J. I. González-Serrano

Observations of the Hubble Deep Field with the Infrared Space Observatory V. Spectral energy distributions starburst models and star formation history

We have modelled the spectral energy distributions of the 13 HDF galaxies reliably detected by ISO. For 2 galaxies the emission detected by ISO is consistent with being starlight or the infrared ’cirrus’ in the galaxies. For the remaining 11 galaxies there is a clear mid-infrared excess, which we interpret as emission from dust associated with a strong starburst. 10 of these galaxies are spirals or interacting pairs, while the remaining one is an elliptical with a prominent nucleus and broad emission lines. We give a new discussion of how the star formation rate can be deduced from the far infrared luminosity and derive star formation rates for these galaxies of 8-1000 φM⊙ per yr, where φ takes account of the uncertainty in the initial mass function. The HDF galaxies detected by ISO are clearly forming stars at a prodigious rate compared with nearby normal galaxies. We discuss the implications of our detections for the history of star and heavy element formation in the universe. Although uncertainties in the calibration, reliability of source detection, associations, and starburst models remain, it is clear that dust plays an important role in star formation out to redshift 1 at least.

Radio spectra and polarization properties of radio-loud broad absorption-line quasars

We present multi-frequency observations of a sample of 15 radio-emitting Broad Absorption Line Quasars (BAL QSOs), covering a spectral range between 74 MHz and 43 GHz. They display mostly convex radio spectra which typically peak at about 1-5 GHz (in the observer’s rest-frame), flatten at MHz frequencies, probably due to synchrotron self-absorption, and become steeper at high frequencies, i.e., ν &20 GHz. VLA 22-GHz maps (HPBW � 80 mas) show unresolved or very compact sources, with linear projected sizes of 61 kpc. About 2/3 of the sample look unpolarised or weakly polarised at 8.4 GHz, frequency in which reasonable upper limits could be obtained for polarised intensity. Statistical comparisons have been made between the spectral index distributions of samples of BAL and non-BAL QSOs, both in the observed and the rest-frame, finding steeper spectra among non-BAL QSOs. However constraining this comparison to compact sources results in no significant differences between both distributions. This comparison is consistent with BAL QSOs not being oriented along a particular line of sight. In addition, our analysis of the spectral shape, variability and polarisation properties shows that radio BAL QSOs share several properties common to young radio sources like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources.

OSIRIS tunable imager and spectrograph for the GTC. Instrument status

OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the optical Day One instrument for the 10.4m Spanish telescope GTC to be installed in the Observatorio del Roque de Los Muchachos (La Palma, Spain). This instrument, operational in mid-2004, covers from 360 up to 1000 nm. OSIRIS observing modes include direct imaging with tunable and conventional filters, long slit and multiple object spectroscopy and fast spectrophotometry. The OSIRIS wide field of view, high efficiency and the new observing modes (tunable imaging and fast spectrophotometry) for 8-10m class telescopes will provide GTC with a powerful tool for their scientific exploitation. The present paper provides an updated overview of the instrument development, of some of the scientific projects that will be tackled with OSIRIS and of the general requirements driving the optical and mechanical design.

OSIRIS tunable imager and spectrograph

The Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) will be a Day-One instrument of the Spanish 10.4 m telescope Gran Telescopio Canarias, whose first light is planned for 2002. GTC will be installed at the Observatorio del Roque de los Muchachos in La Palma, Spain. OSIRIS three primary modes are imaging and low resolution long slit and multiple object spectroscopy. The instrument is designed to operate from 365 to 1000 nm with a field of view of 7 by 7 arcminutes and a maximum spectral resolution of 5000. Among the OSIRIS main features are the use of tunable filters for direct imaging, the use of Volume Phase Holographic Gratings as dispersive elements for spectroscopy, and the implementation of an articulated camera to provide maximum spectroscopic efficiency and versatility. Here we present a general description and an overview of the main instrument characteristics.

Observations of the Hubble Deep Field with the Infrared Space Observatory - IV. Association of sources with Hubble Deep Field galaxies

We discuss the identification of sources detected by ISO at 6.7 and 15μm in the Hubble Deep Field (HDF) region. We conservatively associate ISO sources with objects in existing optical and near-infrared HDF catalogues using the likelihood ratio method, confirming these results (and, in one case, clarifying them) with independent visual searches. We find fifteen ISO sources to be reliably associated with bright [I814(AB) < 23] galaxies in the HDF, and one with an I814(AB) = 19.9 star, while a further eleven are associated with objects in the Hubble Flanking Fields (ten galaxies and one star). Amongst optically bright HDF galaxies, ISO tends to detect luminous, star-forming galaxies at fairly high redshift and with disturbed morphologies, in preference to nearby ellipticals.

