Abstract. We present the new catalog of principal galaxies (PGC2003). It constitutes the framework of the HYPERLEDA database that supersedes the LEDA one, with more data and more capabilities. The catalog is still restricted to confirmed galaxies, i.e. about one million galaxies, brighter than ≈18 B-mag. In order to provide the best possible identification for each galaxy we give: accurate coordinates (typical accuracy better than 2 arcsec), diameter, axis ratio and position angle. Diameters and axis ratios have been homogenized to the RC2 system at the limiting surface brightness of 25B − mag arcsec −2 , using a new method, the EPIDEMIC method. In order to provide the best designation for each galaxy, we collected the names from 50 catalogues. The compatibility of the spelling is tested against NED and SIMBAD, and, as far as possible we used a spelling compatible with both. For some cases, where no consensus exists between NED, SIMBAD and LEDA, we propose some changes that could make the spelling of names fully compatible. The full catalog is distributed through the CDS and can be extracted from HYPERLEDA.

We summarize the first results from the Gould Belt Survey, obtained toward the Aquila rift and Polaris Flare regions during the science demonstration phase of Herschel. Our 70-500 μm images taken in parallel mode with the SPIRE and PACS cameras reveal a wealth of filamentary structure, as well as numerous dense cores embedded in the filaments. Between ∼350 and 500 prestellar cores and ∼45-60 Class 0 protostars can be identified in the Aquila field, while ∼300 unbound starless cores and no protostars are observed in the Polaris field. The prestellar core mass function (CMF) derived for the Aquila region bears a strong resemblance to the stellar initial mass function (IMF), already confirming the close connection between the CMF and the IMF with much better statistics than earlier studies. Comparing and contrasting our Herschel results in Aquila and Polaris, we propose an observationally-driven scenario for core formation according to which complex networks of long, thin filaments form first within molecular clouds, and then the densest filaments fragment into a number of prestellar cores via gravitational instability.

Abstract. We present submillimetre observations obtained using the balloon-borne experiment PRONAOS/SPM, from 200 to 600 µm with an angular resolution of 2-3.5 , of a quiescent dense filament (typically A V ∼ 4) in the Taurus molecular complex. This filament, like many other molecular clouds, presents a deficit in its IRAS I 60 µm /I 100 µm flux ratio in comparison with the diffuse interstellar medium. We show, from the combination of the PRONAOS/SPM and IRAS data, that, inside the filament, there is no evidence for emission from the transiently heated small particles responsible for the 60 µm emission, and that the temperature of large grains in thermal equilibrium with the radiation field is reduced in the inner parts of the filament. The temperature is as low as 12.1 +0.2 −0.1 K with β = 1.9 ± 0.2 (or 12.0 +0.2 −0.1 K using β = 2) toward the filament centre. These phenomena are responsible for the IRAS colour ratio observed toward the filament. In order to explain this cold temperature, we have developed a model for the emission from the filament using star counts from the 2MASS catalog as an independent tracer of the total column density and a radiative transfer code. We first use the optical properties of the dust from the standard model of Désert et al. (1990). The computed brightness profiles fail to reproduce the data inside the filament, showing that the dust properties change inside the filament. An agreement between data and model can be found by removing all the transiently heated particles from the densest parts of the filament, and multiplying the submillimetre emissivity by a significant factor, 3.4 +0.3 −0.7 (for typically n H > 3 ± 1 × 10 3 cm −3 , A V > 2.1 ± 0.5). We show that grain-grain coagulation into fluffy aggregates may occur inside the filament, explaining both the deficit of small grain abundance and the submillimetre emissivity enhancement of the large grains.

We report a study of the relation between dust and gas over a 100 deg 2 area in the Taurus molecular cloud. We compare the H 2 column density derived from dust extinction with the CO column density derived from the 12 CO and 13 CO J = 1 → 0 lines. We derive the visual extinction from reddening determined from 2MASS data. The comparison is done at an angular size of 200 ′′ , corresponding to 0.14 pc at a distance of 140 pc. We find that the relation between visual extinction A V and N (CO) is linear between A V ≃ 3 and 10 mag in the region associated with the B213-L1495 filament. In other regions the linear relation is flattened for A V 4 mag. We find that the presence of temperature gradients in the molecular gas affects the determination of N (CO) by ∼30-70% with the largest difference occurring at large column densities. Adding a correction for this effect and accounting for the observed relation between the column density of CO and CO 2 ices and A V , we find a linear relationship between the column of carbon monoxide and dust for observed visual extinctions up to the maximum value in our data ≃ 23 mag. We have used these data to study a sample of dense cores in Taurus. Fitting an analytical column density profile to these cores we derive an average volume density of about 1.4 × 10 4 cm −3 and a CO depletion age of about 4.2 × 10 5 years. At visual extinctions smaller than ∼3 mag, we find that the CO fractional abundance is reduced by up to two orders of magnitude. The data show a large scatter suggesting a range of physical conditions of the gas. We estimate the H 2 mass of Taurus to be about 1.5 × 10 4 M ⊙ , independently derived from the A V and N (CO) maps. We derive a CO integrated intensity to H 2 conversion factor of about 2.1×10 20 cm −2 (K km s −1 ) −1 , which applies even in the region where the [CO]/[H 2 ] ratio is reduced by up to two orders of magnitude. The distribution of column densities in our Taurus maps resembles a log-normal function but shows tails at large and low column densities. The length scale at which the high-column density tail starts to be noticeable is about 0.4 pc.

Using the 2MASS 2 nd Incremental Data Release and the Zodiacal-Subtracted Mission Average maps of COBE/DIRBE, we estimate the cosmic background in the J (1.25 µm) and K (2.2 µm) bands using selected areas representing ∼ 550 deg 2 of sky. We find a J background of 22.9 ± 7.0 kJy sr −1 (54.0 ± 16.8 nW m −2 sr −1) and a K background of 20.4 ± 4.9 kJy sr −1 (27.8 ± 6.7 nW m −2 sr −1). This large scale study shows that the main uncertainty comes from the residual zodiacal emission. The cosmic background we obtain is significantly higher than integrated galaxy counts (3.6 ± 0.8 kJy sr −1 and 5.3 ± 1.2 kJy sr −1 for J and K, respectively), suggesting either an increase of the galaxy luminosity function for magnitudes fainter than 30 or the existence of another contribution to the cosmic background from primeval stars, black holes, or relic particle decay.