Emilio Romano-Diaz | Bonn Universität (original) (raw)
Papers by Emilio Romano-Diaz
The Astrophysical Journal, 2008
We study the central dark matter (DM) cusp evolution in cosmologically grown galactic halos. Nume... more We study the central dark matter (DM) cusp evolution in cosmologically grown galactic halos. Numerical models with and without baryons (baryons+DM, hereafter BDM model, and pure DM, PDM model, respectively) are advanced from identical initial conditions, obtained using the Constrained Realization method. The DM cusp properties are contrasted by a direct comparison of pure DM and baryonic models. We find a divergent evolution between the PDM and BDM models within the inner few×10 kpc region. The PDM model forms a R −1 cusp as expected, while the DM in the BDM model forms a larger isothermal cusp R −2 instead. The isothermal cusp is stable until z ∼ 1 when it gradually levels off. This leveling proceeds from inside out and the final density slope is shallower than −1 within the central 3 kpc (i.e., expected size of the R −1 cusp), tending to a flat core within ∼ 2 kpc. This effect cannot be explained by a finite resolution of our code which produces only a 5% difference between the gravitationally softened force and the exact Newtonian force of point masses at 1 kpc from the center. Neither is it related to the energy feedback from stellar evolution or angular momentum transfer from the bar. Instead it can be associated with the action of DM+baryon subhalos heating up the cusp region via dynamical friction and forcing the DM in the cusp to flow out and to 'cool' down. The process described here is not limited to low z and can be efficient at intermediate and even high z.
We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyze the matter d... more We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyze the matter distribution and cosmic velocity flows in the Local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution three-dimensional maps fully volume-covering of the volume-weighted velocity and density fields throughout the nearby Universe, out to a distance of 150 Mpc/h. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of theDelaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSCz galaxy sample, produced by Brachini et al. (1999), forms the input sample for...
Monthly Notices of the Royal Astronomical Society
We use the high-resolution zoom-in cosmological simulations of galaxies of Romano-Diaz et al., an... more We use the high-resolution zoom-in cosmological simulations of galaxies of Romano-Diaz et al., and post-process them with a panchromatic 3D radiation transfer code to obtain the galaxy UV luminosity function (LF) at z = 6-12. The galaxy evolution is followed in two regimes: in a rare, heavily overdense region within a ~ 5-sigma density peak, which can host the high-z quasars, and in an average density region in the universe. We find that the overdense regions evolve at a substantially accelerated pace. The most massive galaxy in this region has grown to Mstar ~ 8.4*10^10 Msun by z = 6.3, contains a dust mass of Mdust ~ 4.1*10^8 Msun, and is associated with a very high SFR~ 745 Msun/yr. At the same time, the most massive object in the `normal' region has Mstar~ 3*10^9 Msun and Mdust < 10^7 Msun. The attained SFR - M_star correlation results in the specific SFR slowly increasing with Mstar. We find that most of the UV stellar radiation in high-z massive galaxies is absorbed by ...
We use a high-resolution simulation that tracks the non-equilibrium abundance of molecular hydrog... more We use a high-resolution simulation that tracks the non-equilibrium abundance of molecular hydrogen, H2, within a massive high-redshift galaxy to produce mock ALMA maps of the fine-structure lines of atomic carbon CI 1-0 and CI 2-1. Inspired by recent observational and theoretical work, we assume that CI is thoroughly mixed in giant molecular clouds and demonstrate that its emission is an excellent proxy for H2. The entire H2 mass of a galaxy at redshift z<4 can be detected using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 1 hour of integration time. Low-resolution imaging of the CI lines (in which the target galaxy is resolved into 3-4 beams) will detect nearly 50-60 per cent of the molecular hydrogen in less than 12 hours. In this case, the data cube also provides valuable information regarding the dynamical state of the galaxy. We conclude that ALMA observations of the CI 1-0 and 2-1 emission will...
EAS Publications Series, 2006
The formation and structure of dark matter halos is studied by constrained simulations. A series ... more The formation and structure of dark matter halos is studied by constrained simulations. A series of experiments of the formation of a 10 12 h −1 M⊙ halo is designed to study the dependence of the density profile on its merging history. We find that the halo growth consist of several quiescent phases intermitted by violent events, with the density well approximated by the NFW profile during the former phases. We find that (1) the NFW scale radius Rs stays constant during the quiescent phase and grows abruptly during the violent one. In contrast, the virial radius grows linearly during the quiescent and abruptly during the violent phases. (2) The central density stays unchanged during the quiescent phase while dropping abruptly during the violent phase, and it does not reflect the formation time of the halo. (3) The clear separation of the evolution of an individual halo into quiescent and violent phases implies that its entire evolution cannot be fitted by simple scaling relations.
