Browsing by Author "Motta, V"

Now showing 1 - 16 of 16
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    Advanced camera for surveys observations of a strongly lensed arc in a field elliptical galaxy
    (2004) Blakeslee, JP; Zekser, KC; Benítez, N; Franx, M; White, RL; Ford, HC; Bouwens, RJ; Infante, L; Cross, NJ; Hertling, G; Holden, BP; Illingworth, GD; Motta, V; Menanteau, F; Meurer, GR; Postman, M; Rosati, P; Zheng, W
    We report the discovery of a strongly lensed arc system around a field elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images of a parallel field observed during NICMOS observations of the HST Ultra Deep Field. The ACS parallel data comprise deep imaging in the F435W, F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1."6 from the galaxy center and subtends about 120degrees. Spectroscopic follow-up at Magellan Observatory yields a redshift z = 0.6174 for the lensing galaxy, and we photometrically estimate z(phot) = 2.4 +/- 0.3 for the arc. We also identify a likely counterarc at a radius of 0."6 that shows structure similar to that seen in the main arc. We model this system and find a good fit to an elliptical isothermal potential of velocity dispersion a sigma approximate to 300 km s(-1), the value expected from the fundamental plane, and some external shear. Several other galaxies in the field have colors similar to the lensing galaxy and likely make up a small group.
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    Barrow Entropy Cosmology: an observational approach with a hint of stability analysis
    (2021) Leon, Genly; Magana, Juan; Hernandez-Almada, A.; Garcia-Aspeitia, Miguel A.; Verdugo, Tomas; Motta, V
    In this work, we use an observational approach and dynamical system analysis to study the cosmological model recently proposed by Saridakis (2020), which is based on the modification of the entropy-area black hole relation proposed by Barrow (2020). The Friedmann equations governing the dynamics of the Universe under this entropy modifica-tion can be calculated through the gravity-thermo dynamics conjecture. We investigate two models, one considering only a matter component and the other including matter and ra-diation, which have new terms compared to the standard model sourcing the late cosmic acceleration. A Bayesian analysis is performed in which using five cosmological observations (observational Hubble data, type Ia supernovae, HII galaxies, strong lensing systems, and baryon acoustic oscillations) to constrain the free parameters of both models. From a joint analysis, we obtain constraints that are consistent with the standard cosmological paradigm within 2a-confidence level. In addition, a complementary dynamical system analysis using local and global variables is developed which allows obtaining a qualitative description of the cosmology. As expected, we found that the dynamical equations have a de Sitter solution at late times.
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    Clustering of star-forming galaxies near a radio galaxy at z=5.2
    (2006) Overzier, RA; Miley, GK; Bouwens, RJ; Cross, NJG; Zirm, AW; Benítez, N; Blakeslee, JP; Clampin, M; Demarco, R; Ford, HC; Hartig, GF; Illingworth, GD; Martel, AR; Röttgering, HJA; Venemans, B; Ardila, DR; Bartko, F; Bradley, LD; Broadhurst, TJ; Coe, D; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Homeier, N; Infante, L; Kimble, RA; Krist, JE; Mei, S; Menanteau, F; Meurer, GR; Motta, V; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We present HSTACS observations of the most distant radio galaxy known, TNJ0924-2201 at z = 5.2. This radio galaxy has six spectroscopically confirmed Ly alpha-emitting companion galaxies and appears to lie within an overdense region. The radio galaxy is marginally resolved in i(775) and z(850), showing continuum emission aligned with the radio axis, similar to what is observed for lower redshift radio galaxies. Both the half-light radius and the UV star formation rate are comparable to the typical values found for Lyman break galaxies at z similar to 4-5. The Ly alpha emitters are sub-L-* galaxies, with deduced star formation rates of 1-10 M-circle dot yr(-1). One of the Ly alpha emitters is only detected in Ly alpha. Based on the star formation rate of similar to 3 M-circle dot yr(-1) calculated from Ly alpha, the lack of continuum emission could be explained if the galaxy is younger than similar to 2 Myr and is producing its first stars. Observations in V(606)i(775)z(850) were used to identify additional Lyman break galaxies associated with this structure. In addition to the radio galaxy, there are 22 V-606 break (z similar to 5) galaxies with z(850) < 26.5 (5 sigma), two of which are also in the spectroscopic sample. We compare the surface density of similar to 2 arcmin(-2) to that of similarly selected V-606 dropouts extracted from GOODS and the UDF parallel fields. We find evidence for an overdensity to very high confidence (> 99%), based on a counts-in-cells analysis applied to the control field. The excess suggests that the V-606 break objects are associated with a forming cluster around the radio galaxy.
