Stellar indices and kinematics in Seyfert 1 nuclei

We present spectra of 6 type 1 Seyfert galaxies, 2 Seyfert 2, a starburst galaxy and a compact narrow line radiogalaxy, taken in two spectral ranges centered around the near--IR CaII triplet (CaT) (at ~8600 Angstroms), and the Mgb stellar feature at 5180 Angstroms. We measured the equivalent width (EWs) of these features and the Fe52 and Fe53 spectral indices. We found that the strength of the CaT in type 1 Seyfert galaxies with prominent central point sources, is larger than what would be expected from the observed strength of the blue indices. This could be explained by the presence of red supergiants in the nuclei of Seyfert 1 galaxies. On the other hand, the blue indices of these galaxies could also be diluted by the strong FeII multiplets that can be seen in their spectra. We have also measured the stellar and gas velocity dispersions of the galaxies in the sample. The stellar velocity dispersions were measured using both, the Mgb and CaT stellar features. The velocity dispersion of the gas in the narrow line region (NLR) was measured using the strong emission lines [OIII] 5007, 4959 and [SIII] 9069. We compare the gas and star velocity dispersions and find that both magnitudes are correlated in Seyfert galaxies. Most of the Seyfert 1 we observe have stellar velocity dispersion somehow greater than that of the gas in the NLR.Comment: To appear in MNRAS, 18 pages, 9 figure

High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?

X-shooter and ISIS WHT spectra of the starforming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000km/s) and very broad (FWZI = 4000km/s) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800km/s, previously undetected FeII multiplet (42) absorptions also blueshifted by 800km/s, IR CaII triplet stellar absorptions consistent with [Fe/H] < -2.0 and no broad components or blushifted absorptions in the HeI lines. Based on historical records, we found no optical variability at the 5 sigma level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1mag for the past 24 years. The lack of variability rules out transient phenomena like luminous blue variables or SN IIn as the origin of the blue shifted absorptions of HI and FeII. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster wind.Comment: Accepted for publication in MNRAS; 15 pages, 10 figure

Group, field and isolated early-type galaxies II. Global trends from nuclear data

We have derived ages, metallicities and enhanced-element ratios [alpha/Fe] for a sample of 83 early-type galaxies essentially in groups, the field or isolated objects. The stellar population properties derived for each galaxy corresponds to the nuclear r_e/8 aperture extraction. The median age found for Es is 5.8 +- 0.6 Gyr and the average metallicity is +0.37 +- 0.03 dex. For S0s, the median age is 3.0 +- 0.6 Gyr and [Z/H] = 0.53 +- 0.04 dex. We compare the distribution of our galaxies in the Hbeta-[MgFe] diagram with Fornax galaxies. Our elliptical galaxies are 3-4 Gyr younger than Es in the Fornax cluster. We find that the galaxies lie in a plane defined by [Z/H] = 0.99 log sigma_0 - 0.46 log Age - 1.60. More massive (larger sigma_0) and older galaxies present, on average, large [alpha/Fe] values, and therefore, must have undergone shorter star-formation timescales. Comparing group against field/isolated galaxies, it is not clear that environment plays an important role in determining their stellar population history. In particular, our isolated galaxies show ages differing in more than 8 Gyr. Finally we explore our large spectral coverage to derive log(O/H) metallicity from the N2 indicator and compare it with model-dependent [Z/H]. We find that the O/H abundances are similar for all galaxies, and we can interpret it as if most chemical evolution has already finished in them.Comment: 23 pages, 17 postscript figures; accepted for publication in the MNRA

A high excitation HII region in the faint dwarf elliptical galaxy A0951+68

We present the results of BVRI imaging and optical spectroscopy of the dwarf galaxy A0951+68. The images reveal that, although this galaxy is classified as a dwarf elliptical, it has some properties that are similar to dwarf irregular galaxies. It contains two bright knots of emission, one of which is red and unresolved and the other blue and resolved. The blue knot also shows a high excitation emission line spectrum. The observed line ratios indicate that this is an HII region, although with some line ratios that are border-line with those in AGN. The emission line luminosity is consistent with ionisation by a single, very luminous O star, or several smaller O stars, but the extended blue light in the knot shows that this has occurred as part of a substantial recent star formation event. We find that the metal abundance, while low compared to typical large galaxies, actually seems to be high for such a low luminosity dwarf. The position of A0951 in the literature is incorrect and we provide the correct value.Comment: 8 pages, Latex, 4 encapsulated postscript figures included, 1 separate JPEG figure; to be published in Monthly Notice

