13 research outputs found
Generación de features en la búsqueda de estrellas variables en el relevamiento astronómico VVV
Frente al desarrollo de telescopios terrestres y satelitales que generan relevamientos astronómicos del orden de los Peta-Bytes, se expo-ne en este trabajo la metodología a seguir para la generación de features de series temporales para el descubrimiento de estrellas variables periódicas en el núcleo, bulbo y una parte del disco de nuestra galaxia utilizando datos del VVV-Survey. A lo largo del trabajo se presenta los datos de dicho relevamiento, la forma de regenerar series temporales a partir de ellos y extraer features importantes como el período o diferentes estadísticas de magnitud. Finalmente se proyecta el plan a futuro para utilizar el conocimiento extra do para la creación de catálogos de estrellas variables utilizando aprendizaje automático.Sociedad Argentina de Informática e Investigación Operativa (SADIO
Generación de features en la búsqueda de estrellas variables en el relevamiento astronómico VVV
Frente al desarrollo de telescopios terrestres y satelitales que generan relevamientos astronómicos del orden de los Peta-Bytes, se expo-ne en este trabajo la metodología a seguir para la generación de features de series temporales para el descubrimiento de estrellas variables periódicas en el núcleo, bulbo y una parte del disco de nuestra galaxia utilizando datos del VVV-Survey. A lo largo del trabajo se presenta los datos de dicho relevamiento, la forma de regenerar series temporales a partir de ellos y extraer features importantes como el período o diferentes estadísticas de magnitud. Finalmente se proyecta el plan a futuro para utilizar el conocimiento extra do para la creación de catálogos de estrellas variables utilizando aprendizaje automático.Sociedad Argentina de Informática e Investigación Operativa (SADIO
The slope of the Baryonic Tully-Fisher relation
We present the results of a baryonic Tully-Fisher relation (BTFR) study for a
local sample of relatively isolated disk galaxies. We derive a BTFR with a
slope near 3 measured over about 4 dex in baryon mass for our combined
\textrm{H\,\scriptsize{I}} and bright spiral disk samples. This BTFR is
significantly flatter and has less scatter than the TFR (stellar mass only)
with its slope near 4 reported for other samples and studies. A BTFR slope near
3 is in better agreement with the expected slope from simple CDM
cosmological simulations that include both stellar and gas baryons. The scatter
in the TFR/BTFR appears to depend on : galaxies that rotate slower have
more scatter. The atomic gas--to--stars ratio shows a break near
\kms\, probably associated with a change in star formation efficiency. In
contrast the absence of such a break in the BTFR suggests that this relation
was probably set at the main epoch of baryon dissipation rather than as a
product of later galactic evolution.Comment: AJ - accepte
The Baryonic Tully Fisher Relation
We validate the baryonic Tully Fisher (BTF) relation by exploring the Tully
Fish er (TF) and BTF properties of optically and HI-selected disk galaxies. The
data includes galaxies from: Sakai et al. (2000) calibrator sample; McGaugh et
al. (2000: MC2000) I-band sample; and 18 newly acquired HI-selected field dwarf
galaxies observed with the ANU 2.3m telescope and the ATNF Parkes telescope
from Gurovich's thesis sample (2005).
