We search the complete Hubble Frontier Field data set of Abell 2744 and its parallel field for z ~ 10 sources to further refine the evolution of the cosmic star formation rate density (SFRD) between ...z ~ 8 and z ~ 10. We independently confirm two images of the recently discovered triply imaged z ~ 9.8 source by Zitrin et al. and set an upper limit for similar z ~ 10 galaxies with red colors of J sub(125) - H sub(160) > 1.2 in the parallel field of Abell 2744. We utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at z ~ 10, both in the lensed cluster field and in the adjacent parallel field. We show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves.
We have created specialized target lists for radial velocity surveys that are biased toward stars that (1) possess planets and (2) are easiest to observe with current detection techniques. We use a ...procedure that uniformly estimates fundamental stellar properties of Tycho 2 stars, with errors, using spline functions of broadband photometry and proper motion found in Hipparcos/Tycho 2 and 2MASS. We provide estimates of T sub(eff) and distance for 2.4 x 10 super(6) Tycho 2 stars that lack trigonometric distances. For stars that appear to be FGK dwarfs, we also derive Fe/H and identify unresolved binary systems with mass ratios 1.25 < M sub(1)/M sub(2) < 3.0. For FGK dwarfs with photometric error s sub(V) < 0.05, or V < 9, our temperature model gives a 1 s error of s sub(T) = +58.7/ -65.9 K and our metallicity model gives a 1 s error of s sub(Fe/H) =+0.13/ -0.14 dex. The binarity model can be used to remove 70% of doubles with 1.25 < M sub(1)/M sub(2) < 3.0 from a magnitude-limited sample of dwarfs at a cost of cutting 20% of the sample. Our estimates of distance and spectral type enable us to isolate 354,822 Tycho 2 dwarfs, 321,996 absent from Hipparcos, with giant contamination of 2.6% and 7.2%, respectively. Roughly 100,000 of these stars, not in Hipparcos, have sufficiently low photometric errors to retain 0.13-0.3 dex Fe/H accuracy and 80-100 K temperature accuracy (1 s). Our metallicity estimates have been used to identify targets for N2K, a large-scale radial velocity search for hot jupiters, which has verified the errors presented here. The catalogs that we publish can be used to further large-scale studies of Galactic structure and chemical evolution and to provide potential reference stars for narrow-angle astrometry programs such as the Space Interferometry Mission and large-aperture optical interferometry.
Active galaxies hosting two accreting and merging supermassive black holes (SMBHs)--dual active galactic nuclei (AGNs)--are predicted by many current and popular models of black-hole-galaxy ...co-evolution. We present here the results of a program that has identified a set of probable dual AGN candidates based on near-infrared laser guide star adaptive optics imaging with the Keck II telescope. These candidates are selected from a complete sample of radio-quiet quasi-stellar objects (QSOs) drawn from the Sloan Digital Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the 12 AGNs imaged, we find 6 with double galaxy structure, of which four are in galaxy mergers. We measure the ionization of the two velocity components in the narrow AGN lines to test the hypothesis that both velocity components come from an active nucleus. The combination of a well-defined parent sample and high-quality imaging allows us to place constraints on the fraction of SDSS QSOs that host dual accreting black holes separated on kiloparsec scales: ~0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during a typical merger and find a value that is much lower than estimates that arise from QSO space densities and galaxy merger statistics. We discuss possible reasons for this difference. Finally, we compare the SMBH mass distributions of single and dual AGNs and find little difference between the two within the limited statistics of our program, hinting that most SMBH growth happens in the later stages of a merger process.
We investigate the utility of the asymptotic giant branch (AGB) and the red giant branch (RGB) as probes of the star formation history (SFH) of the nearby (D = 2.5 Mpc) dwarf irregular galaxy, KKH ...98. Near-infrared (near-IR) Keck Laser Guide Star Adaptive Optics (AO) images resolve 592 IR-bright stars reaching over 1 mag below the tip of the RGB. Significantly deeper optical (F475W and F814W) Hubble Space Telescope images of the same field contain over 2500 stars, reaching to the red clump and the main-sequence turnoff for 0.5 Gyr old populations. Compared to the optical color-magnitude diagram (CMD), the near-IR CMD shows significantly tighter AGB sequences, providing a good probe of the intermediate-age (0.5-5 Gyr) populations. We match observed CMDs with stellar evolution models to recover the SFH of KKH 98. On average, the galaxy has experienced relatively constant low-level star formation (5 x 10{sup -4} M{sub sun} yr{sup -1}) for much of cosmic time. Except for the youngest main-sequence populations (age <0.1 Gyr), which are typically fainter than the AO data flux limit, the SFH estimated from the 592 IR-bright stars is a reasonable match to that derived from the much larger optical data set. Differences between the optical- and IR-derived SFHs for 0.1-1 Gyr populations suggest that current stellar evolution models may be overproducing the AGB by as much as a factor of 3 in this galaxy. At the depth of the AO data, the IR-luminous stars are not crowded. Therefore, these techniques can potentially be used to determine the stellar populations of galaxies at significantly further distances.
Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the ...Gemini Planet Imager, we discovered a planet orbiting the ∼20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10–6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold-start" core-accretion process that may have formed Jupiter.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
•We demonstrate capabilities of amateur astronomers to observe and track large cloud systems in Neptune's atmosphere presenting data from 2013 to 2015.•Two bright discrete features Neptune's South ...mid-latitudes in 2014 seem to have collided into a single bright feature observed over 2015.•A bright large feature at planetographic latitude −40° in 2015 was linked to a dark spot observed in Hubble Space Telescope images.•We present zonal wind results from a long-term tracking of several cloud systems in 2013–2015.
