20 research outputs found
Ancient giants: on the farthest galaxy at z=8.6
The observational frontiers for the detection of high-redshift galaxies have
recently been pushed to unimaginable distances with the record-holding Lyman
Alpha Emitter (LAE) UDFy-38135539 discovered at redshift z=8.6. However, the
physical nature and the implications of this discovery have yet to be assessed.
By selecting galaxies with observed luminosities similar to UDFy-38135539 in
state-of-the-art cosmological simulations tuned to reproduce the large scale
properties of LAEs, we bracket the physical nature of UDFy-38135539: it has a
star formation rate ~ 2.7-3.7 solar masses/yr, it contains ~ 10^{8.3-8.7} solar
mass of stars 50-80 Myr old, with stellar metallicity ~ 0.03-0.12 of the solar
value. For any of the simulated galaxies to be visible as a LAE in the observed
range, the intergalactic neutral hydrogen fraction at z=8.6 must be <= 0.2 and
extra ionizing radiation from sources clustered around UDFy-38135539 is
necessary. Finally, we predict that there is a 70% (15%) probability of
detecting at least 1 such source from JWST (HST/WFC3) observations in a
physical radius ~ 0.4 Mpc around UDFy-38135539.Comment: Accepted to MNRAS letter
The neutral gas extent of galaxies as derived from weak intervening CaII absorbers
(Abridged) We present a systematic study of weak intervening CaII absorbers
at low redshift (z<0.5), based on the analysis of archival high resolution
(R>45,000) optical spectra of 304 quasars and active galactic nuclei observed
with VLT/UVES. Along a total redshift path of Dz~100 we detected 23 intervening
CaII absorbers in both the CaII H & K lines, with rest frame equivalent widths
W_r,3934=15-799 mA and column densities log N(CaII)=11.25-13.04. We obtain a
bias corrected number density of weak intervening CaII absorbers of
dN/dz=0.117+-0.044 at z=0.35 for absorbers with log N(CaII)>11.65. This is ~2.6
times the value obtained for damped Lyman alpha absorbers (DLAs) at low
redshift. From ionization modeling we conclude that intervening CaII absorption
with log N(CaII)>11.5 arises in optically thick neutral gas in DLAs, sub-DLAs
and Lyman limit systems (LLS) at HI column densities of log N(HI)>17.4. The
relatively large cross section of these absorbers together with the frequent
detection of CaII absorption in high velocity clouds (HVCs) in the halo of the
Milky Way suggests that a considerable fraction of the intervening CaII systems
trace dusty neutral gas structures in the halos and circumgalactic environment
of galaxies (i.e., they are HVC analogs). Considering all galaxies with
luminosities L>0.05L* we calculate that the characteristic radial extent of
(partly) neutral gas clouds with log N(HI)>17.4 around low-redshift galaxies is
R_HVC ~ 55 kpc.Comment: 20 pages, 15 figures; A&A, in press; this revision contains several
changes that improve clarity of presentation reflecting the suggestions made
by the refere
High-Ion Absorption in Seven GRB Host Galaxies at z=2-4: Evidence for both Circumburst Plasma and Outflowing Interstellar Gas
(Abridged) We use VLT/UVES high-resolution optical spectroscopy of seven GRB
afterglows at z_GRB>2 to investigate circumburst and interstellar plasma in the
host galaxies. Our sample consists of GRBs 021004, 050730, 050820, 050922C,
060607, 071031, and 080310. Four of these spectra were taken in rapid-response
mode, within 30 minutes of the Swift GRB detection. We identify several
distinct categories of high-ion absorption at velocities close to z_GRB: (i)
Strong high-ion components at z_GRB itself are always seen in OVI, CIV, and
SiIV, and usually (in 6 of 7 cases) in NV. We discuss circumburst and
interstellar models for the origin of this absorption. Using the non-detection
of SIV* toward GRB 050730 together with a UV photo-excitation model, we place a
lower limit of 400 pc on the distance of the SIV-bearing gas from the GRB. (ii)
Complex, multi-component CIV and SiIV profiles extending over 100-400 km/s
around z_GRB are observed in each spectrum; these velocity fields are similar
to those measured in damped Lyman-alpha systems at similar redshifts,
