Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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.
| Using Line Profiles to Test the Fraternity of Type Ia Supernovae at High and Low Redshifts
Using archival data of low-redshift (z<0.01 Center for Astrophysicsand SUSPECT databases) Type Ia supernovae (SNe Ia) and recentobservations of high-redshift (0.161.7] SNe Ia, which are also subluminous. Inaddition, we give the first direct evidence in two high-z SN Ia spectraof a double-absorption feature in Ca II λ3945, an event alsoobserved, although infrequently, in low-redshift SN Ia spectra (6 out of22 SNe Ia in our local sample). Moreover, echoing the recent studies ofDessart & Hillier in the context of Type II supernovae (SNe II), wesee similar P Cygni line profiles in our large sample of SN Ia spectra.First, the magnitude of the velocity location at maximum profileabsorption may underestimate that at the continuum photosphere, asobserved, for example, in the optically thinner line S II λ5640.Second, we report for the first time the unambiguous and systematicintrinsic blueshift of peak emission of optical P Cygni line profiles inSN Ia spectra, by as much as 8000 km s-1. All the high-z SNeIa analyzed in this paper were discovered and followed up by the ESSENCEcollaboration and are now publicly available.Based in part on observations obtained at the Cerro TololoInter-American Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA), Inc., under cooperativeagreement with the National Science Foundation (NSF); the EuropeanSouthern Observatory, Chile (ESO program 170.A-0519) the GeminiObservatory, which is operated by AURA under a cooperative agreementwith the NSF on behalf of the Gemini partnership (the NSF [UnitedStates], the Particle Physics and Astronomy Research Council [UnitedKingdom], the National Research Council [Canada], CONICYT [Chile], theAustralian Research Council [Australia], CNPq [Brazil], and CONICET[Argentina]) (programs GN-2002B-Q-14, GN-2003B-Q-11, and GS-2003B-Q-11)the Magellan Telescopes at Las Campanas Observatory; the MMTObservatory, a joint facility of the Smithsonian Institution and theUniversity of Arizona; and the F. L. Whipple Observatory, which isoperated by the Smithsonian Astrophysical Observatory. Some of the datapresented herein were obtained at the W. M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California, and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W. M. Keck Foundation.
| Integral Field Spectroscopy of 23 Spiral Bulges
We have obtained integral-field spectroscopy for 23 spiral bulges usingINTEGRAL on the William Herschel Telescope and SPIRAL on theAnglo-Australian Telescope. This is the first two-dimensional surveydirected solely at the bulges of spiral galaxies. Eleven galaxies of thesample do not have previous measurements of the stellar velocitydispersion (σ*). These data are designed to complementour Space Telescope Imaging Spectrograph program for estimating blackhole masses in the range 106-108 Msolarusing gas kinematics from nucleated disks. These observations will serveto derive the stellar dynamical bulge properties using the traditionalMg b and Ca II triplets. We use both cross-correlation and maximumpenalized likelihood to determine projected σ* in thesesystems and present radial velocity fields, major axis rotation curves,curves of growth, and σ* fields. Usingcross-correlation to extract the low-order two-dimensional stellardynamics we generally see coherent radial rotation and irregularvelocity dispersion fields suggesting that σ* is anontrivial parameter to estimate.
