A. Javier Cenarro

Mild Velocity Dispersion Evolution of Spheroid-Like Massive Galaxies Since z ~ 2

Making use of public spectra from Cimatti et al., we measure for the first time the velocity dispersion of spheroid-like massive (M {sub *} {approx} 10{sup 11} M {sub sun}) galaxies at z {approx} 1.6. By comparing with galaxies of similar stellar mass at lower redshifts, we find evidence for a mild evolution in velocity dispersion, decreasing from {approx}240 km s{sup -1} at z {approx} 1.6 down to {approx}180 km s{sup -1} at z {approx} 0. Such mild evolution contrasts with the strong change in size (a factor of {approx}4) found for these type of objects in the same cosmic time, and it is consistent with a progressive larger role, at lower redshift, of the dark matter halo in setting the velocity dispersion of these galaxies. We discuss the implications of our results within the context of different scenarios proposed for the evolution of these massive objects.

A New Method for Isolating M31 Red Giant Stars: The Discovery of Stars out to a Radial Distance of 165 kpc

We present a method for isolating a clean sample of red giant branch stars in the outer regions of M31. Our study is based on an ongoing spectroscopic survey using the DEIMOS instrument on the Keck II 10 m telescope. The survey aims to study the kinematics, (sub)structure, and metallicity of M31s halo. Although most of our spectroscopic targets were photometrically screened to reject foreground Milky Way dwarf star contaminants, dwarf stars still constitute a substantial fraction of the observed spectra in the sparse outer halo. Our likelihood-based method for isolating M31 red giants uses five criteria: (1) radial velocity, (2) photometry in the intermediate-width DDO51 band to measure the strength of the MgH/Mg b absorption features, (3) strength of the Na I λ8190 absorption line doublet, (4) location within an (I, V - I) color-magnitude diagram, and (5) comparison of photometric (color-magnitude diagram based) versus spectroscopic (Ca II λ8500 triplet based) metallicity estimates. We also discuss other potential giant/dwarf separation criteria: the strength of the K I absorption lines at 7665 and 7699 A and the TiO bands at 7100, 7600, and 8500 A. Training sets consisting of definite M31 red giants and Galactic dwarf stars are used to derive empirical probability distribution functions for each diagnostic. These functions are used to calculate the likelihood that a given star is a red giant in M31 versus a Milky Way dwarf star. Using our diagnostic method, we isolate 40 M31 red giants beyond a projected distance of R = 60 kpc from the galaxys center, including three red giants at R ~ 165 kpc. The ability to identify individual M31 red giant stars gives us an unprecedented level of sensitivity in studying the properties of the galaxys outer halo.

Stellar Populations of Globular Clusters in the Elliptical Galaxy NGC 1407

We present high-quality Keck spectroscopic data for a sample of 20 globular clusters (GCs) in the massive E0 galaxy NGC 1407. A subset of 20 line-strength indices of the Lick/IDS system has been measured for both the GC system and the central integrated starlight of the galaxy. Ages, metallicities, and [α/Fe] ratios have been derived using several different approaches. The majority of GCs in NGC 1407 studied are old, follow a tight metallicity sequence reaching values slightly above solar, and exhibit mean [α/Fe] ratios of ~0.3 dex. In addition, three GCs are formally derived to be young (~4 Gyr), but we argue that they are actually old GCs hosting blue horizontal branches. We report, for the first time, evidence for the existence of two chemically distinct subpopulations of metal-rich (MR) GCs. We find that some MR GCs exhibit significantly larger [Mg/Fe] and [C/Fe] ratios. Different star formation timescales are proposed to explain the correlation between Mg and C abundances. We also find striking CN overabundances over the entire GC metallicity range. It is interesting to note that the behavior of C and N in metal-poor GCs clearly deviates from that in MR GCs. In particular, for MR GCs, N increases dramatically while C essentially saturates. This may be interpreted as a consequence of the increasing importance of the CNO cycle with increasing metallicity.

