Roberto Terlevich

Classification parameters for the emission-line spectra of extragalactic objects

An investigation is made of the merits of various emission-line intensity ratios for classifying the spectra of extragalactic objects. It is shown empirically that several combinations of easily-measured lines can be used to separate objects into one of four categories according to the principal excitation mechanism: normal H II regions, planetary nebulae, objects photoionized by a power-law continuum, and objects excited by shock-wave heating. A two-dimensional quantitative classification scheme is suggested.

Spectroscopy and photometry of elliptical galaxies. I: a new distance estimator

On presente des donnees cinematiques et photometriques concernant 97 galaxies elliptiques, membres de six amas riches

Lyα Emission in Starbursts: Implications for Galaxies at High Redshift*

We present the results of a high resolution UV 2-D spectroscopic survey of star forming galaxies observed with HST-STIS. Our main aim was to map the Lyman alpha profiles to learn about the gas kinematics and its relation with the escape of Lyman alpha photons and to detect extended Lyman alpha emission due to scattering in gaseous halos. We have combined our data with previously obtained UV spectroscopy on other three star-forming galaxies. We find that the P-Cygni profile is spatially extended, smooth and spans several kiloparsecs covering a region much larger than the starburst itself. We propose a scenario whereby an expanding super-shell is generated by the interaction of the combined stellar winds and supernova ejecta from the young starbursts, with an extended low density halo. The variety of observed Lyman alpha profiles both in our sample and in high redshift starbursts is explained as phases in the time evolution of the super-shell expanding into the disk and halo of the host galaxy. The observed shapes, widths and velocities are in excellent agreement with the super-shell scenario predictions and represent a time sequence. We confirm that among the many intrinsic parameters of a star forming region that can affect the properties of the observed Lyman alpha profiles, velocity and density distributions of neutral gas along the line of sight are by far the dominant ones, while the amount of dust will determine the intensity of the emission line, if any.

The evolution of superbubbles and the detection of Lyα in star‐forming galaxies

The detection of Lyemission in star-forming galaxies in different shapes and in- tensities (always smaller than predicted for case B recombination) has puzzled the astronomical community for more than a decade. Here we use two dimensional cal- culations 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 Lyemission from a nuclear H II region, and the variety of profiles that may be expected as a function of time.

Violent star formation in NGC 2363

This is an electronic version of an article published in The Astrophysical Journal. Gonzalez-Delgado, R.M. et al. Violent star formation in NGC 2363. The Astrophysical Journal 437 (1994): 239-261

An Empirical Calibration of Star Formation Rate Estimators

ABSTRA C T The observational determination of the behaviour of the star formation rate (SFR) with lookback time or redshift has two main weaknesses: (i) the large uncertainty of the dust/extinction corrections, and (ii) that systematic errors may be introduced by the fact that the SFR is estimated using different methods at different redshifts. Most frequently, the luminosity of the Ha emission line, that of the forbidden line [O II] l3727 and that of the far-ultraviolet continuum are used with low-, intermediate- and high-redshift galaxies, respectively. To assess the possible systematic differences among the different SFR estimators and the role of dust, we have compared SFR estimates using Ha ,[ OII] l3727 A ˚ , ultraviolet (UV) and far-infrared (FIR) luminosities [SFR(Ha), SFR(O II), SFR(UV) and SFR(FIR), respectively] of a sample comprising the 31 nearby star-forming galaxies that have high-quality photometric data in the UV, optical and FIR. We review the different ‘standard’ methods for the estimation of the SFR and find that while the standard method provides good agreement between SFR(Ha) and SFR(FIR), both SFR(O II) and SFR(UV) are systematically higher than SFR(FIR), irrespective of the extinction law. We show that the excess in the SFR(O II) and SFR(UV) is mainly due to an overestimation of the extinction resulting from the effect of underlying stellar Balmer absorptions in the measured emission line fluxes. Taking this effect into consideration in the determination of the extinction brings the SFR(O II) and SFR(UV) in line with the SFR(FIR), and simultaneously reduces the internal scatter of the SFR estimations. Based on these results, we have derived ‘unbiased’ SFR expressions for the SFR(UV), SFR(O II) and SFR(Ha). We have used these estimators to recompute the SFR history of the Universe using the results of published surveys. The main results are that the use of the unbiased SFR estimators brings into agreement the results of all surveys. Particularly important is the agreement achieved for the SFR derived from the FIR/millimetre and optical/UV surveys. The ‘unbiased’ star formation history of the Universe shows a steep rise in the SFR from za 0t oza 1 with SFR/O1a zU 4:5 , followed by a decline for z . 2 where SFR/O1a zU 21:5 . Galaxy formation models tend to have a much flatter slope from za 0t o za 1.

