The X-ray data are smoothed with a three-pixel Gaussian in order to highlight the structure. The colour coding shows the brightness levels from 1.3 counts pix−1 to 13.36 counts pix−1 in logarithmic scale from yellow to black. The masers from the field are indicated with blue and white crosses at velocities ∼−65 and ∼−22 km s−1, respectively. The diamond shows the extended non-thermal X-ray source CXOU J171419.8–383023. The location of HESS J1714–385 is represented by the circle, in which the positional error is specified with the radius of 1.2 arcmin. The coordinates (RA and Dec.) refer to epoch J2000.
Background-subtracted XIS spectra of CTB 37A in the 0.3–10 keV energy band fitted with an absorbed VMEKAL and PL model. XIS1, XIS0 and XIS3 are shown in red, black and green, respectively. The bottom panel shows the residuals from the best-fitting model.
The radial variation of the electron temperature of CTB 37A.
Article
We present here the results of the observation of CTB 37A obtained with the X-ray Imaging Spectrometer onboard the {\it Suzaku} satellite. The X-ray spectrum of CTB 37A is well fitted by two components, a single-temperature ionization equilibrium component (VMEKAL) with solar abundances, an electron temperature of $kT_{\rm e}\sim0.6$ keV, absorbing column density of $N_{\rm H}\sim3\times10^{22}$ ${\rm cm^{-2}}$ and a power-law component with photon index of $\Gamma$ $\sim 1.6$. The X-ray spectrum of CTB 37A is characterized by clearly detected K-shell emission lines of Mg, Si, S, and Ar. The plasma with solar abundances supports the idea that the X-ray emission originates from the shocked interstellar material. The ambient gas density, and age of the remnant are estimated to be $\sim1f^{-1/2}$${\rm cm^{-3}}$ and $\sim3\times10^{4}f^{1/2}$ yr, respectively. The center-filling X-ray emission surrounded by a shell-like radio structure and other X-ray properties indicate that this remnant would be a new member of mixed-morphology supernova remnant class.
 
Article
In this paper, we present the analysis of a deep (99.6 ks) observation of G304.6+0.1 with the X-ray Imaging Spectrometer on board the Suzaku satellite. The X-ray spectral data are well fitted with a plasma model consisting of a thermal component, in collisional ionization equilibrium, and a non-thermal component. The thermal emission is well fitted with the vmekal model with an electron temperature of kTe∼ 0.75 keV, a high absorbing column density of NH∼ 3.9 × 1022 cm−2 and near/lower solar abundances, which indicate that the X-ray emitting plasma of G304.6+0.1 is dominated by a swept-up ambient medium. The non-thermal component is well fitted with a power-law model with a photon index of Γ∼ 1.4. We have found a relatively high electron density ne∼ 2.3f−1/2 cm−3, an age t∼ 1.4 × 104f1/2 yr and an X-ray emitting mass Mx∼ 380f1/2 M⊙ at an adopted distance of d= 10 kpc. Using the morphological and spectral X-ray data, we confirm that the remnant is a new member of the mixed-morphology supernova remnants.
 
Article
Most of the baryons in the Universe are thought to be contained within filaments of galaxies, but as yet, no single study has published the observed properties of a large sample of known filaments to determine typical physical characteristics such as temperature and electron density. This paper presents a comprehensive large-scale search conducted for X-ray emission from a population of 41 bona fide filaments of galaxies to determine their X-ray flux and electron density. The sample is generated from the filament catalogue of Pimbblet et al., which is in turn sourced from the two-degree Field Galaxy Redshift Survey (2dFGRS). Since the filaments are expected to be very faint and of very low density, we used stacked ROSAT All-Sky Survey data. We detect a net surface brightness from our sample of filaments of (1.6 ± 0.1) × 10−14 erg cm−2 s−1 arcmin−2 in the 0.9–1.3 keV energy band for 1-keV plasma, which implies an electron density of ne= (4.7 ± 0.2) × 10−4 h1/2100 cm−3. Finally, we examine if a filament’s membership to a supercluster leads to an enhanced electron density as reported by Kull & Böhringer. We suggest it remains unclear if supercluster membership causes such an enhancement.
 
The three BPT diagrams showing the selection criteria defined by Kewley et al. (2006) used to classify the emission-line galaxies as: Seyfert (black dots) and LINER (grey crosses) AGN. The solid lines separate the star-forming galaxies from the AGN and the dashed lines represent the Seyfert-LINER demarcation. 
Normalized distributions of matched system properties for: Seyfert-HR (black solid lines), Seyfert-LR (grey solid lines) and their respective control samples, Control-HR galaxies (black dashed lines) and Control-LR galaxies (grey dotted lines). 
Top: Total stellar mass (per bin) of the blue neighbouring galaxies around the target samples as a function of galaxy density within 1h −1 Mpc. Bottom: Total stellar mass (per bin) of the red neighbouring galaxies.
Local number density of galaxies, within rp = 1h −1 Mpc, as a function of stellar mass, M * , of the targets.
Article
We analyse different properties of the small scale environment of Seyfert 2 for two samples selected according to the accretion rate parameter, R, from the DR7-SDSS survey. We compare the results with two control samples of non-active galaxies that cover the same redshift range, luminosity, colours, morphology, age and stellar mass content. Our study shows that both high and low accretion rate subsamples reside in bluer and lower density environments than the control samples. However, we find that this difference is at least two times stronger for the low accretion rate Seyferts. In the vicinity of Seyfert 2, red galaxies have systematically lower values of stellar-mass as compared with corresponding control samples. The lower values of stellar mass for red neighbours is more significant at higher density environments and it is more evident for low accretion rate Seyfert. We also find that this effect is independent of the host's stellar mass. Our results are consistent with a scenario where AGN occurrence is higher in lower/medium density environments with a higher merger rate and a lack of a dense intergalactic medium (that can strip gas from these systems) that provide suitable conditions for the central black hole feeding. We find this particularly evident for the low accretion rate Seyferts that could compensate through the intergalactic medium the lack of gas of their hosts.
 
Article
Using a method to discover and classify supernovae (SNe) in galaxy spectra, we find 90 Type Ia SNe (SNe Ia) and 10 Type II SNe among the ∼700 000 galaxy spectra in the Sloan Digital Sky Survey Data Release 7 that have star-formation histories (SFHs) derived with the VErsatile SPectral Analysis code (vespa). We use the SN Ia sample to measure SN Ia rates per unit stellar mass. We confirm, at the median redshift of the sample, z = 0.1, the inverse dependence on galaxy mass of the SN Ia rate per unit mass, previously reported by Li et al. for a local sample. We further confirm, following Kistler et al., that this relation can be explained by the combination of galaxy ‘downsizing’ and a power-law delay-time distribution (DTD; the distribution of times that elapse between a hypothetical burst of star formation and the subsequent SN Ia explosions) with an index of −1, inherent to the double-degenerate progenitor scenario. We use the method of Maoz et al. to recover the DTD by comparing the number of SNe Ia hosted by each galaxy in our sample with the vespa-derived SFH of the stellar population within the spectral aperture. In this galaxy sample, which is dominated by old and massive galaxies, we recover a ‘delayed’ component to the DTD of 4.5 ± 0.6 (statistical) ${_{-0.5}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!^{\rm +0.3}}$ (systematic) × 10− 14 SNe M⊙− 1 yr− 1 for delays in the range >2.4 Gyr. The mass-normalized SN Ia rate, averaged over all masses and redshifts in our galaxy sample, is $R_{{\rm Ia,M}}(z=0.1) = 0.10 \pm 0.01\ (\rm statistical) \pm 0.01\ (\rm systematic)\ {\rm SNuM}$, and the volumetric rate is RIa, V(z = 0.1) = 0.247 ${_{-0.026}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!^{\rm +0.029}}$ (statistical) ${_{-0.031}\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!^{\rm +0.016}}$ (systematic) × 10− 4 SNe yr− 1 Mpc− 3. This rate is consistent with the rates and rate evolution from other recent SN Ia surveys, which together also indicate a ∼t−1 DTD.
 
