Showing papers by "Elaine M. Sadler published in 2000"
TL;DR: In this paper, the authors present observations of SN 1997cy, a supernova (SN) discovered as part of the Mount Stromlo Abell Cluster SN Search (Reiss et al.), which does not easily fit into the traditional classification scheme for supernovae.
Abstract: We present observations of SN 1997cy, a supernova (SN) discovered as part of the Mount Stromlo Abell Cluster SN Search (Reiss et al.), which does not easily fit into the traditional classification scheme for supernovae. This object's extraordinary optical properties and coincidence with GRB 970514, a short duration gamma-ray burst (GRB), suggest a second case, after SN 1998bw/GRB 980425, for a SN-GRB association. SN 1997cy is among the most luminous SNe yet discovered (MR ll -20.1, H0 = 65) and has a peculiar spectrum. We present evidence that SN 1997cy ejected approximately 2.6 M☉ of 56Ni, supported by its late-time light curve and Fe II/[Fe III] lines in its spectrum, although it is possible that both these observations can be explained via circumstellar interaction. While SN 1998bw and SN 1997cy appear to be very different objects with respect to both their gamma-ray and optical properties, SN 1997cy and the optical transient associated with GRB 970508 have roughly similar late-time optical behavior. This similarity may indicate that the late-time optical output of these two intrinsically bright transient events have a common physical process. Although the connection between GRB 970514 and SN 1997cy is suggestive, it is not conclusive. However, if this association is real, follow-up of short duration GRBs detected with BATSE or HETE2 should reveal objects similar to SN 1997cy.
124 citations
TL;DR: In this paper, the authors show that the Centaurus feature can be reproduced by the tidal debris of a spiral galaxy that has been tidally disrupted by the gravitational potential of NGC 4709.
Abstract: Deep images of the Centaurus and Coma clusters reveal two spectacular arcs ofdiffuse light that stretch for over 100 kpc, yet are just a few kpc wide. At a surfacebrightness of m b ∼ 27−28th arcsec −2 , the Centaurus arc is the most striking exampleknown of structure in the diffuse light component of a rich galaxy cluster. We usenumerical simulations to show that the Centaurus feature can be reproduced by thetidal debris of a spiral galaxy that has been tidally disrupted by the gravitational po-tential of NGC 4709. The surface brightness and narrow dimensions of the diffuse lightsuggest that the disk was co-rotating with its orbital path past pericenter. Featuresthis prominent in clusters will be relatively rare, although at fainter surface bright-ness levels the diffuse light will reveal a wealth of structure. Deeper imaging surveysmay be able to trace this feature for several times its presently observed extent andsomewhere along the tidal debris, a fraction of the original stellar component of thedisk will remain bound, but transformed into a faint spheroidal galaxy. It should bepossible to confirm the galactic origin of the Centaurus arc by observing planetarynebulae along its length with redshifts close to that of NGC 4709.Key words: galaxies: evolution – galaxies: clusters – galaxies: interactions – galaxies:formation.
84 citations
TL;DR: A blind survey for H I-bright galaxies in the southern zone of avoidance (212° ≤ l ≤ 36°, |b| ≤ 5°) has been made with the 21 cm multibeam receiver on the Parkes 64 m radio telescope as discussed by the authors.
Abstract: A blind survey for H I–bright galaxies in the southern zone of avoidance (212° ≤ l ≤ 36°, |b| ≤ 5°) has been made with the 21 cm multibeam receiver on the Parkes 64 m radio telescope. The survey, sensitive to normal spiral galaxies to a distance of ~40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67 have no counterparts cataloged in the NASA/IPAC Extragalactic Database. In general, the uncataloged galaxies lie behind thicker obscuration than do the cataloged objects. All the newly discovered galaxies have H I flux integrals that are more than an order of magnitude lower than those of the Circinus galaxy. The survey recovers the Puppis Cluster and foreground group, and the Local Void remains empty. The H I mass function derived for the sample is satisfactorily fitted by a Schechter function with parameters α = 1.51 ± 0.12, Φ* = 0.006 ± 0.003, and log M* = 9.7 ± 0.10.
61 citations
TL;DR: A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212 deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver on the Parkes 64 m radiotelescope.
Abstract: A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212 deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110 galaxies. Of these, 67 have no counterparts in the NASA/IPAC Extragalactic Database. In general, the uncataloged galaxies lie behind thicker obscuration than do the cataloged objects. All of the newly-discovered galaxies have HI flux integrals more than an order of magnitude lower than the Circinus galaxy. The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg & Huchtmeier 1992), and the Local Void remains empty. The HI mass function derived for the sample is satisfactorily fit by a Schechter function with parameters alpha = 1.51 +- 0.12, Phi* = 0.006 +- 0.003, and log M* = 9.7 +- 0.10.
55 citations
TL;DR: In this paper, the authors reported the discovery of an isolated cloud of neutral hydrogen, which they believe to be extragalactic, from the H I Parkes All-Sky Survey (HIPASS), using an estimated distance of similar to 3.2 Mpc.
