115 research outputs found
Antlia Dwarf Galaxy: Distance, quantitative morphology and recent formation history via statistical field correction
We apply a statistical field correction technique originally designed to
determine membership of high redshift galaxy clusters to Hubble Space Telescope
imaging of the Antlia Dwarf Galaxy; a galaxy at the very edge of the Local
Group. Using the tip of the red giant branch standard candle method coupled
with a simple Sobel edge detection filter we find a new distance to Antlia of
1.31 +/- 0.03 Mpc. For the first time for a Local Group Member, we compute the
concentration, asymmetry and clumpiness (CAS) quantitative morphology
parameters for Antlia from the distribution of resolved stars in the HST/ACS
field, corrected with a new method for contaminants and complement these
parameters with the Gini coefficient (G) and the second order moment of the
brightest 20 per cent of the flux (M_20). We show that it is a classic dwarf
elliptical (C = 2.0, A = 0.063, S = 0.077, G = 0.39 and M_20 = -1.17 in the
F814W band), but has an appreciable blue stellar population at its core,
confirming on-going star-formation. The values of asymmetry and clumpiness, as
well as Gini and M_20 are consistent with an undisturbed galaxy. Although our
analysis suggests that Antlia may not be tidally influenced by NGC 3109 it does
not necessarily preclude such interaction.Comment: Accepted for publication in MNRA
How the extinction of extragalactic background light affects surface photometry of galaxies, groups and clusters
The faint regions of galaxies, groups and clusters hold important clues about
how these objects formed, and surface photometry at optical and near-infrared
wavelengths represents a powerful tool for studying such structures. Here, we
identify a hitherto unrecognized problem with this technique, related to how
the night sky flux is typically measured and subtracted from astronomical
images. While most of the sky flux comes from regions between the observer and
the target object, a small fraction - the extragalactic background light (EBL)
- comes from behind. We argue that since this part of the sky flux can be
subject to extinction by dust present in the galaxy/group/cluster studied,
standard reduction procedures may lead to a systematic oversubtraction of the
EBL. Even very small amounts of extinction can lead to spurious features in
radial surface surface brightness profiles and colour maps of extended objects.
We assess the likely impact of this effect on a number of topics in
extragalactic astronomy where very deep surface photometry is currently
attempted, including studies of stellar halos, starburst host galaxies, disc
truncations and diffuse intragroup/intracluster light. We argue that EBL
extinction may provide at least a partial explanation for the anomalously red
colours reported for the halos of disc galaxies and the hosts of local
starburst galaxies. EBL extinction effects also mimic truncations in discs with
unusually high dust opacities, but are unlikely to be the cause of such
features in general. Failure to account for EBL extinction can also give rise
to a non-negligible underestimate of intragroup and intracluster light at the
faintest surface brightness levels currently probed. (Abridged)Comment: 15 pages, 10 figures, accepted for publication in MNRA
Modelling the spectral energy distribution of galaxies. V. The dust and PAH emission SEDs of disk galaxies
We present a self-consistent model of the spectral energy distributions
(SEDs) of spiral galaxies from the ultraviolet (UV) to the mid-infrared
(MIR)/far-infrared (FIR)/submillimeter (submm) based on a full radiative
transfer calculation of the propagation of starlight in galaxy disks. This
model predicts not only the total integrated energy absorbed in the UV/optical
and re-emitted in the infrared/submm, but also the colours of the dust emission
based on an explicit calculation of the strength and colour of the UV/optical
radiation fields heating the dust, and incorporating a full calculation of the
stochastic heating of small dust grains and PAH molecules.
The geometry of the translucent components of the model is empirically
constrained using the results from the radiation transfer analysis of Xilouris
et al. on spirals in the middle range of the Hubble sequence, while the
geometry of the optically thick components is constrained from physical
considerations with a posteriori checks of the model predictions with
observational data.
These geometrical constraints enable the dust emission to be predicted in
terms of a minimum set of free parameters: the central face-on dust opacity in
the B-band tau^f_B, a clumpiness factor F for the star-forming regions, the
star-formation rate SFR, the normalised luminosity of the old stellar
population old and the bulge-to-disk ratio B/D. We show that these parameters
are almost orthogonal in their predicted effect on the colours of the dust/PAH
emission.
