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Luminosity
Kinds of Luminosity Terms modified by Luminosity Selected AbstractsApplication of a digital technique in evaluating the reliability of shade guidesJOURNAL OF ORAL REHABILITATION, Issue 5 2004E. Cal summary, There appears to be a need for a reliable method for quantification of tooth colour and analysis of shade. Therefore, the primary objective of this study was to show the applicability of graphic software in colour analysis and secondly to investigate the reliability of commercial shade guides produced by the same manufacturer, using this digital technique. After confirming the reliability and reproducibility of the digital method by using self-assessed coloured images, three shade guides of the same manufacturer were photographed in daylight and in studio environments with a digital camera and saved in tagged image file format (TIFF) format. Colour analysis of each photograph was performed using the Adobe Photoshop 4·0 graphic program. Luminosity, and red, green, blue (L and RGB) values of each shade tab of each shade guide were measured and the data were subjected to statistical analysis using the repeated measure Anova test. The L and RGB values of the images taken in daylight differed significantly from those of the images taken in studio environment (P < 0·05). In both environments, the luminosity and red values of the shade tabs were significantly different from each other (P < 0·05). It was concluded that, when the environmental conditions were kept constant, the Adobe Photoshop 4·0 colour analysis program could be used to analyse the colour of images. On the other hand, the results revealed that the accuracy of shade tabs widely being used in colour matching should be readdressed. [source] The properties of the stellar populations in ULIRGs , I. Sample, data and spectral synthesis modellingMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009J. Rodríguez Zaurín ABSTRACT We present deep long-slit optical spectra for a sample of 36 ultraluminous infrared galaxies (ULIRGs), taken with the William Herschel Telescope on La Palma with the aim of investigating the star formation histories and testing evolutionary scenarios for such objects. Here we present the sample, the analysis techniques and a general overview of the properties of the stellar populations; a more detailed discussion will be presented in a forthcoming paper. Spectral synthesis modelling has been used in order to estimate the ages of the stellar populations found in the diffuse light sampled by the spectra in both the nuclear and extended regions of the target galaxies. We find that adequate fits can be obtained using combinations of young stellar populations (YSPs; tYSP, 2 Gyr), with ages divided into two groups: very young stellar populations (VYSPs; tVYSP, 100 Myr) and intermediate-young stellar populations (IYSPs; 0.1 < tIYSP, 2 Gyr). Our results show that YSPs are present at all locations of the galaxies covered by our slit positions, with the exception of the northern nuclear region of the ULIRG IRAS 23327+2913. Furthermore, VYSPs are present in at least 85 per cent of the 133 extraction apertures used for this study, being more significant in the nuclear regions of the galaxies. Old stellar populations (OSPs; tOSP > 2 Gyr) do not make a major contribution to the optical light in the majority of the apertures extracted. In fact they are essential for fitting the spectra in only 5 per cent (seven) of the extracted apertures. The estimated total masses for the YSPs (VYSPs + IYSPs) are in the range 0.18 × 1010,MYSP, 50 × 1010 M,. We have also estimated the bolometric luminosities associated with the stellar populations detected at optical wavelengths, finding that they fall in the range 0.07 × 1012 < Lbol < 2.2 × 1012 L,. In addition, we find that reddening is significant at all locations in the galaxies. This result emphasizes the importance of accounting for reddening effects when modelling the stellar populations of star-forming galaxies. [source] The haloes of planetary nebulae in the mid-infrared: evidence for interaction with the interstellar mediumMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009G. Ramos-Larios ABSTRACT The motion of planetary nebulae through the interstellar medium (ISM) is thought to lead to a variety of observational consequences, including the formation of bright rims, deformation and fragmentation of the shells, and a shift of the central stars away from the geometric centres of the envelopes. These and other characteristics have been noted through imaging in the visual wavelength regime. We report further observations of such shells taken in the mid-infrared (MIR), acquired through programmes of Infrared Array Camera imaging undertaken using the SpitzerSpace Telescope. NGC 2440 and NGC 6629 are shown to possess likely interacting haloes, together with ram-pressure-stripped material to one side of their shells. Similarly, the outer haloes of NGC 3242 and NGC 6772 appear to have been fragmented through Rayleigh,Taylor (RT) instabilities, leading to a possible flow of ISM material towards the inner portions of their envelopes. If this interpretation is correct, then it would suggest that NGC 3242 is moving towards the NE, a suggestion which is also supported through the presence of a 60 ,m tail extending in the opposite direction, and curved bands of H, emission in the direction of motion , components which may arise through RT instabilities in the magnetized ISM. NGC 2438 possesses strong scalloping at the outer limits of its asymptotic giant branch (AGB) halo, probably reflecting RT instabilities at the nebular/ISM interface We also note that the interior structure of the source has been interpreted in terms of a recombining shell, a hypothesis which may not be consistent with the central star luminosities. Finally, we point out that two of the rims (and likely shock interfaces) appear to have a distinct signature in the MIR, whereby relative levels of 8.0 ,m emission are reduced. This may imply that the grain emission agents are depleted in the post-shock AGB regimes. [source] On the interstellar medium and star formation demographics of galaxies in the local universeMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009Matthew S. Bothwell ABSTRACT We present a demographic analysis of integrated star formation and gas properties for a sample of galaxies representative of the overall population at z, 0. This research was undertaken in order to characterize the nature of star formation and interstellar medium (ISM) behaviour in