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Lifetime of nuclear velocity dispersion drops in barred galaxies
We have made hydro/N-body simulations with and without star formation toshed some light on the conditions under which a central kinematicallycold stellar component (characterized by a velocity dispersion drop orσ-drop) could be created in a hot medium (e.g. a bulge) andsurvive enough time to be observed. We found that the time-scale for aσ-drop formation could be short (less than 500 Myr), whereas itslifetime could be long (more than 1 Gyr) provided that the centralregion is continuously or regularly fed by fresh gas which leads to acontinuous star formation activity. Star formation in the centralregion, even at a low rate as 1Msolaryr-1, ismandatory to sustain a permanent σ-drop by replacing heatedparticles by new low-σ ones. We moreover show that as soon as starformation is switched off, the σ-drop begins to disappear.
| Globular cluster systems in low-luminosity early-type galaxies near the Fornax cluster centre
We present a photometric study of the globular cluster systems (GCSs) ofthe Fornax cluster galaxies NGC1374, NGC1379 and NGC1387. The dataconsist of images from the wide-field MOSAIC imager of the Cerro TololoInter-American Observatory (CTIO) 4-m telescope, obtained withWashington C and Kron-Cousins R filters. The images cover a field of 36× 36arcmin2, corresponding to 200 ×200kpc2 at the Fornax distance. Two of the galaxies, NGC1374and NGC1379, are low-luminosity ellipticals while NGC1387 is alow-luminosity lenticular. Their cluster systems are still embedded inthe cluster system of NGC1399. Therefore, the use of a large field iscrucial and some differences to previous work can be explained by this.The colour distributions of all GCSs are bimodal. NGC1387 presents aparticularly distinct separation between red and blue clusters and anoverproportionally large population of red clusters. The radialdistribution is different for blue and red clusters, red clusters beingmore concentrated towards the respective galaxies. The different colourand radial distributions point to the existence of two globular clustersubpopulations in these galaxies. Specific frequencies are in the rangeSN= 1.4-2.4, smaller than the typical values for ellipticalgalaxies. These galaxies might have suffered tidal stripping of blueglobular clusters by NGC1399.
| An imaging study of the globular cluster systems of NGC 1407 and 1400
We present wide-field Keck telescope imaging of the globular cluster(GC) systems around NGC 1407 and 1400 in the Eridanus galaxy cloud. Thisis complemented by Hubble Space Telescope (HST) images from the AdvancedCamera for Surveys of NGC 1407 and Wide Field and Planetary Camera 2images of NGC 1400. We clearly detect bimodality in the GC colourdistribution of NGC 1407. The blue GC subpopulation has a mean colour ofB-I= 1.61 and a relative contribution of around 40 per cent, whereas thered subpopulation with B-I= 2.06 contributes 60 per cent to the overallGC system. Assuming old ages, this corresponds to [Fe/H]=-1.45 and-0.19. Both subpopulations are intrinsically broad in colour (indicatinga range in ages and/or metallicities), with the red subpopulation beingbroader than the blue. The GC colour distribution for NGC 1400 is lessclear cut than for NGC 1407, however, we also find evidence for abimodal distribution. We find the NGC 1407 red GCs to be 20 per centsmaller in size than the blue ones. This is consistent with theexpectations of mass segregation in an old coeval GC system. Half adozen large objects (20-40 pc), with GC-like colours are identified,which are probably background galaxies.The HST data sets allow us to probe to small galactocentric radii. Herewe find both GC systems to possess a GC surface density distributionwhich is largely constant in these inner galaxy regions. We fitisothermal-like profiles and derive GC system core radii of 9.4 kpc forNGC 1407 and 5.8 kpc for NGC 1400. For NGC 1407 we are able to separatethe surface density distribution into blue and red subpopulations,giving 17.8 and 7.6 kpc, respectively. Outside this central region, theradial profile of the GC surface density is similar to that of thegalaxy light for NGC 1407 but it is flatter for NGC 1400. The mean GCmagnitude appears to be constant with galactocentric radius. We findthat for both galaxies, the GC systems have a similar ellipticity andazimuthal distribution as the underlying galaxy starlight. A fit to theGC luminosity function gives a distance modulus of 31.6, which is ingood agreement with distances based on the Faber-Jackson relation andthe Virgo infall corrected velocity.
| The Look-Back Time Evolution of the UV Upturn Phenomenon
In order to investigate the origin of the far-UV (FUV) flux fromearly-type galaxies, Galaxy Evolution Explorer (GALEX) is collecting theUV data for the elliptical-rich clusters at moderate redshifts (z <0.25) where the dominant FUV source is predicted to be hothorizontal-branch (HB) stars and their post-HB progeny. The earlyresults show that the FUV flux of quiescent early-type galaxies doesevolve substantially during the last 1--2 Gyr of look-back time, and theobserved UV fading is consistent with the variation predicted by thepopulation synthesis models where the mean temperature of HB starsdeclines rapidly with increasing look-back time.
