Showing papers by "Joss Bland-Hawthorn published in 2002"

The New Galaxy: Signatures of Its Formation

Abstract: ▪ Abstract The formation and evolution of galaxies is one of the great outstanding problems of astrophysics. Within the broad context of hierachical structure formation, we have only a crude picture of how galaxies like our own came into existence. A detailed physical picture where individual stellar populations can be associated with (tagged to) elements of the protocloud is far beyond our current understanding. Important clues have begun to emerge from both the Galaxy (near-field cosmology) and the high redshift universe (far-field cosmology). Here we focus on the fossil evidence provided by the Galaxy. Detailed studies of the Galaxy lie at the core of understanding the complex processes involved in baryon dissipation. This is a necessary first step toward achieving a successful theory of galaxy formation.

The 2dF Galaxy Redshift Survey: The environmental dependence of galaxy star formation rates near clusters

Abstract: We have measured the equivalent width of the Hα emission line for 11 006 galaxies brighter than M_b-=-−19 (Ω_Λ = 0.7, Ω_m = 0.3, H_0 = 70 km s^(−1) Mpc^(−1)) at 0.05 < z < 0.1 in the 2dF Galaxy Redshift Survey (2dFGRS), in the fields of 17 known galaxy clusters. The limited redshift range ensures that our results are insensitive to aperture bias, and to residuals from night sky emission lines. We use these measurements to trace μ*, the star formation rate normalized to L*, as a function of distance from the cluster centre, and local projected galaxy density. We find that the distribution of μ* steadily skews toward larger values with increasing distance from the cluster centre, converging to the field distribution at distances greater than ∼3 times the virial radius. A correlation between star formation rate and local projected density is also found, which is independent of cluster velocity dispersion and disappears at projected densities below ∼1 galaxy Mpc^(−2) (brighter than M_b = −19). This characteristic scale corresponds approximately to the mean density at the cluster virial radius. The same correlation holds for galaxies more than two virial radii from the cluster centre. We conclude that environmental influences on galaxy properties are not restricted to cluster cores, but are effective in all groups where the density exceeds this critical value. The present-day abundance of such systems, and the strong evolution of this abundance, makes it likely that hierarchical growth of structure plays a significant role in decreasing the global average star formation rate. Finally, the low star formation rates well beyond the virialized cluster rule out severe physical processes, such as ram pressure stripping of disc gas, as being completely responsible for the variations in galaxy properties with environment.

The 2dF Galaxy Redshift Survey: correlation functions, peculiar velocities and the matter density of the Universe

Abstract: We present a detailed analysis of the two-point correlation function, from the 2dF Galaxy Redshift Survey (2dFGRS). We estimate the redshift-space correlation function, xi(s), from which we measure the redshift-space clustering length, s_0=6.82+/-0.28 Mpc/h. We also estimate the projected correlation function, Xi(sigma), and the real-space correlation function, xi(r), which can be fit by a power-law, with r_0=5.05+/-0.26Mpc/h, gamma_r=1.67+/-0.03. For r>20Mpc/h, xi drops below a power-law as is expected in the popular LCDM model. The ratio of amplitudes of the real and redshift-space correlation functions on scales of 8-30Mpc/h gives an estimate of the redshift-space distortion parameter beta. The quadrupole moment of xi on scales 30-40Mpc/h provides another estimate of beta. We also estimate the distribution function of pairwise peculiar velocities, f(v), including rigorously the effect of infall velocities, and find that it is well fit by an exponential. The accuracy of our xi measurement is sufficient to constrain a model, which simultaneously fits the shape and amplitude of xi(r) and the two redshift-space distortion effects parameterized by beta and velocity dispersion, a. We find beta=0.49+/-0.09 and a=506+/-52km/s, though the best fit values are strongly correlated. We measure the variation of the peculiar velocity dispersion with projected separation, a(sigma), and find that the shape is consistent with models and simulations. Using the constraints on bias from recent estimates, and taking account of redshift evolution, we conclude that beta(L=L*,z=0)=0.47+/-0.08, and that the present day matter density of the Universe is 0.3, consistent with other 2dFGRS estimates and independent analyses.

