Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
A First Attempt to Calibrate the Baryonic Tully-Fisher Relation with Gas-Dominated Galaxies
We calibrate the baryonic Tully-Fisher (BTF) relation using a sample ofgas-dominated galaxies. These determine the absolute scale of thebaryonic mass-rotation speed relation independent of the choice ofstellar mass estimator. We find a BTF slope of 3.94 ± 0.07(random) ±0.08 (systematic) and a zero point of 1.79 ±0.26 (random) ±0.25 (systematic). We apply this relation toestimate the stellar masses of star-dominated galaxies. This procedurereproduces the trend of mass-to-light ratio with color predicted bypopulation synthesis models. The normalization is also correct,consistent with empirical estimates of the initial mass function used insuch models.
| GALEX Observations of Low Surface Brightness Galaxies: UV Color and Star Formation Efficiency
We present GALEX UV observations of a sample of low surface brightness(LSB) galaxies for which H I data are available, allowing us to estimatetheir star formation efficiency. We find that the UV light extends tolarger radii than the optical light (some galaxies, but not all, looksimilar to the recently discovered XUV-disk galaxies). Using a standardcalibration to convert the UV light into star formation rates, we obtainlower star formation efficiencies in LSB galaxies than in high surfacebrightness galaxies by about one order of magnitude. We show, however,that standard calibrations may not apply to these galaxies, as theFUV-NUV color obtained from the two GALEX bands (FUV and NUV;λeff=1516 and 2267 Å, respectively) is redderthan expected for star-forming galaxies. This color can be interpretedas a result of internal extinction, modified initial mass function, orstar formation histories characterized by bursts followed by quiescentphases. Our analysis favors this latter hypothesis.Based on observations made with the NASA Galaxy Evolution Explorer.GALEX is operated for NASA by the California Institute of Technologyunder NASA contract NAS5-98034.
| Dark energy and dark matter as curvature effects?
Astrophysical observations are pointing out huge amounts of “darkmatter” and “dark energy” needed to explain theobserved large scale structures and cosmic accelerating expansion. Up tonow, no experimental evidence has been found, at fundamental level, toexplain such mysterious components. The problem could be completelyreversed considering dark matter and dark energy as“shortcomings” of General Relativity and claiming for the“correct” theory of gravity as that derived by matching thelargest number of observational data. As a result, accelerating behaviorof cosmic fluid and rotation curves of spiral galaxies are reproduced bymeans of “curvature effects”.
| Low surface brightness galaxy rotation curves in the low energy limit of Rn gravity: no need for dark matter?
We investigate the possibility that the observed flatness of therotation curves of spiral galaxies is not evidence for the existence ofdark matter haloes, but rather a signal of the breakdown of GeneralRelativity. To this aim, we consider power-law fourth-order theories ofgravity obtained by replacing the scalar curvature R with f(R) =f0 Rn in the gravity Lagrangian. We show that, inthe low energy limit, the gravitational potential generated by apoint-like source may be written as Φ(r) ~ r-1[1 +(r/rc)β] with β a function of the slopen of the gravity Lagrangian and rc a scalelength depending onthe gravitating system properties. In order to apply the model torealistic systems, we compute the modified potential and the rotationcurve for spherically symmetric and for thin disc mass distributions. Itturns out that the potential is still asymptotically decreasing, but thecorrected rotation curve, although not flat, is higher than theNewtonian one, thus offering the possibility to fit rotation curveswithout dark matter. To test the viability of the model, we consider asample of 15 low surface brightness galaxies with combined HI andHα measurements of the rotation curve extending in the putativedark matter dominated region. We find a very good agreement between thetheoretical rotation curve and the data using only stellar disc andinterstellar gas when the slope n of the gravity Lagrangian is set tothe value n = 3.5 (giving β = 0.817) obtained by fitting the TypeIa supernova Hubble diagram with the assumed power-law f(R) model and nodark matter. The excellent agreement between theoretical and observedrotation curves and the values of the stellar mass-to-light ratios inagreement with the predictions of population synthesis models make usconfident that Rn gravity may represent a good candidate tosolve both the dark energy problem on cosmological scales and the darkmatter one on galactic scales with the same value of the slope n of thehigher-order gravity Lagrangian.
