Type-II surface brightness profiles in edge-on galaxies produced by flares

Previous numerical studies had apparently ruled out the possibility that flares in galaxy discs could give rise to the apparent breaks in their luminosity profiles when observed edge-on. However the studies have not, until now, analyzed this hypothesis systematically using realistic models for the disc, the flare, and the bulge. We revisit this theme by analyzing a series of models which sample a wide range of observationally based structural parameters for these three components. We have considered realistic distributions of bulge to disc ratios, morphological parameters of bulges and discs, vertical scale heights of discs and their radial gradients defining the flare for different morphological types and stellar mass bins, based on observations. The surface brightness profiles for the face-on and edge-on views of each model were simulated to find out whether the flared disc produces a Type-II break in the disc profile when observed edge-on, and if so under what conditions. Contrary to previous claims, we find that discs with realistic flares can produce significant breaks in discs when observed edge-on. Specifically a flare with the parameters of that of the Milky Way would produce a significant break of the disc at a Rbreak of ~8.6 kpc if observed edge-on. Central bulges have no significant effects on the results. These simulations show that flared discs can explain the existence of many Type-II breaks observed in edge-on galaxies, in a range of galaxies with low-to-intermediate break strength values of -0.25<S<-0.1.Comment: Published in Astronomy & Astrophysics. 5 pages, 5 figures. Language corrections by the journal included in this new versio

Photometric scaling relations of antitruncated stellar discs in S0-Scd galaxies

It has been recently found that the characteristic photometric parameters of antitruncated discs in S0 galaxies follow tight scaling relations. We investigate if similar scaling relations are satisfied by galaxies of other morphological types. We have analysed the trends in several photometric planes relating the characteristic surface brightness and scalelengths of the breaks and the inner and outer discs of local antitruncated S0-Scd galaxies, using published data and fits performed to the surface brightness profiles of two samples of Type-III galaxies in the R and Spitzer 3.6 microns bands. We have performed linear fits to the correlations followed by different galaxy types in each plane, as well as several statistical tests to determine their significance. We have found that: 1) the antitruncated discs of all galaxy types from Sa to Scd obey tight scaling relations both in R and 3.6 microns, as observed in S0s; 2) the majority of these correlations are significant accounting for the numbers of the available data samples; 3) the trends are clearly linear when the characteristic scalelengths are plotted on a logarithmic scale; and 4) the correlations relating the characteristic surface brightnesses of the inner and outer discs and the breaks with the various characteristic scalelengths significantly improve when the latter are normalized to the optical radius of the galaxy. The results suggest that the scaling relations of Type-III discs are independent of the morphological type and the presence (or absence) of bars within the observational uncertainties of the available datasets, although larger and deeper samples are required to confirm this. The tight structural coupling implied by these scaling relations impose strong constraints on the mechanisms proposed for explaining the formation of antitruncated stellar discs in the galaxies across the whole Hubble Sequence (Abridged).Comment: Accepted for publication in Astronomy & Astrophysics, 18 pages, 12 figures, 7 table

Formation of S0 galaxies through mergers. Evolution in the Tully-Fisher relation since z∼1z\sim1

(Abridged version) We explore whether a scenario that combines an origin by mergers at $z\sim$1.8-1.5 with a subsequent passive evolution of the resulting S0 remnants since $z \sim$0.8-1 is compatible with observational data of S0s in the Tully-Fisher relation (TFR). We studied a set of major and minor merger experiments from the GalMer database that generate massive S0 remnants. We analysed the location of these remnants in the photometric and stellar TFRs assuming that they correspond to $z\sim0.8$ galaxies. We then estimated their evolution in these planes over the last 7 Gyr. The results were compared with data of real S0s and spirals at different redshifts. We also tested how the use of Vcirc or Vrot,max affects the results. We found that just after $\sim$1-2 Gyr of coalescence, major mergers generate S0 remnants that are outliers of the local photometric and stellar TFRs at $z\sim0.8$. After $\sim$4-7 Gyr of passive evolution in isolation, the S0 remnants move towards the local TFR, although the initial scatter among them persists. This scatter is sensitive to the indicator used for the rotation velocity: Vcirc values yield a lower scatter than when Vrot,max values are considered instead. In the planes involving Vrot,max, a clear segregation of the S0 remnants in terms of the spin-orbit coupling of the model is observed, in which the remnants of retrograde encounters overlap with local S0s hosting counter-rotating discs. The location of the S0 remnants at $z\sim 0$ agrees well with the observed distribution of local S0 galaxies in the $\sigma_0$-$M_K$, Vcirc-$\sigma_0$ and Vrot,max-$\sigma_0$ planes. Thus, massive S0 galaxies may have been formed through major mergers that occurred at high redshift and have later evolved towards the local TFR through passive evolution in relative isolation, a mechanism that would also contribute to the scatter observed in this relation.Comment: 19 pages, 15 figures. Accepted for publication in A&