The 2dF Galaxy Redshift Survey: The bias of galaxies and the density of the Universe

Abstract: We compute the bispectrum of the 2dF Galaxy Redshift Survey (2dFGRS) and use it to measure the bias parameter of the galaxies. This parameter quantifies the strength of clustering of the galaxies relative to the mass in the Universe. By analysing 80 x 10 6 triangle configurations in the wavenumber range 0.1 < k < 0.5 h Mpc - 1 (i.e. on scales roughly between 5 and 30 h - 1 Mpc) we find that the linear bias parameter is consistent with unity: b 1 = 1.04 ′ 0.11, and the quadratic (non-linear) bias is consistent with zero: b 2 = -0.054 ′ 0.08. Thus, at least on large scales, optically selected galaxies do indeed trace the underlying mass distribution. The bias parameter can be combined with the 2dFGRS measurement of the redshift distortion parameter β ≃ Ω 0 . 6 m /b 1 , to yield Ωm = 0.27 ′0.06 for the matter density of the Universe, a result that is determined entirely from this survey, independent of other data sets. Our measurement of the matter density of the Universe should be interpreted as Ω m at the effective redshift of the survey (z = 0.17).

The 2dF Galaxy Redshift Survey: the dependence of galaxy clustering on luminosity and spectral type

Abstract: We investigate the dependence of galaxy clustering on luminosity and spectral type using the 2dF Galaxy Redshift Survey (2dFGRS). Spectral types are assigned using the principal-component analysis of Madgwick et al. We divide the sample into two broad spectral classes: galaxies with strong emission lines ('late types') and more quiescent galaxies ('early types'). We measure the clustering in real space, free from any distortion of the clustering pattern owing to peculiar velocities, for a series of volume-limited samples. The projected correlation functions of both spectral types are well described by a power law for transverse separations in the range 2<(σ/h-1 Mpc)<15, with a marginally steeper slope for early types than late types. Both early and late types have approximately the same dependence of clustering strength on luminosity, with the clustering amplitude increasing by a factor of 2.5 between L* and 4L*. At all luminosities, however, the correlation function amplitude for the early types is 50 per cent higher than that of the late types. These results support the view that luminosity, and not type, is the dominant factor in determining how the clustering strength of the whole galaxy population varies with luminosity.

The 2dF Galaxy Redshift Survey: The bJ-band galaxy luminosity function and survey selection function

Abstract: We use more than 110 500 galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) to estimate the bJ-band galaxy luminosity function at redshift z = 0, taking account of evolution, the distri- bution of magnitude measurement errors and small corrections for incompleteness in the galaxy catalogue. Throughout the interval −16.5 > MbJ − 5 log10 h > −22, the luminosity function is accurately described by a Schechter function with MJ − 5 log10 h =− 19.66 ± 0.07, α = −1.21 ± 0.03 and � � = (1.61 ± 0.08) × 10 −2 h 3 Mpc −3 , giving an integrated luminosity den- sity of ρL = (1.82 ± 0.17) × 10 8 h LMpc −3 (assuming an � 0 = 0.3, 0 = 0.7 cosmology). The quoted errors have contributions from the accuracy of the photometric zero-point, from large-scale structure in the galaxy distribution and, importantly, from the uncertainty in the ap- propriate evolutionary corrections. Our luminosity function is in excellent agreement with, but has much smaller statistical errors than, an estimate from the Sloan Digital Sky Survey (SDSS) data when the SDSS data are accurately translated to the bJ band and the luminosity functions are normalized in the same way. We use the luminosity function, along with maps describing the redshift completeness of the current 2dFGRS catalogue, and its weak dependence on ap- parent magnitude, to define a complete description of the 2dFGRS selection function. Details and tests of the calibration of the 2dFGRS photometric parent catalogue are also presented.

