arXiv subjects

Jorge Moreno

Publications and source records attributed to Jorge Moreno.

87 records · Page 5Linked to original sources

arXiv2015

Mapping galaxy encounters in numerical simulations: The spatial extent of induced star formation

We employ a suite of 75 simulations of galaxies in idealised major mergers (stellar mass ratio ~2.5:1), with a wide range of orbital parameters, to investigate the spatial extent of interaction-induced star formation. Although the total star formation in galaxy encounters is generally elevated relative to isolated galaxies, we find that this elevation is a combination of intense enhancements within the central kpc and moderately suppressed activity at large galacto-centric radii. The radial dependence of the star formation enhancement is stronger in the less massive galaxy than in the primary, and is also more pronounced in mergers of more closely aligned disc spin orientations. Conversely, these trends are almost entirely independent of the encounter's impact parameter and orbital eccentricity. Our predictions of the radial dependence of triggered star formation, and specifically the suppression of star formation beyond kph-scales, will be testable with the next generation of integral-field spectroscopic surveys.

astro-ph.GA↗

arXiv2014

Rings of star formation: Imprints of a close galaxy encounter

In this talk, I report results from galaxy merger simulations, which suggest the existence of a ring of star formation produced by close galaxy encounters. This is a generic feature of all galaxy interactions, provided that the disc spins are sufficiently aligned. This signature can be used to identify close galaxy pairs that have actually suffered a close interaction.

astro-ph.GA↗

arXiv2014

Why do galaxies stop forming stars? I. The passive fraction - black hole mass relation for central galaxies

We derive the dependence of the fraction of passive central galaxies on the mass of their supermassive black holes for a sample of over 400,000 SDSS galaxies at z < 0.2. Our large sample contains galaxies in a wide range of environments, with stellar masses 8 < log(M*/Msun) < 12, spanning the entire morphological spectrum from pure disks to spheroids. We derive estimates for the black hole masses from measured central velocity dispersions and bulge masses, using a variety of published empirical relationships. We find a very strong dependence of the passive fraction on black hole mass, which is largely unaffected by the details of the black hole mass estimate. Moreover, the passive fraction relationship with black hole mass remains strong and tight even at fixed values of galaxy stellar mass (M*), dark matter halo mass (Mhalo), and bulge-to-total stellar mass ratio (B/T). Whereas, the passive fraction dependence on M*, Mhalo and B/T is weak at fixed MBH. These observations show that, for central galaxies, MBH is the strongest correlator with the passive fraction, consistent with quenching from AGN feedback.

astro-ph.GA↗

arXiv2014

Bulge mass is king: The dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey

We investigate the origin of galaxy bimodality by quantifying the relative role of intrinsic and environmental drivers to the cessation (or `quenching') of star formation in over half a million local Sloan Digital Sky Survey (SDSS) galaxies. Our sample contains a wide variety of galaxies at z=0.02-0.2, with stellar masses of 8 < log(M*/M_sun) < 12, spanning the entire morphological range from pure disks to spheroids, and over four orders of magnitude in local galaxy density and halo mass. We utilise published star formation rates and add to this recent GIM2D photometric and stellar mass bulge + disk decompositions from our group. We find that the passive fraction of galaxies increases steeply with stellar mass, halo mass, and bulge mass, with a less steep dependence on local galaxy density and bulge-to-total stellar mass ratio (B/T). At fixed internal properties, we find that central and satellite galaxies have different passive fraction relationships. For centrals, we conclude that there is less variation in the passive fraction at a fixed bulge mass, than for any other variable, including total stellar mass, halo mass, and B/T. This implies that the quenching mechanism must be most tightly coupled to the bulge. We argue that radio-mode AGN feedback offers the most plausible explanation of the observed trends.

astro-ph.GA↗

arXiv2014

Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe

We compare state-of-the-art semi-analytic models of galaxy formation as well as advanced sub-halo abundance matching models with a large sample of early-type galaxies from SDSS at z < 0.3. We focus our attention on the dependence of median sizes of central galaxies on host halo mass. The data do not show any difference in the structural properties of early-type galaxies with environment, at fixed stellar mass. All hierarchical models considered in this work instead tend to predict a moderate to strong environmental dependence, with the median size increasing by a factor of about 1.5-3 when moving from low to high mass host haloes. At face value the discrepancy with the data is highly significant, especially at the cluster scale, for haloes above log Mhalo > 14. The convolution with (correlated) observational errors reduces some of the tension. Despite the observational uncertainties, the data tend to disfavour hierarchical models characterized by a relevant contribution of disc instabilities to the formation of spheroids, strong gas dissipation in (major) mergers, short dynamical friction timescales, and very short quenching timescales in infalling satellites. We also discuss a variety of additional related issues, such as the slope and scatter in the local size-stellar mass relation, the fraction of gas in local early-type galaxies, and the general predictions on satellite galaxies.