| Chemistry and Star Formation in the Host Galaxies of Type Ia Supernovae
We study the effect of environment on the properties of Type Iasupernovae by analyzing the integrated spectra of 57 local Type Iasupernova host galaxies. We deduce from the spectra the metallicity,current star formation rate, and star formation history of the host andcompare these to the supernova decline rates. Additionally, we comparethe host properties to the difference between the derived supernovadistance and the distance determined from the best-fit Hubble law. Fromthis we investigate possible uncorrected systematic effects inherent inthe calibration of Type Ia supernova luminosities using light-curvefitting techniques. Our results indicate a statistically insignificantcorrelation in the direction of higher metallicity spiral galaxieshosting fainter Type Ia supernovae. However, we present qualitativeevidence suggesting that progenitor age is more likely to be the sourceof variability in supernova peak luminosities than is metallicity. We donot find a correlation between the supernova decline rate and hostgalaxy absolute B magnitude, nor do we find evidence of a significantrelationship between decline rate and current host galaxy star formationrate. A tenuous correlation is observed between the supernova Hubbleresiduals and host galaxy metallicities. Further host galaxyobservations will be needed to refine the significance of this result.Finally, we characterize the environmental property distributions forType Ia supernova host galaxies through a comparison with two larger,more general galaxy distributions using Kolmogorov-Smirnov tests. Theresults show the host galaxy metallicity distribution to be similar tothe metallicity distributions of the galaxies of the NFGS and SDSS.Significant differences are observed between the SN Ia distributions ofabsolute B magnitude and star formation histories and the correspondingdistributions of galaxies in the NFGS and SDSS. Among these is an abruptupper limit observed in the distribution of star formation histories ofthe host galaxy sample, suggesting a Type Ia supernovae characteristicdelay time lower limit of approximately 2.0 Gyr. Other distributiondiscrepancies are investigated and the effects on the supernovaproperties are discussed.
| Reddening, Absorption, and Decline Rate Corrections for a Complete Sample of Type Ia Supernovae Leading to a Fully Corrected Hubble Diagram to v < 30,000 km s-1
Photometric (BVI) and redshift data corrected for streaming motions arecompiled for 111 ``Branch-normal,'' four 1991T-like, seven 1991bg-like,and two unusual supernovae of Type Ia (SNe Ia). Color excessesE(B-V)host of normal SNe Ia, due to the absorption of thehost galaxy, are derived by three independent methods, giving excellentagreement leading to the intrinsic colors at maximum of(B-V)00=-0.024+/-0.010 and (V-I)00=-0.265+/-0.016if normalized to a common decline rate of Δm15=1.1. Thestrong correlation between redshift absolute magnitudes (based on anarbitrary Hubble constant of H0=60 km s-1Mpc-1), corrected only for the extrinsic Galactic absorption,and the derived E(B-V)host color excesses leads to thewell-determined yet abnormal absorption-to-reddening ratios ofRBVI=3.65+/-0.16, 2.65+/-0.15, and 1.35+/-0.21.Comparison with the canonical Galactic values of 4.1, 3.1, and 1.8forces the conclusion that the law of interstellar absorption in thepath length to the SN in the host galaxy is different from the localGalactic law, a result consistent with earlier conclusions by others.Improved correlations of the fully corrected absolute magnitudes (on thesame arbitrary Hubble constant zero point) with host galaxymorphological type, decline rate, and intrinsic color are derived. Werecover the result that SNe Ia in E/S0 galaxies are ~0.3 mag fainterthan in spiral galaxies for possible reasons discussed in the text. Thenew decline rate corrections to absolute magnitudes are smaller thanthose by some authors for reasons explained in the text. The fourspectroscopically peculiar 1991T-type SNe are significantly overluminousas compared to Branch-normal SNe Ia. The overluminosity of the seven1999aa-like SNe is less pronounced. The seven 1991bg types in the sampleconstitute a separate class of SNe Ia, averaging in B 2 mag fainter thanthe normal Ia. New Hubble diagrams in B, V, and I are derived out to~30,000 km s-1 using the fully corrected magnitudes andvelocities, corrected for streaming motions. Nine solutions for theintercept magnitudes in these diagrams show extreme stability at the0.02 mag level using various subsamples of the data for both low andhigh extinctions in the sample, proving the validity of the correctionsfor host galaxy absorption. We shall use the same precepts for fullycorrecting SN magnitudes for the luminosity recalibration of SNe Ia inthe forthcoming final review of our Hubble Space Telescope Cepheid-SNexperiment for the Hubble constant.
