N. Loaring

The XMM-Newton serendipitous survey - IV. Optical identification of the XMM-Newton medium sensitivity survey (XMS)

Aims. X-ray sources at intermediate fluxes (a few x 10(-14) erg cm(-2) s(-1)) with a sky density of similar to 100 deg(-2) are responsible for a significant fraction of the cosmic X-ray background at various energies below 10 keV. The aim of this paper is to provide an unbiased and quantitative description of the X-ray source population at these fluxes and in various X-ray energy bands. Methods. We present the XMM-Newton Medium sensitivity Survey (XMS), including a total of 318 X-ray sources found among the serendipitous content of 25 XMM-Newton target fields. The XMS comprises four largely overlapping source samples selected at soft (0.5-2 keV), intermediate (0.5-4.5 keV), hard (2-10 keV) and ultra-hard (4.5-7.5 keV) bands, the first three of them being flux-limited. Results. We report on the optical identification of the XMS samples, complete to 85-95%. At the flux levels sampled by the XMS we find that the X-ray sky is largely dominated by Active Galactic Nuclei. The fraction of stars in soft X-ray selected samples is below 10%, and only a few per cent for hard selected samples. We find that the fraction of optically obscured objects in the AGN population stays constant at around 15-20% for soft and intermediate band selected X-ray sources, over 2 decades of flux. The fraction of obscured objects amongst the AGN population is larger (similar to 35-45%) in the hard or ultra-hard selected samples, and constant across a similarly wide flux range. The distribution in X-ray-to-optical flux ratio is a strong function of the selection band, with a larger fraction of sources with high values in hard selected samples. Sources with X-ray-to-optical flux ratios in excess of 10 are dominated by obscured AGN, but with a significant contribution from unobscured AGN.

The metallicity extremes of the Sagittarius dSph: SALT spectroscopy of PNe

In this work we present the first spectroscopic results obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. We find that the Sagittarius dwarf spheroidal galaxy (Sgr) contains a youngest stellar population with [O/H] ≈ -0.2 and age t > 1 Gyr, and an oldest population with [O/H] = -2.0. The values are based on spectra of two planetary nebulae (PNe), using empirical abundance determinations. We calculated abundances for O, N, Ne, Ar, S, Cl, Fe, C and He. We confirm the high abundances of PN StWr2-21 with 12 + log(O/H) = 8.57 ± 0.02 dex. The other PN studied, BoBn 1, is an extraordinary object in that the neon abundance exceeds that of oxygen. The abundances of S, Ar and Cl in BoBn 1 yield the original stellar metallicity, corresponding to 12 + log(O/H) = 6.72 ± 0.16 dex which is 1/110 of the solar value. The actual [O/H] is much higher: third dredge-up enriched the material by a factor of ∼12 in oxygen, ∼240 in nitrogen and ∼70 in neon. Neon as well as nitrogen and oxygen content may have been produced in the intershell of low-mass asymptotic giant branch (AGB) stars. Well defined broad WR lines are present in the spectrum of StWr2-21 and absent in the spectrum of BoBn 1. This puts the fraction of [WR]-type central PNe stars to 67 per cent for dSph galaxies.

The 2dF QSO Redshift Survey- XV. Correlation analysis of redshift-space distortions

We analyse the redshift-space (z-space) distortions of quasi-stellar object (QSO) clustering in the 2-degree field instrument (2dF) QSO Redshift Survey (2QZ). To interpret the z-space correlation function, ξ(σ, π), we require an accurate model for the QSO real-space correlation function, ξ(r). Although a single power-law ξ(r) oc r -γ model fits the projected correlation function [ω p (σ)] at small scales, it implies somewhat too shallow a slope for both w p (σ) and the z-space correlation function, ξ(s), at larger scales (?20 h -1 Mpc). Motivated by the form for ξ(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard A cold dark matter (CDM) predictions, we use a double power-law model for ξ(r), which gives a good fit to ξ(s) and w p (σ). The model is parametrized by a slope of y = 1.45 for 1 < r < 10 h -1 Mpc and y = 2.30 for 10 < r < 40 h -1 Mpc. As found for the 2dFGRS, the value of β determined from the ratio of ξ(s)/ξ(r) depends sensitively on the form of ξ(r) assumed. With our double power-law form for ξ(r), we measure β(z = 1.4) = 0.32 +0.09 -0.11 . Assuming the same model for ξ(r), we then analyse the z-space distortions in the 2QZ ξ(σ, π) and put constraints on the values of Ω 0 m and β(z = 1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Ω 0 m = 0.35 +0.19 -0.13 , β(z = 1.4) = 0.50 +0.13 -0.15 , in agreement with our ξ(s)/ξ(r) results at the ∼ 1σ level.

