arXiv subjects

N. D. Padilla

Publications and source records attributed to N. D. Padilla.

17 recordsLinked to original sources

arXiv2023

Active galactic nuclei and gravitational redshifts

Context: Gravitational redshift is a classical effect of Einstein's General Relativity, already measured in stars, quasars and clusters of galaxies. Aims: We here aim to identify the signature of gravitational redshift in the emission lines of active galaxies due to supermassive black holes, and compare to what is found for inactive galaxies. Methods: Using the virial theorem, we estimate gravitational redshifts for quasars from the 14th data release of the Sloan Digital Sky Survey, and compare these with measured ones from the difference between the redshifts of emission lines of Sydney Australian Astronomical Observatory Multi-object Integral Field (SAMI) galaxies in central and outer annuli of their integral field spectra. Results: Firstly, from the full width at half maximum of $H_β$ lines of 57 Seyfert type I galaxies of the AGN Black Hole Mass Database, we derive a median gravitational redshift $z_g = 1.18 \times 10^{-4}$. Expanding this analysis to 86755 quasars from DR14 of SDSS we have a median value $z_g = 1.52 \times 10^{-4}$. Then, by comparing the redshifts of $34$ lines measured at central and outer regions of LINER galaxies in the SAMI survey we obtain $z_g = (0.68 \pm 0.09) \times 10^{-4}$, which increases to $z_g = (1.0 \pm 0.1) \times 10^{-4}$ when using $H_α$ and $H_β$ lines. These numbers are compatible with central black holes of $\approx 10^9$ solar masses and broad line regions of $\approx 1$pc. For non-AGN galaxies the gravitational redshift is compatible with zero.

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arXiv2022

Satellite galaxies in groups in the CIELO Project I. Gas removal from galaxies and its re-distribution in the intragroup medium

We study the impact of the environment on galaxies as they fall in and orbit in the potential well of a Local Group (LG) analogue, following them with high cadence. The analysis is performed on eight disc satellite galaxies from the CIELO suite of hydrodynamical simulations. All galaxies have stellar masses within the range $[10^{8.1} - 10^{9.56}] M_{\sun} $h$^{-1}$. We measure tidal torques, ram pressure and specific star formation rates (sSFR) as a function of time, and correlate them with the amount of gas lost by satellites along their orbits. Stronger removal episodes occur when the disc plane is oriented perpendicular to the direction of motion. More than one peripassage is required to significantly modify the orientations of the discs with respect to the orbital plane. The gas removed during the interaction with the central galaxies may be also found opposite to the direction of motion, depending on the orbital configuration. Satellites are not totally quenched when the galaxies reach their first peripassage, and continue forming about $10\%$ of the final stellar mass after this event. The fraction of removed gas is found to be the product of the joint action of tidal torque and ram pressure, which can also trigger new star formation activity and subsequent supernova feedback.

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arXiv2021

Gravitational redshifting of galaxies in the SPIDERS cluster catalogue

Data from the SPectroscopic IDentification of ERosita Sources (SPIDERS) are searched for a detection of the gravitational redshifting of light from $\sim\!20\,000$ galaxies in $\sim\!2500$ galaxy clusters using three definitions of the cluster centre: its Brightest Cluster Galaxy (BCG), the redMaPPer identified Central Galaxy (CG), or the peak of X-ray emission. Distributions of velocity offsets between galaxies and their host cluster's centre, found using observed redshifts, are created. The quantity $\hatΔ$, the average of the radial velocity difference between the cluster members and the cluster systemic velocity, reveals information on the size of a combination of effects on the observed redshift, dominated by gravitational redshifting. The change of $\hatΔ$ with radial distance is predicted for SPIDERS galaxies in General Relativity (GR), and $f(R)$ gravity, and compared to the observations. The values of $\hatΔ=-13.5\pm4.7$ km s$^{-1}$, $\hatΔ=-12.5\pm5.1$ km s$^{-1}$, and $\hatΔ=-18.6\pm4.8$ km s$^{-1}$ for the BCG, X-ray and CG cases respectively broadly agree with the literature. There is no significant preference of one gravity theory over another, but all cases give a clear detection ($>2.5σ$) of $\hatΔ$. The BCG centroid is deemed to be the most robust method in this analysis, due to no well defined central redshift when using an X-ray centroid, and CGs identified by redMaPPer with no associated spectroscopic redshift. For future gravitational redshift studies, an order of magnitude more galaxies, $\sim\!500\,000$, will be required-a possible feat with the forthcoming Vera C. Rubin Observatory, Euclid and eROSITA.

