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We present a detailed study of how the Star Formation Rate (SFR) relates to the interstellar medium (ISM) of M31 at ~140pc scales. The SFR is calculated using the far-ultraviolet and 24um emission, corrected for the old stellar population in M31. We find a global value for the SFR of 0.25+/-0.05Msun/yr and compare this with the SFR found using the total far-infrared (FIR) luminosity. There is general agreement in regions where young stars dominate the dust heating. Atomic hydrogen (HI) and molecular gas (traced by carbon monoxide, CO) or the dust mass is used to trace the total gas in the ISM. We show that the global surface densities of SFR and gas mass place M31 amongst a set of low-SFR galaxies in the plot of Kennicutt (1998b). The relationship between SFR and gas surface density is tested in six radial annuli across M31, assuming a power law relationship with index, N. The star formation law using total gas traced by HI and CO gives a global index of N=2.03+/-0.04, with a significant variation with radius; the highest values are observed in the 10kpc ring. We suggest that this slope is due to HI turning molecular at ~10Msun/pc2. When looking at H2 regions, we measure a higher mean SFR suggesting a better spatial correlation between H2 and SF. We find N~0.6 with consistent results throughout the disk - this is at the low end of values found in previous work and argues against a superlinear SF law on small scales., Comment: 12 pages, 10 figures

International audience; We empirically MD test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.060.46 with both Ha detection [from 20k redshift Cosmological Evolution (zCOSMOS) survey] and new far-IR Herschel data (100 and 160 mu m). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B - V) and LIR that allows us to estimate extinction values for each galaxy even if the H beta emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 mu m the spectral energy distribution (SED) that is best fitting our data. We compare the SFR(Ha) with the SFR(LIR). We find a very good agreement between the two star formation rate (SFR) estimates, with a slope of m = 1.01 +/- 0.03 in the log SFR(LIR) versus log SFR(Ha) diagram, a normalization constant of a = -0.08 +/- 0.03 and a dispersion of s = 0.28 dex. We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)SFR(Ha) relation, such as the redshift, the mass, the specific star formation rate (SSFR) or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by similar to 0.6 dex from metal-poor to metal-rich galaxies [8.1 \textless log?(O/H) + 12 \textless 9.2]. This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and in normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fitting slope becomes much steeper (m = 1.62 +/- 0.43), but it is still consistent with 1 at the 1.5s level, because of the reduced statistics of this sub-sample.

We present the first results of a multi-wavelength survey, incoporating Herschel-SPIRE, Spitzer, GALEX and ATCA observations, of a 1 deg x 1 deg field centred on Centaurus A. As well as detecting the inner lobes of the active galactic nucleus (AGN) jet and counterjet, we have found two clouds, bright at sub-mm wavelengths, ~15 kpc from the centre of Cen A that are co-aligned with the jets. Flux measurements at Herschel wavelengths have proved vital in constraining fits to the Spectral Energy Distributions (SEDs). The clouds are well fit by a single-temperature, modified blackbody spectrum (beta=2) indicating that we are looking at two cold dust clouds on the outskirts of Cen A. The temperature and masses of the clouds are: T_{north} = 12.6^{+1.1}_{-1.2} K, T_{south} = 15.1^{+1.7}_{-1.6} K; log(M_{north} / M_o) = 5.8^{+0.2}_{-0.2}, log(M_{south} / M_o) = 5.6^{+0.2}_{-0.2} and the gas-dust ratio for both clouds is ~100. The measured values for the northern dust cloud are consistent with previous measurements from ISO while the southern cloud is a new sub-mm detection. The two dust clouds are located at the termini of the partial HI ring that surrounds Cen A which is also where the gas column density peaks... abridged, Comment: 16 pages, 9 figures, Accepted for publication in MNRAS, author email: robbie.auld@astro.cf.ac.uk