arXiv subjects

L. S. Pilyugin

Publications and source records attributed to L. S. Pilyugin.

At least 55 records · Page 3Linked to original sources

arXiv2007

On the maximum value of the cosmic abundance of oxygen and the oxygen yield

We search for the maximum oxygen abundance in spiral galaxies. Because this maximum value is expected to occur in the centers of the most luminous galaxies, we have constructed the luminosity - central metallicity diagram for spiral galaxies, based on a large compilation of existing data on oxygen abundances of HII regions in spiral galaxies. We found that this diagram shows a plateau at high luminosities (-22.3 < M_B < -20.3), with a constant maximum value of the gas-phase oxygen abundance 12+log(O/H) ~ 8.87. This provides strong evidence that the oxygen abundance in the centers of the most luminous metal-rich galaxies reaches the maximum attainable value of oxygen abundance. Since some fraction of the oxygen (about 0.08 dex) is expected to be locked into dust grains, the maximum value of the true gas+dust oxygen abundance in spiral galaxies is 12+log(O/H) ~ 8.95. This value is a factor of ~ 2 higher than the recently estimated solar value. Based on the derived maximum oxygen abundance in galaxies, we found the oxygen yield to be about 0.0035, depending on the fraction of oxygen incorporated into dust grains.

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arXiv2006

On the electron temperature determination in high-metallicity HII regions

The problem of determination of the electron temperature t_2 in the OII zone of high-metallicity HII region was examined. It was shown that the ratio of nebular to auroral nitrogen line intensities, which is an indicator of the electron temperature t_2, can be expressed in terms of the nebular line intensities of oxygen. This solves the problem of the determination of the electron temperature t_2, since the oxygen nebular lines are strong and, consequently, are readily observable. A relation between electron temperatures in the OII and OIII zones in high-metallicity HII regions was studied. It was found that there is no one-to-one correspondance between t_2 and t_3 temperatures. Instead the t_2 - t_3 relation is dependent on excitation parameter.

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arXiv2006

On the relation between electron temperatures in the O+ and O++ zones in high-metallicity HII regions

We suggest a new way to establish the relation between the electron temperature t3 within the [OIII] zone and the electron temperature t2 within the [OII] zone in high-metallicity (12+log(O/H) > 8.25) HII regions. The t2 - t3 diagram is constructed by applying our method to a sample of 372 HII regions. We find that the correlation between t2 and t3 is tight and can be approximated by a linear expression. The new t2 - t3 relation can be used to determine t2 and accurate abundances in high-metallicity HII regions with a measured t3. It can also be used in conjunction with the ff relation for the determination of t3 and t2 and oxygen abundances in high-metallicity HII regions where the [OIII]4363 auroral line is not detected. The derived t2 - t3 relation is independent of photoionization models of HII regions.

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arXiv2006

Oxygen abundances in the most oxygen-rich spiral galaxies

Oxygen abundances in the spiral galaxies expected to be richest in oxygen are estimated. The new abundance determinations are based on the recently discovered ff-relation between auroral and nebular oxygen line fluxes in HII regions. We find that the maximum gas-phase oxygen abundance in the central regions of spiral galaxies is 12+log(O/H)~8.75. This value is significantly lower than the previously accepted value. The central oxygen abundance in the Milky Way is similar to that in other large spirals.

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arXiv2005

On the relationship between auroral and nebular oxygen line intensities in spectra of HII regions

We investigate relationships between observed auroral and nebular oxygen line fluxes in spectra of HII regions. We find a relation that is metallicity-dependent at low metallicities, but becomes independent of metallicity (within the uncertainties of the available data) above 12+logO/H ~ 8.25, i.e. there is one-to-one correspondance (the ff - relation) between auroral and nebular oxygen line fluxes in spectra of high-metallicity HII regions. The ff - relation allows one to estimate the flux in the auroral line from strong oxygen line measurements. This solves the problem of the electron temperature (and, consequently, abundance) determination in high-metallicity HII regions. The ff - relation confirms the basic idea of the empirical method, proposed by Pagel et al. (1979) a qurter of a century ago, that the oxygen abundance in HII region can be estimated from the strong oxygen lines measurements only.