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type

Abstract: We calculate the optical bJ luminosity function of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, �, which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter � identifies the average emission and absorption line strength in the galaxy rest-frame spectrum and hence is a useful indicator of the present star formation. We use a total of 75,000 galaxies in our calculations, chosen from a sample of high signal-tonoise ratio, low redshift galaxies observed before January 2001. We find that there is a systematic steepening of the faint end slope (�) as one moves from passive (� = 0.54) to active (� = 1.50) star-forming galaxies, and that there is also a corresponding faintening of the rest-frame characteristic magnitude M � 5log10(h) (from 19.6 to 19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies (MbJ 5log10(h) fainter than 16.0), perhaps suggesting the presence of a significant dwarf population. The luminosity functions presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent K-corrections and investigate possible fibreaperture biases.

Parameter constraints for flat cosmologies from cosmic microwave background and 2dFGRS power spectra

Abstract: We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega(m), which arises mainly from preserving the location of the peaks in the angular power spectrum. This 'horizon-angle degeneracy' is considered in some detail and is shown to follow the simple relation Omega(m) h(3.4) = constant. Adding the 2dFGRS power spectrum constrains Omega(m) h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant of h = 0.665 +/- 0.047, the matter density Omega(m) = 0.313 +/- 0.055, and the physical cold dark matter and baryon densities Omega(c)h(2) = 0.115 +/- 0.009, Omega(b)h(2) = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set an upper limit to the tensor-to-scalar ratio of r < 0.7 at a 95 per cent confidence level. We then show how these data can be used to constrain the equation of state of the vacuum, and find w < -0.52 at 95 per cent confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from http://www.roe.ac.uk/similar towjp/.

Parameter constraints for flat cosmologies from CMB and 2dFGRS power spectra

Abstract: We constrain flat cosmological models with a joint likelihood analysis of a new compilation of data from the cosmic microwave background (CMB) and from the 2dF Galaxy Redshift Survey (2dFGRS). Fitting the CMB alone yields a known degeneracy between the Hubble constant h and the matter density Omega_m, which arises mainly from preserving the location of the peaks in the angular power spectrum. This `horizon-angle degeneracy' is considered in some detail and shown to follow a simple relation Omega_m h^{3.4} = constant. Adding the 2dFGRS power spectrum constrains Omega_m h and breaks the degeneracy. If tensor anisotropies are assumed to be negligible, we obtain values for the Hubble constant h=0.665 +/- 0.047, the matter density Omega_m=0.313 +/- 0.055, and the physical CDM and baryon densities Omega_c h^2 = 0.115 +/- 0.009, Omega_b h^2 = 0.022 +/- 0.002 (standard rms errors). Including a possible tensor component causes very little change to these figures; we set a upper limit to the tensor-to-scalar ratio of r<0.7 at 95% confidence. We then show how these data can be used to constrain the equation of state of the vacuum, and find w<-0.52 at 95% confidence. The preferred cosmological model is thus very well specified, and we discuss the precision with which future CMB data can be predicted, given the model assumptions. The 2dFGRS power-spectrum data and covariance matrix, and the CMB data compilation used here, are available from this http URL

Evidence for a non-zero Λ and a low matter density from a combined analysis of the 2dF Galaxy Redshift Survey and cosmic microwave background anisotropies

