Preflight SL-1/SL-3 Skylab VHF ranging coverage (nominal TPI). Antenna and propagation studies for spacecraft systems, task E-531

A preflight assessment of the Skylab VHF ranging coverage for the rendezvous portion of the nominal SL-1/SL-3 mission is reported, assuming a 27 July 1973 SL-3 launch. Data are based on a nominal attitude trajectory, which has the Saturn workshop in a solar inertial attitude throughout the rendezvous; the CSM terminal phase initiation maneuver is nominal. An addendum to this report is being prepared, which considers the effects of early and late TPI maneuvers. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 600 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function

Antenna and propagation studies for spacecraft systems: Addendum to preflight SL-1/SL-3 Skylab VHF ranging coverage (early and late TPI)

A preflight assessment is presented of the expected Skylab VHF ranging coverage for the rendezvous portion of the SL-1/SL-3 mission, assuming a 28 July 1973 launch date, for the alternative trajectory cases characterized by either an early TPI or a late TPI. In this assessment early TPI and late TPI are used to indicate a TPI maneuver occurring 10 minutes prior to or after the nominally scheduled TPI maneuver, respectively. The Saturn workshop (SWS) maintains a solar inertial (SI) attitude throughout rendezvous for both trajectory cases. The results summarized concern VHF ranging function performance during that period most likely to be affected by off-nominal TPI conditions, i.e., NSR (5:56 g.e.t.) to station keeping. Curves are presented which show the variation in received power levels on both spacecraft-to-spacecraft links from about 100 n.mi. range to CSM and SWS station keeping. Appropriate threshold levels are shown on these received power curves to indicate zero circuit margins for the ranging function

Intense Star-formation and Feedback at High Redshift: Spatially-resolved Properties of the z=2.6 Submillimeter Galaxy SMMJ14011+0252

We present a detailed analysis of the spatially-resolved properties of the lensed submillimeter galaxy SMMJ14011+0252 at z=2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multi-wavelength data sets. The broad characteristics of SMMJ14011+0252 are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star-formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift ``maximal starbursts'', while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for "self-regulated" star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within about 20 kpc, M_dyn \sim 1\times 10^{11} M_sun. The relative metallicity of J2 is 0.4 dex lower than in J1n/s, suggesting different star formation histories. SED fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z=0.25 interloper. When removing J1c, the stellar continuum and H-alpha line emission appear well aligned spatially in two individual components J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ULIRGs, which are often merger-driven maximal starbursts, and suggests that the intrinsic mechanisms of star-formation and related feedback are similar to low-redshift strongly star-forming systems.Comment: Some of the figures changed from b/w to colo

Calcium isotopic composition of high-latitude proxy carrier Neogloboquadrina pachyderma (sin.)

International audienceThe accurate reconstruction of sea surface temperature (SST) history in climate-sensitive regions (e.g. tropical and polar oceans) became a challenging task in palaeoceanographic research. However, biogenic shell carbonate SST proxies successfully developed for tropical regions often fail in cool water environments. Their major regional shortcomings and the cryptic diversity now found within the major high latitude proxy carrier Neogloboquadrina pachyderma (sin.) highlight an urgent need to develop complementary SST proxies for these cool water regions. Here we incorporate the genetic component into a calibration study of a new SST proxy for the high latitudes. We found that the calcium isotopic composition (?44/40Ca) of calcite from genotyped net catches and core-top samples of the planktonic foraminifera Neogloboquadrina pachyderma (sin) is strongly related to temperature and unaffected by genetic variations. The temperature sensitivity has been found to be 0.17 (±0.04)? per 1°C highlighting its potential for downcore applications in open marine cool-water environments. Our results further indicate that however in extreme polar environments, below a critical threshold temperature of 2.0 (±0.5)°C and salinity of 33.0 (±0.5)? a prominent shift in biomineralization affect the Ca isotope composition of N. pachyderma (sin.) becoming insensitive to temperature. These findings highlight the need of systematic calibration studies to unravel the influencing factors on Ca isotope fractionation and to validate the proxies' applicability

Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56

Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we have studied the spatially-resolved dynamics in the z=3.2 strongly lensed galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy (seen at a spatial resolution of about 200 pc in the source plane), whereas the fainter ``arc'' is a more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z=3 Lyman break galaxy. The overall shape of the position-velocity diagram resembles the ``rotation curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected velocities rise rapidly to 75 km/s within the core. This implies a dynamical mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this system the equivalent of the mass of a present-day L* bulge at the same radius was already in place by z>=3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with large-scale clustering studies of Lyman break galaxies. The baryonic collapse fraction is low compared to actively star-forming ``BX'' and low-redshift galaxies around z=2, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for ``inside-out'' galaxy formation models.Comment: Accepted for publication in the Astrophysical Journa

