Alice C. Quillen

The radial velocity experiment (RAVE): First data release

We present the first data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, and surface gravity) of up to one million stars using the Six Degree Field multiobject spectrograph on the 1.2 m UK Schmidt Telescope of the Anglo-Australian Observatory. The RAVE program started in 2003, obtaining medium-resolution spectra (median R 1⁄4 7500) in the Ca-triplet region (8410–8795 8) for southern hemisphere stars drawn from the Tycho-2 and SuperCOSMOS catalogs, in the magnitude range 9 < I < 12. The first data release is described in this paper and contains radial velocities for 24,748 individual stars (25,274 measurements when including reobservations). Those data were obtained on 67 nights between 2003 April 11 and 2004 April 3. The total sky coverage within this data release is 4760 deg. The average signal-to-noise ratio of the observed spectra is 29.5, and 80% of the radial velocities have uncertainties better than 3.4 km s . Combining internal errors and zero-point errors, the mode is found to be 2 km s . Repeat observations are used to assess the stability of our radial velocity solution, resulting in a variance of 2.8 km s . We demonstrate that the radial velocities derived for the first data set do not show any systematic trend with color or signal-to-noise ratio. The RAVE radial velocities are complemented in the data release with proper motions from Starnet 2.0, Tycho-2, and SuperCOSMOS, in addition to photometric data from the major optical and infrared catalogs (Tycho-2, USNO-B, DENIS, and the TwoMicron All Sky Survey). The data release can be accessed via the RAVE Web site.

The Frequency of Barred Spiral Galaxies in the Near-Infrared

We have determined the fraction of barred galaxies in the H-band for a statistically well-defined sample of 186 spirals drawn from the Ohio State University Bright Spiral Galaxy Survey. We find 56% of our sample to be strongly barred in the H band while another 16% is weakly barred. Only 27% of our sample is unbarred in the near-infrared. The RC3 and the Carnegie Atlas of Galaxies both classify only about 30% of our sample as strongly barred. Thus strong bars are nearly twice as prevalent in the near-infrared as in the optical. The frequency of genuine optically hidden bars is significant but lower than many claims in the literature: 40% of the galaxies in our sample that are classified as unbarred in the RC3 show evidence for a bar in the H band while the Carnegie Atlas lists this fraction as 66%. Our data reveal no significant trend in bar fraction as a function of morphology in either the optical or H band. Optical surveys of high-redshift galaxies may be strongly biased against finding bars, as bars are increasingly difficult to detect at bluer rest wavelengths.

MULTIWAVELENGTH MONITORING OF THE DWARF SEYFERT 1 GALAXY NGC 4395. I. A REVERBERATION-BASED MEASUREMENT OF THE BLACK HOLE MASS

A reverberation-mapping program on NGC 4395, the least luminous known Seyfert 1 galaxy, undertaken with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope yields a measurement of the mass of the central black hole MBH = (3.6 ± 1.1) × 105 M☉. The observations consist of two visits of five orbits each, in 2004 April and July. During each of these visits, the UV continuum varied by at least 10% (rms), and only C IV λ1549 showed corresponding variations large enough to reliably determine the emission-line lag, which was measured to be of order 1 hr for both visits. The size of the C IV-emitting region is about a factor of 3 smaller than expected if the slope of the broad-line region radius-luminosity relationship is identical to that for the Hβ emission line. NGC 4395 is underluminous even for its small black hole mass; the Eddington ratio of ~1.2 × 10-3 is lower than that of any other active galactic nucleus for which a black hole mass measurement has been made by emission-line reverberation.

An Infrared Survey of Brightest Cluster Galaxies. II. Why are Some Brightest Cluster Galaxies Forming Stars

Quillen et al. presented an imaging survey with the Spitzer Space Telescope of 62 brightest cluster galaxies with optical line emission located in the cores of X-ray-luminous clusters. They found that at least half of these sources have signs of excess IR emission. Here we discuss the nature of the IR emission and its implications for cool core clusters. The strength of the mid-IR excess emission correlates with the luminosity of the optical emission lines. Excluding the four systems dominated by an AGN, the excess mid-IR emission in the remaining brightest cluster galaxies is likely related to star formation. The mass of molecular gas (estimated from CO observations) is correlated with the IR luminosity as found for normal star-forming galaxies. The gas depletion timescale is about 1 Gyr. The physical extent of the IR excess is consistent with that of the optical emission-line nebulae. This supports the hypothesis that star formation occurs in molecular gas associated with the emission-line nebulae and with evidence that the emission-line nebulae are mainly powered by ongoing star formation. We find a correlation between mass deposition rates () estimated from the X-ray emission and the star formation rates estimated from the IR luminosity. The star formation rates are 1/10 to 1/100 of the mass deposition rates, suggesting that the reheating of the intracluster medium is generally very effective in reducing the amount of mass cooling from the hot phase but not eliminating it completely.