Rest-frame g − r colour-stellar mass diagrams for eagle galaxies using photometry and dust reddening from model GD+O at z = 0 . 1 for simulation Ref-100 ( left panel ), and a composite set of eagle galaxies obtained by combining the higher-resolution model Recal-25 for galaxies with M 10 9 M and Ref-100 for M > 10 9 M ( right panel ), cross-fading the sampling probability of the two galaxy populations linearly in log 10 ( M / M ) (see text for details). Colours represent the point density of eagle galaxies of given M and g − r colour (see text for details), with black points representing individual outlying eagle galaxies. Contours represent the colour- M distribution for a volume-limited set of gama galaxies from Taylor et al. (2014), with grey points representing individual outlying galaxies. The masses of observed galaxies are obtained through SED fitting, see Taylor et al. (2014). The colours are mapped to their equivalent contours in the colour bar. The colour bar covers 2 dex in point density with a contour spacing of 0.28 dex. A lack of numerical resolution makes lower-mass eagle galaxies too red in the left panel. The transition of colours of observed galaxies, from the red-sequence at stellar masses above M ∼ 10 10 . 5 M to the blue cloud at lower stellar masses, is reproduced in the simulation, although the blue cloud extends to slightly higher M . 
Rest-frame g − r colour as a function of r -band absolute magnitude for eagle galaxies (colours) compared to a volume- limited sample of gama galaxies (Taylor et al. 2014, contour lines). contours and point shading is the same as in Fig 2. eagle photometry is obtained using the GD+O model. A composite eagle galaxy population is used, consisting of galaxies from Ref-100 at M > 10 9 M and Recal-25 at M < 10 9 M as in 
Figure C1. g − r colour distributions for eagle galaxies for the dust-free model. The 4 panels show colour distributions for 4 bins of stellar mass, as indicated by the legend. The solid, dotted and dashed lines show the eagle SSP values and the eagle SSP values with Gallazzi et al. (2005) metallicities and ages respectively. Gallazzi metallicities and ages are assigned to each galaxy, based on the median parameter values at the galactic stellar mass. Z values are simply taken as the observed median value. The LWA values are sampled from a normal distribution with standard deviation taken from Gallazzi et. al. (2005), assuming that the scatter in age and metallicity is uncorrelated. We see that the complex star formation histories of eagle provide a better match to the observed colour distributions than a single SSP model using empirical values for age and metallicity.
Article
We calculate the colours and luminosities of redshift z = 0.1 galaxies from the EAGLE simulation suite using the GALAXEV population synthesis models. We take into account obscuration by dust in birth clouds and diffuse ISM using a two-component screen model, following the prescription of Charlot and Fall. We compare models in which the dust optical depth is constant to models where it depends on gas metallicity, gas fraction and orientation. The colours of EAGLE galaxies for the more sophisticated models are in broad agreement with those of observed galaxies. In particular, EAGLE produces a red sequence of passive galaxies and a blue cloud of star forming galaxies, with approximately the correct fraction of galaxies in each population and with g-r colours within 0.1 magnitudes of those observed. Luminosity functions from UV to NIR wavelengths differ from observations at a level comparable to systematic shifts resulting from a choice between Petrosian and Kron photometric apertures. Despite the generally good agreement there are clear discrepancies with observations. The blue cloud of EAGLE galaxies extends to somewhat higher luminosities than in the data, consistent with the modest underestimate of the passive fraction in massive EAGLE galaxies. There is also a moderate excess of bright blue galaxies compared to observations. The overall level of agreement with the observed colour distribution suggests that EAGLE galaxies at z = 0.1 have ages, metallicities and levels of obscuration that are comparable to those of observed galaxies.
 
Article
We combine in a self-consistent way the constraints from both gravitational lensing and stellar kinematics to perform a detailed investigation of the internal mass distribution, amount of dark matter, and dynamical structure of the 16 early-type lens galaxies from the SLACS Survey, at z = 0.08 - 0.33, for which both HST/ACS and NICMOS high-resolution imaging and VLT VIMOS IFU spectroscopy are available. Based on this data set, we analyze the inner regions of the galaxies, i.e. typically within one (3D) effective radius r_e, under the assumption of axial symmetry and by constructing dynamical models supported by two-integral stellar DFs. For all systems, the total mass density distribution is found to be well approximated by a simple power-law: this profile is on average slightly super-isothermal, with a logarithmic slope <gamma'> = 2.074^{+0.043}_{-0.041} (68% CL) and an intrinsic scatter 0.144^{+0.055}_{-0.014}, and is fairly round, with an average axial ratio = 0.77+/-0.04. The lower limit for the dark matter fraction (fDM) inside r_e ranges, in individual systems, from nearly zero to almost a half, with a median value of 12%. By including stellar masses derived from SPS models with a Salpeter IMF, we obtain an average fDM = 31%. The fDM rises to 61% if, instead, a Chabrier IMF is assumed. For both IMFs, the dark matter fraction increases with the total mass of the galaxy (3-sigma correlation). Based on the intrinsic angular momentum parameter calculated from our models, we find that the galaxies can be divided into two dynamically distinct groups, which are shown to correspond to the usual classes of the slow and fast rotators. Overall, the SLACS systems are structurally and dynamically very similar to their nearby counterparts, indicating that the inner regions of early-type galaxies have undergone little, if any, evolution since redshift z ~ 0.35. (Abridged)
 