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    Cosmic acceleration in unimodular gravity
    (2019) Garcia-Aspeitia, Miguel A.; Martinez-Robles, C.; Hernandez-Almada, A.; Magana, Juan; Motta, V
    We study unimodular gravity in the context of cosmology, particularly some interesting consequences that might be able to describe the background cosmology and the late cosmic acceleration. We focus our attention on the hypothesis of nonconservation of the energy momentum tensor. This characteristic has an interesting outcome: we can obtain a modified Friedmann equation along with the acceleration equation and also new fluid equations related to a third order derivative of the scale factor, known in cosmography as the jerk parameter. As a consequence of this theory, it seems that radiation and the cosmological constant are intimately related, in agreement with what some authors have called the third coincidence problem. Their connection is the parameter z(ini), which has a value of 11.29 and coincides with the reionization epoch. As a result, we are able to explain the late acceleration as a natural consequence of the equations, associating the new fluid with radiation and, thus, eliminating the need for another component (i.e., dark energy). Finally, we interpret the results and discuss the pros and cons of using the cosmological constant under the hypothesis of nonconservation of the energy momentum tensor in the unimodular gravity scenario.
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    Cosmography using strong-lensing systems and cosmic chronometers
    (2021) Lizardo, Andres; Amante, Mario H.; Garcia-Aspeitia, Miguel A.; Magana, Juan; Motta, V
    Using a new sub-sample of observed strong gravitational lens systems, for the first time, we present the equation for the angular diameter distance in the y-redshift scenario for cosmography and use it to test the cosmographic parameters. In addition, we also use the observational Hubble data from cosmic chronometers and a joint analysis of both data are performed. Among the most important conclusions are that this new analysis for cosmography using strong-lensing systems (SLSs) is equally competitive to constrain the cosmographic parameters as others presented in literature. Additionally, we present the reconstruction of the effective equation of state inferred from our samples, showing that at z = 0 those reconstructions from SLSs and joint analysis are in concordance with the standard model of cosmology.
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    Evolution in the cluster early-type galaxy size-surface brightness relation at z ≃ 1
    (2005) Holden, BP; Blakeslee, JP; Postman, M; Illingworth, GD; Demarco, R; Franx, M; Rosati, P; Bouwens, RJ; Martel, AR; Ford, H; Clampin, M; Hartig, GF; Benítez, N; Cross, NJG; Homeier, N; Lidman, C; Menanteau, F; Zirm, A; Ardila, DR; Bartko, F; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Feldman, PD; Golimowski, DA; Goto, T; Gronwall, C; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Magee, D; Mei, S; Meurer, GR; Miley, GK; Motta, V; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We investigate the evolution in the distribution of surface brightness, as a function of size, for elliptical and S0 galaxies in the two clusters RDCS J1252.9 - 2927 ( z = 1: 237) and RX J0152.7 - 1357 ( z = 0: 837). We use multicolor imaging with the Advanced Camera for Surveys on the Hubble Space Telescope to determine these sizes and surface brightnesses. Using three different estimates of the surface brightnesses, we find that we reliably estimate the surface brightness for the galaxies in our sample with a scatter of < 0.2 mag and with systematic shifts of <= 0.05 mag. We construct samples of galaxies with early- type morphologies in both clusters. For each cluster, we use a magnitude limit in a band that closely corresponds to the rest- frame B, to magnitude limit of M-B = - 18: 8 at z = 0, and select only those galaxies within the color- magnitude sequence of the cluster or by using our spectroscopic redshifts. We measure evolution in the rest- frame B surface brightness and find - 1: 41 +/- 0: 14 mag from the Coma Cluster of galaxies for RDCS J1252.9 - 2927 and - 0: 90 +/- 0: 12 mag of evolution for RX J0152.7 - 1357, or an average evolution of ( - 1: 13 +/- 0: 15) z mag. Our statistical errors are dominated by the observed scatter in the size - surface brightness relation, sigma = 0: 42 +/- 0: 05 mag for RX J0152.7 - 1357 and sigma = 0: 76 +/- 0: 10 mag for RDCS J1252.9 - 2927. We find no statistically significant evolution in this scatter, although an increase in the scatter could be expected. Overall, the pace of luminosity evolution we measure agrees with that of the fundamental plane of early- type galaxies, implying that the majority of massive early- type galaxies observed at z similar or equal to 1 formed at high redshifts.
