arXiv subjects

Elena Terlevich

Publications and source records attributed to Elena Terlevich.

66 records · Page 4Linked to original sources

arXiv2003

On the Detectability of the SZ Effect of Massive Young Galaxies

The Sunyaev-Zel'dovich (SZ) effect expected to be associated with massive star-formation activity produced during the formation of the most luminous bulges of normal galaxies is discussed. Using 1-D chemohydrodynamical models for spheroidal galaxy evolution we show that during the early epochs of galaxy evolution the gas in massive events of star formation may reach temperatures and densities high enough to produce values of the comptonisation parameter "y" comparable to those present in galaxy clusters. In this scenario, we discuss the possibility of detection of the SZ signature in high redshift starforming galaxies with the next generation of mm telescopes capable of arcsecond resolution and equipped with high sensitivity detectors. We show how millimeter colour--colour diagrams or diagnostic diagrams could be used to distinguish between the dust emission and the SZ effect and suggest the use of simultaneous multifrequency observations to improve the chances of detecting the SZ effect.

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arXiv2002

Regions of Star Formation: Chemical Issues.(Discussion Session)

Three are the main questions that were posed to the audience during this discussion session: a) Can galaxy abundances be believed?, b) What progress can we expect soon and from where? and c) Can we agree, as a community, on topics in which effort should be concentrated in the next five years? In what follows, the different contributions by people in the audience are reflected as they were said trying to convey the lively spirit that enlightened the discussion.

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arXiv2002

A comprehensive study of reported high metallicity giant HII regions. II. Ionising stellar populations

The ionising stellar populations of eleven HII regions in the spiral galaxies: NGC628, NGC925, NGC1232 and NGC1637, all of them reported to have solar or oversolar abundances according to empirical calibrations, have been analysed using stellar population synthesis models. Four of the observed regions in the sample, show features which indicate the presence of a population of Wolf-Rayet (WR) stars with ages between 2.3 and 4.1 Myr. This population is sufficient to explain the emission line spectrum of the low metallicity region H13 in NGC628. This is not the case for the rest of the regions for which a second ionising population is required to simultaneously reproduce both the WR features and the emission line spectrum. For two of the regions showing WR features, no consistent solution is found, since the population containing WR stars produces a spectral energy distribution which is too hard to explain the emission of the gas. Several solutions are proposed to solve this problem.

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arXiv2001

New light on the search for low metallicity galaxies I. The N2 method

We present a simple metallicity estimator based on the logarithmic [NII]6584 / Halpha ratio, hereafter N2, which we envisage will become very useful for ranking galaxies in a metallicity sequence from redshift survey quality data even for moderately low spectral resolution. We have calibrated the N2 estimator using a compilation of HII galaxies having accurate oxygen abundances, plus photoionization models covering a wide range of abundances. The comparison of models and observations indicates that both primary and secondary nitrogen are important for the relevant range of metallicities. The N2 estimator follows a linear relation with log(O/H) that holds for the whole abundance range covered by the sample, from about 1/50th to twice the Solar value (7.2 < 12+log(O/H) < 9.1). We suggest that the ([SII]6717,6731 / Halpha) ratio (hereafter S2) can also be used as a rough metallicity indicator. Because of its large scatter the S2 estimator will be useful only in systems with very low metallicity, where [NII]6584 is not detected or in low resolution spectra where [NII]6584 is blended with Halpha.