Abstract: We perform a joint likelihood analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGRS) and the cosmic microwave background (CMB) anisotropies under the assumptions that the initial fluctuations were adiabatic, Gaussian and well described by power laws with scalar and tensor indices of n(s) and n(t). On its own, the 2dFGRS sets Light limits on the parameter combination Omega(m)h, but relatively weak limits on the fraction of the cosmic matter density in baryons Omega(b)/Omega(m)- (Here h is Hubble's constant H-0 in units of 100 km s(-1) Mpc(-1). The cosmic densities in baryons, cold dark matter and vacuum energy are denoted by Omega(b), Omega(c) and Omega(Lambda), respectively. The total matter density is Omega(m) = Omega(b) + Omega(c) and the curvature is fixed by Omega(k) = 1 - Omega(m) - Omega(Lambda).) The CMB anisotropy data alone set poor constraints on the cosmological constant and Hubble constant because of a 'geometrical degeneracy' among parameters. Furthermore, if tensor modes are allowed, the CMB data allow a wide range of values for the physical densities in baryons; and cold dark matter (omega(b) = Omegabh(2) and omega(c) = Omega(c)h(2)). Combining the CMB and 2dFGRS data sets helps to break both the geometrical and tensor mode degeneracies. The values of the parameters derived here are consistent with the predictions of the simplest models of inflation, with the baryon density derived from primordial nucleosynthesis and with direct measurements of the Hubble parameter. In particular, we find strong evidence for a positive cosmological constant with a +/-2sigma, range of 0.65 < U(U) < 0.85, independently of constraints on Omega(Lambda) derived from Type Ia supernovae.

Radio sources in the 2dF Galaxy Redshift Survey - II. Local radio luminosity functions for AGN and star-forming galaxies at 1.4 GHz

Abstract: We have cross–matched the 1.4GHz NRAO VLA Sky Survey (NVSS) with the first 210 fields observed in the 2dF Galaxy Redshift Survey (2dFGRS), covering an effective area of 325 square degrees (about 20% of the final 2dFGRS area). This yields a set of optical spectra of 912 candidate NVSS counterparts, of which we identify 757 as genuine radio IDs — the largest and most homogeneous set of radio–sourcespectra ever obtained. The 2dFGRS radio sources span the redshift range z = 0.005 to 0.438, and are a mixture of active galaxies (60%) and star–forming galaxies (40%). About 25% of the 2dFGRS radio sources are spatially resolved by NVSS, and the sample includes three giant radio galaxies with projected linear size greater than 1Mpc. The high quality of the 2dF spectra means we can usually distinguish unambiguously between AGN and star–forming galaxies. We have made a new determination of the local radio luminosity function at 1.4GHz for both active and star–forming galaxies, and derive a local star–formation density of 0.022±0.004 M⊙ yr −1 Mpc −3 (H0=50kms −1 Mpc −1 ).

The 2dF Galaxy Redshift Survey: The Amplitudes of fluctuations in the 2dFGRS and the CMB, and implications for galaxy biasing

Abstract: We compare the amplitudes of fluctuations probed by the 2dF Galaxy Redshift Survey (2dFGRS) and by the latest measurements of the cosmic microwave background (CMB) anisotropies. By combining the 2dFGRS and CMB data, we find the linear-theory rms mass fluctuations in 8 h (-1) Mpc spheres to be sigma (8m) =0.73+/-0.05 (after marginalization over the matter density parameter Omega(m) and three other free parameters). This normalization is lower than the COBE normalization and previous estimates from cluster abundance, but it is in agreement with some revised cluster abundance determinations. We also estimate the scale-independent bias parameter of present-epoch L (s) =1.9L * APM-selected galaxies to be b (L (s) ,z =0)=1.10+/-0.08 on comoving scales of 0.02

The 2dF Galaxy Redshift Survey: the luminosity function of cluster galaxies

Abstract: We have determined the composite luminosity function (LF) for galaxies in 60 clusters from the 2dF Galaxy Redshift Survey. The LF spans the range $-22.5

New Upper Limit on the Total Neutrino Mass from the 2 Degree Field Galaxy Redshift Survey

Abstract: We constrain f(nu) identical with Omega(nu)/Omega(m), the fractional contribution of neutrinos to the total mass density in the Universe, by comparing the power spectrum of fluctuations derived from the 2 Degree Field Galaxy Redshift Survey with power spectra for models with four components: baryons, cold dark matter, massive neutrinos, and a cosmological constant. Adding constraints from independent cosmological probes we find f(nu)<0.13 (at 95% confidence) for a prior of 0.1

