25 research outputs found
Tides in colliding galaxies
Long tails and streams of stars are the most noticeable upshots of galaxy
collisions. Their origin as gravitational, tidal, disturbances has however been
recognized only less than fifty years ago and more than ten years after their
first observations. This Review describes how the idea of galactic tides
emerged, in particular thanks to the advances in numerical simulations, from
the first ones that included tens of particles to the most sophisticated ones
with tens of millions of them and state-of-the-art hydrodynamical
prescriptions. Theoretical aspects pertaining to the formation of tidal tails
are then presented. The third part of the review turns to observations and
underlines the need for collecting deep multi-wavelength data to tackle the
variety of physical processes exhibited by collisional debris. Tidal tails are
not just stellar structures, but turn out to contain all the components usually
found in galactic disks, in particular atomic / molecular gas and dust. They
host star-forming complexes and are able to form star-clusters or even
second-generation dwarf galaxies. The final part of the review discusses what
tidal tails can tell us (or not) about the structure and content of present-day
galaxies, including their dark components, and explains how tidal tails may be
used to probe the past evolution of galaxies and their mass assembly history.
On-going deep wide-field surveys disclose many new low-surface brightness
structures in the nearby Universe, offering great opportunities for attempting
galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in
Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most
welcom
A Herschel/PACS Far-infrared line emission survey of local luminous infrared galaxies
We present an analysis of [OI]63, [OIII]88, [NII]122 and [CII]158 far-infrared (FIR) fine-structure line observations obtained with Herschel/PACS, for ~240 local luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS). We find pronounced declines -deficits- of line-to-FIR-continuum emission for [NII]122, [OI]63 and [CII]158 as a function of FIR color and infrared luminosity surface density, . The median electron density of the ionized gas in LIRGs, based on the [NII]122/[NII]205 ratio, is = 41 cm. We find that the dispersion in the [CII]158 deficit of LIRGs is attributed to a varying fractional contribution of photo-dissociation-regions (PDRs) to the observed [CII]158 emission, f([CII]PDR) = [CII]PDR/[CII], which increases from ~60% to ~95% in the warmest LIRGs. The [OI]63/[CII]158PDR ratio is tightly correlated with the PDR gas kinetic temperature in sources where [OI]63 is not optically-thick or self-absorbed. For each galaxy, we derive the average PDR hydrogen density, , and intensity of the interstellar radiation field, in units of G, and find G/ ratios ~0.1-50 cm, with ULIRGs populating the upper end of the distribution. There is a relation between G/ and , showing a critical break at ~ 5 x 10 Lsun/kpc. Below , G/ remains constant, ~0.32 cm, and variations in are driven by the number density of star-forming regions within a galaxy, with no change in their PDR properties. Above , G/ increases rapidly with , signaling a departure from the typical PDR conditions found in normal star-forming galaxies towards more intense/harder radiation fields and compact geometries typical of starbursting sources
[CII]157.7um feature in LIRGs
VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'Explaining the [C II]157.7 {mu}m deficit in luminous infrared galaxies - First results from a Herschel/PACS study of the GOALS sample.' (bibcode: 2013ApJ...774...68D
Desempenho produtivo de vacas leiteiras alimentadas com silagem pré-seca de alfafa adicionada de inoculante microbiano Performance of lactating dairy cows fed alfalfa haylage with microbial inoculant
Objetivou-se, com o presente estudo, avaliar os efeitos da inoculação microbiana da silagem pré-seca de alfafa sobre o consumo de matéria seca, a produção e composição do leite de vacas da raça Holandesa, multÃparas, com 135 ± 16,4 dias de lactação, distribuÃdas em delineamento em reversão simples com seqüência balanceada ("cross-over"), com dois perÃodos sucessivos. Os tratamentos corresponderam à silagem pré-seca de alfafa (50,0% de MS e 16,5% de PB) controle ou inoculada com o produto Silobac® (Lactobacillus plantarum e Pediococcus pentosaceus). Cada perÃodo experimental teve duração de 21 dias, sendo os cinco últimos dias destinados à coleta de dados. Não se observou efeito da inoculação sobre o CMS (inoculada = 17,8 vs. controle = 17,8 kg/animal/dia), a produção de leite corrigida para 4,0% de gordura (21,0 vs. 20,4 kg/dia), produção de leite (23,0 vs. 22,4 kg/dia), porcentagem de gordura (3,46 vs. 3,47%), proteÃna (2,96 vs. 2,93%), lactose (4,64 vs. 4,67%), sólidos totais (11,9 vs. 11,9%) e sólidos desengordurados (8,49 vs. 8,48%), CCS (5,43 vs. 5,16 log cel/10³/mL), NUL (11,7 vs. 12,1 mg/dl), acidez (15,9 vs. 16,4ºD), densidade (1030,1 vs. 1030,0) e crioscopia (-0,529 vs. -0,531ºH).<br>The objective of this study was to evaluate the effects of feeding alfalfa haylage with microbial inoculat on dry matter intake, milk yield and composition in Holstein cows, at 135 ± 16.4 days in milk. A cross-over design with two periods of sampling was used. Treatments were alfalfa haylage (50.0% DM and 16.5% CP) control or microbially inoculated with Silobac® product (Lactobacillus plantarum and Pediococcus pentosaceus). Each experimental period extended for twenty-one days, the last five used for data collection. The inoculation did not influence DMI (inoculated = 17.8 vs. control = 17.8 kg/animal/day), 4%FCM (21.0 vs. 20.4 kg/day), milk yield (23.0 vs. 22.4 kg/day), fat (3.46 vs. 3.47%), protein (2.96 vs. 2.93%), lactose (4.64 vs. 4.67%), total solids (11.9 vs. 11.9%) and fat free solids percentage (8.49 vs. 8.48%), SCC (5.43 vs. 5.16 log cell/10³/mL), MUN (11.7 vs. 12.1 mg/dl), acidity (15.9 vs. 16.4ºD), density (1030.1 vs. 1030.0) and cryoscopic index (-0.529 vs. -0.531ºH)