Showing papers by "European Southern Observatory published in 2008"

Improved Cosmological Constraints from New, Old, and Combined Supernova Data Sets

Abstract: We present a new compilation of Type Ia supernovae (SNe Ia), a new data set of low-redshift nearby-Hubble-flow SNe, and new analysis procedures to work with these heterogeneous compilations This "Union" compilation of 414 SNe Ia, which reduces to 307 SNe after selection cuts, includes the recent large samples of SNe Ia from the Supernova Legacy Survey and ESSENCE Survey, the older data sets, as well as the recently extended data set of distant supernovae observed with the Hubble Space Telescope (HST) A single, consistent, and blind analysis procedure is used for all the various SN Ia subsamples, and a new procedure is implemented that consistently weights the heterogeneous data sets and rejects outliers We present the latest results from this Union compilation and discuss the cosmological constraints from this new compilation and its combination with other cosmological measurements (CMB and BAO) The constraint we obtain from supernovae on the dark energy density is ΩΛ = 0713+ 0027−0029(stat)+ 0036−0039(sys) , for a flat, ΛCDM universe Assuming a constant equation of state parameter, w, the combined constraints from SNe, BAO, and CMB give w = − 0969+ 0059−0063(stat)+ 0063−0066(sys) While our results are consistent with a cosmological constant, we obtain only relatively weak constraints on a w that varies with redshift In particular, the current SN data do not yet significantly constrain w at z > 1 With the addition of our new nearby Hubble-flow SNe Ia, these resulting cosmological constraints are currently the tightest available

Confirmation of the Remarkable Compactness of Massive Quiescent Galaxies at z ~ 2.3: Early-Type Galaxies Did not Form in a Simple Monolithic Collapse* **

Abstract: Using deep near-infrared spectroscopy, Kriek et al. found that ∼45% of massive galaxies at have evolved z ∼ 2.3 stellar populations and little or no ongoing star formation. Here we determine the sizes of these quiescent galaxies using deep, high-resolution images obtained with HST/NIC2 and laser guide star (LGS)–assisted Keck/adaptive optics (AO). Considering that their median stellar mass is , the galaxies are remarkably small, with 11 1.7 # 10 M, a median effective radius kpc. Galaxies of similar mass in the nearby universe have sizes of ≈5 kpc and r p 0.9 e average stellar densities that are 2 orders of magnitude lower than the galaxies. These results extend earlier z ∼ 2.3 work at and confirm previous studies at that lacked spectroscopic redshifts and imaging of sufficient z ∼ 1.5 z 1 2 resolution to resolve the galaxies. Our findings demonstrate that fully assembled early-type galaxies make up at most ∼10% of the population of K-selected quiescent galaxies at , effectively ruling out simple monolithic z ∼ 2.3 models for their formation. The galaxies must evolve significantly after , through dry mergers or other z ∼ 2.3 processes, consistent with predictions from hierarchical models. Subject headings: cosmology: observations — galaxies: evolution — galaxies: formation

Laser Frequency Combs for Astronomical Observations

Abstract: A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects However, this would require measurements of Doppler velocity drifts of approximately 1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance We demonstrated the first use of a laser frequency comb for wavelength calibration of an astronomical telescope Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of approximately 9 meters per second at approximately 15 micrometers-beyond state-of-the-art accuracy We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration

GMASS ultradeep spectroscopy of galaxies at $z$ ~ 2 - II. Superdense passive galaxies: how did they form and evolve?

Abstract: Aims. The aim of this work is to investigate the physical, structur al and evolutionary properties of old, passive galaxies at z> 1.4 and to place new constraints on massive galaxy formation and evolution. Methods. We combine ultradeep optical spectroscopy from the GMASS project (Galaxy Mass Assembly ultradeep Spectroscopic Survey) with GOODS multi-band (optical to mid‐infrared) photometry and HST imaging to study a sample of spectroscopically identified passive galaxies at 1.39 2. No X-ray emission was found neither from individual galaxies nor from a stacking analysis of the sample. Only one galaxy shows a marginal detection at 24� m. These galaxies have morphologies that are predominantly compact and spheroidal. However, their sizes (Re. 1 kpc) are much smaller than those of spheroids in the present‐day Universe. Their stellar mass surface densities are consequently hig her by≈1 dex if compared to spheroids at z≈ 0 with the same mass. Their rest-frame B-band surface brightness scales with the effective radius, but the offset with respect to the surface brightness of the local Korme ndy relation is too large to be explained by simple passive evolution. At z≈ 1, a larger fraction of passive galaxies follows the z≈ 0 size ‐ mass relation. Superdense relics with Re≈ 1 kpc are extremely rare at z≈ 0 with respect to z> 1, and absent if Re 2. The results are compared with theoretical models and the main implications discussed in the framework of massive galaxy formation and evolution.

