(abridged) The present work is a first step to collect homogeneous abundances and near-infrared (NIR) luminosities for a sample of dwarf irregular (dIrr) galaxies, located in nearby groups. The use of NIR luminosities is intended to provide a better proxy to mass than the blue luminosities commonly used in the literature; in addition, selecting group members reduces the impact of uncertain distances. Accurate abundances are derived to assess the galaxy metallicity. Optical spectra are collected for Hii regions in the dIrrs, allowing the determination of oxygen abundances by means of the temperature-sensitive method. For each dIrr galaxy H-band imaging is performed and the total magnitudes are measured via surface photometry. This high-quality database allows us to build a well-defined luminosity-metallicity relation in the range -13 >= M(H) >= -20. The scatter around its linear fit is reduced to 0.11 dex, the lowest of all relations currently available. There might exist a difference between the relation for dIrrs and the relation for giant galaxies, although a firm conclusion should await direct abundance determinations for a significant sample of massive galaxies. This new dataset provides an improved luminosity-metallicity relation, based on a standard NIR band, for dwarf star-forming galaxies. The relation can now be compared with some confidence to the predictions of models of galaxy evolution. Exciting follow-ups of this work are (a) exploring groups with higher densities, (b) exploring nearby galaxy clusters to probe environmental effects on the luminosity-metallicity relation, and (c) deriving direct oxygen abundances in the central regions of star-forming giant galaxies, to settle the question of a possible dichotomy between the chemical evolution of dwarfs and that of massive galaxies.
Irregular (Irr) galaxies are gas-rich objects with recent or ongoing star formation. In absence of spiral density waves, star formation occurs largely stochastically. The scattered star-forming regions tend to be long-lived and migrate slowly. Older populations have a spatially more extended and regular distribution. In fast-rotating Irrs high star formation rates with stronger concentration toward the galaxies' center are observed, and cluster formation is facilitated. In slowly or nonrotating dwarf Irrs (dIrrs) star formation occurs more quiescently, and the formation of OB associations is c…
We present HST/WFPC2 photometry of the central regions of the Phoenix dwarf. Accurate photometry allows us to: 1) confirm the existence of the horizontal branch previously detected by ground-based observations, and use it to determine a distance to Phoenix, 2) clearly detect the existence of multiple ages in the stellar population of Phoenix, 3) determine a mean metallicity of the old red giant branch stars in Phoenix, and suggest that Phoenix has evolved chemically over its lifetime, 4) extract a rough star formation history for the central regions which suggests that Phoenix has been forming…
We examine the dust-to-gas ratio as a function of metallicity for dwarf galaxies [dwarf irregular galaxies (dIrrs) and blue compact dwarf galaxies (BCDGs)]. Using a one-zone model and adopting the instantaneous recycling approximation, we prepare a set of basic equations which describes processes of dust formation and destruction in a galaxy. Four terms are included for the processes: dust formation from heavy elements ejected by stellar mass loss, dust destruction in supernova remnants, dust destruction in star-forming regions, and accretion of heavy elements onto preexisting dust grains. Sol…
On the basis of the propagating star-formation model, we investigated the star-formation activities of dwarf irregular galaxies (dIrrs) by considering two processes: the heating from stellar feedback and the cooling of the heated gas. After examining the timescales of the two processes, we propose that continuous global star-formation activity is difficult in dIrrs, since their small sizes make the feedback efficient and their small metallicities prevent the cooling from becoming effective. Thus, the intermittent nature of the star-formation activities of dIrrs, which is due to the small metal…