The Astrophysical Journal, 2012
Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most ma... more Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most massive and luminous galaxies at high redshift are surrounded by overdensities of fainter companions. We test this prediction with Hubble Space Telescope observations acquired by our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very bright z ∼ 8 candidates as Y 098 -dropout sources in four of the 23 non-contiguous WFC3 fields observed. We extend here the search for Y 098dropouts to fainter luminosities (M * galaxies with M AB ∼ −20), with detections at 5σ confidence (compared to the 8σ confidence threshold adopted earlier) identifying 17 new candidates. We demonstrate that there is a correlation between number counts of faint and bright Y 098 -dropouts at 99.84% confidence. Field BoRG58, which contains the best bright z ∼ 8 candidate (M AB = −21.3), has the most significant overdensity of faint Y 098 -dropouts. Four new sources are located within 70 ′′ (corresponding to 3.1 comoving Mpc at z = 8) from the previously known brighter z ∼ 8 candidate. The overdensity of Y 098 -dropouts in this field has a physical origin to very high confidence (p > 99.975%), independent of completeness and contamination rate of the Y 098 -dropout selection. We modeled the overdensity by means of cosmological simulations and estimate that the principal dark matter halo has mass M h ≈ (4 − 7) × 10 11 M ⊙ (∼ 5σ density peak) and is surrounded by several M h ≈ 10 11 M ⊙ halos which could host the fainter dropouts. In this scenario, we predict that all halos will eventually merge into a M h > 2 × 10 14 M ⊙ galaxy cluster by z = 0. Follow-up observations with ground and space 2 Trenti et al.
Monthly Notices of the Royal Astronomical Society, 2014
We introduce a sub-grid model for the non-equilibrium abundance of molecular hydrogen in cosmolog... more We introduce a sub-grid model for the non-equilibrium abundance of molecular hydrogen in cosmological simulations of galaxy formation. We improve upon previous work by accounting for the unresolved structure of molecular clouds in a phenomenological way which combines both observational and numerical results on the properties of the turbulent interstellar medium. We apply the model to a cosmological simulation of the formation of a Milky-Way-sized galaxy at z = 2, and compare the results to those obtained using other popular prescriptions that compute the equilibrium abundance of H 2 . In these runs we introduce an explicit link between star formation and the local H 2 abundance, and perform an additional simulation in which star formation is linked directly to the density of cold gas. We find that, although the global properties of the simulated galaxy are relatively insensitive to the sub-grid H 2 models, the resulting spatial distribution of H 2 is not: molecules extend further into the outer disc of the galaxy in our non-equilibrium model. In addition, the destruction of molecules by supernovae, if substantial, may result in a depletion of the H 2 abundance in the innermost 2 − 3 kpc. Finally, we study dwarf-sized galaxies that lie in the high-resolution region of our simulations and show that their star formation histories are significantly affected by both early metal enrichment and numerical resolution. We conclude that further work is needed in order to verify recent claims on the abundance of dark galaxies at high redshift.
Monthly Notices of the Royal Astronomical Society: Letters, 2014
ABSTRACT We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundan... more ABSTRACT We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundance of molecular hydrogen within a massive high-redshift galaxy to produce mock Atacama Large Millimeter Array (ALMA) maps of the fine-structure lines of atomic carbon, C i 1–0 and C i 2–1. Inspired by recent observational and theoretical work, we assume that C i is thoroughly mixed within giant molecular clouds and demonstrate that its emission is an excellent proxy for H2. Nearly all of the H2 associated with the galaxy can be detected at redshifts z < 4 using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 4 h of integration time. Low-resolution imaging of the C i lines (in which the target galaxy is resolved into three to four beams) will detect ∼80 per cent of the H2 in less than 12 h of aperture synthesis. In this case, the resulting data cube also provides the crucial information necessary for determining the dynamical state of the galaxy. We conclude that ALMA observations of the C i 1–0 and 2–1 emission are well-suited for extending the interval of cosmic look-back time over which the H2 distributions, the dynamical masses, and the Tully–Fisher relation of galaxies can be robustly probed.
The Astrophysical Journal, 2014
We have explored prevailing modes of galaxy growth for redshifts z ∼ 6 − 14, comparing substantia... more We have explored prevailing modes of galaxy growth for redshifts z ∼ 6 − 14, comparing substantially overdense and normal regions of the universe, using high-resolution zoom-in cosmological simulations. Such rare overdense regions have been projected to host high-z quasars. We demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmological filaments which dominates the mass input from major, intermediate and minor mergers. We find that by z ∼ 6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the overdense regions, and by a factor of 5 in the normal environments. Moreover, the rate of the stellar mass input from mergers also lies below that of an in-situ star formation (SF) rate. The fraction of stellar masses in galaxies contributed by mergers in overdense regions is ∼ 12%, and ∼ 33% in the normal regions, at these redshifts. Our median SF rates for ∼ few × 10 9 M galaxies agrees well with the recently estimated rates for z ∼ 7 galaxies from Spitzer's SURF-UP survey. Finally, we find that the main difference between the normal and overdense regions lies in the amplified growth of massive galaxies in massive dark matter halos. This leads to the formation of > ∼ 10 10 M galaxies due to the ∼ 100-fold increase in mass during the above time period. Such galaxies are basically absent in the normal regions at these redshifts.