| Halo Mass Profiles and Low Surface Brightness Galaxy Rotation Curves
A recent study has claimed that the rotation curve shapes and massdensities of low surface brightness (LSB) galaxies are largelyconsistent with ΛCDM predictions, in contrast to a large body ofobservational work. I demonstrate that the method used to derive thisconclusion is incapable of distinguishing the characteristic steep CDMmass-density distribution from the core-dominated mass-densitydistributions found observationally: even core-dominatedpseudoisothermal halos would be inferred to be consistent with CDM. Thismethod can therefore make no definitive statements regarding the(dis)agreement between the data and CDM simulations. After introducingan additional criterion that does take the slope of the massdistribution into account, I find that only about a quarter of the LSBgalaxies investigated are possibly consistent with CDM. However, formost of these, the fit parameters are so weakly constrained that this isnot a strong conclusion. Of the 20 galaxies with tightly constrained fitparameters, only 3 are consistent with ΛCDM. Two of thesegalaxies are likely dominated by stars, leaving only one possible darkmatter-dominated, CDM-consistent candidate. These conclusions are basedon comparison of data and simulations at identical radii and fits to theentire rotation curves. LSB galaxies that are consistent with CDMsimulations, if they exist, seem to be rare indeed.
| A Digital Archive of H I 21 Centimeter Line Spectra of Optically Targeted Galaxies
We present a homogeneous compilation of H I spectral parametersextracted from global 21 cm line spectra for some 9000 galaxies in thelocal universe (heliocentric velocity-200
| Gas and Stars in an H I-Selected Galaxy Sample
We present the results of a J-band study of the H I-selected AreciboDual-Beam Survey and Arecibo Slice Survey galaxy samples using TwoMicron All Sky Survey data. We find that these galaxies span a widerange of stellar and gas properties. However, despite the diversitywithin the samples, we find a very tight correlation between luminosityand size in the J band, similar to that found in a previous paper byRosenberg & Schneider between the H I mass and size. We also findthat the correlation between the baryonic mass and the J-band diameteris even tighter than that between the baryonic mass and the rotationalvelocity.
| Oxygen abundances and chemical evolution in low surface brightness galaxies
We report the oxygen abundances of the HII regions of a sample of lowsurface brightness (LSB) galaxies. We provide analytic functionsdescribing McGaugh's calibration of the R23 method. We usethis and the equivalent width (EW) method to determine oxygenabundances, and also make direct estimates in a few cases where thetemperature-sensitive [OIII]λ4363 line is available. We find LSBgalaxies to be metal-poor, consistent with the luminosity-metallicity(L-Z) relation of other galaxies. The large gas mass fractions of theseobjects provide an interesting test of chemical evolution models. Wefind no obvious deviation from the closed-box model of galactic chemicalevolution. Based on our abundance and gas mass fraction measurements, weinfer that LSB galaxies are not fundamentally different from othergalaxy types but are perhaps at an early stage of evolution.
| The inner structure of ΛCDM haloes - II. Halo mass profiles and low surface brightness galaxy rotation curves
We use a set of high-resolution cosmological N-body simulations toinvestigate the inner mass profile of galaxy-sized cold dark matter(CDM) haloes. These simulations extend the numerical convergence studypresented in Paper I of this series, and demonstrate that the massprofile of CDM galaxy haloes can be robustly estimated beyond a minimumconverged radius of order rconv~ 1h-1 kpc in ourhighest-resolution runs. The density profiles of simulated haloes becomeprogressively shallower from the virial radius inwards, and show no signof approaching a well-defined power law near the centre. Atrconv, the density profile is steeper than expected from theformula proposed by Navarro, Frenk & White, which has aρ~r-1 cusp, but significantly shallower than the steeplydivergent ρ~r-1.5 cusp proposed by Moore et al. Weperform a direct comparison of the spherically averaged dark mattercircular velocity profiles with Hα rotation curves of a sample oflow surface brightness (LSB) galaxies. We find that most galaxies in thesample (about 70 per cent) have rotation curves that are consistent withthe structure of CDM haloes. Of the remainder, 20 per cent have rotationcurves which cannot be fit by any smooth fitting function with few freeparameters, and 10 per cent are inconsistent with CDM haloes. However,the latter consist mostly of rotation curves that do not extend to largeenough radii to accurately determine their shapes and maximumvelocities. We conclude that the inner structure of CDM haloes is notmanifestly inconsistent with the rotation curves of LSB galaxies.
| Is the initial mass function of low surface brightness galaxies dominated by low-mass stars?
