Roberto Juan Terlevich

The star formation history of Seyfert 2 nuclei

We present a study of the stellar populations in the central ∼200 pc of a large and homogeneous sample comprising 79 nearby galaxies, most of which are Seyfert 2s. The star formation history of these nuclei is reconstructed by means of state-of-the-art population synthesis modelling of their spectra in the 3500‐5200 A interval. A quasar-like featureless continuum (FC) is added to the models to account for possible scattered light from a hidden active galactic nucleus (AGN). We find the following. (1) The star formation history of Seyfert 2 nuclei is remarkably heterogeneous: young starbursts, intermediate-age and old stellar populations all appear in significant and widely varying proportions. (2) A significant fraction of the nuclei show a strong FC component, but this FC is not always an indication of a hidden AGN: it can also betray the presence of a young, dusty starburst. (3) We detect weak broad Hβ emission in several Seyfert 2s after cleaning the observed spectrum by subtracting the synthesis model. These are most likely the weak scattered lines from the hidden broad-line region envisaged in the unified model, given that in most of these cases independent spectropolarimetry data find a hidden Seyfert 1. (4) The FC strengths obtained by the spectral decomposition are substantially larger for the Seyfert 2s which present evidence of broad lines, implying that the scattered nonstellar continuum is also detected. (5) There is no correlation between the star formation in the nucleus and either the central or overall morphology of the parent galaxies. Ke yw ords: galaxies: active ‐ galaxies: Seyfert ‐ galaxies: statistics ‐ galaxies: stellar content.

Emission-line properties of Seyfert 2 nuclei

This is the third paper of a series devoted to the study of the global properties of Joguet’s sample of 79 nearby galaxies observable from the southern hemisphere, of which 65 are Seyfert 2 galaxies. We use the population synthesis models of Paper II to derive ‘pure’ emission-line spectra for the Seyfert 2 galaxies in the sample, and thus explore the statistical properties of the nuclear nebular components and their relation to the stellar populations. We find that the emission-line clouds suffer substantially more extinction than the starlight, and we confirm the correlations between stellar and nebular velocity dispersions and between emission-line luminosity and velocity dispersions, although with substantial scatter. Nuclear luminosities correlate with stellar velocity dispersions, but Seyferts with conspicuous star-forming activity deviate systematically towards higher luminosities. Removing the contribution of young stars to the optical continuum produces a tighter and steeper relation, L ∝ σ 4 , consistent with the Faber‐Jackson law. Emission-line ratios indicative of the gas excitation such as [O III]/Hβ and [O III]/[O II] are statistically smaller for Seyferts with significant star formation, implying that ionization by massive stars is responsible for a substantial and sometimes even a dominant fraction of the Hβ and [O II] fluxes. We use our models to constrain the maximum fraction of the ionizing power that can be generated by a hidden active galactic nucleus (AGN). We correlate this fraction with classical indicators of AGN photoionization (i.e. X-ray luminosity and nebular excitation), but find no significant correlations. Thus, while there is a strong contribution of starbursts to the excitation of the nuclear nebular emission in low-luminosity Seyferts, the contribution of the hidden AGN remains elusive even in hard X-rays.

NEW MEASUREMENTS OF HELIUM IN H II GALAXIES.

The determination of the pregalactic helium mass-fraction is addressed. Previous attempts to empirically determine Yp from a constant parameter dY/dZ are critically discussed, and new results based on extensive spectroscopy of emission-line galaxies by Terlevich and Melnick (1981) are examined. It is concluded from these new results that helium may correlate better with nitrogen than with oxygen. If Y is plotted against N/H, a single relationship holds for all objects, all the relationships extrapolating back to Yp = 0.237 + or - 0.005. It is suggested that the large value of dY/dZ in blue compact galaxies and the (Y, N/H) relation are due to local contamination by winds from Wolf-Rayet stars.

Early Science with the Large Millimeter Telescope: CO and [C ii] Emission in the z = 4.3 AzTEC J095942.9+022938 (COSMOS AzTEC-1)

Measuring redshifted CO line emission is an unambiguous method for obtaining an accurate redshift and total cold gas content of optically faint, dusty starburst systems. Here, we report the first successful spectroscopic redshift determination of AzTEC J095942.9+022938 (COSMOS AzTEC-1), the brightest 1.1mm continuum source found in the AzTEC/JCMT survey (Scott et al. 2008), through a clear detection of the redshifted CO (4-3) and CO (5-4) lines using the Redshift Search Receiver on the Large Millimeter Telescope. The CO redshift of

On the evolution of ejecta fragments in compact supernova remnants

z=4.3420pm0.0004

Evolution of the X‐ray luminosity in young H ii galaxies★

is confirmed by the detection of the redshifted 158 micron [C II] line using the Submillimeter Array. The new redshift and Herschel photometry yield

Wavelength Calibration for OSIRIS/GTC1 Tunable Filters

L_{FIR}=(1.1pm0.1)times 10^{13} L_odot

FLUX CALIBRATED EMISSION LINE IMAGING OF EXTENDED SOURCES USING GTC/OSIRIS TUNABLE FILTERS ∗

and

The near-infrared colours of H II galaxies

SFR = 1300, M_odot

The AGN Dance: Astrometric Variability as the Result of Supernova Explosions in Nuclear Starbursts

yr