2,335 research outputs found
Characterizing the radial oxygen abundance distribution in disk galaxies
We examine the possible dependence of the radial oxygen abundance
distribution on non-axisymmetrical structures (bar/spirals) and other
macroscopic parameters such as the mass, the optical radius R25, the color g-r,
and the surface brightness of the galaxy. A sample of disk galaxies from the
CALIFA DR3 is considered. We adopted the Fourier amplitude A2 of the surface
brightness as a quantitative characteristic of the strength of non-axisymmetric
structures in a galactic disk, in addition to the commonly used morphologic
division for A, AB, and B types based on the Hubble classification. To
distinguish changes in local oxygen abundance caused by the non-axisymmetrical
structures, the multiparametric mass--metallicity relation was constructed as a
function of parameters such as the bar/spiral pattern strength, the disk size,
color index g-r in the SDSS bands, and central surface brightness of the disk.
The gas-phase oxygen abundance gradient is determined by using the R
calibration. We find that there is no significant impact of the
non-axisymmetric structures such as a bar and/or spiral patterns on the local
oxygen abundance and radial oxygen abundance gradient of disk galaxies.
Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients
in units of dex/kpc, but this effect is significantly less prominent for the
oxygen abundance gradients in units of dex/R25 and almost disappears when the
inner parts are avoided. We show that the oxygen abundance in the central part
of the galaxy depends neither on the optical radius R25 nor on the color g-r or
the surface brightness of the galaxy. Instead, outside the central part of the
galaxy, the oxygen abundance increases with g-r value and central surface
brightness of the disk.Comment: 11 pages, 6 figures; accepted for publication in A&
Two types of distribution of the gas velocity dispersion of MaNGA galaxies
The distribution of the gas velocity dispersion sigma across the images of
1146 MaNGA galaxies is analyzed. We find that there are two types of
distribution of the gas velocity dispersion across the images of galaxies: (i)
the distributions of 909 galaxies show a radial symmetry with or without the
sigma enhancement at the center (R distribution) and (ii) distributions with a
band of enhanced sigma along the minor axis in the images of 159 galaxies with
or without the sigma enhancement at the center (B distribution) The sigma
distribution across the images of 78 galaxies cannot be reliable classified. We
select 806 galaxies with the best defined characteristics (this sample includes
687 galaxies with R distribution and 119 galaxies with B distribution) and
compare the properties of galaxies with R and B distributions. We find that the
median value of the gas velocity dispersion sigma_m in galaxies with B
distribution is higher by around 5 km/s, on average, than that of galaxies with
R distribution. The optical radius R_25 of galaxies with B distribution is
lower by around 0.1 dex, on average, than that of galaxies with similar masses
with R distribution. Thus the properties of a galaxy are related to the type of
distribution of the gas velocity dispersion across its image. This suggests
that the presence of the band of the enhanced gas velocity dispersion can be an
indicator of a specific evolution (or a specific stage in the evolution) of a
galaxy.Comment: 5 pages, 4 figures, accepted to Astron.Astrophys. arXiv admin note:
text overlap with arXiv:2005.1274
The metallicity - redshift relations for emission-line SDSS galaxies: examination of the dependence on the star formation rate
We analyse the oxygen abundance and specific star formation rates (sSFR)
variations with redshift in star-forming SDSS galaxies of different masses. We
find that the maximum value of the sSFR, sSFRmax, decreases when the stellar
mass, Ms, of a galaxy increases, and decreases with decreasing of redshift. The
sSFRmax can exceed the time-averaged sSFR by about an order of magnitude for
massive galaxies. The metallicity - redshift relations for subsamples of
galaxies with sSFR = sSFRmax and with sSFR = 0.1sSFRmax coincide for massive
(log(Ms/Mo) > 10.5, with stellar mass Ms in solar units) galaxies and differ
for low-mass galaxies. This suggests that there is no correlation between
oxygen abundance and sSFR in massive galaxies and that the oxygen abundance
correlates with the sSFR in low-mass galaxies. We find evidence in favour of
that the irregular galaxies show, on average, higher sSFR and lower oxygen
abundances than the spiral galaxies of similar masses and that the mass -
metallicity relation for spiral galaxies differs slightly from that for
irregular galaxies. The fact that our sample of low-mass galaxies is the
mixture of spiral and irregular galaxies can be responsible for the dependence
of the metallicity - redshift relation on the sSFR observed for the low-mass
SDSS galaxies. The mass - metallicity and luminosity - metallicity relations
obtained for irregular SDSS galaxies agree with corresponding relations for
nearby irregular galaxies with direct abundance determinations. We find that
the aperture effect does not make a significant contribution to the redshift
variation of oxygen abundances in SDSS galaxies.Comment: 14 pages, 7 figures, accepted for publication in the MNRA
Calibration-based abundances in the interstellar gas of galaxies from slit and IFU spectra
In this work we make use of available Integral Field Unit (IFU) spectroscopy
and slit spectra of several nearby galaxies. The pre-existing empirical R and S
calibrations for abundance determinations are constructed using a sample of HII
regions with high quality slit spectra. In this paper, we test the
applicability of those calibrations to the IFU spectra. We estimate the
calibration-based abundances obtained using both the IFU and the slit
spectroscopy for eight nearby galaxies. The median values of the slit and IFU
spectra-based abundances in bins of 0.1 in fractional radius Rg (normalized to
the optical radius) of a galaxy are determined and compared. We find that the
IFU and the slit spectra-based abundances obtained through the R calibration
are close to each other, the mean value of the differences of abundances is
0.005 dex and the scatter in the differences is 0.037 dex for 38 datapoints.
