664 research outputs found
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
Comparative nanostructure analysis of gasoline turbocharged direct injection and diesel soot-in-oil with carbon black
Two gasoline turbocharged direct injection (GTDI) and two diesel soot-in-oil samples were compared with one flame-generated soot sample. High resolution transmission electron microscopy imaging was employed for the initial qualitative assessment of the soot morphology. Carbon black and diesel soot both exhibit core-shell structures, comprising an amorphous core surrounded by graphene layers; only diesel soot has particles with multiple cores. In addition to such particles, GTDI soot also exhibits entirely amorphous structures, of which some contain crystalline particles only a few nanometers in diameter. Subsequent quantification of the nanostructure by fringe analysis indicates differences between the samples in terms of length, tortuosity, and separation of the graphitic fringes. The shortest fringes are exhibited by the GTDI samples, whilst the diesel soot and carbon black fringes are 9.7% and 15.1% longer, respectively. Fringe tortuosity is similar across the internal combustion engine samples, but lower for the carbon black sample. In contrast, fringe separation varies continuously among the samples. Raman spectroscopy further confirms the observed differences. The GTDI soot samples contain the highest fraction of amorphous carbon and defective graphitic structures, followed by diesel soot and carbon black respectively. The AD1:AG ratios correlate linearly with both the fringe length and fringe separation
The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry
In order to determine the causes of kinematic asymmetry in the H gas
in the SAMI Galaxy Survey sample, we investigate the comparative influences of
environment and intrinsic properties of galaxies on perturbation. We use
spatially resolved H velocity fields from the SAMI Galaxy Survey to
quantify kinematic asymmetry () in nearby galaxies and
environmental and stellar mass data from the GAMA survey.
{We find that local environment, measured as distance to nearest neighbour,
is inversely correlated with kinematic asymmetry for galaxies with
, but there is no significant correlation for
galaxies with . Moreover, low mass galaxies
() have greater kinematic asymmetry at all
separations, suggesting a different physical source of asymmetry is important
in low mass galaxies.}
We propose that secular effects derived from gas fraction and gas mass may be
the primary causes of asymmetry in low mass galaxies. High gas fraction is
linked to high (where is H velocity
dispersion and the rotation velocity), which is strongly correlated with
, and galaxies with have offset
from the rest of the sample. Further,
asymmetry as a fraction of dispersion decreases for galaxies with
. Gas mass and asymmetry are also inversely correlated
in our sample. We propose that low gas masses in dwarf galaxies may lead to
asymmetric distribution of gas clouds, leading to increased relative
turbulence.Comment: 15 pages, 20 figure
Galaxy And Mass Assembly (GAMA) : The mechanisms for quiescent galaxy formation at z<1
© 2016 The Authors. One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the Galaxy And Mass Assembly and VIsible MultiObject Spectrograph Public Extragalactic Redshift surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies.We identify potentially rapidly transitioning post-starburst (PSB) galaxies and slower transitioning green-valley galaxies. Over the last 8Gyr, the quiescent population has grown more slowly in number density at high masses (M * > 10 11 M ⊙ ) than at intermediate masses (M * > 10 10.6 M ⊙ ). There is evolution in both the PSB and green-valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times.At intermediatemasses (M * > 10 10.6 M ⊙ ), we find a green-valley transition time-scale of 2.6 Gyr. Alternatively, at z ~ 0.7, the entire growth rate could be explained by fast-quenching PSB galaxies, with a visibility time-scale of 0.5 Gyr. At lower redshift, the number density of PSBs is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at z 10 11 M ⊙ ), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high-mass PSB and green-valley galaxies are transitioning from star forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation
Galaxy and mass assembly (GAMA): the clustering of galaxy groups
We explore the clustering of galaxy groups in the Galaxy and Mass Assembly (GAMA) survey to investigate the dependence of group bias and profile on separation scale and group mass. Due to the inherent uncertainty in estimating the group selection function, and hence the group autocorrelation function, we instead measure the projected galaxy–group cross-correlation function. We find that the group profile has a strong dependence on scale and group mass on scales r⊥≲1h−1 role= presentation style= box-sizing: border-box; margin: 0px; padding: 0px; border: 0px; font-variant: inherit; font-stretch: inherit; line-height: normal; font-family: inherit; vertical-align: baseline; display: inline; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative; \u3er⊥≲1h−1r⊥≲1h−1. We also find evidence that the most massive groups live in extended, overdense, structures. In the first application of marked clustering statistics to groups, we find that group-mass marked clustering peaks on scales comparable to the typical group radius of r⊥ ≈ 0.5 h−1. While massive galaxies are associated with massive groups, the marked statistics show no indication of galaxy mass segregation within groups. We show similar results from the IllustrisTNG simulations and the L-GALAXIES model, although L-GALAXIES shows an enhanced bias and galaxy mass dependence on small scales
Galaxy And Mass Assembly (GAMA): blue spheroids within 87 Mpc
