Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
The Survey for Ionization in Neutral Gas Galaxies. I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG),a census of star formation in H I-selected galaxies. The survey consistsof Hα and R-band imaging of a sample of 468 galaxies selected fromthe H I Parkes All Sky Survey (HIPASS). The sample spans three decadesin H I mass and is free of many of the biases that affect otherstar-forming galaxy samples. We present the criteria for sampleselection, list the entire sample, discuss our observational techniques,and describe the data reduction and calibration methods. This paperfocuses on 93 SINGG targets whose observations have been fully reducedand analyzed to date. The majority of these show a single emission linegalaxy (ELG). We see multiple ELGs in 13 fields, with up to four ELGs ina single field. All of the targets in this sample are detected inHα, indicating that dormant (non-star-forming) galaxies withMHI>~3×107 Msolar are veryrare. A database of the measured global properties of the ELGs ispresented. The ELG sample spans 4 orders of magnitude in luminosity(Hα and R band), and Hα surface brightness, nearly 3 ordersof magnitude in R surface brightness and nearly 2 orders of magnitude inHα equivalent width (EW). The surface brightness distribution ofour sample is broader than that of the Sloan Digital Sky Survey (SDSS)spectroscopic sample, the EW distribution is broader than prism-selectedsamples, and the morphologies found include all common types ofstar-forming galaxies (e.g., irregular, spiral, blue compact dwarf,starbursts, merging and colliding systems, and even residual starformation in S0 and Sa spirals). Thus, SINGG presents a superior censusof star formation in the local universe suitable for further studiesranging from the analysis of H II regions to determination of the localcosmic star formation rate density.
| SN 1998A: explosion of a blue supergiant
We present spectroscopic and photometric observations of the peculiarType II supernova (SN) 1998A. The light curves and spectra closelyresemble those of SN 1987A, suggesting that the SN 1998A progenitorexploded when it was a compact blue supergiant. However, the comparisonwith SN 1987A also highlights some important differences: SN 1998A ismore luminous and the spectra show bluer continua and larger expansionvelocities at all epochs. These observational properties indicate thatthe explosion of SN 1998A is more energetic than SN 1987A and moretypical of Type II supernovae. Comparing the observational data withsimulations, we deduce that the progenitor of SN 1998A was a massivestar (~25 Msolar) with a small pre-supernova radius (<~6× 1012 cm). The BaII lines, unusually strong in SN1987A and some faint II-P events, are almost normal in the case of SN1998A, indicating that the temperature plays a key role in determiningtheir strength.
| The Classification of Galaxies: Early History and Ongoing Developments
"You ask what is the use of classification, arrangement,systematization. I answer you; order and simplification are the firststeps toward the mastery of a subject the actual enemy is the unknown."
| Determination of the Thickness of Non-Edge-on Disk Galaxies
We propose a method to determine the thickness of non-edge-on diskgalaxies from their observed structure of spiral arms, based on thesolution of the truly three-dimensional Poisson's equation for alogarithmic disturbance of density and under the condition where theself-consistency of the density wave theory is no longer valid. Fromtheir measured number of arms, pitch angle and location of the innermostpoint of the spiral arms, we derive and present the thicknesses of 34spiral galaxies.
| The 1000 Brightest HIPASS Galaxies: H I Properties
We present the HIPASS Bright Galaxy Catalog (BGC), which contains the1000 H I brightest galaxies in the southern sky as obtained from the H IParkes All-Sky Survey (HIPASS). The selection of the brightest sourcesis based on their H I peak flux density (Speak>~116 mJy)as measured from the spatially integrated HIPASS spectrum. The derived HI masses range from ~107 to 4×1010Msolar. While the BGC (z<0.03) is complete inSpeak, only a subset of ~500 sources can be consideredcomplete in integrated H I flux density (FHI>~25 Jy kms-1). The HIPASS BGC contains a total of 158 new redshifts.These belong to 91 new sources for which no optical or infraredcounterparts have previously been cataloged, an additional 51 galaxiesfor which no redshifts were previously known, and 16 galaxies for whichthe cataloged optical velocities disagree. Of the 91 newly cataloged BGCsources, only four are definite H I clouds: while three are likelyMagellanic debris with velocities around 400 km s-1, one is atidal cloud associated with the NGC 2442 galaxy group. The remaining 87new BGC sources, the majority of which lie in the zone of avoidance,appear to be galaxies. We identified optical counterparts to all but oneof the 30 new galaxies at Galactic latitudes |b|>10deg.Therefore, the BGC yields no evidence for a population of``free-floating'' intergalactic H I clouds without associated opticalcounterparts. HIPASS provides a clear view of the local large-scalestructure. The dominant features in the sky distribution of the BGC arethe Supergalactic Plane and the Local Void. In addition, one can clearlysee the Centaurus Wall, which connects via the Hydra and Antlia Clustersto the Puppis Filament. Some previously hardly noticable galaxy groupsstand out quite distinctly in the H I sky distribution. Several newstructures, including some not behind the Milky Way, are seen for thefirst time.