PySALT: the SALT science pipeline

PySALT is the python/PyRAF-based data reduction and analysis pipeline for the Southern African Large Telescope (SALT), a modern 10m class telescope with a large user community consisting of 13 partner institutions. The two first generation instruments on SALT are SALTICAM, a wide-field imager, and the Robert Stobie Spectrograph (RSS). Along with traditional imaging and spectroscopy modes, these instruments provide a wide range of observing modes, including Fabry-Perot imaging, polarimetric observations, and high-speed observations. Due to the large user community, resources available, and unique observational modes of SALT, the development of reduction and analysis software is key to maximizing the scientific return of the telescope. PySALT is developed in the Python/PyRAF environment and takes advantage of a large library of open-source astronomical software. The goals in the development of PySALT are: (1) Provide science quality reductions for the major operational modes of SALT, (2) Create analysis tools for the unique modes of SALT, and (3) Create a framework for the archiving and distribution of SALT data. The data reduction software currently provides support for the reduction and analysis of regular imaging, high-speed imaging, and long slit spectroscopy with planned support for multi-object spectroscopy, high-speed spectroscopy, Fabry-Perot imaging, and polarimetric data sets. We will describe the development and current status of PySALT and highlight its benefits through early scientific results from SALT.

Adaptive optics imaging and optical spectroscopy of a multiple merger in a luminous infrared galaxy

We present near-infrared (NIR) adaptive optics imaging obtained with VLT/NACO and optical spectroscopy from the Southern African Large Telescope of a luminous IR galaxy (LIRG) IRAS 19115-2124. Thes ...

The 2dF QSO Redshift Survey – XIII. A measurement of Λ from the quasi‐stellar object power spectrum, PS(k∥, k⊥)

We report on measurements of the cosmological constant, Lambda, and the redshift space distortion parameter beta=Omega_m^0.6/b, based on an analysis of the QSO power spectrum parallel and perpendicular to the observers line of sight, from the final catalogue of the 2dF QSO Redshift Survey. We derive a joint Lambda - beta constraint from the geometric and redshift-space distortions in the power spectrum. By combining this result with a second constraint based on mass clustering evolution, we break this degeneracy and obtain strong constraints on both parameters. Assuming a flat cosmology and a Lambda cosmology r(z) function to convert from redshift into comoving distance, we find best fit values of Omega_Lambda=0.71^{+0.09}_{-0.17} and beta(z~1.4)=0.45^{+0.09}_{-0.11}. Assuming instead an EdS cosmology r(z) we find that the best fit model obtained, with Omega_Lambda=0.64^{+0.11}_{-0.16} and beta(z~1.4)=0.40^{+0.09}_{-0.09}, is consistent with the Lambda r(z) results, and inconsistent with a Lambda=0 flat cosmology at over 95 per cent confidence.

Photometry of 2006 RH120: an asteroid temporary captured into a geocentric orbit

Aims. From July 2006 to July 2007 a very small asteroid orbited the Earth within its Hill sphere. We used this opportunity to study its rotation and estimate its diameter and shape. Methods. Due to its faintness, 2006 RH120 was observed photometrically with the new 10-m SALT telescope at the SAAO (South Africa). We obtained data on four nights: 11, 15, 16, and 17 March 2007 when the solar phase angle remained almost constant at 74 ◦ . The observations lasted about an hour each night and the object was exposed for 7−10 s through the “clear” filter. Results. From the lightcurves obtained on three nights we derived two solutions for a synodical period of rotation: P1 = 1.375 ± 0.001 min and P2 = 2.750 ± 0.002 min. The available data are not sufficient to choose between them. The absolute magnitude of the object was found to be H = 29.9 ± 0.3 mag (with the assumed slope parameter G = 0.25) and its effective diameter D = 2− 7m , depending on the geometric albedo pV (with the most typical near-Earth asteroids albedo pV = 0.18 its diameter would be D = 3.3 ± 0.4 m). The body has an elongated shape with the a/b ratio greater than 1.4. It probably originates in low-eccentricity Amor or Apollo orbits. There is still a possibility, which needs further investigation, that it is a typical near-Earth asteroid that survived the aerobraking in the Earth’s atmosphere and returned to a heliocentric orbit similar to that of the Earth.