| The Ages of Elliptical Galaxies from Infrared Spectral Energy Distributions
The mean ages of early-type galaxies obtained from the analysis ofoptical spectra give a mean age of 8 Gyr at z=0, with 40% being youngerthan 6 Gyr. Independent age determinations are possible by usinginfrared spectra (5-21 μm), which we have obtained with the InfraredSpectrograph on Spitzer. This age indicator is based on the collectivemass-loss rate of stars, in which mass loss from AGB stars produces asilicate emission feature at 9-12 μm. This feature decreases morerapidly than the shorter wavelength continuum as a stellar populationages, providing an age indicator. From observations of 30 nearbyearly-type galaxies, 29 show a spectral energy distribution dominated bystars, and one has significant emission from the ISM and is excluded.The infrared age indicators for the 29 galaxies show them all to be old,with a mean age of about 10 Gyr and a standard deviation of only a fewGyr. This is consistent with the ages inferred from the values ofM/LB, but is inconsistent with the ages derived from theoptical line indices, which can be much younger. All of these ageindicators are luminosity weighted and should be correlated, even ifmultiple-age components are considered. The inconsistency indicates thatthere is a significant problem with either the infrared and theM/LB ages, which agree, or with the ages inferred from theoptical absorption lines.
| Mid-Infrared Spectral Diagnostics of Nuclear and Extranuclear Regions in Nearby Galaxies
Mid-infrared diagnostics are presented for a large portion of theSpitzer Infrared Nearby Galaxies Survey (SINGS) sample plus archivaldata from ISO and Spitzer. The SINGS data set includes low- andhigh-resolution spectral maps and broadband imaging in the infrared forover 160 nuclear and extranuclear regions within 75 nearby galaxiesspanning a wide range of morphologies, metallicities, luminosities, andstar formation rates. Our main result is that these mid-infrareddiagnostics effectively constrain a target's dominant power source. Thecombination of a high-ionization line index and PAH strength serves asan efficient discriminant between AGNs and star-forming nuclei,confirming progress made with ISO spectroscopy on starbursting andultraluminous infrared galaxies. The sensitivity of Spitzer allows us toprobe fainter nuclear and star-forming regions within galaxy disks. Wefind that both star-forming nuclei and extranuclear regions stand apartfrom nuclei that are powered by Seyfert or LINER activity. In fact, weidentify areas within four diagnostic diagrams containing >90%Seyfert/LINER nuclei or >90% H II regions/H II nuclei. We also findthat, compared to starbursting nuclei, extranuclear regions typicallyseparate even further from AGNs, especially for low-metallicityextranuclear environments. In addition, instead of the traditionalmid-infrared approach to differentiating between AGNs and star-formingsources that utilizes relatively weak high-ionization lines, we showthat strong low-ionization cooling lines of X-ray-dominated regions like[Si II] 34.82 μm can alternatively be used as excellentdiscriminants. Finally, the typical target in this sample showsrelatively modest interstellar electron density (~400 cm-3)and obscuration (AV~1.0 mag for a foreground screen),consistent with a lack of dense clumps of highly obscured gas and dustresiding in the emitting regions.
| Chandra Observations of Gas Stripping in the Elliptical Galaxy NGC 4552 in the Virgo Cluster
We use a 54.4 ks Chandra observation to study ram pressure stripping inNGC 4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandraimages in the 0.5-2 keV band show a sharp leading edge in the surfacebrightness 3.1 kpc north of the galaxy center, a cool(kT=0.51+0.09-0.06 keV) tail with mean densityne~(5.4+/-1.7)×10-3 cm-3extending ~10 kpc to the south of the galaxy, and two 3-4 kpc horns ofemission extending southward away from the leading edge. These are allfeatures characteristic of supersonic ram pressure stripping of galaxygas, due to NGC 4552's motion through the surrounding Virgo ICM. Fittingthe surface brightness profile and spectra across the leading edge, wefind the galaxy gas inside the edge is cooler(kT=0.43+0.03-0.02 keV) and denser(ne~0.010 cm-3) than the surrounding Virgo ICM[kT=2.2+0.7-0.4 keV andne=(3.0+/-0.3)×10-4 cm-3]. Theresulting pressure ratio between the free-streaming ICM and cluster gasat the stagnation point is ~7.6+3.4-2.0 for galaxygas metallicities of 0.5+0.5-0.3Zsolar, which suggests that NGC 4552 is moving supersonicallythrough the cluster with a velocity v~1680+390-220km s-1 (Mach 2.2+0.5-0.3) at an angleξ~35deg+/-7deg toward us with respect to theplane of the sky.
| The Complex X-Ray Morphology of NGC 7618: A Major Group-Group Merger in the Local Universe?
