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Nova in M31
We report the discovery of a possible nova in M31 on a R-band CCD imageat JD 2453894.52 (2006, June 8.02 UT) with 18.0 mag (accuracy 0.1 mag).The image was obtained with the Wendelstein telescope (0.8 m, 1k x 1kCCD camera with 24mu sq. pixels). The position obtained for the novacandidate is RA(2000) = 00h 42m 32.77s, Dec(2000) = +41° 16'49.2" with an accuracy of 0.1". At the position of the nova candidatealready on JD 2453880.55 (2006, May 25.05 UT) a fainter source with 18.5mag (accuracy 0.2 mag) was visible.
| Nova in M31
We report the discovery of a possible nova in M31 on a R band CCD imageat JD 2453877.5 (2006, May 22.1 UT) with 18.7 mag (accuracy 0.1 mag).The image was obtained with the Wendelstein telescope (0.8 m, 1k x 1kCCD camera with 24mu sq. pixels). The position obtained for the novacandidate is RA(2000) = 00h 43m 11.81s, Dec(2000) = +41° 13'44.7" with an accuracy of 0.1". At the position of the nova candidate nostar brighter than 21.5 mag (1 sigma) was detected on 2006, May 12.2 UTon a Wendelstein R band image.
| RR Lyrae-based calibration of the Globular Cluster Luminosity Function
We test whether the peak absolute magnitude MV(TO) of theGlobular Cluster Luminosity Function (GCLF) can be used for reliableextragalactic distance determination. Starting with the luminosityfunction of the Galactic Globular Clusters listed in Harris catalogue,we determine MV(TO) either using current calibrations of theabsolute magnitude MV(RR) of RR Lyrae stars as a function ofthe cluster metal content [Fe/H] and adopting selected cluster samples.We show that the peak magnitude is slightly affected by the adoptedMV(RR)-[Fe/H] relation, with the exception of that based onthe revised Baade-Wesselink method, while it depends on the criteria toselect the cluster sample. Moreover, grouping the Galactic GlobularClusters by metallicity, we find that the metal-poor (MP) ([Fe/H]<-1.0, <[Fe/H]>~-1.6) sample shows peak magnitudes systematicallybrighter by about 0.36mag than those of the metal-rich (MR) ([Fe/H]>-1.0, (<[Fe/H]>~-0.6) one, in substantial agreement with thetheoretical metallicity effect suggested by synthetic Globular Clusterpopulations with constant age and mass function. Moving outside theMilky Way, we show that the peak magnitude of the MP clusters in M31appears to be consistent with that of Galactic clusters with similarmetallicity, once the same MV(RR)-[Fe/H] relation is used fordistance determination. As for the GCLFs in other external galaxies,using Surface Brightness Fluctuations (SBF) measurements we giveevidence that the luminosity functions of the blue (MP) GlobularClusters peak at the same luminosity within ~0.2mag, whereas for the red(MR) samples the agreement is within ~0.5mag even accounting for thetheoretical metallicity correction expected for clusters with similarages and mass distributions. Then, using the SBF absolute magnitudesprovided by a Cepheid distance scale calibrated on a fiducial distanceto Large Magellanic Cloud (LMC), we show that the MV(TO)value of the MP clusters in external galaxies is in excellent agreementwith the value of both Galactic and M31 ones, as inferred by an RR Lyraedistance scale referenced to the same LMC fiducial distance. Eventually,adopting μ0(LMC) = 18.50mag, we derive that the luminosityfunction of MP clusters in the Milky Way, M31, and external galaxiespeak at MV(TO) =-7.66 +/- 0.11, - 7.65 +/- 0.19 and -7.67 +/-0.23mag, respectively. This would suggest a value of -7.66 +/- 0.09mag(weighted mean), with any modification of the LMC distance modulusproducing a similar variation of the GCLF peak luminosity.
| A new method for determining mass-to-light ratios of nearly face-on spiral galaxies
Context: . Aims: .This letter gives a new method for determiningmass-to-light ratios of nearly face-on spiral galaxies. Methods:.The method is based on the effective thickness of the galactic disk,the distribution of the vertical velocity dispersion, and the surfacebrightness of a spiral galaxy. Results: .As examples, the resultsof the determination of NGC 1566 and NGC 5247 in B-band are presented,and their mass-to-light ratios are 4.86 8.99 {M_ȯ L_ȯ-1} and 5.02 6.90 {M_ȯ L_ȯ -1}respective. Conclusions: .
| Hubble's top 10.