The rotation curves of low surface brightness (LSB) galaxies suggestthat they possess significantly higher mass-to-light (M/L) ratios thantheir high surface brightness counterparts, indicating that LSB galaxiesmay be dark matter dominated. This interpretation is hampered by thedifficulty of disentangling the disc and dark halo contributions fromthe disc dynamics of LSB galaxies. Recently, Fuchs has attempted such adisentanglement using spiral arm density wave and swing amplificationtheory, allowing an independent measurement of the disc mass; this worksuggests that LSB discs are significantly more massive than previouslybelieved. This would considerably reduce the amount of matter requiredin the dark haloes in fitting the rotation curves. Interestingly, thehigh mass-to-light ratios derived for the discs appear inconsistent withstandard stellar population synthesis models.In this paper, we investigate whether the high M/L ratios for the FuchsLSB discs might be understood by adopting a very `bottom heavy' initialmass function (IMF). We find that an IMF with a power-law exponent ofaround α= 3.85 (compared with the standard Salpeter IMF, α=2.35) is sufficient to explain the unusually high M/L ratios of theFuchs sample. Within the context of the models, the blue colours[(B-R)0 < 1.0] of the sample galaxies result from beingmetal-poor ([Fe/H]=-1.5 ~-1.0) and having undergone recent (~1-3 Gyrago) star formation.
| Infrared Observations of Galaxies in the Local Universe. II. 391 Calibrated Images with Photometric and Structural Measurements
This paper presents empirical results from a deep imaging survey ofgalaxies in the local universe at the J and Ks wavelengths.Three hundred ninety-one images have been obtained and calibrated usingthe same camera and filter set with the Steward Observatory 1.6 m KuiperTelescope on Mount Bigelow and the 2.3 m Bok Telescope on Kitt Peak. Thelimiting magnitude is typically 22 mag arcsec-1 at J and 21mag arcsec-1 at Ks. The central surfacebrightness, apparent magnitudes, sizes, scale lengths, and inclinationsare tabulated from measurements made using these data. The purpose ofthis paper is to provide basic near-infrared data on a variety of galaxytypes.
| The WSRT wide-field H I survey. I. The background galaxy sample
We have used the Westerbork array to carry out an unbiased wide-fieldsurvey for H I emission features, achieving an RMS sensitivity of about18 mJy/Beam at a velocity resolution of 17 km s-1 over 1800deg2 and between -1000 < VHel <+6500 kms-1. The primary data consists of auto-correlation spectrawith an effective angular resolution of 49' FWHM, althoughcross-correlation data were also acquired. The survey region is centeredapproximately on the position of Messier 31 and is Nyquist-sampled over60x 30o in RA x Dec. More than 100 distinct features aredetected at high significance in each of the two velocity regimes(negative and positive LGSR velocities). In this paper we present theresults for our H I detections of external galaxies at positive LGSRvelocity. We detect 155 external galaxies in excess of 8sigma inintegrated H I flux density. Plausible optical associations are foundwithin a 30' search radius for all but one of our H I detections in DSSimages, although several are not previously cataloged or do not havepublished red-shift determinations. Our detection without a DSSassociation is at low galactic latitude. Twenty-three of our objects aredetected in H I for the first time. We classify almost half of ourdetections as ``confused'', since one or more companions is catalogedwithin a radius of 30' and a velocity interval of 400 km s-1.We identify a handful of instances of significant positional offsetsexceeding 10 kpc of unconfused optical galaxies with the associated H Icentroid, possibly indicative of severe tidal distortions or uncatalogedgas-rich companions. A possible trend is found for an excess of detectedH I flux in unconfused galaxies within our large survey beam relative tothat detected previously in smaller telescope beams, both as function ofincreasing distance and increasing gas mass. This may be an indicationfor a diffuse gaseous component on 100 kpc scales in the environment ofmassive galaxies or a population of uncataloged low mass companions. Weuse our galaxy sample to estimate the H I mass function from our surveyvolume. Good agreement is found with the HIPASS BGC results, but onlyafter explicit correction for galaxy density variations with distance.