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Context. Extragalactic surveys are a key tool for better understanding the evolution of galaxies. Both deep and wide-field surveys serve to provide a clearer emerging picture of the physical processes that take place in and around galaxies, and to identify which of these processes are the most important in shaping the properties of galaxies. Aims. The Lockman Spectroscopic Redshift Survey using Osiris (Lockman-SpReSO) aims to provide one of the most complete optical spectroscopic follow-ups of the far-infrared (FIR) sources detected by the \textit{Herschel} Space Observatory in the Lockman Hole (LH) field. The optical spectroscopic study of the FIR-selected galaxies supplies valuable information about the relation between fundamental FIR and optical parameters, including extinction, star formation rate, and gas metallicity. In this article, we introduce and provide an in-depth description of the Lockman-SpReSO project and of its early results. Methods. We selected FIR sources from \textit{Herschel} observations of the central 24 arcmin $\times$ 24 arcmin of the LH field with an optical counterpart up to 24.5 $R_{\rm C}$(AB). The sample comprises 956 \textit{Herschel} FIR sources, plus 188 additional interesting objects in the field. These are point X-ray sources, cataclysmic variable star candidates, high-velocity halo star candidates, radio sources, very red quasi-stellar objects, and optical counterparts of sub-millimetre galaxies. The faint component of the catalogue ($R_{\rm C}(\mathrm{AB})\geq20$) was observed using the OSIRIS instrument on the 10.4 m Gran Telescopio Canarias in multi-object spectroscopy (MOS) mode. The bright component was observed using two multi-fibre spectrographs: the AF2-WYFFOS at the William Herschel Telescope and the HYDRA instrument at the WYIN telescope., Comment: 22 pages, 12 figures

Off-centered spots of the enhanced gas velocity dispersion, s, are revealed in some galaxies from the MaNGA survey. Aiming to clarify the origin of the spots of enhanced s, we examine the distributions of the surface brightness, the line-of-sight velocity, the oxygen abundance, the gas velocity dispersion, and the BPT spaxel classification in seven galaxies. We find that the enhanced s spots in six galaxies can be attributed to a (minor) interaction with a satellite. Three galaxies in our sample have a very close satellite. The spots of enhanced s in those galaxies are located at the edge of the galaxy close to the satellite. The spots of enhanced s in three other galaxies are related to bright spots in the photometric B band within the galaxy, which can be due to the projection of a satellite in the line of sight of the galaxy. The oxygen abundances in the spots in these three galaxies are reduced. This suggests that the low-metallicity gas from the satellite is mixed with the interstellar medium of the disk. The spectra of the spaxels within a spot are usually HII-region-like, suggesting that the interaction in those galaxies does not result in appreciable shocks. In contrast, the spot of the enhanced s in the galaxy M-8716-12703 is associated with an off-centered AGN-like radiation distribution. One can suggest that the spot of the enhanced s in the M-8716-12703 galaxy is different in origin, or that the characteristics of gas infall in this case differs from that in other galaxies., Comment: 25 pages, 22 figures, accepted to AA

HII regions in the arms of spiral galaxies are indicators of recent star-forming processes. They may have been caused by the passage of the density wave or simply created by other means near the arms. The study of these regions may give us clues to clarifying the controversy over the existence of a triggering scenario, as proposed in the density wave theory. Using H$\alpha$ direct imaging, we characterize the HII regions from a sample of three grand design galaxies: NGC5457, NGC628 and NGC6946. Broad band images in R and I were used to determine the position of the arms. The HII regions found to be associated with arms were selected for the study. The age and the star formation rate of these HII regions was obtained using measures on the H$\alpha$ line. The distance between the current position of the selected HII regions and the position they would have if they had been created in the centre of the arm is calculated. A parameter, T, which measures whether a region was created in the arm or in the disc, is defined. With the help of the T parameter we determine that the majority of regions were formed some time after the passage of the density wave, with the regions located `behind the arm' (in the direction of the rotation of the galaxy) the zone they should have occupied had they been formed in the centre of the arm. The presence of the large number of regions created after the passage of the arm may be explained by the effect of the density wave, which helps to create the star-forming regions after its passage. There is clear evidence of triggering for NGC5457 and a co-rotation radius is proposed. A more modest triggering seems to exist for NGC628 and non significant evidence of triggering are found for NGC6946., Comment: 10 pages, 20 figures, accepted for publication in A&A

