1,055 research outputs found
Machine-learning identification of galaxies in the WISExSuperCOSMOS all-sky catalogue
The two currently largest all-sky photometric datasets, WISE and SuperCOSMOS,
were cross-matched by Bilicki et al. (2016) (B16) to construct a novel
photometric redshift catalogue on 70% of the sky. Galaxies were therein
separated from stars and quasars through colour cuts, which may leave
imperfections because of mixing different source types which overlap in colour
space. The aim of the present work is to identify galaxies in the
WISExSuperCOSMOS catalogue through an alternative approach of machine learning.
This allows us to define more complex separations in the multi-colour space
than possible with simple colour cuts, and should provide more reliable source
classification. For the automatised classification we use the support vector
machines learning algorithm, employing SDSS spectroscopic sources cross-matched
with WISExSuperCOSMOS as the training and verification set. We perform a number
of tests to examine the behaviour of the classifier (completeness, purity and
accuracy) as a function of source apparent magnitude and Galactic latitude. We
then apply the classifier to the full-sky data and analyse the resulting
catalogue of candidate galaxies. We also compare thus produced dataset with the
one presented in B16. The tests indicate very high accuracy, completeness and
purity (>95%) of the classifier at the bright end, deteriorating for the
faintest sources, but still retaining acceptable levels of 85%. No significant
variation of classification quality with Galactic latitude is observed.
Application of the classifier to all-sky WISExSuperCOSMOS data gives 15 million
galaxies after masking problematic areas. The resulting sample is purer than
the one in B16, at a price of lower completeness over the sky. The automatic
classification gives a successful alternative approach to defining a reliable
galaxy sample as compared to colour cuts.Comment: 12 pages, 15 figures, accepted for publication in A&A. Obtained
catalogue will be included in the public release of the WISExSuperCOSMOS
galaxy catalogue available from http://ssa.roe.ac.uk/WISExSCO
Preliminary effects of fertilization on ecochemical soil condition in mature spruce stands experiencing dieback in the Beskid Śla̧ski and Żywiecki Mountains, Poland
In recent years, there has been the phenomena of spruce dieback in Europe. Significant areas of spruce low mortality now cover both sides of the Polish southern border. We evaluated ecochemical parameters influencing the heavy dieback occurring in mature spruce stands in the Polish Carpathian Mountains. Dolomite, magnesite and serpentinite fertilizers were applied to experimental plots located in 100-year-old stands in the autumn of 2008. The experimental plots were located in the mid-elevational forest zone (900-950 m) on two nappes of the flysch Carpathians: Magura (Ujsoły Forest District) and Silesian (Wisła Forest District). The saturation of the studied soils demonstrates moderate resilience of soils in Wisła Forest District in relation to acid load and high flexibility of the Ujsoły soils. After application of the fertilizers, an increase of Mg, Ca and Mb was noted in the soil solution, determined in the overlaying highly acidic organic horizons through the ion-exchange buffering mechanism of highly protonated functional groups with high buffering capacity. Magnesium concentration increased following fertilization, presenting a potential improvement of forest growth capacity without the hazard of adverse side effects of liming. Aluminium stress in old spruce is unlikely, while trees in the control plots in Wisła Forest District may already be sensitive to aluminium stress. Serpentinite fertilization improved the supply of soils in magnesium without causing significant changes in the pH of the soil. Such changes in the pH were found in dolomite and magnesite fertilizer. © The Author(s) 2014
[Ultra] Luminous Infrared Galaxies selected at 90 m in the AKARI deep field: a study of AGN types contributing to their infrared emission
The aim of this work is to characterize physical properties of Ultra Luminous
Infrared Galaxies (ULIRGs) and Luminous Infrared Galaxies (LIRGs) detected in
the far-infrared (FIR) 90um band in the AKARI Deep Field-South (ADF-S) survey.