Abstract: We report the discovery, from the H I Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen, which we believe to be extragalactic. The H I mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10(7) M-circle dot, using an estimated distance of similar to 3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits [mu(B) similar to 27 mag arcsec(-2)]. HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, H I 1225 + 01 (the Virgo H. I cloud) and has a size of at least 15 kpc. The mean velocity dispersion measured with the Australia Telescope Compact Array (ATCA) is only 4 km s(-1) for the main component and, because of the weak or nonexistent star formation, possibly reflects the thermal line width (T < 2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 1019 cm(-2), which is estimated to be a factor of 2 below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognized class of compact high-velocity clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud-Galaxy system at perigalacticon similar to 2 x 10(8) yr ago.
49 citations
TL;DR: The HIPASS J1712-64 (HIPASS) as discussed by the authors is an isolated cloud of neutral hydrogen which was discovered from the HI Parkes All-Sky Survey and is assumed to be extragalactic.
Abstract: We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an estimated distance of ~3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits (mu(B)~ 27 mag arcsec^-2). HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, HI 1225+01 (the Virgo HI Cloud) and has a size of at least 15 kpc. The mean velocity dispersion, measured with the Australia Telescope Compact Array (ATCA), is only 4 km/s for the main component and because of the weak or non-existent star-formation, possibly reflects the thermal linewidth (T<2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 10^19 cm^-2, which is estimated to be a factor of two below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognised class of Compact High Velocity Clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud/Galaxy system at perigalacticon ~ 2 x 10^8 yr ago.
45 citations
TL;DR: In this paper, the authors present H I data cubes of four low-luminosity early-type (E/S0 and S0) galaxies that are currently forming stars.
Abstract: We present H I data cubes of four low-luminosity early-type (E/S0 and S0) galaxies that are currently forming stars. These galaxies have absolute magnitudes in the range MB = -17.9 to -19.9 (H0 = 50 km s-1 Mpc-1). Their H I masses range between a few times 108 and a few times 109 M⊙, and the corresponding values for MHI/LB are between 0.07 and 0.42, so these systems are H I–rich for their morphological type. In all four galaxies, the H I is strongly centrally concentrated with high central H I surface densities, in contrast to what is typically observed in more luminous early-type galaxies. Star formation is occurring only in the central regions. In two galaxies (NGC 802 and ESO 118-G34), the kinematics of the H I suggests that the gas is in a strongly warped disk, which we take as evidence for recent accretion of H I. In the other two galaxies (NGC 2328 and ESO 027-G21), the H I must have been part of the systems for a considerable time. The H I properties of low-luminosity early-type galaxies appear to be systematically different from those of many more luminous early-type galaxies, and we suggest that these differences are due to a different evolution of the two classes. The star formation history of these galaxies remains unclear. Their UBV colors and Hα emission-line strengths are consistent with having formed stars at a slowly declining rate for most of the past 1010 yr. If so, their star formation history would be intermediate between late-type spiral disks and giant elliptical galaxies. However, the current data do not rule out a small burst of recent star formation overlaid on an older stellar population. Three of the galaxies have weak radio continuum emission, and the ratio of the far-infrared (FIR) to radio continuum emission is very similar to that of spirals of similar FIR or radio luminosity. We find that, except in the largest galaxy observed, the radio continuum emission can be accounted for solely by thermal (free-free) emission from H II regions, with no nonthermal (synchrotron) disk component. Thus, although these galaxies have gaseous disks, a disk magnetic field may be very weak or absent.
38 citations
Journal Article•
35 citations
TL;DR: A blind neutral hydrogen survey for galaxies using the 21 cm multibeam receiver on the Parkes 64 m telescope is reported in this paper. But the authors do not report on the results of this survey.
Abstract: We report on a blind neutral hydrogen survey for galaxies using the 21 cm multibeam receiver on the Parkes 64 m telescope. The surveyed region covers |b| ≤ 5° in the zone of avoidance (ZOA) from Galactic longitude 308° to 332°. The survey represents the first phase of a blind H I survey covering the southern ZOA (l = 212° to 36°). We have detected H I in 42 galaxies above a 3 σ limit of 60 mJy. The galaxies detected in this survey have velocities out to 6000 km s-1 and H I masses in the range 4 × 107 to 3 × 1010M⊙ (h). Only eight of the 42 galaxies have velocities previously measured. A further nine galaxies appear to have optical counterparts in the Woudt's 1998 catalog. In total, 16 of the galaxies appear to be associated with IRAS sources, although only three of these are without optical counterparts. The estimated median extinction for the 20 galaxies with optical or IR counterparts is AB = 3.8 mag. For the 22 galaxies with no counterparts, the estimated median extinction is AB = 5.6 mag. The distribution of galaxies is suggestive of a connection between the Centaurus supercluster above the Galactic plane and the Pavo-Indus supercluster beneath the plane. No previously hidden concentrations of galaxies were found.