We present results from a short Chandra ACIS-S observation of NGC 7618,the dominant central galaxy of a nearby (z=0.017309, d=74.1 Mpc) group.We detect a sharp surface brightness discontinuity 14.4 kpc north of thenucleus subtending an angle of 130° with an X-ray tail extending ~70kpc in the opposite direction. The temperature of the gas inside andoutside the discontinuity is 0.79+/-0.03 and 0.81+/-0.07 keV,respectively. There is marginal evidence for a discontinuous change inthe elemental abundance (Zinner=0.65+/-0.25,Zouter=0.17+/-0.21 at 90% confidence), suggesting that thismay be an ``abundance'' front. Fitting a two-temperature model to theASCA GIS spectrum of the NGC 7618/UGC 12491 pair shows the presence of asecond, much hotter (T=~2.3 keV) component. We consider severalscenarios for the origin of the edge and the tail, including a radiolobe/IGM interaction, nonhydrostatic ``sloshing,'' equal-mass merger andcollision, and ram pressure stripping. In the last case, we consider thepossibility that NGC 7618 is falling into UGC 12491 or that both groupsare falling into a gas-poor cluster potential. There are significantproblems with the first two models, however, and we conclude that thediscontinuity and tail are most likely the result of ram pressurestripping of the NGC 7618 group, as it falls into a larger dark matterpotential.
| Scaling Mass Profiles around Elliptical Galaxies Observed with Chandra and XMM-Newton
We investigated the dynamical structure of 53 elliptical galaxies usingthe Chandra archival X-ray data. In X-ray-luminous galaxies, temperatureincreases with radius and gas density is systematically higher at theoptical outskirts, indicating the presence of a significant amount ofthe group-scale hot gas. In contrast, X-ray-dim galaxies show a flat ordeclining temperature profile against radius and the gas density isrelatively lower at the optical outskirts. Thus, it is found thatX-ray-bright and faint elliptical galaxies are clearly distinguished bythe temperature and gas density profile. The mass profile is well scaledby a virial radius r200 rather than an optical half-radiusre, is quite similar at (0.001-0.03)r200 betweenX-ray-luminous and dim galaxies, and smoothly connects to those profilesof clusters of galaxies. At the inner region of(0.001-0.01)r200 or (0.1-1)re, the mass profilewell traces a stellar mass with a constant mass-to-light ratio ofM/LB=3-10 Msolar/Lsolar. TheM/LB ratio of X-ray-bright galaxies rises up steeply beyond0.01r200 and thus requires a presence of massive dark matterhalo. From the deprojection analysis combined with the XMM-Newton data,we found that X-ray-dim galaxies NGC 3923, NGC 720, and IC 1459 alsohave a high M/LB ratio of 20-30 at 20 kpc, comparable to thatof X-ray-luminous galaxies. Therefore, dark matter is indicated to becommon in elliptical galaxies; their dark matter distribution, as wellas that of galaxy clusters, almost follows the NFW profile.
| First Results from SAPAC: Toward a Three-dimensional Picture of the Fornax Cluster Core
A sophisticated surface brightness fluctuation (SBF) analysis packagehas been developed, designed to measure distances of early-type galaxiesby means of SBFs of unresolved stars. This suite of programs, calledSAPAC, is made readily available to the astronomical community forextensive testing, with the long-term goal of providing the necessarytools for systematic distance surveys of early-type galaxies usingmodern optical/near-IR telescopes equipped with wide-field cameras. Wediscuss the technical and scientific concepts of SAPAC and demonstrateits capabilities by analyzing deep B- and R-band CCD images of 10 dwarfelliptical galaxy candidates in the Fornax Cluster obtained with FORS1at the Very Large Telescope. All candidates are confirmed as clustermembers. We then turn our attention to the innermost region of theFornax Cluster. A total of 29 early-type galaxies closer than threecluster core radii (2deg) to the central galaxy NGC 1399 haveradial velocities and SBF distances. Their Hubble diagram exhibits apronounced S-shaped infall pattern, suggesting that Fornax is still inthe process of formation during the present epoch through a generalcollapse and possible accretion of distinct groups of galaxies. Fromfitting a model we estimate the cluster mass within 720 kpc projecteddistance of NGC 1399 to be 2.3+/-0.3×1014Msolar. The associated collapse time istcoll=2.9+1.6-0.9 Gyr. After cleansing our galaxy sample of afew kinematical outliers, the true distance of the Fornax Cluster coreis determined at 20.13+/-0.40 Mpc [(m-M)0=31.51+/-0.04 mag].Applying a bootstrap resampling technique on the distance distributionwith individual distance errors taken into account further reveals asmall intrinsic cluster depth of σint=0.74+0.52-0.74Mpc, in best agreement with the cluster's linear extension in the sky:σR.A.=σdecl.~0.5 Mpc. We conclude thatthe early-type galaxy population in the Fornax Cluster must be spatiallywell constrained, with no evidence of elongation along the line ofsight, in contrast to the Virgo Cluster. Moreover, we find marginalevidence for substructure, a result that is consistent with the youngevolutionary state of the cluster and the overall galaxy infall.Combining the kinematically defined cluster distance with the meancosmological velocity for the central cluster galaxy sample yields aHubble constant of H0=63+/-5 km s-1Mpc-1.Based on observations collected at the ESO Very Large Telescope, underprogram ESO 68.A-0176.