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arXiv2001

A comprehensive study of reported high metallicity giant HII regions. I. Detailed abundance analysis

We present long-slit observations in the optical and near infrared of fourteen HII regions in the spiral galaxies: NGC 628, NGC 925, NGC 1232 and NGC 1637, all of them reported to have solar or oversolar abundances according to empirical calibrations. For seven of the observed regions, ion-weighted temperatures from optical forbidden auroral to nebular line ratios have been obtained and for six of them, the oxygen abundances derived by standard methods turn out to be significantly lower than solar. The other one, named CDT1 in NGC 1232, shows an oxygen abundance of 12+log(O/H) = 8.95+-0.20 and constitutes, to the best of our knowledge, the first high metallicity HII region for which accurate line temperatures, and hence elemental abundances, have been derived. For the rest of the regions no line temperature measurements could be made and the metallicity has been determined by means of both detailed photoionisation modelling and the sulphur abundance parameter S_23. Only one of these regions shows values of O_23 and S_23 implying a solar or oversolar metallicity. According to our analysis, only two of the observed regions can therefore be considered as of high metallicity. The two of them fit the trends previously found in other high metallicity HII regions, i.e. N/O and S/O abundance ratios seem to be higher and lower than solar respectively.

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arXiv2001

Stellar populations in the nuclear regions of nearby radiogalaxies

We present optical spectra of the nuclei of seven luminous (P(178MHz) > 10**25 W Hz**(-1) Sr**(-1)) nearby (z<0.08) radiogalaxies, which mostly correspond to the FR II class. In two cases, Hydra A and 3C 285, the Balmer and 4000A break indices constrain the spectral types and luminosity classes of the stars involved, revealing that the blue spectra are dominated by blue supergiant and/or giant stars. The ages derived for the last burst of star formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about 10 Myr. The rest of the narrow-line radiogalaxies (four) have 4000A break and metallic indices consistent with those of elliptical galaxies. The only broad-line radiogalaxy in our sample, 3C 382, has a strong featureless blue continuum and broad emission lines that dilute the underlying blue stellar spectra. We are able to detect the Ca II triplet in absorption in the seven objects, with good quality data for only four of them. The strengths of the absorptions are similar to those found in normal elliptical galaxies, but these values are both consistent with single stellar populations of ages as derived from the Balmer absorption and break strengths, and, also, with mixed young+old populations.

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arXiv2000

Evolution of the X-ray luminosity and metallicity of starburst blown superbubbles

We calculate the time-dependent metal production expected from starbursts and use them as boundary conditions in our 2D simulations of evolving superbubbles. We assume that the produced metals (oxygen and iron) thoroughly mix with the ejected stellar envelopes, and/or with the matter thermally evaporated from the superbubble cold outer shell. The metal production process determines the time-dependent metallicity in hot superbubble interiors, and leads to values of Z greater or equal than solar, when oxygen is used as tracer, and under-solar when the metallicity is measured with respect to iron. In either case, the enhanced metallicity boosts the X-ray emissivity of superbubbles, bringing theory and observations closer together.

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arXiv2000

Chemical Abundances and Ionizing Clusters of HII Regions in the LINER Galaxy NGC 4258

We present long-slit observations in the optical and near infrared of eight HII regions in the spiral galaxy NGC 4258. Six of the observed regions are located in the SE inner spiral arms and the other two are isolated in the northern outer arms. A detailed analysis of the physical conditions of the gas has been performed. For two of the regions, an electron temperature has been derived from the [SIII] 6312 A line. For the rest, an empirical calibration based on the red and near infrared sulphur lines has been used. The oxygen abundances derived by both methods are found to be significantly lower (by a factor of two) than previously derived by using empirical calibrations based on the optical oxygen lines. In the brightest region, 74C, the observation of a prominent feature due to Wolf-Rayet stars provides an excellent constraint over some properties of the ionizing clusters. In the light of the current evolutionary synthesis models, no consistent solution is found to explain at the same time both the WR feature characteristics and the emission line spectrum of this region. In principle, the presence of WR stars could lead to large temperature fluctuations and also to a hardening of the ionizing radiation. None of these effects are found in region 74C for which the electron temperatures found from the [SIII] 6312A and the Paschen discontinuity at 8200A are equal within the errors and the effective temperature of the ionizing radiation is estimated at around 35,300K. Both more observations of confirmed high metallicity regions and a finer metallicity grid for the evolutionary synthesis models are needed in order to understand the ionizing populations of HII regions.