the local Universe, and test the extent to which global star formation rates (SFRs) can be seen as dependent on the interstellar gas content. Archival 21-cm derived H i data are compiled from the literature, and are combined with CO (J =1 , 0) derived H2 masses to calculate and characterize the total gas content for a large sample of local galaxies. The distribution in stellar mass-normalized H i content is found to exhibit the noted characteristic transition at stellar masses of ,3 × 1010 M,, turning off towards low values, but no such transition is observed in the equivalent distribution of molecular gas. H, based SFRs and specific star formation rates (SSFRs) are also compiled for a large (1110) sample of local galaxies. We confirm two transitions as found in previous work: a turnover towards low SFRs at high luminosities, indicative of the quenching of SF characteristic of the red sequence; and a broadening of the SF distribution in low-luminosity dwarf galaxies, again to extremely low SFRs of <10,3 M, yr,1. However, a new finding is that while the upper luminosity transition is mirrored by the turnover in H i content, suggesting that the low SFRs of the red sequence result from a lack of available gas supply, the transition towards a large spread of SFRs in the least luminous dwarf galaxies is not matched by a prominent increase in scatter in gas content. Possible mass-dependent quenching mechanisms are discussed, along with speculations that in low-mass galaxies, the H, luminosity may not faithfully trace the SFR. [source] The properties of the heterogeneous Shakhbazyan groups of galaxies in the SDSSMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009D. Capozzi ABSTRACT We present a systematic study of the subsample of Shakhbazyan (SHK) groups covered by the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). SHK groups probe an environment with characteristics which are intermediate between those of loose and very compact groups. Surprisingly, we found that several groups identifying algorithms, e.g. Berlind et al. and Tago et al., miss this type of structures. Using the SDSS DR5 spectroscopic data and the photometric redshifts derived in D'Abrusco et al., we identified possible group members in photometric redshift space and derived, for each group, several individual properties (richness, size, mean photometric redshift, fraction of red galaxies, etc.). We also combined pointed and stacked Rosat All Sky Survey (RASS) data to investigate the X-ray luminosities of these systems. Our study confirms that the majority of groups are physical entities with richness in the range 3,13 galaxies, and properties ranging between those of loose and compact groups. We confirm that SHK groups are richer in early-type galaxies than the surrounding environment and the field, as expected from the morphology,density relation and from the selection of groups of red galaxies. Furthermore, our work supports the existence of two subclasses of structures, the first one being formed by compact and isolated groups and the second formed by extended structures. We suggest that while the first class of objects dwells in less dense regions like the outer parts of clusters or the field, possibly sharing the properties of Hickson Compact Groups, the more extended structures represent a mixture of [core + halo] configurations and cores of rich clusters. X-ray luminosities for SHK groups are generally consistent with these results and with the expectations for the LX,,v relation, but also suggest the velocity dispersions reported in literature are underestimated for some of the richest systems. [source] A halo model of galaxy colours and clustering in the Sloan Digital Sky SurveyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009Ramin A. Skibba ABSTRACT Successful halo-model descriptions of the luminosity dependence of clustering distinguish between the central galaxy in a halo and all the others (satellites). To include colours, we provide a prescription for how the colour,magnitude relation of centrals and satellites depends on halo mass. This follows from two assumptions: (i) the bimodality of the colour distribution at a fixed luminosity is independent of halo mass and (ii) the fraction of satellite galaxies which populate the red sequence increases with luminosity. We show that these two assumptions allow one to build a model of how galaxy clustering depends on colour without any additional free parameters than those required to model the luminosity dependence of galaxy clustering. We then show that the resulting model is in good agreement with the distribution and clustering of colours in the Sloan Digital Sky Survey, both by comparing the predicted correlation functions of red and blue galaxies with measurements and by comparing the predicted colour,mark correlation function with the measured one. Mark correlation functions are powerful tools for identifying and quantifying correlations between galaxy properties and their environments: our results indicate that the correlation between halo mass and environment is the primary driver for correlations between galaxy colours and the environment; additional correlations associated with halo ,assembly bias' are relatively small. Our approach shows explicitly how to construct mock catalogues which include both luminosities and colours , thus providing realistic training sets for, e.g., galaxy cluster-finding algorithms. Our prescription is the first step towards incorporating the entire spectral energy distribution into the halo model approach. [source] A semi-empirical model of the infrared emission from galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008D. C. Ford ABSTRACT We present a semi-empirical model for the infrared emission of dust around star-forming sites in galaxies. Our approach combines a simple model of radiative transfer in dust clouds with a state-of-the-art model of the microscopic optical properties of dust grains pioneered by Draine & Li. In combination with the starburst99 stellar spectral synthesis package, this framework is able to produce synthetic spectra for galaxies which extend from the Lyman limit through to the far-infrared. We use it to probe how model galaxy spectra depend on the physical characteristics of their dust grain populations, and on the energy sources which heat that dust. We compare the predictions of our model with the 8- and 24-,m luminosities of sources in the Spitzer First Look Survey, and conclude by using the models to analyse the relative merits of various colour diagnostics in distinguishing systems out to a