| The old globular cluster system of the dIrr galaxy NGC 1427A in the Fornax cluster
We present a study of the old globular cluster (GC) population of thedwarf irregular galaxy NGC 1427A using multi-wavelength VLT observationsin U,B,V,I, Hα and J bands under excellent observing conditions.We applied color and size selection criteria to select old GC candidatesand made use of archival ACS images taken with the Hubble SpaceTelescope to reject contaminating background sources and blended objectsfrom the GC candidates' list. The Hα observations were used tocheck for contamination due to compact, highly reddened young starclusters whose colors and sizes could mimic those of old GCs. Afteraccounting for contamination we obtain a total number of 38±8 GCcandidates with colors consistent with an old (~10 Gyr) and metal-poor(Z<0.4× Zȯ) population as judged by simplestellar population models. Our contamination analysis indicates that thedensity distribution of GCs in the outskirts of the Fornax central cDgalaxy NGC 1399 may not be spherically symmetric. Wederive a present-day specific frequency SN of 1.6 for NGC1427A, a value significantly larger than what is observed in the LocalGroup dwarf irregular galaxies and comparable with the values found forthe same galaxy types in the Virgo and Fornax clusters. Assuming auniversal globular cluster luminosity function turnover magnitude, wederive a distance modulus to NGC 1427A of 31.01±0.21 mag whichplaces it 3.2±2.5 (statistic)±1.6 (systematic) Mpc infront of the Fornax central cD galaxy NGC 1399. The implications of thisresult for the relationship between NGC 1427A and the clusterenvironment are briefly discussed.
| Large-scale study of the NGC 1399 globular cluster system in Fornax
We present a Washington C and Kron-Cousins R photometric study of theglobular cluster system of NGC 1399, the central galaxy of the Fornaxcluster. A large areal coverage of 1 square degree around NGC 1399 isachieved with three adjoining fields of the MOSAIC II Imager at the CTIO4-m telescope. Working on such a large field, we can perform the firstindicative determination of the total size of the NGC 1399 globularcluster system. The estimated angular extent, measured from the NGC 1399centre and up to a limiting radius where the areal density of blueglobular clusters falls to 30 per cent of the background level, is 45± 5 arcmin, which corresponds to 220-275 kpc at the Fornaxdistance. The bimodal colour distribution of this globular clustersystem, as well as the different radial distribution of blue and redclusters, up to these large distances from the parent galaxy, areconfirmed. The azimuthal globular cluster distribution exhibitsasymmetries that might be understood in terms of tidal stripping ofglobulars from NGC 1387, a nearby galaxy. The good agreement between theareal density profile of blue clusters and a projected dark-matter NFWdensity profile is emphasized.
| Surface-brightness fluctuations in stellar populations. IAC-star models for the optical and near-IR wavelengths
Aims.A new theoretical calibration of surface-brightness fluctuations(SBF) for single age, single metallicity stellar populations ispresented for the optical and near-IR broad-band filters, as well as forthe HST WFPC2 and ACS filters. Methods: .The IAC-star code isused. Two Padua and the Teramo stellar evolution libraries have beenconsidered. A set of single-burst stellar populations (SSP) with a widerange of ages (3 Gy-15 Gy) and metallicities (Z = 0.0001-0.03) have beencomputed using each one of the three considered stellar evolutionlibraries. For each SSP, color indexes and SBF magnitudes are given forthe filters U, B, V, R, I, J, H, K, {F218W}, {F336W}, {F439W}, {F450W},{F555W} and {F814W}, and for the first time, an uncertainty has beenestimated for the SBF theoretical calibration. Results: .Althoughsome differences might be addressed, the Padua and Teramo stellarevolution libraries provide comparable SBF results. A detailedcomparison of the present SBF calibrations with both previouscalibrations and observational data is also presented. Comparing thedifferent models with observational data, Padua based models reproducefairly well the optical data for globular clusters, while Teramo basedmodels fits both optical galaxies and globular clusters data, as well.In the near-IR wavelengths, the Teramo based models provide the only SBFtheoretical calibration to date able to properly reproduce theobservational data for superclusters, with intermediate-to-lowmetallicity. As a conclusion, Teramo based models work better than anyother calibration reproducing observational data for the near-IRwavelengths. Furthermore, the age-metallicity degeneracy is broken forlow metallicity (Z≤0.0037) stellar populations. Finally, a clearrelation between the B SBF absolute magnitude of a stellar populationand its metallicity is found for intermediate to old populations, so theB-band fluctuation magnitude is proposed as a metallicity tracer. Thepresent theoretical calibration shows that the analysis of SBF providesa very powerful tool in the study and characterization of unresolvedstellar populations.