Article
We present the results from our 21-cm absorption survey of a sample of five quasar–galaxy pairs (QGPs), with the redshift of the galaxies in the range 0.03 ≤zg≤ 0.18, selected from the Sloan Digital Sky Survey (SDSS). The H i 21-cm absorption was searched towards the nine sightlines with impact parameters ranging from ∼10 to ∼55 kpc using the Giant Metrewave Radio Telescope (GMRT). 21-cm absorption was detected only in one case, i.e. towards the quasar (zq= 2.625 SDSS J124157.54+633241.6)–galaxy (zg= 0.143 SDSS J124157.26+633237.6) pair with the impact parameter ∼11 kpc. The quasar sightline in this case pierces through the stellar disc of a galaxy having near solar metallicity [i.e. (O/H)+12 = 8.7] and star formation rate uncorrected for dust attenuation of 0.1 M⊙ yr−1. The quasar spectrum reddened by the foreground galaxy is well fitted with the Milky Way extinction curve (with an AV of 0.44) and the estimated H i column density is similar to the value obtained from 21-cm absorption assuming a spin temperature (TS) of 100 K. In the remaining cases, our GMRT spectra provide upper limit on N(H i) in the range (1017–1018) ×TS cm−2. Combining our sample with the z≤ 0.1 data available in the literature, we find the detectability of 21-cm absorption with integrated optical depth greater than 0.1 km s−1 to be 50 per cent for the impact parameter less than 20 kpc. Using the surface brightness profiles and a well-established relationship between the optical size and extent of the H i disc known for nearby galaxies, we conclude that in most of the cases of 21-cm absorption non-detection, the sightlines may not be passing through the H i gas (1σ column density of a few times 1019 cm−2). We also find that in comparison to the absorption systems associated with these QGPs, z < 1 damped Lyman-α absorbers (DLAs) with 21-cm absorption detections have lower Ca ii equivalent widths despite having higher 21-cm optical depths and smaller impact parameters. This suggests that the current sample of DLAs may be a biased population that avoids sightlines through dusty star-forming galaxies. A systematic survey of QGPs over a wider redshift range using a large sample is needed to confirm these findings and understand the nature of 21-cm absorbers.
 
Article
We use data from the Galaxy And Mass Assembly (GAMA) survey in the redshift range 0.01 < z < 0.1 (8399 galaxies in g to Ks bands) to derive the stellar mass–half-light radius relations for various divisions of ‘early’- and ‘late’-type samples. We find that the choice of division between early and late (i.e. colour, shape, morphology) is not particularly critical; however, the adopted mass limits and sample selections (i.e. the careful rejection of outliers and use of robust fitting methods) are important. In particular, we note that for samples extending to low stellar mass limits (${<}10^{10}\mathcal {M_{\odot }}$) the Sérsic index bimodality, evident for high-mass systems, becomes less distinct and no-longer acts as a reliable separator of early- and late-type systems. The final set of stellar mass–half-light radius relations are reported for a variety of galaxy population subsets in 10 bands (ugrizZY JHKs) and are intended to provide a comprehensive low-z benchmark for the many ongoing high-z studies. Exploring the variation of the stellar mass–half-light radius relations with wavelength, we confirm earlier findings that galaxies appear more compact at longer wavelengths albeit at a smaller level than previously noted: at $10^{10}\mathcal {M_{\odot }}$ both spiral systems and ellipticals show a decrease in size of 13 per cent from g to Ks (which is near linear in log wavelength). Finally, we note that the sizes used in this work are derived from 2D Sérsic light profile fitting (using galfit3), i.e. elliptical semimajor half-light radii, improving on earlier low-z benchmarks based on circular apertures.
 
The pointing centre and the primary beam size of the WSRT are overlaid on a SDSS image of CNOC2 0920+37. The solid line and the broken line indicate the HPBW of the primary beam ( ∼ 36 ′ ) and 10 per cent level of the primary beam ( ∼ 1.0 ◦ in diameter), respectively. The blue and red circles indicate 
The radio continuum image of the CNOC2 0920+37 field at z ∼ 0.1 without applying primary beam correction. This image shows ∼ 1.4 deg 2 of 
Article
We measure the neutral atomic hydrogen (H i) gas content of field galaxies at intermediate redshifts of z ∼ 0.1 and ∼0.2 using hydrogen 21-cm emission lines observed with the Westerbork Synthesis Radio Telescope. In order to make high signal-to-noise ratio detections, an H i signal stacking technique is applied: H i emission spectra from multiple galaxies, optically selected by the second Canadian Network for Observational Cosmology redshift survey project, are co-added to measure the average H i mass of galaxies in the two redshift bins. We calculate the cosmic H i gas densities (ΩHi) at the two redshift regimes and compare those with measurements at other redshifts to investigate the global evolution of the H i gas density over cosmic time. From a total of 59 galaxies at z ∼ 0.1 we find ΩHi = (0.33 ± 0.05) × 10−3, and at z ∼ 0.2 we find ΩHi = (0.34 ± 0.09) × 10−3, based on 96 galaxies. These measurements help bridge the gap between high-z damped Lyman α observations and blind 21-cm surveys at z = 0. We find that our measurements of ΩHi at z ∼ 0.1 and ∼0.2 are consistent with the H i gas density at z ∼ 0 and that all measurements of ΩHi from 21-cm emission observations at z ≲ 0.2 are in agreement with no evolution of the H i gas content in galaxies during the last 2.4 Gyr.
 
Article
We present galaxy cluster mass–richness relations found in the Sloan Digital Sky Survey Stripe 82 co-add using clusters found using a Voronoi tessellation cluster finder. These relations were found using stacked weak lensing shear observed in a large sample of galaxy clusters. These mass–richness relations are presented for four redshift bins, 0.1 < z ≤ 0.4, 0.4 < z ≤ 0.7, 0.7 < z ≤ 1.0 and 0.1 < z ≤ 1.0. We describe the sample of galaxy clusters and explain how these clusters were found using a Voronoi tessellation cluster finder. We fit a Navarro-Frenk-White profile to the stacked weak lensing shear signal in redshift and richness bins in order to measure virial mass (M200). We describe several effects that can bias weak lensing measurements, including photometric redshift bias, the effect of the central BCG, halo miscentering, photometric redshift uncertainty and foreground galaxy contamination. We present mass–richness relations using richness measure NVT with each of these effects considered separately as well as considered altogether. We also examine redshift evolution of the mass–richness relation. As a result, we present measurements of the mass coefficient (M200|20) and the power-law slope (α) for power-law fits to the mass and richness values in each of the redshift bins. We find values of the mass coefficient of 8.49 ± 0.526, 14.1 ± 1.78, 30.2 ± 8.74 and 9.23 ± 0.525 × 1013 h−1 M⊙ for each of the four redshift bins, respectively. We find values of the power-law slope of 0.905 ± 0.0585, 0.948 ± 0.100, 1.33 ± 0.260 and 0.883 ± 0.0500, respectively.
 