The Radial Velocity Experiment (RAVE)

We present the second data release of the Radial Velocity Experiment (RAVE), an ambitious spectroscopic survey to measure radial velocities and stellar atmosphere parameters (temperature, metallicity, surface gravity, and rotational velocity) of up to one million stars using the 6dF multi-object spectrograph on the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO). The RAVE program started in 2003, obtaining medium resolution specUniversity of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia Astrophysikalisches Institut Potsdam, Potsdam, Germany Observatoire de Strasbourg, Strasbourg, France INAF, Osservatorio Astronomico di Padova, Sede di Asiago, Italy RSAA, Australian national University, Canberra, Australia Anglo Australian Observatory, Sydney, Australia Johns Hopkins University, Baltimore MD, USA Macquarie University, Sydney, Australia Institute of Astronomy, University of Cambridge, UK e2v Centre for Electronic Imaging, School of Engineering and Design, Brunel University, Uxbridge, UK Astronomisches Rechen-Institut, Center for Astronomy of the University of Heidelberg, Heidelberg, Germany Kapteyn Astronomical Institute, University of Groningen, Groningen, the Netherlands University of Victoria, Victoria, Canada Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Australia Rudolf Pierls Center for Theoretical Physics, University of Oxford, UK Institute of Astronomy, School of Physics, University of Sydney, NSW 2006, Australia Sterrewacht Leiden, University of Leiden, Leiden, the Netherlands University of Leicester, Leicester, UK MPI fuer extraterrestrische Physik, Garching, Germany University of Central Lancashire, Preston, UK University of Rochester, Rochester NY, USA University of Edinburgh, Edinburgh, UK

Predictions for a planet just inside Fomalhaut's eccentric ring

We propose that the eccentricity and sharpness of the edge of Fomalhaut’s disk are due to a planet just interior to the ring edge. The collision timescale consistent with the disk opacity is long enough that spiral density waves cannot be driven near the planet. The ring edge is likely to be located at the boundary of a chaotic zone in the corotation region of the planet. We find that this zone can open a gap in a particle disk as long as the collision timescale exceeds the removal or ejection timescale in the zone. We use the slope measured from the ring edge surface brightness profile to place an upper limit on the planet mass. The removal timescale in the chaotic zone is used to estimate a lower limit. The ring edge has eccentricity caused by secular perturbations from the planet. These arguments imply that the planet has a mass between that of Neptune and that of Saturn, a semi-major axis of approximately 119 AU and longitude of periastron and eccentricity, 0.1, the same as that of the ring edge.

Radial migration does little for Galactic disc thickening

Non-axisymmetric components, such as spirals and central bars, play a major role in shaping galactic discs. An important aspect of the disc secular evolution driven by these perturbers is the radial migration of stars. It has been suggested recently that migration can populate a thick-disc component from inner-disc stars with high vertical energies. Since this has never been demonstrated in simulations, we study in detail the effect of radial migration on the disc velocity dispersion and disc thickness, by separating simulated stars into migrators and non-migrators. We apply this method to three isolated barred Tree-SPH N-body galaxies with strong radial migration. Contrary to expectations, we find that as stellar samples migrate, on the average, their velocity dispersion change (by as much as 50%) in such a way as to approximately match the non-migrating population at the radius at which they arrive. We show that, in fact, migrators suppress heating in parts of the disc. To confirm the validity of our findings, we also apply our technique to three cosmological re-simulations, which use a completely different simulation scheme and, remarkably, find very similar results. We believe the inability of migration to thicken discs is a fundamental property of internal disc evolution, irrespective of the migration mechanism at work. We explain this with the approximate conservation of the (average) vertical and radial actions rather than the energy. This “action mixing” can be used to constrain the migration rate in the Milky Way: estimates of the average vertical action in observations for different populations of stars should reveal flattening with radius for older groups of stars.

Near-Infrared and Optical Morphology of Spiral Galaxies

We announce the initial release of data from the Ohio State University (OSU) Bright Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications from Sa through Scd appear about one T type earlier in the H band than in the B band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B- and H-band images for a set of 17 galaxies chosen as type examples and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength.

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

We investigate the evolution of galactic disks in N-body Tree-SPH simulations. We find that disks, initially truncated a t three scalelengths, can triple their radial extent, solely driven by se cular evolution. At the same time, the initial radial metall icity gradients are flattened and even reversed in the outer disks. Both Type I (si ngle exponential) and Type II (down-bending) observed disk surfacebrightness profiles can be explained by our findings. We show t hat profiles with breaks beyond the bar’s outer Lindblad reso nance, at present only explained as the effect of star-formation threshold, can occur even if no star fo rmation is considered. We explain these results with the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns, such as central bars and spiral waves of different multiplicity. We find that even for stars ending up on co ld orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. We show that the bars in all of our simulations are the most effective drivers of radial migration through their corotatio n resonance, throughout the 3 Gyr of evolution studied. Focussing on one of our models, we find evidence for non-linear coupling among m = 1, 2, 3 and 4 density waves, where m is the pattern multiplicity. In this way the waves involved c onspire to carry the energy and angular momentum extracted by the first mode from the inner parts of the disk muc h farther out than a single mode could. We suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disk density profiles, provided spiral s are present at such large distances. We also consider the effect of gas inflow and show that when in-plane smooth gas accretion of∼ 5 M⊙/yr is included, the outer disks become more unstable, leading to a strong increase in the stellar velocity dispersion. This, i n turn, causes the formation of a Type III (up-bending) profil e in the old stellar population. We propose that observations of Type III surface brightness profiles, combined with an up-turn in the stella r velocity dispersions beyond the disk break, could be a signature of ongoing gas-accretion. The results of this study suggest that disk outskirts comprised of stars migrated from the inner disk would have relatively large radial velocity dispersions (> 30 km/s at 6 scale-lengths for Milky Way-size systems), and significant thickness when seen edge-on.

Sagittarius A* Companion S0-2: A Probe of Very High Mass Star Formation

The star S0-2, which is orbiting Sgr A* with a 15 yr period, almost certainly did not form in situ. We propose that it was injected into this close orbit by the tidal disruption of a massive-star binary, whose primary was more massive than S0-2 and at least 60 M☉. From numerical integrations we find that 1%-2% of incoming binaries with closest approach equal to 130 AU leave the secondary in an orbit with eccentricity within 0.01 of that of S0-2. If additional stars are found orbiting Sgr A* with relatively short periods, they could be used to probe the formation of massive stars in the Galactocentric region, even though the massive stars themselves have long since perished.