Browsing by Subject "galaxies: formation"

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  • Smolcic, V.; Miettinen, O.; Tomicic, N.; Zamorani, G.; Finoguenov, A.; Lemaux, B. C.; Aravena, M.; Capak, P.; Chiang, Y. -K.; Civano, F.; Delvecchio, I.; Ilbert, O.; Jurlin, N.; Karim, A.; Laigle, C.; Le Fevre, O.; Marchesi, S.; McCracken, H. J.; Riechers, D. A.; Salvato, M.; Schinnerer, E.; Tasca, L.; Toft, S. (2017)
    We investigate the environment of 23 submillimetre galaxies (SMGs) drawn from a signal-to-noise (S/N)-limited sample of SMGs originally discovered in the James Clerk Maxwell Telescope (JCMT)/AzTEC 1.1 mm continuum survey of a Cosmic Evolution Survey (COSMOS) subfield and then followed up with the Submillimetre Array and Plateau de Bure Interferometer at 890 mu m and 1.3 mm, respectively. These SMGs already have well-defined multiwavelength counterparts and redshifts. We also analyse the environments of four COSMOS SMGs spectroscopically confirmed to lie at redshifts z(spec) > 4 : 5, and one at z(spec) = 2 : 49 resulting in a total SMG sample size of 28. We search for overdensities using the COSMOS photometric redshifts based on over 30 UV-NIR photometric measurements including the new UltraVISTA data release 2 and Spitzer/SPLASH data, and reaching an accuracy of sigma(Delta z/(1+z)) = (1 + z) = 0 : 0067 (0 : 0155) at z <3 : 5 (> 3.5). To identify overdensities we apply the Voronoi tessellation analysis, and estimate the redshift-space overdensity estimator delta(g) as a function of distance from the SMG and/or overdensity centre. We test and validate our approach via simulations, X-ray detected groups or clusters, and spectroscopic verifications using VUDS and zCOSMOS catalogues which show that even with photometric redshifts in the COSMOS field we can e ffi ciently retrieve overdensities out to z approximate to 5. Our results yield that 11 out of 23 (48%) JCMT/AzTEC 1.1 mm SMGs occupy overdense environments. Considering the entire JCMT/AzTEC 1.1 mm S = N >= 4 sample and taking the expected fraction of spurious detections into account, this means that 35-61% of the SMGs in the S/N-limited sample occupy overdense environments. We perform an X-ray stacking analysis in the 0.5-2 keV band using a 32 '' aperture and our SMG positions, and find statistically significant detections. For our z <2 subsample we find an average flux of (4.0 +/- 0.8) x 10(-16) erg s(-1) cm(-2) and a corresponding total mass of M-200 = 2.8 x 10(13) M-circle dot. The z > 2 subsample yields an average flux of (1.3 +/- 0.5) x 10(-16) erg s(-1) cm(-2) and a corresponding total mass of M-200 = 2 x 10(13) M-circle dot. Our results suggest a higher occurrence of SMGs occupying overdense environments at z >= 3 than at z <3. This may be understood if highly star-forming galaxies can only be formed in the highest peaks of the density field tracing the most massive dark matter haloes at early cosmic epochs, while at later times cosmic structure may have matured su ffi ciently that more modest overdensities correspond to su ffi ciently massive haloes to form SMGs.
  • Wang, Tao; Elbaz, David; Daddi, Emanuele; Finoguenov, Alexis; Liu, Daizhong; Schreiber, Corentin; Martin, Sergio; Strazzullo, Veronica; Valentino, Francesco; van der Burg, Remco; Zanella, Anita; Ciesla, Laure; Gobat, Raphael; Le Brun, Amandine; Pannella, Maurilio; Sargent, Mark; Shu, Xinwen; Tan, Qinghua; Cappelluti, Nico; Li, Yanxia (2016)
    We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z(spec) = 2.506, which contains 11 massive (M-* greater than or similar to 10(11) M-circle dot) galaxies in the central 80 kpc region (11.6 sigma overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from Ha. The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M-200c = 10(13.9 +/- 0.2) M-circle dot, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches similar to 3400 M-circle dot yr(-1) with a. gas depletion time of similar to 200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (similar to 25%, compared to 3%-5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.
