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Search Results: 1 - 10 of 494704 matches for " Alan F. M. Moorwood "
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Probing the evolution of galaxies using redshifted H-alpha emission
Paul P. van der Werf,Alan F. M. Moorwood,Lin Yan
Physics , 2001,
Abstract: In this paper we review the present status and implications of H-alpha surveys at various redshifts. With the advent of sensitive wide-format near-infrared detectors on large telescopes, deep and extensive H-alpha surveys are now feasible to redshift z~2.5. The cosmic star formation history can therefore be traced out to this redshift using H-alpha alone, avoiding complications arising from the comparison of different tracers at different redshifts. The H-alpha surveys to date confirm the rapid increase in luminosity density from z=0 out to z=1, and show that this increase flattens off at higher redshifts, remaining approximately constant out to at least z~2.2. We also discuss the prospects for determining the masses of high redshift galaxies based on emission lines. A set of high-quality H-alpha rotation curves of samples of disk galaxies at a number of different redshifts would allow a study of the evolution of the Tully-Fisher relation and address fundamental issues in disk galaxy formation. Such a program remains challenging even with present-day large telescopes.
Halpha emitting galaxies and the cosmic star formation rate at z = 2.2
Alan F. M. Moorwood,Paul P. van der Werf,Jean Gabriel Cuby,Tino Oliva
Physics , 2000,
Abstract: About 10 candidate Halpha emitting galaxies at z = 2.2 have been detected in a 2.1 um narrow band imaging survey covering an area of 100 sq. arcmin including the WFPC2 and STIS fields in the Hubble Deep Field South. Six of these have subsequently been confirmed spectroscopically using ISAAC at the ESO VLT. Star formation rates of the individual galaxies derived from their Halpha fluxes are 20-35 Msolar/yr, without any correction for extinction, whereas SFRs derived from their rest frame UV continuum fluxes are up to a factor of 4 lower - consistent with lower extinction to Halpha. Velocity dispersions are typically ~ 100km/s and one galaxy, observed under the most favorable conditions, shows a rotation curve with a terminal velocity ~ 140 km/s at ~ 3kpc radius which is within the range observed for nearby spiral galaxies. These thus appear to be relatively massive systems at high redshift. Comparison with the HST NICMOS grism Halpha survey of Yan et al. (1999) reveals little or no evolution in the Halpha luminosity function between z ~ 1.3 and 2.2. The inferred star formation rate density of 0.12 Msolar/Mpc^3/yr at z = 2.2 is also equal to that at z ~ 3-4.5 derived by Steidel et al.(1999) from extinction corrected UV continuum fluxes.
H-alpha Spectroscopy of Galaxies at z>2: Kinematics and Star Formation
Dawn K. Erb,Alice E. Shapley,Charles C. Steidel,Max Pettini,Kurt L. Adelberger,Matthew P. Hunt,Alan F. M. Moorwood,Jean-Gabriel Cuby
Physics , 2003, DOI: 10.1086/375316
Abstract: We present near-infrared spectroscopy of H-alpha emission lines in a sample of 16 star-forming galaxies at redshifts 2.04e10 M_sun. One-dimensional velocity dispersions for the 16 galaxies range from ~50 to ~260 km/s, and in cases where we have both virial masses implied by the velocity dispersions and dynamical masses derived from the spatially extended emission lines, they are in rough agreement. We compare our kinematic results to similar measurements made at z~3, and find that both the observed rotational velocities and velocity dispersions tend to be larger at z~2 than at z~3. We find a mean SFR_H-alpha of 16 M_sun/yr and an average SFR_H-alpha/SFR_UV ratio of 2.4, without correcting for extinction. We see moderate evidence for an inverse correlation between the UV continuum luminosity and the ratio SFR_H-alpha/SFR_UV, such as might be observed if the UV-faint galaxies suffered greater extinction. We discuss the effects of dust and star formation history on the SFRs, and conclude that extinction is the most likely explanation for the discrepancy between the two SFRs.
