We present the deepest 100 to 500 μm far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3–500 μm spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer, and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes. We find that the ratio of total IR luminosity to rest-frame 8 μm luminosity, IR8 (≡ L IR tot), follows a Gaussian distribution centered on IR8 = 4 (σ = 1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population (<20%) is shown to consist of starbursts with compact projected star formation densities. IR8 can be used to separate galaxies with normal and extended modes of star formation from compact starbursts with high–IR8, high projected IR surface brightness (ΣIR > 3 × 1010 L ⊙ kpc-2) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 Å size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample. Locally, luminous and ultraluminous IR galaxies, (U)LIRGs (L IR tot), are systematically in the starburst mode, whereas most distant (U)LIRGs form stars in the “normal” main sequence mode. This confusion between two modes of star formation is the cause of the so-called “mid-IR excess” population of galaxies found at z > 1.5 by previous studies. Main sequence galaxies have strong polycyclic aromatic hydrocarbon (PAH) emission line features, a broad far-IR bump resulting from a combination of dust temperatures (T dust ~ 15–50 K), and an effective T dust ~ 31 K, as derived from the peak wavelength of their infrared SED. Galaxies in the starburst regime instead exhibit weak PAH equivalent widths and a sharper far-IR bump with an effective T dust ~ 40 K. Finally, we present evidence that the mid-to-far IR emission of X-ray active galactic nuclei (AGN) is predominantly produced by star formation and that candidate dusty AGNs with a power-law emission in the mid-IR systematically occur in compact, dusty starbursts. After correcting for the effect of starbursts on IR8, we identify new candidates for extremely obscured AGNs.

We present integral field unit observations covering the [O iii]λλ4959, 5007 and Hβ emission lines of 16 z < 0.2 type 2 active galactic nuclei (AGN). Our targets are selected from a well-constrained parent sample of ≈24 000 AGN so that we can place our observations into the context of the overall AGN population. Our targets are radio quiet with star formation rates (SFRs; ≲[10–100] M_⊙ yr⁻¹) that are consistent with normal star-forming galaxies. We decouple the kinematics of galaxy dynamics and mergers from outflows. We find high-velocity ionized gas (velocity widths ≈600–1500 km s⁻¹; maximum velocities ≤1700 km s⁻¹) with observed spatial extents of ≳(6–16) kpc in all targets and observe signatures of spherical outflows and bi-polar superbubbles. We show that our targets are representative of z < 0.2, luminous (i.e. L_[O iii] > 10^41.7 erg s⁻¹) type 2 AGN and that ionized outflows are not only common but also in ≥70 per cent (3σ confidence) of cases, they are extended over kiloparsec scales. Our study demonstrates that galaxy-wide energetic outflows are not confined to the most extreme star-forming galaxies or radio-luminous AGN; however, there may be a higher incidence of the most extreme outflow velocities in quasars hosted in ultraluminous infrared galaxies. Both star formation and AGN activity appear to be energetically viable to drive the outflows and we find no definitive evidence that favours one process over the other. Although highly uncertain, we derive mass outflow rates (typically ≈10 times the SFRs), kinetic energies (≈0.5–10 per cent of L_AGN) and momentum rates (typically ≳10–20 × L_AGN/c) consistent with theoretical models that predict AGN-driven outflows play a significant role in shaping the evolution of galaxies.

We use infrared spectroscopy and photometry to empirically define the intrinsic mid- to far-infrared spectral energy distribution (i.e. 6–100 μm SED)

Using a sample of 24 264 optically selected active galactic nuclei (AGNs) from the SDSS DR7 data base, we characterize how the profile of the [O iii] λ5007 emission line relates to bolometric luminosity (L_AGN), Eddington ratio, radio loudness, radio luminosity (L_1.4 GHz) and optical class (i.e. broad/narrow-line Seyfert 1, type 2) to determine what drives the kinematics of this kpc-scale line emitting gas. First, we use spectral stacking to characterize how the average [O iii] λ5007 profile changes as a function of these five variables. After accounting for the known correlation between L_AGN and L_1.4 GHz, we report that L_1.4 GHz has the strongest influence on the [O iii] λ5007 profile, with AGNs of moderate radio luminosity (L_1.4 GHz = 10²³–10²⁵ W Hz⁻¹) having the broadest [O iii] λ5007 profiles. Conversely, we find only a modest change in the [O iii] λ5007 profile with increasing radio loudness and find no significant difference between the [O iii] λ5007 profiles of broad- and narrow-line Seyfert 1s. When binned according to Eddington ratio, only the AGNs in our highest bin (i.e. >0.3) show any signs of having broadened [O iii] λ5007 profiles, although the small numbers of such extreme AGNs in our sample mean we cannot rule out that other processes (e.g. radio jets) are responsible for this broadening. The [O iii] λ5007 profiles of type 1 and type 2 AGNs show the same trends in terms of line width, but type 1 AGNs display a much stronger ‘blue wing’, which we interpret as evidence of outflowing ionized gas. We perform multicomponent fitting to the Hβ, [O iii] λλ4959, 5007, [N ii] λλ6548, 6584 and Hα lines for all the AGNs in our sample to calculate the proportions of AGNs with broad [O iii] λ5007 profiles. The individual fits confirm the results from our stacked spectra; AGNs with L_1.4 GHz > 10²³ W Hz⁻¹ are roughly five times more likely to have extremely broad [O iii] λ5007 lines (full width at half-maximum, FWHM_Avg > 1000 km s⁻¹) compared to lower L_1.4 GHz AGNs, and the width of the [O iii] λ5007 line peaks in moderate-radio-luminosity AGNs (L_1.4 GHz ∼ 10²⁴ W Hz⁻¹). Our results are consistent with the most disturbed gas kinematics being induced by compact radio cores (rather than powerful radio jets), although broadened [O iii] λ5007 lines are also present, but much rarer, in low-L_1.4 GHz systems. Our catalogue of multicomponent fits is freely available as an online resource for statistical studies of the kinematics and luminosities of the narrow- and broad-line AGN regions and the identification of potential targets for follow-up observations at http://sites.google.com/site/sdssalpaka.