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| The great Milky Way -Andromeda collision.
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| A quasar in every galaxy ?
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| Out of the dark ages : the first stars.
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| Deciphering the globular-cluster code.
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| SPITZER : living life to the fullest.
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| Can Sterile Neutrinos Be Ruled Out as Warm Dark Matter Candidates?
We present constraints on the mass of warm dark matter (WDM) particlesfrom a combined analysis of the matter power spectrum inferred from theSloan Digital Sky Survey Lyman-α flux power spectrum at2.2
| Bias-free Measurement of Giant Molecular Cloud Properties
We review methods for measuring the sizes, line widths, and luminositiesof giant molecular clouds (GMCs) in molecular-line data cubes with lowresolution and sensitivity. We find that moment methods are robust andsensitive, making full use of both position and intensity information,and we recommend a standard method to measure the position angle, majorand minor axis sizes, line width, and luminosity using moment methods.Without corrections for the effects of beam convolution and sensitivityto GMC properties, the resulting properties may be severely biased. Thisis particularly true for extragalactic observations, where resolutionand sensitivity effects often bias measured values by 40% or more. Wecorrect for finite spatial and spectral resolutions with a simpledeconvolution, and we correct for sensitivity biases by extrapolatingproperties of a GMC to those we would expect to measure with perfectsensitivity (i.e., the 0 K isosurface). The resulting method recoversthe properties of a GMC to within 10% over a large range of resolutionsand sensitivities, provided the clouds are marginally resolved with apeak signal-to-noise ratio greater than 10. We note that interferometerssystematically underestimate cloud properties, particularly the fluxfrom a cloud. The degree of bias depends on the sensitivity of theobservations and the (u,v) coverage of the observations. In an Appendixto the paper we present a conservative, new decomposition algorithm foridentifying GMCs in molecular-line observations. This algorithm treatsthe data in physical rather than observational units (i.e., parsecsrather than beams or arcseconds), does not produce spurious clouds inthe presence of noise, and is sensitive to a range of morphologies. As aresult, the output of this decomposition should be directly comparableamong disparate data sets.
| DDO 44 and UGC 4998: Distances, Metallicities, and Star Formation Histories
We have obtained deep HST imaging of two candidate dwarf systems in thenearby M81 Group, DDO 44 and UGC 4998. Both are isolated, low surfacebrightness systems, but with likely very different star formationhistories based on their mean colors and color fluctuations. Thecolor-magnitude diagrams of these galaxies have been used to estimatetheir distances using the tip of the red giant branch (RGB), and theirmean metallicities from the colors of the RGB. For DDO 44 we find adistance of D=3.01+/-0.18 Mpc-confirming it to be a member of the M81Group-and a mean metallicity of [Fe/H]=-1.54+/-0.14. We also find fromthe properties and numbers of a population of luminous asymptotic giantbranch (AGB) stars that about 20% of the luminous population of DDO 44consists of ``intermediate-age'' stars (with ages between about 2 and 8Gyr) that give rise to the observed AGB. There is no difference in thespatial distribution of the RGB and AGB stars in this galaxy. For UGC4998 we derive a metallicity of [Fe/H]=-1.58+/-0.21 and a distance ofD=8.24+/-0.43 Mpc. The latter puts UGC 4998 well behind the M81 Group,confirming results from previous measurements. We find this galaxy tocontain a population of young (<50 Myr old) stars, and there isevidence of older RGB stars. The young stars are considerably morecentrally concentrated than the older stars. The current star formationrate in UGC 4998 is ~9×10-4 Msolaryr-1 over the entire galaxy, or ~5×10-4Msolar yr-1 kpc-2. Given its H I mass(1×107 Msolar), this galaxy can continue toform stars at this rate for another ~11 Gyr.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. These observations are associated with proposalGO-8137.
