790 research outputs found
Relations between abundance characteristics and rotation velocity for star-forming MaNGA galaxies
We derive rotation curves, surface brightness profiles, and oxygen abundance
distributions for 147 late-type galaxies using the publicly available
spectroscopy obtained by the MaNGA survey. Changes of the central oxygen
abundance (O/H)_0, the abundance at the optical radius (O/H)_R25, and the
abundance gradient with rotation velocity V_rot are examined for galaxies with
rotation velocities from 90 km/s to 350 km/s. We found that each relation shows
a break at V_rot^* ~200 km/s. The central (O/H)_0 abundance increases with
rising V_rot and the slope of the (O/H)_0 - V_rot relation is steeper for
galaxies with V_rot < V_rot^*. The mean scatter of the central abundances
around this relation is 0.053 dex. The relation between the abundance at the
optical radius of a galaxy and its rotation velocity is similar; the mean
scatter in abundances around this relation is 0.081 dex. The radial abundance
gradient expressed in dex/kpc flattens with the increase of the rotation
velocity. The slope of the relation is very low for galaxies with V_rot >
V_rot^*. The abundance gradient expressed in dex/R25 is rougly constant for
galaxies with V_rot < V_rot^*, flattens towards V_rot^*, and then again is
roughly constant for galaxies with V_rot > V_rot^*. The change of the gradient
expressed in terms of dex/h_d (where h_d is the disc scale length) with
rotation velocity is similar to that for gradient in dex/R25. The relations
between abundance characteristics and other basic parameters (stellar mass,
luminosity, and radius) are also considered.Comment: Accepted for publication in the Astronomy and Astrophysic
Breaks in surface brightness profiles and radial abundance gradients in the discs of spiral galaxies
We examine the relation between breaks in the surface brightness profiles and
radial abundance gradients within the optical radius in the discs of 134 spiral
galaxies from the CALIFA survey. The distribution of the radial abundance (in
logarithmic scale) in each galaxy was fitted by simple and broken linear
relations. The surface brightness profile was fitted assuming pure and broken
exponents for the disc. We find that the maximum absolute difference between
the abundances in a disc given by broken and pure linear relations is less than
0.05 dex in the majority of our galaxies and exceeds the scatter in abundances
for 26 out of 134 galaxies considered. The scatter in abundances around the
broken linear relation is close (within a few percent) to that around the pure
linear relation. The breaks in the surface brightness profiles are more
prominent. The scatter around the broken exponent in a number of galaxies is
lower by a factor of two or more than that around the pure exponent. The shapes
of the abundance gradients and surface brightness profiles within the optical
radius in a galaxy may be different. A pure exponential surface brightness
profile may be accompanied by a broken abundance gradient and vise versa. There
is no correlation between the break radii of the abundance gradients and
surface brightness profiles. Thus, a break in the surface brightness profile
does not need to be accompanied by a break in the abundance gradient.Comment: 18 pages, 17 figures, accepted for publication in A&
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.Comment: 8 pages, 7 postscript figures, accepted for publication in MNRA
Abundance determination from global emission-line SDSS spectra: exploring objects with high N/O ratios
We have compared the oxygen and nitrogen abundances derived from global
emission-line SDSS spectra of galaxies using (1) the Te method and (2) two
recent strong line calibrations: the ON and NS calibrations. Using the Te
method, anomously high N/O abundances ratios have been found in some SDSS
galaxies. To investigate this, we have Monte Carlo simulated the global spectra
of composite nebulae by a mix of spectra of individual components, based on
spectra of well-studied HII regions in nearby galaxies. We found that the Te
method results in an underestimated oxygen abundance (and hence in an
overestimated nitrogen-to-oxygen ratio) if HII regions with different physical
properties contribute to the global spectrum of composite nebulae. This effect
is somewhat similar to the small-scale temperature fluctuations in HII regions
discussed by Peimbert. Our work thus suggests that the high Te-based N/O
abundances ratios found in SDSS galaxies may not be real. However, such an
effect is not expected to be present in dwarf galaxies since they have
generally an uniform chemical composition. The ON and NS calibrations give O
and N abundances in composite nebulae which agree with the mean
luminosity-weighted abundances of their components to within 0.2 dex.Comment: 12 pages, 9 figures, accepted for publication in MNRA
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