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/829 and Fig. 3 is onlyavailable in electronic form at http://www.edpsciences.org
| Mass-to-light ratios from the fundamental plane of spiral galaxy discs
The best-fitting two-dimensional plane within the three-dimensionalspace of spiral galaxy disc observables (rotational velocityvrot, central disc surface brightnessμ0=-2.5logI0 and disc scalelength h) has beenconstructed. Applying the three-dimensional bisector method ofregression analysis to a sample of ~100 spiral galaxy discs that spanmore than 4magarcsec-2 in central disc surface brightnessyields vrot\proptoI0.50\pm0.050\,h0.77\pm 0.07 (B band)and vrot\proptoI0.43\pm0.040\,h0.69\pm 0.07 (R band).Contrary to popular belief, these results suggest that in the B band,the dynamical mass-to-light ratio (within four disc scalelengths) islargely independent of the surface brightness, varying as I0.00\pm0.100\,h0.54\pm 0.14. Consistentresults were obtained when the range of the analysis was truncated byexcluding the low-surface-brightness galaxies. Previous claims thatM/LBvaries withI-1/20,Bareshown to be misleading and/or caused by galaxy selection effects - notall low-surface-brightness disc galaxies are dark matter dominated. Thesituation is, however, different in the near-infrared whereLK'~v4 and M/LK' is shown to vary asI-1/20,K\prime. Theoretical studies ofspiral galaxy discs should therefore not assume a constant M/L ratiowithin any given passband. The B-band dynamical mass-to-light ratio(within four disc scalelengths) has no obvious correlation with (B-R)disc colour, while in the K' band it varies as -1.25+/-0.28(B-R).Combining the present observational data with recent galaxy modelpredictions implies that the logarithm of the stellar-to-dynamical massratio is not a constant value, but increases as discs become redder,varying as 1.70+/-0.28(B-R).
| High-resolution rotation curves of low surface brightness galaxies
We present high-resolution rotation curves of a sample of 26 low surfacebrightness galaxies. From these curves we derive mass distributionsusing a variety of assumptions for the stellar mass-to-light ratio. Weshow that the predictions of current Cold Dark Matter models for thedensity profiles of dark matter halos are inconsistent with the observedcurves. The latter indicate a core-dominated structure, rather than thetheoretically preferred cuspy structure. based on observations at theObservatoire de Haute Provence.
| Modified Newtonian Dynamics as an Alternative to Dark Matter
Modified Newtonian dynamics (MOND) is an empirically motivatedmodification of Newtonian gravity or inertia suggested by Milgrom as analternative to cosmic dark matter. The basic idea is that ataccelerations below ao ~ 10-8 cm/s2 ~cHo/6 the effective gravitational attraction approaches√(gnao), where gn is the usualNewtonian acceleration. This simple algorithm yields flat rotationcurves for spiral galaxies and a mass-rotation velocity relation of theform M ∝ V4 that forms the basis for the observedluminosity-rotation velocity relation-the Tully-Fisher law. We reviewthe phenomenological success of MOND on scales ranging from dwarfspheroidal galaxies to superclusters and demonstrate that the evidencefor dark matter can be equally well interpreted as evidence for MOND. Wediscuss the possible physical basis for an acceleration-basedmodification of Newtonian dynamics as well as the extention of MOND tocosmology and structure formation.
