1,298 research outputs found
Detection of [OI] 6300 and Other Diagnostic Emission Lines in the Diffuse Ionized Gas of M33 with Gemini-North
We present spectroscopic observations of diffuse ionized gas (DIG) in M33
near the HII region NGC 604. We present the first detection of [OI] 6300 in the
DIG of M33, one of the critical lines for distinguishing photo- from shock
ionization models. We measure [OI]/Ha in the range of 0.04 to 0.10 and an
increase in this ratio with decreasing emission measure. Our measurements of
[SII]/Ha and [NII]/Ha also rise with decreasing emission measure, while our
[OIII]/Hb measurements remain fairly constant. We have one tentative detection
of He I in the region of brightest emission measure, with a ratio of He I/Ha =
0.033 +- 0.019, indicating that the helium is at least partially ionized. We
compare our observed emission line ratios to photoionization models and find
that field star ionization models do not fit our data well. Leaky HII region
models are consistent with our data, without the need to invoke additional
ionization mechanisms to fit our [OI] or [OIII] measurements. The closest large
HII region is NGC 604 and is therefore a likely candidate for the source of the
ionizing photons for the gas in this region.Comment: 12 pages, 4 figures, accepted by ApJ
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios.Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in
the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been include
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&
Is There a Fundamental Line for Disk Galaxies?
We show that there are strong local correlations between metallicity, surface
brightness, and dynamical mass-to-light ratio within M33, analogous to the
fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using
near-infrared imaging from 2MASS, the published rotation curve of M33, and
literature measurements of the metallicities of HII regions and supergiant
stars, we demonstrate that these correlations hold for points at radial
distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given
metallicity or surface brightness, M33 has a mass-to-light ratio approximately
four times as large as the Local Group dwarf galaxies; other than this constant
offset, we see broad agreement between the M33 and dwarf galaxy data. We use
analytical arguments to show that at least two of the three fundamental line
correlations are basic properties of disk galaxies that can be derived from
very general assumptions. We investigate the effect of supernova feedback on
the fundamental line with numerical models and conclude that while feedback
clearly controls the scatter in the fundamental line, it is not needed to
create the fundamental line itself, in agreement with our analytical
calculations. We also compare the M33 data with measurements of a simulated
disk galaxy, finding that the simulation reproduces the trends in the data
correctly and matches the fundamental line, although the metallicity of the
simulated galaxy is too high, and the surface brightness is lower than that of
M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap
Stellar abundances and molecular hydrogen in high-redshift galaxies -the far-ultraviolet view
FUSE spectra of star-forming regions in nearby galaxies are compared to
composite spectra of Lyman-break galaxies (LBGs), binned by strength of Lyman
alpha emission and by mid-UV luminosity. Several far-UV spectral features,
including lines dominated by stellar wind and by photospheric components, are
very sensitive to stellar abundances. Their measurement in Lyman-break galaxies
is compromised by the strong interstellar absorption features, allowing in some
cases only upper limits. The derived C and N abundances in the LBGs are no
higher than half solar (scaled to oxygen abundance for comparison with
emission-line analyses), independent of the strength of Lyman alpha emission. P
V absorption indicates abundances as low as 0.1 solar, with an upper limit near
0.4 solar in the reddest and weakest-emission galaxies. Unresolved interstellar
absorption components would further lower the derived abundances. Trends of
line strength, and derived abundances, are stronger with mid-UV luminosity than
with Lyman-alpha strength. H2 absorption in the Lyman and Werner bands is very
weak in the LBGs. Template H2 absorption spectra convolved to appropriate
resolution show that strict upper limits N(H2)< 10^18 cm^-2 apply in all cases,
with more stringent values appropriate for the stronger-emission composites and
for mixes of H2 level populations like those on Milky Way sight lines. Since
the UV-bright regions are likely to be widespread in these galaxies, these
results rule out massive diffuse reservoirs of H2, and suggest that the
dust/gas ratio is already fairly large at z~3.Comment: Astron J., in press (June 2006
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