Thermal Emission from HII Galaxies: Discovering the Youngest Systems

We studied the radio properties of very young massive regions of star formation in HII galaxies, with the aim of detecting episodes of recent star formation in an early phase of evolution where the first supernovae start to appear. Our sample consists of 31 HII galaxies, characterized by strong Hydrogen emission lines, for which low resolution VLA 3.5cm and 6cm observations were obtained. The radio spectral energy distribution has a range of behaviours; 1) there are galaxies where the SED is characterized by a synchrotron-type slope, 2) galaxies with a thermal slope, and, 3) galaxies with possible free-free absorption at long wavelengths. The latter SEDs were found in a few galaxies and represent a signature of heavily embedded massive star clusters closely related to the early stages of massive star formation. Based on the comparison of the star formation rates determined from the recombination lines and those determined from the radio emission we find that SFR(Ha) is on average five times higher than SFR(1.4GHz). We confirm this tendency by comparing the ratio between the observed flux at 20 cm and the expected one, calculated based on the Ha star formation rates, both for the galaxies in our sample and for normal ones. This analysis shows that this ratio is a factor of 2 smaller in our galaxies than in normal ones, indicating that they fall below the FIR/radio correlation. These results suggest that the emission of these galaxies is dominated by a recent and massive star formation event in which the first supernovae (SN) just started to explode. We conclude that the systematic lack of synchrotron emission in those systems with the largest equivalent width of Hb can only be explained if those are young starbursts of less than 3.5Myr of age.Comment: Accepted for publication in Ap

Optical Monitoring of Quasars: I. Variability

We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratorio Nacional de Astrofisica, Brazil, between March 1993 and July 1996. A distinctive feature of this survey is its photometric accuracy, ~ 0.02 V mag, achieved through differential photometry with CCD detectors, what allows the detection of faint levels of variability. We find that the relative variability, delta = sigma / L, observed in the V band is anti-correlated with both luminosity and redshift, although we have no means of discovering the dominant relation, given the strong coupling between luminosity and redshift for the objects in our sample.We introduce a model for the dependence of quasar variability on frequency that is consistent with multi-wavelength observations of the nuclear variability of the Seyfert galaxy NGC 4151. We show that correcting the observed variability for this effect slightly increases the significance of the trends of variability with luminosity and redshift. Assuming that variability depends only on the luminosity, we show that the corrected variability is anti-correlated with luminosity and is in good agreement with predictions of a simple Poissonian model. The energy derived for the hypothetical pulses, ~ 10^50 erg, agrees well with those obtained in other studies. We also find that the radio-loud objects in our sample tend to be more variable than the radio-quiet ones, for all luminosities and redshifts.Comment: 17 pages, 12 figures, accepted for publication in MNRAS (uses MNRAS style

Optical and X-ray Variability in The Least Luminous AGN, NGC4395

We report the detection of optical and X-ray variability in the least luminous known Seyfert galaxy, NGC4395. The featureless continuum changed by a factor of 2 in 6 months, which is typical of more luminous AGN. The largest variation was seen at shorter wavelengths, so that the spectrum becomes `harder' during higher activity states. In a one week optical broad band monitoring program, a 20% change was seen between successive nights. In a 1 month period the spectral shape changed from a power law with spectral index alpha ~0 (characteristic of quasars) to a spectral index alpha ~2 (as observed in other dwarf AGN). ROSAT HRI and PSPC archive data show a variable X-ray source coincident with the galactic nucleus. A change in X-ray flux by a factor \~2 in 15 days has been observed. When compared with more luminous AGN, NGC4395 appears to be very X-ray quiet. The hardness ratio obtained from the PSPC data suggests that the spectrum could be absorbed. We also report the discovery of weak CaIIK absorption, suggesting the presence of a young stellar cluster providing of the order of 10% of the blue light. Using HST UV archive data, together with the optical and X-ray observations, we examine the spectral energy distribution for NGC4395 and discuss the physical conditions implied by the nuclear activity under the standard AGN model. The observations can be explained by either an accreting massive black hole emitting at about 10^(-3) L_(Edd) or by a single old compact SNR with an age of 50 to 500 yr generated by a small nuclear starburst.Comment: 19 pages, 9 figures, to appear in MNRA