| FLASH redshift survey - I. Observations and catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of4613 galaxies brighter than bJ= 16.7 (corrected for Galacticextinction) over a 700-deg2 region of sky in the generaldirection of the Local Group motion. The survey region is a70°× 10° strip spanning the sky from the ShapleySupercluster to the Hydra cluster, and contains 3141 galaxies withmeasured redshifts. Designed to explore the effect of the galaxyconcentrations in this direction (in particular the Supergalactic planeand the Shapley Supercluster) upon the Local Group motion, the 68 percent completeness allows us to sample the large-scale structure betterthan similar sparsely-sampled surveys. The survey region does notoverlap with the areas covered by ongoing wide-angle (Sloan or 2dF)complete redshift surveys. In this paper, the first in a series, wedescribe the observation and data reduction procedures, the analysis forthe redshift errors and survey completeness, and present the surveydata.
| Vertical Scale Parameter Estimates for 48 Non-edge-on Spiral Galaxies
In the first paper of this series, we directly studied the mathematicalforms, symmetry of spiral structure, and the projection of galacticdiscs on the images, and measured the pitch angles of the spiral armsand inclination angles of the galactic discs for 60 spiral galaxies. Inthis second paper, we estimate the vertical scale parameters of 48non-edge-on spiral galaxies based on the method proposed by Peng et al.and on the results given in Paper I. As we know, for edge-on discgalaxies we can obtain the vertical scale parameter from the photometry,once a mathematical form is specified for the vertical lightdistribution. For non-edge-on galaxies, some other methods have to beused. The statistical result was that the vertical scale parameter iscomparable for edge-on and non-edge-on galaxies, although it is obtainedfrom two very different methods.
| A search for Low Surface Brightness galaxies in the near-infrared. III. Nançay H I line observations
A total of 334 Low Surface Brightness galaxies detected in the 2MASSall-sky near-infrared survey have been observed in the 21 cm H I lineusing the Nançay telescope. All have a Ks-band meancentral surface brightness, measured within a 5'' radius, fainter than18 mag arcsec-2 and a Ks-band isophotal radius atthe 20 mag arcsec-2 level larger than 20''. We present globalH I line parameters for the 171 clearly detected objects and the 23marginal detections, as well as upper limits for the undetected objects.The 171 clear detections comprise 50 previously uncatalogued objects and41 objects with a PGC entry only.Tables 3-5 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/465Figures 1 and 2 are only available in electronic form athttp://www.edpsciences.org
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| An H I/Optical Atlas of Isolated Galaxies
We present an H I and optical survey of 41 extremely isolated galaxiesin an attempt to search for the gaseous remnants of the galaxy formationprocess, predicted to exist by hierarchical models of galaxy formation.By observing extremely isolated, quiescent, nonpeculiar galaxies weminimize the chances that any extragalactic H I found will be anothergalaxy, tidal debris, or ejecta from a galactic fountain or superwind.We have obtained new and archival data from the VLA and ATCA in a searchfor H I clouds down to MHI~107 Msolararound these galaxies. We found 13 H I-rich companions around 10 of the41 galaxies surveyed. Optical imaging finds spatially coincident starsassociated with all 13 companions. We find that the isolated galaxieshave properties fairly similar to those of field galaxies, while thecompanions are similar to dwarf irregular galaxies. The presence ofstars in all 13 companions suggests that H I clouds without starsdiscovered by other authors around field galaxies are not primordial andmost likely have either a tidal or ejecta origin.
| 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.