| Mass Density Profiles of Low Surface Brightness Galaxies
We derive the mass density profiles of dark matter halos that areimplied by high spatial resolution rotation curves of low surfacebrightness galaxies. We find that, at small radii, the mass densitydistribution is dominated by a nearly constant density core with a coreradius of a few kiloparsecs. For ρ(r)~rα, thedistribution of inner slopes α is strongly peaked aroundα=-0.2. This is significantly shallower than the cuspyα<=-1 halos found in cold dark matter simulations. While theobserved distribution of α does have a tail toward such extremevalues, the derived value of α is found to depend on the spatialresolution of the rotation curves: α~-1 is found only for theleast well resolved galaxies. Even for these galaxies, our data are alsoconsistent with constant-density cores (α=0) of modest (~1 kpc)core radius, which can give the illusion of steep cusps wheninsufficiently resolved. Consequently, there is no clear evidence for acuspy halo in any of the low surface brightness galaxies observed.
| The Various Kinematics of Dwarf Irregular Galaxies in Nearby Groups and Their Dark Matter Distributions
Eight dwarf irregular galaxies, in the two nearby groups of galaxiesSculptor and Centaurus A (at 2.5 Mpc and 3.5 Mpc), have been imaged inneutral hydrogen (H I) with the Australia Telescope and the Very LargeArray. These galaxies have absolute magnitudes ranging fromMB=-15.7 to -11.3. Yet they are mostly rotationallysupported, with maximum velocities going from 19 to 67 kms-1. Multicomponent mass models have been fitted to therotation curves to investigate the properties of their dark matter halosand the scaling laws of dark matter halo parameters. Dwarf galaxieshave, on average, a higher dark to luminous mass ratio, as well ashigher dark halo central densities than spiral galaxies. They have alarger dispersion of their dark matter properties both in terms of theirtotal dark matter amount and of their dark halo parameters, compared tospiral galaxies. It is therefore very difficult to predict a dwarfgalaxy rotation curve shape based only on its optical properties. Dwarfsare not well fitted by cold dark matter (CDM) halos of the type proposedby Navarro, Frenk, & White, even for ΛCDM models withΩ0 as low as 0.3. For two of our dwarfs we also haveHα rotation curves confirming the H I velocities, so thediscrepancy with the CDM models cannot be attributed to beam-smearingeffects.
| The Arecibo Dual-Beam Survey: Arecibo and VLA Observations
The Arecibo Dual-Beam Survey is a ``blind'' 21 cm search for galaxiescovering ~430 deg2 of sky. We present the data from thedetection survey as well as from the follow-up observations to confirmdetections and improve positions and flux measurements. We find 265galaxies, many of which are extremely low surface brightness. Some ofthese previously uncataloged galaxies lie within the zone of avoidance,where they are obscured by the gas and dust in our Galaxy. Eighty-one ofthese sources are not previously cataloged optically, and there are 11galaxies that have no associated optical counterpart or are onlytentatively associated with faint wisps of nebulosity on the DigitizedSky Survey images. We discuss the properties of the survey, and inparticular we make direct determinations of the completeness andreliability of the sample. The behavior of the completeness and itsdependencies is essential for determining the H I mass function. Weleave the discussion of the mass function for a later paper, but do notethat we find many low surface brightness galaxies and seven sources withMHI<108 Msolar. The AreciboObservatory is part of the National Astronomy and Ionosphere Center,which is operated by Cornell University under cooperative agreement withthe National Science Foundation. in Puerto Rico.
| The evolution of the stellar populations in low surface brightness galaxies
We investigate the star formation history and chemical evolution of lowsurface brightness (LSB) disk galaxies by modelling their observedspectro-photometric and chemical properties using a galactic chemical{and photometric} evolution model incorporating a detailed metallicitydependent set of stellar input data. For a large fraction of the LSBgalaxies in our sample, observed properties are best explained by modelsincorporating an exponentially decreasing global star formation rate(SFR) ending at a present-day gas fraction M_gas/(M_gas+M_stars) = 0.5for a galaxy age of 14 Gyr. For some galaxies small amplitude starformation bursts are required to explain the contribution of the young(5-50 Myr old) stellar population to the galaxy integrated luminosity.This suggests that star formation has proceeded in a stochastic manner.The presence of an old stellar population in many late-type LSB galaxiessuggests that LSB galaxies roughly follow the same evolutionary historyas HSB galaxies, except at a much lower rate. In particular, our resultsimply that LSB galaxies do not form late, nor have a delayed onset ofstar formation, but simply evolve slowly.