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arXiv2019

Following the crumbs: Statistical effects of Ram Pressure in Galaxies

We analyse the presence of dust around galaxy group members through the reddening of background quasars. By taking into account quasar colour and their dependence on redshift and angular position, we derive mean quasar colours excess in projected regions around member galaxies and infer the associated dust mass. For disc-like galaxies perpendicular to the plane of the sky, and at group-centric distances of the order of the virial radius, thus likely to reside in the infall regions of groups, we find systematic colour excess values $e \sim 0.009 \pm 0.004$ for $g-r$ colour. Under the hypothesis of Milky Way dust properties we derive dust masses of $5.8 \pm 2.5 \cdot 10^8 M_{\odot}/h$, implying that a large fraction of dust is being stripped from galaxies in their path to groups. We also studied the photometry of member galaxies to derive a colour asymmetry relative to the group centre direction from a given galaxy. We conclude that the regions of galaxies facing the centre are bluer, consistent with the effects of gas compression and star-formation. We also combine these two procedures finding that galaxies with a small colour asymmetry show the largest amounts of dust towards the external regions compared to a control sample. We conclude that dust removal is very efficient in galaxies on infall. The fact that galaxies redder towards groups centres are associated to the strongest reddening of background quasars suggest that gas removal induced by ram pressure stripping plays a key role in galaxy evolution and dust content.

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arXiv2017

Stellar Populations in a semi-analytic model I: bulges of Milky Way-like galaxies

We study the stellar populations of bulges of Milky Way-like (MW-like) galaxies with the aim of identifying the physical processes involved in the formation of the bulge of our Galaxy. We use the semi-analytic model of galaxy formation and evolution SAG adapted to this aim; this kind of models can trace the properties of galaxies and their components like stellar discs, bulges and halos, but resolution limits prevent them from reaching the scale of stellar populations (SPs). Properties of groups of stars formed during single star formation events are stored and tracked in the model and results are compared with observations of stars in the galactic bulge. MW-like galaxies are selected using two different criteria. One of them considers intrinsic photo-metric properties and the second is focused on the cosmological context of the local group of galaxies (LG). We compare our model results with spectroscopic and photometric stellar metallicity distributions. We find that 87% of stars in bulges of MWtype galaxies in our model are accreted and formed in starbursts during disc instability events. Mergers contribute to 13% of the mass budget of the bulge and are responsible for the low metallicity tail of the distribution. Abundance ratios of α elements with respect to iron, [α/Fe], are measured in SPs of model galaxies. The patterns found in the model for SPs with different origins help to explain the lack of a gradient of [α/Fe] ratios in observed stars along the minor axis of the bulge.

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arXiv2015

The origin of the atomic and molecular gas contents of early-type galaxies. II. Misaligned gas accretion