| On the alignment between binary spiral galaxies
We show some significance against the null hypothesis of randominteractions of binary spiral galaxies, and in favour of the alternativethat more interactions than expected occur for axes either nearlyparallel (spins being parallel or anti-parallel) or nearly orthogonal.We discuss this in the context of similar prior studies, using adifferent statistical focus in such a way that we are able toincorporate additional data.
| Nuclear Properties of a Sample of Nearby Spiral Galaxies from Hubble Space Telescope STIS Imaging
We present surface photometry for the central regions of a sample of 48spiral galaxies (mostly unbarred and barred of type Sbc or Sc) observedwith the Space Telescope Imaging Spectrograph on board the Hubble SpaceTelescope. Surface brightness profiles (SBPs) were derived and modeledwith a Nuker law. We also analyzed archival Wide Field Planetary Camera2 images with a larger field of view, which are available for 18galaxies in our sample. We modeled the extracted bulge SBPs with anexponential, an r1/4, or an rn profile. Inagreement with previous studies, we find that bulges of Sbc galaxiesfall into two categories: bulges well described by an exponentialprofile and those well described by an r1/4 profile. Only onegalaxy requires the use of a more general Sérsic profile toproperly describe the bulge. Nuclear photometrically distinct componentsare found in ~55% of the galaxies. For those that we classify as starclusters on the basis of their resolved extent, we find absolutemagnitudes that are brighter on average than those previously identifiedin spiral galaxies. This might be due to a bias in our sample towardstar-forming galaxies, combined with a trend for star-forming galaxiesto host brighter central clusters.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The PDS versus Markarian starburst galaxies: comparing strong and weak IRAS emitter at 12 and 25 μm in the nearby Universe
The characteristics of the starburst galaxies from the Pico dos Diassurvey (PDS) are compared with those of the nearby ultraviolet (UV)bright Markarian starburst galaxies, having the same limit in redshift(vh < 7500 km s-1) and absolute B magnitude(MB < -18). An important difference is found: theMarkarian galaxies are generally undetected at 12 and 25 μm in IRAS.This is consistent with the UV excess shown by these galaxies andsuggests that the youngest star-forming regions dominating thesegalaxies are relatively free of dust.The far-infrared selection criteria for the PDS are shown to introduce astrong bias towards massive (luminous) and large size late-type spiralgalaxies. This is contrary to the Markarian galaxies, which are found tobe remarkably rich in smaller size early-type galaxies. These resultssuggest that only late-type spirals with a large and massive disc arestrong emitters at 12 and 25 μm in IRAS in the nearby Universe.The Markarian and PDS starburst galaxies are shown to share the sameenvironment. This rules out an explanation of the differences observedin terms of external parameters. These differences may be explained byassuming two different levels of evolution, the Markarian being lessevolved than the PDS galaxies. This interpretation is fully consistentwith the disc formation hypothesis proposed by Coziol et al. to explainthe special properties of the Markarian SBNG.