We present a study of the old globular clusters (GC) using archival F606W and F814W HST/ACS images of 19 Magellanic-type dwarf Irregular (dIrr) galaxies found in nearby (2 - 8 Mpc) associations of only dwarf galaxies. All dIrrs have absolute magnitudes fainter than or equal to the SMC (Mv = -16.2 mag). We detect 50 GC candidates in 13 dIrrs, of which 37 have (V-I) colors consistent with "blue" (old, metal-poor) GCs (bGC). The luminosity function (LF) of the bGCs in our sample peaks at Mv = -7.41 +/- 0.22 mag, consistent with other galaxy types. The width of the LF is sigma = 1.79 +/- 0.31 whic…
We present the results of a study of the morphology of the dwarf galaxy population in Abell 868, a rich, intermediate redshift (z=0.154) cluster which has a galaxy luminosity function with a steep faint-end slope (alpha=-1.26 +/- 0.05). A statistical background subtraction method is employed to study the B-R colour distribution of the cluster galaxies. This distribution suggests that the galaxies contributing to the faint-end of the measured cluster LF can be split into three populations: dIrrs with B-R<1.4; dEs with 1.4<B-R<2.5; and contaminating background giant ellipticals (gEs) with B-R>2.…
We have compared the metallicity (represented by oxygen abundance), and the dust-to-gas ratio, in a sample of dwarf galaxies. For dwarf irregulars (dIrrs) we find a good correlation between the two quantities, with a power-law index ${0.54\pm 0.2}$. Blue Compact Dwarf (BCD) galaxies do not show such a good correlation; in addition both the dust-to-gas ratio and the metallicity tend to be higher than for dIrrs. We have then developed a simple but physical analytical model for the above relation. Comparing the model results with the data, we conclude that: (i) for low values of the dust-to-gas r…
Dwarf spheroidal (dSph) galaxies present an evolutionary puzzle that we explore in 40 early- and late-type dwarfs in the Local Group and nearby field. Although dSphs formed stars over extended periods, today all but one are free of detectable interstellar matter (ISM), even in the Fornax dSph, where stars still formed 100 Myr ago. Combining metallicities for red giants with HI data from the literature, we show that the well-known offset in luminosity-metallicity (L-Z) relations for dSphs and dwarf irregular (dIrr) galaxies exists also when comparing only their old stellar populations: dSphs ha…
We present a study of the old globular cluster (GC) population of the dwarf irregular galaxy NGC 1427A using multi-wavelength VLT observations in U, B, V, I, H_alpha, J, H, and Ks bands under excellent observing conditions. We applied color and size selection criteria to select old GC candidates and made use of archival ACS images taken with the Hubble Space Telescope to reject contaminating background sources and blended objects from the GC candidates' list. The H_alpha observations were used to check for contamination due to compact, highly reddened young star clusters whose colors and sizes…
We demonstrate a successful strategy for identifying extremely metal poor galaxies. Our preliminary survey of 24 candidates contains 10 metal poor galaxies of which 4 have 12+log(O/H)<7.65, some of the lowest metallicity blue compact galaxies known to date. Interestingly, our sample of metal poor galaxies have systematically lower metallicity for their luminosity than comparable samples of blue compact galaxies, dIrrs, and normal star-forming galaxies. Our metal poor galaxies share very similar properties, however, with the host galaxies of nearby long-duration gamma-ray bursts (GRBs), includi…
We study the evolution of the Stellar Mass-Metallicity Relation and the Luminosity-Metallicity Relation by performing numerical simulations in a cosmological framework. We find that the slope and the zero point of the Luminosity-Metallicity Relation evolve in such a way that, at a given metallicity, systems were ~3 mag brighter at z=3 compared to galaxies in the local universe, which is consistent with the observational trend. The local Stellar Mass-Metallicity Relation shows also a good agreement with recent observations. We identify a characteristic stellar mass M_c ~ 10^(10.2) M_sun/h at wh…