redshift of 2 with ongoing star formation from those with only old stellar populations. [source] The transverse proximity effect in the z, 2 Lyman , forest suggests quasi-stellar object episodic lifetimes of ,1 MyrMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008David Kirkman ABSTRACT We look for signs of the H i transverse proximity effect in the spectra of 130 quasi-stellar object (QSO) pairs, most with transverse separations in the plane of the sky of 0.1,3 Mpc at z, 2.2. We expected to see a decrease in Ly, forest H i absorption in the spectrum of background QSOs near the position of foreground QSOs. Instead, we see no change in the absorption in front of the foreground QSOs, and we see evidence for a 50 per cent increase in the absorption out to 6 Mpc behind the foreground QSOs. Further, we see no change in the H i absorption along the line-of-sight to the foreground QSOs, the normal line-of-sight proximity effect. We may account for the lack of change in the H i absorption if the effect of extra ultraviolet photons is cancelled by higher gas density around QSOs. If so, the increase in absorption behind the QSOs then suggests that the higher gas density there is not cancelled by the UV radiation from the QSOs. We can explain our observations if QSOs have had their current UV luminosities for less than approximately a million years, a time-scale that has been suggested for accretion disc instabilities and gas depletion. [source] A survey for redshifted molecular and atomic absorption lines , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 20083 Parkes quarter-Jansky flat-spectrum sample, Associated H i, millimetre lines in the z ABSTRACT We present the results of a z, 2.9 survey for H i 21-cm and molecular absorption in the hosts of radio quasars using the Giant Metrewave Radio Telescope and the Tidbinbilla 70-m telescope. Although the atomic gas has been searched to limits capable of detecting most known absorption systems, no H i was detected in any of the 10 sources. Previously published searches, which are overwhelmingly at redshifts of z, 1, exhibit a 42 per cent detection rate (31 out of 73 sources), whereas the inclusion of our survey yields a 17 per cent detection rate (two out of 12 sources) at z > 2.5. We therefore believe that our high-redshift selection is responsible for our exclusive non-detections, and find that at ultraviolet (UV) luminosities of LUV, 1023 W Hz,1, 21-cm absorption has never been detected. We also find this to not only apply to our targets, but also those at low redshift exhibiting similar luminosities, giving zero detections out of a total of 16 sources over z= 0.24 to 3.8. This is in contrast to the LUV, 1023 W Hz,1 sources where there is a near 50 per cent detection rate of 21-cm absorption. The mix of 21-cm detections and non-detections is currently attributed to orientation effects, where according to unified schemes of active galactic nuclei, 21-cm absorption is more likely to occur in sources designated as radio galaxies (type 2 objects, where the nucleus is viewed through dense obscuring circumnuclear gas) than in quasars (type 1 objects, where we have a direct view to the nucleus). However, due to the exclusively high UV luminosities of our targets it is not clear whether orientation effects alone can wholly account for the distribution, although there exists the possibility that the large luminosities are indicative of a changing demographic of galaxy types. We also find that below luminosities of LUV, 1023 W Hz,1, both type 1 and type 2 objects have a 50 per cent likelihood of exhibiting 21-cm absorption. Finally, we do not detect molecular gas in any of the sources. The lack of H i absorption, combined with the results from Paper I, suggests these sources are not conducive to high molecular abundances. [source] Where are the cosmic metals at z, 3?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Jesper Sommer-Larsen ABSTRACT The global temperature distribution of the cosmic gas-phase oxygen at z, 3 is determined by combining high-resolution cosmological simulations of individual protogalactic as well as larger regions with the observed, extinction-corrected, rest-frame V -band galaxy luminosity function. The simulations have been performed with three different stellar initial mass functions (IMFs), a Kroupa (K98), a Salpeter (S) and an Arimoto,Yoshii (AY), spanning a range of a factor of 5 in chemical yield and specific supernova type II energy feedback. Gas-phase oxygen is binned according to T as log(T) , 4.0 (,cold'), log(T) , 4.5 (,warm') and log(T) , 5.0, 5.5, 6.0, 6.5, 7.0 (,hot' phases). Oxygen is found to be distributed over all T phases, in particular for the top-heavy AY IMF. But, at variance with previous works, it is found that for the K98 and S IMFs the cold phase is the most important. For these IMFs it contains 47 and 37 per cent, respectively, of all gas-phase oxygen, mainly at fairly high density, nH, 0.1 cm,3. The implications of this in relation to observational damped Ly, absorber studies are discussed. In relation to ,missing metals' it is found that a significant fraction of the oxygen is located in a warm/hot phase that may be very difficult to detect. Moreover, it is found that less than about 20,25 per cent of the cosmic oxygen is associated with galaxies brighter than MV,,22, i.e. the faintest galaxy luminosities probed by current metallicity determinations for Lyman-break galaxies (LBGs). Hence, 75,80 per cent of the oxygen is also in this sense ,missing'. From the LBG-based, ,, 1500Å ultraviolet luminosity density history at z, 3, we obtain an essentially IMF-independent constraint on the mean oxygen density at z= 3. We compare this to what is obtained from our models, for the three different IMFs. We find that the K98 IMF is strongly excluded, as the chemical yield is simply too small, the Salpeter is marginally excluded, and the AY matches the constraint well. The K98 IMF can only match the data if the ,, 1500Å extinction corrections have been overestimated by factor of ,4, which seems highly unlikely. The yields for K98 are also far too small to match the observational data for C iv. The optimal IMF should have a yield intermediate between the S and AY. [source] The 2dF-SDSS LRG and QSO survey: QSO clustering and the L,z degeneracyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008J. DaÂngela ABSTRACT We combine the quasi-stellar object (QSO) samples from the 2dF QSO Redshift Survey (2QZ) and the 2dF-Sloan Digital Sky Survey luminous red galaxy (LRG) and QSO Survey (2dF-SDSS LRG and QSO, hereafter 2SLAQ) in order