| Constraints on the Structure of Dark Matter Halos from the Rotation Curves of Low Surface Brightness Galaxies
We reexamine the disk-halo decompositions of the rotation curves of lowsurface brightness (LSB) galaxies with Vmax>=80 kms-1, taking full account of the effects of beam smearing. Weshow that the spatial resolution of the data is not sufficient to putany meaningful constraints on the density profiles of the dark halos, oron cosmological parameters. This is in strong contrast to claims made inthe literature that these LSB rotation curves are only consistent withdark matter halos with shallow central cusps, and it has importantimplications regarding the halos of LSB galaxies, such as theself-similarity of their rotation curves, and their inconsistency withcertain cosmological models or with cold dark matter altogether. Only inone case are the data of sufficient spatial resolution to obtainreliable constraints on the slope of the central density distribution ofthe dark matter halo. For this single case, we find a central cuspρ~r-α with 0.55<α<1.26 at the 99.73%confidence level. This contrasts strongly with the results for two dwarfgalaxies (Vmax<70 km s-1) that we analyze,which yield α<0.5 at the same level of confidence. Thispossibly suggests that halos with constant-density cores are restrictedto low-mass systems. We show that violent outflows of baryonic matter bysupernova feedback can reproduce this mass dependence of halo cuspslopes.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Testing Modified Newtonian Dynamics with Low Surface Brightness Galaxies: Rotation Curve FITS
We present modified Newtonian dynamics (MOND) fits to 15 rotation curvesof low surface brightness (LSB) galaxies. Good fits are readily found,although for a few galaxies minor adjustments to the inclination areneeded. Reasonable values for the stellar mass-to-light ratios arefound, as well as an approximately constant value for the total (gas andstars) mass-to-light ratio. We show that the LSB galaxies investigatedhere lie on the one, unique Tully-Fisher relation, as predicted by MOND.The scatter on the Tully-Fisher relation can be completely explained bythe observed scatter in the total mass-to-light ratio. We address thequestion of whether MOND can fit any arbitrary rotation curve byconstructing a plausible fake model galaxy. While MOND is unable to fitthis hypothetical galaxy, a normal dark-halo fit is readily found,showing that dark matter fits are much less selective in producing fits.The good fits to rotation curves of LSB galaxies support MOND,especially because these are galaxies with large mass discrepancies deepin the MOND regime.
| Dark Matter Distribution in Low-Density Spiral and Dwarf Galaxies
A sample of low-density dwarf and spiral galaxies with H I rotationcurves available in the literature is used to search for a relation ofcoupling between the dark mass radial distribution and the visible mass(gas and stars), or between the dark mass and the mass in gas. Relationsof the form M_d(r) ~ gammaM^alpha(r)r between visible mass M(r) and halodark mass M_d(r) within radius r are tested. These models combined withNewtonian dynamics provide very good fits to the H I rotation curves,and the average value of alpha is found to be sharply peaked at alpha =1/2. In models with alpha = 1/2, gamma has the dimension of the squareroot of a surface density, and the asymptotic velocity of dark halos isin V^4 ~ M. In our sample the average surface density, sigma_gamma =gamma^2/pi has approximately the value of Freeman's central surfacedensity of disk galaxies. An exponential disk galaxy, with a dark halosatisfying the above relation of structure, has a flat rotation curve.If it obeys Freeman's central surface density law, the dark matter andthe stellar component have the same central surface density. The aboverelation is valid for gas dominated galaxies like DDO 154 and UGC 2684;therefore, it seems to apply prior to any process of star formation. Inseveral cases the relation of coupling between dark mass and visiblemass (gas and stars) requires unrealistic values of the stellar disk M/Lratio. In such cases the same form of relation of coupling applied tothe dark mass and the mass in gas only provides good fits to therotation curves with reasonable M/L ratios.