We study the Luminosity-Metallicity Relation and the Stellar Mass-Metallicity Relation by performing chemo-dynamical simulations in a cosmological scenario. Our results predict a tight linear correlation between oxygen chemical abundance and luminosity for galactic systems up to z=3. The Luminosity-Metallicity Relation evolves with redshift in such a way that systems at a given oxygen abundance were ~3 dex brighter at z=3 compared to local ones, in good agreement with observations. We determin also a characteristic stellar mass M_c~10^(10.2) M_sun/h above which the Stellar Mass-Metallicity Rel…
We investigate the use of the rest-frame 24microns luminosity as an indicator of the star formation rate (SFR) in galaxies with different metallicities by comparing it to the (extinction corrected) Halpha luminosity. We carry out this analysis in 2 steps: First, we compare the emission from HII regions in different galaxies with metallicities between 12+log(O/H) = 8.1 and 8.9. We find that the 24microns and the extinction corrected Halpha luminosities from individual HII regions follow the same correlation for all galaxies, independent of their metallicity. Second, the role of metallicity is e…
We present deep $BVI$ observations of the dwarf irregular galaxy UKS1927-177 in Sagittarius. Statistically cleaned $V$, $(B-I)$ CMDs clearly display the key evolutionary features in this galaxy. Previously detected C stars are located in the CMDs and shown to be variable, thus confirming the presence of a significant upper-AGB intermediate age population. A group of likely red supergiants is also identified, whose magnitude and color is consistent with a 30 Myr old burst of star formation. The observed colors of both blue and red stars in SagDIG are best explained by introducing a differential…
We present preliminary results of an observational campaign devoted at establishing the influence of chemical composition on the Cepheid Period-Luminosity relation. The data are in good agreement with theoretical predictions based on non-linear convective models, suggesting a fairly strong dependence of the Period-Luminosity relation on metallicity in the sense of more metal rich stars being intrinsically fainter than otherwise expected. Our data indicate that the error on the inferred distance can be as large as 10% if the role of metallicity is neglected.
We report on the recent developments of our long-term investigation of the near-IR luminosity-metallicity relation for dwarf irregular galaxies in nearby groups. A very well-defined relation is emerging from our observational database, and a preliminary discussion of its implications is given.
The low-luminosity dwarf irregular galaxies are considered. The oxygen abundances in HII regions of dwarf irregular galaxies were recalculated from published spectra through the recently suggested P - method. It has been found that the metallicity of low-luminosity dwarf irregular galaxies, with a few exceptions, correlates well with galaxy luminosity. The dispersion of oxygen abundances around the metallicity - luminosity relationship increases with decreasing of galaxy luminosity, as was found by Richer and McCall (1995). No relationship between the oxygen abundance and the absolute magnitud…
We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and a preliminary result is presented. The 12+log(O/H) vs.H plane must be populated with more low-luminosity galaxies before a definite conclusion can be drawn.
We describe the two projects by which we are assembling a database of near-IR luminosities and direct oxygen abundances for both high- and low-mass star-forming galaxies in the nearby Universe. This will eventually allow us to construct the first reliable and homogeneous luminosity-metallicity relation, to be compared to theoretical models of galactic evolution, and to the relations for galaxies at higher redshifts.