The S calibration can produce systematically underestimated values of the IFU
spectra-based abundances at high metallicities, the mean value of the
differences is -0.059 dex for 21 datapoints, while at lower metallicities the
mean value of the differences is -0.018 dex and the scatter is 0.045 dex for 36
data points. This evidences that the R calibration produces more consistent
abundance estimations between the slit and the IFU spectra than the S
calibration. We find that the same calibration can produce close estimations of
the abundances using IFU spectra obtained with different spatial resolution and
different spatial samplings. This is in line with the recent finding that the
contribution of the diffuse ionized gas to the large aperture spectra of HII
regions has a secondary effect.Comment: 15 pages, 14 figures, accepted to the Astronomy and Astrophysic
Circumnuclear regions of different BPT types in star-forming MaNGA galaxies: AGN detectability
We consider the circumnuclear regions of MaNGA galaxies. The spectra are
classified as AGN-like, HII-region-like (or SF-like), and intermediate (INT)
spectra according to their positions on the BPT diagram. There are the
following four configurations of the radiation distributions in the
circumnuclear regions: 1) AGN+INT, the innermost region of the AGN-like
radiation is surrounded by a ring of radiation of the intermediate type; 2)
INT, the central area of radiation of the intermediate type; 3) SF+INT, the
inner region of the HII-region-like radiation is surrounded by a ring of
radiation of the intermediate type; and 4) SF, the HII-region-like radiation
only. The LINERS of configurations 1 and 2 are examined. The spaxel spectra of
the LINERs form a sequences on the BPT diagram. The line ratios change smoothly
with radius, from AGN-like at the center to HII-region-like at larger
distances. This is in agreement with the paradigm that the LINERs are excited
by AGN activity. The AGN and INT radiation in the circumnuclear region is
accompanied by an enhanced gas velocity dispersion, s_g. The radius of the area
of the AGN and INT radiation is similar to the radius of the area with enhanced
s_g, and the central s_g,c correlates with the luminosity of the AGN+INT area.
We assume that the gas velocity dispersion can serve as an indicator of the AGN
activity. The values of s_g,c for the SF-type centers partly overlap with those
of the AGN-type centers. We find that there is a demarcation line between the
positions of the AGN-type and SF-type objects on the s_g,c - central Halpha
surface brightness diagram.Comment: 17 pages, 14 figures, accepted for publication in the A&
Galaxy And Mass Assembly (GAMA): growing up in a bad neighbourhood - how do low-mass galaxies become passive?
Both theoretical predictions and observations of the very nearby Universe
suggest that low-mass galaxies (log[M/M]<9.5) are likely
to remain star-forming unless they are affected by their local environment. To
test this premise, we compare and contrast the local environment of both
passive and star-forming galaxies as a function of stellar mass, using the
Galaxy and Mass Assembly survey. We find that passive fractions are higher in
both interacting pair and group galaxies than the field at all stellar masses,
and that this effect is most apparent in the lowest mass galaxies. We also find
that essentially all passive log[M/M]<8.5 galaxies are
found in pair/group environments, suggesting that local interactions with a
more massive neighbour cause them to cease forming new stars. We find that the
effects of immediate environment (local galaxy-galaxy interactions) in forming
passive systems increases with decreasing stellar mass, and highlight that this
is potentially due to increasing interaction timescales giving sufficient time
for the galaxy to become passive via starvation. We then present a simplistic
model to test this premise, and show that given our speculative assumptions, it
is consistent with our observed results.Comment: 20 pages, 12 figures, Accepted to MNRA
Galaxy And Mass Assembly (GAMA) : stellar mass functions by Hubble type
This work was supported by the Austrian Science Foundation FWF under grant P23946. AWG was supported under the Australian Research Council's funding scheme FT110100263.We present an estimate of the galaxy stellar mass function and its division by morphological type in the local (0.025 < z < 0.06) Universe. Adopting robust morphological classifications as previously presented (Kelvin et al.) for a sample of 3727 galaxies taken from the Galaxy And Mass Assembly survey, we define a local volume and stellar mass limited sub-sample of 2711 galaxies to a lower stellar mass limit of M = 109.0 MΘ. We confirm that the galaxy stellar mass function is well described by a double-Schechter function given by Μ* = 1010.64 MΘ, α1 = 