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Showing papers by "Mike Irwin published in 1998"


Journal Article
TL;DR: Perlmutter et al. as discussed by the authors presented evidence for a low-mass density/positive cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae.
Abstract: This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described. More extensive analyses of these results with some additional methods and data are presented in the more recent LBNL report #41801 (Perlmutter et al., 1998; accepted for publication in Ap.J.), astro-ph/9812133 . This Lawrence Berkeley National Laboratory reprint is a reduction of a poster presentation from the Cosmology Display Session #85 on 9 January 1998 at the American Astronomical Society meeting in Washington D.C. It is also available on the World Wide Web at http://supernova.LBL.gov/ This work has also been referenced in the literature by the pre-meeting abstract citation: Perlmutter et al., B.A.A.S., volume 29, page 1351 (1997).

164 citations


Journal ArticleDOI
TL;DR: In this paper, the results from the first season of follow-up spectroscopy were reported, showing that N-type carbon stars formed in the halo in isolation from other star-forming regions.
Abstract: A by-product of the APM high-redshift quasar survey was the discovery of several distant (20–100 kpc) N-type carbon stars at high galactic latitude. Following on from this, we have started a systematic all-sky survey at galactic latitudes ⊢b⊢>30° to find further examples of these rare objects, and we report here on the results from the first season of follow-up spectroscopy. Faint, high-latitude carbon (FHLC) giants make excellent probes of the kinematic structure of the outer Galactic halo. Therefore, in addition to detailed spectrophotometry covering a wide wavelength range, we have obtained high-resolution (∼1 A) spectra centred on the CN bands at ∼8000 A, and have derived accurate (≲10 km s−1) radial velocities for the known FHLC stars. From the initial phase of our survey covering ≈6500 deg2, we find a surface density of faint N-type carbon stars in the halo of ≈1 per 200 deg2, roughly a factor of 4 less than the surface density of CH-type carbon stars in the halo. Intermediate-age, N-type carbon stars seem unlikely to have formed in the halo in isolation from other star-forming regions, and one possibility that we are investigating is that they either arise from the disruption of tidally captured dwarf satellite galaxies or are a manifestation of the long-sought optical component of the Magellanic Stream.

145 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the discovery of a highly luminous, broad absorption line quasar at a redshift of z = 3.87, which is positionally coincident, within 1'', with the IRAS Faint Source Catalog source F08279+5255.
Abstract: We report on the discovery of a highly luminous, broad absorption line quasar at a redshift of z = 3.87, which is positionally coincident, within 1'', with the IRAS Faint Source Catalog source F08279+5255. A chance alignment of the quasar and the IRAS source is extremely unlikely, and we argue that the optical and far-infrared flux are different manifestations of the same object. With an R-band magnitude of 15.2 and an IRAS 60 μm flux of 0.51 Jy, APM 08279+5255 is (apparently) easily the most intrinsically luminous object known, with LBol ~ 5 × 1015 L☉. Optical CCD photometry of the system, taken in good seeing, shows evidence that the system is slightly elongated. Although these data are consistent with the superposition of the quasar on a vastly luminous galaxy, we argue that a more likely scenario is that the optical image implies the presence of two unresolved point sources. Such a configuration suggests that gravitational lensing may play a significant role in amplifying the intrinsic properties of the system. Point-spread function fitting of two discrete sources gives a separation of ~04 and an intensity ratio ~1.1. The optical spectrum of the quasar clearly reveals the presence of three potential lensing galaxies, Mg II absorption systems at z = 1.18 and z = 1.81, and a damped Lyα absorption system at z = 3.07. Additional, as yet unseen, lensing galaxies may also be present. We estimate the total amplification of the optical component to be ≈ 40 but, owing to the larger scale of the emitting region, would expect the infrared amplification to be significantly less. Even making the conservative assumption that all wavelengths are amplified by a factor 40, APM 08279+5255 still possesses a phenomenal luminosity of 1014 L☉, indicating that it belongs to a small but significant population of high-redshift, hyperluminous objects with copious infrared emission.