Since 2013, observations of Neptune with small telescopes (28–50 cm) have resulted in several detections of long-lived bright atmospheric features that have also been observed by large telescopes such as Keck II or Hubble. The combination of both types of images allows the study of the long-term evolution of major cloud systems in the planet. In 2013 and 2014 two bright features were present on the planet at southern mid-latitudes. These may have merged in late 2014, possibly leading to the formation of a single bright feature observed during 2015 at the same latitude. This cloud system was first observed in January 2015 and nearly continuously from July to December 2015 in observations with telescopes in the 2-10-m class and in images from amateur astronomers. These images show the bright spot as a compact feature at −40.1 ± 1.6° planetographic latitude well resolved from a nearby bright zonal band that extended from −42° to −20°. The size of this system depends on wavelength and varies from a longitudinal extension of 8000 ± 900 km and latitudinal extension of 6500 ± 900 km in Keck II images in H and Ks bands to 5100 ± 1400 km in longitude and 4500 ± 1400 km in latitude in HST images in 657 nm. Over July to September 2015 the structure drifted westward in longitude at a rate of 24.48 ± 0.03°/day or −94 ± 3 m/s. This is about 30 m/s slower than the zonal winds measured at the time of the Voyager 2 flyby. Tracking its motion from July to November 2015 suggests a longitudinal oscillation of 16° in amplitude with a 90-day period, typical of dark spots on Neptune and similar to the Great Red Spot oscillation in Jupiter. The limited time covered by high-resolution observations only covers one full oscillation and other interpretations of the changing motions could be possible. HST images in September 2015 show the presence of a dark spot at short wavelengths located in the southern flank (planetographic latitude −47.0°) of the bright compact cloud observed throughout 2015. The drift rate of the bright cloud and dark spot translates to a zonal speed of −87.0 ± 2.0 m/s, which matches the Voyager 2 zonal speeds at the latitude of the dark spot. Identification of a few other features in 2015 enabled the extraction of some limited wind information over this period. This work demonstrates the need of frequently monitoring Neptune to understand its atmospheric dynamics and shows excellent opportunities for professional and amateur collaborations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We present empirical calibrations that provide estimates of stellar metallieity, effective temperature, and surface gravity as a function of Lick IDS indices. These calibrations have been derived ...from a training set of 261 stars for which (1) high-precision measurements of Fe/H, T sub(eff), and log g have been made using spectral-synthesis analysis of HIRES spectra, and (2) Lick indices have also been measured. Estimation of atmospheric parameters with low-resolution spectroscopy rather than photometry has the advantage of producing a highly accurate metallicity calibration, and requires only one observation per star. Our calibrations have identified a number of bright (V< 9) metal-rich stars that are now being screened for hot-Jupiter-type planets. Using the Yonsei-Yale stellar models, we show that the calibrations provide distance estimates accurate to 620% for nearby stars. We have also investigated the possibility of constructing a "planeticity" calibration to predict the presence of planets based on stellar abundance ratios but find no evidence that a convincing relation of this type can be established. High metallicity remains the best single indicator that a given star is likely to harbor extrasolar planets.
In this work, we search the complete Hubble Frontier Field data set of Abell 2744 and its parallel field for $z\sim 10$ sources to further refine the evolution of the cosmic star formation rate ...density (SFRD) between $z\sim 8$ and $z\sim 10$. We independently confirm two images of the recently discovered triply imaged $z\sim 9.8$ source by Zitrin et al. and set an upper limit for similar $z\sim 10$ galaxies with red colors of ${J}_{125}-{H}_{160}\gt 1.2$ in the parallel field of Abell 2744. We utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at $z\sim 10$, both in the lensed cluster field and in the adjacent parallel field. Particular care is taken to include position-dependent lensing shear to accurately account for the expected sizes and morphologies of highly magnified sources. We show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves. These effects have a significant, but largely overlooked, impact on the detectability of high-redshift sources behind clusters, and substantially reduce the expected number of highly magnified sources. The detections and limits from both pointings result in an SFRD which is consistent within the uncertainties with previous estimates at $z\sim 10$ from blank fields. The combination of these new results with all other estimates is also consistent with a rapidly declining SFRD in the 170 Myr from $z\sim 8$ to $z\sim 10$ as predicted by cosmological simulations and dark-matter halo evolution in ΛCDM. Once biases introduced by magnification-dependent completeness are accounted for, the full six cluster and parallel Frontier Field program will be an extremely powerful new data set to probe the evolution of the galaxy population at $z\gt 8$ before the advent of the James Webb Space Telescope.
ABSTRACT We search the complete Hubble Frontier Field data set of Abell 2744 and its parallel field for sources to further refine the evolution of the cosmic star formation rate density (SFRD) ...between and . We independently confirm two images of the recently discovered triply imaged source by Zitrin et al. and set an upper limit for similar galaxies with red colors of in the parallel field of Abell 2744. We utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at , both in the lensed cluster field and in the adjacent parallel field. Particular care is taken to include position-dependent lensing shear to accurately account for the expected sizes and morphologies of highly magnified sources. We show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves. These effects have a significant, but largely overlooked, impact on the detectability of high-redshift sources behind clusters, and substantially reduce the expected number of highly magnified sources. The detections and limits from both pointings result in an SFRD which is consistent within the uncertainties with previous estimates at from blank fields. The combination of these new results with all other estimates is also consistent with a rapidly declining SFRD in the 170 Myr from to as predicted by cosmological simulations and dark-matter halo evolution in ΛCDM. Once biases introduced by magnification-dependent completeness are accounted for, the full six cluster and parallel Frontier Field program will be an extremely powerful new data set to probe the evolution of the galaxy population at before the advent of the James Webb Space Telescope.
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