28 citations
TL;DR: In this article, the authors investigated the evolution of the spectrum between 7 and 94 d after V-band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event.
Abstract: Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ-ray burst In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 23-m telescope We investigate the evolution of the spectrum between 7 and 94 d after V-band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope
16 citations
TL;DR: In this paper, the authors summarize the HI properties of early-type galaxies, in particular the differences in HI morphologies observed in early type galaxies of different luminosities, and discuss these different HI characteristics in the context of other properties that correlate with luminosity.
Abstract: We summarize the HI properties of early-type galaxies, in particular the differences in HI morphologies observed in early-type galaxies of different luminosities. We find that in low-luminosity early-type galaxies the HI is almost always in a disk-like structure, with central surface densities high enough for star formation to occur. In a few luminous early-type galaxies the HI is also in a disk or in a ring-like structure, but in most luminous early-type galaxies the HI has a relatively irregular morphology. The surface densities in the HI disks in luminous early-type galaxies are lower than in the HI disks in low-luminosity early-type galaxies and no large-scale star formation should occur in these disks. We discuss these different HI characteristics in the context of other properties of early-type galaxies that correlate with luminosity.
TL;DR: The first results of a survey of blue horizontal branch (BHB) stars in the Galactic bulge were presented in this paper, with 164 candidates with 15 = 7250K, of which seven have the gravities of young stars, three are ambiguous, and 37 are HB stars.
Abstract: We present the first results of a survey of blue horizontal branch (BHB) stars in the Galactic bulge. 164 candidates with 15 = 7250K, of which seven have the gravities of young stars, three are ambiguous, and 37 are HB stars. They span a wide metallicity range, from solar to 1/300 solar. The warmer BHB's are more metal-poor and loosely concentrated towards the Galactic center, while the cooler ones are of somewhat higher metallicity and closer to the center. Their red B-V colors overlap main-sequence stars, but the U-B vs. B-V diagram separates them until E(B-V) > 0.5. We detect two cool solar-metallicity HB stars in the bulge of our own Galaxy, the first such stars known. Still elusive are their hot counterparts, the metal-rich sdB/O stars causing excess UV light in metal-rich galaxies; they have V ~ 20.5 in the Bulge.
Journal Article•
TL;DR: The Fornax Spectroscopic Survey as mentioned in this paper used the 2dF field to obtain spectra for a complete sample of all 14,000 objects with 16.5 <=Bj<=19.7 in a 12 square degree area centred on the Fornasax Cluster.
Abstract: The Fornax Spectroscopic Survey will use the Two degree Field spectrograph (2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on the Fornax Cluster. By selecting all objects---both stars and galaxies---independent of morphology, we cover a much larger range of surface brightness and scale size than previous surveys. In this paper we present results from the first 2dF field. Redshift distributions and velocity structures are shown for all observed objects in the direction of Fornax, including Galactic stars, galaxies in and around the Fornax Cluster, and for the background galaxy population. The velocity data for the stars show the contributions from the different Galactic components, plus a small tail to high velocities. We find no galaxies in the foreground to the cluster in our 2dF field. The Fornax Cluster is clearly defined kinematically. The mean velocity from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be traced behind the cluster to a redshift beyond z=0.3. Background compact galaxies and low surface brightness galaxies are found to follow the general galaxy distribution.
Posted Content•
TL;DR: The Fornax Spectroscopic Survey as mentioned in this paper used the 2dF field to obtain spectra for a complete sample of all 14,000 objects with 16.5 <=Bj<=19.7 in a 12 square degree area centred on the Fornasax Cluster.
Abstract: The Fornax Spectroscopic Survey will use the Two degree Field spectrograph (2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on the Fornax Cluster. By selecting all objects---both stars and galaxies---independent of morphology, we cover a much larger range of surface brightness and scale size than previous surveys. In this paper we present results from the first 2dF field. Redshift distributions and velocity structures are shown for all observed objects in the direction of Fornax, including Galactic stars, galaxies in and around the Fornax Cluster, and for the background galaxy population. The velocity data for the stars show the contributions from the different Galactic components, plus a small tail to high velocities. We find no galaxies in the foreground to the cluster in our 2dF field. The Fornax Cluster is clearly defined kinematically. The mean velocity from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be traced behind the cluster to a redshift beyond z=0.3. Background compact galaxies and low surface brightness galaxies are found to follow the general galaxy distribution.
Posted Content•
TL;DR: In this article, a class of low-luminosity E/S0 galaxies which have both HI disks and (in contrast to more luminous E /S0s with HI) ongoing star formation is discussed.
Abstract: We discuss a class of low-luminosity E/S0 galaxies which have both HI disks and (in contrast to more luminous E/S0s with HI) ongoing star formation. We suggest that such objects are common, but that only a few are known at present because optical magnitude-limited galaxy catalogues are biased against them. The HI Parkes All-Sky Survey (HIPASS) should eventually detect many more. We suggest that `boxy' and `disky' ellipticals are distinct not only in their structure and kinematics, but in their star-formation history.