128 citations


Journal ArticleDOI
TL;DR: It is shown that PCA can compress the spectra by a factor of over 30 while retaining essentially all of the useful information in the data set, and that this compression optimally removes noise and can be used to identify unusual spectra.
Abstract: We investigate the application of neural networks to the automation of MK spectral classification. The data set for this project consists of a set of over 5000 optical (3800–5200 A) spectra obtained from objective prism plates from the Michigan Spectral Survey. These spectra, along with their two-dimensional MK classifications listed in the Michigan Henry Draper Catalogue, were used to develop supervised neural network classifiers. We show that neural networks can give accurate spectral type classifications (σ68= 0.82 subtypes, σrms= 1.09 subtypes) across the full range of spectral types present in the data set (B2–M7). We show also that the networks yield correct luminosity classes for over 95 per cent of both dwarfs and giants with a high degree of confidence. Stellar spectra generally contain a large amount of redundant information. We investigate the application of principal components analysis (PCA) to the optimal compression of spectra. We show that PCA can compress the spectra by a factor of over 30 while retaining essentially all of the useful information in the data set. Furthermore, it is shown that this compression optimally removes noise and can be used to identify unusual spectra. This paper is a continuation of the work carried out by von Hippel et al. (Paper I).

125 citations


Journal ArticleDOI
TL;DR: In this paper, the authors reported the discovery of a highly luminous, broad absorption line quasar at a redshift of 3.87, which is positionally coincident, within one arcsecond, with the IRAS FSC source F08279+5255.
Abstract: We report on the discovery of a highly luminous, broad absorption line quasar at a redshift of $z=3.87$ which is positionally coincident, within one arcsecond, with the IRAS FSC source F08279+5255. A chance alignment of the quasar and the IRAS source is extremely unlikely and we argue that the optical and FIR flux are different manifestations of the same object. With an R-band magnitude of 15.2, and an IRAS 60$\mum$ flux of $0.51\jy$, APM 08279+5255 is (apparently) easily the most intrinsically luminous object known, with $ L_{Bol}\sim5\times10^{15}L_{\odot}}$. Imaging suggests that gravitational lensing may play a role in amplifying the intrinsic properties of the system. The optical spectrum of the quasar clearly reveals the presence of three potential lensing galaxies, \mg absorption systems at $z=1.18$ and $z=1.81$, and a \ly absorption system at $z=3.07$. We estimate the total amplification of the optical component to be $\approx40$, but, due to the larger scale of the emitting region, would expect the infrared amplification to be significantly less. Even making the conservative assumption that all wavelengths are amplified by a factor 40, APM 08279+5255 still possesses a phenomenal luminosity of $\simgt 10^{14L_{\odot}}$, indicating that it belongs to a small, but significant population of high--redshift, hyperluminous objects with copious infrared emission.

113 citations


Journal ArticleDOI
TL;DR: In this article, the influence of gravitational lensing on these models is considered, and it is shown that while the emission from the central continuum-emitting region may be significantly enhanced, lensing-induced magnification cannot easily reconcile the models with the observations.
Abstract: With an inferred bolometric luminosity of 5?10 -->15 L?, the recently identified z=3.87, broad absorption line quasar APM 08279+5255 is apparently the most luminous object currently known. Since half of its prodigious emission occurs in the infrared, APM 08279+5255 also represents the most extreme example of an ultraluminous infrared galaxy. Here we present new submillimeter observations of this phenomenal object; while indicating that a vast quantity of dust is present, these data prove to be incompatible with the current models of emission and reprocessing mechanisms in ultraluminous systems. The influence of gravitational lensing on these models is considered, and we find that while the emission from the central continuum-emitting region may be significantly enhanced, lensing-induced magnification cannot easily reconcile the models with the observations. We conclude that further modeling, including the effects of any differential magnification, is required to explain the observed emission from APM 08279+5255.

72 citations


Journal ArticleDOI
TL;DR: In this article, the authors present the first direct spectroscopic evidence for this effect, providing a limit on the scale of the continuum and the broad line emission regions at the center of a source quasar (2237+0305).
Abstract: The degree of microlensing induced amplification is dependent upon the size of a source. As quasar spectra consist of the sum of emission from different regions this scale dependent amplification can produce spectral differences between the images of a macrolensed quasar. This paper presents the first direct spectroscopic evidence for this effect, providing a limit on the scale of the continuum and the broad line emission regions at the center of a source quasar (2237+0305). Lack of centroid and profile differences in the emission lines indicate that substructure in the broad emission line region is > 0.05 parsecs.

