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Bulge Evolution in Face-On Spiral and Low Surface Brightness Galaxies
It is an observational fact that bulges of spiral galaxies contain ahigh fraction of old and metal-rich stars. Following this observationalfact, we have investigated the colors of 21 bulges hosted by a selectedsample of high surface brightness spiral galaxies and low surfacebrightness galaxies observed in the B and R optical bands and the J andKs near-IR bands. Using structural parameters derived fromthese observations, we obtain evidence that bulges could be formed bypure disk evolution (secular evolution), in agreement with suggestionsby some authors. The color profiles, especially the near-IR ones, shownull or almost null color gradients, supporting the hypothesis that thedisk stellar populations are similar to those present in the bulgeand/or that some bulges can be understood as disks with enhanced stellardensity (or pseudobulges). In the optical, half of the galaxies presentan inverse color gradient, giving additional evidence in favor ofsecular evolution for the sample investigated. The comparison of theobserved colors with those obtained from spectrophotometric models ofgalaxy evolution suggests that bulges of the selected sample have solarand subsolar metallicities and are independent of the current stellarformation rate. Also, we obtain evidence suggesting that galaxieshosting small bulges tend to be systematically metal-poor compared tothose with larger bulges. These results are being checked more carefullywith high signal-to-noise ratio spectroscopy.
| Discovery of high-amplitude X-ray variability in the Seyfert-LINER transition galaxy NGC7589
We present the first result of a programme to search for large fluxvariations in the X-ray sources of the XMM Serendipitous Survey comparedto previous ROSAT observations. An increase in X-ray flux by a factor>10 was discovered from the nucleus of the galaxy NGC7589 on atime-scale of less than 5yr. The 0.4-10keV XMM spectrum can beapproximated by a power law with photon index of 1.7-1.8, though itseems to flatten above 5keV, suggesting a possible complex model, suchas partial covering or disc reflection. A classification based on ananalysis of its optical spectrum places NGC7589 in the Seyfert region,but close to the Seyfert-LINER (low-ionization nuclear emission-lineregion) borderline on the active galactic nucleus (AGN) diagnosticdiagrams. We classify NGC7589 as either Seyfert1.9 or LINERI, in thelight of the detection of a broad Hα line, which makes NGC7589 anAGN in the low-luminosity regime. We interpret the observed variabilityin terms of either changes in covering factor of absorbing gas in theAGN, or variability in the intrinsic X-ray luminosity. Should the latterbe the case, the inferred Eddington accretion rate increased from theradiatively inefficient accretion-dominated regime to a value close tothe putative critical value, at which a transition of the accretion modeis supposed to take place. This possibility presents a new prospect ofstudying accretion physics in the central black holes of externalgalaxies by direct observing changes of `spectral state', as is commonin stellar black hole binary systems.
| The field surrounding NGC 7603: Cosmological or non-cosmological redshifts?
We present new observations of the field surrounding the Seyfert galaxyNGC 7603, where four galaxies with different redshifts - NGC 7603(z=0.029), NGC 7603B (z=0.057) and two fainter emission line galaxies(z=0.245 and z=0.394) - are apparently connected by a narrow filament,leading to a possible case of anomalous redshift. The observationscomprise broad and narrow band imaging and intermediate resolutionspectroscopy of some of the objects in the field. The new data confirmthe redshift of the two emission-line objects found within the filamentconnecting NGC 7603 and NGC 7603B, and settles their type with betteraccuracy. Although both objects are point-like in ground based images,using HST archive images we show that the objects have structure with aFWHM = 0.3-0.4 arcsec. The photometry in the R-band obtained duringthree different campaigns spread over two years does not show any signsof variability in these objects above 0.3-0.4 mag. All the aboveinformation and the relative strength and width of the main spectrallines allow us to classify these as HII galaxies with very vigorous starformation, while the rest of the filament and NGC 7603B lack starformation. We delineate the halo of NGC 7603 out to 26.2mag/arcsec2 in the Sloan r band filter and find evidence forstrong internal distortions. New narrow emission line galaxies atz=0.246, 0.117 and 0.401 are also found at respectively 0.8, 1.5 and 1.7arcmin to the West of the filament within the fainter contour of thishalo. We have studied the spatial distribution of objects in the fieldwithin 1.5 arcmin of NGC 7603. We conclude that the density of QSOs isroughly within the expected value of the limiting magnitude of ourobservations. However, the configuration of the four galaxies apparentlyconnected by the filament appears highly unusual. The probability ofthree background galaxies of any type with apparent B-magnitudes up to16.6, 21.1 and 22.1 (the observed magnitudes, extinction correctionincluded) being randomly projected on the filament of the fourth galaxy(NGC 7603) is ≈ 3× 10-9. Furthermore, the possibledetection of very vigorous star formation observed in the HII galaxiesof the filament would have a low probability if they were backgroundnormal-giant galaxies; instead, the intensity of the lines is typical ofdwarf HII galaxies. Hence, a set of coincidences with a very lowprobability would be necessary to explain this as a fortuitousprojection of background sources. Several explanations in terms ofcosmological or non-cosmological redshifts are discussed.
