Browsing by Subject "galaxies: evolution"
Now showing 1 - 10 of 10
Results Per Page
Sort Options
- ItemOpen AccessCO in Hickson compact group galaxies with enhanced warm H 2 emission: Evidence for galaxy evolution?(2014) Lisenfeld, U; Appleton, P N; Cluver, M E; Guillard, P; Alatalo, K; Ogle, PContext. Galaxies in Hickson Compact Groups (HCGs) are believed to experience morphological transformations from blue, star-forming galaxies to red, early-type galaxies. Galaxies with a high ratio between the luminosities of the warm H2 to the 7.7 μm PAH emission (so-called Molecular Hydrogen Emission Galaxies, MOHEGs) are predominantly in an intermediate phase, the green valley. Their enhanced H2 emission suggests that the molecular gas is affected in the transition.
- ItemOpen AccessConstraining AGN triggering mechanisms through the clustering analysis of active black holes(2016) Gatti, M; Shankar, F; Bouillot, V; Menci, N; Lamastra, A; Hirschmann, M; Fiore, FThe triggering mechanisms for active galactic nuclei (AGN) are still debated. Some of the most popular ones include galaxy interactions (IT) and disc instabilities (DIs). Using an advanced semi-analytic model (SAM) of galaxy formation, coupled to accurate halo occupation distribution modelling, we investigate the imprint left by each separate triggering process on the clustering strength of AGN at small and large scales. Our main results are as follows: (i) DIs, irrespective of their exact implementation in the SAM, tend to fall short in triggering AGN activity in galaxies at the centre of haloes with
- ItemOpen AccessCosmological model dependence of the galaxy luminosity function: far-infrared results in the Lemaître-Tolman-Bondi model(2013) Iribarrem, A; Andreani, P; Gruppioni, C; February, S; Ribeiro, M B; Berta, S; Le Floc’h, E; Magnelli, B; Nordon, R; Popesso, P; Pozzi, F; Riguccini, LAims. This is the first paper of a series aiming at investigating galaxy formation and evolution in the giant-void class of the Lemaître-Tolman-Bondi (LTB) models that best fits current cosmological observations. Here we investigate the luminosity function (LF) methodology, and how its estimates would be affected by a change on the cosmological model assumed in its computation. Are the current observational constraints on the allowed cosmology enough to yield robust LF results?
- ItemOpen AccessHerschel observations of Hickson compact groups of galaxies: Unveiling the properties of cold dust(2014) Bitsakis, T; Charmandaris, V; Appleton, P N; Díaz-Santos, T; Le Floc’h, E; da Cunha, E; Alatalo, K; Cluver, MWe present a Herschel far-IR and sub-mm study of a sample of 120 galaxies in 28 Hickson Compact Groups. Fitting their UV to sub-mm spectral energy distributions with the model of da Cunha et al. (2008), we accurately estimate the dust masses, luminosities and temperatures of the individual galaxies. We find that nearly half of the late-type galaxies in dynamically "old" groups, those with more than 25% of early-type members and redder UV-optical colours, have also significantly lower dust-to-stellar mass ratios compared to those of actively star-forming galaxies of the same mass found both in HCGs and the field. Examining their dust-to-gas mass ratios we conclude that dust was stripped out of these systems as a result of the gravitational and hydrodynamic interactions, experienced due to previous encounters with other group members. About 40% of the early-type galaxies (mostly lenticulars), in dynamically "old" groups, display dust properties similar to those of the UV-optical red late-type galaxies. Given their stellar masses, star formation rates and UV-optical colours, we suggest that red late-type and dusty lenticular galaxies represent transition populations between blue star-forming disk galaxies and quiescent early-type ellipticals. [...ABRIDGED...] Our deep Herschel observations also allow us to detect the presence of diffuse cold intragroup dust in 4 HCGs. We also find that the fraction of 250micron emission which is located outside of the main bodies of the red late-type galaxies as well as of the dusty lenticulars is 15-20% of their integrated emission at this band. All these findings are consistent with an evolutionary scenario in which gas dissipation, shocks and turbulence in addition to tidal interactions, shape the evolution of galaxies in compact groups.
- ItemOpen AccessHI in group interactions: HCG 44(2017) Hess, Kelley M; Cluver, M E; Yahya, Sahba; Leisman, Lukas; Serra, Paolo; Lucero, Danielle M; Passmoor, Sean S; Carignan, ClaudeExtending deep observations of the neutral atomic hydrogen (H I) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example, and we have combined H I data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N _{H {I}}
- ItemOpen AccessRelativistic cosmology number densities in void-Lemaître-Tolman-Bondi models(2014) Iribarrem, A; Andreani, P; February, S; Gruppioni, C; Lopes, A R; Ribeiro, M B; Stoeger, W RAims. The goal of this work is to compute the number density of far-IR selected galaxies in the comoving frame and along the past lightcone of observationally constrained Lemaître-Tolman-Bondi “giant void” models and to compare those results with their standard model counterparts.
- ItemOpen AccessStellar population and kinematics of NGC 404(2010) Bouchard, A; Prugniel, P; Koleva, M; Sharina, MContext. NGC 404 is a nearly face-on, nearby low-luminosity lenticular galaxy. Probing its characteristics provides a wealth of information on the details of the possible evolution processes of dS0 galaxies, which may not be possible in other, more distant objects.