| Active Galactic Nucleus Activity in Giant, Low Surface Brightness Galaxies
A search of large, H i-rich disk galaxies finds a significantly higherfraction of low-luminosity active galactic nucleus (AGN) signaturescompared with other late-type galaxies. Approximately half the galaxiesselected in this sample have AGN-like behavior in their cores; the resthave H ii nuclei resulting from simple star formation. Since AGNbehavior is not evident in all the sample galaxies, which where selectedby high gas mass, we speculate that it is the fuel flow rate that is thecommon feature between late-type low surface brightness disks and otheractive nuclear galaxies.
| Galaxy formation and evolution: low-surface-brightness galaxies
We investigate in detail the hypothesis that low-surface-brightnessgalaxies (LSBs) differ from ordinary galaxies simply because they formin haloes with large spin parameters. We compute star formation ratesusing the Schmidt law, assuming the same gas infall dependence onsurface density as used in models of the Milky Way. We build stellarpopulation models, predicting colours, spectra and chemical abundances.We compare our predictions with observed values of metallicity andcolours for LSBs, and find excellent agreement with all observables. Inparticular, integrated colours, colour gradients, surface brightness andmetallicity match very well to the observed values of LSBs for modelswith ages larger than 7 Gyr and high values (lambda>0.05) for thespin parameter of the haloes. We also compute the global star formationrate (SFR) in the Universe due to LSBs, and show that it has a flatterevolution with redshift than the corresponding SFR for normal discs. Wefurthermore compare the evolution in redshift of [Zn/H] for our modelsto those observed in damped Lyman alpha systems by Pettini et al. andshow that damped Lyman alpha system abundances are consistent with thepredicted abundances at different radii for LSBs. Finally, we show howthe required late redshift of collapse of the halo may constrain thepower spectrum of fluctuations.
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Star formation and the interstellar medium in low surface brightness galaxies. I. Oxygen abundances and abundance gradients in low surface brightness disk galaxies
We present measurements of the oxygen abundances in 64 Hii regions in 12LSB galaxies. We find that oxygen abundances are low. No regions withsolar abundance have been found, and most have oxygen abundances ~ 0.5to 0.1 solar. The oxygen abundance appears to be constant as a functionof radius, supporting the picture of quiescently and sporadicallyevolving LSB galaxies.
| Kinematics of the local universe. VII. New 21-cm line measurements of 2112 galaxies
This paper presents 2112 new 21-cm neutral hydrogen line measurementscarried out with the meridian transit Nan\c cay radiotelescope. Amongthese data we give also 213 new radial velocities which complement thoselisted in three previous papers of this series. These new measurements,together with the HI data collected in LEDA, put to 6 700 the number ofgalaxies with 21-cm line width, radial velocity, and apparent diameterin the so-called KLUN sample. Figure 5 and Appendices A and B forcorresponding comments are available in electronic form at thehttp://www.edpsciences.com
| Infrared Observations of Galaxies in the Local Universe. I. The Survey and Some Representative Results
This paper introduces a continuing survey of galaxies in the localuniverse. Consistent deep images are being acquired for a representativesample of 321 galaxies in the Uppsala General Catalogue down to 21.7 magarcsec-2 at Ks (2.16 mu m) and 22.4 mag arcsec-2 at J (1.25 mu m) usinga NICMOS camera with a 3.'8 x 3.'8 field of view attached to the 61 inch(1.5 m) telescope on Mount Bigelow. We provide some examples of theresults being obtained by employing 64 deep images of a subset of 44galaxies. Bulge-to-disk ratios are tabulated for 30 galaxies. Thebrightness of the central region of 44 galaxies declines approximately 5mag from Hubble type S0 to Sm. An exponential vertical scale height atKs is found to be 500 pc for the disk of UGC 5173. Arm amplitudes offour nearly face-on spiral galaxies are found to range between 11% and88% compared to the interarm region. There is some evidence that the armamplitude is larger at Ks than it is at J. Color gradients are measuredfor 15 galaxies with only one showing a significant nonzero result. Ameasurement of galactic symmetry applied to 64 deep images reveals anaverage asymmetry of 7.6% ( sigma = 4.6%) for these galaxies.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
Каталоги и обозначения:
|
