Galaxy formation and evolution

Abstract:

We present the final band-merged European Large-Area ISO Survey (ELAIS) Catalogue at 6.7, 15, 90 and 175 μm, and the associated data at U, g′, r′, i′, Z, J, H, K and 20 cm. The origin of the survey, infrared and radio observations, data-reduction and optical identifications are briefly reviewed, and a summary of the area covered and the completeness limit for each infrared band is given. A detailed discussion of the band-merging and optical association strategy is given. The total Catalogue consists of 3762 sources. 23 per cent of the 15-μm sources and 75 per cent of the 6.7-μm sources are stars. For extragalactic sources observed in three or more infrared bands, colour-colour diagrams are presented and discussed in terms of the contributing infrared populations. Spectral energy distributions (SEDs) are shown for selected sources and compared with cirrus, M82 and Arp220 starburst, and active galactic nuclei (AGN) dust torus models. Spectroscopic redshifts are tabulated, where available. For the N1 and N2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permits photometric redshifts to be estimated for galaxies and quasars. These agree well with the spectroscopic redshifts, within the uncertainty of the photometric method [∼ 10 per cent in (1 + z) for galaxies]. The redshift distribution is given for selected ELAIS bands and colour-redshift diagrams are discussed. There is a high proportion of ultraluminous infrared galaxies (log10 of 1-1000 μm luminosity Lir > 12.22) in the ELAIS Catalogue (14 per cent of 15-μm galaxies with known z), many with Arp220-like SEDs. 10 per cent of the 15-μm sources are genuine optically blank fields to r′ = 24: these must have very high infrared-to-optical ratios and probably have z > 0.6, so are high-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminous infrared galaxies (Lir > 13.22) and nine extremely red objects (EROs) (r - K > 6) are found in the survey. The latter are interpreted as ultraluminous dusty infrared galaxies at z ∼ 1. The large numbers of ultraluminous galaxies imply very strong evolution in the star formation rate between z = 0 and 1. There is also a surprisingly large population of luminous (Lir > 11.5), cool (cirrus-type SEDs) galaxies, with Lir - L opt > 0, implying Av > 1.

Abstract:

VLT J- to M\p-band adaptive optics observations of the Circinus Galaxy on parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9 $\pm$ 0.6 pc. This source is only visible at wavelengths longward of 1.6 $\mu$m and coincides in position with the peak of the [Si VII]~2.48 $\mu$m coronal line emission. With respect to the peak of the central optical emission, the source is shifted by $\sim$ 0.15\arcsec (2.8 pc) to the south-east. Indeed, it defines the vertex of a fairly collimated beam which extends for $\sim$ 10 pc, and which is seen in both continuum light shortward of 1.6 $\mu$m and in H$\alpha$ line emission. The source also lies at the center of a $\sim$ 19 pc size [Si VII] ionization {\it bicone}. Identifying this source as the nucleus of Circinus, its size is compatible with a putative parsec-scale torus. Its spectral energy distribution, characterized by a prominent narrow peak, is compatible with a dust temperature of 300 K. Hotter dust within a 1 pc radius of the center is not detected. The AGN luminosity required to heat this dust is in the range of X-ray luminosities that have been measured toward the central source. This in turn supports the existence of highly obscuring material, with column densities of $10^{24}$ cm$^{-2}$, that must be located within 1 pc of the core.

Abstract:

We have used the SAURON panoramic integral field spectrograph to study the structure of the Lyα emission-line halo, LAB1, surrounding the submillimetre galaxy SMM J221726+0013. This emission-line halo was discovered during a narrow-band imaging survey of the z = 3.1 large-scale structure in the SSA 22 region. Our observations trace the emission halo out to almost 100 kpc from the submillimetre source and identify two distinct Lyα 'mini-haloes' around the nearby Lyman-break galaxies. The main emission region has a broad line profile, with variations in the line profile seeming chaotic and lacking evidence for a coherent velocity structure. The data also suggest that Lyα emission is suppressed around the submillimetre source. Interpretation of the line structure needs care because Lyα may be resonantly scattered, leading to complex radiative transfer effects, and we suggest that the suppression in this region arises because of such effects. We compare the structure of the central emission-line halo with local counterparts, and find that the emission-line halo around NGC 1275 in the Perseus cluster may be a good local analogue, although the high-redshift halo is factor of ∼ 100 more luminous and appears to have higher velocity broadening. Around the Lyman-break galaxy C15, the emission line is narrower, and a clear shear in the emission wavelength is seen. A plausible explanation for the line profile is that the emission gas is expelled from C15 in a bipolar outflow, similar to that seen in M82.