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    Evolution of the color-magnitude relation in high-redshift clusters
    (2006) Mei, S; Blakeslee, JP; Stanford, SA; Holden, BP; Rosati, P; Strazzullo, V; Homeier, N; Postman, M; Franx, M; Rettura, A; Ford, H; Illingworth, GD; Ettori, S; Bouwens, RJ; Demarco, R; Martel, AR; Clampin, M; Hartig, GF; Eisenhardt, P; Ardila, DR; Bartko, F; Benítez, N; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Golimowski, DA; Goto, T; Gronwall, C; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Menanteau, F; Meurer, GR; Miley, GK; Motta, V; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    The color-magnitude relation has been determined for the RDCS J0910+5422 cluster of galaxies at redshift z = 1.106. Cluster members were selected from the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) images, combined with ground-based near-IR imaging and optical spectroscopy. The observed early-type color-magnitude relation (CMR) in i(775) - z(850) versus z(850) shows an intrinsic scatter in color of 0.060 +/- 0.009 mag, within 10 from the cluster X-ray emission center. Both the elliptical and the S0 galaxies show small scatter about the CMR of 0.042 +/- 0.010 and 0.044 +/- 0.020 mag, respectively. From the scatter about the CMR, a mean luminosity weighted age t > 3: 3 Gyr (z(f) approximate to 3) is derived for the elliptical galaxies, assuming a simple stellar population modeling (single-burst solar metallicity). Strikingly, the S0 galaxies in RDCS J0910+5422 are systematically bluer in i(775) - z(850), by 0.07 +/- 0.02 mag, than the ellipticals. The ellipticity distribution as a function of color indicates that the face-on S0s in this particular cluster have likely been classified as elliptical. Thus, if anything, the offset in color between the elliptical and S0 populations may be even more significant. The color offset between S0 and E galaxies corresponds to an age difference of approximate to 1 Gyr for a single-burst solar-metallicity model. A solar-metallicity model with an exponential decay in star formation will reproduce the offset for an age of 3.5 Gyr; i.e., the S0s have evolved gradually from star-forming progenitors. The early-type population in this cluster appears to be still forming. The blue early-type disk galaxies in RDCS J0910+5422 likely represent the direct progenitors of the more evolved S0s that follow the same red sequence as elliptical galaxies in other clusters. Thirteen red galaxy pairs are observed, and the galaxies associated in pairs constitute similar to 40% of the CMR galaxies in this cluster.