to investigate the clustering of z, 1.5 QSOs and measure the correlation function (,). The clustering signal in redshift-space and projected along the sky direction is similar to that previously obtained from the 2QZ sample alone. By fitting functional forms for ,(,, ,), the correlation function measured along and across the line of sight, we find, as expected, that ,, the dynamical infall parameter and ,0m, the cosmological density parameter, are degenerate. However, this degeneracy can be lifted by using linear theory predictions under different cosmological scenarios. Using the combination of the 2QZ and 2SLAQ QSO data, we obtain: ,QSO(z= 1.5) = 0.60+0.14,0.11, ,0m= 0.25+0.09,0.07 which imply a value for the QSO bias, b(z= 1.4) = 1.5 ± 0.2. The combination of the 2QZ with the fainter 2SLAQ QSO sample further reveals that QSO clustering does not depend strongly on luminosity at fixed redshift. This result is inconsistent with the expectation of simple ,high peaks' biasing models where more luminous, rare QSOs are assumed to inhabit higher mass haloes. The data are more consistent with models which predict that QSOs of different luminosities reside in haloes of similar mass. By assuming ellipsoidal models for the collapse of density perturbations, we estimate the mass of the dark matter haloes which the QSOs inhabit as ,3 × 1012 h,1 M,. We find that this halo mass does not evolve strongly with redshift nor depend on QSO luminosity. Assuming a range of relations which relate halo to black hole mass, we investigate how black hole mass correlates with luminosity and redshift, and ascertain the relation between Eddington efficiency and black hole mass. Our results suggest that QSOs of different luminosities may contain black holes of similar mass. [source] Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007J. Thomas ABSTRACT Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB=,18.79 and ,22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1,4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10,50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss,Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations. [source] Parallel tracks in infrared versus X-ray emission in black hole X-ray transient outbursts: a hysteresis effect?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007David M. Russell ABSTRACT We report the discovery of a new hysteresis effect in black hole X-ray binary state transitions, that of the near-infrared (NIR) flux (which most likely originates in the jets) versus X-ray flux. We find, looking at existing data sets, that the IR emission of black hole X-ray transients appears to be weaker in the low/hard state rise of an outburst than the low/hard state decline of an outburst at a given X-ray luminosity. We discuss how this effect may be caused by a shift in the radiative efficiency of the inflowing or outflowing matter, or variations in the disc viscosity or the spectrum/power of the jet. In addition we show that there is a correlation (in slope but not in normalization) between IR and X-ray luminosities on the rise and decline, for all three low-mass black hole X-ray binaries with well-sampled IR and X-ray coverage: LNIR,L0.5,0.7X. In the high/soft state this slope is much shallower; LNIR,L0.1,0.2X, and we find that the NIR emission in this state is most likely dominated by the viscously heated (as opposed to X-ray heated) accretion disc in all three sources. [source] The XMM-SSC survey of hard-spectrum XMM,Newton sources , I. Optically bright sourcesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007M. J. Page ABSTRACT We present optical and X-ray data for a sample of serendipitous XMM,Newton sources that are selected to have 0.5,2 versus 2,4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2,4.5 keV X-ray flux ,10,14 erg cm,2 s,1, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association rather than the correct identification of the X-ray source. The X-ray spectra of all the sources are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them, including the two sources with 2,10 keV intrinsic luminosities of <1042 erg s,1, appear to be absorbed active galactic nuclei (AGN). The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type 2 AGN. Three sources have 2,10 keV luminosities of >1044 erg s,1, and two of these sources have optical spectra which are dominated by narrow emission lines, that is, are type 2 QSOs. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 1023 cm,2. This implies that ratios of X-ray absorption to optical/ultraviolet extinction equivalent to >100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few per cent of the population), and may be restricted to broad absorption line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law; all seven are narrow emission-line objects with z < 0.3 and 2,10 keV intrinsic luminosities <1043 erg s,1. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that >4 per cent of broad-line AGN (BLAGN) have ionized absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray-absorbed BLAGN in our sample the X-ray spectrum requires an ionized absorber, consistent with this picture. [source] Searches for ultracompact dwarf galaxies in galaxy groupsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007E. A. Evstigneeva ABSTRACT We present the results of a search for ultracompact dwarf galaxies (UCDs) in six different galaxy groups: Dorado, NGC 1400, 0681, 4038, 4697 and 5084. We searched in the apparent magnitude range 17.5 ,bJ, 20.5 (except NGC 5084: 19.2 ,bJ, 21.0). We found one definite plus two possible UCD candidates in the Dorado group and two possible UCD candidates in the NGC 1400 group. No UCDs were found in the other groups. We compared these results with predicted luminosities of UCDs in the groups according to the hypothesis that UCDs are globular clusters formed in galaxies. The theoretical predictions broadly agree with the observational results, but deeper surveys are needed to fully test the predictions. [source] VIMOS-VLT spectroscopy of the giant Ly, nebulae associated with three z, 2.5 radio galaxies,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007M. Villar-Martín ABSTRACT The morphological and spectroscopic properties of the giant (>60 kpc) Ly, nebulae associated with three radio galaxies at z, 2.5 (MRC 1558,003, 2025,218 and 0140,257) have been investigated using integral field spectroscopic data obtained with the Visible Multi-Object Spectrograph (VIMOS) on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within ,30°. The total Ly, luminosities are in the range (0.3,3.4) × 