The stellar halos of spiral galaxies bear important chemo-dynamical signatures of galaxy formation. We present here the analysis of 89 semi-cosmological spiral galaxy simulations, spanning ~ 4 magnitudes in total galactic luminosity. These simulations sample a wide variety of merging histories and show significant dispersion in halo metallicity at a given total luminosity - more than a factor of ten in metallicity. Our preliminary analysis suggests that galaxies with a more extended merging history possess halos which have younger and more metal rich stellar populations than the stellar halos …
On the basis of new theoretical results useful predictions concerning the Period-Luminosity (PLR) and Period-Luminosity-Color (PLCR) relations both for optical and infrared magnitudes are presented. It is shown that, following the dependence of the instability strip on metallicity, there is a non negligible dependence of the PLRs and PLCRs on the metallicity of the pulsating stars, mainly for optical bands. In particular theoretical results predict a dependence of the PLR on metals which is reversed with respect to current empirical evaluations. To give a possible explanation for this discrepa…
We consider the roles of two widely invoked mechanisms for the metallicity-luminosity correlation among late-type galaxies: higher astration level and decreasing efficiency of heavy-element loss with increasing luminosity. We find that both mechanisms contribute about equally to the range in oxygen abundance between low (logL_B = 8) and high (logL_B = 10.5) luminosity galaxies. We also consider the transition from spirals to irregulars, finding that both the oxygen abundance deficiency (indicating the degree of mass exchange between a galaxy and its environment) and the gas fraction vary smoot…
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects galaxies with very low continuum brightness by using an imaging Fabry-Perot interferometer. With spectroscopic follow-up observations of MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining these measurements with published oxygen abundances of galaxies with MB<~-19 we find evidence that a metallicity-luminosity relation exists at medium redshift, but it is displaced to lower abundances and higher luminosities c…
Using HST and the WFPC2 we have acquired very deep V- and I-band photometry of stars in NGC 2420 and NGC 2477 to study cluster luminosity functions at approximately solar metallicity. We have determined these cluster luminosity functions down to $M_I$ = 10.5 (0.2 M$_{\odot}$) and find that the luminosity function of NGC 2420 turns over at $M_I$ $\approx$ 9.0, and possibly stops altogether by $M_I$ $\approx$ 9.5. The luminosity function of NGC 2477 may flatten at $M_I$ $\geq$ 9.5. We compare our open cluster luminosity functions to the solar neighborhood field star luminosity function of Kroupa…
In this work, we study the Luminosity-Metallicity relation (LMR) and the Stellar Mass -Metallicity relation (MMR) of galactic systems in a hierarhical clustering scenario. We performed numerical hydrodynamical simulations with the chemical GADGET-2 of Scannapieco et al.(2005) in a LCDM universe. We found that our simulated galactic systems reproduce the observed local LMR and its evolution in zero point and slope. The simulated MMR is also in agreement with recent observational results. From the analysis of the evolution of the MMR, we found a characteristic mass at ~10^(10.2) M_sun / h which …
We present the results of an observational campaign undertaken to assess the influence of the iron content on the Cepheid Period-Luminosity relation. Our data indicate that this dependence is not well represented by a simple linear relation. Rather, the behaviour is markedly non monotonic, with the correction peaking at about solar metallicity and declining for higher and lower values of [Fe/H].
In this contribution we report our recent investigation of the gas metallicity in active galactic nuclei and its dependence on luminosity and redshift. We compile large spectroscopic datasets of broad-line and narrow-line AGNs, and compare them with the results of our photoionization models. Through the analysis of both the broad and the narrow emission-line regions, we find that: (1) for a given luminosity, there is no redshift dependence of the gas metallicity; (2) for a given redshift, there is a significant correlation between gas metallicity and luminosity; (3) the luminosity-metallicity …