We report the PACS-100um/160um detections of a sample of 42 GALEX-selected and FIR-detected Lyman break galaxies (LBGs) at z ~ 1 located in the COSMOS field and analyze their ultra-violet (UV) to far-infrared (FIR) properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger, more massive, dustier, redder in the UV continuum, and UV-brighter than PACS-undetected LBGs. PACS-detected LBGs at z ~ 1 are mostly disk-like galaxies and are located over the green-valley and red sequence of the color-magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star-formation rates (SFRs) than other PACS-detected UV-selected galaxies within their same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs are LIRGs. However, none of them are in the ULIRG regime, where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX-$\beta$ diagram, PACS-detected LBGs at z ~ 1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at their same redshift. Consequently, the dust-correction factors obtained with their UV continuum slope allow to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in age-dependent way: the overestimation factor is higher in younger galaxies., Comment: Accepted for publication in MNRAS

Lyman break galaxies (LBGs) represent one of the kinds of star-forming galaxies that are found in the high-redshift universe. The detection of LBGs in the FIR domain can provide very important clues on their dust attenuation and total SFR, allowing a more detailed study than those performed so far. In this work we explore the FIR emission of a sample of 16 LBGs at z ~ 3 in the GOODS-North and GOODS-South fields that are individually detected in PACS-100um or PACS-160um. These detections demonstrate the possibility of measuring the dust emission of LBGs at high redshift. We find that PACS-detected LBGs at z ~ 3 are highly obscured galaxies which belong to the Ultra luminous IR galaxies or Hyper luminous IR galaxies class. Their total SFR cannot be recovered with the dust attenuation factors obtained from their UV continuum slope or their SED-derived dust attenuation employing Bruzual & Charlot (2003) templates. Both methods underestimate the results for most of the galaxies. Comparing with a sample of PACS-detected LBGs at z ~ 1 we find evidences that the FIR emission of LBGs might have changed with redshift in the sense that the dustiest LBGs found at z ~ 3 have more prominent FIR emission, are dustier for a given UV slope, and have higher SFR for a given stellar mass than the dustiest LBGs found at z ~ 1., Comment: Accepted for publication in A&A letters

Using the OSIRIS tunable narrow band imager on the 10.4m GTC (La Palma) we have mapped the SAB(rs)cd galaxy NGC 6946 over a 7.3x7.5 square arcminutes field in the emission lines of the [SII]\lambda\lambda, 6717, 6731 doublet, and in H\alpha. From these maps we have produced catalogs of the H\alpha luminosities and effective radii of 557 HII regions across the disk, and derived the [SII] emission line ratios of 370 of these. The H\alpha observations were used to derive the mean luminosity-weighted electron densities for the regions of the sample, while the [SII] line ratios allowed us to derive values of the in situ electron densities in the denser zones from which the major fraction of the radiation in these lines is emitted, for 58 of the regions. This is by far the largest data set of its kind for a single galaxy. A classical two phase model is used to derive the filling factors of the regions. We find that although the mean electron density decreases with the square root of the radius of the regions, the in situ density is essentially independent of this radius. Thus the filling factor falls systematically, as the radius and the luminosity of the regions increases, with a power law of exponent -2.23 between filling factor and radius. These measurements should enhance the perspectives for more refined physical models of HII regions., Comment: 10 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters

With the aim of investigating galaxies with two strong simultaneous starbursts, we have extracted a sample of galaxies with double-peaked emission lines in their global spectra from the SDSS spectral database. We then fitted the emission lines Halpha, Hbeta, [OIII]5007, [NII]6584, [SII]6717 and [SII]6731 of 129 spectra by two Gaussians to separate the radiation of the two (blue and red) components. A more or less reliable decomposition of the all those emission lines have been found for 55 spectra. Using a standard BPT classification diagram, we have been able to divide the galaxies from our sample into two subsamples: Sample A consisting of 18 galaxies where both components belong to the photoionised class of objects, and Sample B containing 37 galaxies which show non-thermal ionisation (AGNs). We have examined the properties of the blue and red components, and found that the differences between radial velocities of components lie within 200 - 400 km/s for galaxies of both subsamples. The equivalent number of ionising stars is in the range 10^4 - 10^5 O7V stars for each component in the galaxies of Sample A. We have estimated the oxygen and nitrogen abundances as well as the electron temperatures for each component using the recent NS-calibration and from global spectra for galaxies from Sample A using both the NS and ON-calibration. We have found that the global oxygen abundance is typically in between the measured abundances of individual components for our sample of galaxies, and that both calibrations provide consistent global abundances. Finally, we suggest the classical O/H -- N/O diagram is used to test the reliability of the dividing lines between starburst-like objects and AGNs in the so-called BPT diagram., Comment: 13 pages, 13 figures, 1 table, accepted for publication in MNRAS

