Ignacio Martín-Navarro

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

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Publications (7)10.45 Total impact

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    ABSTRACT: Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies. However, no observations have yet been able to disentangle the physical driver. We analyse here a sample of 24 early-type galaxies drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy towards metal-rich populations. Our result, combined with the galaxy mass-metallicity relation, naturally explains previous claims of a galaxy mass-IMF relation, derived from non-IFU spectra. If we assume that - within the star formation environment of early-type galaxies - metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.
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    ABSTRACT: Massive relic galaxies formed the bulk of their stellar component before z~2 and have remained unaltered since then. Therefore, they represent a unique opportunity to study in great detail the frozen stellar population properties of those galaxies that populated the primitive Universe. We have combined optical to near-infrared line-strength indices in order to infer, out to 1.5 Reff, the IMF of the nearby relic massive galaxy NGC 1277. The IMF of this galaxy is bottom-heavy at all radii, with the fraction of low-mass stars being at least a factor of two larger than that found in the Milky Way. The excess of low-mass stars is present throughout the galaxy, while the velocity dispersion profile shows a strong decrease with radius. This behaviour suggests that local velocity dispersion is not the only driver of the observed IMF variations seen among nearby early-type galaxies. In addition, the excess of low-mass stars shown in NGC 1277 could reflect the effect on the IMF of dramatically different and intense star formation processes at z~2, compared to the less extreme conditions observed in the local Universe.
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    ABSTRACT: Several authors have reported that the dynamical masses of massive compact galaxies (M_star > 10^11 M_sun, r_e ~ 1 kpc), computed as M_dyn = 5.0 sigma_e^2 r_e / G, are lower than their stellar masses M_star. In a previous study from our group, the discrepancy is interpreted as a breakdown of the assumptions of virial equilibrium and homology that underlie the M_dyn determinations. Here we present new spectroscopy of six redshift z~1.0 massive compact ellipticals from the Extended Groth Strip, obtained with the 10.4-m Gran Telescopio Canarias. We obtain velocity dispersions in the range 161 to 340 km s^-1. As found by previous studies of massive compact galaxies, our velocity dispersions are lower than the virial expectation, and all of our galaxies show M_dyn < M_star. Adding data from the literature, we build a sample covering a range of stellar masses and compactness in a narrow redshift range z~1.0. This allows us to exclude systematic effects on the data and evolutionary effects on the galaxy population, which could have affected previous studies. We confirm that mass discrepancy scales with galaxy compactness. We use the stellar mass plane (M_star, sigma_e, r_e) populated by our sample to constrain a generic evolution mechanism. We find that the simulations of the growth of massive ellipticals due to mergers agree with our constraints and discard the homologous virial theorem.
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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.
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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). DOI:10.1093/mnras/stu2480 · 5.23 Impact Factor
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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). DOI:10.1093/mnras/stu767 · 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.