| Stellar populations in a complete sample of local radio galaxies
We investigate the nature of the continuum emission and stellarpopulations in the inner 1-3 kpc of a complete sample of 24 southernradio galaxies, and we compare the results with a control sample of 18non-active early-type galaxies. 12 of the radio galaxies are classifiedas Fanaroff-Riley type I (FR I), eight as FR II and four as intermediateor undefined type (FR x). Optical long-slit spectra are used to performspectral synthesis as a function of distance from the nucleus at anaverage sampling of 0.5-1.0 kpc and to quantify the relativecontributions of a blue featureless continuum and stellar populationcomponents of different ages. Our main finding is a systematicdifference between the stellar populations of the radio and controlsample galaxies: the former have a larger contribution from anintermediate-age (1 Gyr) component, suggesting a connection between thepresent radio activity and a starburst which occurred ~1 Gyr ago. Inaddition, we find a correlation between the contribution of the 1-Gyrcomponent and the radio power, suggesting that more massive starburstshave led to more powerful radio emission. A similar relation is foundbetween the radio power and the mean age of the stellar population, inthe sense that stronger nuclear activity is found in younger galaxies.We also find that the stellar populations of FR I galaxies are, onaverage, older and more homogeneous than those of FR IIs. Significantpopulation gradients were found in only four radio galaxies, which arealso those with more than 10 per cent of their total flux at 4020Åcontributed by age components younger than 100 Myr and/or afeatureless continuum (indistinguishable from a 3-Myr-old stellarpopulation).
| The cool wake around 4C 34.16 as seen by XMM-Newton
We present XMM-Newton observations of the wake-radio galaxy system 4C34.16, which shows a cool and dense wake trailing behind the host galaxyof 4C 34.16. A comparison with numerical simulations is enlightening, asthey demonstrate that the wake is produced mainly by ram pressurestripping during the galactic motion through the surrounding cluster.The mass of the wake is a substantial fraction of the mass of the X-rayhalo of an elliptical galaxy. This observational fact supports a wakeformation scenario similar to that recently demonstrated numerically byAcreman et al.: the host galaxy of 4C 34.16 has fallen into its cluster,and is currently crossing its central regions. A substantial fraction ofits X-ray halo has been stripped by ram pressure, and remains behind toform the galaxy wake.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| O VI in Elliptical Galaxies: Indicators of Cooling Flows
Early-type galaxies often contain a hot X-ray-emitting interstellarmedium [(3-8)×106 K] with an apparent radiative coolingtime much less than a Hubble time. If unopposed by a heating mechanism,the gas will radiatively cool to temperatures <~104 K at arate proportional to LX/TX, typically 0.03-1Msolar yr-1. We can test whether gas is coolingthrough the 3×105 K range by observing the O VIdoublet, whose luminosity is proportional to the cooling rate. Here wereport on a study of an unbiased sample of 24 galaxies, obtaining FarUltraviolet Spectroscopic Explorer spectra to complement the X-ray dataof ROSAT and Chandra. The O VI line emission was detected in about 40%of the galaxies and at a luminosity level similar to the prediction fromthe cooling flow model. There is a correlation betweenM˙OVI and M˙X, although there issignificant dispersion about the relationship, where the O VI isbrighter or dimmer than expected by a factor of 3 or more. If thecooling flow picture is to be retained, then this dispersion requiresthat cooling flows be time-dependent, as might occur by the activity ofan AGN. However, of detected objects, those with the highest or lowestvalues of M˙OVI/M˙X are not systematicallyhot or cool, as one might predict from AGN heating.
| Planetary Nebulae and Stellar Kinematics in the Flattened Elliptical Galaxy NGC 1344
We present photometric and kinematic information obtained by measuring197 planetary nebulae (PNs) discovered in the flattened Fornaxelliptical galaxy NGC 1344 (also known as NGC 1340) with an on-band,off-band, and grism+on-band filter technique. We build the PN luminosityfunction (PNLF) and use it to derive a distance modulus m-M=31.4+/-0.18,which is slightly smaller than, but in good agreement with, the surfacebrightness fluctuation distance. The PNLF also provides an estimate ofthe specific PN formation rate: (6+/-3)×10-12 PNsyr-1 L-1solar. If we combine thepositional information from the on-band image with PN positions measuredon the grism+on-band image, we can measure the radial velocities of 195PNs, some of them distant more than three effective radii from thecenter of NGC 1344. We complement this data set with stellar kinematicsderived from integrated spectra along the major and minor axes andparallel to the major axis of NGC 1344. The line-of-sight velocitydispersion profile indicates the presence of a dark matter halo aroundthis galaxy.Some of the data presented herein were obtained at the European SouthernObservatory, Chile, in programs ESO 67.B-0231 and 68.B-0173A.
| A Fundamental Plane Relation for the X-Ray Gas in Normal Elliptical Galaxies
We report on the discovery of a new correlation between globalparameters of the hot interstellar gas in elliptical galaxies. Wereanalyze archival Chandra data for 30 normal early-type systems,removing the contributions of resolved and unresolved point sources toreveal the X-ray morphology of the hot gas. We determine the half-lightradius, RX, and the mean surface brightness, IX,from the gas surface brightness profiles. A spectral analysis determinesthe temperature, TX, of the gas within 3 optical effectiveradii. We find that the galaxies lie on an X-ray gas fundamental plane(XGFP) of the formTX~R0.28XI0.22X.This is close to, but distinct from, a simple luminosity-temperaturerelation. The intrinsic width of the XGFP is only 0.07 dex, nearlyidentical to that of the stellar (optical) fundamental plane (SFP). Thisis surprising since X-ray gas masses are typically ~10-2 ofthe stellar masses. We show that the XGFP is not a simple consequence ofthe virial theorem or hydrostatic equilibrium and that it is essentiallyindependent of the SFP. The XGFP thus represents a genuinely newconstraint on the hydrodynamical evolution of elliptical galaxies.