| Cosmological Results from High-z Supernovae
The High-z Supernova Search Team has discovered and observed eight newsupernovae in the redshift interval z=0.3-1.2. These independentobservations, analyzed by similar but distinct methods, confirm theresults of Riess and Perlmutter and coworkers that supernova luminositydistances imply an accelerating universe. More importantly, they extendthe redshift range of consistently observed Type Ia supernovae (SNe Ia)to z~1, where the signature of cosmological effects has the oppositesign of some plausible systematic effects. Consequently, thesemeasurements not only provide another quantitative confirmation of theimportance of dark energy, but also constitute a powerful qualitativetest for the cosmological origin of cosmic acceleration. We find a ratefor SN Ia of(1.4+/-0.5)×10-4h3Mpc-3yr-1at a mean redshift of 0.5. We present distances and host extinctions for230 SN Ia. These place the following constraints on cosmologicalquantities: if the equation of state parameter of the dark energy isw=-1, then H0t0=0.96+/-0.04, andΩΛ-1.4ΩM=0.35+/-0.14. Includingthe constraint of a flat universe, we findΩM=0.28+/-0.05, independent of any large-scalestructure measurements. Adopting a prior based on the Two Degree Field(2dF) Redshift Survey constraint on ΩM and assuming aflat universe, we find that the equation of state parameter of the darkenergy lies in the range -1.48-1, we obtain w<-0.73 at 95% confidence.These constraints are similar in precision and in value to recentresults reported using the WMAP satellite, also in combination with the2dF Redshift Survey.Based in part on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS 5-26555. This research is primarily associatedwith proposal GO-8177, but also uses and reports results from proposalsGO-7505, 7588, 8641, and 9118.Based in part on observations taken with the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, le Centre National de la Recherche Scientifique de France, and the University of Hawaii. CTIO: Based in part on observations taken at the Cerro Tololo Inter-American Observatory.Keck: Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, and theNational Aeronautics and Space Administration. The Observatory was madepossible by the generous financial support of the W. M. Keck Foundation.UH: Based in part on observations with the University of Hawaii 2.2 mtelescope at Mauna Kea Observatory, Institute for Astronomy, University ofHawaii. UKIRT: Based in part on observations with the United KingdomInfrared Telescope (UKIRT) operated by the Joint Astronomy Centre on behalfof the UK. Particle Physics and Astronomy Research Council. VLT: Based inpart on observations obtained at the European Southern Observatory,Paranal, Chile, under programs ESO 64.O-0391 and ESO 64.O-0404. WIYN: Based in part on observations taken at the WIYN Observatory, a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.
| An Atlas of Hubble Space Telescope Spectra and Images of Nearby Spiral Galaxies
We have observed 54 nearby spiral galaxies with the Space TelescopeImaging Spectrograph (STIS) on the Hubble Space Telescope to obtainoptical long-slit spectra of nuclear gas disks and STIS optical (~Rband) images of the central 5''×5'' of thegalaxies. These spectra are being used to determine the velocity fieldof nuclear disks and hence to detect the presence of central massiveblack holes. Here we present the spectra for the successfulobservations. Dust obscuration can be significant at opticalwavelengths, and so we also combine the STIS images with archivalNear-Infrared Camera and Multi-Object Spectrometer H-band images toproduce color maps to investigate the morphology of gas and dust in thecentral regions. We find a great variety in the different morphologies,from smooth distributions to well-defined nuclear spirals and dustlanes.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| Bar Galaxies and Their Environments
The prints of the Palomar Sky Survey, luminosity classifications, andradial velocities were used to assign all northern Shapley-Ames galaxiesto either (1) field, (2) group, or (3) cluster environments. Thisinformation for 930 galaxies shows no evidence for a dependence of barfrequency on galaxy environment. This suggests that the formation of abar in a disk galaxy is mainly determined by the properties of theparent galaxy, rather than by the characteristics of its environment.
| Observations of five supernovae in 1995 1997
We present the results of photometric observations of the type Iasupernovae SN 1995al, 1996bo, 1996bk, the type Ib/c supernova SN 1997X,and the type II supernova SN 1996an. The photometric characteristics ofSN 1995al are close to the average for type Ia supernovae. Our analysishas revealed possible peculiarities in the light-curve shape anddeviations from the average photometric parameters for SN 1996bk and1996bo. Sn 1996an probably belongs to type IIP. The light curve of SN1997X resembles that of the type Ic supernova SN 1994I. Light-curveparameters and absolute magnitude estimates are presented.
