The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands

Observations have shown that passively evolving massive galaxies at high redshift are much more compact than local galaxies with the same stellar mass. We argue that the observed strong evolution in size is directly related to the quasar feedback, which removes huge amounts of cold gas from the central regions in a Salpeter time, inducing an expansion of the stellar distribution. The new equilibrium configuration, with a size increased by a factor տ3, is attained after ∼40 dynamical times, corresponding to ∼2 Gyr. This means that massive galaxies observed at will settle on the fundamental plane by -1. In less massive galaxies ( ), the nuclear 10 z ≥ 1 z ∼ 0.8 M Շ 2 # 10 M , feedback is subdominant, and the mass loss is mainly due to stellar winds. In this case, the mass-loss timescale is longer than the dynamical time and results in adiabatic expansion that may increase the effective radius by a factor of up to ∼2 in 10 Gyr, although a growth by a factor of Ӎ1.6 occurs within the first 0.5 Gyr. Since observations are focused on relatively old galaxies, with ages տ1 Gyr, the evolution for smaller galaxies is more difficult to perceive. Significant evolution of velocity dispersion is predicted for both small and large galaxies.

Exploiting the H-ATLAS Science Demonstration Phase (SDP) survey data, we have determined the luminosity functions (LFs) at rest-frame wavelengths of 100 and 250 µm and at several redshifts z 1, for bright sub-mm galaxies with star formation rates (SFR) 100 M ⊙ yr −1 . We find that the evolution of the comoving LF is strong up to z ≈ 2.5, and slows down at higher redshifts. From the LFs and the information on halo masses inferred from clustering analysis, we derived an average relation between SFR and halo mass (and its scatter). We also infer that the timescale of the main episode of dust-enshrouded star formation in massive halos (M H 3 × 10 12 M ⊙ ) amounts to ∼ 7 × 10 8 yr. Given the SFRs, which are in the range 10 2 − 10 3 M ⊙ yr −1 , this timescale implies final stellar masses of order of 10 11 − 10 12 M ⊙ . The corresponding stellar mass function matches the observed mass function of passively evolving galaxies at z 1. The comparison of the statistics for sub-mm and UV selected galaxies suggests that the dust-free, UV bright phase, is 10 2 times shorter than the sub-mm bright phase, implying that the dust must form soon after the onset of star formation. Using a single reference Spectral Energy Distribution (SED; the one of the z ≈ 2.3 galaxy SMM J2135-0102), our simple physical model is able to reproduce not only the LFs at different redshifts > 1 but also the counts at wavelengths ranging from 250 µm to ≈ 1 mm. Owing to the steepness of the counts and their relatively broad frequency range, this result suggests that the dispersion of sub-mm SEDs of z > 1 galaxies around the reference one is rather small.

Massive (stellar mass M ⋆ 3 × 10 10 M ⊙ ), passively evolving galaxies at redshifts z 1 exhibit on the average physical sizes smaller by factors ≈ 3 than local early type galaxies (ETGs) endowed with the same stellar mass. Small sizes are in fact expected on theoretical grounds, if dissipative collapse occurs. Recent results show that the size evolution at z 1 is limited to less than 40%, while most of the evolution occurs at z 1, where both compact and already extended galaxies are observed and the scatter in size is remarkably larger than locally. The presence at high redshift of a significant number of ETGs with the same size as their local counterparts as well as of ETGs with quite small size ( 1/10 of the local one), points to a timescale to reach the new, expanded equilibrium configuration of less than the Hubble time t H (z). We demonstrate that the projected mass of compact, high redshift galaxies and that of local ETGs within the same physical radius, the nominal half−luminosity radius of high redshift ETGs, differ substantially, in that the high redshift ETGs are on the average significantly denser. This result suggests that the physical mechanism responsible for the size increase should also remove mass from central galaxy regions (r 1 kpc). We propose that quasar activity, which peaks at redshift z ∼ 2, can remove large amounts of gas from central galaxy regions on a timescale shorter than, or of order of the dynamical one, triggering a puffing up of the stellar component at constant stellar mass; in this case the size increase goes together with a decrease of the central mass. The size evolution is expected to parallel that of the quasars and the inverse hierarchy, or downsizing, seen in the quasar evolution is mirrored in the size evolution. Exploiting the virial theorem, we derive the relation between the stellar velocity dispersion of ETGs and the characteristic velocity of their hosting halos at the time of formation and collapse. By combining this relation with the halo formation rate at z 1 we predict the local velocity dispersion distribution function. On comparing it to the observed one, we show that velocity dispersion evolution of massive ETGs is fully compatible with the observed average evolution in size at constant stellar mass. Less massive ETGs (with stellar masses M ⋆ 3 × 10 10 M ⊙ ) are expected to evolve less both in size and in velocity dispersion, because their evolution is ruled essentially by supernova feedback, which cannot yield winds as powerful as those triggered by quasars. The differential evolution is expected to leave imprints in the size vs. luminosity/mass, velocity dispersion vs. luminosity/mass, central black hole mass vs. velocity dispersion relationships, as observed in local ETGs.