Article
We present the first results of a combined VLT VIMOS integral-field unit and Hubble Space Telescope (HST)/ACS study of the early-type lens galaxy SDSS J2321-097 at z=0.0819, extending kinematic studies to a look-back time of 1 Gyr. This system, discovered in the Sloan Lens ACS Survey (SLACS), has been observed as part of a VLT Large Programme with the goal of obtaining two-dimensional stellar kinematics of 17 early-type galaxies to z~0.35 and Keck spectroscopy of an additional dozen lens systems. Bayesian modelling of both the surface brightness distribution of the lensed source and the two-dimensional measurements of velocity and velocity dispersion has allowed us, under the only assumptions of axisymmetry and a two-integral stellar distribution function (DF) for the lens galaxy, to dissect this galaxy in three dimensions and break the classical mass--anisotropy, mass-sheet and inclination--oblateness degeneracies. Our main results are that the galaxy (i) has a total density profile well described by a single power-law rho propto r^{-gamma'} with gamma'=2.06^{+0.03}_{-0.06}; (ii) is a very slow rotator (specific stellar angular momentum parameter lambda_R = 0.075); (iii) shows only mild anisotropy (delta ~ 0.15); and (iv) has a dark matter contribution of ~30 per cent inside the effective radius. Our first results from this large combined imaging and spectroscopic effort with the VLT, Keck and HST show that the structure of massive early-type galaxies beyond the local Universe can now be studied in great detail using the combination of stellar kinematics and gravitational lensing. Extending these studies to look-back times where evolutionary effects become measurable holds great promise for the understanding of formation and evolution of early-type galaxies. Comment: 16 pages, 12 figures; accepted for publication in MNRAS; corrected typos
 
Article
A new serendipitous XMM survey in the area of the Sloan Digital Sky Survey is described (XMM/SDSS), which includes features such as merging of overlapping fields to increase the sensitivity to faint sources, use of a new parametrization of the XMM point spread function for the source detection and photometry and an accurate estimation of the survey sensitivity. About 40 000 X-ray point sources are detected over a total area of 122 deg2. A subsample of 209 sources detected in the 2–8 keV spectral band with SDSS spectroscopic redshifts in the range of 0.03 < z < 0.2, optical magnitudes r < 17.77 mag and (erg s−1) is selected to explore their distribution on the colour–magnitude diagram. This is compared with the colour–magnitude diagram of X-ray AGN in the AEGIS field at z≈ 0.8. We find no evidence for evolution of the rest-frame colours of X-ray AGN hosts from z= 0.8 to 0.1. This suggests that the dominant accretion mode of the AGN population, which is expected to imprint on the properties of their host galaxies, does not change since z= 0.8. This argues against scenarios that attribute the rapid decline of the accretion power of the Universe with time (1 dex since z= 0.8) to changes in the AGN fuelling/triggering mode.
 
Modelled properties of the massive dense cores and compiled observational velocity dispersions 
Linear fits to the Nmm vs N Jeans relations of Fig. 2, which correspond to different cases of core support 
Article
We combine previously published interferometric and single-dish data of relatively nearby massive dense cores that are actively forming stars to test whether their ‘fragmentation level’ is controlled by turbulent or thermal support. We find no clear correlation between the fragmentation level and velocity dispersion, nor between the observed number of fragments and the number of fragments expected when the gravitationally unstable mass is calculated including various prescriptions for ‘turbulent support’. On the other hand, the best correlation is found for the case of pure thermal Jeans fragmentation, for which we infer a core formation efficiency around 13 per cent, consistent with previous works. We conclude that the dominant factor determining the fragmentation level of star-forming massive dense cores at 0.1 pc scale seems to be thermal Jeans fragmentation.
 
Article
Using a suite of X-ray, mid-infrared (mid-IR) and optical active galactic nuclei (AGN) luminosity indicators, we search for Compton-thick AGNs with intrinsic LX > 1042 erg s−1 at z∼ 0.03–0.2, a region of parameter space which is currently poorly constrained by deep narrow-field and high-energy (E > 10 keV) all-sky X-ray surveys. We have used the widest XMM–Newton survey (the serendipitous source catalogue) to select a representative subsample (14; ≈10 per cent) of the 147 X-ray undetected candidate Compton-thick AGNs in the Sloan Digital Sky Survey (SDSS) with fX/f[O iii] < 1; the 147 sources account for ≈50 per cent of the overall type-2 AGN population in the SDSS–XMM overlap region. We use mid-IR spectral decomposition analyses and emission-line diagnostics, determined from pointed Spitzer-InfraRed Spectrograph spectroscopic observations of these candidate Compton-thick AGNs, to estimate the intrinsic AGN emission [predicted 2–10 keV X-ray luminosities, LX≈ (0.2–30) × 1042 erg s−1]. On the basis of the optical [O iii], mid-IR [O iv] and 6 −μ m AGN continuum luminosities, we conservatively find that the X-ray emission in at least 6/14 ( per cent) of our sample appears to be obscured by Compton-thick material with NH > 1.5 × 1024 cm−2. Under the reasonable assumption that our 14 AGNs are representative of the overall X-ray undetected AGN population in the SDSS–XMM parent sample, we find that per cent of the optical type-2 AGN population are likely to be obscured by Compton-thick material. This implies a space density of log for Compton-thick AGNs with at z∼ 0.1, which we suggest may be consistent with that predicted by X-ray background synthesis models. Furthermore, using the 6 −μ m continuum luminosity to infer the intrinsic AGN luminosity and the stellar velocity dispersion to estimate MBH, we find that the most conservatively identified Compton-thick AGNs in this sample may harbour some of the most rapidly growing black holes (median M BH≈ 3 × 107 M⊙) in the nearby Universe, with a median Eddington ratio of η≈ 0.2.
 
Article
We present Submillimeter Array (SMA) $\lambda =$ 0.88 and 1.3 mm broad band observations, and the Jansky Very Large Array (VLA) observations in $\rm{NH_3}$ $(J,K) = (1,1)$ up to $(5,5)$, $\rm{H_2O}$ and $\rm{CH_3OH}$ maser lines toward the two most massive molecular clumps in infrared dark cloud (IRDC) G11.11-0.12. Sensitive high-resolution images reveal hierarchical fragmentation in dense molecular gas from the $\sim 1$ pc clump scale down to $\sim 0.01$ pc condensation scale. At each scale, the mass of the fragments is orders of magnitude larger than the Jeans mass. This is common to all four IRDC clumps we studied, suggesting that turbulence plays an important role in the early stages of clustered star formation. Masers, shock heated $\rm{NH_3}$ gas, and outflows indicate intense ongoing star formation in some cores while no such signatures are found in others. Furthermore, chemical differentiation may reflect the difference in evolutionary stages among these star formation seeds. We find $\rm{NH_3}$ ortho/para ratios of $1.1\pm0.4$, $2.0\pm0.4$, and $3.0\pm0.7$ associated with three outflows, and the ratio tends to increase along the outflows downstream. Our combined SMA and VLA observations of several IRDC clumps present the most in depth view so far of the early stages prior to the hot core phase, revealing snapshots of physical and chemical properties at various stages along an apparent evolutionary sequence.
 
Article
We present complete, low resolution IJHK spectroscopy of the ultracompact HII region, G45.12+0.13. From the observed HI line strengths, we derive a near infrared extinction law that is slightly steeper than the average. After correction with this extinction law, we find good agreement between the observed line ratios of HeI, Fe+, Fe++, S+ and S++ and the available atomic data. Our data show that the density within the core of G45.12+0.13 must be at least 10^4/cm^3. This is consistent with the known radio structure of the HII region and in considerable disagreement with previous work using mid and far infrared lines. There must also be considerable opacity in the HeI 2 3P-2 3S transition, and we show how the observed strengths of the other HeI lines are consistent with this. From modelling the photoionisation structure, we find good agreement with most of the observed data if the hottest star present has Teff < 42000K. Consideration of the helium ionisation state places a lower limit on this value so that we can also constrain Teff > 38000K. Discrepancies still exist between some of the observed and model line ratios, but the most obvious tend to be the mid-IR observations.
 