  • Crespo, N. Alvarez; Smolic, V.; Finoguenov, A.; Barrufet, L.; Aravena, M. (2021)
    Aims. Submillimetre galaxies (SMGs) are bright sources at submillimetre wavelengths (F-850 mu m>2-5 mJy). Made up of mostly of high-z galaxies (z>1), SMGs are amongst the most luminous dusty galaxies in the Universe. These galaxies are thought to be the progenitors of the massive elliptical galaxies in the local Universe and to reside in massive haloes at early epochs. Studying their environments and clustering strength is thus important to put these galaxies in a cosmological context.Methods. We present an environmental study of a sample of 116 SMGs in 96 ALMA observation fields, which were initially discovered with the AzTEC camera on ASTE and identified with high-resolution 1.25 mm ALMA imaging within the COSMOS survey field, having either spectroscopic or unambiguous photometric redshift. We analysed their environments making use of the latest release of the COSMOS photometric catalogue, COSMOS2015, a catalogue that contains precise photometric redshifts for more than half a million objects over the 2 deg(2) COSMOS field. We searched for dense galaxy environments computing the so-called overdensity parameter as a function of distance within a radius of 5 from the SMG. We validated this approach spectroscopically for those SMGs for which spectroscopic redshift is available. As an additional test, we searched for extended X-ray emission as a proxy for the hot intracluster medium, performing an X-ray stacking analysis in the 0.5-2 keV band with a 32 '' aperture and our SMG position using all available XMM-Newton and Chandra X-ray observations of the COSMOS field.Results. We find that 27% (31 out of 116) of the SMGs in our sample are located in a galactic dense environment; a fraction that is similar to previous studies. The spectroscopic redshift is known for 15 of these 31 sources, thus this photometric approach is tested using spectroscopy. We are able to confirm that 7 out of 15 SMGs lie in high-density peaks. However, the search for associated extended X-ray emission via an X-ray stacking analysis leads to a detection that is not statistically significant.
  • McAlpine, Stuart; Harrison, Chris M.; Rosario, David J.; Alexander, David M.; Ellison, Sara L.; Johansson, Peter H.; Patton, David R. (2020)
    We investigate the connection between galaxy-galaxy mergers and enhanced black hole (BH) growth using the cosmological hydrodynamical EAGLE simulation. We do this via three methods of analysis, investigating: the merger fraction of AGN, the AGN fraction of merging systems, and the AGN fraction of galaxies with close companions. In each case, we find an increased abundance of AGN within merging systems relative to control samples of inactive or isolated galaxies (by up to a factor of approximate to 3 depending on the analysis method used), confirming that mergers are enhancing BH accretion rates for at least a subset of the galaxy population. The greatest excess of AGN triggered via a merger are found in lower mass (M-* similar to 10(10) M-circle dot) gas rich (f(gas) > 0.2) central galaxies with lower mass BHs (M-BH similar to 10(7) M-circle dot) at lower redshifts (z <1). We find no enhancement of AGN triggered via mergers in more massive galaxies (M-* greater than or similar to 10(11) M-circle dot). The enhancement of AGN is not uniform throughout the phases of a merger, and instead peaks within the early remnants of merging systems (typically lagging approximate to 300 Myr post-coalescence of the two galaxies at z = 0.5). We argue that neither major (M-*,M-1/M-*,M-2 = 1/4) nor minor mergers (1/10 <M-*,M-1/M-*,M-2 <1/4) are statistically relevant for enhancing BH masses globally. Whilst at all redshifts the galaxies experiencing a merger have accretion rates that are on average 2-3 times that of isolated galaxies, the majority of mass that is accreted on to BHs occurs outside the periods of a merger. We compute that on average no more than 15 per cent of a BHs final day mass comes from the enhanced accretion rates triggered via a merger.