Tightly Correlated X-Ray/Hα-emitting Filaments in the Superbubble and Large-Scale Superwind of NGC 3079

Abstract: Using Chandra and HST, we show that X-ray and Hα filaments that form the 1.3 kpc diameter superbubble of NGC 3079 have strikingly similar patterns at ~08 resolution. This tight optical line/X-ray match seems to arise from cool disk gas that has been driven by the wind, with X-rays being emitted from upstream, standoff bow shocks or by conductive cooling at the cloud/wind interfaces. We find that the soft X-ray plasma has thermal and kinetic energies ETH ~ 2 × 1056η ergs and EKE ~ 5 × 1054η ergs, where ηX is the filling factor of the X-ray gas and may be small; these are comparable to the energies of the optical line-emitting gas if ηX is large. Hydrodynamical simulations reproduce the observations well using a disk-mass loaded superwind. X-rays are also seen from the base of the radio counterbubble which is obscured optically by the galaxy disk and from the nucleus (whose spectrum shows the Fe Kα line at 6 keV as well as gas absorbed by a moderate neutral hydrogen column). The superbubble is surrounded by a fainter conical halo of X-ray emission that fills the area delineated by high-angle, Hα-emitting filaments, supporting our previous assertion that these filaments form the contact discontinuity/shock between galaxy gas and shocked wind. This X-ray emission is not significantly edge brightened, indicating a partially filled volume of warm gas within the shocked wind, not a shell of conductively heated gas. About 40'' (3 kpc) above the galaxy disk, an X-ray arc may partially close above the bubble, but the northeast quadrant remains open at the surface brightness attained by Chandra, consistent with the notion that the superwind reaches into at least the galaxy halo.

The 2dF Galaxy Redshift Survey: a targeted study of catalogued clusters of galaxies

Abstract: We have carried out a study of known clusters within the 2dF Galaxy Redshift Survey (2dFGRS) observed areas and have identified 431 Abell, 173 APM and 343 EDCC clusters. Precise redshifts, velocity dispersions and new centroids have been measured for the majority of these objects, and this information is used to study the completeness of these catalogues, the level of contamination from foreground and background structures along the cluster's line of sight, the space density of the clusters as a function of redshift, and their velocity dispersion distributions. We find that the Abell and EDCC catalogues are contaminated at the level of about 10 per cent, whereas the APM catalogue suffers only 5 per cent contamination. If we use the original catalogue centroids, the level of contamination rises to approximately 15 per cent for the Abell and EDCC catalogues, showing that the presence of foreground and background groups may alter the richness of clusters in these catalogues. There is a deficiency of clusters at z ∼ 0.05 that may correspond to a large underdensity in the Southern hemisphere. From the cumulative distribution of velocity dispersions for these clusters, we derive a space density of σ > 1000 km s - 1 clusters of 3.6 × 10 - 6 h 3 Mpc - 3 . This result is used to constrain models for structure formation; our data favour low-density cosmologies, subject to the usual assumptions concerning the shape and normalization of the power spectrum.

The 2dF Galaxy Redshift Survey: Constraints on cosmic star formation history from the cosmic spectrum

Abstract: We present the first results on the history of star formation in the universe based on the ‘‘ cosmic spectrum,’’ in particular the volume-averaged, luminosity-weighted, stellar absorption-line spectrum of presentday galaxies from the 2dF Galaxy Redshift Survey. This method is novel in that, unlike previous studies, it is not an estimator based on total luminosity density. The cosmic spectrum is fitted with models of population synthesis, tracing the history of star formation before the epoch of the observed galaxies, using a method we have developed that decouples continuum and spectral line variations and is robust against spectrophotometric uncertainties. The cosmic spectrum can only be fitted with models incorporating chemical evolution, and it indicates that there was a peak in the star formation rate (SFR) in the past of at least 3 times the current value and that the increase back to z = 1, assuming it scales as (1 + z) � , has a strong upper limit of � 1: e.g., if � > 2, then the SFR for 1 1. Our results are consistent with the best-fit results from compilations of cosmic SFR estimates based on UV luminosity density, which yield 1.8 <�< 2.9 and � 1.0 <�< 0.7, and are also consistent with estimates of stars based on the K-band luminosity density. Subject headings: cosmology: miscellaneous — cosmology: observations — galaxies: evolution — stars: formation On-line material: color figures

