The Fornax Cluster Spectroscopic Survey: a sample of confirmed cluster dwarfs

The Fornax Cluster Spectroscopic Survey (FCSS) project utilizes the Two-degree Field (2dF) multi-object spectrograph on the Anglo-Australian Telescope (AAT). Its aim is to obtain spectra for a complete sample of all 14 000 objects with 16 5 less than or equal to b(j) less than or equal to 19 7 irrespective of their morphology in a 12 deg(2) area centred on the Fornax cluster. A sample of 24 Fornax cluster members has been identified from the first 2dF field (3.1 deg(2) in area) to be completed. This is the first complete sample of cluster objects of known distance with well-defined selection limits. Nineteen of the galaxies (with -15.8 < M-B < 12.7) appear to be conventional dwarf elliptical (dE) or dwarf S0 (dS0) galaxies. The other five objects (with -13.6 < M-B < 11.3) are those galaxies which were described recently by Drinkwater et al. and labelled 'ultracompact dwarfs' (UCDs). A major result is that the conventional dwarfs all have scale sizes alpha greater than or similar to 3 arcsec (similar or equal to300 pc). This apparent minimum scale size implies an equivalent minimum luminosity for a dwarf of a given surface brightness. This produces a limit on their distribution in the magnitude-surface brightness plane, such that we do not observe dEs with high surface brightnesses but faint absolute magnitudes. Above this observed minimum scale size of 3 arcsec, the dEs and dS0s fill the whole area of the magnitude-surface brightness plane sampled by our selection limits. The observed correlation between magnitude and surface brightness noted by several recent studies of brighter galaxies is not seen with our fainter cluster sample. A comparison of our results with the Fornax Cluster Catalog (FCC) of Ferguson illustrates that attempts to determine cluster membership solely on the basis of observed morphology can produce significant errors. The FCC identified 17 of the 24 FCSS sample (i.e. 71 per cent) as being 'cluster' members, in particular missing all five of the UCDs. The FCC also suffers from significant contamination: within the FCSS's field and selection limits, 23 per cent of those objects described as cluster members by the FCC are shown by the FCSS to be background objects.

The HIPASS catalogue - II. Completeness reliability and parameter accuracy

The H I Parkes All Sky Survey (HIPASS) is a blind extragalactic H I 21-cm emission-line survey covering the whole southern sky from declination -90degrees to +25degrees. The HIPASS catalogue (HICAT), containing 4315 H I-selected galaxies from the region south of declination +2degrees, is presented in Meyer et al. (Paper I). This paper describes in detail the completeness and reliability of HICAT, which are calculated from the recovery rate of synthetic sources and follow-up observations, respectively. HICAT is found to be 99 per cent complete at a peak flux of 84 mJy and an integrated flux of 9.4 Jy km. s(-1). The overall reliability is 95 per cent, but rises to 99 per cent for sources with peak fluxes >58 mJy or integrated flux >8.2 Jy km s(-1). Expressions are derived for the uncertainties on the most important HICAT parameters: peak flux, integrated flux, velocity width and recessional velocity. The errors on HICAT parameters are dominated by the noise in the HIPASS data, rather than by the parametrization procedure.

A class of compact dwarf galaxies from disruptive processes in galaxy clusters

Dwarf galaxies have attracted increased attention in recent years, because of their susceptibility to galaxy transformation processes within rich galaxy clusters. Direct evidence for these processes, however, has been difficult to obtain, with a small number of diffuse light trails and intra-cluster stars, being the only signs of galaxy disruption. Furthermore, our current knowledge of dwarf galaxy populations may be very incomplete, because traditional galaxy surveys are insensitive to extremely diffuse or compact galaxies. Aware of these concerns, we recently undertook an all-object survey of the Fornax galaxy cluster. This revealed a new population of compact members, overlooked in previous conventional surveys. Here we demonstrate that these 'ultra-compact' dwarf galaxies are structurally and dynamically distinct from both globular star clusters and known types of dwarf galaxy, and thus represent a new class of dwarf galaxy. Our data are consistent with the interpretation that these are the remnant nuclei of disrupted dwarf galaxies, making them an easily observed tracer of galaxy disruption.