Global Scaling Relations for Elliptical Galaxies and Implications for Formation

Two recent surveys of elliptical galaxy structural properties are described. E galaxies are seen to populate a planar distribution in the global logarithmic parameter space (R e , σ e , I e ). Two-dimensionality implies that the virial theorem is the only tight constraint on E structure. There is an additional, weaker constraint on radius versus mass that was presumably imposed at formation. The best-fitting plane in logarithmic coordinates has the equation R e ~ σ1.35±0.07 I e-0.84±0.03, implies (M/L) e ~L 0.24±0.04 I e 0.00±0.06. The planar relation can be used to determine distances to E galaxies to an accuracy of ±23%. M/Ls agree well, implying that ellipticals are mainly baryon dominated within R e and that M/Ls are stellar. The effects of other variables such as ellipticity, aspect angle, and rotation on the basic planar relation seem to be small.

NEW DIAGNOSTIC METHODS FOR EMISSION-LINE GALAXIES IN DEEP SURVEYS

ABSTRACT We present new quantitative classification methods for emission-line galaxies,which are specially designed to be used in deep galaxy redshift surveys. A good seg-regation between starbursts and active galactic nuclei, i.e. Seyferts 2 and LINERs, isobtained from diagnostic diagrams involving the [O II]λ3727 ˚A, [Ne III]λ3869 ˚A, Hβand [O III]λ5007 ˚A relative intensities or the [O II]λ3727 ˚A and Hβ equivalent widths.Furthermore, the colour index of the continuum underlying [O II]λ3727 ˚A and Hβprovides an additional separation parameter between the two types of emission-linegalaxies.We have applied the equivalent widths method to the 0 < z ≤0.3 emission-linegalaxies of the Canada-France Redshift Survey. Our results are in very good agreementwith those obtained using the standard diagnostic diagrams including all the strongoptical emission-line intensity ratios.Key words: surveys – H II regions – galaxies: active – galaxies: starburst – galaxies:Seyfert 1 INTRODUCTIONDeep redshift surveys have produced in the past few years arelatively large number of optical/near UV spectra of galax-ies at redshifts z < 0.7 − 0.8 (e.g., Dressler & Gunn 1983;Couch & Sharples 1987; Broadhurst, Ellis & Shanks 1988;Lavery & Henry 1988; Colless et al. 1990; Colless et al.1993;Songaila et al. 1994; Glazebrook et al. 1995; Le F`evre etal. 1995). A large percentage of galaxies in these deep sur-veys present narrow emission lines. The analysis of the spec-trum of these distant emission-line galaxies (hereafter ELGs)should provide important information about their intrinsicproperties (stellar population, rate of star formation, metal-licity, etc.) and the evolution of these parameters with in-creasing look-back time. But a central problem is that verylittle is known about the nature, either H II galaxies or ac-tive galaxies⋆, of the ELGs discovered in these deep surveys.

The VRI colours of H ii galaxies

We present a high spatial resolution CCD surface photometry study in the optical V, R and I broadband filters of a sample of 15 HII galaxies. The colours of the starburst continuum and of the underlying galaxy are measured. The distribution of colours of the underlying galaxy in HII galaxies is similar to the colours of other late type low surface brightness galaxies which suggests a close kinship of these with the quiescent phases of HII galaxies. However, comparison with recent evolutionary population synthesis models shows that the observational errors and the uncertainties in the models are still too large to put strict constraints on their past star formation history.

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

We have derived ages, metallicities and enhanced-element ratios [α/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 correspond to the nuclear re/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 Hβ-[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 σ 0 − 0.46 log(age) − 1.60, or in linear terms Z ∝ σ 0 × (age) −0.5 . More massive (larger σ 0) and older galaxies present, on average, large [α/Fe] values, and therefore must have undergone shorter star-formation time-scales. 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 by more than 8 Gyr. Finally we explore our large spectral coverage to derive log (O/H) metallicity from the Hα and N II λ6584 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 these galaxies. Ke yw ords: galaxies: abundances ‐ galaxies: elliptical and lenticular, cD ‐ galaxies: evolution ‐g alaxies: nuclei ‐ galaxies: stellar content.