| The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Overview
The Keck Observatory began science observations with a laser guide staradaptive optics system, the first such system on an 8-10 m classtelescope, in late 2004. This new capability greatly extends thescientific potential of the Keck II Telescope, allowingnear-diffraction-limited observations in the near-infrared using naturalguide stars as faint as 19th magnitude. This paper describes theconceptual approach and technical implementation followed for thissystem, including lessons learned, and provides an overview of the earlyscience capabilities.
| Slitless Grism Spectroscopy with the Hubble Space Telescope Advanced Camera for Surveys
The Advanced Camera for Surveys on board the Hubble Space Telescope isequipped with one grism and three prisms for low-resolution, slitlessspectroscopy in the range 1150-10500 Å. The G800L grism providesoptical spectroscopy between 5500 Å and >1 μm, with a meandispersion of 39 and 24 Å pixel-1 (in the firstspectral order) when coupled with the Wide Field and the High ResolutionChannels, respectively. Given the lack of any on-board calibration lampsfor wavelength and narrowband flat-fielding, the G800L grism can only becalibrated using astronomical targets. In this paper, we describe thestrategy used to calibrate the grism in orbit, with special attentiongiven to the treatment of the field dependence of the grism flat field,wavelength solution, and sensitivity in both channels.The Hubble Space Telescope is a project of international cooperationbetween NASA and the European Space Agency (ESA). The Space TelescopeScience Institute is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555.
| Spectral Energy Distributions of M81 Globular Clusters in the BATC Multicolor Survey
In this paper, we give the spectral energy distributions (SEDs) of 42M81 globular clusters in 13 intermediate-band filters from 4000 to 10000Å using the CCD images of M81, observed as part of theBeijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey. TheBATC multicolor filter system is specifically designed to exclude mostof the bright and variable night-sky emission lines, including the OHforest. Hence, it can present accurate SEDs of the observed objects.These SEDs are low-resolution spectra and can reflect the stellarpopulations of the globular clusters. This paper confirms theconclusions of Schroder et al., that M81 contains clusters as young as afew Gyr, which were also observed in both M31 and M33.
| OSIRIS: AO-assisted integral-field spectroscopy at the Keck Observatory
OSIRIS (OH-Suppressing Infra-Red Integral-field Spectrograph) is a newfacility instrument for the Keck Observatory. After seeing first lightin February 2005, OSIRIS is currently undergoing commissioning. OSIRISprovides the capability of performing three-dimensional spectroscopy inthe near-infrared z, J, H, and K bands at the resolution limit of theKeck II telescope, which is equipped with adaptive optics and a laserguide star. The science case for OSIRIS is summarized, and theinstrument and associated data reduction software are described.
| PSF-fitting techniques for crowded field 3D spectroscopy
From a historical point of view, it was only through the advent of theCCD as a linear, high dynamic range panoramic detector that it becamepossible to overcome the source confusion problem for stellarphotometry, e.g., in star clusters or nearby galaxies. The ability ofaccurately sampling the point-spread-function (PSF) in two dimensionsand to use it as a template for fitting severely overlapping stellarimages is of fundamental importance for crowded-field photometry, andhas thus become the foundation for the determination of accuratecolor-magnitude diagrams of globular clusters and the study of resolvedstellar populations in nearby galaxies. Analogous to CCDs, theintroduction of integral field spectrographs has opened a new avenue forcrowded-field 3D spectroscopy, which benefits in the same way fromPSF-fitting techniques as CCD photometry does. This paper presents firstexperience with sampling the PSF in 3D spectroscopy, reviews the effectsof atmospheric refraction, discusses background subtraction problems,and presents several science applications as obtained from observationswith the PMAS instrument at Calar Alto Observatory.