Detection and measurement from narrow‐band tunable filter scans

Abstract: The past 5 years have seen a rapid rise in the use of tunable filters in many diverse fields of astronomy, through Taurus Tunable Filter (TTF) instruments at the Anglo-Australian and William Herschel Telescopes. Over this time we have continually refined aspects of operation and developed a collection of special techniques to handle the data produced by these novel imaging instruments. In this paper, we review calibration procedures and summarize the theoretical basis for Fabry–Perot photometry that is central to effective tunable imaging. Specific mention is made of object detection and classification from deep narrow-band surveys containing several hundred objects per field. We also discuss methods for recognizing and dealing with artefacts (scattered light, atmospheric effects, etc.), which can seriously compromise the photometric integrity of the data if left untreated. Attention is paid to the different families of ghost reflections encountered, and the strategies used to minimize their presence. In our closing remarks, future directions for tunable imaging are outlined and contrasted with the Fabry–Perot technology employed in the current generation of tunable imagers.

The 2dF Galaxy Redshift Survey: the population of nearby radio galaxies at the 1-mJy level

Abstract: We use redshift determinations and spectral analysis of galaxies in the 2dF Galaxy Redshift Survey to study the properties of local radio sources with S greater than or equal to1 mJy. 557 objects (hereafter called the spectroscopic sample) drawn from the FIRST survey, corresponding to 2.3 per cent of the total radio sample, are found in the 2dFGRS catalogue within the area 9(h) 48(m) less than or similar toRA(2000)less than or similar to14(h) 32(m) and -277less than or similar toDec.(2000)less than or similar to225, down to a magnitude limit b (J) =19.45. The excellent quality of 2dF spectra allows us to divide these sources into classes, according to their optical spectra.Absorption-line systems make up 63 per cent of the spectroscopic sample. These may or may not show emission lines due to AGN activity, and correspond to 'classical' radio galaxies belonging mainly to the FRI class. They are characterized by relatively high radio-to-optical ratios, red colours, and high radio luminosities (10(21) less than or similar toP (1.4 GHz) /W Hz(-1) sr(-1) less than or similar to10(24) ). Actively star-forming galaxies contribute about 32 per cent of the sample. These objects are mainly found at low redshifts (z less than or similar to0.1) and show low radio-to-optical ratios, blue colours and low radio luminosities. We also found 18 Seyfert 2 galaxies (3 per cent) and four Seyfert 1s (1 per cent).Analysis of the local radio luminosity function (LF) shows that radio galaxies are well described by models that assume pure luminosity evolution, at least down to radio powers P (1.4 GHz) less than or similar to10(20.5) W Hz(-1) sr(-1). Late-type galaxies, whose relative contribution to the radio LF is found to be lower than was predicted by previous works, present an LF which is comparable with the IRAS galaxy LF. This class of sources therefore plausibly constitutes the radio counterpart of the dusty spirals and starbursts that dominate the counts at 60 mum.