We study the origin of the wide distribution of angles between the angular momenta of the stellar and gas components, $α_{\rm G,S}$, in early-type galaxies (ETGs). We use the GALFORM model of galaxy formation, set in the $Λ$ cold dark matter framework, and coupled it with a Monte-Carlo simulation to follow the angular momenta flips driven by matter accretion onto haloes and galaxies. We consider a gas disk to be misaligned with respect to the stellar body if $α_{\rm G,S}>30$~degrees. By assuming that the only sources of misaligments in galaxies are galaxy mergers, we place a lower limit of $2-5$ per cent on the fraction of ETGs with misaligned gas/stellar components. These low fractions are inconsistent with the observed value of $\approx 42\pm 6$ per cent in ATLAS$^{\rm 3D}$. In the more general case, in which smooth gas accretion in addition to galaxy mergers can drive misalignments, our calculation predicts that $\approx 46$ per cent of ETGs have $α_{\rm G,S}>30$~degrees. In this calculation, we find correlations between $α_{\rm G,S}$ and stellar mass, cold gas fraction and star formation rate, such that ETGs with high masses, low cold gas fractions and low star formation rates are more likely to display aligned cold gas and stellar components. We confirm these trends observationally for the first time using ATLAS$^{\rm 3D}$ data. We argue that the high fraction of misaligned gas discs observed in ETGs is mostly due to smooth gas accretion (e.g. cooling from the hot halo of galaxies) which takes place after most of the stellar mass of the galaxy is in place and comes misaligned with respect to the stellar component. Galaxies that have accreted most of their cold gas content prior to the time where most of the stellar mass was in place show aligned components.

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arXiv2014

Chemo-Archaeological Downsizing in a Hierarchical Universe: Impact of a Top Heavy IGIMF

We make use of a semi-analytical model of galaxy formation to investigate the origin of the observed correlation between [a/Fe] abundance ratios and stellar mass in elliptical galaxies. We implement a new galaxy-wide stellar initial mass function (Top Heavy Integrated Galaxy Initial Mass Function, TH-IGIMF) in the semi-analytic model SAG and evaluate its impact on the chemical evolution of galaxies. The SFR-dependence of the slope of the TH-IGIMF is found to be key to reproducing the correct [a/Fe]-stellar mass relation. Massive galaxies reach higher [a/Fe] abundance ratios because they are characterized by more top-heavy IMFs as a result of their higher SFR. As a consequence of our analysis, the value of the minimum embedded star cluster mass and of the slope of the embedded cluster mass function, which are free parameters involved in the TH-IGIMF theory, are found to be as low as 5 solar masses and 2, respectively. A mild downsizing trend is present for galaxies generated assuming either a universal IMF or a variable TH-IGIMF. We find that, regardless of galaxy mass, older galaxies (with formation redshifts > 2) are formed in shorter time-scales (< 2 Gyr), thus achieving larger [a/Fe] values. Hence, the time-scale of galaxy formation alone cannot explain the slope of the [a/Fe]-galaxy mass relation, but is responsible for the big dispersion of [a/Fe] abundance ratios at fixed stellar mass.We further test the hyphothesis of a TH-IGIMF in elliptical galaxies by looking into mass-to-light ratios, and luminosity functions. Models with a TH-IGIMF are also favoured by these constraints. In particular, mass-to-light ratios agree with observed values for massive galaxies while being overpredicted for less massive ones; this overprediction is present regardless of the IMF considered.

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arXiv2014

The origin of the atomic and molecular gas contents of early-type galaxies. I. A new test of galaxy formation physics

We study the atomic (HI) and molecular hydrogen (H2) contents of early-type galaxies (ETGs) and their gas sources using the GALFORM model of galaxy formation. This model uses a self-consistent calculation of the star formation rate (SFR), which depends on the H2 content of galaxies. We first present a new analysis of HIPASS and ATLAS3D surveys, with special emphasis on ETGs. The model predicts HI and H2 contents of ETGs in agreement with the observations from these surveys only if partial ram pressure stripping of the hot gas is included, showing that observations of neutral gas in `quenched' galaxies place stringent constraints on the treatment of the hot gas in satellites. We find that ~90% of ETGs at z=0 have neutral gas contents supplied by radiative cooling from their hot halos, 8% were supplied by gas accretion from minor mergers that took place in the last 1Gyr, while 2% were supplied by mass loss from old stars. The model predicts neutral gas fractions strongly decreasing with increasing bulge fraction. This is due to the impeded disk regeneration in ETGs, resulting from both active galactic nuclei feedback and environmental quenching by partial ram pressure stripping of the hot gas.