| Late Light Curves of Type Ia Supernovae
We extend earlier efforts to determine whether the late (t>=60 days)light curves of Type Ia SNe are better explained by the escape ofpositrons from the ejecta or by the complete deposition of positronkinetic energy in a trapping magnetic field. We refine our selection ofIa SNe, using those that have extensive BVRI photometry 35 days or moreafter maximum light. Assuming that all SNe within a givenΔm15(B) range form a distinct subclass, we fit acombined light curve for all class members with a variety of models. Weimprove our previous calculations of energy deposition rates byincluding the transport of the Comptonized electrons. Their nonlocal andtime-dependent energy deposition produces a correction of as much as0.10 mag for Chandrasekhar-mass models and 0.18 mag forsub-Chandrasekhar-mass models. We produce bolometric corrections,derived from measured spectra, to B, V, R, and I light curves after day50. Comparisons of the resulting bolometric light curves with simulatedenergy deposition rates demonstrate that the energy deposition from thephotons and positrons created in 56Co-->56Fedecays are consistent with the observations if positron escape isassumed. This implies that there is no evidence of additional sources ofenergy deposition or of a shift of emission into unobserved wavelengthranges between days 60 and 900. The V band is shown to be an accurateindicator of total emission in the 3500-9700 Å range, with aconstant fraction (~25%) appearing in the V band after day 50. Thissuggests that the V band scales with the bolometric luminosity and thatthe deposited energy is instantaneously recycled into optical emissionduring this epoch. We see significant evolution of the colors of SNe Iabetween days 50 and 170. We suggest that this may be due to thetransition from spectra dominated by emission lines from the radioactivenucleus, 56Co, to those from the stable daughter nucleus,56Fe.
| The Progenitors of Subluminous Type Ia Supernovae
We find that spectroscopically peculiar subluminous Type Ia supernovae(SNe Ia) come from an old population. Of the 16 subluminous SNe Iaknown, 10 are found in E/S0 galaxies, and the remainder are found inearly-type spiral galaxies. The probability that this is a chanceoccurrence is only 0.2%. The finding that subluminous SNe Ia areassociated with an older stellar population indicates that for asufficiently large look-back time (already accessible in currenthigh-redshift searches) they will not be found. Due to a scarcity in oldpopulations, hydrogen and helium main-sequence stars and He red giantstars that undergo Roche lobe overflow are unlikely to be theprogenitors of subluminous SNe Ia. Earlier findings that overluminousSNe Ia [Δm15(B)<~0.95] come from a young progenitorpopulation are confirmed. The fact that subluminous SNe Ia andoverluminous SNe Ia come from different progenitor populations and alsohave different properties is a prediction of the CO white dwarf mergerprogenitor scenario.
| The formation of galaxy bulges: Spectrophotometric constraints
We have measured Mg2, Fe 5270 and Fe 5335 spectrophotometricindices (LICK system) in the bulge of 89 galaxies, mostly spirals fromthe Héraudeau (\cite{her96}) sample. The indices are reduced to anull velocity dispersion and normalized to an aperture of 0.2h-1 kpc. The mean errors are 0.009 mag on Mg2, and0.3 Å on the iron indices. These measurements almost double theamount of similar data already available on spiral galaxies. Our dataconfirm the existence of the relation between Mg2, andsigma0, the central stellar velocity dispersion; we find aneven tighter relation between Mg2, andVmrot, the maximum rotational velocity of thegalaxy, deduced from HI observations. For the most massive bulges, thesecorrelations may be interpreted as a mass-metallicity relation. However,the presence of young stellar populations, traced by the detection of[OIII] lambda 5007 Å, emission, provides clear evidence that ageeffects do play a role. Since the contribution of the young populationis anti-correlated to the mass of the galaxy, it continues theMg2, vs. sigma0 , relation toward thelow-sigma0, region and globally increases its slope. We alsopresent evidence for a new positive correlation between Fe indices andsigma0, and for a significant correlation between theline-strength indices and the total or disk luminosity. We propose tomodel the whole sequence of bulges within the folowing framework: bulgesare composed of a primary population formed prior to the disk, duringthe initial collapse, and of a secondary population formed during itsevolution. The whole family of bulges can be classified into threeclasses: (A) the bulges dominated by young populations are generallysmall, have ionized gas, low velocity dispersion and low line strengths;(B) the bulges dominated by the primary population lie along themass-metallicity sequence defined for elliptical galaxies; and (C) thebulges where the secondary population is significant are lessMg-over-abundant than (B)-type bulges and deviate from theMg2, vs. sigma0, relation of elliptical galaxies.Based on observations collected at the Observatoire de Haute-Provence.Table 3 is presented in electronic form only at the CDS. Tables 1 and 2are also available form at the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/68
| The UK Nova/Supernova Patrol-The First 25 Years
The history, accomplishments, and activities of the UK Nova/SupernovaPatrol are described.