| Spectropolarimetry of the Type II Supernovae 1997ds, 1998A, and 1999gi
We present single-epoch spectropolarimetry of the Type II supernovae(SNe II) 1997ds, 1998A, and 1999gi. SN 1997ds and SN 1998A were bothobserved during the early photospheric phase, less than 50 days afterexplosion, while spectropolarimetry of SN 1999gi was obtained near thestart of the transition to the nebular phase, about 110 days afterexplosion. Uncorrected for interstellar polarization (ISP), SN 1997ds ischaracterized by pV=0.85%+/-0.02%, SN 1998A haspV=0.24%+/-0.05%, and SN 1999gi is polarized atpV=5.72%+/-0.01%. SN 1997ds and SN 1999gi exhibit distinctpolarization modulations (up to Δptot=1.6% in SN 1997dsand Δptot=1.0% in SN 1999gi) at the wavelengths of thestrongest spectral line features. While no spectral polarizationfeatures were observed in SN 1998A, the data are insensitive topolarization features at the levels confirmed in the other two objects.The low continuum polarization inferred for SN 1997ds and SN 1998A andthe amplitude of (or limits on) the polarization modulations areconsistent with those measured at similar epochs for SN 1987A and theType II plateau SN 1999em and supports the growing consensus thatcore-collapse events with hydrogen envelopes substantially intact at thetime of explosion are not significantly aspherical during the earlyphotospheric phase. The spectral shape of the high continuumpolarization of SN 1999gi closely resembles a ``Serkowski'' ISP curve(characterized by pmax=5.8%, θ=154deg, andλmax=5300 Å) and is inconsistent with thewavelength-independent nature of electron scattering expected for anaspherical SN atmosphere. Since Galactic reddening is minimal along thisline of sight, the majority of the observed polarization in SN 1999gi isbelieved to be due to ISP of the host galaxy, although significant (upto p~2%) intrinsic polarization cannot be ruled out. The potential powerof SN spectropolarimetry to study the properties of interstellar dust inexternal galaxies is described and applied to the SN 1999gi data, whereit is shown that if the polarization is indeed predominantlyinterstellar in origin, then RV=3.0+/-0.2 for the dust alongthis line of sight in NGC 3184.
| A Method of Obtaining the Pitch Angle of Spiral Arms and the Inclination of Galactic Discs
We investigate the mathematical form, the symmetry of spiral structureand the projected images of galactic discs. The measured pitch angles ofspiral arms and inclination angles of galactic discs for 60 spiralgalaxies are presented. The global spiral structure is emphasized in thestudy. It is found that, except for small-scale distortions, the spiralarms of those galaxies that were classified as AC 12 in the armclassification system of Elmegreen & Elmegreen, can be representedby the logarithmic spiral form.
| Supernovae 1998A, 1998S, and 1999gn
IAUC 7435 available at Central Bureau for Astronomical Telegrams.
| Supernova 1998A in IC 2627
IAUC 6849 available at Central Bureau for Astronomical Telegrams.
| Supernovae
IAUC 6823 available at Central Bureau for Astronomical Telegrams.
| Supernova 1998A in IC 2627
IAUC 6805 available at Central Bureau for Astronomical Telegrams.
| Light curves of SN 1998A and comparison with similar unusual SNe
Preliminary photometric data for SN 1998A are presented, showing that itincreased in brightness by 1.0+/-0.1 mag in RI over the 80-d periodfollowing discovery. Maximum brightness occurred approximately 70 dafter discovery, centred within a broad plateau-like peak lasting about30 d. The shapes of the light curves during the entire 170-d period aresimilar to those of SNe 1987A and 1909A, suggesting that SNe 1998A and1909A may also have had blue supergiant progenitors. Spectroscopic andfurther photometric study of SN 1998A will allow more detailedcomparisons between this and other unusual Type II supernovae.
| Extensive Spiral Structure and Corotation Resonance
Spiral density wave theories demand that grand-design spiral structurebe bounded, at most, between the inner and outer Lindblad resonances ofthe spiral pattern. The corotation resonance lies between the outer andthe inner Lindblad resonances. The locations of the resonances are atradii whose ratios to each other are rather independent of the shape ofthe rotation curve. The measured ratio of outer to inner extent ofspiral structure for a given spiral galaxy can be compared to thestandard ratio of corotation to inner Lindblad resonance radius. In thecase that the measured ratio far exceeds the standard ratio, it islikely that the corotation resonance is within the bright optical disk.Studying such galaxies can teach us how the action of resonances sculptsthe appearance of spiral disks. This paper reports observations of 140disk galaxies, leading to resonance ratio tests for 109 qualified spiralgalaxies. It lists candidates that have a good chance of having thecorotation resonance radius within the bright optical disk.
| 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.
| Visual supernova searching with the 40 inch telescope at Siding Spring Observatory
Preliminary results are presented arising from the use of the 40 inchtelescope at Siding Spring Observatory for visual supernova hunting overa period of about 18 months. The use of the telescope in this way iscontinuing. These results are compared with the performance of my 41 cmbackyard telescope over the same 18-month period, and with recentlyannounced results from the Perth Observatory's Automated SupernovaSearch using their 61 cm telescope over a three-year period.