Shocks, illumination cones and intrinsic gas structures in the extreme radio galaxy 3C 265

Abstract: We present deep, narrow-band and continuum images of the powerful high-redshift radio galaxy 3C 265 (z=0.811), taken with the TAURUS Tunable Filter on the William Herschel Telescope, together with detailed long-slit spectroscopic observations along the axis defined by the UV/optical emission elongation. The deep images reveal the existence of cones in the ionization structure of 3C 265 within ∼7 arcsec (58 kpc) of the nucleus, where the emission-line structure is not observed to be closely aligned with the radio axis. This indicates that anisotropic illumination from the central active nucleus dominates on a small scale. In contrast, at larger distances (≳10 arcsec; 80 kpc) from the nucleus, low-ionization emission gas is closely aligned with the radio axis, suggesting that jet–cloud interactions may become the dominant mechanism in the line-emitting gas on a larger scale. Moreover, the presence of a high-velocity cloud at 2.5 arcsec from the nucleus, close to the radio axis, indicates that even close to the nucleus (∼20 kpc) jet-induced shocks have an important kinematic effect. However, spectroscopic analysis of this region reveals that the ionization state of the high-velocity gas is similar to or higher than that of the surroundings, which is opposite to what we would expect for a cloud that has been compressed and accelerated by jet-induced shocks. Our images show that, while on a large scale the low-ionization emission-line structures are aligned with the radio axis, on a smaller scale, where AGN-photoionization dominates, the highest surface-brightness structure is aligned with the closest companion galaxy (misaligned with the radio axis). This suggest that much of the emission-line structure reflects the intrinsic gas distribution, rather than the ionization pattern imprinted by the radio jets or by illumination from the central AGN. Overall, our results underline the need for a variety of mechanisms to explain the properties of the extended emission-line gas in the haloes of radio galaxies.

The Large-scale Bipolar Wind in the Galactic Center

Abstract: During a 9-month campaign (1996--1997), the Midcourse Space Experiment (MSX) satellite mapped the Galactic Plane at mid-infrared wavelengths (4.3--21.3um). Here we report evidence for a spectacular limb- brightened, bipolar structure at the Galactic Center extending more than a degree (170 pc at 8.0 kpc) on either side of the plane. The 8.3um emission shows a tight correlation with the 3, 6 and 11 cm continuum structure over the same scales. Dense gas and dust are being entrained in a large-scale bipolar wind powered by a central starburst. The inferred energy injection at the source is ~10^54/kappa erg for which \kappa is the covering fraction of the dusty shell (kappa <= 0.1). There is observational evidence for a galactic wind on much larger scales, presumably from the same central source which produced the bipolar shell seen by MSX. Sofue has argued that the North Polar Spur -- a thermal x-ray/radio loop which extends from the Galactic Plane to b = +80 deg -- was powered by a nuclear explosion (1-30 x 10^55 erg) roughly 15 Myr ago. We demonstrate that an open-ended bipolar wind (~10^55 erg), when viewed in near-field projection, provides the most natural explanation for the observed loop structure. The ROSAT 1.5 keV diffuse x-ray map over the inner 45 deg provides compelling evidence for this interpretation. Since the faint bipolar emission would be very difficult to detect beyond the Galaxy, the phenomenon of large-scale galactic winds may be far more common than has been observed to date.

Laser Telemetry from Space

Abstract: Space missions currently on the drawing boards are expected to gather data at rates exceeding the transmission capabilities of today's telemetry systems by many orders of magnitude. Even on current missions, onboard data compression techniques are being implemented to compensate for lack of transmission speed. But while data compression can minimize the loss of data, it is no substitute for transmitting all of the data through a faster communications link. The transmission problem will soon reach crisis proportions and will affect astronomical, Earth resources, geophysical, meteorological, planetary and other space science missions. To overcome this communications bottleneck, the authors advocate the implementation of telemetry systems based on near-infrared laser transmission techniques. The fiber-optics communications industry has developed most of the basic components required for signal transmission in this wavelength band, which should make such a system affordable on scales relevant to the cost of anticipated space science missions.

Galaxies: The Third Dimension -- Conference Summary

Abstract: ``Galaxies: the Third Dimension'' continues a tradition which started in Marseilles 1994 with the ``Tridimensional Optical Spectroscopic Methods in Astrophysics'' meeting, followed by ``Imaging the Universe in Three Dimensions'' at Walnut Creek in 1999. Since then, there have been developments both in instrumentation and in the way astronomy is conducted, and these need to be seen against a broad canvas. As we emphasize below, one of the main reasons for satisfaction is the trend towards talks focused on scientific results rather than on `yet another 3D spectroscopic technology.'