Scalable Visualization of Galaxies, Oceans, and Brains

One of the challenges in scientific visualization is to generate software libraries suitable for the large-scale data emerging from tera-scale simulations and instruments. We describe the efforts currently under way at SDSC and NPACI to address these challenges. The scope of the SDSC project spans data handling, graphics, visualization, and scientific application domains. Components of the research focus on the following areas: intelligent data storage, layout and handling, using an associated “Floor-Plan” (meta data); performance optimization on parallel architectures; extension of SDSC’s scalable, parallel, direct volume renderer to allow perspective viewing; and interactive rendering of fractional images (“imagelets”), which facilitates the examination of large datasets. These concepts are coordinated within a data-visualization pipeline, which operates on component data blocks sized to fit within the available computing resources. A key feature of the scheme is that the meta data, which tag the data blocks, can be propagated and applied consistently. This is possible at the disk level, in distributing the computations across parallel processors; in “imagelet” composition; and in feature tagging. The work reflects the emerging challenges and opportunities presented by the ongoing progress in high-performance computing (HPC) and the deployment of the data, computational, and visualization Grids.

Protein fold recognition without Boltzmann statistics or explicit physical basis

We present a fast method for finding optimal parameters for a low-resolution (threading) force field intended to distinguish correct from incorrect folds for a given protein sequence. In contrast to other methods, the parameterization uses information from >10(7) misfolded structures as well as a set of native sequence-structure pairs. In addition to testing the resulting force field's performance on the protein sequence threading problem, results are shown that characterize the number of parameters necessary for effective structure recognition.

High surface brightness dwarf galaxies in the Fornax cluster

We describe a search for compact dwarf galaxies in the Fornax cluster using the FLAIR spectrograph on the UK Schmidt Telescope. We measured radial velocities of 453 compact galaxies brighter than B-T approximate to 17.3 and found seven new compact dwarf cluster members that were not classified in previous surveys as members of the cluster. These are amongst the most compact, high surface brightness dwarf galaxies known. The inclusion of these galaxies in the cluster does not change the total luminosity function significantly, but they are important because of their extreme nature; one in particular appears to be a dwarf spiral. Three of the new dwarfs have strong emission lines and we identify them as blue compact dwarfs (BCDs), doubling the number of confirmed BCDs in the cluster. We also determined that none of the compact dwarf elliptical (M32-like) candidates is in the cluster, down to an absolute magnitude M-B = -13.2. We have investigated the claim of Irwin et al. that there is no strong relation between surface brightness and magnitude for the cluster members and find some support for this for the brighter galaxies (B-T < 17.3), but fainter galaxies still need to be measured.

Critical values for unit root and cointegration test statistics - the use of response surface equations

This note considers the value of surface response equations which can be used to calculate critical values for a range of unit root and cointegration tests popular in applied economic research.

The fornax spectroscopic survey: the number of unresolved compact galaxies

We describe a sample of 13 bright (18.5 < B-J < 20.1), compact galaxies at low redshift (0.05 < z < 0.21) behind the Fornax Cluster. These galaxies are unresolved on UK Schmidt sky survey plates, and so they would be missing from most galaxy catalogs compiled from this material. The objects were found during initial observations of The Fornax Spectroscopic Survey. This project is using the Two-degree Field spectrograph on the Anglo-Australian Telescope to obtain spectra for a complete sample of all 14,000 objects, stellar and nonstellar, with 16.5 < B-J < 19.7, in a 12 deg(2) area centered on the Fornax Cluster of galaxies. The surface density of compact galaxies with magnitudes 16.5 < B-J < 19.7 is 7 +/- 3 deg(-2), representing 2.8% +/- 1.6% of all local (z < 0.2) galaxies to this limit. There are 12 +/- 3 deg(-2) with 16.5 < B-J < 20.2. They are luminous (-21.5 < M-B < -18.0, for H-o = 50 km s(-1) Mpc(-1)), and most have strong emission lines (H alpha equivalent widths of 40-200 Angstrom) and small sizes typical of luminous H II galaxies and compact narrow emission line galaxies. Four out of 13 have red colors and early-type spectra, and so they are unlikely to have been detected in any previous surveys.