Article
The Australia Telescope Compact Array (ATCA) has been used to map class I methanol masers at 36 and 44 GHz in G309.38−0.13. Maser spots are found at nine locations in an area of 50 × 30 arcsec2, with both transitions reliably detected at only two locations. The brightest spot is associated with shocked gas traced by 4.5-μm emission. The data allowed us to make a serendipitous discovery of a high-velocity 36-GHz spectral feature, which is blueshifted by about 30 km s−1 from the peak velocity at this frequency, but spatially located close to (within a few arcseconds of) the brightest maser spot. We interpret this as indicating an outflow parallel to the line of sight. Such a high-velocity spread of maser features, which has not been previously reported in the class I methanol masers associated with a single molecular cloud, suggests that the outflow most likely interacts with a moving parcel of gas.
 
Continuum map toward G20.08-0.14N at 0.9 mm. The contours are at-4, 4, 8, 12, 20, 28, 36, 44 and 49 σ. The rms noise level is 0.03 Jy beam −1 (1σ). The synthesized beam (2.0 ′′ × 1.2 ′′ ) with P.A.= 72 • is shown in the lower right corner. " * " indicates the position of three HII region (Wood & Churchwell 1989; Galván-Madrid et al. 2009). H 2 O maser is shown with blue filled triangle. The velocity component of the blue contours is from 32.5 km s −1 to 36.0 km s −1 , while the velocity component of the red contours is from 47.0 km s −1 to 51.7 km s −1 , whose levels are the 20%, 40%, 60%, 80%, and 100% of the peak values. 
Observed Parameters of Each Line
Article
We present Submillimeter Array observations of the massive star-forming region G20.08-0.14N at 335 and 345 GHz. With the SMA data, 41 molecular transitions were detected related to 11 molecular species and their isotopologues, including SO2, SO, C34S, NS, C17O, SiO, CH3OH, HC3N, H13CO+, HCOOCH3 and NH2CHO. In G20.08-0.14N, 10 transition lines of the detected 41 transition lines belong to SO2, which dominates the appearance of the submillimeter-wave spectrum. To obtain the spatial kinematic distribution of molecules in G20.08-0.14N, we chose the strongest and unblended lines for the channel maps. The channel maps of C34S an SiO, together with their position-velocity diagrams, present that there are two accretion flows in G20.08-0.14N. Additionally, SiO emission shows a collimated outflow at the NE-SW direction. The direction of the outflow is for the first time revealed. The rotational temperature and the column density of CH3OH are 105 K and 3.1*10^{17} cm^{-2}, respectively. Our results confirm that a hot core is associated with G20.08-0.14N. The hot core is heated by a protostar radiation at it center, not by the external excitation from shocks. The images of the spatial distribution of different species have shown that the different molecules are located at the different positions of the hot core. Through comparing the spatial distributions and abundances of the molecules, we discuss possible chemical processes for producing the complex sulfur-bearing, nitrogen-bearing and oxygen-bearing molecules in G20.08-0.14N.
 
Energy level diagram of the HDO lines. Green solid arrows: the IRAM-30m observations; blue short dashed arrows: the PRISMAS/HIFI observations; red long dashed arrows: the Open Time HIFI observations; magenta dotted arrow: the CSO observation. The frequencies are given in GHz. (A color version of this figure is available in the online journal.)
HDO and H 18 2 O transitions observed towards the ultra-compact HII region G34 (1) .
HDO and H 2 O abundances obtained for different jump temperatures T j 
IRAM-30m observations (in black) of the para-H 18 2 O 3 1,3-2 2,0 transition at 203.4 GHz. The frequency of the H 18 2 O line is indicated by a blue dotted line ( = 58 km s −1 ). The other lines observed in this spectra are the SO 2 =0 12 0,12-11 1,11 line at 81.5 km s −1 (green long dashed line), the C 2 H 5 CN =0 23 2,22-22 2,21 line at 74.1 km s −1 (yellow short dashed line) and several CH 3 OCH 3 lines (magenta solid lines). A LTE modeling of the CH 3 OCH 3 lines (in magenta) was carried out to estimate the contamination of the para-H 18 2 O line by the CH 3 OCH 3 3 3,1,1-2 2,1,1 transition. (A color version of this figure is available in the online journal.)
Rotational diagram of the HDO lines. The fundamental line at 894 GHz is excluded from the figure. A source size of 4 is assumed. The error bars correspond to uncertainties of 20%. A linear fit was made using only the lines with low critical densities (81, 226, and 242 GHz, indicated by red triangles) to estimate the HDO column density (∼ 1.6 × 10 16 cm −2 ) and the excitation temperature (∼ 79 K) in the hot core (see text). (A color version of this figure is available in the online journal.)  
Article
Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H$_2^{18}$O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the Heterodyne Instrument for the Far-Infrared (HIFI) instrument onboard the Herschel Space Observatory, as well as with ground-based single-dish telescopes. 10 HDO lines and three H$_2^{18}$O lines covering a broad range of upper energy levels (22–204 K) were detected. We used a non-local thermal equilibrium 1D analysis to determine the HDO/H2O ratio as a function of radius in the envelope. Models with different water abundance distributions were considered in order to reproduce the observed line profiles. The HDO/H2O ratio is found to be lower in the hot core (∼3.5 × 10−4–7.5 × 10−4) than in the colder envelope (∼1.0 × 10−3–2.2 × 10−3). This is the first time that a radial variation of the HDO/H2O ratio has been found to occur in a high-mass source. The chemical evolution of this source was modelled as a function of its radius and the observations are relatively well reproduced. The comparison between the chemical model and the observations leads to an age of ∼105 yr after the infrared dark cloud stage.
 