Using the Hubble Space Telescope, we have resolved individual red-giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look at the systematic trends in halo stellar populations. We have found that bright galaxies tend to have broad red-giant branch star color distributions with redder mean colors, suggesting that the heavy element abundance spread increases with the parent galaxy luminosity. The mean metallicity of the stellar halo, estimated using the mean colors …
We present a comparison of the predictions of stellar models with the luminosity of the lower main sequence ($5.5 < M_V < 7.3$) using K dwarfs in the Hipparcos catalog. The parallaxes of our comparison stars are known to better than 15% and metallicities have been recently determined from photometry. A major advantage of our comparison is that distances in our sample are known with good accuracy, while tests that involve open and globular clusters are constrained by potentially inaccurate distances. We show that the luminosity of the lower main sequence relative to a fiducial (solar metallicit…
We derive metal abundance estimates for a large sample of starbursting emission-line galaxies (ELGs). Our sample is drawn from the KPNO International Spectroscopic Survey (KISS) which has discovered over 2000 ELG candidates to date. Follow-up optical spectra have been obtained for ~900 of these objects. A three step process is used to obtain metal abundances for these galaxies. We first calculate accurate nebular abundances for 12 galaxies whose spectra cover the full optical region from [OII]3726,29 to beyond [SII]6717,31 and include detection of [OIII]4363. Using secondary metallicity indica…
We have assessed the influence of the stellar iron content on the Cepheid Period-Luminosity (PL) relation by relating the V band residuals from the Freedman et al (2001) PL relation to [Fe/H] for 68 Galactic and Magellanic Cloud Cepheids. The iron abundances were measured from FEROS and UVES high-resolution and high signal-to-noise optical spectra. Our data indicate that the stars become fainter as metallicity increases, until a plateau or turnover point is reached at about solar metallicity. This behavior appears at odds both with the PL relation being independent from iron abundance and with…
For a sample of 25 dwarf irregular galaxies with distances D < 5 Mpc and measured oxygen abundances, we present results derived from stellar masses and galaxy luminosities from near-infrared imaging with IRAC on the Spitzer Space Telescope. We have constructed the appropriate luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relations, and compared these relations with their corresponding relations from the Sloan Digital Sky Survey (SDSS). We obtain the following results. 1. The dispersion in the near-infrared L-Z relation is reduced with respect to the dispersion in the optical L-Z rela…
I present results on the correlation between galaxy mass, luminosity, and metallicity for a sample of spiral and irregular galaxies having well-measured abundance profiles, distances, and rotation speeds. Additional data for low surface brightness galaxies from the literature are also included for comparison. These data are combined to study the metallicity-luminosity and metallicity-rotation speed correlations for spiral and irregular galaxies. The metallicity luminosity correlation shows its familiar form for these galaxies, a roughly uniform change in the average present-day O/H abundance o…
Using spectroscopic data from the Deep Extragalactic Evolutionary Probe (DEEP) Groth Strip survey (DGSS), we analyze the gas-phase oxygen abundances for 56 emission-line field galaxies in the redshift range 0.26<z<0.82. Oxygen abundances relative to hydrogen range between 8.4<12+log(O/H)<9.0 with typical uncertainties of 0.17 dex. The 56 DGSS galaxies collectively exhibit a correlation between B-band luminosity and metallicity, i.e., an L-Z relation. Subsets of DGSS galaxies binned by redshift also exhibit L-Z correlations but with different zero points. Galaxies in the highest redshift bin (z…
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…
The theoretical period-luminosity relation for Cepheids was deduced from stellar evolution and pulsation computations. Questions concerning the metallicity dependence of the relation as well as the constancy of the pulsation `constant' Q in the instablility strip were addressed. We found no significant metallicity dependence of either the slope or of the zero-point of the period-luminosity relation. The Q-value, however, varies across the instability strip, in effective temperature as well as in luminosity; its metallicity dependence, on the other hand, is marginal.