| 3D NIR spectroscopy at subarcsecond resolution
We present a scientific case approached through high quality 3D NIRspectroscopy performed with CIRPASS, attached to the Gemini Southtelescope. A binary mass concentration at the nucleus of the galaxy M 83was suggested by Thatte et al. [A&A 364 (2000) L47] and Mast et al.[BAAA 45 (2002) 98. Astroph#0505264] determined the possible position ofthe hidden secondary mass concentration with 2D H-alpha kinematics. Thepreliminary results of the NIR study presented here are based in almost1500 spectra centered in the wavelength 1.3 μm, with a spectralresolving power of 3200. They allow us to unveil, with 0.36″ (6.4pc) sampling and subarcsecond resolution, the velocity field in a regionof 13″ × 9″ around the optical nucleus. We confirmthat the optical nucleus is not located at the most important center ofsymmetry of the ionized gas velocity field. The largest black hole thatcould fit to the circular motion in this kinematic center should have amass not larger than 3 × 106(sin i)‑1Mȯ solar masses.
| Scalar potential model of redshift and discrete redshift
On the galactic scale the universe is inhomogeneous and redshift z isoccasionally less than zero. A scalar potential model (SPM) that linksthe galaxy scale z to the cosmological scale z of the Hubble Law ispostulated. Several differences among galaxy types suggest that spiralgalaxies are Sources and that early type, lenticular, and irregulargalaxies are Sinks of a scalar potential field. The morphology-radiusand the intragalactic medium cluster observations support the movementof matter from Source galaxies to Sink galaxies. A cell structure ofgalaxy groups and clusters is proposed to resolve a paradox concerningthe scalar potential like the Olber’s paradox concerning light.For the sample galaxies, the ratio of the luminosity of Source galaxiesto the luminosity of Sink galaxies approaches 2.7 ± 0.1. Anequation is derived from sample data, which is anisotropic andinhomogeneous, relating z of and the distance D to galaxies. Thecalculated z has a correlation coefficient of 0.88 with the measured zfor a sample of 32 spiral galaxies with D calculated using Cepheidvariable stars. The equation is consistent with z < 0 observations ofclose galaxies. At low cosmological distances, the equation reduces to z≈ exp(KD)‑1 ≈ KD, where K is a constant, positive value. Theequation predicts z from galaxies over 18 Gpc distant approaches aconstant value on the order of 500. The SPM of z provides a physicalbasis for the z of particle photons. Further, the SPM qualitativelysuggests the discrete variations in z, which was reported by Tifft[Tifft, W.G., 1997. Astrophy. J. 485, 465] and confirmed by others, areconsistent with the SPM.
| Mass determination of groups of galaxies: Effects of the cosmological constant
The spherical infall model first developed by Lemaıˆtre andTolman was modified in order to include the effects of a dark energyterm. The resulting velocity distance relation was evaluatednumerically. This equation, when fitted to actual data, permits thesimultaneous evaluation of the central mass and of the Hubble parameter.Application of this relation to the Local Group, when the dark energy ismodeled by a cosmological constant, yields a total mass for theM31-Milky Way pair of (2.5 ± 0.7) ×1012Mȯ, a Hubble parameter H0 = 74± 4 km s‑1 Mpc‑1 and a 1-Dvelocity dispersion for the flow of about 39 km s‑1.The zero-velocity and the marginally bound surfaces of the Local Groupare at about 1.0 and 2.3 Mpc, respectively, from the center of mass. Asimilar analysis for the Virgo cluster yields a mass of (1.10 ±0.12) × 1015Mȯ and H0 = 65± 9 km s‑1 Mpc‑1. Thezero-velocity is located at a distance of 8.6 ± 0.8 Mpc from thecenter of the cluster. The predicted peculiar velocity of the LocalGroup towards Virgo is about 190 km s‑1, in agreementwith other estimates. Slightly lower masses are derived if the darkenergy is represented by a fluid with an equation of state P = wϵwith w = ‑2/3.