The Fornax spectroscopic survey I. Survey strategy and preliminary results on the redshift distribution of a complete sample of stars and galaxies

The Fornax Spectroscopic Survey will use the Two degree Field spectrograph (2dF) of the Angle-Australian Telescope to obtain spectra for a complete sample of all 14000 objects with 16.5 less than or equal to b(j) less than or equal to 19.7 in a 12 square degree area centred on the Fornax Cluster. The aims of this project include the study of dwarf galaxies in the cluster (both known low surface brightness objects and putative normal surface brightness dwarfs) and a comparison sample of background field galaxies. We will also measure quasars and other active galaxies, any previously unrecognised compact galaxies and a large sample of Galactic stars. 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 first describe the design of the survey. Our targets are selected from UK Schmidt Telescope sky survey plates digitised by the Automated Plate Measuring (APM) facility. We then describe the photometric and astrometric calibration of these data and show that the APM astrometry is accurate enough for use with the 2dF. We also describe a general approach to object identification using cross-correlations which allows us to identify and classify both stellar and galaxy spectra. 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(-1). They show a velocity dispersion of 380 +/- 50 km s(-1). 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.

Accelerating seismic energy release and evolution of event time and size statistics: Results from two heterogeneous cellular automaton models

The evolution of event time and size statistics in two heterogeneous cellular automaton models of earthquake behavior are studied and compared to the evolution of these quantities during observed periods of accelerating seismic energy release Drier to large earthquakes. The two automata have different nearest neighbor laws, one of which produces self-organized critical (SOC) behavior (PSD model) and the other which produces quasi-periodic large events (crack model). In the PSD model periods of accelerating energy release before large events are rare. In the crack model, many large events are preceded by periods of accelerating energy release. When compared to randomized event catalogs, accelerating energy release before large events occurs more often than random in the crack model but less often than random in the PSD model; it is easier to tell the crack and PSD model results apart from each other than to tell either model apart from a random catalog. The evolution of event sizes during the accelerating energy release sequences in all models is compared to that of observed sequences. The accelerating energy release sequences in the crack model consist of an increase in the rate of events of all sizes, consistent with observations from a small number of natural cases, however inconsistent with a larger number of cases in which there is an increase in the rate of only moderate-sized events. On average, no increase in the rate of events of any size is seen before large events in the PSD model.

Compact stellar systems in the Fornax Cluster: Super-massive star clusters or extremely compact dwarf galaxies?

We describe a population of compact objects in the centre of the Fornax Cluster which were discovered as part of our 2dF Fornax Spectroscopic Survey. These objects have spectra typical of old stellar systems, but are unresolved on photographic sky survey plates. They have absolute magnitudes - 13 < M-B

Galaxy threshing and the formation of ultracompact dwarf galaxies

Recent spectroscopic and morphological observational studies of galaxies around NGC 1399 in the Fornax Cluster have discovered several ultracompact dwarf galaxies with intrinsic sizes of similar to 100 pc and absolute B-band magnitudes ranging from -13 to -11 mag. In order to elucidate the origin of these enigmatic objects, we perform numerical simulations on the dynamical evolution of nucleated dwarf galaxies orbiting NGC 1399 and suffering from its strong tidal gravitational field. Adopting a plausible scaling relation for dwarf galaxies, we find that the outer stellar components of a nucleated dwarf are totally removed. This is due to them being tidally stripped over the course of several passages past the central region of NGC 1399. The nucleus, however, manages to survive. We also find that the size and luminosity of the remnant are similar to those observed for ultracompact dwarf galaxies, if the simulated precursor nucleated dwarf has a mass of similar to 10(8) M.. These results suggest that ultracompact dwarf galaxies could have previously been more luminous dwarf spheroidal or elliptical galaxies with rather compact nuclei.