Proceedings of the International Astronomical Union, 2004
We present a weak lensing analysis and comparison to optical and Xray maps of the close pair of m... more We present a weak lensing analysis and comparison to optical and Xray maps of the close pair of massive clusters A222/223. Indications for a filamentary connection between the clusters are found and discussed. * Based on observations made at ESO/La Silla under program Nos. 064.L-0248, 064.O-0248, 66.A-0165, 68.A-0269. † dietrich@astro.uni-bonn.de
The Astrophysical Journal, 2008
We study formation and evolution of bar-disk systems in fully self-consistent cosmological simula... more We study formation and evolution of bar-disk systems in fully self-consistent cosmological simulations of galaxy formation in the ΛCDM WMAP3 Universe. In a representative model we find that the first generation of bars form in response to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly decay. Subsequent bar generations form and are destroyed during the major merger epoch permeated by interactions with a DM substructure (subhalos). A long-lived bar is triggered by a tide from a subhalo and survives for ∼ 10 Gyr. The evolution of this bar is followed during the subsequent numerous minor mergers and interactions with the substructure. Together with intrinsic factors, these interactions largely determine the stellar bar evolution. The bar strength and its pattern speed anticorrelate, except during interactions and when the secondary (nuclear) bar is present. For about 5 Gyr bar pattern speed increases substantially despite the loss of angular momentum to stars and cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk and relate them to the underlying dynamics. While the bar is made mainly of an intermediate age, ∼ 5 − 6 Gyr, disk stars at z = 0, a secondary nuclear bar which surfaces at z ∼ 0.1 is made of younger, ∼ 1 − 3 Gyr stars.
The Astrophysical Journal, 2007
The evolution of the phase-space density profile in dark matter (DM) halos is investigated by mea... more The evolution of the phase-space density profile in dark matter (DM) halos is investigated by means of constrained simulations, designed to control the merging history of a given DM halo. Halos evolve through a series of quiescent phases of a slow accretion intermitted by violent events of major mergers. In the quiescent phases the density of the halo closely follows the NFW profile and the phase-space density profile, Q(r), is given by the Taylor & Navarro power law, r −β , where β ≈ 1.9 and stays remarkably stable over the Hubble time. Expressing the phase-space density by the NFW parameters, Q(r) = Q s (r/R s ) −β , the evolution of Q is determined by Q s . We have found that the effective mass surface density within R s , Σ s ≡ ρ s R s , remains constant throughout the evolution of a given DM halo along the main branch of its merging tree. This invariance entails that Q s ∝ R
The Astrophysical Journal, 2006
The formation and structure of dark matter (DM) halos is studied by means of constrained realizat... more The formation and structure of dark matter (DM) halos is studied by means of constrained realizations of Gaussian fields using N -body simulations. A series of experiments of the formation of a 10 12 h −1 M ⊙ halo is designed to study the dependence of the density profile on its merging history. We confirm that the halo growth consists of violent and quiescent phases, with the density well approximated by the Navarro-Frenk-White (NFW) profile during the latter phases. We find that (1) the NFW scale radius R s stays constant during the quiescent phase and grows abruptly during the violent one. In contrast, the virial radius grows linearly during the quiescent and abruptly during the violent phases.
The Astrophysical Journal, 2009
We compare the substructure evolution in pure dark matter (DM) halos with those in the presence o... more We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons, hereafter PDM and BDM models. The prime halos have been analyzed in the previous work, Romano-Diaz et al. Models have been evolved from identical initial conditions which have been constructed by means of the Constrained Realization method. The BDM model includes star formation and feedback from stellar evolution onto the gas. A comprehensive catalog of subhalo populations has been compiled and individual and statistical properties of subhalos analyzed, including their orbital differences. We find that subhalo population mass functions in PDM and BDM are consistent with a single power law, M α sbh , for each of the models in the mass range of ∼ 2 × 10 8 M ⊙ − 2 × 10 11 M ⊙ . However, we detect a nonnegligible shift between these functions, the time-averaged α ∼ −0.86 for the PDM and −0.98 for the BDM models. Overall, α appears to be a nearly constant with variations of ±15%. Second, we find that the radial mass distribution of subhalo populations can be approximated by a power law, R γ sbh with a steepening that occurs at the radius of a maximal circular velocity, R vmax , in the prime halos. Here we find that the γ sbh ∼ −1.5 for the PDM and -1 for the BDM models, when averaged over time inside R vmax . The slope is steeper outside this region and approaches −3. We detect little spatial bias (less than 10%) between the subhalo populations and the DM distribution of the main halos. Also, the subhalo population exhibits much less triaxiality in the presence of baryons, in tandem with the shape of the prime halo. Finally, we find that, counter-intuitively, the BDM population is depleted at a faster rate than the PDM one within the central 30 kpc of the prime halo. The reason for this is that although the baryons provide a substantial glue to the subhalos, the main halo exhibits the same trend. This assures a more efficient tidal disruption of the BDM subhalo population. However, this effect can be reversed for a more efficient feedback from stellar evolution and the central supermassive black holes, which will expel baryons from the center and decrease the central concentration of the prime halo. We compare our results with via Lactea and Aquarius simulations and other published results.