| Infrared Spectral Energy Distributions of Nearby Galaxies
The Spitzer Infrared Nearby Galaxies Survey (SINGS) is carrying out acomprehensive multiwavelength survey on a sample of 75 nearby galaxies.The 1-850 μm spectral energy distributions (SEDs) are presented usingbroadband imaging data from Spitzer, 2MASS, ISO, IRAS, and SCUBA. Theinfrared colors derived from the globally integrated Spitzer data aregenerally consistent with the previous generation of models that weredeveloped using global data for normal star-forming galaxies, althoughsignificant deviations are observed. Spitzer's excellent sensitivity andresolution also allow a detailed investigation of the infrared SEDs forvarious locations within the three large, nearby galaxies NGC 3031(M81), NGC 5194 (M51), and NGC 7331. A wide variety of spectral shapesis found within each galaxy, especially for NGC 3031, the closest of thethree targets and thus the galaxy for which the smallest spatial scalescan be explored. Strong correlations exist between the local starformation rate and the infrared colors fν(70μm)/fν(160 μm) and fν(24μm)/fν(160 μm), suggesting that the 24 and 70 μmemission are useful tracers of the local star formation activity level.Preliminary evidence indicates that variations in the 24 μm emission,and not variations in the emission from polycyclic aromatic hydrocarbonsat 8 μm, drive the variations in the fν(8.0μm)/fν(24 μm) colors within NGC 3031, NGC 5194, andNGC 7331. If the galaxy-to-galaxy variations in SEDs seen in our sampleare representative of the range present at high redshift, thenextrapolations of total infrared luminosities and star formation ratesfrom the observed 24 μm flux will be uncertain at the factor of 5level (total range). The corresponding uncertainties using theredshifted 8.0 μm flux (e.g., observed 24 μm flux for a z=2source) are factors of 10-20. Considerable caution should be used wheninterpreting such extrapolated infrared luminosities.
| The Chandra Fornax Survey. I. The Cluster Environment
We present the first results of a deep Chandra survey of the inner~1° of the Fornax cluster of galaxies. Ten 50 ks pointings wereobtained in a mosaic centered on the giant elliptical galaxy NGC 1399 atthe nominal cluster center. Emission and temperature maps of Fornax arepresented, and an initial study of more than 700 detected X-ray pointsources is made. Regions as small as 100 pc are resolved. Theintracluster gas in Fornax exhibits a highly asymmetric morphology andtemperature structure, dominated by a 180 kpc extended ``plume'' of lowsurface brightness, cool (<=1 keV) gas to the northeast of NGC 1399with a sharper edge to the southwest. The elliptical galaxy NGC 1404also exhibits a cool halo of X-ray gas within the cluster, with a highlysharpened leading edge as it presumably falls into the cluster and acomet-like tail. We estimate that some ~200-400 point sources arephysically associated with Fornax. Confirming earlier works, we findthat the globular cluster population in NGC 1399 is highly X-ray active,extending to globular clusters that may in fact be intracluster systems.We have also found a remarkable correlation between the location ofgiant and dwarf cluster galaxies and the presence of X-ray counterparts,such that systems inhabiting regions of low gas density are more likelyto show X-ray activity. Not only does this correlate with the asymmetryof the intracluster gas, but it also correlates with the axis joiningthe center of Fornax to an infalling group 1 Mpc to the southwest. Wesuggest that Fornax may be experiencing either an intergalactic``headwind'' due to motion relative to the surrounding large-scalestructure or that the intracluster medium has been disturbed relative tothe overall cluster gravitational potential by previous activity.
| XMM-Newton Observation of an X-Ray Trail between the Spiral Galaxy NGC 6872 and the Central Elliptical Galaxy NGC 6876 in the Pavo Group
We present XMM-Newton observations of a trail of enhanced X-ray emissionextending along the full 8.7 arcmin ×4' region betweenthe large spiral galaxy NGC 6872 and the dominant elliptical galaxy NGC6876 in the Pavo group, the first known X-ray trail associated with aspiral galaxy in a poor galaxy group and, with a projected length of 90kpc, one of the longest known X-ray trails. The X-ray surface brightnessin the trail region is roughly constant beyond ~20 kpc of NGC 6876 inthe direction of the spiral galaxy. The trail is hotter (~1 keV) thanthe undisturbed Pavo IGM (~0.5 keV) and has low metal abundances (0.2Zsolar). The 0.5-2 keV luminosity of the trail, measuredusing a 67×90 kpc rectangular region, is 6.6×1040ergs s-1. We compare the properties of gas in the trail tothe spectral properties of gas in the spiral galaxy NGC 6872 and in theelliptical galaxy NGC 6876 to constrain its origin. We suggest that theX-ray trail is either IGM gas gravitationally focused into a Bondi-Hoylewake, a thermal mixture of ~60% Pavo IGM gas with ~40% galaxy gas thathas been removed from the spiral galaxy NGC 6872 by turbulent viscousstripping, or both, due to the spiral galaxy's supersonic motion atangle ξ~40deg with respect to the plane of the sky,through the densest region of the Pavo IGM. Assumingξ=40deg and a filling factor η in a cylindrical volumewith radius 33 kpc and projected length 90 kpc, the mean electrondensity and total hot gas mass in the trail are1×10-3η-1/2 cm-3 and1.1×1010η1/2 Msolar,respectively.