astro-ph.CO↗

arXiv2013

The Dynamics of Galaxy Pairs in a Cosmological Setting

We use the Millennium Simulation, and an abundance-matching framework, to investigate the dynamical behaviour of galaxy pairs embedded in a cosmological context. Our main galaxy-pair sample, selected to have separations under 250 kpc/h, consists of over 1.3 million pairs at redshift z = 0, with stellar masses greater than 10^9 Msun, probing mass ratios down to 1:1000. We use dark matter halo membership and energy to classify our galaxy pairs. In terms of halo membership, central-satellite pairs tend to be in isolation (in relation to external more massive galaxies), are energetically- bound to each other, and are also weakly-bound to a neighbouring massive galaxy. Satellite-satellite pairs, instead, inhabit regions in close proximity to a more massive galaxy, are energetically-unbound, and are often bound to that neighbour. We find that 60% of our paired galaxies are bound to both their companion and to a third external object. Moreover, only 9% of our pairs resemble the kind of systems described by idealised binary merger simulations in complete isolation. In sum, we demonstrate the importance of properly connecting galaxy pairs to the rest of the Universe.

astro-ph.CO↗

arXiv2013

Spatially unassociated galaxies contribute significantly to the blended submillimetre galaxy population: predictions for follow-up observations of ALMA sources

There is anecdotal evidence that spatially and physically unassociated galaxies blended into a single submillimetre (submm) source contribute to the submm galaxy (SMG) population. This work is the first to theoretically predict the number counts of such sources. We generate mock SMG catalogues using lightcones derived from the Bolshoi cosmological simulation; to assign submm flux densities to the mock galaxies, we use a fitting function previously derived from the results of dust radiative transfer performed on hydrodynamical simulations of isolated disc and merging galaxies. We then calculate submm number counts for different beam sizes and without blending. We predict that > ~50 per cent of blended SMGs have at least one spatially unassociated component with S_850 > 1 mJy. For a 15-arcsec beam, blends of >2 galaxies in which at least one component is spatially unassociated dominate the blended sources with total S_850 > ~3 mJy. The distribution of the redshift separations amongst the components is strongly bimodal. The typical redshift separation of spatially unassociated blended sources is ~1. Our predictions for the contributions of spatially unassociated components and the distribution of redshift separations are not testable with currently available data, but they will be easily tested once sufficiently accurate redshifts for the individual subcomponents (resolved by, e.g., ALMA) of a sufficient number of single-dish-detected blended SMGs are available.

astro-ph.CO↗

arXiv2011

Halo Pairs in the Millennium Simulation: Love & Deception

In this work I investigate the statistical properties of a huge catalog of closely interacting pairs of dark matter haloes, extracted from the Millennium Simulation database. Only haloes that reach a minimum mass greater than 8.6 \times 10^10 Msun/h (corresponding to 100 particles) are considered. Close pairs are selected if they come within a critical distance dcrit. I explore the effects of replacing dcrit = 1 Mpc/h with 200 kpc/h on the evolution of separations, lifetimes, total masses and mass ratios of these pairs.

astro-ph.CO↗

arXiv2011

The Cosmic Evolution of Halo Pairs: I. Global Trends

Accumulating evidence suggests that galaxy interactions play an important role in shaping the properties of galaxies. For this reason, cosmological studies focused on the evolution of halo/subhalo pairs are vital. In this paper I describe a large catalogue of halo pairs extracted from the publicly available Millennium Simulation (Springel et. al. 2005). (Throughout this work I use the term `halo' to refer both to individual haloes in the field and subhaloes embedded in larger structures.) Pairs are selected according to whether or not they come within a given critical (comoving) distance dcrit, without the prerequisite that they must merge. Also, a condition requiring haloes to surpass a critical mass Mcrit during their history is imposed. The primary catalogue, consisting of 502,705 pairs, is selected by setting dcrit=1 Mpc/h and Mcrit = 8.6 10^10 Msun/h (equivalent to 100 simulation particles). One of the central goals of this paper is to evaluate the effects of modifying these criteria. For this purpose, additional subcatalogues with more stringent proximity and mass conditions are constructed (i.e., dcrit=200 kpc/h or/and Mcrit=8.6 10^11 Msun/h =1,000 simulation particles). I use a simple five stage picture to perform statistical analyses of their separations, redshifts, masses, mass ratios, and relevant lifetimes. The fraction of pairs that never merge (because one of the members is absorbed by an external halo or both members survive until today) is accounted for. These results provide a broad picture that captures the essential characteristics behind the evolution of halo pairs. This is the first of a series of papers aimed to explore the huge wealth of information encoded in this catalogue. Such investigations will play a fundamental role in future cosmological studies of interacting galaxies and binary (and multiple) quasars.

astro-ph.CO↗

arXiv2009

Dark matter halo creation in moving barrier models

In hierarchical models, the time derivative of the halo mass function may be thought of as the difference of two terms - a creation term, which describes the increase in the number of haloes of mass m from mergers of less massive objects, and a destruction term, which describes the decrease in the number of m-haloes as these merge with other haloes, creating more massive haloes as a result. In models where haloes form from a spherical collapse, the distribution of halo creation times can be estimated from the same formalism which is used to estimate halo abundances: the constant-barrier excursion-set approach. In the excursion set approach, moving, rather than constant-barriers, are necessary for estimating halo abundances when the collapse is triaxial. We show how the corresponding estimates are modified by providing analytic estimates of the creation rate for a wide range of halo masses. We then show that these moving-barrier based predictions are in better agreement with measurements in numerical simulations than are the corresponding predictions of the spherical collapse model. These results should be useful for studies of merger-driven star-formation rates and AGN activity. We also present a similar study of creation of haloes conditioned on belonging to an object of a certain mass today, and reach similar conclusions - the moving barrier based estimates are in substantially better agreement with the simulations. This part of the study may be useful for understanding the tendency for the oldest stars to exist in the most massive objects.