The monopole moment of the correlation function of the MGS. The solid line shows the mean of the mocks and the error bars come from the diagonal elements of the covariance matrix calculated from our 1000 mock realisations. 
The quadrupole moment of the correlation function of the MGS and the mean of our mock galaxy catalogues. Though the agreement by eye looks poor on large scales, there exists significant covariance between the points at different scales, such that the chi-squared between the data and mocks is small. 
The marginalised f σ 8 and bσ 8 values and one-sigma errors from fitting to the mean of the mocks for the 10 cases listed in Table 1. The dashed line indicates the expected growth rate assuming our fiducial ΛCDM cosmology. The shaded band indicates the expected linear galaxy bias as measured from our HOD fits to the MGS sample, we use a band rather than a line to account for the fact that the calculated value depends slightly on the range of scales used.
The average monopole and quadrupole of our 1000 mock catalogues (points) shown alongside the best-fit model for our fiducial fitting case (solid) which includes both priors on α and σ 8. The errors are derived from the covariance matrix and are the errors on a single realisation. The CLPT model does a fantastic job of reproducing the measured clustering on all scales of interest. 
Comparison of measurements of the growth rate using the two-point clustering statistics from a variety of galaxy surveys below z = 0.8. We split the results into two groups: those that perform a full shape fit and hence include the Alcock-Paczynski degeneracy; and those that just fit the growth rate for a fixed cosmology, neglecting this degeneracy. Our measurement is shown as a filled red star, with other data points representing the 6dFGS (filled diamond; Beutler et al. 2012), 2dFGRS (empty diamond; Percival et al. 2004), SDSS-II LRG (filled triangle; Samushia et al. 2012 (no AP), Oka et al. 2014 (AP)), BOSS (filled circle; Chuang et al. 2013 (z=0.32), Samushia et al. 2014 (z=0.57)), WiggleZ (open square; Blake et al. 2011a,b), VVDS (open circle; Guzzo et al. 2008) and VIPERS (filled square; de la Torre et al. 2013) surveys. We have also included Planck predictions for the growth rate for values of γ = 0.42, 0.55 and 0.68 as solid bands. 
Article
We measure redshift space distortions in the two-point correlation function of a sample of 63 163 spectroscopically identified galaxies with z < 0.2, an epoch where there are currently only limited measurements, from the Sloan Digital Sky Survey Data Release 7 main galaxy sample (MGS). Our sample, which we denote MGS, covers 6813 deg2 with an effective redshift zeff = 0.15 and is described in our companion paper (Paper I), which concentrates on baryon acoustic oscillation (BAO) measurements. In order to validate the fitting methods used in both papers, and derive errors, we create and analyse 1000 mock catalogues using a new algorithm called picola to generate accurate dark matter fields. Haloes are then selected using a friends-of-friends algorithm, and populated with galaxies using a halo-occupation distribution fitted to the data. Using errors derived from these mocks, we fit a model to the monopole and quadrupole moments of the MGS correlation function. If we assume no Alcock–Paczynski (AP) effect (valid at z = 0.15 for any smooth model of the expansion history), we measure the amplitude of the velocity field, fσ8, at z = 0.15 to be $0.49_{-0.14}^{+0.15}$. We also measure fσ8 including the AP effect. This latter measurement can be freely combined with recent cosmic microwave background results to constrain the growth index of fluctuations, γ. Assuming a background Λ cold dark matter cosmology and combining with current BAO data, we find γ = 0.64 ± 0.09, which is consistent with the prediction of general relativity (γ ≈ 0.55), though with a slight preference for higher γ and hence models with weaker gravitational interactions.
 
Article
We present a Chandra study of 38 X-ray luminous clusters of galaxies in the ROSAT Brightest Cluster Sample (BCS) that lie at z~0.15-0.4. We find that the majority of clusters at moderate redshift generally have smooth, relaxed morphologies with some evidence for mild substructure perhaps indicative of recent minor merger activity. Using spatially-resolved spectral analyses, cool cores appear to still be common at these redshifts. At a radius of 50 kpc, we find that at least 55 per cent of the clusters in our sample exhibit signs of mild cooling [t(cool)<10 Gyr], while in the central bin at least 34 per cent demonstrate signs of strong cooling [t(cool)<2 Gyr]. These percentages are nearly identical to those found for luminous, low-redshift clusters of galaxies, suggesting little evolution in cluster cores since z~0.4 and that heating and cooling mechanisms may already have stabilised by this epoch. Comparing the central cooling times to central Halpha emission in BCS clusters, we find a strong correspondence between the detection of Halpha and central cooling time. (Abridged) Comment: 10 pages, 8 figures, accepted to MNRAS
 
The right ascension and declination positions (J2000) of the 63,163 SDSS DR7 main galaxy survey galaxies we include in our sample. Their footprint occupies 6813 deg 2 . 
Article
We create a sample of spectroscopically identified galaxies with z < 0.2 from the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), covering 6813 deg2. Galaxies are chosen to sample the highest mass haloes, with an effective bias of 1.5, allowing us to construct 1000 mock galaxy catalogues (described in Paper II), which we use to estimate statistical errors and test our methods. We use an estimate of the gravitational potential to ‘reconstruct’ the linear density fluctuations, enhancing the baryon acoustic oscillation (BAO) signal in the measured correlation function and power spectrum. Fitting to these measurements, we determine DV(zeff = 0.15) = (664 ± 25)(rd/rd, fid) Mpc; this is a better than 4 per cent distance measurement. This ‘fills the gap’ in BAO distance ladder between previously measured local and higher redshift measurements, and affords significant improvement in constraining the properties of dark energy. Combining our measurement with other BAO measurements from Baryon Oscillation Spectroscopic Survey and 6-degree Field Galaxy Redshift Survey galaxy samples provides a 15 per cent improvement in the determination of the equation of state of dark energy and the value of the Hubble parameter at z = 0 (H0). Our measurement is fully consistent with the Planck results and the Λ cold dark matter concordance cosmology, but increases the tension between Planck+BAO H0 determinations and direct H0 measurements.
 
Redshift distribution for the A-clusters (left panel) and A+S clusters (right panel). The solid lines are the expected number of clusters in spherical shells of ∆z = 0.01 using a constant space density of clusters corresponding to the most completely surveyed redshifts for each distribution, namely 0.03 < z < 0.07 for the all-sky distribution of A-clusters, and z < 0.05 for the A+S clusters in the southern (δ < −17 • ) sample. These values are: 7.4×10 −6 h 3 70 Mpc −3 for only the A-clusters and 2.8×10 −5 h 3 70 Mpc −3 for A-and S-clusters together in the south. The first value is comparable to the one found by Einasto et al. (1997) (8.9×10 −6 h 3 70 Mpc −3 ) for Abell/ACO clusters. The dashed line in the right panel indicates the same function as the solid line in the left panel. These curves grow according to r 2 where r = r(z) is the comoving distance as described by Hogg (2000). 
Redshift distribution for the northern and southern Abell/ACO clusters. For the northern subsample, the solid histogram is for the northern sky without the SDSS region and the dashed histogram is the one for the SDSS region. For the southern subsample, the solid histogram is the distribution for A clusters and the dashed histogram is the one for A+S clusters. 
Article
We present two new catalogues of superclusters of galaxies out to a redshit of z = 0.15, based on the Abell/ACO cluster redshift compilation maintained by one of us (HA). The first of these catalogues, the all-sky Main SuperCluster Catalogue (MSCC), is based on only the rich (A-) Abell clusters, and the second one, the Southern SuperCluster Catalogue (SSCC), covers declinations delta < -17 deg and includes the supplementary Abell S-clusters. A tunable Friends-of-Friends (FoF) algorithm was used to account for the cluster density decreasing with redshift and for different selection functions in distinct areas of the sky. We present the full list of Abell clusters used, together with their redshifts and supercluster memberships and including the isolated clusters. The SSCC contains about twice the number of superclusters than MSCC for delta < -17 deg, which we found to be due to: (1) new superclusters formed by A-clusters in their cores and surrounded by S-clusters (50%), (2) new superclusters formed by S-clusters only (40%), (3) redistribution of member clusters by fragmentation of rich (multiplicity m > 15) superclusters (8%), and (4) new superclusters formed by the connection of A-clusters through bridges of S-clusters (2%). Power-law fits to the cumulative supercluster multiplicity function yield slopes of alpha = -2.0 and alpha = -1.9 for MSCC and SSCC respectively. This power-law behavior is in agreement with the findings for other observational samples of superclusters, but not with that of catalogues based on cosmological simulations.
 