We study the spatial distribution of the physical properties and of oxygen and nitrogen abundances in three Blue Compact Dwarf Galaxiess (HS 0128+2832, HS 0837+4717 and Mrk 930) with a reported excess of N/O in order to investigate the nature of this excess and, particularly, if it is associated with Wolf-Rayet (WR) stars We have observed these BCDs by using PMAS integral field spectroscopy in the optical spectral range (3700 - 6900 {\AA}), mapping their physical-chemical properties, using both the direct method and appropriate strong-line methods. We make a statistical analysis of the resulting distributions and we compare them with the integrated properties of the galaxies. Our results indicate that outer parts of the three galaxies are placed on the "AGN-zone" of the [NII]/H{\alpha} vs. [OIII]/H{\beta} diagnostic diagram most likely due to a high N/O combined with the excitation structure in these regions. From the statistical analysis, it is assumed that a certain property can be considered as spatially homogeneous (or uniform) if a normal gaussian function fits its distribution in several regions of the galaxy. Moreover, a disagreement between the integrated properties and the mean values of the distribution usually appears when a gaussian does not fit the corresponding distribution. We find that for Mrk 930, the uniformity is found for all parameters, except for electron density and reddening. The rotation curve together with the H{\alpha} map and UV images, reveal a perturbed morphology and possible interacting processes. The N/O is found to be constant in the three studied objects at spatial scales of the order of several kpc so we conclude that the number of WR stars estimated from spectroscopy is not sufficient to pollute the ISM and to produce the observed N/O excess in these objects, Comment: 17 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

Spatially resolved spectroscopy has been obtained for a sample of 27 star-forming (SF) galaxies selected from our deep Halpha survey of the Hercules cluster. We have applied spectral synthesis models to all emission-line spectra of this sample using the population synthesis code STARLIGHT. We have obtained fundamental parameters of the stellar components, as the mean metallicity and age, and we have corrected the emission-line spectra for underlying stellar absorption. O/H and N/O gas chemical abundances were obtained using the latest empirical calibrations. The effects of cluster environment on the chemical evolution of galaxies and on their mass-metallicity (MZ) and luminosity-metallicity (LZ) relations were studied combining the derived gas metallicities, the mean stellar metallicities and ages, the masses and luminosities of galaxies and their existing HI data. We have found that our Hercules SF galaxies divide into three main subgroups: a) chemically evolved spirals with truncated ionized-gas disks and nearly flat oxygen gradients, witnessing the effect of ram-pressure stripping, b) chemically evolved dwarfs/irregulars populating the highest local densities, possible products of tidal interactions in preprocessing events, or c) less metallic dwarf galaxies which appear to be "newcomers" to the cluster, experiencing pressure-triggered star-formation. Most Hercules SF galaxies follow well defined MZ and LZ sequences (for both O/H and N/O); though the dwarf/irregular galaxies located at the densest regions appear to be outliers to these global relations, suggesting a physical reason for the dispersion in these fundamental relations. The Hercules cluster appears to be currently assembling via the merger of smaller substructures, providing an ideal laboratory where the local environment has been found to be a key parameter to understand the chemical history of galaxies., Comment: 49 pages, 18 figures

Spectra of high-metallicity (12+log(O/H) > 8.2) HII regions where oxygen auroral lines are measurable in both the O+ and O++ zones, have been extracted from the Data Release 6 of the Sloan Digital Sky Survey (SDSS). Our final sample consists of 181 SDSS spectra of HII regions in galaxies in the redshift range from ~0.025 to ~0.17. The t_2,O-t_3,O diagram is examined. In the SDSS HII regions, the electron temperature t_2,O is found to have a large scatter at a given value of the electron temperature t_3,O. The majority of the SDSS HII regions lie below the t_2,O-t_3,O relation derived for HII regions in nearby galaxies, i.e. the positions of the SDSS HII regions show a systematic shift towards lower t_2,O temperatures or/and towards higher t_3,O temperatures. The scatter and shift of the SDSS HII regions in the t_2,O-t_3,O diagram can be understood if they are composite nebulae excited by two or more ionizing sources of different temperatures., Comment: 14 pages, 11 figures accepted for publication in the MNRAS

This paper presents the first results of an Halpha imaging survey of galaxies in the central regions of the A2151 cluster. A total of 50 sources were detected in Halpha. The morphologies of the 43 H$\alpha$ selected galaxies range from grand design spirals and interacting galaxies to blue compacts and tidal dwarfs or isolated extragalactic HII regions, spanning a range of magnitudes of -21 <= MB <= -12.5 mag. A comparison with the clusters Coma and A1367 and a sample of field galaxies has shown the presence of cluster galaxies with L(Halpha) lower than expected for their MB, a consecuence of the cluster environment. This fact results in differences in the L(Halpha) vs. EW(Halpha) and L(H\alpha) distributions of the clusters with respect to the field, and in cluster to cluster variations of these quantities, which we propose are driven by a global cluster property as the total mass. Overall, we conclude that both, the global cluster environment as well as the cluster merging history play a non negligible role in the integral star formation properties of clusters of galaxies., Comment: 38 pages, 11 figures. Accepted for publication in Astronomical Journal