X-ray spectra of sources in the 13HXMM–Newton/Chandra deep field

We present the X-ray spectra of 86 optically identified sources in the 13^H XMM–Newton/Chandra deep field which have >70 X-ray counts. The majority of these sources have 2–10 keV fluxes between 10^(−1)5 and 5 × 10^(−1)4 erg cm^(−2) s^(−1). The sample consists of 50 broad-line active galactic nuclei (BLAGN), 25 narrow emission-line galaxies (NELGs), six absorption-line galaxies and five Galactic stars. The majority (42/50) of the BLAGN have X-ray spectra which are consistent with a power-law shape. They have a mean photon index 〈Γ〉= 2.0 ± 0.1 and an intrinsic dispersion σ_Γ= 0.4 ± 0.1. Three of the BLAGN show curved spectra, with more emission near the high- and low-energy ends of the spectrum relative to the emission in the 1–2 keV range than can be reproduced by the power-law model. Five BLAGN show a deficit of soft X-rays, indicating absorption. We consider a source to be significantly absorbed if a power-law model fit is rejected with >99 per cent confidence and an absorbed power-law model produces an acceptable fit, or if the best-fitting power law is abnormally hard (Γ < 1). Significant absorption is more common in the NELGs (13/25) and absorption-line galaxies (2/6) than in the BLAGN (5/50), but is not universal in any of these classes of object. The majority of the 20 absorbed sources have X-ray spectra consistent with a simple cold photoelectric absorber, but a significant minority (6/20) require more complex models with either an additional component of soft X-ray emitting plasma, or an ionized absorber. Of the 16 narrow emission- and absorption-line galaxies which do not show evidence for X-ray absorption, only two objects are likely to be powered by star formation, and both have 2–10 keV X-ray luminosities of ≤ 10^(40) erg s^(−1). The X-ray emission in the other 14 unabsorbed NELGs and galaxies is most likely powered by AGN, which are not detected in the optical because they are outshone by their luminous host galaxies. The Galactic stars show multitemperature thermal spectra which peak between 0.5 and 1 keV. Star/AGN discrimination is possible for four of the five stars solely from their X-ray spectra.

Determining the extragalactic extinction law with SALT

We present CCD imaging observations of early-type galaxies with dark lanes obtained with the Southern African Large Telescope (SALT) during its performance-verification phase. The observations were performed in six spectral bands that span the spectral range from the near-ultraviolet atmospheric cutoff to the near-infrared. We derive the extinction law by the extragalactic dust in the dark lanes in the spectral range 1.11�m −1 < λ −1 < 2.94�m −1 by fitting model galaxies to the unextinguished parts of the image, and subtracting from these the actual images. This procedure allows the derivation, with reasonably high signal-to-noise, of the extinction in each spectral band we used for each resolution element of the image. We also introduce an alternative method to derive the extinction values by comparing various colour-indices maps under the assumption of negligible intrinsic colour gradients in these galaxies. We than compare the results obtained using these two methods. We compare the total-to-selective extinction derived for these galaxies with previously obtained results and with similar extinction values of Milky Way dust to derive conclusions about the properties of extragalactic dust in different objects and conditions. We find that the extinction curves run parallel to the Galactic extinction curve, which implies that the properties of dust in the extragalactic enviroment are similar to those of the Milky Way, despite our original expectations. The ratio of the total V band extinction to the selective extinction between the V and B bands is derived for each galaxy with an average of 2.82±0.38, compared to a canonical value of 3.1 for the Milky Way. The similar values imply that galaxies with well-defined dark lanes have characteristic dust grain sizes similar to those of Galactic dust. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them in the range 10 4 to 10 7 M⊙.

Determining the extragalactic extinction law with SALT – II. Additional sample

We present new results from an ongoing programme to study the dust extragalactic extinction law in E/S0 galaxies with dust lanes with the Southern African Large Telescope (SALT) during its performance verification phase. The wavelength dependence of the dust extinction for seven galaxies is derived in six spectral bands ranging from the near-ultraviolet atmospheric cut-off to the near-infrared. The derivation of an extinction law is performed by fitting model galaxies to the unextinguished parts of the image in each spectral band, and subtracting from these the actual images. We compare our results with the derived extinction law in the Galaxy and find them to run parallel to the Galactic extinction curve with a mean total-to-selective extinction value of R V = 2.71 ± 0.43. We use total optical extinction values to estimate the dust mass for each galaxy, compare these with dust masses derived from IRAS measurements, and find them to range from 10 4 to 10 7 M ⊙ . We study the case of the well-known dust-lane galaxy NGC 2685 for which Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2) data are available to test the dust distribution on different scales. Our results imply a scale-free dust distribution across the dust lanes, at least within ~ 1 arcsec (~60 pc) regions.