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Abstract:

Lynds dark cloud LDN1622 represents one of the best examples of anomalous dust emission, possibly originating from small spinning dust grains. We present Cosmic Background Imager (CBI) 31 GHz data of LDN1621, a diffuse dark cloud to the north of LDN1622 in a region known as Orion East. A broken ring with diameter g\approx 20 arcmin of diffuse emission is detected at 31 GHz, at \approx 20-30 mJy beam$^{-1}$ with an angular resolution of \approx 5 arcmin. The ring-like structure is highly correlated with Far Infra-Red emission at $12-100 \mu$m with correlation coefficients of r \approx 0.7-0.8, significant at $\sim10\sigma$. Multi-frequency data are used to place constraints on other components of emission that could be contributing to the 31 GHz flux. An analysis of the GB6 survey maps at 4.85 GHz yields a $3\sigma$ upper limit on free-free emission of 7.2 mJy beam$^{-1}$ ($\la 30 per cent of the observed flux) at the CBI resolution. The bulk of the 31 GHz flux therefore appears to be mostly due to dust radiation. Aperture photometry, at an angular resolution of 13 arcmin and with an aperture of diameter 30 arcmin, allowed the use of IRAS maps and the {\it WMAP} 5-year W-band map at 93.5 GHz. A single modified blackbody model was fitted to the data to estimate the contribution from thermal dust, which amounts to $\sim$ 10 per cent at 31 GHz. In this model, an excess of 1.52\pm 0.66 Jy (2.3\sigma) is seen at 31 GHz. Future high frequency $\sim$ 100-1000 GHz data, such as those from the {\it Planck} satellite, are required to accurately determine the thermal dust contribution at 31 GHz. Correlations with the IRAS $100 \mu$m gave a coupling coefficient of $18.1\pm4.4 \mu$K (MJy/sr)$^{-1}$, consistent with the values found for LDN1622.

Abstract:

We use the semi-analytic model GalICS to predict the Tully-Fisher relation in the B, I and for the first time, in the K band, and its evolution with redshift, up to z~1. We refined the determination of the disk galaxies rotation velocity, with a dynamical recipe for the rotation curve, rather than a simple conversion from the total mass to maximum velocity. The new recipe takes into account the disk shape factor, and the angular momentum transfer occurring during secular evolution leading to the formation of bulges. This produces model rotation velocities that are lower by ~20-25% for the majority of the spirals. We implemented stellar population models with a complete treatment of the TP-AGB, which leads to a revision of the mass-to-light ratio in the near-IR. I/K band luminosities increase by ~0.3/0.5 mags at redshift z=0 and by ~0.5/1 mags at z=3. With these two new recipes in place, the comparison between the predicted Tully-Fisher relation with a series of datasets in the optical and near-IR, at redshifts between 0 and 1, is used as a diagnostics of the assembly and evolution of spiral galaxies in the model. At 0.4