As in MC2000, we re-cast the TF and BTF relations as relationships between
baryo n mass and W_{20}. First we report some numerical errors in MC2000. Then,
we c alculate weighted bi-variate linear fits to the data, and finally we
compare the fits of the intrinsically fainter dwarfs with the brighter galaxies
of Sakai et al. (2000). With regards to the local calibrator disk galaxies of
Sakai et al. (2000), our results suggest that the BTF relation is indeed
tighter than the T F relation and that the slopes of the BTF relations are
statistically flatter th an the equivalent TF relations. Further, for the
fainter galaxies which include the I-band MCG2000 and HI-selected galaxies of
Gurovich's thesis sample, we calc ulate a break from a simple power law model
because of what appears to be real c osmic scatter. Not withstanding this
point, the BTF models are marginally better models than the equivalent TF ones
with slightly smaller reduced chi^2.Comment: 3 pages, 3 figs, refereed conference proceeding based on an invited
talk at the Structure and Dynamics in the Local Universe, a Sydney workshop
to honour Brent Tully's 60th birthday. To appear in Publications of the
Astronomical Society of Australia, ed. J. Bland-Hawthor
Radiogalaxies in the Sloan Digital Sky Survey: spectral index-environment correlations
We analyze optical and radio properties of radiogalaxies detected in the
Sloan Digital Sky Survey (SDSS). The sample of radio sources are selected from
the catalogue of Kimball & Ivezi\'c (2008) with flux densities at 325, 1400 and
4850 MHz, using WENSS, NVSS and GB6 radio surveys and from flux measurements at
74 MHz taken from VLA Low-frequency Sky Survey \citep{cohen}. We study
radiogalaxy spectral properties using radio colour-colour diagrams and find
that our sample follows a single power law from 74 to 4850 MHz. The spectral
index vs. spectroscopic redshift relation () is not significant for
our sample of radio sources. We analyze a subsample of radio sources associated
with clusters of galaxies identified from the maxBCG catalogue and find that
about 40% of radio sources with ultra steep spectra (USS, , where
) are associated with galaxy clusters or groups of
galaxies. We construct a Hubble diagram of USS radio sources in the optical
band up to .8 and compare our results with those for normal galaxies
selected from different optical surveys and find that USS radio sources are
around as luminous as the central galaxies in the maxBCG cluster sample and
typically more than 4 magnitudes brighter than normal galaxies at .3.
We study correlations between spectral index, richness and luminosity of
clusters associated with radio sources. We find that USS at low redshift are
rare, most of them reside in regions of unusually high ambient density, such of
those found in rich cluster of galaxies. Our results also suggest that clusters
of galaxies associated with steeper than the average spectra have higher
richness counts and are populated by luminous galaxies in comparison with those
environments associated to radio sources with flatter than the average spectra.
A plausible explanation for our results is that radio emission is more pressure
confined in higher gas density environments such as those found in rich
clusters of galaxies and as a consequence radio lobes in rich galaxy clusters
will expand adiabatically and lose energy via synchrotron and inverse Compton
losses, resulting in a steeper radio spectra.Comment: 13 pages, 14 figures; accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journal
Dichotomy in host environments and signs of recycled AGN
We analyse the relation between AGN host properties and large scale
environment for a representative red and blue AGN host galaxy sample selected
from the DR4 SDSS. A comparison is made with two carefully constructed control
samples of non-active galaxies, covering the same redshift range and color
baseline. The cross-correlation functions show that the density distribution of
neighbours is almost identical for blue galaxies, either active, or non-active.
Although active red galaxies inhabit environments less dense compared to
non-active red galaxies, both reside in environments considerably denser than
those of blue hosts. Moreover, the radial density profile of AGN, relative to
galaxy group centres is less concentrated than galaxies. This is particularly
evident when comparing red AGN and non-active galaxies.
The properties of the neighbouring galaxies of blue and red AGN and non
active galaxies reflect this effect. While the neighbourhood of the blue
samples is indistinguishable, the red AGN environs show an excess of blue-star
forming galaxies with respect to their non-active counterpart. On the other
hand, the active and non-active blue systems have similar environments but
markedly different morphological distributions, showing an excess of blue
early-type AGN, which are argued to be late stage mergers. This comparison
reveals that the observable differences between active red and blue host galaxy
properties including star formation history and AGN activity depends on the
environment within which the galaxies form and evolve.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
GW150914: First search for the electromagnetic counterpart of a gravitational-wave event by the TOROS collaboration
We present the results of the optical follow-up conducted by the TOROS
collaboration of the first gravitational-wave event GW150914. We conducted
unfiltered CCD observations (0.35-1 micron) with the 1.5-m telescope at Bosque
Alegre starting ~2.5 days after the alarm. Given our limited field of view
(~100 square arcmin), we targeted 14 nearby galaxies that were observable from
the site and were located within the area of higher localization probability.
We analyzed the observations using two independent implementations of
difference-imaging algorithms, followed by a Random-Forest-based algorithm to
discriminate between real and bogus transients. We did not find any bona fide
transient event in the surveyed area down to a 5-sigma limiting magnitude of
r=21.7 mag (AB). Our result is consistent with the LIGO detection of a binary
black hole merger, for which no electromagnetic counterparts are expected, and
with the expected rates of other astrophysical transients.Comment: ApJ Letters, in pres