64 citations


Journal ArticleDOI
TL;DR: In this article, the influence of gravitational lensing upon these models is considered and it is shown that while the emission from the central continuum emitting region may be significantly enhanced, lensing induced magnification cannot easily reconcile the models with observations.
Abstract: With an inferred bolometric luminosity of $5\times10^{15}{\rm \lsun}$, the recently identified z=3.87, broad absorption line quasar APM 08279+5255 is apparently the most luminous object currently known. As half of its prodigious emission occurs in the infrared, APM 08279+5255 also represents the most extreme example of an Ultraluminous Infrared Galaxy. Here, we present new submillimeter observations of this phenomenal object; while indicating that a vast quantity of dust is present, these data prove to be incompatible with current models of emission mechanisms and reprocessing in ultraluminous systems. The influence of gravitational lensing upon these models is considered and we find that while the emission from the central continuum emitting region may be significantly enhanced, lensing induced magnification cannot easily reconcile the models with observations. We conclude that further modeling, including the effects of any differential magnification is required to explain the observed emission from APM 08279+5255.

63 citations


Journal ArticleDOI
TL;DR: In this article, the authors detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies and ascribe the correlations to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies.
Abstract: We detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies. The QSOs are taken from the optically selected LBQS Catalogue, while the galaxies are from the APM Survey. The correlation amplitude is about a few per cent on angular scales of over a degree. It is a function of QSO redshift and apparent magnitude, in a way expected from weak lensing, and inconsistent with QSO–galaxy correlations being caused by physical associations, or uneven obscuration by Galactic dust. The correlations are ascribed to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies. The amplitude of the effect found here is compared to the analytical predictions from the literature, and to the predictions of a phenomenological model, which is based on the observed counts-in-cells distribution of APM galaxies. While the latter agree reasonably well with the analytical predictions (namely those of Dolag &38; Bartelmann and Sanz et al.), both underpredict the observed correlation amplitude on degree angular scales. We consider the possible ways to reconcile these observations with theory, and discuss the implications that these observations have on some aspects of extragalactic astronomy.

36 citations


Posted Content
TL;DR: Perlmutter et al. as discussed by the authors presented evidence for a low-mass density/positive cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae.
Abstract: This presentation reports on first evidence for a low-mass-density/positive-cosmological-constant universe that will expand forever, based on observations of a set of 40 high-redshift supernovae. The experimental strategy, data sets, and analysis techniques are described. More extensive analyses of these results with some additional methods and data are presented in the more recent LBNL report #41801 (Perlmutter et al., 1998; accepted for publication in Ap.J.), astro-ph/9812133 . This Lawrence Berkeley National Laboratory reprint is a reduction of a poster presentation from the Cosmology Display Session #85 on 9 January 1998 at the American Astronomical Society meeting in Washington D.C. It is also available on the World Wide Web at this http URL This work has also been referenced in the literature by the pre-meeting abstract citation: Perlmutter et al., B.A.A.S., volume 29, page 1351 (1997).

8 citations




Journal ArticleDOI
TL;DR: In this paper, a catalogue driven plate solution approach was proposed to extract spectra from high dispersion objective prism plates, making use of the Right Ascension and Declination coordinates for the target objects.
Abstract: We describe a method for the extraction of spectra from high dispersion objective prism plates. Our method is a catalogue driven plate solution approach, making use of the Right Ascension and Declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images, and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in fully-reduced, wavelength justified spectra. We also discuss a method of removing stellar continua using a combination of non-linear filtering algorithms. The method described is used to extract over 12,000 spectra from a set of 92 objective prism plates. These spectra are used in an associated project to develop automated spectral classifiers based on neural networks.

Journal ArticleDOI
TL;DR: In this article, a catalogue driven plate solution approach was proposed to extract spectra from high dispersion objective prism plates, making use of the Right Ascension and Declination coordinates for the target objects.
Abstract: We describe a method for the extraction of spectra from high dispersion objective prism plates. Our method is a catalogue driven plate solution approach, making use of the Right Ascension and Declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images, and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in fully-reduced, wavelength justified spectra. We also discuss a method of removing stellar continua using a combination of non-linear filtering algorithms. The method described is used to extract over 12,000 spectra from a set of 92 objective prism plates. These spectra are used in an associated project to develop automated spectral classifiers based on neural networks.