Evolution induced by dry minor mergers onto fast-rotator S0 galaxies

Tapia, Trinidad et al.[Context] Numerical studies have shown that the properties of the S0 galaxies with kinematics intermediate between fast and slow rotators are difficult to explain by a scenario of major mergers.[Aims] We investigate whether the smoother perturbation induced by minor mergers can reproduce these systems.[Methods] We analysed collisionless N-body simulations of intermediate and minor dry mergers onto S0s to determine the structural and kinematic evolution induced by the encounters. The original primary galaxies represent gas-poor fast-rotator S0b and S0c galaxies with high intrinsic ellipticities. The original bulges are intrinsically spherical and have low rotation. Different mass ratios, parent bulges, density ratios, and orbits were studied.[Results] Minor mergers induce a lower decrease of the global rotational support (as provided by λe) than encounters of lower mass ratios, which results in S0s with properties intermediate between fast and slow rotators. The resulting remnants are intrinsically more triaxial, less flattened, and span the whole range of apparent ellipticities up to εe ∼ 0.8. They do not show lower apparent ellipticities in random projections than initially; on the contrary, the formation of oval distortions and the disc thickening increase the percentage of projections at 0.4 0.9), but exhibit a wide range of triaxialities (0.20 < T < 1.00). In the plane of global anisotropy of velocities (δ) vs.? intrinsic ellipticity (εe,intr), some of our models extend the linear trend found in previous major merger simulations towards higher ε e,intr values, while others clearly depart from it (depending on the progenitor S0). This is consistent with the wide dispersion exhibited by real S0s in this diagram compared with ellipticals, which follow the linear trend drawn by major merger simulations.[Conclusions] The smoother changes induced by minor mergers can explain the existence of S0s with intermediate kinematic properties between fast and slow rotators that are difficult to explain with major mergers. The different trends exhibited by ellipticals and S0 galaxies in the δ - εe diagram may be pointing to the different role played by major mergers in the build-up of each morphological type. © ESO 2014.Supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under projects AYA2006-12955, AYA2009-10368, AYA2009-11137, AYA2012- 30717, AYA2010-21322-C03-02, AYA2010-21887-C04-04, and by the Madrid Regional Government through the AstroMadrid Project (CAM S2009/ESP-1496, http://www.laeff.cab.inta-csic.es/projects/astromadrid/main/index.php). Funded by the Spanish MICINN under the Consolider-Ingenio 2010 Program grant CSD2006- 0070: “First Science with the GTC” (http://www.iac.es/consolider-ingenio-gtc/), and by the Spanish programme of International Campus of Excellence Moncloa (CEI). A.C.G.G. is a Ramón y Cajal Fellow of the Spanish MINECO.Peer Reviewe

Evolution of the anti-truncated stellar profiles of S0 galaxies since z=0.6z=0.6 in the SHARDS survey: I - Sample and Methods