| Unravelling the mystery of the M31 bar
The inclination of M31 is too close to edge-on for a bar component to beeasily recognized and is not sufficiently edge-on for a boxy/peanutbulge to protrude clearly out of the equatorial plane. Nevertheless, asufficient number of clues allow us to argue that this galaxy is barred.We use fully self-consistent N-body simulations of barred galaxies andcompare them with both photometric and kinematic observational data forM31. In particular, we rely on the near-infrared photometry presented ina companion paper. We compare isodensity contours to isophotal contoursand the light profile along cuts parallel to the galaxy major axis andoffset towards the north, or the south, to mass profiles along similarcuts on the model. All these comparisons, as well as position-velocitydiagrams for the gaseous component, give us strong arguments that M31 isbarred. We compare four fiducial N-body models to the data and thus setconstraints on the parameters of the M31 bar, as its strength, lengthand orientation. Our `best' models, although not meant to be exactmodels of M31, reproduce in a very satisfactory way the main relevantobservations. We present arguments that M31 has both a classical and aboxy/peanut bulge. Its pseudo-ring-like structure at roughly 50arcmin isnear the outer Lindblad resonance of the bar and could thus be an outerring, as often observed in barred galaxies. The shape of the isophotesalso argues that the vertically thin part of the M31 bar extendsconsiderably further out than its boxy bulge, that is, that the boxybulge is only part of the bar, thus confirming predictions from orbitalstructure studies and from previous N-body simulations. It seems verylikely that the backbone of M31's boxy bulge is families of periodicorbits, members of the x1-tree and bifurcating from thex1 family at its higher order vertical resonances, such asthe x1v3 or x1v4 families.
| The internal dynamics of the Local Group dwarf elliptical galaxies NGC 147, 185 and 205
We present three-integral dynamical models for the three Local Groupdwarf elliptical galaxies: NGC 147, 185 and 205. These models are fittedto the Two-Micron All-Sky Survey (2MASS) J-band surface-brightnessdistribution and the major-axis kinematics (mean streaming velocity andvelocity dispersion) and, in the case of NGC 205, also to the minor-axiskinematics. The kinematical information extends out to 2Re inthe case of NGC 205 and out to about 1Re in the case of NGC147 and 185. It is the first time models are constructed for the LocalGroup dwarf ellipticals (dEs) that allow for the presence of dark matterat large radii and that are constrained by kinematics out to at leastone half-light radius. The B-band mass-to-light ratios of all the threegalaxies are rather similar, (M/L)B ~3-4Msolar/Lsolar,B. Within the innertwo half-light radii, about 40-50 per cent of the mass is in the form ofdark matter, so dEs contain about as much dark matter as brightellipticals.Based on their appreciable apparent flattening, we modelled NGC 205 and147 as being viewed edge-on. For NGC 185, having a much rounderappearance on the sky, we produced models for different inclinations.NGC 205 and 147 have a relatively isotropic velocity dispersion tensorwithin the region where the internal dynamics are strongly constrainedby the data. Our estimated inclination for NGC 185 is i ~ 50°because in that case the model has an intrinsic flattening close to thepeak of the intrinsic shape distribution of dEs and it, like thebest-fitting models for NGC 147 and 205, is nearly isotropic. We alsoshow that the dynamical properties of the bright nucleus of NGC 205 arenot unlike those of a massive globular cluster.Based on observations collected at the Observatoire de Haute-Provence.E-mail: sven.derijcke@UGent.be (SDR) ‡Postdoctoral Fellow of the Fund for Scientific Research - Flanders(Belgium)(F.W.O).
