Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Delayed Photoionization Feedback in a Super Star Cluster in SBS 0335-052E
SBS 0335-052 is a well-studied blue compact dwarf galaxy with one of thelowest metallicities of any known galaxy. It also contains sixpreviously identified super star clusters. We combine archival HSTNICMOS images in the Paα line and the 1.6 μm continuum of theeastern component, SBS 0335-052E, with other space- and ground-baseddata to perform a multiwavelength analysis of the super star clusters.We concentrate on the southernmost clusters, designated S1 and S2, whichappear to be the youngest clusters and are the strongest emitters ofPaα, radio, and X-ray flux. Our analysis leads to a possible modelfor S1 and perhaps S2 as a cluster of very young, massive stars withstrong stellar winds. The wind density can be high enough to absorb themajority of ionizing photons within less than 1000 AU of the stars,creating very compact H II regions that emit optically thick radiationat radio wavelengths. These winds would then effectively quench thephotoionizing flux very close to the stars. This can delay the onset ofnegative feedback by photoionization and photodissociation on starformation in the clusters. This is significant since SBS 0335-052Eresembles the conditions that were probably common for high-redshiftstar formation in galaxies near the epoch of reionization.
| Classifications of the Host Galaxies of Supernovae, Set III
A homogeneous sample comprising host galaxies of 604 recent supernovae,including 212 objects discovered primarily in 2003 and 2004, has beenclassified on the David Dunlap Observatory system. Most SN 1991bg-likeSNe Ia occur in E and E/Sa galaxies, whereas the majority of SN1991T-like SNe Ia occur in intermediate-type galaxies. This differenceis significant at the 99.9% level. As expected, all types of SNe II arerare in early-type galaxies, whereas normal SNe Ia occur in all Hubbletypes. This difference is significant at the 99.99% level. A smallnumber of SNe II in E galaxies might be due to galaxy classificationerrors or to a small young-population component in these mainly oldobjects. No significant difference is found between the distributionsover the Hubble type of SNe Ibc and SNe II. This confirms that both ofthese types of objects have similar (massive) progenitors. The presentdata show that in order to understand the dependence of supernova typeon host-galaxy population, it is more important to obtain accuratemorphological classifications than it is to increase the size of thedata sample.
| Supernovae 2003lo and 2003lp
IAUC 8261 available at Central Bureau for Astronomical Telegrams.
| H I and CO in Blue Compact Dwarf Galaxies: Haro 2 and Haro 4
We present Very Large Array H I imaging of two blue compact dwarfgalaxies, Haro 2 and Haro 4, and of the spiral galaxy Haro 26, which isprojected some 22' southwest of Haro 4. We also show a map of theCO(1-0) distribution of Haro 2 obtained with the Owens Valley RadioObservatory Millimeter Array, as well as derive an upper limit forCO(2-1) emission from Haro 4 obtained with the Caltech SubmillimeterObservatory. The H I data of Haro 2 reveal that the kinematical majoraxis lies perpendicular to the photometric major axis, indicating thatthe atomic hydrogen rotates about the major axis of the galaxy. Thisconfirms earlier indications based on CCD photometry that Haro 2 is adust-lane dE rather than a dIrr. We propose that the present neutral andmolecular ISM configuration is due to recent gas accretion or a merger.The H I distribution and dynamics of Haro 4 and the neighboring spiralHaro 26 suggest that they are currently undergoing a tidal interaction,reinforcing the notion that interactions play an important role intriggering the star formation witnessed in blue compact galaxies.
| Neutral Hydrogen Observations of the Extremely Metal-Poor Blue Compact Dwarf Galaxy SBS 0335-052
We present VLA H I observations of one of the most metal-deficient bluecompact dwarf (BCD) galaxies known, SBS 0335-052, which sports an oxygenabundance of only 1/40 that of the Sun. We study the structure anddynamics of the neutral gas in this chemically young object at a spatialresolution of 20''×15'' ( 5.4×3.9 kpc at a distance of 54Mpc), and a velocity resolution of 21.2 kms-1.
| Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177supernovae (SNe) that have been discovered since 1997 during the courseof the Lick Observatory Supernova Search with the Katzman AutomaticImaging Telescope. Whereas SNe Ia occur in all galaxy types, it isfound, at a high level of statistical confidence, that SNe Ib, Ic, andII are strongly concentrated in late-type galaxies. However, attentionis drawn to a possible exception provided by SN 2001I. This SN IInoccurred in the E2 galaxy UGC 2836, which was not expected to harbor amassive young supernova progenitor.
| The H I Line Width/Linear Diameter Relationship as an Independent Test of the Hubble Constant
The relationship between corrected H I line widths and linear diameters(LW/LD) for spiral galaxies is used as an independent check on the valueof the Hubble constant. After calibrating the Tully-Fisher (TF) relationin both the B and I bands, the B-band relation is used for galaxies ofmorphological/luminosity types Sc I, Sc I.2, Sc I.3, Sab, Sb, Sb I-II,and Sb II to derive the LW/LD relation. We find that for this sample thescatter in the LW/LD is smallest with a Hubble constant of 90-95 kms-1 Mpc-1. Lower values of the Hubble constantproduce a separation in the LW/LD relation that is a function ofmorphological type. Since a Hubble constant of 90-95 is significantlylarger than the final Key Project value of 72 km s-1Mpc-1, a comparison of TF, surface brightness fluctuation(SBF), and fundamental plane (FP) is made. This comparison indicatesthat the Key Project TF distances to 21 clusters may be too large. For asample of 11 clusters, the Key Project TF distances provide anunweighted mean Hubble constant of 77 km s-1Mpc-1, while a combination of the FP, SBF, and our TFdistances for the same 11 clusters gives H0=91 kms-1 Mpc-1. A more subtle result in our data is amorphological dichotomy in the Hubble constant. The data suggest that ScI galaxies follow a Hubble constant of 90-95 while Sb galaxies follow aHubble constant closer to 75 km s-1 Mpc-1.Possible explanations for this result are considered, but it is shownthat this Sb/Sc I Hubble flow discrepancy is also present in the VirgoCluster and is consistent with previous investigations that indicatethat some galaxies carry a component of age-related intrinsic redshift.
| 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.
| The Void Phenomenon
Advances in theoretical ideas on how galaxies formed have not beenstrongly influenced by the advances in observations of what might be inthe voids between the concentrations of ordinary optically selectedgalaxies. The theory and observations are maturing, and the search for areconciliation offers a promising opportunity to improve ourunderstanding of cosmic evolution. I comment on the development of thissituation and present an update of a nearest neighbor measure of thevoid phenomenon that may be of use in evaluating theories of galaxyformation.
| VLA H I Line Observations of the Extremely Metal-Poor Blue Compact Dwarf Galaxy SBS 0335-052
We present the results of H I mapping with the NRAO2 VLA of one of themost metal-deficient blue compact dwarf (BCD) galaxies known, SBS0335-052, with an oxygen abundance only 1/40 that of the Sun. We studythe structure and dynamics of the neutral gas in this chemically youngobject with a spatial resolution of 20.5"×15" (~5.4×3.9 kpcat an assumed distance of 54.3 Mpc), a sensitivity at the 2 σdetection level of ~2.0 K or 7.5×1019 cm-2and a velocity resolution of 21.2 km s-1. We detected a largeH I complex associated with this object having an overall size of about66 by 22 kpc and elongated in the east-west direction. There are twoprominent, slightly resolved peaks visible in the integrated H I map,separated in the east-west direction by 22 kpc (84"). The eastern peakis nearly coincident with the position of the optical galaxy SBS0335-052. The western peak is about a factor of 1.3 brighter in the H Iline and is identified with a faint blue compact dwarf galaxy, SBS0335-052W, with mB=19.4, and a metallicity close to thelowest values known for BCDs, about 1/50 that of the Sun. The radialvelocities of both systems are similar, suggesting that the two BCDs,SBS 0335-052 and SBS 0335-052W, constitute a pair of dwarf galaxiesembedded in a common H I envelope. Alternatively, the BCDs may be thenuclei of two distinct interacting primordial H I clouds. The estimatedtotal dynamical mass, assuming the BCDs form a bound system, is largerthan ~6×109 Msolar, compared with a totalgaseous mass Mgas=2.1×109 Msolarand a total stellar mass Mstar<=108Msolar. Hence, the mass of the SBS 0335-052 system isdominated by dark matter. Because of the disturbed H I velocity fieldand the presence of what might be tidal tails at either end of thesystem, we favor the hypothesis of tidal triggering of the starformation in this system. It can be due to either the nearby giantgalaxy NGC 1376 or the mutual gravitational interaction of the two H Iclouds.