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arXiv2004

Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic properties

We performed a compilation of more than 1000 published spectra of HII regions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. The radial distributions of oxygen and nitrogen abundances were derived. The correlations between oxygen abundance and macroscopic properties are examined. There is a significant difference between the L-Z relationship obtained here and that based on the oxygen abundances determined through the R_23-calibrations. The oxygen abundance of NGC 5457 recently determined using direct measurements of Te (Kennicutt, Bresolin & Garnett 2003) agrees with the L-Z relationship derived here, but is in conflict with the L-Z relationship derived with the R_23-based oxygen abundances. The obtained L-Z relation for spirals is compared to that for irregulars. Our sample of galaxies shows evidence that the slope of the O/H-M_B relationship for spirals is slightly more shallow than that for irregulars. The effective oxygen yields were estimated for spiral and irregular galaxies. The effective oxygen yield increases with increasing luminosity from M_B=-11 to M_B=-18 (or with increasing rotation velocity from Vrot=10 km/s to Vrot=100 km/s) and then remains approximately constant. Irregular galaxies from our sample have effective oxygen yields lowered by a factor of 3 at maximum, i.e. irregular galaxies usually keep at least 1/3 of the oxygen they manufactured during their evolution.

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arXiv2004

Chemical abundances in spiral and irregular galaxies. O and N abundances derived from global emission--line spectra

The validity of oxygen and nitrogen abundances derived from the global emission-line spectra of galaxies via the P-method has been investigated using a collection of published spectra of individual HII regions in irregular and spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that global emission-line spectra can reliably indicate the chemical properties of galaxies has been confirmed. It has been shown that the comparison of the global spectrum of a galaxy with a collection of spectra of individual HII regions can be used to distinguish high and low metallicity objects and to estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen abundances in samples of UV-selected and normal nearby galaxies have been determined. It has been found that the UV-selected galaxies occupy the same area in the N/O -- O/H diagram as individual HII regions in nearby galaxies. Finally, we show that intermediate-redshift galaxies systematically deviate from the metallicity -- luminosity trend of local galaxies.

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arXiv2003

On the oxygen abundance in our Galaxy

The compilation of published spectra of Galactic HII regions with available diagnostic [OIII]4363 line has been carried out. Our list contains 71 individual measurements of 13 HII regions in the range of galactocentric distances from 6.6 to 14.8 kpc. The oxygen abundances in all the HII regions were recomputed in the same way, using the classic Te - method. The oxygen abundance at the solar galactocentric distance traced by those HII regions is in agreement with the oxygen abundance in the interstellar medium in the solar vicinity derived with high precision from the interstellar absorption lines towards stars. The derived radial oxygen abundance distribution was compared with that for HII regions from the Shaver et al. (1983) sample which is the basis of many models for the chemical evolution of our Galaxy. It was found that the original Shaver et al.'s oxygen abundances are overestimated by 0.2-0.3 dex. Oxygen abundances in HII regions from the Shaver et al. sample have been redetermined with the recently suggested P - method. The radial distribution of oxygen abundances from the Shaver et al. sample redetermined with the P - method is in agreement with our radial distribution of (O/H)_Te abundances.

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arXiv2002

Abundance determinations in HII regions: model fitting versus Te-method

The discrepancy between the oxygen abundances in high-metallicity HII regions determined through the Te-method (and/or through the corresponding "strong lines - oxygen abundance" calibration) and that determined through the model fitting (and/or through the corresponding "strong lines - oxygen abundance" calibration) is discussed. It is suggested to use the interstellar oxygen abundance in the solar vicinity, derived with very high precision from the high-resolution observations of the weak interstellar absorption lines towards the stars, as a "Rosetta stone" to verify the validity of the oxygen abundances derived in HII regions with the Te-method at high abundances. The agreement between the value of the oxygen abundance at the solar galactocentric distance traced by the abundances derived in HII regions through the Te-method and that derived from the interstellar absorption lines towards the stars is strong evidence in favor of that i) the two-zone model for Te seems to be a realistic interpretation of the temperature structure within HII regions, and ii) the classic Te-method provides accurate oxygen abundances in HII regions. It has been concluded that the "strong lines - oxygen abundance" calibrations must be based on the HII regions with the oxygen abundances derived with the Te-method but not on the existing grids of the models for HII regions.