This work is devoted to improving empirical mass-luminosity relations and mass-metallicity-luminosity relation for low mass stars. For these stars, observational data in the mass-luminosity plane or the mass-metallicity-luminosity space subject to non-negligible errors in all coordinates with different dimensions. Thus a reasonable weight assigning scheme is needed for obtaining more reliable results. Such a scheme is developed, with which each data point can have its own due contribution. Previous studies have shown that there exists a plateau feature in the mass-luminosity relation. Taking i…
The well known relationship between metallicity and luminosity in AGN is addressed by introducing new metallicity measurements (based on the method of Hamann & Ferland 1993; HF93) for a sample of narrow-line Seyfert 1 (NLS1) galaxies. Our new results, based on a sample of 162 AGN, including 9 NLS1s, indicate that, while broad-line AGN trace a metallicity--luminosity power law with an index of ~0.2, NLS1s deviate significantly from this relationship at low luminosities. Adopting the HF93 method based on the N V/C IV line ratio, we find that NLS1 metallicities are similar to those of some high-r…
(ABRIDGED) We have applied the near-IR Barnes-Evans realization of the Baade-Wesselink method as calibrated by Fouque & Gieren (1997) to five metal-poor Cepheids with periods between 13 and 17 days in the Small Magellanic Cloud as well as to a sample of 34 Galactic Cepheids to determine the effect of metallicity on the period-luminosity (P-L) relation. For ten of the Galactic Cepheids we present new accurate and well sampled radial-velocity curves. The Baade-Wesselink analysis provides accurate individual distances and luminosities to the Cepheids in the two samples, allowing us to constrain d…
We obtained high resolution ELODIE and CORALIE spectra for both components of 20 wide visual binaries composed of an F-, G- or K-dwarf primary and an M-dwarf secondary. We analyse the well understood spectra of the primaries to determine metallicities ([Fe/H]) for these 20 systems, and hence for their M dwarf components. We pool these metallicities with determinations from the literature to obtain a precise (+- 0.2 dex) photometric calibration of M dwarf metallicities. This calibration represents a breakthrough in a field where discussions have had to remain largely qualitative, and it helps u…
This is the fifth paper in a series studying the stellar components, star formation histories, star formation rates and metallicities of a blue compact galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic observations, we have determined the electron temperatures, electron densities, nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our sample, using different oxygen abundance indicators. The oxygen abundance covers the range 7.15 < 12 + log (O/H)< 9.0, and nitrogen is found to be mostly a product of secondary nucleosynthesis for 12 + log (O/H)>8.2 and …
Using spectroscopic data from the Deep Extragalactic Evolutionary Probe (DEEP) Groth Strip survey (DGSS), we analyze the gas-phase oxygen abundances in the warm ionized medium for 64 emission-line field galaxies in the redshift range 0.26<z<0.82. Oxygen abundances relative to hydrogen range between 8.4<12+log(O/H)<9.0 with typical internal plus systematic measurement uncertainties of 0.17 dex. The 64 DGSS galaxies collectively exhibit an increase in metallicity with B-band luminosity. DGSS galaxies in the highest redshift bin (z=0.6-0.82) are brighter, on average, by ~1 mag at fixed metallicit…
We present new and accurate Near-Infrared J and Ks-band data of the Large Magellanic Cloud cluster Reticulum. Data were collected with SOFI available at NTT and covering an area of approximately (5 x 5) arcmin^2 around the center of the cluster. Current data allowed us to derive accurate mean K-band magnitudes for 21 fundamental and 9 first overtone RR Lyrae stars. On the basis of the semi-empirical K-band Period-Luminosity-Metallicity relation we have recently derived, we find that the absolute distance to this cluster is 18.52 +- 0.005 (random) +- 0.117 (systematic). Note that the current er…
With the aid of stellar atmosphere models, we derive iron abundances [Fe/H] from the OGLE B, V, I photometry on the Magellanic Cloud Cepheids. We show that in both clouds the average metallicities of the first overtone variables are lower than those of the fundamental ones (by ~0.2 and ~0.3 dex in the LMC and SMC, respectively). Consequently, there is a correlation between the overall [Fe/H] and luminosity; the lower luminosity stars tend to be also of lower metallicity. These metallicity dependencies are concordant with the ones derived for the two types of double-mode Cepheids from pulsation…