  • Ford, E. Darragh; Laigle, C.; Gozaliasl, G.; Pichon, C.; Devriendt, J.; Slyz, A.; Arnouts, S.; Dubois, Y.; Finoguenov, A.; Griffiths, R.; Kraljic, K.; Pan, H.; Peirani, S.; Sarron, F. (2019)
    Cosmic filaments are the channel through which galaxy groups assemble their mass. Cosmic connectivity, namely the number of filaments connected to a given group, is therefore expected to be an important ingredient in shaping group properties. The local connectivity is measured in COSMOS around X-ray-detected groups between redshift 0.5 and 1.2. To this end, large-scale filaments are extracted using the accurate photometric redshifts of the COSMOS2015 catalogue in two-dimensional slices of thickness 120 comoving Mpc centred on the group's redshift. The link between connectivity, group mass, and the properties of the brightest group galaxy (BGG) is investigated. The same measurement is carried out on mocks extracted from the light-cone of the hydrodynamical simulation HORIZON-AGN in order to control systematics. More massive groups are on average more connected. At fixed group mass in low-mass groups, BGG mass is slightly enhanced at high connectivity, while in high-mass groups BGG mass is lower at higher connectivity. Groups with a star-forming BGG have on average a lower connectivity at given mass. From the analysis of the HORIZON-AGN simulation, we postulate that different connectivities trace different paths of group mass assembly: at high group mass, groups with higher connectivity are more likely to have grown through a recent major merger, which might be in turn the reason for the quenching of the BGG. Future large-field photometric surveys, such as Euclid and LSST, will be able to confirm and extend these results by probing a wider mass range and a larger variety of environment.
  • Laigle, C.; Davidzon, I.; Ilbert, O.; Devriendt, J.; Kashino, D.; Pichon, C.; Capak, P.; Arnouts, S.; de la Torre, S.; Dubois, Y.; Gozaliasl, G.; Le Borgne, D.; Lilly, S.; McCracken, H. J.; Salvato, M.; Slyz, A. (2019)
    Using the light-cone from the cosmological hydrodynamical simulation horizon-AGN, we produced a photometric catalogue over 0 <z <4 with apparent magnitudes in COSMOS, Dark Energy Survey, Large Synoptic Survey Telescope (LSST)-like, and Euclid-like filters at depths comparable to these surveys. The virtual photometry accounts for the complex star formation history (SFH) and metal enrichment of horizon-AGN galaxies, and consistently includes magnitude errors, dust attenuation, and absorption by intergalactic medium. The COSMOS-like photometry is fitted in the same configuration as the COSMOS2015 catalogue. We then quantify random and systematic errors of photometric redshifts, stellar masses, and star formation rates (SFR). Photometric redshifts and redshift errors capture the same dependencies on magnitude and redshift as found in COSMOS2015, excluding the impact of source extraction. COSMOS-like stellar masses are well recovered with a dispersion typically lower than 0.1 dex. The simple SFHs and metallicities of the templates induce a systematic underestimation of stellar masses at z <1.5 by at most 0.12 dex. SFR estimates exhibit a dust-induced bimodality combined with a larger scatter (typically between 0.2 and 0.6 dex). We also use our mock catalogue to predict photometric redshifts and stellar masses in future imaging surveys. We stress that adding Euclid near-infrared photometry to the LSST-like baseline improves redshift accuracy especially at the faint end and decreases the outlier fraction by a factor similar to 2. It also considerably improves stellar masses, reducing the scatter up to a factor 3. It would therefore be mutually beneficial for LSST and Euclid to work in synergy.
  • Campbell, David J. R.; Frenk, Carlos S.; Jenkins, Adrian; Eke, Vincent R.; Navarro, Julio F.; Sawala, Till; Schaller, Matthieu; Fattahi, Azadeh; Oman, Kyle A.; Theuns, Tom (2017)
    The observed stellar kinematics of dispersion-supported galaxies are often used to measure dynamical masses. Recently, several analytical relationships between the stellar line-of-sight velocity dispersion, the projected (2D) or deprojected (3D) half-light radius and the total mass enclosed within the half-light radius, relying on the spherical Jeans equation, have been proposed. Here, we use the APOSTLE cosmological hydrodynamical simulations of the Local Group to test the validity and accuracy of such mass estimators for both dispersion and rotation-supported galaxies, for field and satellite galaxies, and for galaxies of varying masses, shapes and velocity dispersion anisotropies. We find that the mass estimators of Walker et al. and Wolf et al. are able to recover the masses of dispersion-dominated systems with little systematic bias, but with a 1 sigma scatter of 25 and 23 per cent, respectively. The error on the estimated mass is dominated by the impact of the 3D shape of the stellar mass distribution, which is difficult to constrain observationally. This intrinsic scatter becomes the dominant source of uncertainty in the masses estimated for galaxies like the dwarf spheroidal (dSph) satellites of the Milky Way, where the observational errors in their sizes and velocity dispersions are small. Such scatter may also affect the inner density slopes of dSphs derived from multiple stellar populations, relaxing the significance with which Navarro-Frenk-White profiles may be excluded, depending on the degree to which the relevant properties of the different stellar populations are correlated. Finally, we derive a new optimal mass estimator that removes the residual biases and achieves a statistically significant reduction in the scatter to 20 per cent overall for dispersion-dominated galaxies, allowing more precise and accurate mass estimates.