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arXiv2002

The bends in the slopes of radial abundance gradients in the disks of spiral galaxies -- do they exist?

Spiral galaxies with a reported bend in the slope of gradient in the oxygen abundances (O/H)_R23, derived with traditionally used R23 - method, were examined. It is shown that the artificial origin of the reported bends can be naturally explained. Two reasons that result in a false bend in the slope of (O/H)_R23 gradient are indicated. It is concluded that at the present time there is no example of a galaxy with an undisputable established bend in the slope of the oxygen abundance gradient.

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arXiv2002

On the origin of nitrogen

The problem of the origin of nitrogen is considered within the framework of an empirical approach. The oxygen abundances and nitrogen to oxygen abundances ratios are derived in HII regions of a number of spiral galaxies through the recently suggested P-method using more than six hundred published spectra. The N/O - O/H diagram for HII regions in irregular and spiral galaxies is constructed. It is found that the N/O values in HII regions of spiral galaxies of early morphological types are higher than those in HII regions with the same metallicity in spiral galaxies of late morphological types. This suggests a long-time-delayed contribution to the nitrogen production. The N/O ratio of a galaxy can then be used as an indicator of the time that has elapsed since the bulk of star formation occurred, or in other words of the nominal "age" of the galaxy as suggested by Edmunds and Pagel more than twenty years ago. The scatter in N/O values at a given O/H can be naturally explained by differences in star formation histories in galaxies. While low-metallicity dwarf galaxies with low N/O do not contain an appreciable amount of old stars, low-metallicity dwarf galaxies with an appreciable fraction of old stars have high N/O. Consideration of planetary nebulae in the Small Magellanic Cloud and in the Milky Way Galaxy suggests that the contribution of low-mass stars to the nitrogen production is significant, confirming the conclusion that there is a long-time-delayed contribution to the nitrogen production.

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arXiv2001

Oxygen and nitrogen abundances in Virgo and field spirals

The oxygen and nitrogen abundances in the HII regions of the nine Virgo spirals of the sample from Skillman et al (1996) and in nine field spiral galaxies are re-determined with the recently suggested P - method. We confirm that there is an abundance segregation in the sample of Virgo spirals in the sense that the HI deficient Virgo spirals near the core of the cluster have higher oxygen abundances in comparison to the spirals at the periphery of the Virgo cluster. At the same time both the Virgo periphery and core spirals have counterparts among field spirals. We conclude that if there is a difference in the abundance properties of the Virgo and field spirals, this difference appears to be small and masked by the observational errors.

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arXiv2001

Oxygen abundances in dwarf irregular galaxies and the metallicity - luminosity relationship

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 magnitude in the blue band for irregular galaxies obtained by Hidalgo-Gamez and Olofsson (1998) can be explained by the large uncertainties in the oxygen abundances derived through the Te - method, that in turn can be explained by the large uncertainties in the measurements of the strengths of the weak oxygen line [OIII]4363 used in the Te - method.