In particular, we want to estimate the AGN contribution to the [U]LIRGs'
infrared emission and which types of AGNs are related to their activity. We
examined 69 galaxies at z>0.05 detected at 90um by the AKARI satellite in the
ADF-S, with optical counterparts and spectral coverage from the ultraviolet to
the FIR. We used two independent spectral energy distribution fitting codes:
one fitting the SED from FIR to FUV (CIGALE) and gray-body + power spectrum fit
for the infrared part of the spectra (CMCIRSED) in order to identify a
subsample of [U]LIRGs, and to estimate their properties. Based on the CIGALE
SED fitting, we have found that [U]LIRGs selected at the 90um AKARI band
compose ~56% of our sample (we found 17 ULIRGs and 22 LIRGs, spanning over the
redshift range 0.06<z<1.23). Their physical parameters, such as stellar mass,
star formation rate (SFR), and specific SFR are consistent with the ones found
for other samples selected at IR wavelengths. We have detected a significant
AGN contribution to the MIR luminosity for 63% of LIRGs and ULIRGs. Our LIRGs
contain Type 1, Type 2, and intermediate types of AGN, whereas for ULIRGs, a
majority (more than 50%) of AGN emission originates from Type 2 AGNs. The
temperature--luminosity and temperature--mass relations for the dust component
of ADF--S LIRGs and ULIRGs indicate that these relations are shaped by the dust
mass and not by the increased dust heating. We conclude that LIRGs contain Type
1, Type 2, and intermediate types of AGNs, with an AGN contribution to the MIR
emission at the median level of 13+/-3%, whereas the majority of ULIRGs contain
Type 2 AGNs, with a median AGN fraction equal to 19+/-8%.Comment: 24 pages, 21 figures, accepted for publication in Astronomy &
Astrophysic
Absolute properties of BG Ind - a bright F3 system just leaving the Main Sequence
We present photometric and spectroscopic analysis of the bright detached
eclipsing binary BG Ind. The masses of the components are found to be 1.428 +-
0.008 and 1.293 +- 0.008 Msun and the radii to be 2.290+-0.017 and 1.680+-0.038
Rsun for primary and secondary stars, respectively. Spectra- and
isochrone-fitting coupled with color indices calibration yield
[Fe/H]=-0.2+-0.1. At an age of 2.65+-0.20 Gyr BG Ind is well advanced in the
main-sequence evolutionary phase - in fact, its primary is at TAMS or just
beyond it. Together with three similar systems (BK Peg, BW Aqr and GX Gem) it
offers an interesting opportunity to test the theoretical description of
overshooting in the critical mass range 1.2-1.5 Msun.Comment: 8 pages, 5 figures, corrected bugs in author lis
Unsupervised classification reveals new evolutionary pathways
While we already seem to have a general scenario of the evolution of
different types of galaxies, a complete and satisfactory understanding of the
processes that led to the formation of all the variety of today's galaxy types
is still beyond our reach. To solve this problem, we need both large datasets
reaching high redshifts and novel methodologies for dealing with them. The
VIPERS survey statistical power, which observed galaxies at , and the application of an unsupervised clustering algorithm allowed us to
distinguish 12 galaxy classes. Studies of their environmental dependence
indicate that this classification may actually reflect different galaxy
evolutionary paths. For instance, a class of the most passive red galaxies
gathers galaxies smaller than other red galaxies of a similar
stellar mass, revealing the first sample of red nuggets at intermediate
redshift. On the other end, a class of blue dwarf galaxies is composed mainly
of AGN, challenging commonly used mid-infrared AGN selections.Comment: Accepted for publication in the ML4ASTRO (ICML 2022) proceeding boo
The slippery slope of dust attenuation curves: Correlation of dust attenuation laws with star-to-dust compactness up to z = 4
Aims. We investigate dust attenuation of 122 heavily dust-obscured galaxies
detected with the Atacama Large Millimeter Array (ALMA) and Herschel in the
COSMOS field. We search for correlations between dust attenuation recipes and
the variation of physical parameters, mainly the effective radii of galaxies,
their star formation rates (SFR), and stellar masses, and aim to understand
which of the commonly used laws best describes dust attenuation in dusty
star-forming galaxies at high redshift. Methods. We make use of the extensive
photometric coverage of the COSMOS data combined with highly-resolved dust
continuum maps from ALMA. We use CIGALE to estimate various physical properties
of these dusty objects, mainly their SFR, their stellar masses and their
attenuation. We infer galaxy effective radii (Re) using GALFIT in the Y band of
HSC and ALMA continuum maps. We use these radii to investigate the relative
compactness of the dust continuum and the extension of the rest-frame
UV/optical Re(y)/Re(ALMA). Results. We find that the physical parameters
calculated from our models strongly depend on the assumption of dust
attenuation curve. As expected, the most impacted parameter is the stellar
mass, which leads to a change in the "starburstiness" of the objects. We find
that taking into account the relative compactness of star-to-dust emission
prior to SED fitting is crucial, especially when studying dust attenuation of
dusty star-forming galaxies. Shallower attenuation curves did not show a clear
preference of compactness with attenuation, while the Calzetti attenuation
curve preferred comparable spatial extent of unattenuated stellar light and
dust emission. The evolution of the Re(UV)/Re(ALMA) ratio with redshift peeks
around the cosmic noon in our sample of DSFGs, showing that this compactness is
correlated with the cosmic SFR density of these dusty sources.Comment: 18 pages, 13 figures, accepted for publication in A&A. Abstract
abridged for arXiv submissio
Influence of star-forming galaxy selection on the galaxy main sequence
This work aims to determine how the galaxy main sequence (MS) changes using
seven different commonly used methods to select the star-forming galaxies
within VIPERS data over . The form and redshift evolution of
the MS will then be compared between selection methods. The star-forming
galaxies were selected using widely known methods: a specific star-formation
rate (sSFR), Baldwin, Phillips and Terlevich (BPT) diagram, 4000\AA\ spectral
break (D4000) cut and four colour-colour cuts: NUVrJ, NUVrK, u-r, and UVJ. The
main sequences were then fitted for each of the seven selection methods using a
Markov chain Monte Carlo forward modelling routine, fitting both a linear main
sequence and a MS with a high-mass turn-over to the star-forming galaxies. This
was done in four redshift bins of , ,
, and . The slopes of all star-forming
samples were found to either remain constant or increase with redshift, and the
scatters were approximately constant. There is no clear redshift dependency of
the presence of a high-mass turn-over for the majority of samples, with the
NUVrJ and NUVrK being the only samples with turn-overs only at low redshift. No
samples have turn-overs at all redshifts. Star-forming galaxies selected with
sSFR and u-r are the only samples to have no high-mass turn-over in all
redshift bins. The normalisation of the MS increases with redshift, as
expected. The scatter around the MS is lower than the 0.3~dex
typically seen in MS studies for all seven samples. The lack, or presence, of a
high-mass turn-over is at least partially a result of the method used to select
star-forming galaxies. However, whether a turn-over should be present or not is
unclear.Comment: 20 pages, 3 appendices, 14 figures, 5 tables, accepted for
publication in Astronomy & Astrophysic
Star forming galaxies in the AKARI deep field south : identifications and spectral energy distributions
Aims. We investigate the nature and properties of far-infrared (FIR)
sources in the AKARI deep field south (ADF-S).