Broadband observations of the naked-eye gamma-ray burst GRB 080319B

Abstract: Long-duration gamma-ray bursts (GRBs) release copious amounts of energy across the entire electromagnetic spectrum, and so provide a window into the process of black hole formation from the collapse of massive stars Previous early optical observations of even the most exceptional GRBs (990123 and 030329) lacked both the temporal resolution to probe the optical flash in detail and the accuracy needed to trace the transition from the prompt emission within the outflow to external shocks caused by interaction with the progenitor environment Here we report observations of the extraordinarily bright prompt optical and gamma-ray emission of GRB 080319B that provide diagnostics within seconds of its formation, followed by broadband observations of the afterglow decay that continued for weeks We show that the prompt emission stems from a single physical region, implying an extremely relativistic outflow that propagates within the narrow inner core of a two-component jet

Structure and Star Formation in Galaxies out to z = 3: Evidence for Surface Density Dependent Evolution and Upsizing* **

Abstract: We present an analysis of galaxies in the CDF-South. We find a tight relation to -->z = 3 between color and size at a given mass, with red galaxies being small, and blue galaxies being large. We show that the relation is driven by stellar surface density or inferred velocity dispersion: galaxies with high surface density are red and have low specific star formation rates, and galaxies with low surface density are blue and have high specific star formation rates. Surface density and inferred velocity dispersion are better correlated with specific star formation rate and color than stellar mass. Hence stellar mass by itself is not a good predictor of the star formation history of galaxies. In general, galaxies at a given surface density have higher specific star formation rates at higher redshift. Specifically, galaxies with a surface density of -->(1?3) ? 109 M? kpc?2 are red and dead at low redshift, approximately 50% are forming stars at -->z = 1, and almost all are forming stars by -->z = 2. This provides direct additional evidence for the late evolution of galaxies onto the red sequence. The sizes of galaxies at a given mass evolve like -->1/(1 + z)0.59 ? 0.10. Hence galaxies undergo significant upsizing in their history. The size evolution is fastest for the highest mass galaxies and quiescent galaxies. The persistence of the structural relations from -->z = 0 to -->z = 2.5, and the upsizing of galaxies imply that a relation analogous to the Hubble sequence exists out to -->z = 2.5, and possibly beyond. The star-forming galaxies at -->z ? 1.5 are quite different from star-forming galaxies at -->z = 0, as they have likely very high gas fractions, and star formation timescales comparable to the orbital time.

Measuring the cosmological parameters with the Ep,i–Eiso correlation of gamma-ray bursts

Abstract: We have used the E p,i -E iso correlation of gamma-ray bursts (GRBs) to measure the cosmological parameter Ω M . By adopting a maximum likelihood approach which allows us to correctly quantify the extrinsic (i.e. non-Poissonian) scatter of the correlation, we constrain (for a flat universe) Ω M to 0.04-0.40 (68 per cent confidence level), with a best-fitting value of Ω M ∼ 0.15, and exclude Ω M = 1 at >99.9 per cent confidence level. If we release the assumption of a flat universe, we still find evidence for a low value of Ω M (0.04-0.50 at 68 per cent confidence level) and a weak dependence of the dispersion of the E p,i -E iso correlation on Ω Λ (with an upper limit of Ω Λ ∼ 1.15 at 90 per cent confidence level). Our approach makes no assumptions on the E p,i -E iso correlation and it does not use other calibrators to set the 'zero' point of the relation, therefore our treatment of the data is not affected by circularity and the results are independent of those derived via Type Ia supernovae (or other cosmological probes). Unlike other multi-parameters correlations, our analysis grounds on only two parameters, then including a larger number (a factor of ∼3) of GRBs and being less affected by systematics. Simulations based on realistic extrapolations of ongoing (and future) GRB experiments (e.g. Swift, Konus-Wind, GLAST) show that: (i) the uncertainties on cosmological parameters can be significantly decreased and (ii) future data will allow us to get clues on the 'dark energy' evolution.

Metallicity effects on dust properties in starbursting galaxies

Abstract: We present infrared observations of 66 starburst galaxies over the full range of oxygen abundances observed in local star-forming galaxies, from -->12 + log (O/H) = 7.1 to 8.9. The data include imaging and spectroscopy from the Spitzer Space Telescope, supplemented by ground-based near-infrared imaging. We confirm a strong correlation of aromatic emission with metallicity, with a threshold at -->12 + log (O/H) ~ 8. We show that the far-infrared color temperature of the large dust grains increases toward lower metallicity, peaking at a metallicity of 8 before turning over. We compute dust masses and compare them to H I masses from the literature to derive the ratio of atomic gas to dust, which increases by nearly 3 orders of magnitude between solar metallicity and a metallicity of 8, below which it flattens out. The abrupt change in aromatic emission at mid-infrared wavelengths thus appears to be reflected in the far-infrared properties, indicating that metallicity changes affect the composition of the full range of dust grain sizes that dominate the infrared emission. Although the great majority of galaxies show similar patterns of behavior as described above, there are three exceptions, SBS 0335?052E, Haro 11, and SHOC 391. Their infrared SEDs are dominated energetically by the mid-IR near 24 ?m rather than by the 60-200 ?m region. In addition, they have very weak near-infrared outputs and their SEDs are dominated by emission by dust at wavelengths as short as 1.8 ?m. The latter behavior indicates that the dominant star-forming episodes in them are extremely young. The component of the ISM responsible for the usual far-infrared emission appears to be either missing or inefficiently heated in these three galaxies.