0.43, φ1* = 4.18 dex-1 Mpc-3, α2 = −1.50 and φ2* = 0.74 dex-1 Mpc-3. The constituent morphological-type stellar mass functions are well sampled above our lower stellar mass limit, excepting the faint little blue spheroid population of galaxies. We find approximately 71-4+3 per cent of the stellar mass in the local Universe is found within spheroid-dominated galaxies; ellipticals and S0-Sas. The remaining 29-3+4 per cent falls predominantly within late-type disc-dominated systems, Sab-Scds and Sd-Irrs. Adopting reasonable bulge-to-total ratios implies that approximately half the stellar mass today resides in spheroidal structures, and half in disc structures. Within this local sample, we find approximate stellar mass proportions for E : S0-Sa : Sab-Scd : Sd-Irr of 34 : 37 : 24 :5.Publisher PDFPeer reviewe
Metal-THINGS: The association and optical characterization of SNRs with HI holes in NGC 6946
NGC~6946, also known as the `Fireworks' galaxy, is an unusual galaxy that
hosts a total of 225 supernova remnant (SNR) candidates, including 147
optically identified with high [SII]/Ha line ratios. In addition, this galaxy
shows prominent HI holes, which were analyzed in previous studies. Indeed, the
connection between SNRs and HI holes together with their physical implications
in the surrounding gas is worth of attention. This paper explores the
connection between the SNRs and the HI holes, including an analysis of their
physical link to observational optical properties inside and around the rims of
the holes, using new integral field unit (IFU) data from the Metal-THINGS
survey. We present an analysis combining previously identified HI holes, SNRs
candidates, and new integral field unit (IFU) data from Metal-THINGS of the
spiral galaxy NGC 6946. We analyze the distributions of the oxygen abundance,
star formation rate surface density, extinction, ionization, diffuse ionized
gas, and the Baldwin-Phillips-Terlevich classification throughout the galaxy.
By analyzing in detail the optical properties of the 121 previously identify HI
holes in NGC 6946, we find that the SNRs are concentrated at the rims of the HI
holes. Furthermore, our IFU data shows that the star formation rate and
extinction are enhanced at the rims of the holes. To a lesser degree, the
oxygen abundance and ionization parameter show hints of enhancement on the rims
of the holes.
Altogether, this provides evidence of induced star formation taking place at
the rims of the holes, whose origin can be explained by the expansion of
superbubbles created by multiple supernova explosions in large stellar clusters
dozens of Myr ago.Comment: Accepted by A&
Galaxy And Mass Assembly (GAMA) : galaxy close pairs, mergers and the future fate of stellar mass
ASGR acknowledges STFC and SUPA funding that were used to do this work. GAMA is funded by the STFC (UK), the ARC (Australia), the AAO and the participating institutions.We use a highly complete subset of the Galaxy And Mass Assembly II (GAMA-II) redshift sample to fully describe the stellar mass dependence of close pairs and mergers between 10(8) and 10(12)M(circle dot). Using the analytic form of this fit we investigate the total stellar mass accreting on to more massive galaxies across all mass ratios. Depending on how conservatively we select our robust merging systems, the fraction of mass merging on to more massive companions is 2.0-5.6 per cent. Using the GAMA-II data we see no significant evidence for a change in the close pair fraction between redshift z = 0.05 and 0.2. However, we find a systematically higher fraction of galaxies in similar mass close pairs compared to published results over a similar redshift baseline. Using a compendium of data and the function gamma(M) = A(1 + z)(m) to predict the major close pair fraction, we find fitting parameters of A = 0.021 +/- 0.001 and m = 1.53 +/- 0.08, which represents a higher low-redshift normalization and shallower power-law slope than recent literature values. We find that the relative importance of in situ star formation versus galaxy merging is inversely correlated, with star formation dominating the addition of stellar material below M* and merger accretion events dominating beyond M*. We find mergers have a measurable impact on the whole extent of the galaxy stellar mass function (GSMF), manifest as a deepening of the 'dip' in the GSMF over the next similar to Gyr and an increase in M* by as much as 0.01-0.05 dex.Publisher PDFPeer reviewe
Galaxy and mass assembly: Resolving the role of environment in galaxy evolution
We present observations of 18 galaxies from the Galaxy And Mass Assembly (GAMA) survey made with the SPIRAL optical integral field unit (IFU) on the Anglo-Australian Telescope. The galaxies are selected to have a narrow range in stellar mass (6 × 109
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