The Astrophysical Journal, 2011
The temperature profile of hot gas in galaxies and galaxy clusters is largely determined by the d... more The temperature profile of hot gas in galaxies and galaxy clusters is largely determined by the depth of the total gravitational potential and thereby by the dark matter (DM) distribution. We use high-resolution hydrodynamical simulations of galaxy formation to derive a surprisingly simple relation between the gas temperature and DM properties. We show that this relation holds not just for galaxy clusters but also for equilibrated and relaxed galaxies at radii beyond the central stellar-dominated region of typically a few kpc. It is then clarified how a measurement of the temperature and density of the hot gas component can lead to an indirect measurement of the DM velocity anisotropy in galaxies. We also study the temperature relation for galaxy clusters in the presence of self-regulated, recurrent active galactic nuclei (AGN), and demonstrate that this temperature relation even holds outside the inner region of ≈ 30 kpc in clusters with an active AGN.
The Astrophysical Journal, 2007
We have investigated the effect of an assembly history on the evolution of galactic dark matter (... more We have investigated the effect of an assembly history on the evolution of galactic dark matter (DM) halos of 10 12 h −1 M ⊙ using Constrained Realizations of random Gaussian fields. Five different realizations of a DM halo with distinct merging histories were constructed and have been evolved using collisionless high-resolution N -body simulations. Our main results are: A halo evolves via a sequence of quiescent phases of a slow mass accretion intermitted by violent episodes of major mergers. In the quiescent phases, the density is well fitted by an NFW profile, the inner scale radius R s and the mass enclosed within it remain constant, and the virial radius (R vir ) grows linearly with the expansion parameter a. Within each quiescent phase the concentration parameter (c) scales as a, and the mass accretion history (M vir ) is well described by the Tasitsiomi et al. fitting formula. In the violent phases the halos are not in a virial dynamical equilibrium and both R s and R vir grow discontinuously. The violent episodes drive the halos from one NFW dynamical equilibrium to another. The final structure of a halo, including c, depends on the degree of violence of the major mergers and the number of violent events. Next, we find a distinct difference between the behavior of various NFW parameters taken as averages over an ensemble of halos and those of individual halos. Moreover, the simple scaling relations c−M vir do not apply to the entire evolution of individual halos, and so is the common notion that late forming halos are less concentrated than early forming ones. The entire evolution of the halo cannot be fitted by single analytical expressions.
The Astrophysical Journal, 2010
We compare the substructure evolution in pure dark matter (DM) halos with those in the presence o... more We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons, hereafter PDM and BDM models. The prime halos have been analyzed in the previous work, Romano-Diaz et al. Models have been evolved from identical initial conditions which have been constructed by means of the Constrained Realization method. The BDM model includes star formation and feedback from stellar evolution onto the gas. A comprehensive catalog of subhalo populations has been compiled and individual and statistical properties of subhalos analyzed, including their orbital differences. We find that subhalo population mass functions in PDM and BDM are consistent with a single power law, M α sbh , for each of the models in the mass range of ∼ 2 × 10 8 M ⊙ − 2 × 10 11 M ⊙ . However, we detect a nonnegligible shift between these functions, the time-averaged α ∼ −0.86 for the PDM and −0.98 for the BDM models. Overall, α appears to be a nearly constant with variations of ±15%. Second, we find that the radial mass distribution of subhalo populations can be approximated by a power law, R γ sbh with a steepening that occurs at the radius of a maximal circular velocity, R vmax , in the prime halos. Here we find that the γ sbh ∼ −1.5 for the PDM and -1 for the BDM models, when averaged over time inside R vmax . The slope is steeper outside this region and approaches −3. We detect little spatial bias (less than 10%) between the subhalo populations and the DM distribution of the main halos. Also, the subhalo population exhibits much less triaxiality in the presence of baryons, in tandem with the shape of the prime halo. Finally, we find that, counter-intuitively, the BDM population is depleted at a faster rate than the PDM one within the central 30 kpc of the prime halo. The reason for this is that although the baryons provide a substantial glue to the subhalos, the main halo exhibits the same trend. This assures a more efficient tidal disruption of the BDM subhalo population. However, this effect can be reversed for a more efficient feedback from stellar evolution and the central supermassive black holes, which will expel baryons from the center and decrease the central concentration of the prime halo. We compare our results with via Lactea and Aquarius simulations and other published results.
We assess the extent to which the flux-limited PSCz redshift sample is capable of accounting for ... more We assess the extent to which the flux-limited PSCz redshift sample is capable of accounting for the major share of mass concentrations inducing the external tidal forces affecting the peculiar velocities within the Local Supercluster (LS). The investigation is based upon a comparison of the ``true'' velocities in 2 large N-body simulations and their reconstruction from ``observation-mimicking'' mock catalogues. The mildly nonlinear ``mock'' LS and PSCz velocities are analyzed by means of the Least Action Principle technique in its highly optimized implementation of Nusser & Branchini's Fast Action Method (FAM). For both model N-body Universes, we conclude that the dipolar and quadrupolar force field implied by the PSCz galaxy distribution would indeed be sufficiently representing the full external tidal force field.