| Nearby Optical Galaxies: Selection of the Sample and Identification of Groups
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
| On the Relation between Peak Luminosity and Parent Population of Type IA Supernovae: A New Tool for Probing the Ages of Distant Galaxies
We study the properties of Type Ia supernovae (SNe Ia) as functions ofthe radial distance from their host galaxy centers. Using a sample of 62SNe Ia with reliable luminosity, reddening, and decline ratedeterminations, we find no significant radial gradients of SNe Ia peakabsolute magnitudes or decline rates in elliptical+S0 galaxies,suggesting that the diversity of SN properties is not related to themetallicity of their progenitors. We do find that the range inbrightness and light curve width of supernovae in spiral galaxiesextends to brighter, broader values. These results are interpreted assupport for an age, but not metallicity, related origin of the diversityin SNe Ia. If confirmed with a larger and more accurate sample of data,the age-luminosity relation would offer a new and powerful tool to probethe ages and age gradients of stellar populations in galaxies atredshift as high as z~1-2. The absence of significant radial gradientsin the peak (B-V)0 and (V-I)0 colors of SNe Iasupports the reddening correction method of Phillips et al. We find noradial gradient in residuals from the SN Ia luminosity-width relation,suggesting that the relation is not affected by properties of theprogenitor populations and supporting the reliability of cosmologicalresults based upon the use of SNe Ia as distance indicators.
| Supernova Type Ia Luminosities, Their Dependence on Second Parameters, and the Value of H0
A sample of 35 Type Ia supernovae (SNe Ia) with good to excellentphotometry in B and V, minimum internal absorption, and1200
| A Search for Environmental Effects on Type IA Supernovae
We use integrated colors and B and V absolute magnitudes of Type Iasupernova (SN) host galaxies in order to search for environmentaleffects on the SN optical properties. With the new sample of 44 SNe weconfirm the conclusion by Hamuy et al. that bright events occurpreferentially in young stellar environments. We find also that thebrightest SNe occur in the least luminous galaxies, a possibleindication that metal-poor neighborhoods produce the more luminousevents. The interpretation of these results is made difficult, however,because of the fact that galaxies with younger stellar populations arealso lower in luminosity. In an attempt to remove this ambiguity, we usemodels for the line strengths in the absorption spectrum of fiveearly-type galaxies, in order to estimate metallicities and ages of theSN host galaxies. With the addition of abundance estimates from nebularanalysis of the emission spectra of three spiral galaxies, we findpossible further evidence that luminous SNe are produced in metal-poorneighborhoods. Further spectroscopic observations of the SN hostgalaxies will be necessary to test these results and assist indisentangling the age and metallicity effects on Type Ia SNe.
| 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.