Deep Observations of Lyman Break Galaxies
Max Pettini,Charles C. Steidel,Alice E. Shapley,Kurt L. Adelberger,Alan F. M. Moorwood,Jean-Gabriel Cuby,Mark Dickinson,Mauro Giavalisco
Physics , 2001, DOI: 10.1007/10854354_8
Abstract: We summarise the main results of recent work on the Lyman break galaxy population which takes advantage of newly commissioned instrumentation on the VLT and Keck telescopes to push the detection of these objects to new wavelengths and more sensitive limits. We focus in particular on near-infrared observations targeted at detecting emission lines of [O II], [O III], and H-beta and on the first tentative detection of Lyman continuum emission from star forming galaxies at z = 3.
The Rest Frame Optical Spectra of Lyman Break Galaxies: Star Formation, Extinction, Abundances, and Kinematics
Max Pettini,Alice E. Shapley,Charles C. Steidel,Jean-Gabriel Cuby,Mark Dickinson,Alan F. M. Moorwood,Kurt L. Adelberger,Mauro Giavalisco
Physics , 2001, DOI: 10.1086/321403
Abstract: We present the first results of a spectroscopic survey of Lyman break galaxies in the near-infrared aimed at detecting the emission lines of [O II], [O III], and Hbeta from the H II regions of star forming galaxies at z = 3. From observations of 19 objects with the Keck and VLT telescopes, we reach the following main conclusions. Contrary to expectations, the star formation rates deduced from the Hbeta luminosity are on average no larger than those implied by the stellar continuum at 1500 A; presumably any differential extinction between rest-frame optical and UV is small compared with the relative uncertainties in the calibrations of these two star formation tracers. For the galaxies in our sample, the abundance of O can only be determined to within one order of magnitude. Even so, it seems well established that LBGs are the most metal-enriched structures at z = 3, apart from QSOs, with abundances greater than about 1/10 solar. They are also significantly overluminous for their metallicities; this is probably an indication that their mass-to-light ratios are small compared with present-day galaxies. At face value their velocity dispersions, sigma = 50 - 115 km/s imply virial masses of about 10^{10} solar masses within half-light radii of 2.5 kpc. However, we are unable to establish if the widths of the emission lines do reflect the motions of the H II regions within the gravitational potential of the galaxies, even though in two cases we see hints of rotation curves. All 19 LBGs observed show evidence for galactic-scale superwinds; such outflows are important for regulating star formation, distributing metals over large volumes, and allowing Lyman continuum photons to escape and ionize the IGM.
ISO-SWS spectroscopy of IC443 and the origin of the IRAS 12 and 25 micron emission from radiative supernova remnants
E. Oliva,D. Lutz,S. Drapatz,A. F. M. Moorwood
Physics , 1998,
Abstract: ISO-SWS spectral observations of the supernova remnant IC443 are presented. Like other radiative SNRs, this object is characterized by prominent line-emitting filaments and relatively strong IRAS 12 and 25 micron emission which is commonly interpreted as thermal radiation from very small grains stochastically heated by collisions with the hot plasma behind the shock front. This interpretation is challenged by the data presented in this Letter which indicate that most of the 12 and 25 micron IRAS flux is accounted for by ionized line emission (mainly [NeII] and [FeII]). This result also seems to hold for other radiative SNRs. We also discuss the possible contribution of H_2 lines to the IRAS 12 micron flux from the southern rim of IC443 and briefly analyze the element abundances derived from the observed ionic lines.