| Supernovae
IAUC 7344 available at Central Bureau for Astronomical Telegrams.
| 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.
| Supernova 1999go in NGC 1376
IAUC 7339 available at Central Bureau for Astronomical Telegrams.
| Supernova 1999go in NGC 1376
IAUC 7337 available at Central Bureau for Astronomical Telegrams.
| The I-Band Tully-Fisher Relation for SC Galaxies: 21 Centimeter H I Line Data
A compilation of 21 cm line spectral parameters specifically designedfor application of the Tully-Fisher (TF) distance method is presentedfor 1201 spiral galaxies, primarily field Sc galaxies, for which opticalI-band photometric imaging is also available. New H I line spectra havebeen obtained for 881 galaxies. For an additional 320 galaxies, spectraavailable in a digital archive have been reexamined to allow applicationof a single algorithm for the derivation of the TF velocity widthparameter. A velocity width algorithm is used that provides a robustmeasurement of rotational velocity and permits an estimate of the erroron that width taking into account the effects of instrumental broadeningand signal-to-noise. The digital data are used to establish regressionrelations between measurements of velocity widths using other commonprescriptions so that comparable widths can be derived throughconversion of values published in the literature. The uniform H I linewidths presented here provide the rotational velocity measurement to beused in deriving peculiar velocities via the TF method.
| The I-Band Tully-Fisher Relation for SC Galaxies: Optical Imaging Data
Properties derived from the analysis of photometric I-band imagingobservations are presented for 1727 inclined spiral galaxies, mostly oftypes Sbc and Sc. The reduction, parameter extraction, and errorestimation procedures are discussed in detail. The asymptotic behaviorof the magnitude curve of growth and the radial variation in ellipticityand position angle are used in combination with the linearity of thesurface brightness falloff to fit the disk portion of the profile. TotalI-band magnitudes are calculated by extrapolating the detected surfacebrightness profile to a radius of eight disk scale lengths. Errors inthe magnitudes, typically ~0.04 mag, are dominated by uncertainties inthe sky subtraction and disk-fitting procedures. Comparison is made withthe similar imaging database of Mathewson, Ford, & Buchhorn, both aspresented originally by those authors and after reanalyzing theirdigital reduction files using identical disk-fitting procedures. Directcomparison is made of profile details for 292 galaxies observed incommon. Although some differences occur, good agreement is found,proving that the two data sets can be used in combination with onlyminor accommodation of those differences. The compilation of opticalproperties presented here is optimized for use in applications of theTully-Fisher relation as a secondary distance indicator in studies ofthe local peculiar velocity field.
| HI observations of blue compact galaxies from the first and second Byurakan surveys
We present the results of a neutral hydrogen survey of 79 galaxies froma statistical sample of 88 Blue Compact Galaxies (BCGs) selected fromthe First and Second Byurakan objective prism surveys to have a HIIregion-like spectrum, an equivalent width of the [O III] lambda 5007line larger than ~ 50 Å, and a velocity <= 6000 km s(-1) . Thedetection rate for the statistical sample is 74%. HI masses rangebetween 4 10(7)M_sun) and 5 10(9) M_sun with the HI mass distributionpeaking at 3 10(8) M_sun. The full width at half-maximum of the HIprofile varies between ~ 30 km s(-1) and 160 km s(-1) , with a mean of ~92 km s(-1) . These small widths are characteristic of dwarf galaxies.For comparison, we have also observed an additional 92 BCGs with weakerstar formation and/or larger distances, and/or interesting astrophysicalproperties. These in general have larger widths and HI masses.Tables~1,~2,~3 also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| 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.
| The Southern Sky Redshift Survey
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
| The discovery of a second optical component in the H I cloud of the young dwarf galaxy SBS 0335-052: new observations with the 6-m telescope.
