Hintze Centre for Astrophysical Surveys

Abstract:

Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme. © 2010 ESO.

Abstract:

To exploit synergies between the Herschel Space Observatory and next generation radio facilities, we have extended the semi-empirical extragalactic radio continuum simulation of Wilman et al. to the mid- and far-infrared. Here, we describe the assignment of infrared spectral energy distributions (SEDs) to the star-forming galaxies and active galactic nuclei, using Spitzer 24, 70 and 160 μm and SCUBA 850 μm survey results as the main constraints.Star-forming galaxies dominate the source counts, and a model in which their far-infrared-radio correlation and infrared SED assignment procedure are invariant with redshift underpredicts the observed 24 and 70 μm source counts. The 70 μm deficit can be eliminated if the star-forming galaxies undergo stronger luminosity evolution than originally assumed for the radio simulation, a requirement which may be partially ascribed to known non-linearity in the far-infrared-radio correlation at low luminosity if it evolves with redshift. At 24 μm, the shortfall is reduced if the star-forming galaxies develop SEDs with cooler dust and correspondingly stronger polycyclic aromatic hydrocarbon emission features with increasing redshift at a given far-infrared luminosity, but this trend may reverse at z > 1 in order not to overproduce the submillimetre source counts. The resulting model compares favourably with recent Balloon-borne Large Aperture Submillimetre Telescope (BLAST) results, and we have extended the simulation data base to aid the interpretation of Herschel surveys. Such comparisons may also facilitate further model refinement and revised predictions for the Square Kilometre Array and its precursors. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

SS 433 is a high-mass X-ray binary system (XRB) and one of the most persistent sources of relativistic jets in the Milky Way. The object has been intensively studied in radio at arcsecond scales, however the high-resolution observations (i.e. VLBI) are relatively scarce. In 2008 November the system was in outburst. Using the e-VLBI capabilities of the European VLBI Network (EVN) we observed SS 433 for three epochs during the active phase. The data offered a detailed view of the system’s behaviour in outburst at milliarcsecond scales. We used the “kinematic model” (which predicts the position along the jet of any knot ejected at some particular time in the past) to investigate the dynamic parameters of SS 433 and we examined the polarization properties of the ejected material. We report here the preliminary results.

Abstract:

We present the results of our search for high-redshift Lyman-break galaxies over the GOODS-South field. We use Hubble Space Telescope (HST)-ACS data in B, V, i′ & z′, Very Large Telescope (VLT)-ISAAC J and Ks, Spitzer-Infrared Array Camera (IRAC) 3.6, 4.5, 5.8 and 8.0 μm data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galaxies in the redshift range 6 < z < 9. We survey ≈119 arcmin2 to YAB = 25.7 (5σ), of which 37.5 arcmin2 reaches YAB = 25.9. Candidate z′ and Y dropouts were selected on the basis of a colour cut of (Y - J)AB > 0.75 mag and (z′ - Y)AB > 1.0 mag, respectively. We find no robust Y-drops (z ≈ 9) brighter than JAB < 25.4. In our search for z′-band dropouts (z ≈ 6.5-7.5), we identify four possible candidates, two with z′-drop colours and clear Spitzer-IRAC detections and two less likely candidates. We also identify two previously known Galactic T-dwarf stellar contaminants with these colours, and two likely transient objects seen in the Y-band data. The implications if all or none of our candidates is real on the ultraviolet galaxy luminosity functions at z > 6.5 are explored. We find our number of z′-drop candidates to be insufficient based on the expected number of z′ drops in a simple no-evolution scenario from the z = 3 Lyman-break galaxy luminosity function but we are consistent with the observed luminosity function at z ≈ 6 (if all our candidates are real). However, if one or both of our best z′-drop candidates are not z > 6.5 galaxies, this would demand evolution of the luminosity function at early epochs, in the sense that the number density of ultraviolet luminous star- forming galaxies at z > 7 is less than at z ~ 6. We show that the future surveys to be conducted with the European Southern Observatory VISTA telescope over the next 5 yr will be able to measure the bulk of the luminosity function for both z′ and Y dropouts and thus provide the strongest constraints on the level of star-formation within the epoch of reionization. © 2010 The Authors. Journal compilation. © 2010 RAS.

Abstract:

E-VLBI (electronic very long baseline interferometry) is a new implementation of the VLBI technique consisting in transferring the data from the radio telescopes to the correlator over the internet and correlating them in real-time. Time-wise this is a major improvement over the traditional method. e-VLBI is thus offering new opportunities for radio transient studies. Its capability of rapid response enables a more efficient decision making process with respect to potential followup observations. The rapid feedback time also permits to quickly modify the observing strategy to best track the development of the transient phenomena. The results summarized here have been obtained with the EVN (European VLBI Network) in the past few years within a transient ToO programme. The targets were XRBs (X-ray binaries) undergoing periods of enhanced activity (outbursts). The EVN observations were performed at 5 GHz and were often complemented by quasi-simultaneous (within one day) data at other wavelengths (X-ray and optical). The findings reveal a complex behaviour of the accretion/ejection phenomena in the systems investigated and offer insights into the extreme physics close to a compact object.