Browsing by Subject "SATELLITE GALAXIES"

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  • Allevato, V.; Viitanen, A.; Finoguenov, A.; Civano, F.; Suh, H.; Shankar, F.; Bongiorno, A.; Ferrara, A.; Gilli, R.; Miyaji, T.; Marchesi, S.; Cappelluti, N.; Salvato, M. (2019)
    Aims. We perform clustering measurements of 800 X-ray selected Chandra COSMOS Legacy (CCL) Type 2 active galactic nuclei (AGN) with known spectroscopic redshift to probe the halo mass dependence on AGN host galaxy properties, such as galaxy stellar mass M-star, star formation rate (SFR), and specific black hole accretion rate (BHAR; lambda(BHAR)) in the redshift range z;=;[0-3]. Methods. We split the sample of AGN with known spectroscopic redshits according to M-star, SFR and lambda(BHAR), while matching the distributions in terms of the other parameters, including redshift. We measured the projected two-point correlation function w(p)(r(p)) and modeled the clustering signal, for the different subsamples, with the two-halo term to derive the large-scale bias b and corresponding typical mass of the hosting halo. Results. We find no significant dependence of the large-scale bias and typical halo mass on galaxy stellar mass and specific BHAR for CCL Type 2 AGN at mean z;similar to;1, while a negative dependence on SFR is observed, i.e. lower SFR AGN reside in richer environment. Mock catalogs of AGN, matched to have the same X-ray luminosity, stellar mass, lambda(BHAR), and SFR of CCL Type 2 AGN, almost reproduce the observed M-star - M-h, lambda(BHAR) - M-h and SFR-M-h relations, when assuming a fraction of satellite AGN f(AGN)(sat) similar to 0.15fAGNsat similar to 0.15$ f_{\mathrm{AGN}}{\mathrm{sat}} \sim 0.15 $. This corresponds to a ratio of the probabilities of satellite to central AGN of being active Q;similar to;2. Mock matched normal galaxies follow a slightly steeper M-star - M-h relation, in which low mass mock galaxies reside in less massive halos than mock AGN of similar mass. Moreover, matched mock normal galaxies are less biased than mock AGN with similar specific BHAR and SFR, at least for Q > 1.
  • Gaia Collaboration; Helmi, A.; Muinonen, K.; Fedorets, G.; Granvik, M.; Siltala, L. (2018)
    Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Methods. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Results. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (i v) derive a lower limit for the mass of the Milky Way of 9.1(-2.6)(+6.2) x 10(11) M-circle dot based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (v i) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. Conclusions. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.
  • Balogh, Michael L.; Gilbank, David G.; Muzzin, Adam; Rudnick, Gregory; Cooper, Michael C.; Lidman, Chris; Biviano, Andrea; Demarco, Ricardo; McGee, Sean L.; Nantais, Julie B.; Noble, Allison; Old, Lyndsay; Wilson, Gillian; Yee, Howard K. C.; Bellhouse, Callum; Cerulo, Pierluigi; Chan, Jeffrey; Pintos-Castro, Irene; Simpson, Rane; van der Burg, Remco F. J.; Zaritsky, Dennis; Ziparo, Felicia; Victoria Alonso, Maria; Bower, Richard G.; De Lucia, Gabriella; Finoguenov, Alexis; Garcia Lambas, Diego; Muriel, Hernan; Parker, Laura C.; Rettura, Alessandro; Valotto, Carlos; Wetzel, Andrew (2017)
    We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 <z <1.5, selected to span a factor > 10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over lambda similar to 0.6-1.05 mu m, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z' <24.25 and [3.6] mu m <22.5, and is therefore statistically complete for stellar masses M* greater than or similar to 10(10.3) M-circle dot, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 mu m. The spectroscopy is similar to 50 per cent complete as of semester 17A, and we anticipate a final sample of similar to 500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.
  • Galametz, Audrey; Pentericci, Laura; Castellano, Marco; Mendel, Trevor; Hartley, Will G.; Fossati, Matteo; Finoguenov, Alexis; Almaini, Omar; Beifiori, Alessandra; Fontana, Adriano; Grazian, Andrea; Scodeggio, Marco; Kocevski, Dale D. (2018)
    We present a large-scale galaxy structure C1 J021734-0513 at z similar to 0.65 discovered in the UKIDSS UDS field, made of similar to 20 galaxy groups and clusters, spreading over 10 Mpc. We report on a VLT/VIMOS spectroscopic follow-up program that, combined with past spectroscopy, allowed us to confirm four galaxy clusters (M-200 similar to 10(14) M-circle dot) and a dozen associated groups and star-forming galaxy overdensities. Two additional filamentary structures at z similar to 0.62 and 0.69 and foreground and background clusters at 0.6 <z <0.7 were also confirmed along the line of sight. The structure subcomponents are at different formation stages. The clusters have a core dominated by passive galaxies and an established red sequence. The remaining structures are a mix of star-forming galaxy overdensities and forming groups. The presence of quiescent galaxies in the core of the latter shows that 'pre-processing' has already happened before the groups fall into their more massive neighbours. Our spectroscopy allows us to derive spectral index measurements e.g. emission/absorption line equivalent widths, strength of the 4000 angstrom break, valuable to investigate the star formation history of structure members. Based on these line measurements, we select a population of 'post-starburst' galaxies. These galaxies are preferentially found within the virial radius of clusters, supporting a scenario in which their recent quenching could be prompted by gas stripping by the dense intracluster medium. We derive stellar age estimates using Markov Chain Monte Carlo-based spectral fitting for quiescent galaxies and find a correlation between ages and colours/stellar masses which favours a top-down formation scenario of the red sequence. A catalogue of similar to 650 redshifts in UDS is released alongside the paper (via MNRAS online data).