Article
This is the second of a series of papers on low X-ray luminosity galaxy clusters, in which we present the $r^\prime$, $g^\prime$ and $i^\prime$ photometry obtained with GMOS-IMAGE at Gemini North and South telescopes for seven systems in the redshift range of 0.18 to 0.70. Optical magnitudes, colours and morphological parameters, namely, concentration index, ellipticity and visual morphological classification, are also given. At lower redshifts, the presence of a well-defined red cluster sequence extending by more than 4 magnitudes showed that these intermediate-mass clusters had reached a relaxed stage. This was confirmed by the small fraction of blue galaxy members observed in the central regions of $\sim$ 0.75 Mpc. In contrast, galaxy clusters at higher redshifts had a less important red cluster sequence. We also found that the galaxy radial density profiles in these clusters were well fitted by a single power law. At 0.18 $<$ z $<$ 0.70, we observed an increasing fraction of blue galaxies and a decreasing fraction of lenticulars, with the early-type fraction remaining almost constant. Overall, the results of these intermediate-mass clusters are in agreement with those for high mass clusters.
 
The SDSS r-band enhanced greyscale 0.7 arcmin × 0.7 arcmin image of the merger system, centered on source A, on which we have superimposed the FIRST image (1.4 GHz, 5 arcsec resolution) contours in yellow. Contour levels are 0.9, 1.3, 1.8, 2.5 and 3.6 mJy. 
Article
Mergers of gas-poor galaxies, so-called dry mergers, may play a fundamental role in the assembly of the most massive galaxies, and therefore, in galaxy formation theories. Using the Sloan Digital Sky Survey, we have serendipitously discovered a rare system in the observational and theoretical context, possibly a quintuple dry merger at low redshift. As a follow-up, we have obtained Nordic Optical Telescope long-slit spectra of the group, in order to measure the individual redshifts and gain insight into its merger fate. Our results show an isolated, low-redshift galaxy group consisting of massive, quiescent, early-type galaxies, composed of two clumps (possibly themselves in the process of merging), which we estimate will hypothetically merge in roughly less than a Gyr. With the possible exception of the high line-of-sight velocity dispersion, the overall properties of the system may be comparable to a compact Shakhbazyan group. However, when the small projected separations and relative mass ratios of the galaxies are taken into account in cosmological simulations, we find that this system is rather unique. We hypothesize that this group is a dry merger, whose fate will result in the assembly of an isolated, massive elliptical galaxy at low redshift.
 
Article
We present an observational study towards the young high-mass star-forming region G23.44-0.18 using the Submillimeter Array. Two massive, radio-quiet dusty cores MM1 and MM2 are observed in 1.3-mm continuum emission and dense molecular gas tracers including thermal CH3OH, CH3CN, HNCO, SO, and OCS lines. The 12CO (2–1) line reveals a strong bipolar outflow originating from MM2. The outflow consists of a low-velocity component with wide-angle quasi-parabolic shape and a more compact and collimated high-velocity component. The overall geometry resembles the outflow system observed in the low-mass protostar which has a jet-driven fast flow and entrained gas shell. The outflow has a dynamical age of 6 × 103 yr and a mass loss rate ∼10−3 M ⊙ yr-1. A prominent shock emission in the outflow is observed in SO and OCS, and also detected in CH3OH and HNCO. We investigated the chemistry of MM1, MM2 and the shocked region. The dense core MM2 have molecular abundances of three to four times higher than those in MM1. The abundance excess, we suggest, can be a net effect of the stellar evolution and embedded shocks in MM2 that calls for further inspection.
 
The distribution of Hα emitters in the Sausage cluster. The cross marks what we define as the "centre" of the cluster. The background shows a false RGB image from the combination of broad-band images presented in Stroe et al. 2015, while white contours present the weak lensing map (Jee et al. 2015) and in green the 323 MHz radio emission (Stroe et al. 2013). The Hα emitters in our sample reside in a range of different regions, but are found preferably near the shock fronts. Hα emitters also seem to be found just on the outskirts of the hottest X-ray gas-but where the temperatures are still very high (Ogrean et al. 2013). We also find that all AGN are located relatively close to the post-shock front, but all at a couple of hundred projected kpc away from the radio relics. Note that our sample extends beyond this region, as the field of view of the narrow-band survey, and the spectroscopic follow-up of such sources, cover a larger area (see Stroe et al. 2015). We also show star-forming galaxies showing signatures of outflows, mostly from systematically blue-shifted Na D in absorption from 150 to 300 km −1. Note that 100% of the cluster star-forming galaxies which are closest to the hottest X-ray gas (very close to the "centre" of the cluster), have strong signatures of outflows. Potentially, these are also the sources that, if affected by the shock, may have been the first to be affected, up to ∼ 0.7 Gyr ago.
Article
Cluster mergers may play a fundamental role in the formation and evolution of cluster galaxies. Stroe et al. revealed unexpected overdensities of candidate Hα emitters near the ∼1-Mpc-wide shock fronts of the massive (∼2 × 1015 M⊙) ‘Sausage’ merging cluster, CIZA J2242.8+5301. We used the Keck/Deep Imaging Multi-Object Spectrograph and the William Herschel Telescope/AutoFib2+WYFFOS to confirm 83 Hα emitters in and around the merging cluster. We find that cluster star-forming galaxies in the hottest X-ray gas and/or in the cluster subcores (away from the shock fronts) show high [S ii]6716/[S ii]6761 and high [S ii] 6716/Hα, implying very low electron densities (<30 × lower than all other star-forming galaxies outside the cluster) and/or significant contribution from supernovae, respectively. All cluster star-forming galaxies near the cluster centre show evidence of significant outflows (blueshifted Na D ∼200–300 km s−1), likely driven by supernovae. Strong outflows are also found for the cluster Hα active galactic nucleus (AGN). Hα star-forming galaxies in the merging cluster follow the z ∼ 0 mass–metallicity relation, showing systematically higher metallicity (∼0.15–0.2 dex) than Hα emitters outside the cluster (projected R > 2.5 Mpc). This suggests that the shock front may have triggered remaining metal-rich gas which galaxies were able to retain into forming stars. Our observations show that the merger of impressively massive (∼1015 M⊙) clusters can provide the conditions for significant star formation and AGN activity, but, as we witness strong feedback by star-forming galaxies and AGN (and given how massive the merging cluster is), such sources will likely quench in a few 100 Myr.
 