astro-ph↗

arXiv2009

A Merger Tree with Microsolar Mass Resolution: Application to $γ$-ray Emission from Subhalo Population

The hierarchical growth of dark matter haloes, in which galaxies are hosted, has been studied and modeled using various approaches. In this paper we use a modified version the Sheth & Lemson algorithm for a $\mathrmΛ$ cold dark matter power spectrum, and model the growth of a Milky-Way sized halo with microsolar mass resolution, corresponding to the typical Jeans mass for a dark matter Weakly Interacting Massive Particle with mass of 100 GeV. We then compute the \emph{unevolved} subhalo mass function and build-up a Milky-Way halo placing and evolving its satellites. This subhalo population is used to study the $γ$-ray emission from dark matter annihilation. In this case, the subhaloes which populate the host halo have been computed considering only progenitor haloes accreted by the main branch of the tree, so as to correctly treat the embedding of sub-subhaloes inside subhaloes. Each subhalo will indeed host atthe present-time sub-subhaloes accreted when it was an isolated system. In order to compute the sub-subhalo population of a Milky-Way dwarf galaxy, like Draco, and to study its $γ$-ray emission, we first estimate the Draco virial mass at merging redshift $z_m$ and then we run the merger tree from $z_m$ following the halo down to the dark matter Jeans mass. We then study the effect on the Fermi-LAT (GLAST) detectability for both subhaloes in the Milky-Way and in Draco, and we show how subhaloes cannot be responsible for the boost factor needed for detection.

astro-ph↗

arXiv2009

Merger history trees of dark matter haloes in moving barrier models

We present an algorithm for generating merger histories of dark matter haloes. The algorithm is based on the excursion set approach with moving barriers whose shape is motivated by the ellipsoidal collapse model of halo formation. In contrast to most other merger-tree algorithms, ours takes discrete steps in mass rather than time. This allows us to quantify effects which arise from the fact that outputs from numerical simulations are usually in discrete time bins. In addition, it suggests a natural set of scaling variables for describing the abundance of halo progenitors; this scaling is not as general as that associated with a spherical collapse. We test our algorithm by comparing its predictions with measurements in numerical simulations. The progenitor mass fractions and mass functions are in good agreement, as is the predicted scaling law. We also test the formation-redshift distribution, the mass distribution at formation, and the redshift distribution of the most recent major merger; all are in reasonable agreement with N-body simulation data, over a broad range of masses and redshifts. Finally, we study the effects of sampling in discrete time snapshots. In all cases, the improvement over algorithms based on the spherical collapse assumption is significant.

astro-ph↗

arXiv2007

An improved model for the formation times of dark matter haloes

A dark matter halo is said to have formed when at least half its mass hass been assembled into a single progenitor. With this definition, it is possible to derive a simple but useful analytic estimate of the distribution of halo formation times. The standard estimate of this distribution depends on the shape of the conditional mass function--the distribution of progenitor masses of a halo as a function of time. If the spherical collapse model is used to estimate the progenitor mass function, then the formation times one infers systematically underestimate those seen in numerical simulations of hierarchical gravitational clustering. We provide estimates of halo formation which may be related to an ellipsoidal collapse model. These estimates provide a substantially better description of the simulations. We also provide an alternative derivation of the formation time distribution which is based on the assumption that haloes increase their mass through binary mergers only. Our results are useful for models which relate halo structure to halo formation.

astro-ph↗

arXiv2002

Remarks on Noncommutative Solitons

In the first part of this work we consider an unstable non-BPS Dp-\bar{Dp}-brane pair in Type II superstring theory. Turning on a background NS-NS B-field (constant and nonzero along two spatial directions), we show that the tachyon responsible for the unstability has a complex GMS solitonic solution, which is interpreted as the low energy remnant of the resulting D(p-2)-brane. In the second part, we apply these results to construct the noncommutative soliton analogous of Witten's superconducting string. This is done by considering the complex GMS soliton arising from the D3-\bar{D3}-brane annihilation in Type IIB superstring theory. In the presence of left-handed fermions, we apply the Weyl-Wigner-Moyal correspondence and the bosonization technique to show that this object behaves like a superconducting wire.

hep-th↗

arXiv2001

Large B-Fields and Noncommutative Solitons

The purpose of this talk is to review a few issues concerning noncommutativity arising from String Theory. In particular, it is shown how in Type IIB Theory, the annihilation of a D3-\bar{D3} brane pair yields a D1-string. This object, in the presence of a large B-field and fermions, happens to be a complex noncommutative soliton endowed with superconductivity.

hep-th↗