1044 erg s,1. The Ly, spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range ,400,1500 km s,1 and velocity shifts Voffset, 120,600 km s,1. We present an infall model that can successfully explain the morphology, size, surface brightness distribution and the velocity field of the Ly, nebula associated with MRC 1558,003. It can also explain why Ly, is redshifted relative to other emission lines and the FWHM values of the non-resonant He ii line. This adds further support to our previous conclusion that the quiescent giant nebulae associated with this and other high-redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Ly, FWHM values, which might be the consequence of a different mechanism. We have discovered a giant (,85 kpc) Ly, nebula associated with the radio galaxy MRC 0140,257 at z= 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s,1 and Voffset, 120 km s,1), unique among high- z (,2) radio galaxies. [source] Accurate fundamental parameters for lower main-sequence starsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006Luca Casagrande ABSTRACT We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI)CJHKS photometry, excellent parallaxes and good metallicities. Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement. A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology. Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices. We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem. [source] A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula SpectrographMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2006H. R. Merrett ABSTRACT We present a catalogue of positions, magnitudes and velocities for 3300 emission-line objects found by the Planetary Nebula Spectrograph in a survey of the Andromeda galaxy, M31. Of these objects, 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers the whole of M31's disc out to a radius of . Beyond this radius, observations have been made along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high surface brightness region of M31, this survey is complete to a magnitude limit of m5007, 23.75, 3.5 mag into the PN luminosity function. We have identified emission-line objects associated with M31's satellites and other background galaxies. We have examined the data from the region tentatively identified as a new satellite galaxy, Andromeda VIII, comparing it to data in the other quadrants of the galaxy. We find that the PNe in this region have velocities that appear to be consistent with membership of M31 itself. The luminosity function of the surveyed PNe is well matched to the usual smooth monotonic function. The only significant spatial variation in the luminosity function occurs in the vicinity of M31's molecular ring, where the luminosities of PNe on the near side of the galaxy are systematically ,0.2 mag fainter than those on the far side. This difference can be explained naturally by a modest amount of obscuration by the ring. The absence of any difference in luminosity function between bulge and disc suggests that the sample of PNe is not strongly populated by objects whose progenitors are more massive stars. This conclusion is reinforced by the excellent agreement between the number counts of PNe and the R -band light. The number counts of kinematically selected PNe also allow us to probe the stellar distribution in M31 down to very faint limits. There is no indication of a cut-off in M31's disc out to beyond four scalelengths, and no signs of a spheroidal halo population in excess of the bulge out to 10 effective bulge radii. We have also carried out a preliminary analysis of the kinematics of the surveyed PNe. The mean streaming velocity of the M31 disc PNe is found to show a significant asymmetric drift out to large radii. Their velocity dispersion, although initially declining with radius, flattens out to a constant value in the outer parts of the galaxy. There are no indications that the disc velocity dispersion varies with PN luminosity, once again implying that the progenitors of PNe of all magnitudes form a relatively homogeneous old population. The dispersion profile and asymmetric drift results are shown to be mutually consistent, but require that the disc flares with radius if the shape of its velocity ellipsoid remains invariant. [source] Halo model at its best: constraints on conditional luminosity functions from measured galaxy statisticsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Asantha Cooray ABSTRACT Using the conditional luminosity function (CLF; the luminosity distribution of galaxies in a dark matter halo) as the fundamental building block, we present an empirical model for the galaxy distribution. The model predictions are compared with the published luminosity function (LF) and clustering statistics from the Sloan Digital Sky Survey (SDSS) at low redshifts, galaxy correlation functions from the Classifying Objects by Medium-Band Observations 17 (COMBO-17) survey at a redshift of 0.6, the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey at a redshift of unity, the Great Observatories Deep Origins Survey (GOODS) at a redshift around 3 and the Subaru/XMM,Newton Deep Field data at a redshift of 4. The comparison with statistical measurements allows us to constrain certain parameters related to analytical descriptions on the relation between a dark matter halo and its central galaxy luminosity, its satellite galaxy luminosity, and the fraction of early- and late-type galaxies of that halo. With the SDSS r -band LF at Mr < ,17, the lognormal scatter in the central galaxy luminosity at a given halo mass in the central galaxy,halo mass, Lc(M), relation is constrained to be 0.17+0.02,0.01, with 1, errors here and below. For the same galaxy sample, we find no evidence for a low-mass cut-off in the appearance of a single central galaxy in dark matter haloes, with the 68 per cent confidence level upper limit on the minimum mass of dark matter haloes to host a central galaxy, with luminosity Mr < ,17, is 2 × 1010 h,1 M,. If the total luminosity of a dark matter halo varies with halo mass as Lc(M) (M/Msat),s when M > Msat, using SDSS data, we find that Msat= (1.2+2.9,1.1) × 1013 h,1 M, and power-law slope ,s= 0.56+0.19,0.17 for galaxies with Mr < ,17 at z < 0.1. At z, 0.6, the COMBO-17 data allows these parameters for MB < ,18 galaxies to be constrained as (3.3+4.9,3.0) × 1013 h,1 M, and (0.62+0.33,0.27), respectively. At z, 4, Subaru measurements constrain these parameters for MB < ,18.5 galaxies as (4.12+5.90,4.08) × 1012 h,1 M, and (0.55+0.32,0.35), respectively. The redshift evolution associated with