While the selection of strongly lensed galaxies with 500µm flux density S 500 > 100 mJy has proven to be rather straightforward (Negrello et al. 2010), for many applications it is important to analyze samples larger than the ones obtained when confining ourselves to such a bright limit. Moreover, only by probing to fainter flux densities is possible to exploit strong lensing to investigate the bulk of the high-z star-forming galaxy population. We describe HALOS (the Herschel -ATLAS Lensed Objects Selection), a method for efficiently selecting fainter candidate strongly lensed galaxies, reaching a surface density of ≃ 1.5-2 deg −2 , i.e. a factor of about 4 to 6 higher than that at the 100 mJy flux limit. HALOS will allow the selection of up to ∼ 1000 candidate strongly lensed galaxies (with amplifications µ 2) over the full H-ATLAS survey area. Applying HALOS to the H-ATLAS Science Demonstration Phase (SDP) field (≃ 14.4 deg 2 ) we find 31 candidate strongly lensed galaxies, whose candidate lenses are identified in the VIKING near-infrared catalog. Using the available information on candidate sources and candidate lenses we tentatively estimate a ≃ 72% purity of the sample. As expected, the purity decreases with decreasing flux density of the sources and with increasing angular separation between candidate sources and lenses. The redshift distribution of the candidate lensed sources is close to that reported for most previous surveys for lensed galaxies, while that of candidate lenses extends to substantially higher redshifts than found in the other surveys. The counts of candidate strongly lensed galaxies are also in good agreement with model predictions (Lapi et al. 2011). Even though a key ingredient of the method is the deep near-infrared VIKING photometry, we show that H-ATLAS data alone allow the selection of a similarly deep sample of candidate strongly lensed galaxies with an efficiency close to 50%; a slightly lower surface density (≃ 1.45 deg −2 ) can be reached with a ∼ 70% efficiency.

We build a large sample of Seyfert 2 galaxies (Sy2s) with both optical spectropolarimetric and X-ray data available, in which 29 Sy2s with the detection of polarized broad emission line (PBL) and 25 without. We find that for luminous Sy2s with L [O III] > 10 41 erg s −1 , sources with PBL have smaller X-ray absorption column density comparing with those without PBL (at 92.3% confidence level): most of the Sy2s with N H <10 23.8 cm −2 show PBL (86%, 12 out 14), while the fraction is much smaller for sources with heavier obscuration (54%, 15 out 28). The confidence level of the difference in absorption bounces up to 99.1% while using the "T" ratio (F 2−10 keV /F [O III] ) as an indicator. We rule out observation or selection bias as the origin for the difference. Our results, for the first time with high statistical confidence, show that, in additional to the nuclei activity, the nuclear obscuration also plays an important role in the visibility of PBL in Sy2s. These results can be interpreted in the framework of the unified model. We can reach these results in the unified model if: a) the absorption column density is higher at large inclinations and b) the scattering region is obscured at large inclinations.

We compile a large sample of broad absorption lines (BAL) quasars with X-ray observations from the XMM-Newton archive data and Sloan Digital Sky Survey Data Release 5. The sample consists of 41 BAL QSOs. Among 26 BAL quasars detected in X-ray, spectral analysis is possible for twelve objects. X-ray absorption is detected in all of them. Complementary to that of Gallagher et al. (2006) (thereafter G06), our sample spans wide ranges of both BALnicity Index (BI) and maximum outflow velocity (v max ). Combining our sample with G06's, we find very significant correlations between the intrinsic X-ray weakness with both BALnicity Index (BI) and the maximum velocity of absorption trough. We do not confirm the previous claimed correlation between absorption column density and broad absorption line parameters. We tentatively interpret this as that X-ray absorption is necessary to the production of the BAL outflow, but the properties of the outflow are largely determined by intrinsic SED of the quasars.

We report the discovery of a dwarf Seyfert 1 active galactic nucleus (AGN) with a candidate intermediate-mass black hole hosted by the dwarf galaxy SDSS J160531.84+174826.1 at z = 0.032. A broad component of the Hα line with FWHM=781km s −1 is detected in its optical spectrum, and a bright, point-like nucleus is evident from a HST imaging observation. Non-thermal X-ray emission is also detected from the nucleus. The black hole mass, as estimated from the luminosity and width of the broad Hα component, is about 7 × 10 4 M ⊙ . The host galaxy appears to be a disk galaxy with a boxy bulge or nuclear bar; with an absolute magnitude of M R = −17.8, it is among the least luminous host galaxies ever identified for a Seyfert 1.