| Diffuse Ionized Gas in Edge-on Spiral Galaxies: Extraplanar and Outer Disk Hα Emission
We present Hα images of five edge-on galaxies: NGC 891, NGC 4631,NGC 4244, NGC 3003, and UGC 9242. We also analyze [S II]lambdalambda6717, 6731 and [O III] lambda5007 images of NGC 4631. Forseveral of these galaxies, these images are the most sensitive to date.We analyze the ionized gas content, with particular attention to thediffuse ionized gas (DIG). The DIG layer in NGC 891 is traced out to atleast 5 kpc from the midplane, confirming an earlier spectroscopicdetection. The DIG in four of these galaxies contributes 40%-50% of thetotal Hα luminosity, similar to the contribution in face-ongalaxies, but in NGC 891 the DIG contributes 80%-90%. This is likely dueto the higher dust content in the disk of NGC 891, which obscures the HII regions but may also reflect the extraordinary prominence of the DIGlayer in that galaxy. Our very deep image of UGC 9242 shows very lowsurface brightness emission, as low as 0.3 pc cm^-6, reaching 4-5 kpcabove the midplane. This galaxy also exhibits filaments near the brightHα nucleus, an indication of a starburst superwind. In NGC 4631 wesee a very large shell of emission extending 3.5 kpc into the halo. The[S II]/Hα and [O III]/Hα ratios in NGC 4631 are consistentwith the ratios seen in other galaxies, and with photoionization models.There is a region on the southeast side of disk where the [OIII]/(Hα+[N II]) ratio reaches over 1.0 in the DIG, whichcoincides with an H I supershell. We use our very deep images of NGC3003 and UGC 9242 to search for ionized gas in the outer disks as a testof the strength of the metagalactic ionizing radiation field. We find noouter disk emission down to our 1 sigma limit of 0.13 pc cm^-6 on scalesof 1.5 kpc in NGC 3003. Based on this limit we rule out a metagalacticionizing radiation field stronger than 11x10^-23 ergs cm^-2 s^-1 Hz^-1sr^-1. There is an indication of extended disk emission in UGC 9242,which would imply a stronger radiation field, but various concerns, mostimportantly flat-fielding uncertainties due to foreground stars in theimage, lead us to question whether this feature is real.
| BVRI Light Curves for 22 Type IA Supernovae
We present 1210 Johnson/Cousins B, V, R, and I photometric observationsof 22 recent Type Ia supernovae (SNe Ia): SNe 1993ac, 1993ae, 1994M,1994S, 1994T, 1994Q, 1994ae, 1995D, 1995E, 1995al, 1995ac, 1995ak,1995bd, 1996C, 1996X, 1996Z, 1996ab, 1996ai, 1996bk, 1996bl, 1996bo, and1996bv. Most of the photometry was obtained at the Fred Lawrence WhippleObservatory of the Harvard-Smithsonian Center for Astrophysics in acooperative observing plan aimed at improving the database for SNe Ia.The redshifts of the sample range from cz=1200 to 37,000 km s^-1 with amean of cz=7000 km s^-1.
| Stellar kinematic data for the central region of spiral galaxies. II.
We present a second dataset of absorption spectroscopy on the innerregion of spiral galaxies. We have determined the central velocitydispersion for 42 Sa-Sc objects and, for 32 of them, stellar rotationcurves and velocity-dispersion profiles. Some of these profiles arelimited to the bulge, some others do reach a region dominated by theluminosity of the disk. These data are intended to provide basicmaterial for the study of the mass distribution and dynamical status inthe central regions of spiral galaxies. Although no elaboratebulge-and-disk photometric decomposition is performed, we estimate theeffects of limited resolution and contamination by disk light on thecentral velocity dispersion of the bulge. All the material presented inthis paper, in particular the spectra, is available on-line. Based onobservations collected at the Observatoire de Haute-Provence. Tables 2and 3 are presented in electronic form only; Tables 1 through 3 areavailable from the CDS, Strasbourg, via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Pico DOS Dias Survey Starburst Galaxies