| Close Binaries as the Progenitors of the Brightest Planetary Nebulae
We investigate the possible progenitors of the planetary nebulae (PNs)that populate the top 0.5 mag of the [O III] λ5007 planetarynebula luminosity function (PNLF). We show that the absolute luminosityof the PNLF cutoff demands that the central stars of these most luminousPNs be >~0.6 Msolar and that such high-mass PN cores mustexist in every galaxy. We also use the bolometric luminosity-specific PNnumber density to show that in early-type galaxies, [O III]-bright PNsare relatively rare, with only ~10% of stars evolving to these brightmagnitudes. We demonstrate that the combination of these two factsimplies that either all early-type systems contain a small, smoothlydistributed component of young (<~1 Gyr old) stars or that anothermechanism exists for creating high core mass PNs. We argue that binarystar evolution is this second mechanism and demonstrate that bluestragglers have the appropriate core properties and number density toexplain the observations. We discuss the implications of thisalternative mode of stellar evolution and speculate on how coalescedbinaries might affect the use of PNs for measuring a galaxy's starformation history and chemical evolution.
| Probing the Ionizing Continuum of Narrow-Line Seyfert 1 Galaxies. I. Observational Results
We present optical spectra and emission-line ratios of 12 narrow-lineSeyfert 1 (NLS1) galaxies that we observed to study the ionizing EUVcontinuum. A common feature in the EUV continuum of active galacticnuclei is the big blue bump (BBB), generally associated with thermalaccretion disk emission. While Galactic absorption prevents directaccess to the EUV range, it can be mapped by measuring the strength of avariety of forbidden optical emission lines that respond to differentEUV continuum regions. We find that narrow emission line ratiosinvolving [O II] λ3727, Hβ, [O III] λ5007, [O I]λ6300, Hα, [N II] λ6583, and [S II]λλ6716, 6731 indicate no significant difference betweenNLS1 galaxies and broad-line Seyfert 1 (BLS1) galaxies, which suggeststhat the spectral energy distributions of their ionizing EUV-soft X-raycontinua are similar. The relative strength of important forbiddenhigh-ionization lines like [Ne V] λ3426 compared to He IIλ4686 and the relative strength of [Fe X] λ6374 appear toshow the same range as in BLS1 galaxies. However, a trend of weaker F([OI] λ6300)/F(Hα) emission-line ratios is indicated for NLS1galaxies compared to BLS1 galaxies. To recover the broad emission lineprofiles, we used Gaussian components. This approach indicates that thebroad Hβ profile can be well described with a broad component(FWHM~=3275+/-800 km s-1) and an intermediate broad component(FWHM~=1200+/-300 km s-1). The width of the broad componentis in the typical range of normal BLS1 galaxies. The emission-line fluxthat is associated with the broad component in these NLS1 galaxiesamounts to at least 60% of the total flux. Thus, it dominates the totalline flux, similar to BLS1 galaxies.
| Infall of the Elliptical Galaxy NGC 1404 into the Fornax Cluster
We use three Chandra observations, totaling 134.3 ks, to constrain thedynamical motion of NGC 1404 falling toward the dominant elliptical NGC1399 through the Fornax Cluster gas. The surface brightness profile ofNGC 1404 shows a sharp edge at ~8 kpc from its center in the directionof NGC 1399, characteristic of jumplike temperature and densitydiscontinuities from ram pressure stripping of the galaxy gas, caused byits motion through the surrounding intracluster medium (ICM). We findthat the temperature of the galaxy gas inside the edge is ~2.8 timescooler (kT=0.55+0.01-0.02 keV with abundanceA=0.73+0.65-0.16Zsolar) than thecluster gas (kT=1.53+0.10-0.13 keV,A=0.42+0.2-0.13Zsolar). We use theshape of the surface brightness profile across the edge to fit theposition of the edge, the power-law behavior of NGC 1404's densitydistribution in the leading direction, and the density discontinuity atthe edge. The electron density inside the edge(3.9-4.3)×10-3 cm-3 depends strongly on thegas abundance, while the density of the ICM (7-8)×10-4cm-3 depends strongly on the assumed geometry (relativedistance) between NGC 1404 and NGC 1399. The corresponding pressure jumpof 1.7-2.1 across the leading edge of the galaxy and the clusterfree-stream region implies near sonic motion (Mach number 0.83-1.03) forNGC 1404 with a velocity 531-657 km s-1 relative to thesurrounding cluster gas. The inclination angle of the motion, inferredusing the relative radial velocity between NGC 1404 and 1399 asrepresentative of that between NGC 1404 and the cluster ICM, isuncomfortably large (>~40°) given the sharpness of the surfacebrightness edge, suggesting either a nonzero impact parameter betweenNGC 1404 and 1399 or that NGC 1399 is also moving radially with respectto the cluster ICM.