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    Feedback and brightest cluster galaxy formation
    (2005) Zirm, AW; Overzier, RA; Miley, GK; Blakeslee, JP; Clampin, M; De Breuck, C; Demarco, R; Ford, HC; Hartig, GF; Homeier, N; Illingworth, GD; Martel, AR; Röttgering, HJA; Venemans, B; Ardila, DR; Bartko, F; Benítez, NB; Bouwens, RJ; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Feldman, PD; Franx, M; Golimowski, DA; Goto, T; Gronwall, C; Holden, B; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Mei, S; Menanteau, F; Meurer, GR; Motta, V; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We present deep optical imaging of the z 4: 1 radio galaxy TN J1338 - 1942, obtained using the Advanced Camera for Surveys ( ACS) on board the Hubble Space Telescope, as well as ground- based near- infrared imaging data from the European Southern Observatory ( ESO) Very Large Telescope ( VLT). The radio galaxy is known to reside within a large galaxy overdensity ( both in physical extent and density contrast). There is good evidence that this `` protocluster'' region is the progenitor of a present- day rich galaxy cluster. TN J1338 is the dominant galaxy in the protocluster in terms of size and luminosity ( in both the optical and near- infrared) and therefore seems destined to evolve into the brightest cluster galaxy. The high spatial resolution ACS images reveal several kiloparsec- scale features within and around the radio galaxy. The continuum light is aligned with the radio axis and is resolved into two clumps in the i(775) and z(850) bands. These components have luminosities similar to 10(9) L-circle dot and sizes of a few kpc. The estimated nebular continuum, scattered light, synchrotron- and inverse Compton - scattering contributions to the aligned continuum light are only a few percent of the observed total, indicating that the observed flux is likely dominated by forming stars. The estimated star formation rate for the whole radio galaxy is similar to 200M(circle dot) yr(-1). A simple model in which the jet has triggered star formation in these continuum knots is consistent with the available data. A striking, but small, linear feature is evident in the z850 aligned light and may be indicative of a large- scale shock associated with the advance of the radio jet. The rest of the aligned light also seems morphologically consistent with star formation induced by shocks associated with the radio source, as seen in other high- z radio galaxies ( e. g., 4C 41.17). An unusual feature is seen in Ly alpha emission. A wedge- shaped extension emanates from the radio galaxy perpendicularly to the radio axis. This `` wedge'' naturally connects to the surrounding asymmetric, large- scale (similar to 100 kpc) Ly alpha halo. We posit that the wedge is a starburst- driven superwind associated with the first major epoch of formation of the brightest cluster galaxy. The shock and wedge are examples of feedback processes due to both active galactic nucleus and star formation in the earliest stages of massive galaxy formation.
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    Generalized emergent dark energy: observational Hubble data constraints and stability analysis
    (2020) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V
    Recently, a phenomenologically emergent dark energy (PEDE) model was presented with a dark energy density evolving as (Omega) over tilde (DE)(z) = Omega(DE,0)[1 - tanh(log(10)(1 + z))], i.e. with no degree of freedom. Later on, a generalized model was proposed by adding one degree of freedom to the PEDE model, encoded in the parameter Delta. Motivated by these proposals, we constrain the parameter space (h, Omega((0))(m)) and (h, Omega((0))(m), Delta) for PEDE and generalized emergent dark energy (GEDE), respectively, by employing the most recent observational (non-)homogeneous and differential age Hubble data. Additionally, we reconstruct the deceleration and jerk parameters and estimate yield values at z = 0 of q(0) = -0.784(-0.027)(+0.028) and j(0) = 1.241(-0.149)(+0.164) for PEDE and q(0) = -0.730(-0.067)(+0.059) and j(0) = 1.293(-0.187)(+0.194) for GEDE using the homogeneous sample. We report values on the deceleration-acceleration transition redshift with those reported in the literature within 2 sigma CL. Furthermore, we perform a stability analysis of the PEDE and GEDE models to study the global evolution of the Universe around their critical points. Although the PEDE and GEDE dynamics are similar to the standard model, our stability analysis indicates that in both models there is an accelerated phase at early epochs of the Universe evolution.