Distant radio galaxies and their environments

Abstract: We review the properties and nature of luminous high-redshift radio galaxies (HzRGs, z > 2) and the environments in which they are located. HzRGs have several distinct constituents which interact with each other—relativistic plasma, gas in various forms, dust, stars and an active galactic nucleus (AGN). These building blocks provide unique diagnostics about conditions in the early Universe. We discuss the properties of each constituent. Evidence is presented that HzRGs are massive forming galaxies and the progenitors of brightest cluster galaxies in the local Universe. HzRGs are located in overdense regions in the early Universe and are frequently surrounded by protoclusters. We review the properties and nature of these radio-selected protoclusters. Finally we consider the potential for future progress in the field during the next few decades. A compendium of known HzRGs is given in an appendix.

The Chandra Deep Field-South Survey: 2 Ms Source Catalogs

Abstract: We present point-source catalogs for the ≈2 Ms exposure of the Chandra Deep Field-South (CDF-S); this is one of the two most sensitive X-ray surveys ever performed. The survey covers an area of ≈436 arcmin^2 and reaches on-axis sensitivity limits of ≈1.9 × 10^(−17) and ≈1.3 × 10^(−16) ergs cm^(−2) s^(−1) for the 0.5-2.0 and 2-8 keV bands, respectively. Four hundred and sixty-two X-ray point sources are detected in at least one of three X-ray bands that were searched; 135 of these sources are new compared to the previous ≈1 Ms CDF-S detections. Source positions are determined using centroid and matched-filter techniques; the median positional uncertainty is ≈0.36''. The X-ray-to-optical flux ratios of the newly detected sources indicate a variety of source types; ≈55% of them appear to be active galactic nuclei, while ≈45% appear to be starburst and normal galaxies. In addition to the main Chandra catalog, we provide a supplementary catalog of 86 X-ray sources in the ≈2 Ms CDF-S footprint that was created by merging the ≈250 ks Extended Chandra Deep Field-South with the CDF-S; this approach provides additional sensitivity in the outer portions of the CDF-S. A second supplementary catalog that contains 30 X-ray sources was constructed by matching lower significance X-ray sources to bright optical counterparts (R < 23.8); the majority of these sources appear to be starburst and normal galaxies. The total number of sources in the main and supplementary catalogs is 578. Optical R-band counterparts and basic optical and infrared photometry are provided for the X-ray sources in the main and supplementary catalogs. We also include existing spectroscopic redshifts for 224 of the X-ray sources. The average backgrounds in the 0.5-2.0 and 2-8 keV bands are 0.066 and 0.167 counts Ms^(−1) pixel^(−1), respectively, and the background counts follow Poisson distributions. The effective exposure times and sensitivity limits of the CDF-S are now comparable to those of the ≈2 Ms Chandra Deep Field-North (CDF-N). We also present cumulative number counts for the main catalog and compare the results to those for the CDF-N. The soft-band number counts for these two fields agree well with each other at fluxes higher than ≈2 × 10^(−16) ergs cm^(−2) s^(−1), while the CDF-S number counts are up to ≈25% smaller than those for the CDF-N at fluxes below ≈2 × 10^(−16) ergs cm^(−2) s^(−1) in the soft band and ≈2 × 10^(−15) ergs cm^(−2) s^(−1) in the hard band, suggesting small field-to-field variations.

The ACS Virgo Cluster Survey. XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment*

Abstract: The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind. We find the following: (1) GC mass fractions can be high in both giants and dwarfs but are universally low in galaxies with intermediate luminosities. (2) The behavior of specific frequency across galaxy mass is dominated by the blue GCs. (3) GC fractions of low-mass galaxies exhibit a dependence on environment. Nearly all dwarf galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarfs is biased toward dense environments. (4) GC formation in central dwarfs is biased because their stars form earliest and most intensely. Comparisons to the Millennium Simulation show that central dwarfs have older stellar populations and form more stars at higher star formation rates (SFRs) and SFR surface densities. The SFR surface density in simulated dwarfs peaks before the total SFR, naturally producing GC populations that are older and more metal-poor than the field stars. (5) Dwarfs within ~40 kpc of the giant ellipticals M87 and M49 are red and have few or no GCs, suggesting that they have been tidally stripped and have contributed their GCs to the halos of their giant neighbors. The central dwarfs with high GC mass fractions are thus likely to be the survivors most similar to the protogalaxies that assembled the rich M87 globular cluster system.

Evidence for powerful AGN winds at high redshift: dynamics of galactic outflows in radio galaxies during the “Quasar Era”