Monthly Notices of the Royal Astronomical Society, 2007
We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter d... more We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter distribution and cosmic velocity flows in the local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution 3D maps of the volume-weighted velocity and density fields throughout the nearby universe, the basis for a
The Astrophysical Journal, 2008
We study the central dark matter (DM) cusp evolution in cosmologically grown galactic halos. Nume... more We study the central dark matter (DM) cusp evolution in cosmologically grown galactic halos. Numerical models with and without baryons (baryons+DM, hereafter BDM model, and pure DM, PDM model, respectively) are advanced from identical initial conditions, obtained using the Constrained Realization method. The DM cusp properties are contrasted by a direct comparison of pure DM and baryonic models. We find a divergent evolution between the PDM and BDM models within the inner few×10 kpc region. The PDM model forms a R −1 cusp as expected, while the DM in the BDM model forms a larger isothermal cusp R −2 instead. The isothermal cusp is stable until z ∼ 1 when it gradually levels off. This leveling proceeds from inside out and the final density slope is shallower than −1 within the central 3 kpc (i.e., expected size of the R −1 cusp), tending to a flat core within ∼ 2 kpc. This effect cannot be explained by a finite resolution of our code which produces only a 5% difference between the gravitationally softened force and the exact Newtonian force of point masses at 1 kpc from the center. Neither is it related to the energy feedback from stellar evolution or angular momentum transfer from the bar. Instead it can be associated with the action of DM+baryon subhalos heating up the cusp region via dynamical friction and forcing the DM in the cusp to flow out and to 'cool' down. The process described here is not limited to low z and can be efficient at intermediate and even high z.
We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyze the matter d... more We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyze the matter distribution and cosmic velocity flows in the Local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution three-dimensional maps fully volume-covering of the volume-weighted velocity and density fields throughout the nearby Universe, out to a distance of 150 Mpc/h. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of theDelaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSCz galaxy sample, produced by Brachini et al. (1999), forms the input sample for...
Monthly Notices of the Royal Astronomical Society
We use the high-resolution zoom-in cosmological simulations of galaxies of Romano-Diaz et al., an... more We use the high-resolution zoom-in cosmological simulations of galaxies of Romano-Diaz et al., and post-process them with a panchromatic 3D radiation transfer code to obtain the galaxy UV luminosity function (LF) at z = 6-12. The galaxy evolution is followed in two regimes: in a rare, heavily overdense region within a ~ 5-sigma density peak, which can host the high-z quasars, and in an average density region in the universe. We find that the overdense regions evolve at a substantially accelerated pace. The most massive galaxy in this region has grown to Mstar ~ 8.4*10^10 Msun by z = 6.3, contains a dust mass of Mdust ~ 4.1*10^8 Msun, and is associated with a very high SFR~ 745 Msun/yr. At the same time, the most massive object in the `normal' region has Mstar~ 3*10^9 Msun and Mdust < 10^7 Msun. The attained SFR - M_star correlation results in the specific SFR slowly increasing with Mstar. We find that most of the UV stellar radiation in high-z massive galaxies is absorbed by ...
We use a high-resolution simulation that tracks the non-equilibrium abundance of molecular hydrog... more We use a high-resolution simulation that tracks the non-equilibrium abundance of molecular hydrogen, H2, within a massive high-redshift galaxy to produce mock ALMA maps of the fine-structure lines of atomic carbon CI 1-0 and CI 2-1. Inspired by recent observational and theoretical work, we assume that CI is thoroughly mixed in giant molecular clouds and demonstrate that its emission is an excellent proxy for H2. The entire H2 mass of a galaxy at redshift z<4 can be detected using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 1 hour of integration time. Low-resolution imaging of the CI lines (in which the target galaxy is resolved into 3-4 beams) will detect nearly 50-60 per cent of the molecular hydrogen in less than 12 hours. In this case, the data cube also provides valuable information regarding the dynamical state of the galaxy. We conclude that ALMA observations of the CI 1-0 and 2-1 emission will...
EAS Publications Series, 2006
The formation and structure of dark matter halos is studied by constrained simulations. A series ... more The formation and structure of dark matter halos is studied by constrained simulations. A series of experiments of the formation of a 10 12 h −1 M⊙ halo is designed to study the dependence of the density profile on its merging history. We find that the halo growth consist of several quiescent phases intermitted by violent events, with the density well approximated by the NFW profile during the former phases. We find that (1) the NFW scale radius Rs stays constant during the quiescent phase and grows abruptly during the violent one. In contrast, the virial radius grows linearly during the quiescent and abruptly during the violent phases. (2) The central density stays unchanged during the quiescent phase while dropping abruptly during the violent phase, and it does not reflect the formation time of the halo. (3) The clear separation of the evolution of an individual halo into quiescent and violent phases implies that its entire evolution cannot be fitted by simple scaling relations.
