The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel Characterizing UV-irradiated shocks heating and chemistry

We present the first complete similar to 55-671 mu m spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers onboard Herschel. More than 145 lines have been detected, most of them rotationally excited lines of (CO)-C-12 (full ladder from J(u) = 4-3 to 42-41 and E-u/k = 4971 K), H2O (up to 8(18)-7(07) and E-u/k = 1036 K), OH (up to (2)Pi(1/2) J = 7/2-5/2 and E-u/k = 618 K), (CO)-C-13 (up to J(u) = 16-15), HCN and HCO+ (up to J(u) = 12-11). Bright [OI] 63, 145 mu m and weaker [C II] 158 and [C I] 370, 609 mu m lines are also detected, but excited lines from chemically related species (NH3, CH+, CO+, OH+ or H2O+) are not. Mid-infrared spectra retrieved from the Spitzer archive are also first discussed here. The similar to 10-37 mu m spectrum has many fewer lines, but shows clear detections of [Ne II], [Fe II], [Si II] and [Si] fine structure lines, as well as weaker H-2 S(1) and S(2) pure rotational lines. The observed line luminosity is dominated by CO (similar to 54%), H2O (similar to 22%), [OI] (similar to 12%) and OH (similar to 9%) emission. A multi-component radiative transfer model allowed us to approximately quantify the contribution of the three different temperature components suggested by the (CO)-C-12 rotational ladder (T-k(hot) approximate to 800 K, T-k(warm) approximate to 375 K and T-k(cool) approximate to 150 K). Gas densities n(H-2) greater than or similar to 5 x 10(6) cm(-3) are needed to reproduce the observed far-IR lines arising from shocks in the inner protostellar envelope (warm and hot components) for which we derive upper limit abundances of x(CO) less than or similar to 10(-4), x(H2O) less than or similar to 0.2 x 10(-5) and x(OH) less than or similar to 10(-6) with respect to H-2. The lower energy submm (CO)-C-12 and H2O lines show more extended emission that we associate with the cool entrained outflow gas. Fast dissociative J-shocks (v(s) > 60 km s(-1)) within an embedded atomic jet, as well as lower velocity small-scale non-dissociative shocks (vs less than or similar to 20 km s(-1)) are needed to explain both the atomic fine structure lines and the hot CO and H2O lines respectively. Observations also show the signature of UV radiation (weak [C II] and [C I] lines and high HCO+/HCN abundance ratios) and thus, most observed species likely arise in UV-irradiated shocks. Dissociative J-shocks produced by a jet impacting the ambient material are the most probable origin of [OI] and OH emission and of a significant fraction of the warm CO emission. In addition, H2O photodissociation in UV-irradiated non-dissociative shocks along the outflow cavity walls can also contribute to the [OI] and OH emission.