The stellar initial mass function at 0.9 < z < 1.5

We explore the stellar initial mass function (IMF) of a sample of 49 massive quiescent galaxies (MQGs) at 0.9 10(11) M-circle dot), we find an average age of 1.7 +/- 0.3 Gyr and a bottom-heavy IMF (Gamma(b) = 3.2 +/- 0.2). Lighter MQGs (2 x 10(10) < M < 10(11) M-circle dot) at the same redshift are younger on average (1.0 +/- 0.2 Gyr) and present a shallower IMF slope (Gamma(b) = 2.7(-0.4)(+0.3)). 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 similar to 8 Gyr.

Shards: a global view of the star formation activity at z ~ 0.84 and z ~ 1.23

In this paper, we present a comprehensive analysis of star-forming galaxies (SFGs) at intermediate redshifts (z ~ 1). We combine the ultra-deep optical spectro-photometric data from the Survey for High-z Absorption Red and Dead Sources (SHARDS) with deep UV-to-FIR observations in the GOODS-N field. Exploiting two of the 25 SHARDS medium-band filters, F687W17 and F823W17, we select [O II] emission line galaxies at z ~ 0.84 and z ~ 1.23 and characterize their physical properties. Their rest-frame equivalent widths (EWrf([O ii])), line fluxes, luminosities, star formation rates (SFRs), and dust attenuation properties are investigated. The evolution of EW_rf([O II]) closely follows the SFR density evolution of the universe, with a trend of EW_rf([O II]) ∞ (1 + z)^3 up to redshift z ≃1, followed by a possible flattening. The SF properties of the galaxies selected on the basis of their [O II] emission are compared with complementary samples of SFGs selected by their MIR and FIR emission, and also with a general mass-selected sample of galaxies at the same redshifts. We demonstrate observationally that the UVJ diagram (or, similarly, a cut in the specific SFR) is only partially able to distinguish the quiescent galaxies from the SFGs. The SFR–M_* relation is investigated for the different samples, yielding a logarithmic slope ~1, in good agreement with previous results. The dust attenuations derived from different SFR indicators (UV(1600), UV(2800), [O II], IR) are compared and show clear trends with respect to both the stellar mass and total SFR, with more massive and highly star-forming galaxies being affected by stronger dust attenuation.

First scientific observations with MEGARA at GTC

On June 25th 2017, the new intermediate-resolution optical IFU and MOS of the 10.4-m GTC had its first light. As part of the tests carried out to verify the performance of the instrument in its two modes (IFU and MOS) and 18 spectral setups (identical number of VPHs with resolutions R=6000-20000 from 0.36 to 1 micron) a number of astronomical objects were observed. These observations show that MEGARA@GTC is called to fill a niche of high-throughput, intermediateresolution IFU and MOS observations of extremely-faint narrow-lined objects. Lyman-α absorbers, star-forming dwarfs or even weak absorptions in stellar spectra in our Galaxy or in the Local Group can now be explored to a new level. Thus, the versatility of MEGARA in terms of observing modes and spectral resolution and coverage will allow GTC to go beyond current observational limits in either depth or precision for all these objects. The results to be presented in this talk clearly demonstrate the potential of MEGARA in this regard.

MEGARA, the R=6000-20000 IFU and MOS of GTC

MEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28th 2017 and was successfully integrated and commissioned at the telescope from May to August 2017. During the on-sky commissioning we demonstrated that MEGARA is a powerful and robust instrument that provides on-sky intermediate-to-high spectral resolutions RFWHM ~ 6,000, 12,000 and 20,000 at an unprecedented efficiency for these resolving powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3 arcsec2 while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin2. In this paper we describe the instrument main subsystems, including the Folded-Cassegrain unit, the fiber link, the spectrograph, the cryostat, the detector and the control subsystems, and its performance numbers obtained during commissioning where the fulfillment of the instrument requirements is demonstrated.