The controversy about the origin of the structure of S0--E/S0 galaxies may be due to the difficulty of comparing surface brightness profiles with different depths, photometric corrections and PSF effects (almost always ignored). We aim to quantify the properties of Type-III (anti-truncated) discs in a sample of S0 galaxies at 0.2<z<0.6. In this paper, we present the sample selection and describe in detail the methods to robustly trace the structure in their outskirts and correct for PSF effects. We have selected and classified a sample of 150 quiescent galaxies at 0.2<z<0.6 in the GOODS-N field. We perform a quantitative structural analysis of 44 S0-E/S0 galaxies. We corrected their surface brightness profiles for PSF distortions and analysed the biases in the structural and photometric parameters when the PSF correction is not applied. Additionally, we have developed Elbow, an automatic statistical method to determine whether a possible break is significant - or not - and its type and made it publicly available. We found 14 anti-truncated S0-E/S0 galaxies in the range 0.2<z<0.6 (~30% of the final sample). This fraction is similar to the those reported in the local Universe. In our sample, ~25% of the Type-III breaks observed in PSF-uncorrected profiles are artifacts, and their profiles turn into a Type I after PSF correction. PSF effects also soften Type-II profiles. We found that the profiles of Type-I S0 and E/S0 galaxies of our sample are compatible with the inner profiles of the Type-III, in contrast with the outer profiles. We have obtained the first robust and reliable sample of 14 anti-truncated S0--E/S0 galaxies beyond the local Universe, in the range 0.2<z<0.6. PSF effects significantly affect the shape of the surface brightness profiles in galaxy discs even in the case of the narrow PSF of HST/ACS images, so future studies on the subject should make an effort to correct them.Comment: Accepted for publishing in Astronomy & Astrophysics. 75 pages, 57 figure

Understanding the outskirts of disc galaxies

Las regiones externas de las galaxias contienen múltiples pistas sobre los procesos de formación que dieron lugar a los distintos tipos morfológicos observados en la actualidad y su evolución. Sin embargo, el análisis del Universo a bajo brillo superficial esta limitado por la profundidad de las imágenes actuales y la presencia de diversos tipos de efectos sistemáticos; efectos de proyección, contaminación por función de dispersión de punto (PSF), sobre-substracción de nivel de cielo, entre otros. En esta tesis doctoral nos centramos en el estudio de las propiedades de las partes externas de las galaxias de disco, combinando simulaciones, modelos y observaciones con nuevos métodos y herramientas estadísticas para evitar efectos sistemáticos. En la primera parte de esta tesis (Borlaff et al. 2016) nos centramos en el efecto del incremento de la escala vertical de disco como función del radio galáctico sobre los perfiles de brillo superficial de galaxias de canto. Este fenómeno (llamado flaring) ha sido detectado en el disco estelar de simulaciones de galaxias y en galaxias reales, incluyendo la propia Vía Láctea. Mediante el uso de modelos de galaxias 3D realistas basados en observaciones, demostramos que los flares pueden producir truncamientos en los perfiles de brillo superficial de galaxias con muy alta inclinación. Por otro lado, los flares no producen ningún efecto en galaxias a baja inclinación, lo cual explica parcialmente la relativa alta frecuencia de detección de truncamientos en galaxias de canto. Además, nuestros modelos reproducen la distribución del cociente entre la escala de disco interna y externa al truncamiento (Martín-Navarro et al. 2012), previamente asociada a una caída brusca en la tasa de formación estelar. Finalmente, observamos que los flares explican la caída en la intensidad de los truncamientos a mayores distancias del plano galáctico observada por Pohlen et al. (2007) y Martinez-Lombilla et al. (2018). En Borlaff et al. (2017, 2018) analizamos las propiedades de los discos antitruncados de galaxias lenticulares a distancias cosmológicas. El objetivo es comprobar si las relaciones de escala en estructura y fotometría descubiertas previamente en Borlaff et al. (2014) en galaxias lenticulares con perfil Tipo III a z = 0 son compatibles con una muestra de objetos del mismo tipo fuera del Universo local. En Borlaff et al. (2017) identificamos una muestra de galaxias de la secuencia roja en el campo cosmológico GOODS-N, clasificándolas morfológicamente por su forma aparente, perfil de brillo superficial y la tasa de formación estelar (SFR). Después, descomponemos y corregimos las imágenes de efectos de PSF. Generamos perfiles de brillo superficial y los clasificamos en los distintos subtipos mediante el uso de herramientas estadísticamente robustas desarrolladas por nosotros con este objetivo. Finalmente identificamos 14 galaxias S0 con perfiles Tipo III a 0.2 < z < 0.6. En el segundo articulo de la serie (Borlaff et al. 2018), analizamos las propiedades estructurales y fotométricas de los discos antitruncados de esta muestra, comparándolas con una muestra de objetos del mismo tipo en el Universo local. Los resultados mues- tran que la estructura general de los discos antitruncados en galaxias lenticulares no ha cambiado significativamente desde 0.4 < z < 0.6, aunque su brillo en la banda R ha disminuido en ∆μ ∼ 1.5 mag arcsec −2 desde z ∼ 0.6. Comparamos los resultados con una red de evolución de modelos de población estelar única (SSP) con el objetivo de obtener una estimación sobre la época de formación de la población estelar dominante en las galaxias S0 Tipo III. Los modelos muestran que, si la historia de formación estelar (SFH) de las S0 Tipo III puede aproximarse como un único brote de población estelar, este brote tuvo que tener lugar a z < 1.2. En cualquier otro caso, la SFH debe ser más extendida en el tiempo o presentar diversos brotes de formación estelar. El último capítulo de la tesis esta dedicado a las observaciones en infrarrojo cercano (NIR) del Campo Ultra Profundo de Hubble (HUDF). Para continuar el análisis de las partes externas de galaxias de disco hacia rangos mayores de desplazamiento al rojo son necesarias observaciones en el rango espectroscópico del NIR. Sin embargo, el limite de brillo superficial de la mayor parte de las exploraciones desde telescopios en tierra o espaciales esta dominada por efectos sistemáticos, en lugar del cociente de señal a ruido. Los efectos de sobre-sustracción de cielo, contaminación de PSF, persistencia en el NIR y residuos de corrección de campo plano generan desviaciones irreversibles en los mosaicos finales y por lo tanto en los resultados científicos. Mitigar estos efectos requiere un tratamiento cuidadoso y robusto de las exposiciones individuales. Se ha observado que la estructura de bajo brillo superficial de los mosaicos de HUDF obtenidos usando la cámara WFC3/IR del Hubble Space Telescope (ver XDF, Illingworth et al. 2013; HUDF12, Koekemoer et al. 2013) fue significativamente sobre sustraída durante el proceso de reducción de los datos. En Borlaff et al. (submitted) probamos una serie de técnicas para mejorar el proceso de reducción de datos de WFC3/IR en el HUDF. Estos métodos incluyen auto-calibración de campo plano, corrección de persistencia, corrección de gradientes residuales y ajuste del nivel de cielo relativo de las exposiciones, así como combinación robusta de las imágenes. Como resultado de estas mejoras, recuperamos la estructura externa de las galaxias presentes en los mosaicos, aumentando la profundidad de las imágenes debido a la reducción de los efectos sistemáticos. La nueva versión de los mosaicos NIR del HUDF preserva mejor las propiedades de los objetos a todas las escalas angulares y de intensidad, permitiendo de esta manera el estudio del Universo a bajo brillo superficial mediante todas las técnicas actuales y propuestas