| The Look-back Time Evolution of Far-Ultraviolet Flux from Elliptical Galaxies: The Fornax Cluster and A2670
In order to investigate the origin of the far-UV (FUV) flux from theearly-type galaxies, the Galaxy Evolution Explorer is collecting the UVdata for the elliptical-rich clusters at moderate redshifts (z<0.2)where the dominant FUV source is predicted to be hot horizontal-branch(HB) stars and their post-HB progeny. Here we present our first resultfor the early-type galaxies in A2670 at z=0.076. Compared to NGC 1399, anearby giant elliptical galaxy in the Fornax Cluster, it appears thatthe rest-frame FUV-V color of the giant elliptical galaxies gets redderby ~0.7 mag at the distance of A2670 (z=0.076; look-back time~1.0 Gyr).Although a detailed comparison with the models is postponed until morecluster data are accumulated, it is interesting to note that this valueis consistent with the variation predicted by the population synthesismodels where the mean temperature of HB stars declines rapidly withincreasing look-back time.
| The Survival and Destruction of X-Ray Coronae of Early-Type Galaxies in Rich Cluster Environments: A Case Study of A1367
A new Chandra observation of the northwest region of the galaxy clusterA1367 reveals four cool galaxy coronae (0.4-1.0 keV) embedded in the hot(5-6 keV) intracluster medium (ICM). While the large coronae of NGC 3842and NGC 3837 appear symmetric and relaxed, the galaxy coronae of the<~L* galaxies (NGC 3841 and CGCG 97090) are disturbed and beingstripped. Massive galaxies, generally with dense cooling cores, arebetter able to resist ram pressure stripping and survive in richenvironments than <~L* galaxies, whose galactic coronae are generallymuch less dense. The survival of these cool coronae implies that thermalconduction from the hot surrounding ICM has to be suppressed by a factorof at least 60 at the corona boundary. Within the galaxy coronae of NGC3842 and NGC 3837, stellar mass loss or heat conduction with the Spitzervalue may be sufficient to balance radiative cooling. Energy depositionat the ends of collimated jets may heat the outer coronae but allow thesurvival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC4874 in the Coma Cluster). The surviving X-ray coronae becomesignificantly smaller and fainter with the increasing ambient pressure.
| Tramp Novae between Galaxies in the Fornax Cluster: Tracers of Intracluster Light
We report the results of a survey for novae in and between the galaxiesof the Fornax Cluster. Our survey provides strong evidence thatintracluster novae exist and that they provide a useful, independentmeasure of the intracluster light in Fornax. We discovered six strongnova candidates in six distinct epochs spanning 11 yr from 1993 to 2004.The data were taken with the 4 m and the 1.5 m telescopes at CerroTololo Inter-American Observatory. The spatial distribution of the novacandidates is consistent with ~16%-41% of the total light in the clusterbeing in the intracluster light, based on the ratio of the number ofnovae we discovered in intracluster space over the total number of novaediscovered plus a simple completeness correction factor. This estimateis consistent with independent measures of intracluster light in Fornaxand Virgo using intracluster planetary nebulae. The accuracy of theintracluster light measurement improves with each survey epoch as morenovae are discovered.
| New results on the kinematics of the outer cluster system of NGC 1399.
Not Available
| Near infra-red and optical colour gradients in E-type galaxies. Inferences on dust content
Colour gradients are considered for a sample of circa 50 E-type galaxiesin the Local Supercluster. The new data includes isophotal colourprofiles in J-H, J-K, V-J and V-K, measured using 2MASS frames mostlyfrom the Large Galaxies Atlas, V frames from previous work and Vprofiles from the literature. This is supplemented by U-B, B-V, B-R, V-Icolour gradients obtained anew from published photometric data. Colourgradients in E galaxies show remarkably large variations from object toobject and do not correlate with other properties. Metallicity gradientsare the primary cause as shown before. Age gradients with oppositeeffects are possibly needed to explain objects with small colourgradients. Some empirical evidence of such age effects has been foundfor a subset of objects with morphological peculiarities and youngerstars mixed. Dust has only modest effects on colour gradients, as shownby the fact that objects with zero IRAS 100 μ flux have the sameaverage values of the gradients, except in V-J and V-K, as those withnon zero flux (cf. Table 7). This last subsample however exhibits poorbut definite correlations between IRAS flux and gradients, which mightbe caused by the presence of a few relatively dusty galaxies in thesample. Given the absence of a correlation between any gradients andgalaxy velocity dispersion (and hence mass), the observations do notagree with the predictions of the monolithic scenario for the formationof E galaxies. Simulated datasets of “dummy” objectsmimicking the hierarchical scenario have been obtained, and used to testa technique for estimating the dust content of E-galaxies from thecomparison of the V-K (or V-J) colour gradients with the U-B (or B-V)ones: the contents of diffuse dust, gauged in terms of published models,are obtained for a dozen objects.
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