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Abstract:

We observed the neutron star (NS) ultra-compact X-ray binary 4U 0614+091 quasi-simultaneously in the radio band (Very Large Array), mid-infrared (IR)/IR (Spitzer/Multiband Imaging Photometer for Spitzer and Infrared Array Camera), near-IR/optical (Small and Moderate Aperture Research Telescope System), optical-UV (Swift/UV-Optical Telescope), soft and hard X-rays (Swift/X-ray Telescope and Rossi-X-ray Timing Explorer). The source was steadily in its "hard state." We detected the source in the whole range, for the first time in the radio band at 4.86 and 8.46GHz and in the mid-IR at 24 μm, up to 100 keV. The optically thick synchrotron spectrum of the jet is consistent with being flat from the radio to the mid-IR band. The flat jet spectrum breaks in the range ∼(1-4) × 10¹³Hz to an optically thin power-law synchrotron spectrum with spectral index ∼-0.5. These observations allow us to estimate a lower limit on the jet radiative power of 3 × 10 ³² erg s^-1 and a total jet power L J ∼ 10³⁴μ^-1 0.05 E ^0.53 c erg s^-1 (where E c is the high-energy cutoff of the synchrotron spectrum in eV and μ0.05 is the radiative efficiency in units of 0.05). The contemporaneous detection of the optically thin part of the compact jet and the X-ray tail above 30keV allows us to assess the contribution of the jet to the hard X-ray tail by synchrotron self-Compton (SSC) processes. We conclude that, for realistic jet size, boosting, viewing angle, and energy partition, the SSC emission alone, from the post-shock, accelerated, non-thermal population in the jet, is not a viable mechanism to explain the observed hard X-ray tail of the NS 4U 0614+091. © 2010. The American Astronomical Society. All rights reserved.

Abstract:

We have searched for star-forming galaxies at z- 7-10 by applying the Lyman-break technique to newly released Y-, J- and H-band images (1.1, 1.25 and 1.6 μm) from Wide Field Camera 3 (WFC3) on the Hubble Space Telescope. By comparing these images of the Hubble Ultra Deep Field with the Advanced Camera for Surveys (ACS) z'-band (0.85 μm) images, we identify objects with red colours, (z'-Y)AB > 1.3, consistent with the Lyman α forest absorption at z≈ 6.7-8.8. We identify 12 of these z'-drops down to a limiting magnitude YAB < 28.5 (equivalent to a star formation rate of 1.3-M--yr^-1 at z= 7.1), all of which are undetected in the other ACS filters. We use the WFC3 J-band image to eliminate contaminant low-mass Galactic stars, which typically have redder colours than z≈ 7 galaxies. One of our z'-drops is probably a T-dwarf star. The z≈ 7-z'-drops appear to have much bluer spectral slopes than Lyman-break galaxies at lower redshift. Our brightest z'-drop is not present in the NICMOS J-band image of the same field taken 5 years before, and is a possible transient object. From the 10 remaining z≈ 7 candidates we determine a lower limit on the star formation rate density of 0.0017-M--yr^-1-Mpc^-3 for a Salpeter initial mass function, which rises to 0.0025-0.004-M--yr^-1-Mpc^-3 after correction for luminosity bias. The star formation rate density is a factor of ≈10 less than that of Lyman-break galaxies at z= 3-4, and is about half the value at z≈ 6. We also present the discovery of seven Y-drop objects with (Y-J)AB > 1.0 and JAB < 28.5 which are candidate star-forming galaxies at higher redshifts (z≈ 8-9). We find no robust J-drop candidates at z≈ 10. While based on a single deep field, our results suggest that this star formation rate density would produce insufficient Lyman continuum photons to reionize the Universe unless the escape fraction of these photons is extremely high (fesc > 0.5), and the clumping factor of the Universe is low. Even then, we need to invoke a large contribution from galaxies below our detection limit (a steep faint-end slope). The apparent shortfall in ionizing photons might be alleviated if stellar populations at high redshift are of low metallicity or have a top-heavy initial mass function. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg ² of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands. © 2010. The Astronomical Society of the Pacific. All rights reserved.