New results from a survey of galactic outflows in nearby active galactic nuclei

Abstract: RESUMEN Se presentan resultados recientes de un levantamiento multifrecuencia de ujos espacialmente resueltos en galaxias activas cercanas. Se combinan datos espectrosc opicos opticos de Fabry-Perot y de rendija larga con im agenes del VLA (siglas en ingl es de \Very Large Array") y de ROSAT (siglas en alem an de \Roentgen Satellit"), cuando disponibles, para estudiar las componentes gaseosas tibias, relativistas y calientes involucradas en el ujo. Se pone enfasis en objetos que contienen ujos de angulo amplios y escala gal actica, pero tambi en que muestran evidencia de fen omenos tipo jet colimado a longitudes de ondas de radio y opticas (p.ej., Circinus, NGC 4388, y con menor intensidad NGC 2992). Nuestros resultados se comparan con las predicciones publicadas de modelos de vientos t ermicos impulsados por jets.

The New Galaxy: Signatures of its Formation

Abstract: The formation and evolution of galaxies is one of the great outstanding problems of astrophysics. Within the broad context of hierachical structure formation, we have only a crude picture of how galaxies like our own came into existence. A detailed physical picture where individual stellar populations can be associated with (tagged to) elements of the protocloud is far beyond our current understanding. Important clues have begun to emerge from both the Galaxy (near-field cosmology) and the high redshift universe (far-field cosmology). Here we focus on the fossil evidence provided by the Galaxy. Detailed studies of the Galaxy lie at the core of understanding the complex processes involved in baryon dissipation. This is a necessary first step towards achieving a successful theory of galaxy formation.

The Gaiasphere and the limits of knowledge

Abstract: Joss Bland-HawthornAnglo-Australian Observatory, 167 Vimiera Road, Eastwood, NSW2122, Australia; jbh@aao.gov.auAbstract. At the heart of a successful theory of galaxy formation mustbe a detailed physical understanding of the dissipational processes whichform spiral galaxies. To what extent can we unravel the events thatproduced the Galaxy as we see it today? Could some of the residualinhomogeneities from prehistory have escaped the dissipative process atan early stage? To make a comprehensive inventory of surviving inhomo-geneities would require a vast catalog of stellar properties that is presentlyout of reach. The Gaia space astrometry mission, set to launch at theend of the decade, will acquire detailed phase space coordinates for aboutone billion stars, within a sphere of diameter 20 kpc – the Gaiasphere.Here we look forward to a time when all stars within the Gaiasphere havecomplete chemical abundance measurements (including α, s and r pro-cess elements). Even with such a vast increase in information, there mayexist fundamental − but unproven − limits to unravelling the observedcomplexity.1. IntroductionEddington once remarked that ‘the contemplation in natural science of a widerdomain than the actual leads to a far better understanding of the actual.’ Ourintuition is that any dynamical phase early on in the history of the Galaxy whichis dominated by relaxation or dissipation probably removes more informationthan it retains. This remains largely true for controlled experiments withinterrestrial laboratories for the reason that it is exceedingly difficult to track fluidparticles, for example, in order to unravel the process under study. However,at least in principle, the situation may be more tractable in astrophysics inthat individual stars carry information about the birth site at the time of theirformation. Nature offers us a vast untapped reservoir of information in thedetailed chemical abundances stored within stellar atmospheres.The fossil evidence of galaxy formation is not restricted to chemical abun-dances alone. In our review, “The New Galaxy – Signatures of its Formation,”we stress the importance of new observations across a wide range of parameterspace (Freeman & Bland-Hawthorn 2002). We are coming into a new era ofgalactic investigation, in which one can study the fossil remnants of the early1