Abstract: AGN feedback now appears as an attractive mechanism to resolve some of the outstanding problems with the “standard” cosmological models, in particular those related to massive galaxies. At low redshift, evidence is growing that gas cooling and star formation may be efficiently suppressed by mechanical energy input from radio sources. To directly constrain how this may influence the formation of massive galaxies near the peak in the redshift distribution of powerful quasars, z ∼ 2, we present an analysis of the emission-line kinematics of 3 powerful radio galaxies at z ∼ 2−3 (HzRGs) based on rest-frame optical integral-field spectroscopy obtained with SINFONI on the VLT. The host galaxies of powerful radio-loud AGN are among the most massive galaxies, and thus AGN feedback may have a particularly clear signature in these galaxies. We find evidence for bipolar outflows in all HzRGs, with kinetic energies that are equivalent to 0.2% of the rest-mass of the supermassive black hole. Observed total velocity offsets in the outflows are ∼800−1000 km s −1 between the blueshifted and redshifted line emission, and FWHMs ∼ 1000 km s −1 suggest strong turbulence. Line ratios allow to measure electron temperatures, ∼10 4 K from [OIII]λλλ4363, 4959, 5007 at z ∼ 2, electron densities (∼500 cm −3 ) and extinction (AV ∼ 1−4 mag). Ionized gas masses estimated from the Hα luminosity are of order 10 10 M� , similar to the molecular gas content of HzRGs, underlining that these outflows may indicate a significant phase in the evolution of the host galaxy. The total energy release of ∼10 60 erg during a dynamical time of ∼10 7 yrs corresponds to about the binding energy of a massive galaxy, similar to the prescriptions adopted in galaxy evolution models. Geometry, timescales and energy injection rates of order 10% of the kinetic energy flux of the jet suggest that the outflows are most likely driven by the radio source. The global energy density release of ∼10 57 erg s −1 Mpc −3 may also influence the subsequent evolution of the HzRG by enhancing the entropy and pressure in the surrounding halo and facilitating ram-pressure stripping of gas in satellite galaxies that may contribute to the subsequent mass assembly of the HzRG through low-dissipation “dry” mergers.

Structure and star formation in galaxies out to z=3: evidence for surface density dependent evolution and upsizing

Abstract: We present an analysis of galaxies in the CDF-South. We find a tight relation to z=3 between color and size at a given mass, with red galaxies being small, and blue galaxies being large. We show that the relation is driven by stellar surface density or inferred velocity dispersion: galaxies with high surface density are red and have low specific star formation rates, and galaxies with low surface density are blue and have high specific star formation rates. Surface density and inferred velocity dispersion are better correlated with specific star formation rate and color than stellar mass. Hence stellar mass by itself is not a good predictor of the star formation history of galaxies. In general, galaxies at a given surface density have higher specific star formation rates at higher redshift. Specifically, galaxies with a surface density of 1-3 10^9 Msun/kpc^2 are "red and dead" at low redshift, approximately 50% are forming stars at z=1, and almost all are forming stars by z=2. This provides direct additional evidence for the late evolution of galaxies onto the red sequence. The sizes of galaxies at a given mass evolve like 1/(1+z)^(0.59 +- 0.10). Hence galaxies undergo significant upsizing in their history. The size evolution is fastest for the highest mass galaxies, and quiescent galaxies. The persistence of the structural relations from z=0 to z=2.5, and the upsizing of galaxies imply that a relation analogous to the Hubble sequence exists out to z=2.5, and possibly beyond. The star forming galaxies at z >= 1.5 are quite different from star forming galaxies at z=0, as they have likely very high gas fractions, and star formation time scales comparable to the orbital time.

The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure

Abstract: In this paper we present the results of a systematic investigation of an entire population of predominately starless dust cores within a single molecular cloud, the Pipe Nebula. Analysis of extinction data shows the cores to be dense objects characterized by a narrow range of density with a median value of -->n(H2) = 7 ? 103. The nonthermal velocity dispersions measured in molecular emission lines are found to be subsonic for the large majority of the cores and show no correlation with core mass (or size). Thermal pressure is found to be the dominate source of internal gas pressure and support for most of the core population. The total internal pressures of the cores are found to be roughly independent of core mass over the entire (0.2-20 M?) range of the core mass function (CMF) indicating that the cores are in pressure equilibrium with an external source of pressure. This external pressure is most likely provided by the weight of the surrounding molecular cloud. Most of the cores appear to be pressure confined, gravitationally unbound entities whose fundamental physical properties are determined by only a few factors, which include self-gravity, gas temperature, and the simple requirement of pressure equilibrium with the surrounding environment. The entire core population is found to be characterized by a single critical Bonnor-Ebert mass of approximately 2 M?. This mass coincides with the characteristic mass of the Pipe CMF suggesting that the CMF (and ultimately the stellar IMF) has its origin in the physical process of thermal fragmentation in a pressurized medium.

Triaxial orbit based galaxy models with an application to the (apparent) decoupled core galaxy NGC 4365

Abstract: We present a flexible and efficient method to construct triaxial dynamical models of galaxies with a central black hole, using Schwarzschild's orbital superposition approach. Our method is general and can deal with realistic luminosity distributions, which project to surface brightness distributions that may show position angle twists and ellipticity variations. The models are fit to measurements of the full line-of-sight velocity distribution (wherever available). We verify that our method is able to reproduce theoretical predictions of a three-integral triaxial Abel model. In a companion paper by Ven, de Zeeuw & van den Bosch, we demonstrate that the method recovers the phase-space distribution function. We apply our method to two-dimensional observations of the E3 galaxy NGC 4365, obtained with the integral-field spectrograph SAURON, and study its internal structure, showing that the observed kinematically decoupled core is not physically distinct from the main body and the inner region is close to oblate axisymmetric.