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    Hubble Space Telescope Advanced Camera for Surveys coronagraphic imaging of the AU microscopii debris disk
    (2005) Krist, JE; Ardila, DR; Golimowski, DA; Clampin, M; Ford, HC; Illingworth, GD; Hartig, GF; Bartko, F; Benítez, N; Blakeslee, JP; Bouwens, RJ; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Cross, NJG; Demarco, R; Feldman, PD; Franx, M; Goto, T; Gronwall, C; Holden, B; Homeier, N; Infante, L; Kimble, RA; Lesser, MP; Martel, AR; Mei, S; Menanteau, F; Meurer, GR; Miley, GK; Motta, V; Postman, M; Rosati, P; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We present Hubble Space Telescope Advanced Camera for Surveys multicolor coronagraphic images of the recently discovered edge-on debris disk around the nearby (similar to10 pc) M dwarf AU Microscopii. The disk is seen between r = 0".75 and 15" (7.5-150 AU) from the star. It has a thin midplane with a projected FWHM thickness of 2.5-3.5 AU within r < 50 AU of the star that increases to 6.5-9 AU at r similar to 75 AU. The disk's radial brightness profile is generally flat for r < 15 AU, then decreases gradually (I proportional to r(1.8)) out to r approximate to 43 AU, beyond which it falls rapidly (I proportional to r(-4.7)). Within 50 AU the midplane is straight and aligned with the star, and beyond that it deviates by similar to3degrees, resulting in a bowed appearance that was also seen in ground-based images. Three-dimensional modeling of the disk shows that the inner region (r < 50 AU) is inclined to the line of sight by less than 1degrees and the outer disk by similar to3degrees. The inclination of the outer disk and moderate forward scattering (g approximate to 0.4) can explain the apparent bow. The intrinsic, deprojected FWHM thickness is 1.5-10 AU, increasing with radius. The models indicate that the disk is clear of dust within similar to12 AU of the star, in general agreement with the previous prediction of 17 AU based on the infrared spectral energy distribution. The disk is blue, being 60% brighter at B than I relative to the star. One possible explanation for this is that there is a surplus of very small grains compared with other imaged debris disks that have more neutral or red colors. This may be due to the low radiation pressure exerted by the late-type star. Observations at two epochs show that an extended source seen along the midplane is a background galaxy.
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    Kaniadakis-holographic dark energy: observational constraints and global dynamics
    (2022) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V; Saridakis, Emmanuel N.; Yesmakhanova, Kuralay
    We investigate Kaniadakis-holographic dark energy by confronting it with observations. We perform a Markov Chain Monte Carlo analysis using cosmic chronometers, supernovae type Ia, and Baryon Acoustic Oscillations data. Concerning the Kaniadakis parameter, we find that it is constrained around zero, namely around the value in which Kaniadakis entropy recovers standard Bekenstein-Hawking one. Additionally, for the present matter density parameter Omega((0))(m), we obtain a value slightly smaller compared to Lambda CDM scenario. Furthermore, we reconstruct the evolution of the Hubble, deceleration, and jerk parameters extracting the deceleration-acceleration transition redshift as z(T) = 0.86(-0.14)(+0.21). Finally, performing a detailed local and global dynamical system analysis, we find that the past attractor of the Universe is the matter-dominated solution, while the late-time stable solution is the dark-energy-dominated one.
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    Luminosity functions of the galaxy cluster MS 1054-0321 at z=0.83 based on ACS photometry
    (2005) Goto, T; Postman, M; Cross, NJG; Illingworth, GD; Tran, K; Magee, D; Franx, M; Benítez, N; Bouwens, RJ; Demarco, R; Ford, HC; Homeier, NL; Martel, AR; Menanteau, F; Clampin, M; Hartig, GF; Ardila, DR; Bartko, F; Blakeslee, JP; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Feldman, PD; Golimowski, DA; Gronwall, C; Holden, B; Infante, L; Jee, MJ; Krist, JE; Lesser, MP; Mei, S; Meurer, GR; Miley, GK; Motta, V; Overzier, R; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W; Zirm, A
    We present new measurements of the galaxy luminosity function (LF) and its dependence on local galaxy density, color, morphology, and clustocentric radius for the massive z = 0.83 cluster MS 1054-0321. Our analyses are based on imaging performed with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST) in the F606W, F775W, and F850LP passbands and extensive spectroscopic data obtained with the Keck Low-Resolution Imaging Spectrograph. Our main results are based on a spectroscopically selected sample of 143 cluster members with morphological classifications derived from the ACS observations. Our three primary findings are (1) the faint-end slope of the LF is steepest in the bluest filter, (2) the LF in the inner part of the cluster (or highest density regions) has a flatter faint-end slope, and (3) the fraction of early-type galaxies is higher at the bright end of the LF, and gradually decreases toward fainter magnitudes. These characteristics are consistent with those in local galaxy clusters, indicating that, at least in massive clusters, the common characteristics of cluster LFs are established at z = 0.83. These results provide additional support for the hypothesis that the formation of galaxies in MS 1054-0321 began at redshifts considerably greater than unity. We also find a 2 sigma deficit of intrinsically faint, red galaxies (i(775)-z(850) greater than or equal to 0.5, M-i > -19) in this cluster. Although the significance is marginal, this trend may suggest that faint, red galaxies (which are common in z < 0.1 rich clusters) have not yet been created in this cluster at z = 0.83. The giant-to-dwarf ratio in MS 1054-0321 starts to increase inwards of the virial radius or when Sigma > 30 Mpc(-2), coinciding with the environment where the galaxy star formation rate and the morphology-density relation start to appear. A physical process that begins to become effective at around the virial radius or Sigma similar to 30 Mpc(-2) may thus be responsible for the evolution of color and luminosity of cluster galaxies.