© 2017 The Author(s). In this paper, we test if nearby blue spheroid (BSph) galaxies may become the progenitors of star-forming spiral galaxies or passively evolving elliptical galaxies. Our sample comprises 428 galaxies of various morphologies in the redshift range 0.002 < Ζ < 0.02 (8-87 Mpc) with panchromatic data from the Galaxy and Mass Assembly survey. We find that BSph galaxies are structurally (mean effective surface brightness, effective radius) very similar to their passively evolving red counterparts. However, their star formation and other properties such as colour, age, and metallicity are more like star-forming spirals than spheroids (ellipticals and lenticulars). We show that BSph galaxies are statistically distinguishable from other spheroids as well as spirals in the multidimensional space mapped by luminosity-weighted age, metallicity, dust mass, and specific star formation rate. We use HI data to reveal that some of the BSphs are (further) developing their discs, hence their blue colours. They may eventually become spiral galaxies - if sufficient gas accretion occurs - or more likely fade into low-mass red galaxies
Galaxy and mass assembly: group and field galaxy morphologies in the star-formation rate - stellar mass plane
Aims. We study the environment in which a galaxy lies (i.e. field or group) and its connection with the morphology of the galaxy. This is done by examining the distribution of parametric and non-parametric statistics across the star-formation rate (SFR) - stellar mass (M?) plane and studying how these distributions change with the environment in the local universe (z \u3c 0.15). Methods. We determine the concentration (C), Gini, M20, asymmetry, Gini-M20 bulge statistic (GMB), 50% light radius (r50), total Sérsic index, and bulge Sérsic index (nBulge) for galaxies from the Galaxy and Mass Assembly (GAMA) survey using optical images from the Kilo Degree Survey. We determine the galaxy environment using the GAMA group catalogue and split the galaxies into field or group galaxies. The group galaxies are further divided by the group halo mass (Mh) - 11 ≤ log(Mh /M*) \u3c 12, 12 ≤ log(Mh /M*) \u3c 13, and 13 ≤ log(Mh /M*) \u3c 14 - and into central and satellite galaxies. The galaxies in each of these samples are then placed onto the SFR-M? plane, and each parameter is used as a third dimension. We fit the resulting distributions for each parameter in each sample using two two-dimensional Gaussian distributions: one for star-forming galaxies and one for quiescent galaxies. The coefficients of these Gaussian fits are then compared between environments. Results. Using C and r50, we find that galaxies typically become larger as the group mass increases. This change is greater for larger galaxies. There is no indication that galaxies are typically more or less clumpy as the environment changes. Using GMB and nBulge , we see that the star-forming galaxies do not become more bulge or disk dominated as the group mass changes. Asymmetry does not appear to be greatly influenced by environment
Red riding on hood: Exploring how galaxy colour depends on environment
Galaxy populations are known to exhibit a strong colour bimodality,
corresponding to blue star-forming and red quiescent subpopulations. The
relative abundance of the two populations has been found to vary with stellar
mass and environment. In this paper, we explore the effect of environment
considering different types of measurements. We choose a sample of
galaxies with from the Galaxy And Mass Assembly survey. We
study the dependence of the fraction of red galaxies on different measures of
the local environment as well as the large-scale "geometric" environment
defined by density gradients in the surround- ing cosmic web. We find that the
red galaxy fraction varies with the environment at fixed stellar mass. The red
fraction depends more strongly on local environmental measures than on
large-scale geometric environment measures. By comparing the different
environmental densities, we show that no density measurement fully explains the
observed environmental red fraction variation, suggesting the different
measures of environmental density contain different information. We test
whether the local environmental measures, when combined together, can explain
all the observed environmental red fraction variation. The geometric
environment has a small residual effect, and this effect is larger for voids
than any other type of geometric environment. This could provide a test of the
physics applied to cosmological-scale galaxy evolution simulations as it
combines large-scale effects with local environmental impact.Comment: Accepted for publication in MNRAS; 16 pages; 10 figures; 2 tables
The SAMI Galaxy Survey: Asymmetry in Gas Kinematics and its links to Stellar Mass and Star Formation
We study the properties of kinematically disturbed galaxies in the SAMI
Galaxy Survey using a quantitative criterion, based on kinemetry (Krajnovic et
al.). The approach, similar to the application of kinemetry by Shapiro et al.
uses ionised gas kinematics, probed by H{\alpha} emission. By this method
23+/-7% of our 360-galaxy sub-sample of the SAMI Galaxy Survey are
kinematically asymmetric. Visual classifications agree with our kinemetric
results for 90% of asymmetric and 95% of normal galaxies. We find stellar mass
and kinematic asymmetry are inversely correlated and that kinematic asymmetry
is both more frequent and stronger in low-mass galaxies. This builds on
previous studies that found high fractions of kinematic asymmetry in low mass
galaxies using a variety of different methods. Concentration of star forma-
tion and kinematic disturbance are found to be correlated, confirming results
found in previous work. This effect is stronger for high mass galaxies (log(M*)
> 10) and indicates that kinematic disturbance is linked to centrally
concentrated star formation. Comparison of the inner (within 0.5Re) and outer
H{\alpha} equivalent widths of asymmetric and normal galaxies shows a small but
significant increase in inner equivalent width for asymmetric galaxies.Comment: 29 pages, 21 figure
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