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arXiv2012

Low and High Surface Brightness Galaxies at Void Walls

We study the relative fraction of low and high surface brightness galaxies (LSBGs and HSBGs) at void walls in the SDSS DR7. We focus on galaxies in equal local density environments. We assume that the host dark-matter halo mass (for which we use SDSS group masses) is a good indicator of local density. This analysis allows to examine the behavior of the abundance of LSBG and HSBG galaxies at a fixed local density and distinguish the large-scale environment defined by the void geometry. We compare galaxies in the field, and in the void walls; the latter are defined as the volume of void shells of radius equal to that of the void. We find a significant decrement, a factor $\sim 4$, of the relative fraction of blue, active star-forming LSBGs in equal mass groups at the void walls and the field. This decrement is consistent with an increase of the fraction of blue, active star-forming HSBGs. By contrast, red LSBGs and HSBGs show negligible changes. We argue that these results are consistent with a scenario where LSBGs with blue colors and strong star formation activity at the void walls are fueled by gas from the expanding void regions. This process could lead to LSBG to HSBG transformations.

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arXiv2009

Galaxy star formation in different environments

We use a semi-analytic model of galaxy formation to study signatures of large-scale modulations in the star formation (SF) activity in galaxies. In order to do this we carefully define local and global estimators of the density around galaxies. The former are computed using a voronoi tessellation technique and the latter are parameterised by the normalised distance to haloes and voids, in terms of the virial and void radii, respectively. As a function of local density, galaxies show a strong modulation in their SF, a result that is in agreement with those from several authors. When taking subsamples of equal local density at different large-scale environments, we find relevant global effects whereby the fraction of red galaxies diminishes for galaxies in equal local density environments farther away from clusters and closer to voids. In general, the semianalytic simulation is in good agreement with the available observational results, and offers the possibility to disentangle many of the processes responsible for the variation of galaxy properties with the environment; we find that the changes found in samples of galaxies with equal local environment but different distances to haloes or voids come from the variations in the underlying mass function of dark-matter haloes. There is an additional possible effect coming from the host dark-matter halo ages, indicating that halo assembly also plays a small but significant role ($1.14σ$) in shaping the properties of galaxies, and in particular, hints at a possible spatial correlation in halo/stellar mass ages.

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arXiv2006

Cosmological parameters from CMB measurements and the final 2dFGRS power spectrum

We derive constraints on cosmological parameters using the power spectrum of galaxy clustering measured from the final two-degree field galaxy redshift survey (2dFGRS) and a compilation of measurements of the temperature power spectrum and temperature-polarization cross-correlation of the cosmic microwave background radiation. We analyse a range of parameter sets and priors, allowing for massive neutrinos, curvature, tensors and general dark energy models. In all cases, the combination of datasets tightens the constraints, with the most dramatic improvements found for the density of dark matter and the energy-density of dark energy. If we assume a flat universe, we find a matter density parameter of $Ω_{\rm m}=0.237 \pm 0.020$, a baryon density parameter of $Ω_{\rm b} = 0.041 \pm 0.002$, a Hubble constant of $H_{0}=74\pm2 {\rm kms}^{-1}{\rm Mpc}^{-1}$, a linear theory matter fluctuation amplitude of $σ_{8}=0.77\pm0.05$ and a scalar spectral index of $n_{\rm s}=0.954 \pm 0.023$ (all errors show the 68% interval). Our estimate of $n_{\rm s}$ is only marginally consistent with the scale invariant value $n_{\rm s}=1$; this spectrum is formally excluded at the 95% confidence level. However, the detection of a tilt in the spectrum is sensitive to the choice of parameter space. If we allow the equation of state of the dark energy to float, we find $w_{\rm DE}= -0.85_{-0.17}^{+0.18}$, consistent with a cosmological constant. We also place new limits on the mass fraction of massive neutrinos: $f_ν < 0.105$ at the 95% level, corresponding to $\sum m_ν < 1.2$ eV.