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    Observational constraints and dynamical analysis of Kaniadakis horizon-entropy cosmology
    (2022) Hernandez-Almada, A.; Leon, Genly; Magana, Juan; Garcia-Aspeitia, Miguel A.; Motta, V; Saridakis, Emmanuel N.; Yesmakhanova, Kuralay; Millano, Alfredo D.
    We study the scenario of Kaniadakis horizon-entropy cosmology, which arises from the application of the gravity-thermodynamics conjecture using the Kaniadakis modified entropy. The resulting modified Friedmann equations contain extra terms that constitute an effective dark energy sector. We use data from cosmic chronometers, Type Ia supernova, H II galaxies, strong lensing systems, and baryon acoustic oscillation observations, and we apply a Bayesian Markov chain Monte Carlo analysis to construct the likelihood contours for the model parameters. We find that the Kaniadakis parameter is constrained around 0, namely around the value where the standard Bekenstein-Hawking is recovered. Concerning the normalized Hubble parameter, we find h = 0.708(-0.011)(+0.012), a result that is independently verified by applying the H0(z) diagnostic and, thus, we conclude that the scenario at hand can alleviate the H-0 tension problem. Regarding the transition redshift, the reconstruction of the cosmographic parameters gives z(T) = 0.715(-0.041)(+0.042). Furthermore, we apply the Akaike, Bayesian, and deviance information criteria, and we find that in most data sets the scenario is statistical equivalent to Lambda cold dark matter one. Moreover, we examine the big bang nucleosynthesis, and we show that the scenario satisfies the corresponding requirements. Additionally, we perform a phase-space analysis, and we show that the Universe past attractor is the matter-dominated epoch, while at late times the Universe results in the dark-energy-dominated solution. Finally, we show that Kaniadakis horizon-entropy cosmology accepts heteroclinic sequences, but it cannot exhibit bounce and turnaround solutions.
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    Stability analysis and constraints on interacting viscous cosmology
    (2020) Hernandez-Almada, A.; Garcia-Aspeitia, Miguel A.; Magana, Juan; Motta, V
    In this work, we study the evolution of a spatially flat Universe by considering a viscous dark matter and perfect fluids for dark energy and radiation, including an interaction term between dark matter and dark energy. In the first part, we analyze the general properties of the Universe by performing a stability analysis, and then we constrain the free parameters of the model using the latest and cosmological-independent measurements of the Hubble parameter. We find consistency between the viscosity coefficient and the condition imposed by the second law of the thermodynamics. The second part is dedicated to constraining the free parameter of the interacting viscous model (IVM) for three particular cases: the viscous model (VM), interacting model (IM), and the perfect fluid case [Lambda-Cold Dark Matter (LCDM)]. We report the deceleration parameters as q(0) = -0.54(-0.05)(+0.06)-0.58(-0.04)(+0.05), -0.58(-0.05)(+0.05), and -0.63(-0.02)(+0.02), together with the jerk parameters as j(0) = 0.87(-0.09)(+0.06), 0.94(-0.06)(+0.04), 0.91(-0.10)(+0.06), and 1.0 for the IVM, VM, IM, and LCDM respectively, where the uncertainties correspond at 68% confidence level. It is worth mentioning that all the particular cases are in good agreement with LCDM, in some cases producing even better fits, with the advantage of eliminating some problems that afflict the standard cosmological model.