A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192

Abstract: We report the detection of an extrasolar planet of mass ratio q~2×10-4 in microlensing event MOA-2007-BLG-192. The best-fit microlensing model shows both the microlensing parallax and finite source effects, and these can be combined to obtain the lens masses of M=0.060+0.028-0.021 Msolar for the primary and m=3.3+4.9-1.6 M? for the planet. However, the observational coverage of the planetary deviation is sparse and incomplete, and the radius of the source was estimated without the benefit of a source star color measurement. As a result, the 2 ? limits on the mass ratio and finite source measurements are weak. Nevertheless, the microlensing parallax signal clearly favors a substellar mass planetary host, and the measurement of finite source effects in the light curve supports this conclusion. Adaptive optics images taken with the Very Large Telescope (VLT) NACO instrument are consistent with a lens star that is either a brown dwarf or a star at the bottom of the main sequence. Follow-up VLT and/or Hubble Space Telescope (HST) observations will either confirm that the primary is a brown dwarf or detect the low-mass lens star and enable a precise determination of its mass. In either case, the lens star, MOA-2007-BLG-192L, is the lowest mass primary known to have a companion with a planetary mass ratio, and the planet, MOA-2007-BLG-192Lb, is probably the lowest mass exoplanet found to date, aside from the lowest mass pulsar planet.

The metamorphosis of supernova SN 2008D/XRF 080109: a link between supernovae and GRBs/hypernovae.

Abstract: The only supernovae (SNe) to show gamma-ray bursts (GRBs) or early x-ray emission thus far are overenergetic, broad-lined type Ic SNe (hypernovae, HNe). Recently, SN 2008D has shown several unusual features: (i) weak x-ray flash (XRF), (ii) an early, narrow optical peak, (iii) disappearance of the broad lines typical of SN Ic HNe, and (iv) development of helium lines as in SNe Ib. Detailed analysis shows that SN 2008D was not a normal supernova: Its explosion energy (E approximately 6x10(51) erg) and ejected mass [ approximately 7 times the mass of the Sun (M(middle dot in circle))] are intermediate between normal SNe Ibc and HNe. We conclude that SN 2008D was originally a approximately 30 M(middle dot in circle) star. When it collapsed, a black hole formed and a weak, mildly relativistic jet was produced, which caused the XRF. SN 2008D is probably among the weakest explosions that produce relativistic jets. Inner engine activity appears to be present whenever massive stars collapse to black holes.

The Nucleus of the Sagittarius dSph Galaxy and M54: A Window on the Process of Galaxy Nucleation

Abstract: We present the results of a thorough study of the nucleus of the Sgr dwarf spheroidal galaxy (Sgr dSph) and of the bright globular cluster M54 (NGC 6715) that resides within the same nucleus (Sgr,N). We have obtained accurate radial velocities and metallicity estimates for 1152 candidate Red Giant Branch stars of Sgr and M54 lying within ∼ 9 ′ from the center of the galaxy, from Keck/DEIMOS and VLT/FLAMES spectra of the infrared Calcium II triplet. Using both velocity and metallicity information we selected two samples of 425 and 321 very-likely members of M54 and of Sgr,N, respectively. The two considered systems display significantly different velocity dispersion profiles: M54 has a steeply decreasing profile from r = 0 ′ , where σ ≃ 14.2 km/s, to r ≃ 3 ′ where it reaches σ ≃ 5.3 km/s, then it appears to rise again to σ ≃ 10 km/s at r ∼ 7 ′ . In contrast Sgr,N has a uniformly flat profile at σ ≃ 9.6 km/s over the whole 0 ′ ≤ r ≤ 9 ′ range. Using data from the literature we show that the velocity dispersion of Sgr remains constant at least out to r ∼ 100 ′ and there is no sign of the transition between the outer flat-luminosity-profile core and the inner nucleus in the velocity profile. These results - together with a re-analysis of the Surface Brightness profile of Sgr,N and a suite of dedicated N-body simulations - provide very strong support for the hypothesis that the nucleus of Sgr formed independently of M54, which probably plunged to its present position, coincident with Sgr,N, because of significant decay of the original orbit due to dynamical friction. Subject headings: galaxies: dwarf — globular clusters: individual(NGC 6715) — stars: kinematics — galaxies: nuclei — galaxies: individual (Sgr dSph)

TW Hydrae: evidence of stellar spots instead of a Hot Jupiter

Abstract: Context TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime These variations have been attributed to a 10 MJup planet orbiting the star at 004 AU Aims The aim of this letter is to confirm the presence of the giant planet around TW Hya by (i) testing whether the observed RV variations can be caused by stellar spots and (ii) analyzing new optical and infrared data to detect the signal of the planet companion Methods We fitted the RV variations of TW Hya using a cool spot model In addition, we obtained new high-resolution optical & infrared spectra, together with optical photometry of TW Hya and compared them with previous data Results Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 ◦ can reproduce the reported RV variations The model also predicts a bisector semi-amplitude variation <10 m s −1 , which is less than the errors of the RV measurements discussed in Setiawan et al (2008, Nature, 451, 38) The analysis of our new optical RV data, with typical errors of 10 m s −1 , shows a larger RV amplitude that varies depending on the correlation mask used A slight correlation between the RV variation and the bisector is also observed although not at a very significant level The infrared H-band RV curve is almost flat, showing a small variation (<35 m s −1 ) that is not consistent with the published optical orbit All these results support the spot scenario rather than the presence of a hot Jupiter Finally, the photometric data shows a 20% (peak to peak) variability, which is much larger than the 4% variation expected for the modeled cool spot The fact that the optical data are correlated with the surface of the cross-correlation function points towards hot spots as being responsible for the photometric variability Conclusions We conclude that the best explanation for the RV signal observed in TW Hya is the presence of a cool stellar spot and not an orbiting hot Jupiter