The Astrophysical Journal, 2012
Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most ma... more Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most massive and luminous galaxies at high redshift are surrounded by overdensities of fainter companions. We test this prediction with Hubble Space Telescope observations acquired by our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very bright z ∼ 8 candidates as Y 098 -dropout sources in four of the 23 non-contiguous WFC3 fields observed. We extend here the search for Y 098dropouts to fainter luminosities (M * galaxies with M AB ∼ −20), with detections at 5σ confidence (compared to the 8σ confidence threshold adopted earlier) identifying 17 new candidates. We demonstrate that there is a correlation between number counts of faint and bright Y 098 -dropouts at 99.84% confidence. Field BoRG58, which contains the best bright z ∼ 8 candidate (M AB = −21.3), has the most significant overdensity of faint Y 098 -dropouts. Four new sources are located within 70 ′′ (corresponding to 3.1 comoving Mpc at z = 8) from the previously known brighter z ∼ 8 candidate. The overdensity of Y 098 -dropouts in this field has a physical origin to very high confidence (p > 99.975%), independent of completeness and contamination rate of the Y 098 -dropout selection. We modeled the overdensity by means of cosmological simulations and estimate that the principal dark matter halo has mass M h ≈ (4 − 7) × 10 11 M ⊙ (∼ 5σ density peak) and is surrounded by several M h ≈ 10 11 M ⊙ halos which could host the fainter dropouts. In this scenario, we predict that all halos will eventually merge into a M h > 2 × 10 14 M ⊙ galaxy cluster by z = 0. Follow-up observations with ground and space 2 Trenti et al.
Monthly Notices of the Royal Astronomical Society, 2014
We introduce a sub-grid model for the non-equilibrium abundance of molecular hydrogen in cosmolog... more We introduce a sub-grid model for the non-equilibrium abundance of molecular hydrogen in cosmological simulations of galaxy formation. We improve upon previous work by accounting for the unresolved structure of molecular clouds in a phenomenological way which combines both observational and numerical results on the properties of the turbulent interstellar medium. We apply the model to a cosmological simulation of the formation of a Milky-Way-sized galaxy at z = 2, and compare the results to those obtained using other popular prescriptions that compute the equilibrium abundance of H 2 . In these runs we introduce an explicit link between star formation and the local H 2 abundance, and perform an additional simulation in which star formation is linked directly to the density of cold gas. We find that, although the global properties of the simulated galaxy are relatively insensitive to the sub-grid H 2 models, the resulting spatial distribution of H 2 is not: molecules extend further into the outer disc of the galaxy in our non-equilibrium model. In addition, the destruction of molecules by supernovae, if substantial, may result in a depletion of the H 2 abundance in the innermost 2 − 3 kpc. Finally, we study dwarf-sized galaxies that lie in the high-resolution region of our simulations and show that their star formation histories are significantly affected by both early metal enrichment and numerical resolution. We conclude that further work is needed in order to verify recent claims on the abundance of dark galaxies at high redshift.
Monthly Notices of the Royal Astronomical Society: Letters, 2014
ABSTRACT We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundan... more ABSTRACT We use a high-resolution hydrodynamic simulation that tracks the non-equilibrium abundance of molecular hydrogen within a massive high-redshift galaxy to produce mock Atacama Large Millimeter Array (ALMA) maps of the fine-structure lines of atomic carbon, C i 1–0 and C i 2–1. Inspired by recent observational and theoretical work, we assume that C i is thoroughly mixed within giant molecular clouds and demonstrate that its emission is an excellent proxy for H2. Nearly all of the H2 associated with the galaxy can be detected at redshifts z < 4 using a compact interferometric configuration with a large synthesized beam (that does not resolve the target galaxy) in less than 4 h of integration time. Low-resolution imaging of the C i lines (in which the target galaxy is resolved into three to four beams) will detect ∼80 per cent of the H2 in less than 12 h of aperture synthesis. In this case, the resulting data cube also provides the crucial information necessary for determining the dynamical state of the galaxy. We conclude that ALMA observations of the C i 1–0 and 2–1 emission are well-suited for extending the interval of cosmic look-back time over which the H2 distributions, the dynamical masses, and the Tully–Fisher relation of galaxies can be robustly probed.
The Astrophysical Journal, 2014
We have explored prevailing modes of galaxy growth for redshifts z ∼ 6 − 14, comparing substantia... more We have explored prevailing modes of galaxy growth for redshifts z ∼ 6 − 14, comparing substantially overdense and normal regions of the universe, using high-resolution zoom-in cosmological simulations. Such rare overdense regions have been projected to host high-z quasars. We demonstrate that galaxies in such environments grow predominantly by a smooth accretion from cosmological filaments which dominates the mass input from major, intermediate and minor mergers. We find that by z ∼ 6, the accumulated galaxy mass fraction from mergers falls short by a factor of 10 of the cumulative accretion mass for galaxies in the overdense regions, and by a factor of 5 in the normal environments. Moreover, the rate of the stellar mass input from mergers also lies below that of an in-situ star formation (SF) rate. The fraction of stellar masses in galaxies contributed by mergers in overdense regions is ∼ 12%, and ∼ 33% in the normal regions, at these redshifts. Our median SF rates for ∼ few × 10 9 M galaxies agrees well with the recently estimated rates for z ∼ 7 galaxies from Spitzer's SURF-UP survey. Finally, we find that the main difference between the normal and overdense regions lies in the amplified growth of massive galaxies in massive dark matter halos. This leads to the formation of > ∼ 10 10 M galaxies due to the ∼ 100-fold increase in mass during the above time period. Such galaxies are basically absent in the normal regions at these redshifts.