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arXiv2001

The oxygen abundance distribution in M101

The well-observed spiral galaxy M101 was considered. The radial distributions of oxygen abundances determined in three different ways (with the classic Te - method, with the R23 - method, and with the P -- method) were compared. It was found that the parameters (the central oxygen abundance and the gradient) of the radial O/H(P) abundance distribution are close to those of the O/H(Te) abundance distribution. The parameters of the O/H(R23) abundance distribution differ significantly from those of the O/H(Te) abundance distribution: the central O/H(R23) oxygen abundance is higher by around 0.4dex and the gradient is steeper by a factor of around 1.5 as compared to those values in the O/H(Te) abundance distribution. The dispersion in O/H(P) abundance at fixed radius is rather small, around 0.08 dex, and is equal to that in O/H(Te) abundance. The dispersion in O/H(R23) abundance at fixed radius is appreciably larger, around 0.16 dex, compared to that in O/H(Te) abundance. It has been shown that the extra dispersion in O/H(R23) abundances is an artifact and reflects scatter in excitation parameter P at fixed radius.

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arXiv2001

On the oxygen abundance determination in HII regions: High - metallicity regions

This is our second paper devoted to the problem of line intensity - oxygen abundance calibration starting from the idea of McGaugh (1991) that the strong oxygen lines contain the necessary information to determine accurate abundances in HII regions. The high-metallicity HII regions are considered. A relation of the type O/H=f(P,R23) between oxygen abundance and the value of abundance index R23 introduced by Pagel et al. (1979) and the excitation parameter P (which is defined here as the contribution of the radiation in [OIII]4959,5007 lines to the "total" oxygen radiation) has been derived empirically using the available oxygen abundances determined via measurement of a temperature-sensitive line ratio [OIII]4959,5007/[OIII]4363 (Te - method). By comparing oxygen abundances derived with the Te - method and those derived with the suggested relations (P - method), it was found that the precision of oxygen abundance determination with the P - method is around 0.1 dex and is comparable to that of the Te - method. A relation of the type Te=f(P,R23) between electron temperature and the values of abundance index R23 and the excitation parameter P was derived empirically using the available electron temperatures determined via measurement of temperature-sensitive line ratios. The mean difference between electron temperatures derived through the Te=f(P,23 relation and determined via measurement of the temperature-sensitive line ratio is around 500K.

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arXiv2000

On the oxygen abundance determination in HII regions: the problem of the line intensities -- oxygen abundance calibration

The problem of the line intensities -- oxygen abundance calibration has been considered. We confirm the idea of McGaugh (1991) that the strong oxygen lines ([OII] 3727, 3729 and [OIII] 4959, 5007) contain the necessary information for determination of accurate abundances in low-metallicity (and may be also in high-metallicity) HII regions. It has been found that the excitation parameters p3 or p2 (which are defined here as contributions of the radiation in [OIII] 4959, 5007 lines and in [OII] 3727, 3729 lines to the "total" oxygen radiation respectively) allow to take into account the variations in R23 values among HII regions with a given oxygen abundance. Based on this fact a new way of the oxygen abundance determination in HII regions has been constructed and corresponding relations between line intensities and the oxygen abundance have been derived empirically using the available oxygen abundances determined via measurement of temperature-sensitive line ratios. In parallel a new R23 calibration has been derived on the base of recent data and compared to previous calibrations. For oxygen-rich HII regions the present R23 calibration is close to that of Edmunds and Pagel (1984): their calibration has the same slope but is shifted towards higher oxygen abundances by around 0.07 dex as compared to the present calibration.

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arXiv2000

On the origin of the luminosity - metallicity relation for late-type galaxies: Spirals to irregulars transition

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 smoothly along the sequence. Thus we find no "irregular versus spiral dichotomy".

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arXiv2000

The oxygen abundance deficiency in irregular galaxies

The observed oxygen abundances in a number of irregular galaxies have been compared with predictions of the closed-box model of chemical and photometric evolution of galaxies. Oxygen is found to be deficient with respect to the predicted abundances. This is an indicator in favor of loss of heavy elements via galactic winds or/and of infall of low--abundance gas onto the galaxy. The oxygen abundance deficiency observed within the optical edge of a galaxy cannot be explained by mixing with the gas envelope observed outside the optical limit. We confirm the widespread idea that a significant part of the heavy elements is ejected by irregular galaxies in the intergalactic medium.

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