these parameters can be described as a combination of the evolution associated with the halo mass function and the luminosity,halo mass relation. The single parameter well constrained by clustering measurements is the average of the total satellite galaxy luminosity corresponding to the dark matter halo distribution probed by the galaxy sample. For SDSS, ,Lsat,= (2.1+0.8,0.4) × 1010 h,2 L,, while for GOODS at z, 3, ,Lsat, < 2 × 1011 h,2 L,. For SDSS, the fraction of galaxies that appear as satellites is 0.13+0.03,0.03, 0.11+0.05,0.02, 0.11+0.12,0.03 and 0.12+0.33,0.05 for galaxies with luminosities in the r, band from ,22 to ,21, ,21 to ,20, ,20 to ,19 and ,19 to ,18, respectively. In addition to constraints on central and satellite CLFs, we also determine model parameters of the analytical relations that describe the fraction of early- and late-type galaxies in dark matter haloes. We use our CLFs to establish the probability distribution of halo mass in which galaxies of a given luminosity could be found either at halo centres or as satellites. Finally, to help establish further properties of the galaxy distribution, we propose the measurement of cross-clustering between galaxies divided into two distinctly different luminosity bins. Our analysis shows how CLFs provide a stronger foundation to built-up analytical models of the galaxy distribution when compared with models based on the halo occupation number alone. [source] On the orbital period modulation of RS CVn binary systemsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Antonino F. Lanza ABSTRACT The Applegate hypothesis proposed to explain the orbital period modulation of RS Canum Venaticorum (RS CVn) close binaries (Applegate 1992) is considered in the framework of a general model to treat the angular momentum exchanges within the convective envelope of a magnetically active star. This model assumes that the convection zone is strictly adiabatic and that the Taylor,Proudman balance holds, leading to an internal angular velocity constant over cylindrical surfaces co-axial with the rotation axis. It turns out that the angular velocity perturbations, whatever their origin, can be expressed in terms of the eigenfunctions of the equation of angular momentum conservation with stress-free boundary conditions. Moreover, a lower limit for the energy dissipation rate in a turbulent convection zone can be set, thanks to the extremal properties of the eigenfunctions. This approach allows to apply precise constraints on the amplitude and the radial profile of the angular velocity variations that are required to explain the observed orbital period changes in classical RS CVn binaries (i.e. with orbital period longer than 1,2 d and a subgiant secondary component). It is found that an angular velocity change as large as 10 per cent of the unperturbed angular velocity at the base of the stellar convection zone is needed. Such a large change is not compatible with the observations. Moreover, it would produce an energy dissipation rate much larger than the typical luminosities of the active components of RS CVn systems, except in the case that fast rotation and internal magnetic fields reduce the turbulent viscosity by at least 2 orders of magnitude with respect to the value given by the mixing-length theory. Therefore, the model proposed by Applegate should be rejected, at least in the case of classical RS CVn close binaries. Possible alternative models are briefly discussed, emphasizing the effects of intense magnetic fields (, 10 T) on the internal structure of magnetically active stars and the dynamics of close binary systems. [source] Galaxy groups in the Two-degree Field Galaxy Redshift Survey: the luminous content of the groupsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004V. R. Eke ABSTRACT The Two-degree Field Galaxy Redshift Survey (2dFGRS) Percolation-Inferred Galaxy Group (2PIGG) catalogue of ,29 000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. It is found that a Schechter function is a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, and that the characteristic luminosity L, is slightly larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. Luminosity function results are presented in both the bJ and rF wavebands. The variation of the halo mass-to-light ratio, ,, with group size is studied in both of these wavebands. A robust trend of increasing , with increasing group luminosity is found in the 2PIGG data. Going from groups with bJ luminosities equal to 1010 h,2 L, to those 100 times more luminous, the typical bJ -band mass-to-light ratio increases by a factor of 5, whereas the rF -band mass-to-light ratio grows by a factor of 3.5. These trends agree well with the predictions of the simulations which also predict a minimum in the mass-to-light ratio on a scale roughly corresponding to the Local Group. The data indicate that if such a minimum exists, then it must occur at L, 1010h,2 L,, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bJ mass-to-light ratios of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data, the mean bJ luminosity density of the Universe yields an estimate of ,m= 0.26 ± 0.03 (statistical error only). Various possible sources of systematic error are considered, with the conclusion that these could affect the estimate of ,m by a few tens of per cent. [source] Star formation in close pairs selected from the Sloan Digital Sky SurveyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004B. Nikolic ABSTRACT The effect of galaxy interactions on star formation has been investigated using Data Release One of the Sloan Digital Sky Survey (SDSS). Both the imaging and spectroscopy data products have been used to construct a catalogue of nearest companions to a volume-limited (0.03 < z < 0.1) sample of galaxies drawn from the main galaxy sample of SDSS. Of the 13 973 galaxies in the volume-limited sample, we have identified 12 492 systems with companions at projected separations less than 300 kpc. Star formation rates for the volume-limited sample have been calculated from extinction and aperture corrected H, luminosities and, where available, IRAS data. Specific star formation rates were calculated by estimating galaxy masses from z -band luminosities, and r -band concentration indices were used as an indicator of morphological class. The mean specific star formation rate is significantly enhanced for projected separations less than 30 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star formation rate is observed to decrease with increasing recessional velocity difference, but the magnitude of this