Formation of S0 galaxies through mergers. Bulge-disc structural coupling resulting from major mergers

Observations reveal a strong structural coupling between bulge and disc in S0 galaxies, which seems difficult to explain if they have formed from supposedly catastrophic events such as major mergers. We face this question by quantifying the bulge-disc coupling in dissipative simulations of major and minor mergers that result in realistic S0s. We have studied the dissipative N-body binary merger simulations from the GalMer database that give rise to realistic, relaxed E/S0 and S0 remnants (67 major and 29 minor mergers). We simulate surface brightness profiles of these S0-like remnants in the K-band, mimicking typical observational conditions, to perform bulge-disc decompositions analogous to those carried out in real S0s. The global bulge-disc structure of these remnants has been compared with real data, and they distribute in the B/T - r_e - h_d parameter space consistently with real bright S0s, where B/T is the bulge-to-total luminosity ratio, r_e is the bulge effective radius, and h_d is the disc scalelength. Major mergers can rebuild a bulge-disc coupling in the remnants after having destroyed the structures of the progenitors, whereas minor mergers directly preserve them. Remnants exhibit B/T and r_e/h_d spanning a wide range of values, and their distribution is consistent with observations. Many remnants have bulge Sersic indices ranging 1<n<2, flat appearance, and contain residual star formation in embedded discs, a result which agrees with the presence of pseudobulges in real S0s. Contrary to the popular view, mergers (and in particular, major events) can result in S0 remnants with realistically coupled bulge-disc structures in less than ~3 Gyr. In conclusion, the bulge-disc coupling and the presence of pseudobulges in real S0s cannot be used as an argument against the possible major-merger origin of these galaxies.Comment: 23 pages, accepted for publication in Astronomy and Astrophysics (version after minor language corrections