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The correlation between the large-scale distribution of galaxies and their spectroscopic properties at is investigated using the Horizon MareNostrum cosmological run. We have extracted a large sample of 105 galaxies from this large hydrodynamical simulation featuring standard galaxy formation physics. Spectral synthesis is applied to these single stellar populations to generate spectra and colours for all galaxies. We use the skeleton as a tracer of the cosmic web and study how our galaxy catalogue depends on the distance to the skeleton. We show that galaxies closer to the skeleton tend to be redder but that the effect is mostly due to the proximity of large haloes at the nodes of the skeleton, rather than the filaments themselves. This effect translates into a bimodality in the colour distribution of our sample. The origin of this bimodality is investigated and seems to follow from the ram pressure stripping of satellite galaxies within the more massive clusters of the simulation. The virtual catalogues (spectroscopical properties of the MareNostrum galaxies at various redshifts) are available online at . [ABSTRACT FROM AUTHOR]

We present synthetic spectral energy distributions (SEDs) for single-age, single-metallicity stellar populations (SSPs) covering the full optical spectral range at moderately high resolution [full width at half-maximum (FWHM) 2.3 Å]. These SEDs constitute our base models, as they combine scaled-solar isochrones with an empirical stellar spectral library [Medium resolution INT Library of Empirical Spectra (MILES)], which follows the chemical evolution pattern of the solar neighbourhood. The models rely as much as possible on empirical ingredients, not just on the stellar spectra, but also on extensive photometric libraries, which are used to determine the transformations from the theoretical parameters of the isochrones to observational quantities. The unprecedented stellar parameter coverage of the MILES stellar library allowed us to safely extend our optical SSP SED predictions from intermediate- to very-old-age regimes and the metallicity coverage of the SSPs from super-solar to . SSPs with such low metallicities are particularly useful for globular cluster studies. We have computed SSP SEDs for a suite of initial mass function shapes and slopes. We provide a quantitative analysis of the dependence of the synthesized SSP SEDs on the (in)complete coverage of the stellar parameter space in the input library that not only shows that our models are of higher quality than those of other works, but also in which range of SSP parameters our models are reliable. The SSP SEDs are a useful tool to perform the analysis of stellar populations in a very flexible manner. Observed spectra can be studied by means of full spectrum fitting or by using line indices. For the latter, we propose a new line index system to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. Apart from constant resolution as a function of wavelength, the system is also based on flux-calibrated spectra. Data can be analysed at three different resolutions: 5, 8.4 and 14 Å (FWHM), which are appropriate for studying globular cluster, low- and intermediate-mass galaxies, and massive galaxies, respectively. Furthermore, we provide polynomials to transform current Lick/IDS line index measurements to the new system. We provide line index tables in the new system for various popular samples of Galactic globular clusters and galaxies. We apply the models to various stellar clusters and galaxies with high-quality spectra, for which independent studies are available, obtaining excellent results. Finally, we designed a web page from which not only these models and stellar libraries can be downloaded but which also provides a suite of on-line tools to facilitate the handling and transformation of the spectra. [ABSTRACT FROM AUTHOR]

Weak emission line quasars are a rare and puzzling group of objects. In this paper, we present one more object of this class found in the Sloan Digital Sky Survey (SDSS). The quasar SDSS J094533.99+100950.1, lying at , has practically no C iv emission line, a red continuum very similar to the second steepest of the quasar composite spectra of Richards et al., is not strongly affected by absorption and the Mg ii line, although relatively weak, is strong enough to measure the black hole mass. The Eddington ratio in this object is about 0.45, and the line properties are not consistent with the trends expected at high accretion rates. We propose that the most probable explanation of the line properties in this object, and perhaps in all weak emission line quasars, is that the quasar activity has just started. A disc wind is freshly launched so the low ionization lines which form close to the disc surface are already observed but the wind has not yet reached the regions where high ionization lines or narrow line components are formed. The relatively high occurrence of such a phenomenon may additionally indicate that the quasar active phase consists of several subphases, each starting with a fresh build-up of the broad-line region. [ABSTRACT FROM AUTHOR]