  • Sawala, Till; Jenkins, Adrian; McAlpine, Stuart; Jasche, Jens; Lavaux, Guilhem; Johansson, Peter H.; Frenk, Carlos S. (2021)
    We study structure formation in a set of cosmological simulations to uncover the scales in the initial density field that gave rise to the formation of present-day structures. Our simulations share a common primordial power spectrum (here Lambda cold dark matter, Lambda CDM), but the introduction of hierarchical variations of the phase information allows us to systematically study the scales that determine the formation of structure at later times. We consider the variance in z = 0 statistics such as the matter power spectrum and halo mass function. We also define a criterion for the existence of individual haloes across simulations, and determine what scales in the initial density field contain sufficient information for the non-linear formation of unique haloes. We study how the characteristics of individual haloes such as the mass and concentration, as well as the position and velocity, are affected by variations on different scales, and give scaling relations for haloes of different mass. Finally, we use the example of a cluster-mass halo to show how our hierarchical parametrization of the initial density field can be used to create variants of particular objects. With properties such as mass, concentration, kinematics, and substructure of haloes set on distinct and well-determined scales, and its unique ability to introduce variations localized in real space, our method is a powerful tool to study structure formation in cosmological simulations.
  • Habouzit, Melanie; Li, Yuan; Somerville, Rachel S.; Genel, Shy; Pillepich, Annalisa; Volonteri, Marta; Dave, Romeel; Rosas-Guevara, Yetli; McAlpine, Stuart; Peirani, Sebastien; Hernquist, Lars; Anglés-Alcázar, Daniel; Reines, Amy; Bower, Richard; Dubois, Yohan; Nelson, Dylan; Pichon, Christophe; Vogelsberger, Mark (2021)
    The past decade has seen significant progress in understanding galaxy formation and evolution using large-scale cosmological simulations. While these simulations produce galaxies in overall good agreement with observations, they employ different sub-grid models for galaxies and supermassive black holes (BHs). We investigate the impact of the sub-grid models on the BH mass properties of the Illustris, TNG100, TNG300, Horizon-AGN, EAGLE, and SIMBA simulations, focusing on the M-BH - M-star relation and the BH mass function. All simulations predict tight M-BH - M-star relations, and struggle to produce BHs of M-BH = 109M (circle dot) in most of the simulations. The BH mass function is dominated by efficiently accreting BHs ((log(10) f(Edd) >= -2) at high redshifts, and transitions progressively from the high-mass to the low-mass end to be governed by inactive BHs. The transition time and the contribution of active BHs are different among the simulations, and can be used to evaluate models against observations.
  • Sawala, Till; Frenk, Carlos S.; Fattahi, Azadeh; Navarro, Julio F.; Bower, Richard G.; Crain, Robert A.; Dalla Vecchia, Claudio; Furlong, Michelle; Helly, John. C.; Jenkins, Adrian; Oman, Kyle A.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom; Trayford, James; White, Simon D. M. (2016)
    The Local Group galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations appear to be in disagreement with N-body simulations of the 'lambda cold dark matter' (I > CDM) model: there are far fewer satellite galaxies than substructures in CDM haloes (the 'missing satellites' problem); dwarf galaxies seem to avoid the most massive substructures (the 'too-big-to-fail' problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the 'planes of satellites' problem). Here we present results from apostle (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of 12 volumes selected to match the kinematics of the Local Group (LG) members. Applying the eagle code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of haloes and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to the MWs, confirming that such a configuration is not unexpected in I > CDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide estimates of the maximum circular velocity for the haloes of nine MW dwarf spheroidals.