Flares and variability from Sagittarius A*: five nights of simultaneous multi-wavelength observations

Aims. We report on simultaneous observations and modeling of mid-infrared (MIR), near-infrared (NIR), and submillimeter (submm) emission of the source Sgr A* associated with the supermassive black hole at the center of our Galaxy. Our goal was to monitor the activity of Sgr A* at different wavelengths in order to constrain the emitting processes and gain insight into the nature of the close environment of Sgr A*. Methods. We used the MIR instrument VISIR in the BURST imaging mode, the adaptive optics assisted NIR camera NACO, and the sub-mm antenna APEX to monitor Sgr A* over several nights in July 2007. Results. The observations reveal remarkable variability in the NIR and sub-mm during the five nights of observation. No source was detected in the MIR, but we derived the lowest upper limit for a flare at 8.59 microns (22.4 mJy with A_8.59mu = 1.6+/- 0.5). This observational constraint makes us discard the observed NIR emission as coming from a thermal component emitting at sub-mm frequencies. Moreover, comparison of the sub-mm and NIR variability shows that the highest NIR fluxes (flares) are coincident with the lowest sub-mm levels of our five-night campaign involving three flares. We explain this behavior by a loss of electrons to the system and/or by a decrease in the magnetic field, as might conceivably occur in scenarios involving fast outflows and/or magnetic reconnection.Comment: 10 pages, 7 figures, published in A&

SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution

We present 0.5" resolution near-IR integral field spectroscopy of the Ha line emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT. The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of the larger systems are consistent with orbital motions. Four galaxies are well described by rotating disks with clumpy morphologies and we extract rotation curves out to radii > ~10kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun within r_1/2. On average, the dynamical masses are consistent with photometric stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. The specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases implies a ratio of v_c to local velocity dispersion of order 2-4 and accordingly a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue that if our BM/BX galaxies were initially gas rich, their clumpy disks will subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr. [ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 17 pages, 5 color figure

Evidence for a Long-Standing Top-Heavy IMF in the Central Parsec of the Galaxy

We classify 329 late-type giants within 1 parsec of Sgr A*, using the adaptive optics integral field spectrometer SINFONI on the VLT. These observations represent the deepest spectroscopic data set so far obtained for the Galactic Center, reaching a 50% completeness threshold at the approximate magnitude of the helium-burning red clump (Ks ~ 15.5 mag.). Combining our spectroscopic results with NaCo H and Ks photometry, we construct an observed Hertzsprung-Russell diagram, which we quantitatively compare to theoretical distributions of various star formation histories of the inner Galaxy, using a chi-squared analysis. Our best-fit model corresponds to continuous star formation over the last 12 Gyr with a top-heavy initial mass function (IMF). The similarity of this IMF to the IMF observed for the most recent epoch of star formation is intriguing and perhaps suggests a connection between recent star formation and the stars formed throughout the history of the Galactic Center.Comment: 18 pages, 10 figures, Accepted to ApJ: 15 July 200

SINFONI in the Galactic Center: young stars and IR flares in the central light month

We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the central 30 light days of the Galactic Center [...]. To a limiting magnitude of K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7 arcsec from the central black hole have spectral properties of B0-B9, main sequence stars. [...] all brighter early type stars have normal rotation velocities, similar to solar neighborhood stars. We [...] derive improved 3d stellar orbits for six of these S-stars in the central 0.5 arcsec. Their orientations in space appear random. Their orbital planes are not co-aligned with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We can thus exclude [...] that the S-stars as a group inhabit the inner regions of these disks. They also cannot have been located/formed in these disks [...]. [...] we conclude that the S-stars were most likely brought into the central light month by strong individual scattering events. The updated estimate of distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32 kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum spectral energy distributions of these flares are fit by a featureless, red power law [...]. The observed spectral slope is in good agreement with synchrotron models in which the infrared emission comes from [...] radiative inefficient accretion flow in the central R~10 Rs region.Comment: 50 pages, 10 figures, 2 tables, submitted to ApJ, February 6th, 2005, abstract abridge

Star formation in the central 0.5 pc of the Milky Way

The supermassive black hole candidate at the Galactic Center is surrounded by a parsec-scale star cluster, which contains a number of early type stars. The presence of such stars has been called a "paradox of youth" as star formation in the immediate vicinity of a supermassive black hole seemed difficult, as well as the transport of stars from far out in a massive-star lifetime. I will recall 30 years of technological developments which led to the current understanding of the nuclear cluster stellar population. The number of early type stars known at present is sufficient to access the 3D structure of this population and its dynamics, which in turn allows discriminating between the various possible origins proposed along the years.Comment: 8 pages, invited review for the conference "The Universe under the Microscope" (AHAR 2008), to be published in Journal of Physics: Conference Series by Institute of Physics Publishin