suggesting a galactic origin. (iii) Asymmetric, blueshifted, absorption-line
wings covering 65-140 km/s are seen in the CIV, SiIV, and OVI profiles in 4 of
the 7 spectra. The wing kinematics together with the observation that two wings
show "Galactic" CIV/SiIV ratios suggest these features trace outflowing ISM gas
in the GRB host galaxies. (iv) High-velocity (HV; 500-5000 km/s) components are
detected in 6 of the 7 spectra. The HV components show diverse properties. In
the cases of GRBs 071031 and 080310, both the ionization level (very high
CIV/SiIV ratios and absence of neutral-phase absorption) and the kinematics of
the HV components can be explained by Wolf-Rayet winds from the GRB
progenitors.Comment: 20 pages, 9 figures (7 in color), accepted by A&A, updated with proof
corrections including changes to Table
High-resolution observations of two OVI absorbers at z=2 towards PKS 1448-232
To explore the ionization conditions in highly-ionized absorbers at high
redshift we have studied in detail two intervening OVI absorbers at z=2 towards
the quasar PKS1448-232, based on high (R=75,000) and intermediate (R=45,000)
resolution optical VLT/UVES spectra. We find that both absorption systems are
composed of several narrow subcomponents with CIV/OVI Doppler-parameters b<10
km/s, typically. This implies that the gas temperatures are T<10^5 K and that
the absorbers are photoionized by the UV background. The system at z=2.1098
represents a simple, isolated OVI absorber that has only two absorption
components and that is relatively metal-rich (Z\sim 0.6 solar). Ioinization
modeling implies that the system is photoionized with OVI, CIV, and HI
coexisting in the same gas phase. The second system at z=2.1660 represents a
complicated, multi-component absorption system with eight OVI components
spanning almost 300 km/s in radial velocity. The photoionization modeling
implies that the metallicity is non-uniform and relatively low (<= 0.1 solar)
and that the OVI absorption must arise in a gas phase different from that
traced by CIV, CIII, and HI. Our detailed study of the two OVI systems towards
PKS1448-232 shows that multi-phase, multi-component high-ion absorbers like the
one at z=2.1660 require a detailed ionization modeling of the various
subcomponents to obtain reliable results on the physical conditions and
metal-abundances in the gas
Una experiencia educativa acerca de <i>Ginkgo biloba</i>, una especie vegetal con aplicación medicinal
Ginkgo biloba L. (Ginkgoaceae) —un árbol ornamental popular en parques y veredas de nuestra ciudad— es ideal para la forestación urbana debido a su gran resistencia a pestes y contaminación, así como también por su bajo potencial invasivo. Esta especie, también conocida como “fósil viviente”, es considerada una de las más antiguas, ya que ha sobrevivido durante millones de años en la superficie de nuestro planeta, soportando incluso catástrofes nucleares como la bomba de Hiroshima. Las hojas verdes desecadas de ginkgo, cuya primera citación como agente medicinal se remonta al siglo XVI en la farmacopea tradicional China, se han utilizado históricamente para mejorar la calidad de vida de los pacientes y el deterioro cognitivo asociado a la edad. Si bien no se conoce con exactitud cómo actúa esta droga en el organismo, se cree que interviene protegiendo a las neuronas, ya sea de forma directa o indirecta, regulando el flujo sanguíneo o neutralizando las especies reactivas de oxígeno conocidas como radicales libres. Actualmente, el extracto de hojas de ginkgo es una de las drogas de origen vegetal que lleva más tiempo en el mercado, formando parte de variadas formulaciones fitoterapéuticas y suplementos dietarios, comercializados generalmente en forma de comprimidos de administración oral. El proyecto educativo “Forestando con ginkgo” fue desarrollado por la profesora Inés Fangano en el Colegio Secundario Lincoln de la ciudad de La Plata con la propagación de ginkgos y su posterior trasplante a espacios públicos como principales objetivos. Basándonos en las aplicaciones medicinales de los principios activos presentes en las hojas del ginkgo se planteó la actividad de extensión educativa universitaria “Ginkgo: el árbol de la buena memoria” como una articulación con el proyecto antes mencionado.Facultad de Ciencias Médica