| Lopsided Spiral Galaxies and a Limit on the Galaxy Accretion Rate
We present a measurement of lopsidedness for the stellar disks of 60field spiral galaxies in terms of the azimuthal m = 1 Fourier amplitude,A1, of the stellar light. We confirm the previous result (Rix &Zaritsky) that ~30% of field spiral galaxies in a magnitude-limitedsample exhibit significant lopsidedness ( >= 0.2) atlarge radii (R > 1.5 disk scalelengths). We conjecture that thislopsidedness is caused by tidal interactions and calculate an upperlimit on the accretion rate of small galaxies. We exploit thecorrelation between lopsidedness and photometric measures of recent starformation (Zaritsky) to obtain two independent estimates of the lifetimeof these m = 1 distortions. First, we show that lopsided galaxies havean excess of blue luminosity relative to that of symmetric galaxies withthe same H I linewidth, which we attribute to a recent star formationepisode that was triggered by an interaction between the galaxy and acompanion. We use stellar population models (Bruzual & Charlot) toestimate the time since that interaction. Second, we use the N-bodysimulation of an infalling satellite by Walker, Mihos, & Hernquistto estimate how fast tidally induced m = 1 distortions are erasedthrough phase mixing. Both approaches indicate that the observations areconsistent with a hypothesized tidal interaction that occurred about 1Gyr ago for galaxies that are lopsided at the 20% level. By combiningthis lifetime estimate for lopsidedness, the observed frequency of suchdistortions, and a correction to the survey volume that depends on theincrease in luminosity during an interaction, we derive an upper limiton the current companion accretion rate of field spiral galaxies (forcompanion masses ~10% parent galaxy mass) that lies in the range0.07--0.25 Gyr-1. The principal uncertainty in this limit arises fromambiguities in the interpretation of the correlation betweenlopsidedness and MB.
| Scaleheights of 486 southern spiral galaxies and some statistical correlation
Based on Peng's method (1988), we obtain scaleheights of 486 southernspiral galaxies, the images of which are taken from the Digitized SkySurvey at Xinglong Station of Beijing Astronomical Observatory. Thefitted spiral arms of 70 galaxies are compared with their images to gettheir optimum inclinations. The scaleheights of other 416 ones arelisted in Table A1 in Appendix. After compiling and analyzing the data,we find some statistical correlations. The most interesting results arethat a flatter galaxy is bluer and looks brighter, and galaxies becomeflatter along the Hubble sequence Sab -- Scd. Based on photographic dataof the National Geographic Society -- Palomar Observatory Sky Survey(NGS-POSS) obtained using the Oschin Telescope Palomar Mountain. TheNGS-POSS was funded by a grant from the National Geographic Society tothe California Institute of Technology. The plates were processed intothe present compressed digital form with their permission. The DigitizedSky Survey was produced at the Space Telescope Science Institute underUS Government grant NAG W-2166. Table A1 is available in electronic fromonly, via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| The statistics analysis of recent supernovae.
Not Available
| Constraining the Ages of Supernova Progenitors. I. Supernovae and Spiral Arms
We present the first results of a three-part study of supernova (SN)ages using positional age indicators in spiral galaxies. We havemeasured the positions of 90 Spectroscopically identified Type Ia andType II SNs (SNs Ia and SNs II) relative to spiral arms in their hostgalaxies, making a special effort to reduce inhomogeneity in the processof arm tracing for different galaxies. We find that SNs II are moretightly concentrated to the arms than SNs Ia, but both kinds of SNsoccur closer to arms than a random disk population. However, whencompared with the distribution of V and I light relative to the arms,the SNs Ia are no more tightly concentrated than the general stellarpopulation. This indicates that SNs Ia occur in a population old enoughto have diffused away from their formation regions.
| Uncovering Spiral Structure in Flocculent Galaxies
We present K' (2.1 mu m) observations of four nearby flocculent spirals,which clearly show low-level spiral structure and suggest thatkiloparsec-scale spiral structure is more prevalent in flocculentspirals than previously supposed. In particular, the prototypicalflocculent spiral NGC 5055 is shown to have regular, two-arm spiralstructure to a radius of 4.0 kpc in the near-infrared, with anarm-interarm contrast of 1.3. The spiral structure in all four galaxiesis weaker than that in grand design galaxies. Taken in unbarred galaxieswith no large, nearby companions, these data are consistent with themodal theory of spiral density waves, which maintains that density wavesare intrinsic to the disk. As an alternative, mechanisms for drivingspiral structure with nonaxisymmetric perturbers are also discussed.These observations highlight the importance of near-infrared imaging forexploring the range of physical environments in which large-scaledynamical processes, such as density waves, are important.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
Catálogos y designaciones:
|