Proceedings of the International Astronomical Union, 2004
We present a weak lensing analysis and comparison to optical and Xray maps of the close pair of m... more We present a weak lensing analysis and comparison to optical and Xray maps of the close pair of massive clusters A222/223. Indications for a filamentary connection between the clusters are found and discussed. * Based on observations made at ESO/La Silla under program Nos. 064.L-0248, 064.O-0248, 66.A-0165, 68.A-0269. † dietrich@astro.uni-bonn.de
The Astrophysical Journal, 2008
We study formation and evolution of bar-disk systems in fully self-consistent cosmological simula... more We study formation and evolution of bar-disk systems in fully self-consistent cosmological simulations of galaxy formation in the ΛCDM WMAP3 Universe. In a representative model we find that the first generation of bars form in response to the asymmetric dark matter (DM) distribution (i.e., DM filament) and quickly decay. Subsequent bar generations form and are destroyed during the major merger epoch permeated by interactions with a DM substructure (subhalos). A long-lived bar is triggered by a tide from a subhalo and survives for ∼ 10 Gyr. The evolution of this bar is followed during the subsequent numerous minor mergers and interactions with the substructure. Together with intrinsic factors, these interactions largely determine the stellar bar evolution. The bar strength and its pattern speed anticorrelate, except during interactions and when the secondary (nuclear) bar is present. For about 5 Gyr bar pattern speed increases substantially despite the loss of angular momentum to stars and cuspy DM halo. We analyze the evolution of stellar populations in the bar-disk and relate them to the underlying dynamics. While the bar is made mainly of an intermediate age, ∼ 5 − 6 Gyr, disk stars at z = 0, a secondary nuclear bar which surfaces at z ∼ 0.1 is made of younger, ∼ 1 − 3 Gyr stars.
The Astrophysical Journal, 2007
The evolution of the phase-space density profile in dark matter (DM) halos is investigated by mea... more The evolution of the phase-space density profile in dark matter (DM) halos is investigated by means of constrained simulations, designed to control the merging history of a given DM halo. Halos evolve through a series of quiescent phases of a slow accretion intermitted by violent events of major mergers. In the quiescent phases the density of the halo closely follows the NFW profile and the phase-space density profile, Q(r), is given by the Taylor & Navarro power law, r −β , where β ≈ 1.9 and stays remarkably stable over the Hubble time. Expressing the phase-space density by the NFW parameters, Q(r) = Q s (r/R s ) −β , the evolution of Q is determined by Q s . We have found that the effective mass surface density within R s , Σ s ≡ ρ s R s , remains constant throughout the evolution of a given DM halo along the main branch of its merging tree. This invariance entails that Q s ∝ R
The Astrophysical Journal, 2006
The formation and structure of dark matter (DM) halos is studied by means of constrained realizat... more The formation and structure of dark matter (DM) halos is studied by means of constrained realizations of Gaussian fields using N -body simulations. A series of experiments of the formation of a 10 12 h −1 M ⊙ halo is designed to study the dependence of the density profile on its merging history. We confirm that the halo growth consists of violent and quiescent phases, with the density well approximated by the Navarro-Frenk-White (NFW) profile during the latter phases. We find that (1) the NFW scale radius R s stays constant during the quiescent phase and grows abruptly during the violent one. In contrast, the virial radius grows linearly during the quiescent and abruptly during the violent phases.
The Astrophysical Journal, 2009
We compare the substructure evolution in pure dark matter (DM) halos with those in the presence o... more We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons, hereafter PDM and BDM models. The prime halos have been analyzed in the previous work, Romano-Diaz et al. Models have been evolved from identical initial conditions which have been constructed by means of the Constrained Realization method. The BDM model includes star formation and feedback from stellar evolution onto the gas. A comprehensive catalog of subhalo populations has been compiled and individual and statistical properties of subhalos analyzed, including their orbital differences. We find that subhalo population mass functions in PDM and BDM are consistent with a single power law, M α sbh , for each of the models in the mass range of ∼ 2 × 10 8 M ⊙ − 2 × 10 11 M ⊙ . However, we detect a nonnegligible shift between these functions, the time-averaged α ∼ −0.86 for the PDM and −0.98 for the BDM models. Overall, α appears to be a nearly constant with variations of ±15%. Second, we find that the radial mass distribution of subhalo populations can be approximated by a power law, R γ sbh with a steepening that occurs at the radius of a maximal circular velocity, R vmax , in the prime halos. Here we find that the γ sbh ∼ −1.5 for the PDM and -1 for the BDM models, when averaged over time inside R vmax . The slope is steeper outside this region and approaches −3. We detect little spatial bias (less than 10%) between the subhalo populations and the DM distribution of the main halos. Also, the subhalo population exhibits much less triaxiality in the presence of baryons, in tandem with the shape of the prime halo. Finally, we find that, counter-intuitively, the BDM population is depleted at a faster rate than the PDM one within the central 30 kpc of the prime halo. The reason for this is that although the baryons provide a substantial glue to the subhalos, the main halo exhibits the same trend. This assures a more efficient tidal disruption of the BDM subhalo population. However, this effect can be reversed for a more efficient feedback from stellar evolution and the central supermassive black holes, which will expel baryons from the center and decrease the central concentration of the prime halo. We compare our results with via Lactea and Aquarius simulations and other published results.