Molecular hydrogen in high-redshift damped Lyman-α systems : the VLT/UVES database

Abstract: Aims. We present the current status of ongoing searches for molecular hydrogen in high-redshift (1.8 z abs ≤ 4.2) Damped Lyman- α systems (DLAs) capitalising on observations performed with the ESO Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES). Methods. We identify 77 DLAs/strong sub-DLAs, with log N (H I) ≥ 20 and z abs >1.8, which have data that include redshifted H 2 Lyman and/or Werner-band absorption lines. This sample of H I, H 2 and metal line measurements, performed in an homogeneous manner, is more than twice as large as our previous sample (Ledoux et al. 2003) considering every system in which searches for H 2 could be completed so far, including all non-detections. Results. H 2 is detected in thirteen of the systems, which have molecular fractions of values between f $\simeq$ 5$\times$10 -7 and f $\simeq$ 0.1, where f = 2 N (H 2 )/(2 N (H 2 )+N(H I)). Upper limits are measured for the remaining 64 systems with detection limits of typically log N (H 2 )~14.3, corresponding to log f ≥ -1.3 (i.e., 1/20th solar), with X = Zn, S or Si, have molecular fractions log f > -4.5, while H 2 is detected – regardless of the molecular fraction – in ∼ 50% of them. In contrast, only about 4% of the [X/H] f > -4.5. We show that the presence of H 2 does not strongly depend on the total neutral hydrogen column density, although the probability of finding log f > -4.5 is higher for log N (H I) ≥ 20.8 than below this limit (19% and 7% respectively). The overall H 2 detection rate in log N (H I) ≥ 20 DLAs is found to be about 16% (10% considering only log f > -4.5 detections) after correction for a slight bias towards large N (H I). There is a strong preference for H 2 -bearing DLAs to have significant depletion factors, [X/Fe] > 0.4. In addition, all H 2 -bearing DLAs have column densities of iron into dust grains larger than log $N({\rm Fe})_{\rm dust}$~ 14.7, and about 40% of the DLAs above this limit have detected H 2 lines with log f > -4.5. This demonstrates the importance of dust in governing the detectability of H 2 in DLAs. Our extended sample supports neither the redshift evolution of the detection fraction of H 2 -bearing DLAs nor that of the molecular fraction in systems with H 2 detections over the redshift range 1.8 z abs ≤ 3.

The influence of chemical composition on the properties of Cepheid stars. II - The iron content ⋆

Abstract: Context. The Cepheid period-luminosity (PL) relation is unquestionably one of the most powerful tools at our disposal for determining the extragalactic distance scale. While significant progress has been made in the past few years towards its understanding and characterization both on the observational and theoretical sides, the debate on the influence that chemical composition may have on the PL relation is still unsettled.Aims. With the aim to assess the influence of the stellar iron content on the PL relation in the V and K bands, we have related the V -band and the K -band residuals from the standard PL relations of Freedman et al. (2001, ApJ, 553, 47) and Persson et al. (2004, AJ, 128, 2239), respectively, to [Fe/H].Methods. We used direct measurements of the iron abundances of 68 Galactic and Magellanic Cepheids from FEROS and UVES high-resolution and high signal-to-noise spectra.Results. We find a mean iron abundance ([Fe/H]) about solar (= 0.10) for our Galactic sample (32 stars), ~-0.33 dex (σ = 0.13) for the Large Magellanic Cloud (LMC) sample (22 stars) and ~-0.75 dex (σ = 0.08) for the Small Magellanic Cloud (SMC) sample (14 stars). Our abundance measurements of the Magellanic Cepheids double the number of stars studied up to now at high resolution. The metallicity affects the V -band Cepheid PL relation and metal-rich Cepheids appear to be systematically fainter than metal-poor ones. These findings depend neither on the adopted distance scale for Galactic Cepheids nor on the adopted LMC distance modulus. Current data do not allow us to reach a firm conclusion concerning the metallicity dependence of the K -band PL relation. The new Galactic distances indicate a small effect, whereas the old ones support a marginal effect. Conclusions. Recent robust estimates of the LMC distance and current results indicate that the Cepheid PL relation is not Universal.

Searching for Cool Core Clusters at High redshift

Abstract: We investigate the detection of Cool Cores (CCs) in the distant galaxy cluster population, with the purpose of measuring the CC fraction out to redshift 0.7 0.7, and should also be related with the shorter age of distant clusters, implying less time to develop a cool core.

Cosmic dynamics in the era of Extremely Large Telescopes

Abstract: The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution of the Universe's expansion rate. A measurement of this effect would represent a direct and entirely model-independent determination of the expansion history of the Universe over a redshift range that is inaccessible to other methods. Here we investigate the impact of the next generation of Extremely Large Telescopes on the feasibility of detecting and characterising the cosmological redshift drift. We consider the Lyman alpha forest in the redshift range 2 < z < 5 and other absorption lines in the spectra of high redshift QSOs as the most suitable targets for a redshift drift experiment. Assuming photon-noise limited observations and using extensive Monte Carlo simulations we determine the accuracy to which the redshift drift can be measured from the Ly alpha forest as a function of signal-to-noise and redshift. Based on this relation and using the brightness and redshift distributions of known QSOs we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ~20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.