- ItemOpen AccessThe Role of the Most Luminous Obscured AGNs in Galaxy Assembly at z similar to 2(2017) Farrah, Duncan; Petty, Sara; Blain, Andrew; Efstathiou, Andreas; Lacy, Mark; Stern, Daniel; Lake, Sean; Jarrett, Tom; Benford, Dominic; Tsai, Chao-Wei; Assef, Roberto; Moustakas, LeonidasWe present Hubble Space Telescope WFC3 F160W imaging and infrared spectral energy distributions for 12 extremely luminous, obscured active galactic nuclei (AGNs) at 1.8 < z < 2.7. selected via "hot, dust-obscured" mid-infrared colors. Their infrared luminosities span (2-15) x 10(13) L-circle dot, making them among the most luminous objects in the universe at z similar to 2. In all cases, the infrared emission is consistent with arising at least for the. most part from AGN activity. The AGN fractional luminosities are higher than those in either submillimeter galaxies. or AGNs selected via other mid-infrared criteria. Adopting the G, M-20, and A morphological parameters, together with traditional classification boundaries, infers that three-quarters of the sample are mergers. Our sample does not, however, show any correlation between the considered morphological parameters and either infrared luminosity or AGN fractional luminosity. Moreover, the asymmetries and effective radii of our sample are distributed identically to those of massive galaxies at z similar to 2. We conclude that our sample is not preferentially associated with mergers, though a significant merger fraction is still plausible. Instead, we propose that our sample includes. examples of the massive galaxy population at z similar to 2 that harbor a briefly luminous, "flickering" AGN. and in which the G and M-20 values have been perturbed. due to either the AGN. and/or the earliest formation stages of a bulge in an inside-out manner. Furthermore, we find that the mass assembly of the central black holes in our sample leads the mass assembly of any bulge component. Finally, we speculate that our sample represents. a small fraction of the immediate antecedents of compact star-forming galaxies at z similar to 2.
- ItemOpen AccessUV-BRIGHT NEARBY EARLY-TYPE GALAXIES OBSERVED IN THE MID-INFRARED: EVIDENCE FOR A MULTI-STAGE FORMATION HISTORY BY WAY OF WISE AND GALEX IMAGING(2013) Petty, S M; Neill, J D; Jarrett, T H; Blain, A W; Farrah, D G; Rich, R M; Tsai, C W; Benford, D J; Bridge, C R; Lake, S E; Masci, F J; Wright, E LIn the local Universe, 10% of massive elliptical galaxies are observed to exhibit a peculiar property: a substantial excess of ultraviolet emission (UVX) over what is expected from their old, red stellar populations. Several origins for the UVX have been proposed, including a population of hot young stars, or a population of old, blue horizontal branch or extended horizontal branch (BHB or EHB) stars that have undergone substantial mass loss from their outer atmospheres. We explore the radial distribution of ultraviolet excess (UVX) in a selection of 49 nearby E/S0-type galaxies by measuring the extended photometry in the UV-midIR with GALEX, SDSS and WISE. We compare UV/optical and UV/mid-IR colors with the Flexible Stellar Population Synthesis with EHB models (Conroy & Gunn 2010). We find that combined WISE mid-IR and GALEX UV colors are more effective in distinguishing models than optical colors, and that the UV/mid-IR combination is sensitive to EHB fraction. There are strong color gradients with the outer radii bluer than the inner half-light radii by ~1 magnitude. This color difference is easily accounted for with a BHB fraction increase of 0.25 with radius. We estimated the average ages for the inner and outer radii are 7.0+/-0.3 Gyr, and 6.2+/-0.2 Gyr, respectively, with the implication that the outer regions are likely to have formed ~1 Gyr after the inner regions. Additionally, we find that metallicity gradients are likely not a significant factor in the color difference. The separation of color between the inner and outer regions, which agrees with a specific stellar population difference (e.g., higher EHB populations), and the ~0.5-2 Gyr age difference suggests multi-stage formation. Our results are best explained by inside-out formation: rapid star formation within the core at early epochs (>4 Gyr ago) and at least one later stage starburst event coinciding with z~1
- ItemOpen AccessWise detections of known QSOs at redshifts greater than six(2013) Blain, Andrew W; Assef, Roberto; Stern, Daniel; Tsai, Chao-Wei; Eisenhardt, Peter; Bridge, Carrie; Benford, Dominic; Jarrett, Tom; Cutri, Roc; Petty, Sara; Wu, Jingwen; Wright, Edward LWe present WISE All-Sky mid-infrared (IR) survey detections of 55% (17/31) of the known QSOs at z > 6 from a range of surveys: the SDSS, the CFHT-LS, FIRST, Spitzer, and UKIDSS. The WISE catalog thus provides a substantial increase in the quantity of IR data available for these sources: 17 are detected in the WISE W1 (3.4 mu m) band, 16 in W2 (4.6 mu m), 3 in W3 (12 mu m), and 0 in W4 (22 mu m). This is particularly important with Spitzer in its warm-mission phase and no faint follow-up capability at wavelengths longward of 5 mu m until the launch of James Webb Space Telescope (JWST). WISE thus provides a useful tool for understanding QSOs found in forthcoming large-area optical/IR sky surveys using PanSTARRS, SkyMapper, VISTA, DES, and LSST. The rest-UV properties of the WISE-detected and the WISE-non-detected samples differ: the detections have brighter i/z-band magnitudes and redder rest-UV colors. This suggests that a more aggressive hunt for very high redshift QSOs by combining WISE W1 and W2 data with red, observed optical colors could be effective at least for a subset of dusty candidate QSOs. Stacking the WISE images of the WISE-non-detected QSOs indicates that they are, on average, significantly fainter than the WISE-detected examples, and are thus not narrowly missing detection in the WISE catalog. The WISE catalog detection of three of our sample in the W3 band indicates that their mid-IR flux can be detected individually, although there is no stacked W3 detection of sources detected in W1 but not W3. Stacking analyses of WISE data for large active galactic nucleus samples will be a useful tool, and high-redshift QSOs of all types will be easy targets for JWST.