The environment is known to affect the formation and evolution of galaxies considerably best visible through the well-known morphology–density relationship. It is less clear, though, whether the environment is equally important at a given galaxy morphology. In this paper, we study the effect of environment on the evolution of early-type galaxies as imprinted in the fossil record by analysing the stellar population properties of 3360 galaxies morphologically selected by visual inspection from the Sloan Digital Sky Survey in a narrow redshift range ( ). The morphological selection algorithm is critical, as it does not bias against recent star formation. We find that the distribution of ages is bimodal with a strong peak at old ages and a secondary peak at young ages around ∼2.5 Gyr containing about 10 per cent of the objects. This is an analogue to ‘red sequence’ and ‘blue cloud’ identified in galaxy populations usually containing both early- and late-type galaxies. The fraction of the young, rejuvenated galaxies increases with both decreasing galaxy mass and decreasing environmental density up to about 45 per cent, which implies that the impact of environment increases with decreasing galaxy mass. The rejuvenated galaxies have lower ratios than the average and most of them show signs of ongoing star formation through their emission line spectra. All objects that host active galactic nuclei in their centres without star formation are part of the red sequence population. We confirm and statistically strengthen earlier results that luminosity weighted ages, metallicities and element ratios of the red sequence population correlate well with velocity dispersion and galaxy mass. Most interestingly, however, these scaling relations are not sensitive to environmental densities and are only driven by galaxy mass. We infer that early-type galaxy formation has undergone a phase transition a few billion years ago around . A self-regulated formation phase without environmental dependence has recently been superseded by a rejuvenation phase, in which the environment plays a decisive role possibly through galaxy mergers and interactions. [ABSTRACT FROM AUTHOR]

We analyse Spitzer Multiband Imaging Photometer (MIPS) 24- m observations, and Sloan Digital Sky Survey Data Release 7 optical broad-band photometry and spectra, to investigate the star formation (SF) properties of galaxies residing in the Coma supercluster region. We find that SF in dwarf galaxies is quenched only in the high-density environment at the centre of clusters and groups, but that passively evolving massive galaxies are found in all environments, indicating that massive galaxies can become passive via internal processes. The SF–density relation observed for the massive galaxies is weaker relative to the dwarfs, but both show a trend for the fraction of star-forming galaxies ( ) declining to 0 in the cluster cores. We find that active galactic nucleus activity is also suppressed among massive galaxies residing in the cluster cores. We present evidence for a strong dependence of the mechanism(s) responsible for quenching SF in dwarf galaxies on the cluster potential, resulting in two distinct evolutionary pathways. First, we find a significant increase (at the 3 level) in the mean equivalent width of Hα emission among star-forming dwarf galaxies in the infall regions of the Coma cluster and the core of Abell 1367 with respect to the overall supercluster population, indicative of the infalling dwarf galaxies undergoing a starburst phase. We identify these starburst galaxies as the precursors of the post-starburst k + A galaxies. Extending the survey of k + A galaxies over the whole supercluster region, we find 11.4 per cent of all dwarf ( mag 15) galaxies in the Coma cluster and 4.8 per cent in the Abell 1367 have post-starburst like spectra, while this fraction is just 2.1 per cent when averaged over the entire supercluster region (excluding the clusters). This points to a cluster-specific evolutionary process in which infalling dwarf galaxies undergo a starburst and subsequent rapid quenching due to their passage through the dense intracluster medium. In galaxy groups, the SF in infalling dwarf galaxies is instead slowly quenched due to the reduced efficiency of ram-pressure stripping. We show that in the central Mpc of the Coma cluster, the ( ) near-infrared/mid-infrared (MIR) colour of galaxies is correlated with their optical colour and Hα emission, separating all MIR-detected galaxies into two distinct classes of ‘red’ and ‘blue’. By analysing the spatial and velocity distribution of galaxies detected at 24 m in Coma, we find that the (optically) red 24- m detected galaxies follow the general distribution of ‘all’ the spectroscopic members, but their (optically) blue counterparts (i) are almost completely absent in the central Mpc of Coma and (ii) have a remarkable peak in their velocity distribution, corresponding to the mean radial velocity of the galaxy group NGC 4839, suggesting that a significant fraction of the ‘blue’ MIR galaxies are currently on their first infall towards the cluster. The implications of adopting different SF-rate tracers for quantifying evolutionary trends like the Butcher–Oemler effect are also discussed. [ABSTRACT FROM AUTHOR]