| Magnetic jets from swirling discs
A broad swathe of astrophysical phenomena, ranging from tubularplanetary nebulae through Herbig-Haro objects, radio galaxy and quasaremissions to gamma-ray bursts and perhaps high-energy cosmic rays, maybe driven by magnetically dominated jets emanating from accretion discs.We give a self-contained account of the analytic theory ofnon-relativistic magnetically dominated jets wound up by a swirling discand making a magnetic cavity in a background medium of any prescribedpressure, p(z). We solve the time-dependent problem for any specifieddistribution of magnetic flux P(R, 0) emerging from the disc at z = 0,with any specified disc angular velocity Ωd(R). Thephysics required to do this involves only the freezing of the lines offorce to the conducting medium and the principle of minimum energy.In a constant pressure environment, the magnetically dominated cavity ishighly collimated and advances along the axis at a constant speedclosely related to the maximum circular velocity of the accretion disc.Even within the cavity the field is strongly concentrated towards theaxis. The twist in the jet field/<|Bz|> is close to and thewidth of the jet decreases upwards. By contrast, when the backgroundpressure falls off with height with powers approaching z-4,the head of the jet accelerates strongly and the twist of the jet ismuch smaller. The width increases to give an almost conical magneticcavity with apex at the source. Such a regime may be responsible forsome of the longest strongly collimated jets. When the backgroundpressure falls off faster than z-4, there are no quasi-staticconfigurations of well-twisted fields and the pressure confinement isreplaced by a dynamic effective pressure or a relativistic expansion. Inthe regimes with rapid acceleration, the outgoing and incoming fieldslinking the twist back to the source are almost anti-parallel so thereis a possibility that magnetic reconnections may break up the jet into aseries of magnetic `smoke-rings' travelling out along the axis.
| Simultaneous ram pressure and tidal stripping; how dwarf spheroidals lost their gas
We perform high-resolution N-body+SPH (smoothed particle hydrodynamics)simulations of gas-rich dwarf galaxy satellites orbiting within a MilkyWay-sized halo and study for the first time the combined effects oftides and ram pressure. The structure of the galaxy models and theorbital configurations are chosen in accordance with those expected in aLambda cold dark matter (ΛCDM) universe. While tidal stirring ofdisky dwarfs produces objects whose stellar structure and kinematicsresembles that of dwarf spheroidals after a few orbits, ram pressurestripping is needed to entirely remove their gas component.Gravitational tides can aid ram pressure stripping by diminishing theoverall potential of the dwarf, but tides also induce bar formationwhich funnels gas inwards making subsequent stripping more difficult.This inflow is particularly effective when the gas can cool radiatively.Assuming a low density of the hot Galactic corona consistent withobservational constraints, dwarfs with Vpeak < 30 kms-1 can be completely stripped of their gas content on orbitswith pericenters of 50 kpc or less. Instead, dwarfs with more massivedark haloes and Vpeak > 30 km s-1 lose most orall of their gas content only if a heating source keeps the gasextended, partially counteracting the bar-driven inflow. We show thatthe ionizing radiation from the cosmic ultraviolet (UV) background at z> 2 can provide the required heating. In these objects, most of thegas is removed or becomes ionized at the first pericenter passage,explaining the early truncation of the star formation observed in Dracoand Ursa Minor. Galaxies on orbits with larger pericenters and/orfalling into the Milky Way halo at lower redshift can retain significantamounts of the centrally concentrated gas. These dwarfs would continueto form stars over a longer period of time, especially close topericenter passages, as observed in Fornax and other dwarf spheroidalgalaxies (dSphs) of the Local Group. The stripped gas breaks up intoindividual clouds pressure confined by the outer gaseous medium thathave masses, sizes and densities comparable to the HI clouds recentlydiscovered around M31.