If dwarf galaxies are primeval objects in the Universe, as hierarchical galaxy formation scenarios predict, they should show traces of their old stellar populations, perhaps distributed in extended, differentiated structures. The working hypothesis that such a structure could exist is tested for the case of DDO 187, a field dIrr galaxy showing a high gas fraction and low metallicity. For this purpose, the structure, star formation history (SFH) and other properties of the galaxy are analyzed using the spatial distribution of stars, the color-magnitude diagrams (CMDs) of about 1500 resolved sta…
Using a new technique we have determined a value for the constant of proportionality between submillimetre emission and dust mass, the dust mass absorption coefficient at 850 microns. Our method has an advantage over previous methods in that we avoid assumptions about the properties of dust in the interstellar medium. Our only assumption is that the fraction of metals incorporated in the dust is a universal constant. To implement our method we require objects that have submillimetre and far-infrared flux measurements as well as gas mass and metallicity estimates. We present data for all the ga…
Based on consistent evolutionary and pulsation calculations, we analyse the effect of metallicity and of different convection treatments in the stellar models on period - magnitude, - color and - radius relationships. In order to perform an accurate comparison with observations, we have computed grids of atmosphere models and synthetic spectra for different metallicities, covering the range of effective temperatures and gravities relevant for Cepheids. The models are compared to recent observations of galactic and Magellanic Clouds Cepheids. Unprecedented level of agreement is found between mo…
Timmes, Brown & Truran found that metallicity variations could theoretically account for a 25% variation in the mass of 56Ni synthesized in Type Ia supernovae (SNe Ia), and thus account for a large fraction of the scatter in observed SN Ia luminosities. Higher-metallicity progenitors are more neutron-rich, producing more stable burning products relative to radioactive 56Ni. We develop a new method for estimating bolometric luminosity and 56Ni yield in SNe Ia and use it to test the theory with data from the Supernova Legacy Survey. We find that the average 56Ni yield does drop in SNe Ia from hi…
A quantitative spectral analysis of 24 A supergiants in the Sculptor Group spiral galaxy NGC 300 at a distance of 1.9 Mpc is presented. A new method is introduced to analyze low resolution (~5 AE) spectra, which yields metallicities accurate to 0.2 dex including the uncertainties arising from the errors in Teff (5%) and log g (0.2 dex). For the first time the stellar metallicity gradient based on elements such as titanium and iron in a galaxy beyond the Local Group is investigated. Solar metallicity is measured in the center and 0.3 solar in the outskirts and a logarithmic gradient of -0.08 de…
Using photometric data from the 2MASS second incremental release point source catalog we constructed Ks vs. (J-Ks) color-magnitude diagrams (CMDs) of Galactic globular clusters (GGCs) for which the JKs photometric data have been made available up to now. On the CMDs of 13 GGCs we identified RGB bump features and derived luminosities of bumps in Ks and in absolute Ks for 11 of them. We reconfirm the relation between abolute Ks magnitude of bump and metallicity [Fe/H]CG97 or [M/H] such that the luminosity of bump becomes brighter as metallicity [Fe/H]CG97 or [M/H] decreases. This result is simil…
We point out that the absolute magnitude of the Galactic Cepheids, which have been used for local calibrations for Cepheid period-luminosity relation, shows an unexpectedly large metal abundance effect. This indicates that either Cepheids period luminosity relation has a large metallicity dependence, much larger than expected in stellar pulsation models, or the unreddened distances to clusters contain a large systematic error arising from the neglect of the metallicity effect. This effect may introduce an uncertainty of --0.4 to +0.1 mag into the distance to the LMC estimated using the Cepheid…
We investigate the dependence of theoretically generated mass - (absolute magnitude) relations on stellar models. Using up to date physics we compute models in the mass range 0.1 < m < 1M_sun. We compare the solar-metallicity models with our older models, with recent models computed by others, and also with an empirical mass - (absolute magnitude) relation that best fits the observed data. At a given mass below 0.6M_sun the effective temperatures differ substantially from model to model. However taken individually each set of models is in good agreement with observations in the mass - luminosi…