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    The morphology-density relation in z∼1 clusters
    (2005) Postman, M; Franx, M; Cross, NJG; Holden, B; Ford, HC; Illingworth, GD; Goto, T; Demarco, R; Rosati, P; Blakeslee, JP; Tran, KV; Benítez, N; Clampin, M; Hartig, GF; Homeier, N; Ardila, DR; Bartko, F; Bouwens, RJ; Bradley, LD; Broadhurst, TJ; Brown, RA; Burrows, CJ; Cheng, ES; Feldman, PD; Golimowski, DA; Gronwall, C; Infante, L; Kimble, RA; Krist, JE; Lesser, MP; Martel, AR; Mei, S; Menanteau, F; Meurer, GR; Miley, GK; Motta, V; Sirianni, M; Sparks, WB; Tran, HD; Tsvetanov, ZI; White, RL; Zheng, W
    We measure the morphology-density relation (MDR) and morphology-radius relation (MRR) for galaxies in seven z similar to 1 clusters that have been observed with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope. Simulations and independent comparisons of our visually derived morphologies indicate that ACS allows one to distinguish between E, S0, and spiral morphologies down to z(850) = 24, corresponding to L/L* 0.21 and 0.30 at z = 0.83 and 1.24, respectively. We adopt density and radius estimation methods that match those used at lower redshift in order to study the evolution of the MDR and MRR. We detect a change in the MDR between 0: 8 < z < 1.2 and that observed at z similar to 0, consistent with recent work; specifically, the growth in the bulge-dominated galaxy fraction, f(E+S0), with increasing density proceeds less rapidly at z similar to 1 than it does at z similar to 0. At z similar to 1 and Sigma >= 500 galaxies Mpc(-2), we find < f(E+S0)> = 0.72 +/- 0.10. At z similar to 0, an E + S0 population fraction of this magnitude occurs at densities about 5 times smaller. The evolution in the MDR is confined to densities Sigma greater than or similar to 40 galaxies Mpc(-2) and appears to be primarily due to a deficit of S0 galaxies and an excess of Sp+Irr galaxies relative to the local galaxy population. The f(E)-density relation exhibits no significant evolution between z = 1 and 0. We find mild evidence to suggest that the MDR is dependent on the bolometric X-ray luminosity of the intracluster medium. Implications for the evolution of the disk galaxy population in dense regions are discussed in the context of these observations.
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    The Universe acceleration from the Unimodular gravity view point: Background and linear perturbations
    (2021) Garcia-Aspeitia, Miguel A.; Hernandez-Almada, A.; Magana, Juan; Motta, V
    With the goal of studying the cosmological constant (CC) problem, we present an exhaustive analysis of unimodular gravity as a possible candidate to resolve the CC origin and with this, the current Universe acceleration. In this theory, a correction constant (CC-like) in the field equations sources the late cosmic acceleration. This constant is related to a new parameter, z(ini), which is interpreted as the redshift of CC-like emergence. By comparing with the CC value obtained from Planck and Supernovaes measurements, it is possible to estimate z(ini) = 11.15(-0.02)(+0.01) and z(ini) = 11.43(-0.06)(+0.03) respectively, which is close to the reionization epoch. Moreover, we use the observational Hubble data (OHD), Type Ia Supernovae (SnIa), Baryon Acoustic Oscillations (BAO) and the Cosmic Microwave Background Radiation (CMB) distance data to constrain the UG cosmological parameters. A Joint analysis (OHD+SnIa+BAO+CMB), results in z(ini) = 11.47(-0.073)(+0.074) within 1 sigma confidence level consistent with our estimation from Planck and Supernovae measurements. We also include linear perturbations, starting with scalar and tensor perturbations and complementing with the perturbed Boltzmann equation for photons. We show that the 00 term in the UG field equations and the Boltzmann equation for photons contains corrections, meanwhile the other equations are similar as those obtained in standard cosmology. (C) 2021 Elsevier B.V. All rights reserved.