HiZELS: a high-redshift survey of Hα emitters – I. The cosmic star formation rate and clustering at z= 2.23

Abstract: We present results from a near-infrared narrow-band survey of emission-line galaxies at z = 2.23, using the Wide Field Camera on the United Kingdom Infrared Telescope. The H2S1 narrow-band filter ( �c = 2.121µm) we employ selects the Hemission line redshifted to z = 2.23, and is thus suitable for selecting 'typical' star forming g alaxies and active galactic nuclei at this epoch. The pilot study was undertaken in the well studied Cosmological Evolution Survey field (COSMOS) and is already the largest near-infrar ed narrow-band survey at this depth, with a line flux limit of FH� � 10 −16 erg s −1 cm −2 over 0.60 square degrees, probing �220× 10 3 Mpc 3 (co-moving) down to a limiting star formation rate of �30M⊙ yr −1 (3�). In this paper we present the results from our pilot survey and evaluate the Hluminosity function and estimate the clustering properties of Hemitters at z = 2.23 from 55 detected galaxies. The integrated luminosity function is used to est imate the volume averaged star formation rate at z = 2.23: �SFR = 0.17 +0.16 −0.09M⊙ yr −1 Mpc −3 for LH� > 10 42 erg s −1 . For the first time, we use the Hstar-formation tracer to reliably constrainSFR out to z = 2.23 demonstrating the rapid increase inSFR out to this redshift as well as confirming the flattening inSFR betweenz � 1-2. In addition to the luminosity distribution, we analyse t he clustering properties of these galaxies. Using the 2-point angular correlation function, !(�), we estimate a real space correlation length of r0 = 4.2 +0.4 −0.2 h −1 Mpc. In comparison to models of clustering which take into account bias evolution, we estimate that these galaxies are hosted by dark matter halos of mass Mhalo � 10 12 M⊙ consistent with the progenitors of the Milky

The SAURON project – XII. Kinematic substructures in early-type galaxies: evidence for discs in fast rotators

Abstract: We analysed two-dimensional maps of 48 early-type galaxies obtained with the SAURON and OASIS integral-field spectrographs using kinemetry, a gene ralisation of surface photometry to the higher order moments of the line-of-sight velocity distribution (LOSVD). The maps analysed include: reconstructed image, mean velocity, velocity dispersion, h3 and h4 GaussHermite moments. Kinemetry is a good method to recognise structures otherwise missed by using surface photometry, such as embedded disks and kinematic sub-components. In the SAURON sample, we find that 31% of early-type galaxies are sin gle component systems. 91% of the multi-components systems have two kinematic subcomponents, the rest having three. In addition, 29% of galaxies have kinematically decoupled components, nuclear components with significant kinematic twists. We differentiate betwee n slow and fast rotators using velocity maps only and find that fast rotating galaxies contain disks with a large range in mass fractions to the main body. Specifically, we find that the velo city maps of fast rotators closely resemble those of inclined disks, except in the transition r egions between kinematic subcomponents. This deviation is measured with the kinemetric k5/k1 ratio, which is large and noisy in slow rotators and about 2% in fast rotators. In terms of E/S0 classification, this means that 74% of Es and 92% of S0s have components with disk-like kinematics. We suggest that differences in k5/k1 values for the fast and slow rotators arise from their differ ent intrinsic structure which is reflected on the velocity maps. For the majority of fa st rotators, the kinematic axial ratios are equal to or less than their photometric axial rati os, contrary to what is predicted with isotropic Jeans models viewed at different inclinations. T he position angles of fast rotators are constant, while they vary abruptly in slow rotators. Velocity dispersion maps of face-on galaxies have shapes similar to the distribution of light. Veloci ty dispersion maps of the edge-on fast rotators and all slow rotators show differences which can only be partially explained with isotropic models and, in the case of fast rotators, often req uire additional cold components. We constructed local (bin-by-bin) h3 V/σ and h4 V/σ diagrams from SAURON observations. We confirm the classical anti-correlation of h3 and V/σ, but we also find that h3 is almost zero in some objects or even weakly correlated with V/σ. The distribution of h4 for fast and slow rotators is mildly positive on average. In general, fast rot ators contain flattened components characterised by a disk-like rotation. The difference betw een slow and fast rotators is traceable throughout all moments of the LOSVD, with evidence for different intrinsic shapes and orbital contents and, hence, likely different evolutionary paths.

Searching for cool core clusters at high redshift

Abstract: Aims. We investigate the detection of Cool Cores (CCs) in the distant galaxy cluster population with the purpose of measuring the CC fraction out to redshift 0.7 ≤ z 0.7, and should also be related to the shorter age of distant clusters, implying less time to develop a cool core.