| High and Low Surface Brightness Galaxies in the Local Universe. V. Optical and H I Properties
Using optical spectra of the nuclei of 250 galaxies chosen from theAutomated Plate Measuring Facility (APM) survey of UK Schmidt plates, wederive synthetic B-V and V-R colors, estimates of reddening from Balmerdecrements, metallicity via oxygen abundance, and star formation ratefrom the Hα luminosity. We also present mass-to-light ratios andgas mass fractions from 21 cm H I measurements of 238 APM surveygalaxies, 101 of which also have optical spectra. This sample ofgalaxies spans a large range in surface brightness, from high surfacebrightness irregular galaxies down to the kind of low surface brightness(LSB) galaxies that are missing from most magnitude-limited catalogs.The generally blue global colors are best explained by a combination oflow metallicity and active star formation, primarily because of thetremendous scatter in metallicity versus B-V. Optical spectra show thepresence of G and K main-sequence stars in the nuclei of these galaxies,and the stellar mass-to-light ratios and gas mass fractions show thegalaxies as a whole to be gas-rich. LSB galaxies are most likely toexperience sporadic low levels of star formation over gigayeartimescales.
| H I observations of giant low surface brightness galaxies
We have used the Nançay Radio Telescope to obtain new global H Idata for 16 giant low surface brightness (LSB) galaxies. Our targetshave optical luminosities and disk scale lengths at the high end forspiral galaxies (LB~1010 Lsun andh_r>~ 6 kpc for H0=75 km s-1 Mpc-1),but they have diffuse stellar disks, with mean disk surface brightnessesga 1 magnitude fainter than normal giant spirals. Thirteen of thegalaxies previously had been detected in H I by other workers, but thepublished H I observations were either confused, resolved by thetelescope beam, of low signal-to-noise, or showed significantdiscrepancies between different authors. For the other 3 galaxies, no HI data were previously available. Several of the galaxies were resolvedby the Nançay \am{3}{6} E-W beam, so global parameters werederived from multiple-point mapping observations. Typical H I masses forour sample are >~ 1010 M_sun, withM_HI/LB=0.3-1.7 (in solar units). All of the observedgalaxies have published optical surface photometry, and we have compiledkey optical measurements for these objects from the literature. Wefrequently find significant variations among physical parameters ofgiant LSB galaxies reported by various workers. Tables 2 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/365/1 Figure 2 and Tables3, 5 and 6 are only available in electronic form athttp://www.edpsciences.org
| On the survival and destruction of spiral galaxies in clusters
We follow the evolution of disc galaxies within a cluster that formshierarchically in a cold dark matter N-body simulation. At a redshiftz=0.5 we select several dark matter haloes that have quiet mergerhistories and are about to enter the newly forming cluster environment.The haloes are replaced with equilibrium high-resolution model spiralsthat are constructed to represent examples of low surface brightness(LSB) and high surface brightness (HSB) galaxies. Varying the disc andhalo structural parameters reveals that the response of a spiral galaxyto tidal encounters depends primarily on the potential depth of its massdistribution and the disc scalelength. LSB galaxies, characterized byslowly rising rotation curves and large scalelengths, evolvedramatically under the influence of rapid encounters with substructureand strong tidal shocks from the global cluster potential - galaxyharassment. We find that up to 90 per cent of their stars are tidallystripped, and congregate in large diffuse tails that trace the orbitalpath of the galaxy and form the diffuse intracluster light. The boundstellar remnants closely resemble the dwarf spheroidals (dEs) thatpopulate nearby clusters. HSB galaxies are stable to the chaos ofcluster formation and tidal encounters. These discs lie well within thetidally limited dark matter haloes, and their potentials are moreconcentrated. Although very few stars are stripped, the scaleheight ofthe discs increases substantially and no spiral features remain; wetherefore speculate that these galaxies would be identified as S0galaxies in present-day clusters.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Neutral Hydrogen Distributions and Kinematics of Giant Low Surface=20 Brightness Disk Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1858P&db_key=AST
| Low Surface Brightness Galaxies in the Local Universe. I. The Catalog
Data are presented for 693 galaxies identified in a large new survey forlow surface brightness galaxies in the nearby universe (z <~ 0.1).The survey covers 786 square degrees centered on the equator, and itextends significantly the surface brightness range of galaxy surveys inwhich there are a substantial number of galaxies with redshifts. Thedata are derived from the Automated Plate Measuring machine scans ofsurvey plates from the UK Schmidt Telescope and from follow-upobservations at radio and optical wavelengths. Accurate positions, totalB magnitudes, surface brightness parameters, and angular sizes aretabulated for each galaxy. Radial velocities, optical luminosities, andneutral hydrogen masses are listed for a subset of the sample. Findingcharts are also presented for those objects having a large enoughangular size that the scans from survey plates provide somemorphological information. The selection function and the luminosityfunction that can be derived from the survey are discussed in twocompanion papers.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| The mass-to-light ratios of low surface brightness spiral galaxies: Clues from the Tully-Fisher relation
We have obtained 21 cm profiles and CCD surface photometry for a subsetof field low surface brightness (LSB) spiral galaxies found by a largesurvey using the Automated Plate Measuring (APM) machine. We find thatthe LSB spirals generally follow the same Tully-Fisher relations definedby a sample of higher surface brightness (HSB) galaxies drawn from theUrsa Major cluster, albeit with a considerably greater scatter. Thisgeneral trend implies that LSB galaxies of a given total luminosity havemass-to-light ratios (M/L) similar to those of HSB galaxies ofcomparable total luminosity, despite their differences in luminositydensity (i.e., surface brightness). We also find evidence that galaxieswith extremely large half-lit radii (the Malin 1 cousins) tend to beexcessively luminous for their rotation speeds. We find that, at a givenprofile width, the luminosity of an LSB galaxy relative to theTully-Fisher relation seems to be weakly anticorrelated with gasrichness, indicating that some of the higher scatter may be associatedwith the evolutionary status of the LSB galaxies. Finally, we find thatthe LSB galaxies tend to have higher total atomic gas masses than theUrsa Major comparison galaxies, depsite the genrally comparable opticalluminosities between the two sets.
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