The electron temperatures of high-metallicity (12+log(O/H) > 8.2) HII regions have been studied. The empirical ff relations which express the nebular-to- auroral [OIII] line ratio Q_3,O (as well as the nebular-to-auroral [OII] line ratio Q_2,O, and the nebular-to-auroral [NII] line ratio Q_2,N) in terms of the nebular R_3 and R_2 line fluxes in spectra of high-metallicity HII regions are derived, and the electron temperatures t_3,O, t_2,O, and t_2,N in a number of extragalactic HII regions are also determined. Furthermore, the t_2 - t_3 diagram is discussed. It is found that there is a one-to-one correspondence between t_2 and t_3 electron temperatures for HII regions with a weak nebular R_3 lines (logR_ < 0.5). The derived t_2,N - t_3,O relation for these HII regions is similar to commonly used t_2 - t_3 relations. The HII regions with a strong nebular R_3 line flux (logR_3 > 0.5) do not follow this relation. A discrepancy between t_2,N and t_2,O temperatures is found, being the t_2,N temperatures systematically lower than t_2,O ones. The differences are small at low electron temperatures and increases with increasing electron temperatures up to 10% at t=1. The uncertainties in the atomic data may be the cause of this discrepancy., Comment: 14 pages, 19 figures, accepted for publication in MNRAS

We have performed optical polarimetric observations of the SN2006aj associated to the X-ray flash (XRF) of February 18, 2006, XRF060218 that provide information on its expansion geometry. The data were acquired in the R-band with the 0.7m telescope of Crimea, 2.5m Nordic Optical Telescope and the 2.2m of Calar Alto. We report the detection of linear polarization between 3 and 39 days after the gamma-ray event (t-t_0). This represents the first polarization detection of a Ic supernova (SN) associated to an XRF. Our data exhibit a degree of linear polarization (P) around P~4% at t-t_0 ~ 3-5 days, followed by a constant polarization phase with P~1.4% at 13.7 < t-t_0 < 39 days. Our data suggest a decay in P, and more interestingly, show a position angle (\theta) rotation of ~100 degrees comparing data taken before and after the R-band lightcurve peak. The reported polarization measurements can be explained by the evolution of an asymmetric SN expansion. We discuss on several ingredients that could account for the observed \theta rotation., Comment: Submitted to A&A. Revised version, comments of the referee included. 4 pages, 3 figures

In this article we first outline the mounting evidence that a significant fraction of the ionizing photons emitted by OB stars within HII regions escape from their immediate surroundings and explain how an HII region structure containing high density contrast in homogeneities facilitates this escape. Next we describe sets of models containing inhomogeneities which are used to predict tracks in the commonly used diagnostic diagrams (based on ratios of emission lines) whose only independent variable is the photon escape fraction, xi. We show that the tracks produced by the models in two of the most cited of these diagrams conform well to the distribution of observed data points, with the models containing optically thick inhomogeneities ("CLUMPY" models) yielding somewhat better agreement than those with optically thin inhomogeneities ("FF" models). We show how variations in the ionization parameter U, derived from emission line ratios, could be due to photon escape. Using a rather wide range of assumptions about the filling factor of dense clumps we find, for a selected set of regions observed in M51 photon escape fraction ranging between 30% and 50%. We show, using oxygen as the test element, that models with different assumptions about the gas inhomogeneity will give variations in the abundance values derived from diagnostic diagrams, but do not claim here to have a fully developed set of diagnostic tools to improve abundance determinations made in this way. We finally propose a combination of line ratios with the absolute Halpha luminosity of a given HII region, which allows us to determine the photon escape fraction, and hence resolve the degeneracy between U and xi., Comment: 13 pages, 15 figures. Accepted for publication in A&A

We present the oxygen abundance determination for 90 HII regions in the inner parts of the grand design galaxy M101. The abundances were derived employing the P method (Pilyugin 2001a). A comparison is made with previous determinations using another calibration and direct measurements of electron temperature to derive the oxygen abundance. The results show agreement with the abundances derived from the electron temperature method and also show that the older calibration is not as accurate as the P method., Comment: 4 pages, 3 figures. Accepted for publication in A&A