Article
We show the effectiveness of strong lensing in the characterisation of Lyman continuum emission from faint L<~0.1L* star-forming galaxies at redshift >~ 3. Past observations of L>~L* galaxies at redshift >~3 have provided upper limits of the average escape fraction of ionising radiation of fesc~5%. Galaxies with relatively high fesc (>10%) seem to be particularly rare at these luminosities, there is therefore the need to explore fainter limits. Before the advent of giant ground based telescopes, one viable way to probe fesc down to 0.05-0.15L* is to exploit strong lensing magnification. This is investigated with Monte Carlo simulations that take into account the current observational capabilities. Adopting a lensing cross-section of 10 arcmin^2 within which the magnification is higher than 1 (achievable with about 4-5 galaxy clusters), with a U-band survey depth of 30(30.5) (AB, 1-sigma), it is possible to constrain fesc for z~3 star-forming galaxies down to 15(10)% at 3-sigma for L<0.15L* luminosities. This is particularly interesting if fesc increases at fainter luminosities, as predicted from various HI reionization scenarios and radiation transfer modelling. Ongoing observational programs on galaxy clusters are discussed and offer positive prospects for the future, even though from space the HST/WFC3 instrument represents the only option we have to investigate details of the spatial distribution of the Lyman continuum emission arising from z~2-4 galaxies.
 
CO(1-0) spectra of the IRAM sample. The zero velocity corresponds to the optical redshift z SDSS , as derived from [OIII]λ5007. Fits of the line profile are shown with green lines for objects with detections or tentative (SDSS J0236+00) detections. The vertical axis shows T * A in K. 
L ′ CO vs. z (left) and L ′ CO vs. L F IR (right). The left panels show only quasars: type 1 (blue symbols) and type 2 (green symbols). LIRGs (orange crosses) and ULIRGs (red symbols) (no quasars included in these samples) and high z submm sources with no evidence for an AGN are added on the right panels. References: DW (different works); X12 (Xia et al. 2012); C11 (Combes et al. 2011); C12 (Combes et al. 2012); KNC12 (Krips, Neri & Cox 2012); GB (Graciá Carpio et al. 2008); GC12 (García Burillo et al. 2012). 
L ′ CO vs. L F IR (top) for the QSO1 (blue squares) and QSO2 (green circles) in Fig. 3. Upper limits have been excluded. η = L F IR L ′ CO 
F W HM CO(1−0) in km s −1 vs. L F IR for all samples at z 0.5. Symbols as in Fig. 3 except that all QSO2 (KNC12 and this work) are now represented with green solid circles. 
Article
We present results of CO(1-0) spectroscopic observations of 10 SDSS type 2 quasars (QSO2) at z~0.2-0.3 observed with the 30m IRAM radiotelescope and the Australia Telescope Compact Array. We report 5 new confirmed CO(1-0) detections and 1 tentative detection. They have L'(CO)~several x 1e9 K km s-1 pc^2, while upper limits for the non detections are L'(CO)<~ several x 1e9 K km s-1 pc^2. This study increases the total number of QSO2 with CO measurements at z<~1 to 20, with a 50% detection rate.
 
Article
The most extreme cluster mergers can lead to massive cluster-wide travelling shock waves. The CIZA J2242.8+5301 ('sausage') and 1RXS J0603.3+4213 (`toothbrush') clusters ($z\sim0.2$) host enormous radio-emitting shocks with simple geometry. We investigate the role of mergers and shocks in shaping the H$\alpha$ luminosity function, using custom-made narrow-band filters matching the cluster redshifts mounted on the INT. We surveyed $\sim0.28$ deg$^2$ for each cluster and found $181$ line emitters in the `sausage' (volume of $3.371\times10^3$ Mpc$^3$ for H$\alpha$ at $z=0.1945$) and $141$ in the `toothbrush' ($4.546\times10^3$ Mpc$^3$ for H$\alpha$ at $z=0.225$), out of which $49$ (`sausage') and $30$ (`toothbrush') are expected to be H$\alpha$. We build luminosity functions for the field-of-view down to an average limiting star formation rate of $0.14$ M$_{\odot}$ yr$^{-1}$, find good agreement with field luminosity functions at $z=0.2$, but significant differences between the shapes of the luminosity functions for the two clusters. We discover extended, tens-of-kpc-wide H$\alpha$ haloes in galaxies neighbouring relics, which were possibly disrupted by the passage of the shock wave. By comparing the `sausage' cluster with blank fields and other clusters, we also uncover an order of magnitude boost (at $9\sigma$ level) in the normalisation $\phi^*$ of the luminosity function in the relic areas. Our results suggest that cluster mergers may play an important role in the evolution of cluster galaxies through shock-induced star formation.
 
XIS0 image of G346.6-0.2 in the 0 . 3 − 10 keV full energy band. The coordinates are referred to epoch J2000. The calibration source located at the upper right corner, as seen by red-circle, is masked out. The colour-coding is for the X-ray photons in counts/pixel. The overlaid iso-intensity contours are from radio observation at 843 MHz. The contour levels are -7, 6, 25, 50, 95, 135, 165, 190, 210, 230, 255 and 270 mJy/beam, selected the same as the radio works for visual comparison. The regions used to extract spectrum and to determine the background parameters are indicated by blue solid and dotted circles, respectively. The positions of the four masers defined by Koralesky et al. (1998) are marked as crosses. 
G346.6-0.2 XIS0 image in 1 . 5 − 2 . 5 keV (Si-S) energy band. The image is smoothed for 10 σ Gaussian in order highlight the Si-S distribution. Overlaid contours are spaced linearly in intensity (0.01, 0.02, 0.03, 0.05, 0.09 and 0.16 counts/pixel). 
Background-subtracted XIS (XIS0:black, XIS1:red, XIS3:green) spectra of G346.6-0.2 in full energy band (0 . 3 − 10 keV) fitted with an absorbed VNEI and power-law model. The lower panel shows the residuals from the best-fitting model. 
Metal abundances of Mg, S, Ca and Fe relative to solar values and normalized to Si. W7 model for a Type Ia is shown by diamonds while our data are shown by triangles. 
Article
We present here the results of an X-ray analysis of Galactic supernova remnant G346.6−0.2 observed with Suzaku. K-shell emission lines of Mg, Si, S, Ca and Fe are detected clearly for the first time. Strong emission lines of Si and S imply that the X-ray emission nature of G346.6−0.2 is ejecta-dominated. The ejecta-dominated emission is well fitted by a combined model consisting of a thermal plasma in non-equilibrium ionization and a non-thermal component, which can be regarded as synchrotron emission with a photon index of Γ∼ 0.6. An absorbing column density of NH∼ 2.1 × 1022 cm−2 is obtained from the best fit, implying a high-density medium, high electron temperature of kTe∼ 1.2 keV and ionization time-scale of net∼ 2.9 × 1011 cm−3 s, indicating that this remnant may be far from full ionization equilibrium. The relative abundances from the ejecta show that the remnant originates from a Type Ia supernova explosion.
 
Article
Spectrophotometry of the H II region G 333.6-0.2 with a resolution of approximately 100 shows strong emission lines of hydrogen and helium superimposed on a continuum. Spatial variations in the equivalent widths of the lines suggest the presence of very hot (at least 600 K) dust grains within the region. The shape of this very powerful H II region indicates that its dense ionized core is being continuously replenished from a reservoir of neutral gas.
 
Top-cited authors
Simon White
  • Max Planck Institute for Astrophysics
Lars Hernquist
  • Harvard University
George Efstathiou
  • University of Cambridge
Shaun Cole
  • Durham University
Daniel Thomas
  • University of Portsmouth