We report results from the third in a series of nebular abundance studies of emission-line galaxies from the KPNO International Spectroscopic Survey (KISS). Galaxies with coarse metallicity estimates of 12 + log(O/H) less than 8.2 dex were selected for observation. Spectra of 14 galaxies, which cover the full optical region from [OII]3727,3729 to beyond [SII]6717,6731, are presented, and abundance ratios of N, O, Ne, S, and Ar are computed. The auroral [OIII]4363 line is detected in all 14 galaxies. Oxygen abundances determined through the direct electron temperature T_e method confirm that th…
We investigate the universality of the globular cluster luminosity function (GCLF) and the use of this function as an extragalactic distance indicator. Previous studies have found an offset between GCLF distances and those obtained with other techniques. We show that this offset can be understood in terms of a metallicity effect. Specifically, the globular cluster systems used in distance scale studies have traditionally been those around elliptical galaxies. These systems have higher mean metallicities than the Milky Way globular cluster system. Consequently, the peak of the GCLF in the syste…
We investigate the Luminosity-Metallicity (L-Z) relation in the local universe (z < 0.15) using spectra of 6387 star-forming galaxies extracted from the 2dF Galaxy Redshift Survey. This sample is by far the largest to date used to perform such a study. We distinguish star-forming galaxies from AGNs using "standard" diagnostic diagrams to build a homogeneous sample of starburst galaxies for the L-Z study. We propose new diagnostic diagrams using "blue" emission lines ([OII]3727, [OIII]5007 and Hbeta) only to discriminate starbursts from AGNs in intermediate-redshift (z > 0.3) galaxies. Oxygen-t…
We explore the galaxian luminosity-metallicity (L-Z) relationship in both the optical and the near-IR using a combination of optical photometric and spectroscopic observations from the KPNO International Spectroscopic Survey (KISS) and near-infrared photometry from the Two-micron All Sky Survey (2MASS). We supplement the 2MASS data with our own NIR photometry for a small number of lower-luminosity ELGs that are under-represented in the 2MASS database. Our B-band L-Z relationship includes 765 star-forming KISS galaxies with coarse abundance estimates from our follow-up spectra, while the correl…
It is shown that bright cluster dwarf ellipticals follow a relation between metallicity and apparent flattening. Rounder dwarfs tend to be more metal-rich. The evidence is based on colour as well as spectroscopic line-strength data from the literature. The large scatter of dEs around the mean metallicity-luminosity relation, usually ascribed to large observational errors, turns out to be an ellipticity effect. In the magnitude range $-14 \ga M_B \ga -18$ the metallicity of dEs depends more strongly on ellipticity than luminosity. A possible explanation is that galaxies with masses around $10^{…
We use theoretical Period-Luminosity and Period-Luminosity-Color relations in the VI passbands, as based on nonlinear, nonlocal and time-dependent convective pulsating models, to predict the reddening and true distance modulus of distant Cepheids observed with the Hubble Space Telescope. By relying on the pulsating models with metal content Z=0.008, we find that the theoretical predictions agree to the values obtained by the Extragalactic Distance Scale Key Project on the basis of empirical Period-Luminosity relations referenced to LMC variables. In the meantime, from the theoretical relations…
Optical integrated spectra of bulges have been obtained for 28 spiral galaxies. By applying an appropriate aperture size for each galaxy, the unavoidable contamination of disk starlight has been carefully minimized and set to $\sim$ 1/7 of the total stellar light. The sample covers a wide range in bulge luminosity and morphology. The Mg$_2$ index shows a tight correlation with the bulge intrinsic luminosity, similar - and extended at fainter magnitudes - to the relationship known for ellipticals. Other features such as CaIIK, CN, G-band, and TiO show similar trend with the bulge luminosity. On…
In order to test systematic of the Amati relation, the 24 long-duration GRBs with firmly determined $E_{γ,\mathrm{iso}}$ and $E_{\mathrm p}$ are separated into two sub-groups according to B-band luminosity of their host galaxies. The Amati relations in the two subgroups are found to be in agreement with each other within uncertainties. Taking into account of the well established luminosity - metallicity relation of galaxies, no strong evolution of the Amati relation with GRB's environment metallicity is implied in this study.