The environments of luminous radio galaxies and type-2 quasars

We present the results of a comparison between the environments of (1) a complete sample of 46 southern 2-Jy radio galaxies at intermediate redshifts (0.05 <z< 0.7), (2) a complete sample of 20 radio-quiet type-2 quasars (0.3 ≤ z ≤ 0.41), and (3) a control sample of 107 quiescent early-type galaxies at 0.2 ≤ z< 0.7 in the Extended Groth Strip. The environments have been quantified using angular clustering amplitudes (Bgq) derived from deep optical imaging data. Based on these comparisons, we discuss the role of the environment in the triggering of powerful radio-loud and radio-quiet quasars. When we compare the Bgq distributions of the type-2 quasars and quiescent early-type galaxies, we find no significant difference between them. This is consistent with the radio-quiet quasar phase being a short-lived but ubiquitous stage in the formation of all massive early-type galaxies. On the other hand, powerful radio galaxies are in denser environments than the quiescent population, and this difference between distributions of Bgq is significant at the 3σ level. This result supports a physical origin of radio loudness, with high-density gas environments favouring the transformation of active galactic nucleus (AGN) power into radio luminosity, or alternatively, affecting the properties of the supermassive black holes themselves. Finally, focusing on the radio-loud sources only, we find that the clustering of weak-line radio galaxies (WLRGs) is higher than the strong-line radio galaxies (SLRGs), constituting a 3σ result. 82 per cent of the 2-Jy WLRGs are in clusters, according to our definition (Bgq 400), versus only 31 per cent of the SLRGs.

Observations of the Hubble Deep Field with the Infrared Space Observatory - I. Data reduction, maps and sky coverage

We present deep imaging at 6.7 micron and 15 micron from the CAM instrument on the Infrared Space Observatory (ISO), centred on the Hubble Deep Field (HDF). These are the deepest integrations published to date at these wavelengths in any region of sky. We discuss the observation strategy and the data reduction. The observed source density appears to approach the CAM confusion limit at 15 micron, and fluctuations in the 6.7 micron sky background may be identifiable with similar spatial fluctuations in the HDF galaxy counts. ISO appears to be detecting comparable field galaxy populations to the HDF, and our data yields strong evidence that future IR missions (such as SIRTF, FIRST and WIRE) as well as SCUBA and millimetre arrays will easily detect field galaxies out to comparably high redshifts.

Red quasars not so dusty

Webster et al (1995) claimed that up to 80% of QSOs may be obscured by dust. They inferred the presence of this dust from the remarkably broad range of B-K optical-infrared colours of a sample of flat-spectrum PKS radio QSOs. If such dust is typical of QSOs, it will have rendered invisible most of those which would otherwise been have detected by optical surveys. We used the William Herschel Telescope to image 54 B3 radio QSOs in K, and we find that although several have very red optical-infrared colours, most of these can be attributed to an excess of light in K rather than a dust-induced deficit in B. We present evidence that the infrared excess comes from the light of stars in the host galaxy, or from synchrotron radiation associated with flat-spectrum radio sources. Thus, either the Webster et al QSOs are atypical in having large extinctions, or their reddening is not due to dust. Either way, there is no evidence that a large fraction of QSOs has been missed by optical surveys. This work is reported in more detail in Benn et al (1997).

Probing the nuclear and circumnuclear activity of NGC 1365 in the infrared

This development has been supported by the funding agencies BMVIT (Austria), ESA-PRODEX (Belgium), CEA/CNES (France), DLR (Germany), ASI/INAF (Italy) and CICYT/MCYT (Spain). SPIRE has been developed by a consortium of institutes led by Cardiff Univ. (UK) and including Univ. Lethbridge (Canada); NAOC (China); CEA, LAM (France); IFSI, Univ. Padua (Italy); IAC (Spain); Stockholm Observatory (Sweden); Imperial College London, RAL, UCL-MSSL, UKATC, Univ. Sussex (UK); and Caltech, JPL, NHSC, Univ. Colorado (USA). This development has been supported by national funding agencies: CSA (Canada); NAOC (China); CEA, CNES, CNRS (France); ASI (Italy); MCINN (Spain); SNSB (Sweden); STFC, UKSA (UK); and NASA (USA).

INTEGRAL FIELD SPECTROSCOPY OF THE CENTRAL REGIONS OF 3C 120: EVIDENCE OF A PAST MERGING EVENT

Optical integral field spectroscopy (IFS), combined with Hubble Space Telescope (HST) WFPC imaging, was used to characterize the central regions of the Seyfert 1 radio galaxy 3C 120. We carried out the analysis of the data, deriving intensity maps of different emission lines and the continua at different wavelengths from the observed spectra. Applying a two-dimensional modeling to the HST images, we decoupled the nucleus and the host galaxy and analyzed the host morphology. The host is a highly distorted bulge-dominated galaxy, rich in substructures. We developed a new technique to model the IFS data extending the two-dimensional modeling (hereafter three-dimensional modeling). Using this technique, we separated the Seyfert nucleus and the host galaxy spectra and derived a residual data cube with spectral and spatial information of the different structures in 3C 120. Three continuum-dominated structures (named A, B, and C) and three other extended emission-line regions (EELRs, named E1, E2, and E3) are found in 3C 120, which does not follow the general behavior of a bulge-dominated galaxy. We also found shells in the central kiloparsec that may be remnants of a past merging event in this galaxy. The origin of E1 is most probably due to the interaction of the radio jet of 3C 120 with the intergalactic medium (Axon et al. 1989; Sanchez et al. 2004a). Structures A, B, and the shell at the southeast of the nucleus seem to correspond to a larger morphological clumpy structure that may be a tidal tail, a consequence of the past merging event. We found a bright EELR (E2) in the innermost part of this tidal tail, nearby the nucleus, which shows a high ionization level. The kinematics of the E2 region and its connection to the tidal tail suggest that the tail has channeled gas from the outer regions to the center.