The Astrophysical Journal, 2011
The temperature profile of hot gas in galaxies and galaxy clusters is largely determined by the d... more The temperature profile of hot gas in galaxies and galaxy clusters is largely determined by the depth of the total gravitational potential and thereby by the dark matter (DM) distribution. We use high-resolution hydrodynamical simulations of galaxy formation to derive a surprisingly simple relation between the gas temperature and DM properties. We show that this relation holds not just for galaxy clusters but also for equilibrated and relaxed galaxies at radii beyond the central stellar-dominated region of typically a few kpc. It is then clarified how a measurement of the temperature and density of the hot gas component can lead to an indirect measurement of the DM velocity anisotropy in galaxies. We also study the temperature relation for galaxy clusters in the presence of self-regulated, recurrent active galactic nuclei (AGN), and demonstrate that this temperature relation even holds outside the inner region of ≈ 30 kpc in clusters with an active AGN.
The Astrophysical Journal, 2007
We have investigated the effect of an assembly history on the evolution of galactic dark matter (... more We have investigated the effect of an assembly history on the evolution of galactic dark matter (DM) halos of 10 12 h −1 M ⊙ using Constrained Realizations of random Gaussian fields. Five different realizations of a DM halo with distinct merging histories were constructed and have been evolved using collisionless high-resolution N -body simulations. Our main results are: A halo evolves via a sequence of quiescent phases of a slow mass accretion intermitted by violent episodes of major mergers. In the quiescent phases, the density is well fitted by an NFW profile, the inner scale radius R s and the mass enclosed within it remain constant, and the virial radius (R vir ) grows linearly with the expansion parameter a. Within each quiescent phase the concentration parameter (c) scales as a, and the mass accretion history (M vir ) is well described by the Tasitsiomi et al. fitting formula. In the violent phases the halos are not in a virial dynamical equilibrium and both R s and R vir grow discontinuously. The violent episodes drive the halos from one NFW dynamical equilibrium to another. The final structure of a halo, including c, depends on the degree of violence of the major mergers and the number of violent events. Next, we find a distinct difference between the behavior of various NFW parameters taken as averages over an ensemble of halos and those of individual halos. Moreover, the simple scaling relations c−M vir do not apply to the entire evolution of individual halos, and so is the common notion that late forming halos are less concentrated than early forming ones. The entire evolution of the halo cannot be fitted by single analytical expressions.
The Astrophysical Journal, 2010
We compare the substructure evolution in pure dark matter (DM) halos with those in the presence o... more We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons, hereafter PDM and BDM models. The prime halos have been analyzed in the previous work, Romano-Diaz et al. Models have been evolved from identical initial conditions which have been constructed by means of the Constrained Realization method. The BDM model includes star formation and feedback from stellar evolution onto the gas. A comprehensive catalog of subhalo populations has been compiled and individual and statistical properties of subhalos analyzed, including their orbital differences. We find that subhalo population mass functions in PDM and BDM are consistent with a single power law, M α sbh , for each of the models in the mass range of ∼ 2 × 10 8 M ⊙ − 2 × 10 11 M ⊙ . However, we detect a nonnegligible shift between these functions, the time-averaged α ∼ −0.86 for the PDM and −0.98 for the BDM models. Overall, α appears to be a nearly constant with variations of ±15%. Second, we find that the radial mass distribution of subhalo populations can be approximated by a power law, R γ sbh with a steepening that occurs at the radius of a maximal circular velocity, R vmax , in the prime halos. Here we find that the γ sbh ∼ −1.5 for the PDM and -1 for the BDM models, when averaged over time inside R vmax . The slope is steeper outside this region and approaches −3. We detect little spatial bias (less than 10%) between the subhalo populations and the DM distribution of the main halos. Also, the subhalo population exhibits much less triaxiality in the presence of baryons, in tandem with the shape of the prime halo. Finally, we find that, counter-intuitively, the BDM population is depleted at a faster rate than the PDM one within the central 30 kpc of the prime halo. The reason for this is that although the baryons provide a substantial glue to the subhalos, the main halo exhibits the same trend. This assures a more efficient tidal disruption of the BDM subhalo population. However, this effect can be reversed for a more efficient feedback from stellar evolution and the central supermassive black holes, which will expel baryons from the center and decrease the central concentration of the prime halo. We compare our results with via Lactea and Aquarius simulations and other published results.
We assess the extent to which the flux-limited PSCz redshift sample is capable of accounting for ... more We assess the extent to which the flux-limited PSCz redshift sample is capable of accounting for the major share of mass concentrations inducing the external tidal forces affecting the peculiar velocities within the Local Supercluster (LS). The investigation is based upon a comparison of the ``true'' velocities in 2 large N-body simulations and their reconstruction from ``observation-mimicking'' mock catalogues. The mildly nonlinear ``mock'' LS and PSCz velocities are analyzed by means of the Least Action Principle technique in its highly optimized implementation of Nusser & Branchini's Fast Action Method (FAM). For both model N-body Universes, we conclude that the dipolar and quadrupolar force field implied by the PSCz galaxy distribution would indeed be sufficiently representing the full external tidal force field.
Monthly Notices of the Royal Astronomical Society, 2007
We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter d... more We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter distribution and cosmic velocity flows in the local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution 3D maps of the volume-weighted velocity and density fields throughout the nearby universe, the basis for a