Photometric redshifts in the SWIRE Survey

Abstract: We present the SWIRE Photometric Redshift Catalogue 1 025 119 redshifts of unprecedented reliability and of accuracy comparable with or better than previous work. Our methodology is based on fixed galaxy and quasi-stellar object templates applied to data at 0.36–4.5 μm, and on a set of four infrared emission templates fitted to infrared excess data at 3.6–170 μm. The galaxy templates are initially empirical, but are given greater physical validity by fitting star formation histories to them, which also allows us to estimate stellar masses. The code involves two passes through the data, to try to optimize recognition of active galactic nucleus (AGN) dust tori. A few carefully justified priors are used and are the key to supression of outliers. Extinction, A_V , is allowed as a free parameter. The full reduced χ^2_ν (z) distribution is given for each source, so the full error distribution can be used, and aliases investigated. We use a set of 5982 spectroscopic redshifts, taken from the literature and from our own spectroscopic surveys, to analyse the performance of our method as a function of the number of photometric bands used in the solution and the reduced χ^2_ν . For seven photometric bands (5 optical + 3.6, 4.5 μm), the rms value of (z_(phot)−z_(spec)/(1 +z_(spec) is 3.5 per cent, and the percentage of catastrophic outliers [defined as >15 per cent error in (1 +z)], is ∼1 per cent. These rms values are comparable with the best achieved in other studies, and the outlier fraction is significantly better. The inclusion of the 3.6- and 4.5-μm IRAC bands is crucial in supression of outliers. We discuss the redshift distributions at 3.6 and 24 μm. In individual fields, structure in the redshift distribution corresponds to clusters which can be seen in the spectroscopic redshift distribution, so the photometric redshifts are a powerful tool for large-scale structure studies. 10 per cent of sources in the SWIRE photometric redshift catalogue have z > 2, and 4 per cent have z > 3, so this catalogue is a huge resource for high-redshift galaxies. A key parameter for understanding the evolutionary status of infrared galaxies is L_(ir)/L_(opt) . For cirrus galaxies this is a measure of the mean extinction in the interstellar medium of the galaxy. There is a population of ultraluminous galaxies with cool dust and we have shown SEDs for some of the reliable examples. For starbursts, we estimate the specific star formation rate, φ_*/M_* . Although the very highest values of this ratio tend to be associated with Arp220 starbursts, by no means all ultraluminous galaxies are. We discuss an interesting population of galaxies with elliptical-like spectral energy distributions in the optical and luminous starbursts in the infrared. For dust tori around type 1 AGN, L_(tor)/L_(opt) is a measure of the torus covering factor and we deduce a mean covering factor of 40 per cent. Our infrared templates also allow us to estimate dust masses for all galaxies with an infrared excess.

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. XI. Lupus Observed with IRAC and MIPS

Abstract: We present c2d Spitzer/IRAC observations of the Lupus I, III and IV dark clouds and discuss them in combination with optical and near-infrared and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very-low mass stars and it is complete down to M ≈ 0.1M⊙. We find 30-40% binaries with separations between 100 to 2000 AU with no apparent effect in the disk properties of the members. A large majority of the objects are Class II or Class III objects, with only 20 (12%) of Class I or Flat spectrum sources. The disk sample is complete down to “debris”-like systems in stars as small as M ≈ 0.2 M⊙ and includes sub-stellar objects with larger IR excesses. The disk fraction in Lupus is 70 – 80%, consistent with an age of 1 – 2 Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for

From star clusters to dwarf galaxies: the properties of dynamically hot stellar systems

Abstract: Objects with radii of 10pc to 100pc and masses in the range from 10 6 M⊙ to 10 8 M⊙ have been discovered during the past decade. These so-called ultra compact dwarf galaxies (UCDs) constitute a transition between classical star clusters and elliptical galaxies in terms of radii, relaxation times and V -band mass-to-light ratios. Using new data, the increase of typical radii with mass for compact objects more massive than 10 6 M⊙ can be confirmed. There is a continuous transition to the typical, massindependent radii of globular clusters (GCs). It can be concluded from the different relations between mass and radius of GCs and UCDs that at least their evolution must have proceeded differently, while the continuous transition could indicate a common formation scenario. The strong increase of the characteristic radii also implies a strong increase of the median two-body relaxation time, trel, which becomes longer than a Hubble time, τH, in the mass interval between 10 6 M⊙ and 10 7 M⊙. This is also the mass interval where the highest stellar densities are reached. The mass-to-light ratios of UCDs are clearly higher than the ones of GCs, and the departure from mass-tolight ratios typical for GCs happens again at a mass of � 10 6 M⊙. Dwarf spheroidal galaxies turn out to be total outliers compared to all other dynamically hot stellar systems regarding their dynamical mass-to-light ratios. Stellar population models were consulted in order to compare the mass-to-light ratios of the UCDs with theoretical predictions for dynamically unevolved simple stellar populations (SSPs), which are probably a good approximation to the actual stellar populations in the UCDs. The SSP models also allow to account for the effects of metallicity on the mass-to-light ratio. It is found that the UCDs, if taken as a sample, have a tendency to higher mass-to-light ratios than it would be expected from the SSP models assuming that the initial stellar mass function in the UCDs is the same as in resolved stellar populations. This can be interpreted in several ways: As a failure of state-of-the-art stellar evolution and stellar population modelling, as a presence of dark matter in UCDs or as stellar populations which formed with initial stellar mass functions different to the canonical one for resolved populations. But it is noteworthy that evidence for dark matter emerges only in systems with trel ? τH.

A Swedish heterodyne facility instrument for the APEX telescope

Abstract: Aims. In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning. Methods. The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first three bands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K. Results. We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.