Journal Article
TL;DR: In this paper, the authors reported observations of the z = 3.87 broad ab-sorption line quasar APM 08279+5255 (Irwin et al. 1998) with the Adaptive Optics Bonnette (AOB) of the Canada-France- Hawaii Telescope.
Abstract: We report observations of the z = 3.87 broad ab- sorption line quasar APM 08279+5255 (Irwin et al. 1998) with the Adaptive Optics Bonnette (AOB) of the Canada-France- Hawaii Telescope. The object is found to be a double source. The separation of the two images is 0. 35 ± 0. '' 02 and the inten- sity ratio Inorth/Isouth = 1.21 ± 0.25 in the H-band. No other image is detected down to H(5�) = 21.3 within 10 '' from the double image. Strong support for the lensing hypothesis comes from the uniformity of the quasar spectrum as a function of spa- tial position in the image obtained with the integral field sp ec- trograph OASIS at CFHT. From the 2D-spectroscopy, narrow- band images are reconstructed over the wavelength range 5600- 6200 ˚ A to search for emission-line objects in a field of 15 '' ×12 '' around the quasar. We find no such object to a limit of 6 ×10 −17 erg cm −2 s −1 . We use the images centered on the deepest ab- sorption lines of the Lyforest to dim the quasar and to in- crease the sensitivity closer to the line of sight. One of the im- ages, centered at 5766.4 ˚ A, exhibits a 3� excess 1.5 '' from the

Journal ArticleDOI
TL;DR: In this article, the authors detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies and ascribe the correlations to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies.
Abstract: We detect a positive angular correlation between bright, high-redshift QSOs and foreground galaxies. The QSOs are taken from the optically selected LBQS Catalogue, while the galaxies are from the APM Survey. The correlation amplitude is about a few percent on angular scales of over a degree. It is a function of QSO redshift and apparent magnitude, in a way expected from weak lensing, and inconsistent with QSO-galaxy correlations being caused by physical associations, or uneven obscuration by Galactic dust. The correlations are ascribed to the weak lensing effect of the foreground dark matter, which is traced by the APM galaxies. The amplitude of the effect found here is compared to the analytical predictions from the literature, and to the predictions of a phenomenological model, which is based on the observed counts-in-cells distribution of APM galaxies. While the latter agree reasonably well with the analytical predictions (namely those of Dolag & Bartelmann 1997, and Sanz et al. 1997), both under-predict the observed correlation amplitude on degree angular scales. We consider the possible ways to reconcile these observations with theory, and discuss the implications these observations have on some aspects of extragalactic astronomy.

01 Jan 1998
TL;DR: In this article, a new space motion of the Galactic globular clus- ter Pal 5 has been obtained on the basis of the proper mo- tion determination from 11 Schmidt plates with a time base line of 39 years.
Abstract: A new space motion of the Galactic globular clus- ter Pal 5 has been obtained on the basis of the proper mo- tion determination from 11 Schmidt plates with a time base- line of 39 years. A field of 1 square degree with nearly 400 galaxies defining the absolute reference frame has been used in the differential astrometry from plate-to-plate solutions. Resid- ual systematic errors after the solutions with 2 6 plate con- stant polynomials have been investigated and removed. Typical proper motion errors of 2 to 3 mas/yr were obtained for in- dividual stars with magnitudes 12

Posted Content
TL;DR: In this paper, a double source was detected in the broad absorption line quasar APM 08279+5255 with the Adaptive Optics Bonnette (AOB) of the Canada-France-Hawaii Telescope.
Abstract: We report observations of the z = 3.87 broad absorption line quasar APM 08279+5255 (Irwin et al. 1998) with the Adaptive Optics Bonnette (AOB) of the Canada-France-Hawaii Telescope. The object is found to be a double source. The separation of the two images is 0.35" +/- 0.02" and the intensity ratio I_{north}/I_{south} = 1.21 +/- 0.25 in the H-band. No other image is detected down to H(5sigma) = 21.3 within 10" from the double image. Strong support for the lensing hypothesis comes from the uniformity of the quasar spectrum as a function of spatial position in the image obtained with the integral field spectrograph OASIS at CFHT. From the 2D-spectroscopy, narrow-band images are reconstructed over the wavelength range 5600-6200A to search for emission-line objects in a field of 15"x12" around the quasar. We find no such object to a limit of 6x10^{-17} erg cm^{-2} s^{-1}. We use the images centered on the deepest absorption lines of the Ly-alpha forest to dim the quasar and to increase the sensitivity closer to the line of sight. One of the images, centered at 5766.4A, exhibits a 3sigma excess 1.5" from the quasar to the north-east.