effect is small compared to that associated with the projected separation. We also observe a tight relationship between the concentration index and pair separation; the mean concentration index is largest for pairs with separations of approximately 75 kpc and declines rapidly for separations smaller than this. This is interpreted as being due to the presence of tidally triggered nuclear starbursts in close pairs. Further, we find no dependence of star formation enhancement on the morphological type or mass of the companion galaxy. [source] MSX mid-infrared imaging of massive star birth environments , II.MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004Giant H ii regions ABSTRACT We conduct a Galactic census of giant H ii (GH ii) regions, based on the all-sky 6-cm data set of Kuchar & Clark, plus the kinematic distances obtained by Russeil. From an inspection of mid-infrared (MIR) Mid-course Space Experiment (MSX) and far-IR IRAS Sky Survey Atlas images, we identify a total of 56 GH ii regions in the Milky Way, of which 15 per cent (65 per cent) can be seen at optical (near-IR) wavelengths. The mid to far-IR fluxes from each GH ii region are measured, and sample the thermal emission from the ubiquitous dust present within the exciting clusters of OB stars, arising from the integrated luminosity of the hot stars heating the cluster dust, for which we obtain log L(IR) = 5.5,7.3 L,. The MIR 21-,m spatial morphology is presented for each GH ii region, and often indicates multiple emission sources, suggesting complicated cluster formation. IR colour,colour diagrams are presented, providing information concerning the temperature distribution and the optical depth of the dust. For the clusters of our study, the dust is not optically thick to all stellar radiation, thus the measured infrared luminosity is lower than Lbol. As the dust environment of a cluster begins to dissipate, the thermal emission and its optical depth ought to decrease even before the stars evolve appreciably. We see evidence of this in our empirical relationship between the integrated IR and Lyman continuum luminosities. [source] The environmental dependence of radio-loud AGN activity and star formation in the 2dFGRSMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2004P. N. Best ABSTRACT By combining the 2-degree Field Galaxy Redshift Survey with the NRAO VLA Sky Survey at 1.4 GHz, the environments of radio-loud active galactic nuclei (AGN) in the nearby Universe are investigated using both local projected galaxy densities and a friends-of-friends group-finding algorithm. Radio-loud AGN are preferentially located in galaxy groups and poor-to-moderate richness galaxy clusters. The AGN fraction appears to depend more strongly on the large-scale environment (group, cluster, etc.) in which a galaxy is located than on its more local environment, except at the lowest galaxy surface densities where practically no radio-loud AGN are found. The ratio of absorption-line to emission-line AGN changes dramatically with environment, with essentially all radio-loud AGN in rich environments showing no emission lines. This result could be connected with the lack of cool gas in cluster galaxies, and may have important consequences for analyses of optically selected AGN, which are invariably selected on emission-line properties. The local galaxy surface density of the absorption-line AGN is strongly correlated with radio luminosity, implying that the radio luminosities may be significantly boosted in dense environments due to confinement by the hot intracluster gas. The environments of a radio-selected sample of star-forming galaxies are also investigated to provide an independent test of optical studies. In line with those studies, the fraction of star-forming galaxies is found to decrease strongly with increasing local galaxy surface density; this correlation extends across the whole range of galaxy surface densities, with no evidence for the density threshold found in some optical studies. [source] Populating dark matter haloes with galaxies: comparing the 2dFGRS with mock galaxy redshift surveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004Xiaohu Yang ABSTRACT In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as a function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N -body simulations of the standard ,CDM cosmology with ,m= 0.3, ,,= 0.7 and ,8= 0.9. Stacking simulation boxes of 100 h,1 Mpc and 300 h,1 Mpc with 5123 particles each we construct mock galaxy redshift surveys out to a redshift of z= 0.2 with a numerical resolution that guarantees completeness down to 0.01L*. We use these mock surveys to investigate various clustering statistics. The predicted two-dimensional correlation function ,(rp, ,) reveals clear signatures of redshift space distortions. The projected correlation functions for galaxies with different luminosities and types, derived from ,(rp, ,), match the observations well on scales larger than ,3 h,1 Mpc. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Modelling the ,finger-of-God' effect on small scales reveals that the standard ,CDM model predicts pairwise velocity dispersions (PVD) that are ,400 km s,1 too high at projected pair separations of ,1 h,1 Mpc. A strong velocity bias in massive haloes, with bvel,,gal/,dm, 0.6 (where ,gal and ,dm are the velocity dispersions of galaxies and dark matter particles, respectively) can reduce the predicted PVD to the observed level, but does not help to resolve the overprediction of clustering power on small scales. Consistent results can be obtained within the standard ,CDM model only when the average mass-to-light ratio of clusters is of the order of 1000 (M/L), in the B -band. Alternatively, as we show by a simple approximation, a ,CDM model with ,8, 0.75 may also reproduce the observational results. We discuss our results in light of the recent WMAP results and the constraints on ,8 obtained independently from other observations. [source] Dust emission in the far-infrared as a star formation tracer at z= 0: systematic trends with luminosityMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003D. Pierini ABSTRACT We investigate whether dust emission in the far-infrared (far-IR) continuum provides a robust estimate of the star formation rate (SFR) for a nearby, normal late-type galaxy. We focus on the ratio of the 40,1000 ,m luminosity (Ldust) to the far-ultraviolet (far-UV) (0.165 ,m) luminosity, which is connected to recent episodes of star formation. Available total photometry at 0.165, 60, 100 and 170 ,m limits the statistics to 30 galaxies, which, however, span