Characterising the evolving KK-band luminosity function using the UltraVISTA, CANDELS and HUDF surveys

We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z<3.75, based on a nested combination of the UltraVISTA, CANDELS and HUDF surveys. The large dynamic range in luminosity spanned by this new dataset (3-4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z>0.25 is relatively steep (-1.3<alpha<-1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new dataset we find that a double Schechter function provides a significantly improved description of the KLF at z0.25 the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (M_K>-20.5) or bright magnitudes (M_K<-24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at M_K~-23 dropping by a factor of ~5 over the redshift interval 0.25<z<3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (alpha_1=-0.5, alpha_2=-1.5) and a shared characteristic magnitude (M_K*). According to this parameterisation, the normalisation of the component which dominates the faint-end of the KLF remains approximately constant, with phi*_2 decreasing by only a factor of ~2 between z~0 and z~3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z~3. Finally, we note that within this parameterisation, the observed evolution of M_K* between z~0 and z~3.25 is entirely consistent with M_K* corresponding to a constant stellar mass of M*~5x10^10 Msun at all redshifts.Comment: 18 pages, 10 figures, accepted for publication in MNRA

The Mice at play in the CALIFA survey: A case study of a gas-rich major merger between first passage and coalescence

We present optical integral field spectroscopy (IFS) observations of the Mice, a major merger between two massive (>10^11Msol) gas-rich spirals NGC4676A and B, observed between first passage and final coalescence. The spectra provide stellar and gas kinematics, ionised gas properties and stellar population diagnostics, over the full optical extent of both galaxies. The Mice provide a perfect case study highlighting the importance of IFS data for improving our understanding of local galaxies. The impact of first passage on the kinematics of the stars and gas has been significant, with strong bars likely induced in both galaxies. The barred spiral NGC4676B exhibits a strong twist in both its stellar and ionised gas disk. On the other hand, the impact of the merger on the stellar populations has been minimal thus far: star formation induced by the recent close passage has not contributed significantly to the global star formation rate or stellar mass of the galaxies. Both galaxies show bicones of high ionisation gas extending along their minor axes. In NGC4676A the high gas velocity dispersion and Seyfert-like line ratios at large scaleheight indicate a powerful outflow. Fast shocks extend to ~6.6kpc above the disk plane. The measured ram pressure and mass outflow rate (~8-20Msol/yr) are similar to superwinds from local ULIRGs, although NGC4676A has only a moderate infrared luminosity of 3x10^10Lsol. Energy beyond that provided by the mechanical energy of the starburst appears to be required to drive the outflow. We compare the observations to mock kinematic and stellar population maps from a merger simulation. The models show little enhancement in star formation during and following first passage, in agreement with the observations. We highlight areas where IFS data could help further constrain the models.Comment: 23 pages, 13 figures, accepted to A&A. A version with a complete set of high resolution figures is available here: http://www-star.st-and.ac.uk/~vw8/resources/mice_v8_astroph.pd

Caracterización del índice de CO en 2.3 μm y su aplicación al estudio de poblaciones estelares en galaxias de primeros tipos

Esta tesis doctoral se centra en el estudio de las poblaciones estelares de galaxias de primeros tipos analizando índices de intensidad de líneas definidos en la banda K. Por ello, presentamos una nueva biblioteca estelar en este intervalo espectral que contiene estrellas con un buen recubrimiento en los parámetros atmosféricos cuyos espectros están calibrados en flujo relativo, y definimos el índice Dco para medir la absorción del CO en 2.3 micras. Como resultado del trabajo con los nuevos espectros presentamos las funciones de ajuste que caracterizan el comportamiento de este índice en función de los parámetros atmosféricos estelares, las cuales constituyen un ingrediente fundamental de los modelos de síntesis evolutiva cuyas predicciónes preliminares también se presentan en este trabajo. Por último, analizamos las poblaciones estelares de galaxias de primeros tipos en diferentes entornos utilizando los índices en la banda K. Este estudio ha revelado diferencias significativas entre las galaxias de primeros tipos de campo de este trabajo y las galaxias de primeros tipos del cúmulo de Fornax presentadas por Silva et al. (2008), en el sentido de que las galaxias de campo presentan índices de NaI y Dco mayores que los de las galaxias de Fornax. Esto se interpreta como la existencia de diferencias en las historias de la formación estelar de las galaxias que habitan diferentes entornos, de manera que las galaxias de campo han sufrido una historia de la formación estelar más extendida que las de cúmulos, resultado ya apuntado por Sánchez-Blázquez et al. (2003) al analizar los índices espectroscópicos CN2 y C4668 en el óptico. Este trabajo demuestra que la ventana infrarroja abre una nueva puerta a los estudios de poblaciones estelares en galaxias de primeros tipos, poniendo de manifiesto la importancia del análisis de diferentes especies químicas como indicadores cronológicos de las historias de las galaxias

Stellar population study in early-type galaxies:An approach from the K band

A full understanding of the physical properties of integrated stellar systems demands a multiwavelength approach since each spectral window shows us the contribution of different types of stars. However, most of the observational effort in stellar population studies has been focused on the optical range. Now, the new generation of instruments allow us to explore the K band, where RGB and AGB stars dominate the light of the integrated spectra. Here we present a K-band spectroscopic analysis of early-type galaxies in different environments. Our sample comprises 12 field early-type galaxies observed with ISAAC at VLT with medium resolution, and they are compared with 11 Fornax cluster galaxies previously reported by Silva et al. (2008). The clear differences found in the infrared DCO and NaI indices between field and Fornax galaxies are discussed, trying to solve the puzzle formed by the near-infrared and optical measurements