Astronomical instrumentation

Abstract:

Evidence has been found for optical emission from the northern radio jet of 3C 31, the radio source associated with NGC 383. The jet emerges from the dust disc and ring of emission at a radius of 5 arcsec, and within 10.4 arcsec is measured to have a B-band flux of 2.1 μJy and an R-band flux of 2.3 μJy. The radio-to-optical spectral index of this region is 0.78. A second connected region, 11.8 arcsec along the jet in position angle 340°, found to have similar optical colours and radio-to-optical spectral index may also be jet emission. We combine our new data with recent radio and X-ray results to conclude that the emission of the jet is synchrotron from the radio to the X-ray.

Abstract:

We present a mid-infrared (MIR) spectroscopic survey of starburst galaxies as an example of analysis of scientifically focused samples selected from the ISO Data Archive (IDA). We use fine structure lines (FSL) ratios of Ne, Ar and S to construct diagnostic excitation diagrams and, in combination with hydrogen recombination lines (HRL), we determine their elemental abundances. For Ne and Ar, we find that excitation indicators are positively correlated with each other and negatively with abundance. On comparison with a complementary sample of galactic H II regions we find that starbursts are generally of lower excitation. Starbursts exhibiting Wolf-Rayet (WR) features are separated both in excitation and abundance from the remaining starbursts. Most surprisingly, S is found to be underabundant by a factor of ∼ 3 in our low excitation starbursts with respect to the Ne and Ar, contrary to expectations from nucleosynthesis theory. Our results are combined with those of a related sub-sample of Seyfert galaxies (Sturm et al. 2002) to derive diagnostic diagrams discriminating the two types of activity on the basis of excitation traced by MIR lines. The data presented will be useful as a reference for observations of fainter and/or higher redshift sources with future IR observatories such as SIRTF, SOFIA and Herschel.

Abstract:

As a prerequisite for cosmological studies using adaptive optics techniques, we have begun to identify and characterize faint sources in the vicinity of bright stars at high Galactic latitudes. The initial phase of this work has been a program of Ks imaging conducted with SOFI at the ESO NTT. From observations of 42 southern fields evenly divided between the spring and autumn skies, we have identified 391 additional stars and 1589 galaxies lying at separations Δθ ≤ 60″ from candidate guide stars in the magnitude range 9.0 ≤ R ≤ 12.4. When analyzed as a "discrete deep field" with 131 arcmin2 area, our dataset gives galaxy number counts that agree with those derived previously over the range 16 ≤ Ks < 20.5. This consistency indicates that in the aggregate, our fields should be suitable for future statistical studies. We provide our source catalogue as a resource for users of large telescopes in the southern hemisphere.

Abstract:

We present 7-180μm photometry of a sample of hyperluminous infrared galaxies (HyLIGs) obtained with the photometer and camera mounted on the Infrared Space Observatory (ISO). We have used state-of-the-art' radiative transfer models of obscured starbursts and dusty tori to model their broadband spectral energy distributions (SEDs). We find that IRAS F00235+1024, IRAS F14218+3845 and IRAS F15307+3252 require a combination of starburst and AGN components to explain their mid to far-infrared emission, while for TXS0052+471 a dust torus model alone is sufficient. For IRAS F00235+1024 and IRAS F14218+3845 the starburst component is the predominant contributor whereas for IRAS F15307+3252 the dust torus component dominates. The implied star formation rates (SFR) estimated from the starburst infrared luminosities are dM*,all/dt > 1000M⊙yr-1h50-2 and are amongst the highest SFRs estimated to date. We also demonstrate that the well-known radio-FIR correlation observed for extragalactic sources extends into both higher radio and infrared power than previously investigated. The relation for HyLIGs has a mean q value of 1.94. The results of this study imply that better sampling of the IR SEDs of HyLIGs may reveal that both AGN and starburst components are required to explain their emission from the NIR to the sub-millimetre.