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arXiv2005

Spatial and Dynamical Properties of Voids in a LCDM Universe

We study statistical properties of voids in the distribution of mass, dark-matter haloes and galaxies (B_J<-16) in a LCDM numerical simulation populated with galaxies using a semi-analytic galaxy formation model(GALFORM, Cole et al. 2000). We find that the properties of voids selected from GALFORM galaxies are compatible with those of voids identified from a population of haloes with mass M>10^11.5 M_sun/h, similar to the median halo mass, M_med=10^11.3 M_sun/h. We also find that the number density of galaxy- and halo-defined voids can be up to two orders of magnitude higher than mass-defined voids for large void radii. As expected, there are outflow velocities which show their maximum at larger void-centric distances for larger voids (well described by a linear relation). The void-centric distance where this maximum occurs, follows a suitable power law fit of the form, log(d_vmax)=(r_void/A)^B. At sufficiently large distances, we find mild infall motions onto the sub-dense regions. We find that a similar analysis in redshift space would make both outflows and infalls to appear with a lower amplitude. We also find that the velocity dispersion of galaxies and haloes is larger in the direction parallel to the void walls by ~10-20%. We analyse the void-tracer cross-correlation functions in real- and redshift-space as a function of separation, and also as a function of separations parallel and perpendicular to the line of sight. The distortion pattern observed in xi(sigma,pi) is that of an elongation along the line of sight which extends out to large separations. Positive xi contours evidence finger-of-god motions at the void walls. Elongations along the line of sight are roughly comparable between galaxy-, halo- and mass-defined voids. (Abridged)

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arXiv2005

The galaxy luminosity function around groups

We present a study on the variations of the luminosity function of galaxies around clusters in a numerical simulation with semi-analytic galaxies, attempting to detect these variations in the 2dF Galaxy Redshift Survey. We subdivide the simulation box in equal-density regions around clusters, which we assume can be achieved by selecting objects at a given normalised distance ($r/r_{rms}$, where $r_{rms}$ is an estimate of the halo radius) from the group centre. The semi-analytic model predicts important variations in the luminosity function out to $r/r_{rms}\simeq5$. In brief, variations in the mass function of haloes around clusters (large dark-matter haloes with $M>10^{12}$h$^{-1}$M$_{\sun}$) lead to cluster central regions that present a high abundance of bright galaxies (high $M^*$ values) as well as low luminosity galaxies (high $α$); at $r/r_{rms}\simeq 3$ there is a lack of bright galaxies, which shows the depletion of galaxies in the regions surrounding clusters (minimum in $M^*$ and $α$), and a tendency to constant luminosity function parameters at larger cluster-centric distances. We take into account the observational biases present in the real data by reproducing the peculiar velocity effect on the redshifts of galaxies in the simulation box, and also by producing mock catalogues. We find that excluding from the analysis galaxies wich in projection are close to the centres of the groups provides results that are qualitatively consistent with the full simulation box results.