We discuss the nature of the galaxies found in the Pico dos Dias Survey(PDS) for young stellar objects. The PDS galaxies were selected from theIRAS Point Source catalog. They have flux density of moderate or highquality at 12, 25, and 60 μm and spectral indices in the ranges -3.00<= alpha(25, 12) <= + 0.35 and -2.50 <= alpha(60, 25) <=+0.85. These criteria allowed the detection of 382 galaxies, which are amixture of starburst and Seyfert galaxies. Most of the PDS Seyfertgalaxies are included in the catalog of warm IRAS sources by de Grijp etal. The remaining galaxies constitute a homogeneous sample of luminous[log F (L_B/L_ȯ) = 9.9 +/- 0.4] starburst galaxies, 67% of whichwere not recognized as such before. The starburst nature of the PDSgalaxies is established by comparing their L_IR/L_B ratios and IRAScolors with a sample of emission-line galaxies from the literaturealready classified as starburst galaxies. The starburst galaxies show anexcess of FIR luminosity, and their IRAS colors are significantlydifferent from those of Seyfert galaxies-99% of the starburst galaxiesin our sample have a spectral index alpha(60, 25) < -1.9. As opposedto Seyfert galaxies, very few PDS starbursts are detected in X-rays. Inthe infrared, the starburst galaxies form a continuous sequence withnormal galaxies. But they generally can be distinguished from normalgalaxies by their spectral index alpha(60, 25) > -2.5. This colorcutoff also marks a change in the dominant morphologies of the galaxies:the normal IRAS galaxies are preferentially late-type spirals (Sb andlater), while the starbursts are more numerous among early-type spirals(earlier than Sbc). This preference of starbursts for early-type spiralsis not new, but a trait of the massive starburst nucleus galaxies(Coziol et al.). As in other starburst nucleus galaxy samples, the PDSstarbursts show no preference for barred galaxies. No difference isfound between the starbursts detected in the FIR and those detected onthe basis of UV excess. The PDS starburst galaxies represent the FIRluminous branch of the UV-bright starburst nucleus galaxies, with meanFIR luminosity log (L_IR/L_ȯ) = 10.3 +/- 0.5 and redshifts smallerthan 0.1. They form a complete sample limited in flux in the FIR at 2 x10^-10 ergs cm^-2 s^-1.
| Groups of galaxies. III. Some empirical characteristics.
Not Available
| Bulge-Disk Decomposition of 659 Spiral and Lenticular Galaxy Brightness Profiles
We present one of the largest homogeneous sets of spiral and lenticulargalaxy brightness profile decompositions completed to date. The 659galaxies in our sample have been fitted with a de Vaucouleurs law forthe bulge component and an inner-truncated exponential for the diskcomponent. Of the 659 galaxies in the sample, 620 were successfullyfitted with the chosen fitting functions. The fits are generally welldefined, with more than 90% having rms deviations from the observedprofile of less than 0.35 mag. We find no correlations of fittingquality, as measured by these rms residuals, with either morphologicaltype or inclination. Similarly, the estimated errors of the fittedcoefficients show no significant trends with type or inclination. Thesedecompositions form a useful basis for the study of the lightdistributions of spiral and lenticular galaxies. The object base issufficiently large that well-defined samples of galaxies can be selectedfrom it.
| 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
| 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.
| Infrared and optical spectroscopy of Type IA supernovae in the nebular phase
We present near-infrared (NIR) spectra for Type Ia supernovae at epochsof 13 to 338d after maximum blue light. Some contemporary opticalspectra are also shown. All the NIR spectra exhibit considerablestructure throughout the J, H and K bands. In particular, they exhibit aflux `deficit' in the J band which persists as late as 175d. This isresponsible for the well-known red J-H colour. To identify the emissionfeatures and test the ^56Ni hypothesis for the explosion and subsequentlight curve, we compare the NIR and optical nebular-phase data with asimple non-LTE nebular spectral model. We find that many of the spectralfeatures are due to iron-group elements, and that the J-band deficit isdue to a lack of emission lines from species that dominate the rest ofthe IR/optical spectrum. Nevertheless, some emission is unaccounted for,possibly due to inaccuracies in the cobalt atomic data. For somesupernovae, blueshifts of 1000-3000 km s^-1 are seen in infrared andoptical features at 3 months. We suggest that this is due to clumping inthe ejecta. The evolution of the cobalt/iron mass ratio indicates that^56Co-decay dominates the abundances of these elements. The absolutemasses of iron-group elements which we derive support the basicthermonuclear explosion scenario for Type Ia supernovae. A core-collapseorigin is less consistent with our data.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
