Ages and Abundances of Red Sequence Galaxies as a Function of LINER Emission Line Strength

Although the spectrum of a prototypical early-type galaxy is assumed to lack emission lines, a substantial fraction (likely as high as 30%) of nearby red sequence galaxy spectra contain emission lines with line ratios characteristic of low ionization nuclear emission-line regions (LINERs). We use spectra of ~6000 galaxies from the Sloan Digital Sky Survey (SDSS) in a narrow redshift slice (0.06 < z < 0.08) to compare the stellar populations of red sequence galaxies with and without LINER-like emission. The spectra are binned by internal velocity dispersion and by emission properties to produce high S/N stacked spectra. The recent stellar population models of R. Schiavon (2007) make it possible to measure ages, [Fe/H], and individual elemental abundance ratios [Mg/Fe], [C/Fe], [N/Fe], and [Ca/Fe] for each of the stacked spectra. We find that red sequence galaxies with strong LINER-like emission are systematically 2-3.5 Gyr (10-40%) younger than their emission-free counterparts at the same velocity dispersion. This suggests a connection between the mechanism powering the emission (whether AGN, post-AGB stars, shocks, or cooling flows) and more recent star formation in the galaxy. We find that mean stellar age and [Fe/H] increase with velocity dispersion for all galaxies. Elemental abundance [Mg/Fe] increases modestly with velocity dispersion in agreement with previous results, and [C/Fe] and [N/Fe] increase more strongly with velocity dispersion than does [Mg/Fe]. [Ca/Fe] appears to be roughly solar for all galaxies. At fixed velocity dispersion, galaxies with fainter r-band luminosities have lower [Fe/H] and older ages but similar abundance ratios compared to brighter galaxies.Comment: 25 pages, 17 figures, Accepted for publication in ApJ as of 16 July 2007; acceptance status updated, paper unchange

Do observed metallicity gradients of early-type galaxies support a hybrid formation scenario?

We measure radial gradients of the Mg2 index in 15 E-E/S0 and 14 S0 galaxies. Our homogeneous data set covers a large range of internal stellar velocity dispersions (2.0<logsigma<2.5) and Mg2 gradients (dMg2/dlogr/re* up to -0.14mag/dex). We find for the first time, a noticeable lower boundary in the relation between Mg2 gradient and sigma along the full range of sigma, which may be populated by galaxies predominantly formed by monolithic collapse. At high sigma, galaxies showing flatter gradients could represent objects which suffered either important merging episodes or later gas accretion. These processes contribute to the flattening of the metallicity gradients and their increasing importance could define the distribution of the objects above the boundary expected by the ``classical'' monolithic process. This result is in marked contrast with previous works which found a correlation between dMg2/dlogr/re* and sigma confined to the low mass galaxies, suggesting that only galaxies below some limiting sigma were formed by collapse whereas the massive ones by mergers. We show observational evidence that a hybrid scenario could arise also among massive galaxies. Finally, we estimated d[Z/H] from Mg2 and Hbeta measurements and single stellar population models. The conclusions remain the same, indicating that the results cannot be ascribed to age effects on Mg2.Comment: 11 pages, 2 figures, to appear in ApJLetter

Line strengths of early-type galaxies

In this paper we present measurements of velocity dispersions and Lick indices for 509 galaxies in the local Universe, based on high signal-to-noise, long slit spectra obtained with the 1.52 m ESO telescope at La Silla. The conversion of our measurements into the Lick/IDS system was carried out following the general prescription of Worthey and Ottaviani 1997. Comparisons of our measurements with those of other authors show, in general, good agreement. We also examine the dependence between these indices (e.g., Hbeta, Mg_2, Fe5270 and NaD) and the central velocity dispersion (sigma), and we find that they are consistent with those previously reported in the literature. Benefiting from the relatively large size of the sample, we are able to investigate the dependence of these relations on morphology and environment, here represented by the local galaxy density. We find that for metallic lines these relations show no significant dependence on environment or morphology, except in the case of NaD, which shows distinct behavior for E and S0. On the other hand, the Hbeta-logsigma shows a significant difference as a function of the local density of galaxies, which we interpret as being caused by the truncation of star formation in high density environments. Comparing our results with those obtained by other authors we find a few discrepancies, adding to the ongoing debate about the nature of these relations. Finally, we report that the scatter of the Mg indices versus sigma relations correlate with Hbeta, suggesting that age may contribute to the scatter. Furthermore, this scatter shows no significant dependence on morphology or environment. Our results are consistent with the current downsizing model, where low mass galaxies have an extended star formation history (abridged).Comment: 88 pages, 24 figures, to be published in AJ, for further information see http://staff.on.br/ogand

Very Low-Mass Stellar and Substellar Companions to Solar-Like Stars from MARVELS I: A Low Mass Ratio Stellar Companion to TYC 4110-01037-1 in a 79-day Orbit

TYC 4110-01037-1 has a low-mass stellar companion, whose small mass ratio and short orbital period are atypical amongst solar-like (Teff ~< 6000 K) binary systems. Our analysis of TYC 4110-01037-1 reveals it to be a moderately aged (~<5 Gyr) solar-like star having a mass of 1.07 +/- 0.08 MSun and radius of 0.99 +/- 0.18 RSun. We analyze 32 radial velocity measurements from the SDSS-III MARVELS survey as well as 6 supporting radial velocity measurements from the SARG spectrograph on the 3.6m TNG telescope obtained over a period of ~2 years. The best Keplerian orbital fit parameters were found to have a period of 78.994 +/- 0.012 days, an eccentricity of 0.1095 +/- 0.0023, and a semi-amplitude of 4199 +/- 11 m/s. We determine the minimum companion mass (if sin i = 1) to be 97.7 +/- 5.8 MJup. The system's companion to host star mass ratio, >0.087 +/- 0.003, places it at the lowest end of observed values for short period stellar companions to solar-like (Teff ~< 6000 K) stars. One possible way to create such a system would be if a triple-component stellar multiple broke up into a short period, low q binary during the cluster dispersal phase of its lifetime. A candidate tertiary body has been identified in the system via single-epoch, high contrast imagery. If this object is confirmed to be co-moving, we estimate it would be a dM4 star. We present these results in the context of our larger-scale effort to constrain the statistics of low mass stellar and brown dwarf companions to FGK-type stars via the MARVELS survey.Comment: 22 pages; accepted in A