Methods. We performed an extensive search for the counterparts to 1000 ADF-S objects brighter than 0.0301 Jy in the WIDE-S (90 μm)
AKARI band in the public databases (NED and SIMBAD). We analyzed the properties of the resulting sample: statistics of the identified objects, quality of position determination of the ADF-S sources, their number counts, redshift distribution, and comparison of morphological types, when the corresponding information was available. We performed a simplifield analysis of the clustering properties of the ADF-S sources and compliled spectral energy distributions (SEDs) of objects with the highest quality photometry, using three different models.
Results. Among 1000Â investigated ADF-S sources, 545 were identified with sources at other wavelengths in public databases. From them, 518 are known galaxies and 343 of these were previously known as infra-red sources. Among the remaining sources, there are two quasars and both infrared and radio sources of unknown origin. Among six stellar identifications, at least five are probably the effect of contamination. We measured the redshifts of 48Â extragalactic objects and determined the morphological types of 77Â galaxies. We present SED models of 47Â sources with sufficiently good photometric data.
Conclusions. We conclude that the bright FIR point sources observed in the ADF-S are mostly nearby galaxies. Their properties are very similar to the properties of the local population of optically bright galaxies, except for unusually high ratio of peculiar or interacting objects and a lower percentage of elliptical galaxies. The percentage of lenticular galaxies is the same as in the optically bright population, which suggests that galaxies of this type may frequently contain a significant amount of cool dust. It is possible that source confusion plays a significant role in more than 34% of measurements. The SEDs correspond to a variety of galaxy types, from very actively star forming to very quiescent. The AKARI long wavelength bands data have enabled us to determine for the first time that these galaxies are objects with very cool dust
The catalog of short periods stars from the ''Pi of the Sky'' data
Based on the data from the ''Pi of the Sky'' project we made a catalog of the
variable stars with periods from 0.1 to 10 days. We used data collected during
a period of two years (2004 and 2005) and classified 725 variable stars. Most
of the stars in our catalog are eclipsing binaries - 464 (about 64%), while the
number of pulsating stars is 125 (about 17%). Our classification is based on
the shape of the light curve, as in the GCVS catalog. However, some stars in
our catalog were classified as of different type than in the GCVS catalog. We
have found periods for 15 stars present in the GCVS catalog with previously
unknown period.Comment: New Astronomy in prin
MUSE observations of the giant low surface brightness galaxy Malin 1: Numerous HII regions, star formation rate, metallicity, and dust attenuation
Giant low-surface brightness (GLSB) galaxies are an extreme class of objects
with very faint and extended gas-rich disks. Malin 1 is the largest GLSB galaxy
known to date, but its formation is still poorly understood. We use VLT/MUSE
IFU spectroscopic observations of Malin 1 to reveal, for the first time, the
presence of H emission distributed across numerous regions along its
disk, up to radial distances of 100 kpc. We made an estimate of the dust
attenuation using the Balmer decrement and found that Malin 1 has a mean
H attenuation of 0.36 mag. We observe a steep decline in the star
formation rate surface density () within the inner 20 kpc,
followed by a shallow decline in the extended disk. Similarly, the gas phase
metallicity we estimated shows a steep gradient in the inner 20 kpc, followed
by a flattening of the metallicity in the extended disk with a relatively high
value of 0.6 . We found that the normalized abundance gradient
of the inner disk is similar to values found in normal galaxies but with an
extreme value in the extended disk. A comparison of the star formation rate
surface density and gas surface density shows that, unlike normal disk galaxies
or other LSBs, Malin 1 exhibits a very low star formation efficiency. Owing to
the detection of emission lines over a large part of the disk of Malin 1, this
work sheds light on the star formation processes in this unique galaxy,
highlighting its extended star-forming disk, dust attenuation, almost flat
metallicity distribution in the outer disk, and exceptionally low
star-formation efficiency. Our findings contribute to a more detailed
understanding of the formation of the giant disk of Malin 1 and also constrain
possible proposed scenarios on the nature of GLSB galaxies in general.Comment: 12 pages, 9 figures, accepted for publication in A&
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