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arXiv2003

The power spectrum of galaxy clustering in the APM survey

We measure the power spectrum of galaxy clustering in real space from the APM Galaxy Survey. We present an improved technique for the numerical inversion of Limber's equation that relates the angular clustering of galaxies to an integral over the power spectrum in three dimensions. Our approach is underpinned by a large ensemble of mock galaxy catalogues constructed from the Hubble Volume N-body simulations. The mock catalogues are used to test for systematic effects in the inversion algorithm and to estimate the errors on our measurement. We find that we can recover the power spectrum to an accuracy of better than 15% over three decades in wavenumber. A key advantage of the use of mock catalogues to infer errors is that we can apply our technique on scales for which the density fluctuations are not Gaussian, thus probing the regime that offers the best constraints on models of galaxy formation. On large scales, our measurement of the power spectrum is consistent with the shape of the mass power spectrum in the popular ``concordance'' cold dark matter model. The galaxy power spectrum on small scales is strongly affected by nonlinear evolution of density fluctuations, and, to a lesser degree, by galaxy bias. The rms variance in the galaxy distribution, when smoothed in spheres of radius 8 h^(-1)Mpc, is sigma^g_8=0.96^(+0.17)_(-0.20) and the shape of the power spectrum on large scales is described by a simple fitting formula with parameter Gamma= 0.19^(+0.13)_(-0.04) (these errors are the 1-sigma ranges for a two parameter fit). We use our measurement of the power spectrum to estimate the galaxy two point correlation function; the results are well described by a power law with correlation length r_0 = 5.9 +- 0.7 h^(-1)Mpc and slope gamma = 1.61 +- 0.06 for pair separations in the range 0.1 < r/[h^(-1)Mpc] < 20.

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arXiv2003

Anisotropies in the redshift-space correlations of galaxy groups and clusters I: Simulated catalogues

We analyse the correlation function of mock galaxy clusters in redshift space. We constructed several mock catalogues designed to mimic the selection biases inherent in a variety of observational surveys. We explore different effects that contribute to the distortion of the clustering pattern; the pairwise velocity distribution of galaxy systems, coherent bulk motions, redshift errors and systematics in cluster identification. Our tests show that the redshift-space clustering pattern of galaxy systems is highly influenced by effects associated with the identification procedure from two dimensional surveys. These systems show a spuriously large correlation amplitude, an effect that is present and even stronger in a subsample whose angular positions coincide with 3-dimensional identified clusters. The use of a small number of redshift measurements in the determination of the cluster distance has a smaller impact on the measured correlation function. We show that an angular incompleteness in redshift surveys, such as that present in the 2dFGRS 100k public release, has no significant effect in the results. We suggest that the nature of projection effects arise mainly from structures along the line of sight in the filamentary large-scale clustering pattern. Thus spectroscopic surveys are the only means of providing unbiased cluster samples.

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arXiv2003

Anisotropies in the redshift-space correlations of galaxy groups and clusters II: Analysis of observational cluster samples

We study the redshift space correlation function of galaxy clusters for observational samples constructed in different surveys. We explore correlation amplitudes, pairwise velocity distributions and bias factors. Systematics in cluster identification procedures are the main source of biased estimates of the correlation amplitude and inferred velocity dispersions. By comparing our results with those of numerical simulations we explore the strong influence on the clustering distortion pattern in redshift space from effects associated with the cluster identification procedure from two dimensional surveys as is the case of Abell and APM clusters. The identification of clusters in X-ray surveys improves this situation, although there are still systematic effects which are probably due to identification of optical sources in the determination of cluster redshifts. These systematics are particularly strong for the most luminous X-ray selected clusters in the Extended Bright Cluster Survey, which exhibits very large anisotropies, comparable to those present in the Abell catalogue. Our results demonstrate that forthcoming large redshift surveys will be extremely important for the construction of new samples of groups and clusters as well as improving the determination of optical and X-ray selected cluster distances, essential for reliable analyses of the large scale structure.

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arXiv2002

Determination of the Linear Mass Power Spectrum From the Mass Function of Galaxy Clusters

We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation sigma (M) using the expression for the mass function in the Press & Schechter (1974), Sheth, Mo & Tormen (2001) and Jenkins et al. (2001) formalisms. We apply different techniques to recover the adimensional power spectrum Delta ^{2}(k) from sigma (M) namely the k_{eff} approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the tCDM and LCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (1994), FKP, method. We find that the mass function based method presented here can provide a very accurate estimate of the linear power spectrum, particularly for low values of k. This estimate is comparable, or even better behaved, than the FKP solution. The principal advantage of our method is that it allows the determination of the linear mass power spectrum using the joint information of objects of a wide range of masses without dealing with specific assumptions on the bias relative to the underlying mass distribution.

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