a large range in observed (and, thus, attenuated by dust) K -band (2.2 ,m) luminosity, morphology and inclination (i). This sample shows that the ratio of Ldust to the observed far-UV luminosity depends not only on i, as expected, but also on morphology and, in a tighter way, on observed K -band luminosity. We find that Ldust/LFUV, eLK0.62, where LFUV and LK are the unattenuated stellar luminosities in far-UV and K, respectively, and , is the ratio of the attenuation optical depths at 0.165 ,m (,FUV) and 2.2 ,m (,K). This relation is to zeroth order independent of i and morphology. It may be further expressed as Ldust/LFUV,L,K, where ,= 0.61 , 0.02,, under the observationally motivated assumption that, for an average inclination, e,L,0.02K. We adopt calculations of two different models of attenuation of stellar light by internal dust to derive solid-angle-averaged values of ,. We find that , is positive and decreases towards 0 from the more luminous to the less luminous galaxies. This means that there is no universal ratio of far-IR luminosity to unattenuated far-UV luminosity for nearby, normal late-type galaxies. The far-IR luminosity systematically overestimates SFR in more luminous, earlier-type spirals, owing to the increased fractional contribution to dust heating of optical/near-IR photons in these objects. Conversely, it systematically underestimates SFR in fainter, later-type galaxies, the ,FUV of which is reduced. The limited statistics and the uncertainty affecting the previous scaling relations do not allow us to establish quantitative conclusions, but an analogous analysis making use of larger data sets, available in the near future (e.g. from GALEX, ASTRO-F and SIRTF), and of more advanced models will allow a quantitative test of our conclusions. [source] Detection of type 2 quasars in the radio galaxies B3 0731+438 and 3C 257MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003P. M. Derry ABSTRACT We present XMM,Newton observations and spectral fitting of two high-redshift, [O iii]-luminous, narrow-line radio galaxies, B3 0731+438 and 3C 257. Their X-ray continua are well fitted by a partial covering model with intrinsically unabsorbed and absorbed power-law components. The spectral models indicate that both objects harbour highly obscured nuclei, with NH, 0.5,2 × 1023 cm,2. Correcting for this absorption we find large intrinsic luminosities in the range LX, 0.2,1 × 1045 erg s,1. Thus, both sources are type 2 quasars. [source] Galaxies as fluctuations in the ionizing background radiation at low redshiftMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2003Suzanne M. Linder ABSTRACT Some Lyman continuum photons are likely to escape from most galaxies, and these can play an important role in ionizing gas around and between galaxies, including gas that gives rise to Lyman-alpha absorption. Thus the gas surrounding galaxies and in the intergalactic medium will be exposed to varying amounts of ionizing radiation depending upon the distances, orientations and luminosities of any nearby galaxies. The ionizing background can be recalculated at any point within a simulation by adding the flux from the galaxies to a uniform quasar contribution. Normal galaxies are found to almost always make some contribution to the ionizing background radiation at a redshift of zero, as seen by absorbers and at random points in space. Assuming that ,2 per cent of ionizing photons escape from a galaxy such as the Milky Way, we find that normal galaxies make a contribution of at least 30,40 per cent of the assumed quasar background. Lyman-alpha absorbers with a wide range of neutral column densities are found to be exposed to a wide range of ionization rates, although the distribution of photoionization rates for absorbers is found to be strongly peaked. On average, fewer highly ionized absorbers are found to arise further from luminous galaxies, while local fluctuations in the ionization rate are seen around galaxies having a wide range of properties. [source] Hubble Space Telescope Wide Field Planetary Camera 2 observations of hyperluminous infrared galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2002D. Farrah We present Hubble Space Telescope Wide Field Planetary Camera 2 I -band imaging for a sample of nine hyperluminous infrared galaxies (HLIRGs) spanning a redshift range . Three of the sample have morphologies showing evidence for interactions and six are quasi-stellar objects (QSOs). Host galaxies in the QSOs are detected reliably out to . The detected QSO host galaxies have an elliptical morphology with scalelengths spanning and absolute k -corrected magnitudes spanning There is no clear correlation between the infrared (IR) power source and the optical morphology. None of the sources in the sample, including F15307+3252, shows any evidence for gravitational lensing. We infer that the IR luminosities are thus real. Based on these results, and previous studies of HLIRGs, we conclude that this class of object is broadly consistent with being a simple extrapolation of the ULIRG population to higher luminosities; ULIRGs being mainly violently interacting systems powered by starbursts and/or active galactic nuclei. Only a small number of sources, the infrared luminosities of which exceed 1013 L,, are intrinsically less luminous objects that have been boosted by gravitational lensing. [source] A catalogue and analysis of X-ray luminosities of early-type galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001Ewan O'Sullivan We present a catalogue of X-ray luminosities for 401 early-type galaxies, of which 136 are based on newly analysed ROSAT PSPC pointed observations. The remaining luminosities are taken from the literature and converted to a common energy band, spectral model and distance scale. Using this sample we fit the LX : LB relation for early-type galaxies and find a best-fit slope for the catalogue of ,2.2. We demonstrate the influence of group-dominant galaxies on the fit and present evidence that the relation is not well modelled by a single power-law fit. We also derive estimates of the contribution to galaxy X-ray luminosities from discrete-sources and conclude that they provide . We compare this result with luminosities from our catalogue. Lastly, we examine the influence of environment on galaxy X-ray luminosity and on the form of the relation. We conclude that although environment undoubtedly affects the X-ray properties of individual galaxies, particularly those in the centres of groups and clusters, it does not change the nature of whole populations. [source] | |||||||||||||