Ignacio Martín-Navarro

Universidad de La Laguna, San Cristóbal de La Laguna, Canary Islands, Spain

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Publications (4)10.45 Total impact

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    ABSTRACT: We explore the stellar initial mass function (IMF) of a sample of 49 massive quiescent galaxies (MQGs) at 0.9 < z < 1.5. We base our analysis on intermediate resolution spectro-photometric data in the GOODS-N field taken in the near-infrared and optical with the Hubble Space Telescope Wide Field Camera 3 G141 grism and the Survey for High-z Absorption Red and Dead Sources. To constrain the slope of the IMF, we have measured the TiO2 spectral feature, whose strength depends strongly on the content of low-mass stars, as well as on stellar age. Using ultraviolet to near-infrared individual and stacked spectral energy distributions, we have independently estimated the stellar ages of our galaxies. Knowing the age of the stellar population, we interpret the strong differences in the TiO2 feature as an IMF variation. In particular, for the heaviest z ~ 1 MQGs (M > 1011 M ☉), we find an average age of 1.7 ± 0.3 Gyr and a bottom-heavy IMF (Γ b = 3.2 ± 0.2). Lighter MQGs (2 × 1010 < M < 1011 M ☉) at the same redshift are younger on average (1.0 ± 0.2 Gyr) and present a shallower IMF slope (Γ _b=2.7+0.3-0.4). Our results are in good agreement with the findings about the IMF slope in early-type galaxies of similar mass in the present-day universe. This suggests that the IMF, a key characteristic of the stellar populations in galaxies, is bottom-heavier for more massive galaxies and has remained unchanged in the last ~8 Gyr.
    12/2014; 798(1).
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    ABSTRACT: The hypothesis of a universal initial mass function (IMF) -- motivated by observations in nearby stellar systems -- has been recently challenged by the discovery of an IMF systematic variation with the central velocity dispersion, {\sigma}, of early-type galaxies (ETGs), towards an excess of low-mass stars in high {\sigma} galaxies. This trend has been found to hold for the central regions of ETGs, and remains unexplained at the present. To shed new lights on it, we have obtained new, extremely deep, spectroscopy, for three nearby ETGs, two with high {\sigma} (~300 km/s), and one low-mass system, with {\sigma} ~ 100 km/s. From the analysis of IMF-sensitive spectral features, we find that the IMF depends significantly on galactocentric distance in the massive ETGs, with the enhanced fraction of low-mass stars confined to their central regions. For the low-{\sigma} galaxy, no significant radial gradient is detected in the IMF, which is well described by a Milky-Way-like distribution at all radii. Such a result suggests that the IMF should be regarded as a local (rather than global) galaxy property, and suggests a significant difference in the formation process of the core and the outskirts of massive galaxies.
    Monthly Notices of the Royal Astronomical Society 04/2014; 447(2). · 5.23 Impact Factor
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    I. Martín-Navarro, I. Trujillo, J. H. Knapen, J. Bakos, J. Fliri
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    ABSTRACT: The absence of stellar disc truncations in low-inclined spiral galaxies has been a matter of debate in the last decade. Disc truncations are often observed in highly inclined galaxies but no obvious detection of this feature has so far been made in face-on spirals. Here we show, using a simple exponential disc plus stellar halo model based on current observational constraints, that truncations in face-on projections occur at surface brightness levels comparable to the brightness of stellar haloes at the same radial distance. In this sense, stellar haloes outshine the galaxy disc at the expected position of the truncations, forcing their studies only in highly inclined (edge-on) orientations.
    Monthly Notices of the Royal Astronomical Society 01/2014; 441(4). · 5.23 Impact Factor
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    ABSTRACT: We have developed an innovative `index scanning technique" to map the stellar kinematics of early-type galaxies by measuring for the first time the absorption line strength of the near-IR CaII triplet with the Red Tunable Filters of OSIRIS at GTC. Unlike classical spectroscopy, these filters allow us to perform a two-dimensional study, taking advantage of a 10.4 meter class telescope with a unvignetted field of view of 7.8 × 7.8 arcmin. We show the velocity fields obtained for two Virgo elliptical galaxies of very different masses and their globular cluster systems reaching galactocentric distances beyond 2 effective radii.