The results of the calculations are made available in the form of a large
library of simulated dust emission SEDs spanning the whole parameter space of
our model, together with the corresponding library of dust attenuation
calculated using the same model. (see full abstract in the paper)Comment: 39 pages; accepted for publication in Astronomy & Astrophysics; For a
higher resolution version of Fig.1 and Fig.20 see
http://www.star.uclan.ac.uk/~ccp/index.shtm
Galaxy And Mass Assembly: the evolution of the cosmic spectral energy distribution from z = 1 to z = 0
We present the evolution of the cosmic spectral energy distribution (CSED) from z = 1 to 0. Our CSEDs originate from stacking individual spectral energy distribution (SED) fits based on panchromatic photometry from the Galaxy And Mass Assembly (GAMA) and COSMOS data sets in 10 redshift intervals with completeness corrections applied. Below z = 0.45, we have credible SED fits from 100 nm to 1 mm. Due to the relatively low sensitivity of the far-infrared data, our far-infrared CSEDs contain a mix of predicted and measured fluxes above z = 0.45. Our results include appropriate errors to highlight the impact of these corrections. We show that the bolometric energy output of the Universe has declined by a factor of roughly 4 – from 5.1 ± 1.0 at z ∼ 1 to 1.3 ± 0.3 × 1035 h70 W Mpc−3 at the current epoch. We show that this decrease is robust to cosmic sample variance, the SED modelling and other various types of error. Our CSEDs are also consistent with an increase in the mean age of stellar populations. We also show that dust attenuation has decreased over the same period, with the photon escape fraction at 150 nm increasing from 16 ± 3 at z ∼ 1 to 24 ± 5 per cent at the current epoch, equivalent to a decrease in AFUV of 0.4 mag. Our CSEDs account for 68 ± 12 and 61 ± 13 per cent of the cosmic optical and infrared backgrounds, respectively, as defined from integrated galaxy counts and are consistent with previous estimates of the cosmic infrared background with redshift
Galaxy And Mass Assembly (GAMA): the galaxy stellar mass function to z = 0.1 from the r-band selected equatorial regions
We derive the low-redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) data set covering 180 deg2. We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M⋆–μ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 107.5 M⊙. The galaxy distribution in the M–μ plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fitted with a double Schechter function, with M⋆=1010.78±0.01±0.20M⊙ M⋆=1010.78±0.01±0.20M⊙ , ϕ⋆1=(2.93±0.40)×10−3h370 ϕ1⋆=(2.93±0.40)×10−3h703 Mpc−3, α1 = −0.62 ± 0.03 ± 0.15, ϕ⋆2=(0.63±0.10)×10−3h370 ϕ2⋆=(0.63±0.10)×10−3h703 Mpc−3 and α2 = −1.50 ± 0.01 ± 0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M⋆ M⋆ . Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 107.5 M⊙, and assess limits to 106.5 M⊙. Combining GAMA-II with data from G10-COSMOS, we are able to comment qualitatively on the shape of the GSMF down to masses as low as 106 M⊙. Beyond the well-known upturn seen in the GSMF at 109.5, the distribution appears to maintain a single power-law slope from 109 to 106.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω⋆=1.66+0.24−0.23±0.97h−170×10−3 Ω⋆=1.66−0.23+0.24±0.97h70−1×10−3 , inclusive of random and systematic uncertainties
GAMA/H-ATLAS : common star formation rate indicators and their dependence on galaxy physical parameters.
We compare common star formation rate (SFR) indicators in the local Universe in the Galaxy and Mass Assembly (GAMA) equatorial fields (∼160 deg2), using ultraviolet (UV) photometry from GALEX, far-infrared and sub-millimetre (sub-mm) photometry from Herschel Astrophysical Terahertz Large Area Survey, and Hα spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift z = 0.08), we consider three SFR tracers: UV luminosity corrected for dust attenuation using the UV spectral slope β (SFRUV, corr), Hα line luminosity corrected for dust using the Balmer decrement (BD) (SFRH α, corr), and the combination of UV and infrared (IR) emission (SFRUV + IR). We demonstrate that SFRUV, corr can be reconciled with the other two tracers after applying attenuation corrections by calibrating Infrared excess (IRX; i.e. the IR to UV luminosity ratio) and attenuation in the Hα (derived from BD) against β. However, β, on its own, is very unlikely to be a reliable attenuation indicator. We find that attenuation correction factors depend on parameters such as stellar mass (M∗), z and dust temperature (Tdust), but not on Hα equivalent width or Sersic index. Due to the large scatter in the IRX versus β correlation, when compared to SFRUV + IR, the β-corrected SFRUV, corr exhibits systematic deviations as a function of IRX, BD and Tdust
GAMA/H-ATLAS: common star-formation rate indicators and their dependence on galaxy physical parameters