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arXiv1999

V, R, I and Halpha photometry of circumnuclear star forming regions in four galaxies with different levels of nuclear activity

V,R,I continuum bands and Halpha + [NII] photometry for circumnuclear star forming regions (CNSFR) is presented, for galaxies with different kinds of nuclear activity: NGC 7469 (Sy 1), NGC 1068 (Sy 2), NGC 7177 (LINER) and NGC 3310 (Starburst). Their Halpha luminosities (0.02 - 7x10**40 erg/s; uncorrected for internal extinction), are comparable to those observed in other galaxies. No systematic differences in the broad band colours are found for the CNSFR in the different galaxies, except for those in NGC 3310 which are considerably bluer, partially due to a younger stellar population. Using theoretical evolutionary synthesis models some colours can be reproduced by single populations (between 7 and 300 Myr) and extinction 0.5-1.5 mag). However, in many cases, the observed equivalent width of Halpha, require a younger population. NGC 1068, 7177 and 7469, are fitted by a two-burst population model at solar metallicity; the age difference between both populations is around 5-7 Myr and the younger burst involves 3 - 61% of the total mass of the cluster,consistent with the younger burst being originated by supernova activity from the previous one. NGC 3310, requires younger ionizing population ages and lower metallicity. An excess (R-I) observed/predicted, not consistent with a normal reddening law can be atributted to red supergiants present in the older population, and not properly accounted for by the models. The two-population scenario seems to show a trend of the evolutionary state of the CNSFR with the nuclear type of the parent galaxy that remains to be explored.

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arXiv1999

HII Galaxies as deep cosmological probes

We re-investigated the use of the Hubble diagram to measure the cosmological constant ($Λ$) and the mass density of the Universe ($Ω_M$). We find an important focusing effect in $Λ$ for redshifts about 3. This effect implies that the apparent magnitude of a standard candle at redshifts z=2-3 has almost no dependence on $Λ$ for $Ω_M>0.2$. This means that $Ω_M$ can be measured independently of $Ω_Λ$ by targeting the redshift range according to an estimate of the value of $Ω_M$. We explore the evidence in support of the suggestion that extreme starburst galaxies also known as HII galaxies can be used as distance estimators over a wide range of redshifts and reaching very high values. We have compiled literature data of HII galaxies up to $z\sim 3$ and found a good correlation between their luminosity and velocity dispersion measured from their strong emission lines, thus confirming the correlation already known to exist for HII galaxies in the nearby Universe. Several systematic effects such as age, extinction, kinematics, and metallicity are discussed as well as the effects of different cosmologies.

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arXiv1999

The evolution of superbubbles and the detection of Lyman alpha in star-forming galaxies

The detection of Ly alpha emission in star-forming galaxies in different shapes and intensities (always smaller than predicted for case B recombination) has puzzled the astronomical community for more than a decade. Here we use two dimensional calculations to follow the evolution of superbubbles and of the H II regions generated by the output of UV photons from massive stars. We show the impact caused by massive star formation in the ISM of different galaxies and we look at the conditions required to detect Ly alpha emission from a nuclear H II region, and the variety of profiles that may be expected as a function of time.

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arXiv1997

New diagnostic methods for emission-line galaxies in deep surveys

We present new quantitative classification methods for emission-line galaxies, which are specially designed to be used in deep galaxy redshift surveys. A good segregation between starbursts and active galactic nuclei, i.e. Seyferts 2s and LINERs, is obtained from diagnostic diagrams involving the [O II]λ3727 Å, [Ne III]\lambda3869 Å, Hβand [O III]\lambda5007 Årelative intensities or the [O II]λ3727 Åand Hβequivalent widths. Furthermore, the colour index of the continuum underlying [O II]λ3727 Åand Hβprovides an additional separation parameter between the two types of emission-line galaxies. We have applied the equivalent widths method to the 0 < z \leq 0.3 emission-line galaxies of the Canada-France Redshift Survey. Our results are in very good agreement with those obtained using the standard diagnostic diagrams including all the strong optical emission-line intensity ratios.

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