| Properties of intra-group stars and galaxies in galaxy groups: `normal' versus `fossil' groups
Cosmological [cold dark matter (ΛCDM)] TreeSPH simulations of theformation and evolution of 12 galaxy groups of virial mass~1014Msolar have been performed. The simulationsinvoke star formation, chemical evolution with non-instantaneousrecycling, metallicity-dependent radiative cooling, strong star-burstdriven galactic super-winds and effects of a meta-galactic ultraviolet(UV) field. The intra-group (IG) stars are found to contribute 12-45 percent of the total group B-band luminosity at z = 0. The lowest fractionsare found for groups with only a small difference between the R-bandmagnitudes of the first and second ranked group galaxy(Δm12,R <~ 0.5), the larger fractions are typical of`fossil' groups (FGs, Δm12,R >= 2). A similarconclusion is obtained from BVRIJK surface brightness profiles of the IGstar populations. The IG stars in the four FGs are found to be olderthan the ones in the eight `normal' groups (non-FGs), on average byabout 0.3-0.5 Gyr. The typical colour of the IG stellar population is B- R = 1.4-1.5, for both types of systems in good agreement withobservations. The mean iron abundance of the IG stars is slightlysub-solar in the central part of the groups (r ~ 100 kpc) decreasing toabout 40 per cent solar at about half the virial radius. The IG starsare α-element enhanced with a trend of [O/Fe] increasing with rand an overall [O/Fe] ~ 0.45 dex, indicative of dominant enrichment fromType II supernovae. The abundance properties are similar for both typesof systems. The velocity distributions of the IG stars are, at r >~30 kpc, significantly more radially anisotropic for FGs than for thenon-FGs; this also holds for the velocity distributions of the groupgalaxies. This indicates that an important characteristic determiningwhether a group becomes fossil or not, apart from its formation time, asdiscussed by D'Onghia et al., is the `initial' velocity distribution ofthe group galaxies. For FGs, one can dynamically infer the (dark matterdominated) mass distribution of the groups all the way to the virialradius, from the kinematics of the IG stars or group galaxies. For thenon-FGs, this method overestimates the group mass at r>~200 kpc, byup to a factor of 2 at the virial radius. This is interpreted as FGsbeing, in general, more relaxed than non-FGs. Finally, FGs of the abovevirial mass should host ~500 planetary nebulae at projected distancesbetween 100 and 1000 kpc from the first ranked galaxy. All resultsobtained appear consistent with the tidal stripping and merging scenariofor the formation of FGs, put forward by D'Onghia et al.
| Classical novae from the POINT-AGAPE microlensing survey of M31 - II. Rate and statistical characteristics of the nova population
The POINT-AGAPE (Pixel-lensing Observations with the Isaac NewtonTelescope-Andromeda Galaxy Amplified Pixels Experiment) survey is anoptical search for gravitational microlensing events towards theAndromeda galaxy (M31). As well as microlensing, the survey is sensitiveto many different classes of variable stars and transients. In our firstpaper of this series, we reported the detection of 20 classical novae(CNe) observed in Sloan r' and i' passbands.An analysis of the maximum magnitude versus rate of decline (MMRD)relationship in M31 is performed using the resulting POINT-AGAPE CNcatalogue. Within the limits of the uncertainties of extinction internalto M31, good fits are produced to the MMRD in two filters. The MMRDcalibration is the first to be performed for Sloan r' and i' filters.However, we are unable to verify that novae have the same absolutemagnitude 15 d after peak (the t15 relationship), nor anysimilar relationship for either Sloan filter.The subsequent analysis of the automated pipeline has provided us withthe most thorough knowledge of the completeness of a CN survey to date.In addition, the large field of view of the survey has permitted us toprobe the outburst rate well into the galactic disc, unlike previous CCDimaging surveys. Using this analysis, we are able to probe the CNdistribution of M31 and evaluate the global nova rate. Using models ofthe galactic surface brightness of M31, we show that the observed CNdistribution consists of a separate bulge and disc population. We alsoshow that the M31 bulge CN eruption rate per unit r' flux is more thanfive times greater than that of the disc.Through a combination of the completeness, M31 surface brightness modeland our M31 CN eruption model, we deduce a global M31 CN rate of65+16-15 yr-1, a value much higher thanfound by previous surveys. Using the global rate, we derive a M31 bulgerate of 38+15-12 yr-1 and a disc rateof 27+19-15 yr-1. Given ourunderstanding of the completeness and an analysis of other sources oferror, we conclude that the true global nova rate of M31 is at least 50per cent higher than was previously thought and this has consequentimplications for the presumed CN rate in the Milky Way. We deduce aGalactic bulge rate of 14+6-5 yr-1, adisc rate of 20+14-11 yr-1 and a globalGalactic rate of 34+15-12 yr-1,consistent with the Galactic global rate derived elsewhere byindependent methods.