We compare common star-formation rate (SFR) indicators in the local Universe in the GAMA equatorial fields (around 160 sq. deg.), using ultraviolet (UV) photometry from GALEX, far-infrared (FIR) and sub-millimetre (sub-mm) photometry from H-ATLAS, and Halpha spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift 0.08), we consider three SFR tracers: UV luminosity corrected for dust attenuation using the UV spectral slope beta (SFRUV,corr), Halpha line luminosity corrected for dust using the Balmer decrement (BD) (SFRHalpha,corr), and the combination of UV and IR emission (SFRUV+IR). We demonstrate that SFRUV,corr can be reconciled with the other two tracers after applying attenuation corrections by calibrating IRX (i.e. the IR to UV luminosity ratio) and attenuation in the Halpha (derived from BD) against beta. However, beta on its own is very unlikely to be a reliable attenuation indicator. We find that attenuation correction factors depend on parameters such as stellar mass, z and dust temperature (Tdust), but not on Halpha equivalent width (EW) or Sersic index. Due to the large scatter in the IRX vs beta correlation, when compared to SFRUV+IR, the beta-corrected SFRUV,corr exhibits systematic deviations as a function of IRX, BD and Tdust
GAMA/G10-COSMOS/3D-HST: The 0<z<5 cosmic star-formation history, stellar- and dust-mass densities
We use the energy-balance code MAGPHYS to determine stellar and dust masses, and dust corrected star-formation rates for over 200,000 GAMA galaxies, 170,000 G10-COSMOS galaxies and 200,000 3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous dataset spanning a broad range in stellar mass (10^8---10^12 Msol), dust mass (10^6---10^9 Msol), and star-formation rates (0.01---100 Msol per yr), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star-formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous dataset using consistent mass and star-formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our cosmic star-formation history we precisely reproduce the stellar-mass density with an ISM replenishment factor of 0.50 +/- 0.07, consistent with our choice of Chabrier IMF plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065---0.004 units of dust mass is also formed; (2) Over the history of the Universe approximately 90 to 95 per cent of all dust formed has been destroyed and/or ejected
Phenology of Scramble Polygyny in a Wild Population of Chrysolemid Beetles: The Opportunity for and the Strength of Sexual Selection
Recent debate has highlighted the importance of estimating both the strength of sexual selection on phenotypic traits, and the opportunity for sexual selection. We describe seasonal fluctuations in mating dynamics of Leptinotarsa undecimlineata (Coleoptera: Chrysomelidae). We compared several estimates of the opportunity for, and the strength of, sexual selection and male precopulatory competition over the reproductive season. First, using a null model, we suggest that the ratio between observed values of the opportunity for sexual selections and their expected value under random mating results in unbiased estimates of the actual nonrandom mating behavior of the population. Second, we found that estimates for the whole reproductive season often misrepresent the actual value at any given time period. Third, mating differentials on male size and mobility, frequency of male fighting and three estimates of the opportunity for sexual selection provide contrasting but complementary information. More intense sexual selection associated to male mobility, but not to male size, was observed in periods with high opportunity for sexual selection and high frequency of male fights. Fourth, based on parameters of spatial and temporal aggregation of female receptivity, we describe the mating system of L. undecimlineata as a scramble mating polygyny in which the opportunity for sexual selection varies widely throughout the season, but the strength of sexual selection on male size remains fairly weak, while male mobility inversely covaries with mating success. We suggest that different estimates for the opportunity for, and intensity of, sexual selection should be applied in order to discriminate how different behavioral and demographic factors shape the reproductive dynamic of populations
GLOBULAR CLUSTER POPULATIONS: RESULTS INCLUDING S(4)G LATE-TYPE GALAXIES
Using 3.6 and 4.5 mu m images of 73 late-type, edge-on galaxies from the S(4)G survey, we compare the richness of the globular cluster populations of these galaxies to those of early-type galaxies that we measured previously. In general, the galaxies presented here fill in the distribution for galaxies with lower stellar mass, M-*, specifically log(M-*/M-circle dot) < 10, overlap the results for early-type galaxies of similar masses, and, by doing so, strengthen the case for a dependence of the number of globular clusters per 10(9)M(circle dot) of galaxy stellar mass, T-N, on M-*. For 8.5 < log(M-*/M-circle dot) < 10.5 we find the relationship can be satisfactorily described as T-N = (M-*/10(6.7))(-0.56) M-* is expressed in solar masses. The functional form of the relationship is only weakly constrained, and extrapolation outside this range is not advised. Our late-type galaxies, in contrast to our early types, do not show the tendency for low-mass galaxies to split into two T-N families. Using these results and a galaxy stellar mass function from the literature, we calculate that, in a volume-limited, local universe sample, clusters are most likely to be found around fairly massive galaxies (M-* similar to 10(10.8)M(circle dot)) and present a fitting function for the volume number density of clusters as a function of parent-galaxy stellar mass. We find no correlation between T-N and large-scale environment, but we do find a tendency for galaxies of fixed M-* to have larger T-N if they have converted a larger proportion of their baryons into stars.</p
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