The neutral hydrogen content of Fornax cluster galaxies

We present a new set of deep H I observations of member galaxies of the Fornax cluster. We detected 35 cluster galaxies in H I. The resulting sample, the most comprehensive to date, is used to investigate the distribution of neutral hydrogen in the cluster galaxies. We compare the H I content of the detected cluster galaxies with that of field galaxies by measuring H I mass-to-light ratios and the H I deficiency parameter of Solanes et al. (1996). The mean H I mass-to-light ratio of the cluster galaxies is 0.68 +/- 0.15, significantly lower than for a sample of H I-selected field galaxies (1.15 +/- 0.10), although not as low as in the Virgo cluster (0.45 +/- 0.03). In addition, the H I content of two cluster galaxies (NGC1316C and NGC1326B) appears to have been affected by interactions. The mean H I deficiency for the cluster is 0.38 +/- 0.09 (for galaxy types T = 1-6), significantly greater than for the field sample (0.05 +/- 0.03). Both these tests show that Fornax cluster galaxies are H I-deficient compared to field galaxies. The kinematics of the cluster galaxies suggests that the H I deficiency may be caused by ram-pressure stripping of galaxies on orbits that pass close to the cluster core. We also derive the most complete B-band Tully-Fisher relation of inclined spiral galaxies in Fornax. A subcluster in the South-West of the main cluster contributes considerably to the scatter. The scatter for galaxies in the main cluster alone is 0.50 mag, which is slightly larger than the intrinsic scatter of 0.4 mag. We use the Tully-Fisher relation to derive a distance modulus of Fornax relative to the Virgo cluster of -0.38 +/- 0.14 mag. The galaxies in the subcluster are (1.0 +/- 0.5) mag brighter than the galaxies of the main cluster, indicating that they are situated in the foreground. With their mean velocity 95 km s(-1) higher than that of the main cluster we conclude that the subcluster is falling into the main Fornax cluster.

The evolution and star formation of dwarf galaxies in the Fornax Cluster

We present the results of a spectroscopic survey of 675 bright (16.5 < b(J) < 18) galaxies in a 6 degrees field centred on the Fornax cluster with the FLAIR-II spectrograph on the UK Schmidt Telescope. Three galaxy samples were observed: compact galaxies to search for new blue compact dwarfs, candidate M 32-like compact dwarf ellipticals, and a subset of the brightest known cluster members in order to study the cluster dynamics. We measured redshifts for 516 galaxies, of which 108 were members of the Fornax Cluster. Defining dwarf galaxies to be those with b(J) greater than or equal to 15 (M-B greater than or equal to - 16.5), there are a total of 62 dwarf cluster galaxies in our sample. Nine of these are new cluster members previously misidentified as background galaxies. The cluster dynamics show that the dwarf galaxies are still falling into the cluster whereas the giants are virialized. We classified the observed galaxies as late-type if we detected H alpha emission at an equivalent width greater than 1 Angstrom. The spectra were obtained through fixed apertures, so they reflect activity in the galaxy cores, but this does not significantly bias the classifications of the compact dwarfs in our sample. The new classifications reveal a higher rate of star formation among the dwarf galaxies than suggested by morphological classification: 35 per cent have significant H alpha emission indicative of star formations but only 19 per cent were morphologically classified as late-types. The star-forming dwarf galaxies span the full range of physical sizes and we find no evidence in our data for a distinct class of star-forming blue compact dwarf (BCD) galaxy. The distribution of scale sizes is consistent with evolutionary processes which transform late-type dwarfs to early-type dwarfs. The fraction of dwarfs with active star formation drops rapidly towards the cluster centre: this is the usual density-morphology relation confirmed here for dwarf galaxies. The star-forming dwarfs are concentrated in the outer regions of the cluster, the most extreme in an infalling subcluster. We estimate gas depletion time-scales for five dwarfs with detected Hi emission: these are long (of order 10(10) yr), indicating that an active gas removal process must be involved if they are transformed into gas-poor dwarfs as they fall further into the cluster. Finally, in agreement with our previous results, we find no compact dwarf elliptical (M 32-like) galaxies in the Fornax Cluster.