Metal abundances and excitation of extranuclear clouds in the Circinus galaxy -- A new method for deriving abundances of AGN narrow line clouds
E. Oliva,A. Marconi,A. F. M. Moorwood
Physics , 1998,
Abstract: Spectra of extranuclear clouds within the ionization cone of Circinus galaxy are presented and modelled assuming photoionization by the Seyfert 2 nucleus but no preconceived assumption concerning the spectral shape of the ionizing AGN radiation or the gas density distribution. The most important result is that, regardless of the assumed AGN spectral shape or density distribution, the metal abundances are remarkably well (+/-0.2 dex) constrained by the data. Oxygen and neon are found to be a factor of 5 below solar, while nitrogen is solar. The large N/O overabundance is in agreement with the chemical enrichment expected from the old (circum)nuclear starburst. Similar studies of extranuclear clouds in other objects could therefore provide a powerful tool to determine metallicities and trace past starburst activity in AGNs. Other implications such as the role of shock excitation, which is effectively excluded, and the intrinsic shape of the AGN ionizing continuum, which is poorly constrained by the data, are also discussed.
Starbursts in active galaxy nuclei: observational constraints from IR stellar absorption lines
E. Oliva,L. Origlia,R. Maiolino,A. F. M. Moorwood
Physics , 1999,
Abstract: High quality infrared spectra of active galaxies including the stellar absorption features of Si at 1.59 um, CO(6,3) at 1.62 um, and CO(2,0) at 2.29 um are used to measure the stellar mass to light ratio at 1.65 um (M_H/L) and investigate the occurrence circum--nuclear starbursts. We find that old and powerful starbursts are relatively common in obscured AGNs (5 objects out of 13) while absent in genuine Seyfert 1's (0 objects out of 8). The data are also used to derive the non-stellar continuum which is very red and compatible with emission from warm (~1000 K) dust even in bare Sy1's, thus indicating that the near IR nuclear continuum is reprocessed radiation. Hot dust (~800 K) emission is also detected in a few obscured AGNs, including the Seyfert 2 prototype NGC1068. The observed non-stellar flux is too high to be accounted for by scattered light and therefore indicates that the material obscuring the AGN must have a quite small (<~1 pc) projected size.
Infrared spectroscopy of young supernova remnants heavily interacting with the interstellar medium
E. Oliva,A. F. M. Moorwood,S. Drapatz,D. Lutz,E. Sturm
Physics , 1999,
Abstract: ISO spectral observations of the supernova remnant RCW103 are presented. This object is the prototype of relatively young remnants with fast shocks interacting with dense interstellar medium. The spectrum is dominated by prominent lines of [NeII], [SiII], [FeII] and other low excitation species which provide, for the first time, a simple and reliable estimate of the gas abundances of refractory (Si, Fe, Ni) and non-refractory (Ne, P, S, Cl, Ar) species. Apart from nickel, all the derived abundances are close to solar, confirming that the shock has destroyed all dust grains. Like the optical nickel lines, [NiII] 6.64micron yields Ni abundances a factor ~10 solar which we propose results from a large underestimation of the computed Ni+ collision strengths. The observed intensities and velocity widths of ionic lines are compatible with emission from the post-shock region alone with only a very small (if any) contribution from the photoionized precursor. This result does not agree with shock models which predict that the precursor should emit powerful line emission, especially from highly ionized species. The possible consequence of this on the modelling of Seyfert spectra is briefly discussed.
An ISO survey of PAH features in Ultraluminous Infrared Galaxies
D. Lutz,R. Genzel,D. Rigopoulou,H. W. W. Spoon,D. Tran,A. F. M. Moorwood
Physics , 1998,
Abstract: We have obtained ISOPHOT-S low resolution mid-infrared spectra of a sample of 60 Ultraluminous Infrared Galaxies (ULIRGs). We use the strength of the `PAH' mid-infrared features as a discriminator between starburst and AGN activity, and to probe for evolutionary effects. We focus on the fact that observed ratios of PAH features in ULIRGs differ slightly from those in lower luminosity starbursts. We suggest that such PAH ratio changes relate to the conditions in the interstellar medium in these galaxies, and in particular to extinction.
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