| A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph
We present a catalogue of positions, magnitudes and velocities for 3300emission-line objects found by the Planetary Nebula Spectrograph in asurvey of the Andromeda galaxy, M31. Of these objects, 2615 are foundlikely to be planetary nebulae (PNe) associated with M31. The surveyarea covers the whole of M31's disc out to a radius of . Beyond thisradius, observations have been made along the major and minor axes, andthe Northern Spur and Southern Stream regions. The calibrated data havebeen checked for internal consistency and compared with othercatalogues. With the exception of the very central, high surfacebrightness region of M31, this survey is complete to a magnitude limitof m5007 ~ 23.75, 3.5 mag into the PN luminosity function.We have identified emission-line objects associated with M31'ssatellites and other background galaxies. We have examined the data fromthe region tentatively identified as a new satellite galaxy, AndromedaVIII, comparing it to data in the other quadrants of the galaxy. We findthat the PNe in this region have velocities that appear to be consistentwith membership of M31 itself.The luminosity function of the surveyed PNe is well matched to the usualsmooth monotonic function. The only significant spatial variation in theluminosity function occurs in the vicinity of M31's molecular ring,where the luminosities of PNe on the near side of the galaxy aresystematically ~0.2 mag fainter than those on the far side. Thisdifference can be explained naturally by a modest amount of obscurationby the ring. The absence of any difference in luminosity functionbetween bulge and disc suggests that the sample of PNe is not stronglypopulated by objects whose progenitors are more massive stars. Thisconclusion is reinforced by the excellent agreement between the numbercounts of PNe and the R-band light.The number counts of kinematically selected PNe also allow us to probethe stellar distribution in M31 down to very faint limits. There is noindication 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 outto 10 effective bulge radii.We have also carried out a preliminary analysis of the kinematics of thesurveyed PNe. The mean streaming velocity of the M31 disc PNe is foundto show a significant asymmetric drift out to large radii. Theirvelocity dispersion, although initially declining with radius, flattensout to a constant value in the outer parts of the galaxy. There are noindications that the disc velocity dispersion varies with PN luminosity,once again implying that the progenitors of PNe of all magnitudes form arelatively homogeneous old population. The dispersion profile andasymmetric drift results are shown to be mutually consistent, butrequire that the disc flares with radius if the shape of its velocityellipsoid remains invariant.
| Planetary nebula velocities in the disc and bulge of M31
We present radial velocities for a sample of 723 planetary nebulae inthe disc and bulge of M31, measured using the WYFFOS fibre spectrographon the William Herschel Telescope. Velocities are determined using the[OIII]λ5007 emission line. Rotation and velocity dispersion aremeasured to a radius of 50arcmin (11.5kpc), the first stellar rotationcurve and velocity dispersion profile for M31 to such a radius. Ourkinematics are consistent with rotational support at radii well beyondthe bulge effective radius of 1.4kpc, although our data beyond a radiusof 5kpc are limited. We present tentative evidence for kinematicsubstructure in the bulge of M31 to be studied fully in a later work.This paper is part of an ongoing project to constrain the total mass,mass distribution and velocity anisotropy of the disc, bulge and halo ofM31.
| The dipole anisotropy of the 2 Micron All-Sky Redshift Survey
We estimate the acceleration on the Local Group (LG) from the 2 MicronAll-Sky Redshift Survey (2MRS). The sample used includes about 23200galaxies with extinction-corrected magnitudes brighter thanKs= 11.25 and it allows us to calculate the flux-weighteddipole. The near-infrared flux-weighted dipoles are very robust becausethey closely approximate a mass-weighted dipole, bypassing the effectsof redshift distortions and require no preferred reference frame. Thisis combined with the redshift information to determine the change indipole with distance. The misalignment angle between the LG and thecosmic microwave background (CMB) dipole drops to 12°+/- 7° ataround 50h-1Mpc, but then increases at larger distances,reaching 21°+/- 8° at around 130h-1Mpc. Exclusion ofthe galaxies Maffei 1, Maffei 2, Dwingeloo 1, IC342 and M87 brings theresultant flux dipole to 14°+/- 7° away from the CMB velocitydipole. In both cases, the dipole seemingly converges by60h-1Mpc. Assuming convergence, the comparison of the 2MRSflux dipole and the CMB dipole provides a value for the combination ofthe mass density and luminosity bias parametersΩ0.6m/bL= 0.40 +/- 0.09.
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