  • Sawala, Till; Pihajoki, Pauli; Johansson, Peter H.; Frenk, Carlos S.; Navarro, Julio F.; Oman, Kyle A.; White, Simon D. M. (2017)
    The predicted abundance and properties of the low-mass substructures embedded inside larger dark matter haloes differ sharply among alternative dark matter models. Too small to host galaxies themselves, these subhaloes may still be detected via gravitational lensing or via perturbations of the Milky Way's globular cluster streams and its stellar disc. Here, we use the APOSTLE cosmological simulations to predict the abundance and the spatial and velocity distributions of subhaloes in the range 10(6.5)-10(8.5)M(circle dot) inside haloes of mass similar to 10(12) M-circle dot in Lambda cold dark matter. Although these subhaloes are themselves devoid of baryons, we find that baryonic effects are important. Compared to corresponding dark matter only simulations, the loss of baryons from subhaloes and stronger tidal disruption due to the presence of baryons near the centre of the main halo reduce the number of subhaloes by similar to 1/4 to 1/2, independently of subhalo mass, but increasingly towards the host halo centre. We also find that subhaloes have non-Maxwellian orbital velocity distributions, with centrally rising velocity anisotropy and positive velocity bias that reduces the number of low-velocity subhaloes, particularly near the halo centre. We parametrize the predicted population of subhaloes in terms of mass, galactocentric distance and velocities. We discuss implications of our results for the prospects of detecting dark matter substructures and for possible inferences about the nature of dark matter.
  • Starkenburg, Else; Oman, Kyle A.; Navarro, Julio F.; Crain, Robert A.; Fattahi, Azadeh; Frenk, Carlos S.; Sawala, Till; Schaye, Joop (2017)
    We examine the spatial distribution of the oldest and most metal-poor stellar populations of Milky Way-sized galaxies using the A Project Of Simulating The Local Environment (APOSTLE) cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (t(form) <0.8 Gyr) and most metal-poor ([Fe/H] <-2.5) stars, both of which increase outwards. The most metal-poor stars form over an extended period of time; half of them form after z = 5.3, and the last 10 per cent after z = 2.8. The age of the metal-poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy's central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. We investigate the dependence of these results on the assumptions made for metal mixing. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal-poor stars that are very old are systems where metal-poor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.
  • Fattahi, Azadeh; Navarro, Julio F.; Frenk, Carlos S.; Oman, Kyle A.; Sawala, Till; Schaller, Matthieu (2018)
    The shallow faint-end slope of the galaxy mass function is usually reproduced in Lambda cold dark matter (Lambda CDM) galaxy formation models by assuming that the fraction of baryons that turn into stars drops steeply with decreasing halo mass and essentially vanishes in haloes with maximum circular velocities Vmax <20-30 km s(-1). Dark-matter-dominated dwarfs should therefore have characteristic velocities of about that value, unless they are small enough to probe only the rising part of the halo circular velocity curve (i.e. half-mass radii, r(1/2)
  • Carollo, C. M.; Cibinel, A.; Lilly, S. J.; Pipino, A.; Bonoli, S.; Finoguenov, A.; Miniati, F.; Norberg, P.; Silverman, J. D. (2016)
    We use the low-redshift Zurich Environmental Study (ZENS) catalog to study the dependence of the quenched satellite fraction at 10(10.0) M-circle dot -> 10(11.5) M-circle dot, and of the morphological mix of these quenched satellites, on three different environmental parameters: group halo mass, halo-centric distance, and large-scale structure (LSS) overdensity. Within the two mass bins into which we divide our galaxy sample, the fraction of quenched satellites is more or less independent of halo mass and the surrounding. LSS overdensity, but it increases toward the centers of the halos, as found in previous studies. The morphological mix of these quenched satellites is, however, constant with radial position in the halo, indicating that the well-known morphology-density relation results from the increasing fraction of quenched galaxies toward the centers of halos. If the radial variation in the quenched fraction reflects the action of two quenching processes, one related to mass and the other to environment, then the constancy with radius of the morphological outcome suggests that both have the same effect on the morphologies of the galaxies. Alternatively, mass and environment quenching may be two reflections of a single physical mechanism. The quenched satellites have larger bulge-to-total ratios (B/T) and smaller half-light radii than the star-forming satellites. The bulges in quenched satellites have very similar luminosities and surface brightness profiles, and any mass growth of the bulges associated with quenching cannot greatly change these quantities. The differences in the light-defined B/T and in the galaxy half-light radii are mostly due to differences in the disks, which have lower luminosities in the quenched galaxies. The difference in galaxy half-light radii between quenched and star-forming satellites is however larger than can be explained by uniformly fading the disks following quenching, and the quenched disks have smaller scale lengths than in star-forming satellites. This can be explained either by a differential fading of the disks with galaxy radius or the disks being generally smaller in the past, both of which would be expected in an inside-out disk growth scenario. The overall conclusion is that, at least at low redshifts, the structure of massive quenched satellites at these masses is produced by processes that operate before the quenching takes place. A comparison of our results with semianalytic models argues for a reduction in the efficiency of group halos in quenching their disk satellites and for mechanisms to increase the B/T of low-mass quenched satellites.