  • Genina, Anna; Benitez-Llambay, Alejandro; Frenk, Carlos S.; Cole, Shaun; Fattahi, Azadeh; Navarro, Julio F.; Oman, Kyle A.; Sawala, Till; Theuns, Tom (2018)
    The existence of two kinematically and chemically distinct stellar subpopulations in the Sculptor and Fornax dwarf galaxies offers the opportunity to constrain the density profile of their matter haloes by measuring the mass contained within the well-separated half-light radii of the two metallicity subpopulations. Walker and Penarrubia have used this approach to argue that data for these galaxies are consistent with constant-density 'cores' in their inner regions and rule out 'cuspy' Navarro-Frenk-White (NFW) profiles with high statistical significance, particularly in the case of Sculptor. We test the validity of these claims using dwarf galaxies in the APOSTLE (A Project Of Simulating The Local Environment) Lambda cold dark matter cosmological hydrodynamic simulations of analogues of the Local Group. These galaxies all have NFW dark matter density profiles and a subset of them develop two distinct metallicity subpopulations reminiscent of Sculptor and Fornax. We apply a method analogous to that of Walker and Penarrubia to a sample of 50 simulated dwarfs and find that this procedure often leads to a statistically significant detection of a core in the profile when in reality there is a cusp. Although multiple factors contribute to these failures, the main cause is a violation of the assumption of spherical symmetry upon which the mass estimators are based. The stellar populations of the simulated dwarfs tend to be significantly elongated and, in several cases, the two metallicity populations have different asphericity and are misaligned. As a result, a wide range of slopes of the density profile are inferred depending on the angle from which the galaxy is viewed.
  • Davies, Jonathan J.; Crain, Robert A.; McCarthy, Ian G.; Oppenheimer, Benjamin D.; Schaye, Joop; Schaller, Matthieu; McAlpine, Stuart (2019)
    We examine the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day similar to L-star central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy's black hole (BH), but correlates strongly and negatively with the BH's mass, implicating differences in the expulsion of gas by active galactic nucleus feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit elevated star formation rates (SFRs). Diversity in the mass of central BHs stems primarily from diversity in the dark matter halo binding energy, as these quantities are strongly and positively correlated at fixed halo mass, such that similar to L-star galaxies hosted by haloes that are more (less) tightly bound develop central BHs that are more (less) massive than is typical for their halo mass. Variations in the halo gas fraction at fixed halo mass are reflected in both the soft X-ray luminosity and thermal Sunyaev-Zel'dovich flux, suggesting that the prediction of a strong coupling between the properties of galaxies and their halo gas fractions can be tested with measurements of these diagnostics for galaxies with diverse SFRs but similar halo masses.
  • McAlpine, Stuart; Smail, Ian; Bower, Richard G.; Swinbank, A. M.; Trayford, James W.; Theuns, Tom; Baes, Maarten; Camps, Peter; Crain, Robert A.; Schaye, Joop (2019)
    We exploit EAGLE, a cosmological hydrodynamical simulation, to reproduce the selection of the observed submillimetre (submm) galaxy population by selecting the model galaxies at z >= 1 with mock submm fluxes S-850 mu m >= 1mJy. We find a reasonable agreement between the model galaxies within this sample and the properties of the observed submm population, such as their star formation rates (SFRs) at z <3, redshift distribution, and many integrated galaxy properties. We find that the median redshift of the S-850 (mu m) >= 1mJy model population is z approximate to 2.5, and that they are massive galaxies (M-* similar to 10(11)M(circle dot)) with high dust masses (M-dust similar to 10(8)M(circle dot)), gas fractions (f(gas) approximate to 50 per cent), and SFRs ((*) approximate to 100 M-circle dot yr(-1)). In addition, we find that they have major and minor merger fractions similar to the general population, suggesting that mergers are not the sole driver of the high SFRs in the model submm galaxies. Instead, the S-850 (mu m) >= 1mJy model galaxies yield high SFRs primarily because they maintain a significant gas reservoir as a result of hosting an undermassive black hole relative to comparably massive galaxies. Not all 'highly star-forming' ((*) >= 80M(circle dot) yr(-1)) EAGLE galaxies have submm fluxes S-850 (mu m) >= 1 mJy. We investigate the nature of these highly star-forming 'Submm-Faint' galaxies (i.e. (*) = 80 M-circle dot yr(-1) but S-850 (mu m) <1mJy) and find that they are similar to the model submm galaxies, being gas rich and hosting undermassive black holes. However, they are also typically at higher redshifts (z > 4) and are lower mass (M-* similar to 10(10) M-circle dot). These typically higher redshift galaxies show stronger evidence for having been triggered by major mergers, and critically, they are likely missed by most current submm surveys due to their higher dust temperatures and lower dust masses.