Not Available
| Hubble Space Telescope Observations of the Blue Compact Dwarf SBS 0335-052: A Probable Young Galaxy
We present HST WFPC2 V and I images and GHRS UV spectrophotometry of thespectral regions around Ly alpha and O I lambda 1302 of the extremelymetal-deficient (Z ~ Zȯ/41) blue compact dwarf galaxy (BCD) SBS0335-052. All the star formation in the BCD occurs in six super--starclusters (SSCs) with ages <=25 Myr, within a region of ~2" or 520 pcin size. Dust is clearly present and mixed spatially with the SSCs. TheSSCs are roughly aligned in the southeast-northwest direction, and thereis a systematic increase in reddening of the clusters away from thebrightest one. The observed color dependence on position may be thecombined effects of differential extinction by dust and color evolutionwith time due to sequential propagating star formation. There is asupershell of radius ~380 pc, delineating a large supernova cavity. Theinstantaneous star formation rate is ~0.4 Mȯ yr-1. Strong narrow Lyalpha emission is not observed. Rather there is low-intensity broad(FWZI = 20 A) Ly alpha emission superposed on even broader Ly alphaabsorption by the H I envelope. This broad low-intensity emission iscaused by resonant scattering of Ly alpha photons. The absence of strongLy alpha emission may be due partly to dust absorption, but is duemainly to multiple scattering that removes Ly alpha photons from thesmall HST aperture. As the H I cloud is seen nearly edge-on, geometricaleffects may also play a role as photons escape more easily in adirection perpendicular to the plane than along it. The BCD appears tobe a young galaxy, undergoing one of its very first bursts of starformation. This conclusion is based on the following evidence: (1) Theunderlying extended low surface brightness component is irregular andfilamentary, suggesting that a significant part of the emission comesfrom ionized gas. Any underlying stellar population must be younger than~108 yr. (2) The underlying component has very blue colors [-0.34 <=(V-I)0 <= 0.16], consistent with gaseous emission colors. (3) The O Ilambda 1302 line is not detected in absorption in the Goddard HighResolution Spectrograph spectrum, setting an upper limit for N(O)/N(H)in the H I envelope of the BCD of more than 3000 times smaller than thevalue in Orion.
| 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.
| Parameters of 2447 Southern Spiral Galaxies for Use in the Tully-Fisher Relation
I-band luminosities, rotational velocities, and redshifts of 1092 spiralgalaxies have been measured by CCD photometry and Hα spectroscopyusing the 1 m and 2.3 m telescopes at Siding Spring Observatory,respectively. The results are tabulated. Luminosity profiles andHα rotation curves are given for the galaxies. When these resultsare combined with similar data for 1355 spiral galaxies publishedpreviously (Mathewson, Ford, & Buchhorn, hereafter Paper I), itprovides a large, uniform, and unique data set with which to measure,via the Tully-Fisher relation, the peculiar velocities of galaxies inthe local universe to a distance of 11,000 km s^-1^ (Mathewson &Ford). Taking advantage of the opportunity for publishing this data inmachine-readable form, in the CD-ROM, we have also included similar datafor the 1355 galaxies in Paper I.
| 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.
| Bias Properties of Extragalactic Distance Indicators. VI. Luminosity Functions of M31 and M101 Look-alikes Listed in the RSA2: H0 Therefrom
Galaxies whose morphologies are similar to M 101 (Sc I) and M3 1 (Sb I-II) are listed in two tables. The selection is made by inspecting directimages of Shapley-Ames galaxies in the recent Carnegie Atlas ofGalaxies. Absolute magnitudes, calculated from redshifts, give meanvalues of
| Nonaxisymmetric Structures in the Stellar Disks of Galaxies
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...447...82R&db_key=AST
|
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:
|