A population of weak metal-line absorbers surrounding the Milky Way
We report on the detection of a population of weak metal-line absorbers in
the halo or nearby intergalactic environment of the Milky Way. Using
high-resolution ultraviolet absorption-line spectra of bright QSOs obtained
with the Space Telescope Imaging Spectrograph (STIS), along six sight lines we
have observed unsaturated, narrow absorption in OI and SiII together with
mildly saturated CII absorption at high radial velocities (|v_LSR|=100-320
km/s). The measured OI column densities are small, implying that these
structures represent Lyman-Limit Systems and sub-Lyman-Limit System with HI
column densities < 3x10^18 cm^-2, thus below the detection limits of current
21cm all-sky surveys of high-velocity clouds (HVCs). The absorbers apparently
are not directly associated with any of the large high-column density HVC
complexes, but rather represent isolated, partly neutral gas clumps embedded in
a more tenuous, ionized gaseous medium situated in the halo or nearby
intergalactic environment of the Galaxy. We speculate that this absorber
population represents the local analog of weak MgII systems that are commonly
observed in the circumgalactic environment of low- and high-redshift galaxies.Comment: 45 pages, 7 figures, accepted for publication in Ap
Molecular hydrogen in Lyman Alpha Emitters
We present a physically motivated model to estimate the molecular hydrogen
(H2) content of high-redshift (z~5.7,6.6) Lyman Alpha Emitters (LAEs) extracted
from a suite of cosmological simulations. We find that the H2 mass fraction,
(f_H2), depends on three main LAE physical properties: (a) star formation rate,
(b) dust mass, and (c) cold neutral gas mass. At z~5.7, the value of f_H2 peaks
and ranges between 0.5-0.9 for intermediate mass LAEs with stellar mass M_* ~
10^{9-10} solar mass, decreasing for both smaller and larger galaxies. However,
the largest value of the H2 mass is found in the most luminous LAEs. These
trends also hold at z\sim6.6, although, due to a lower dust content,
f_H2(z=6.6)\sim0.5 f_H2(z=5.7) when averaged over all LAEs; they arise due to
the interplay between the H2 formation/shielding controlled by dust and the
intensity of the ultraviolet (UV) Lyman-Werner photo-dissociating radiation
produced by stars. We then predict the carbon monoxide (CO) luminosities for
such LAEs and check that they are consistent with the upper limits found by
Wagg et al. (2009) for two z>6 LAEs. At z\sim(5.7, 6.6), the lowest CO
rotational transition observable for both samples with the actual capabilities
of Atacama Large Millimeter Array (ALMA) is the CO(6-5). We find that at
z\sim5.7, about 1-2% of LAEs, i.e., those with an observed Lyman Alpha
luminosity larger than 10^{43.2} erg/s would be detectable with an integration
time of 5-10 hours (S/N=5); at z\sim6.6 none of the LAEs would be detectable in
CO, even with an ALMA integration time of 10 hours. We also build the CO `flux
function', i.e., the number density of LAEs as a function of the
line-integrated CO flux, S_CO, and show that it peaks at S_CO = 0.1 mJy at
z\sim5.7, progressively shifting to lower values at higher redshifts. We end by
discussing the model uncertainties.Comment: Accepted for publication in MNRA
A high resolution study of intergalactic O VI absorbers at z~2.3
[Abridged] We present a detailed study of the largest sample of intervening O
VI systems in the redshift range 1.9 < z < 3.1 detected in high resolution (R ~
45,000) spectra of 18 bright QSOs observed with VLT/UVES. Based on Voigt
profile and apparent optical depth analysis we find that (i) the Doppler
parameters of the O VI absorption are usually broader than those of C IV (ii)
the column density distribution of O VI is steeper than that of C IV (iii) line
spread (\delta v) of the O VI and C IV are strongly correlated (at 5.3\sigma
level) with \delta v(O VI) being systematically larger than \delta v(C IV) and
(iv) \delta v(O VI) and \delta v(C IV) are also correlated (at > 5\sigma level)
with their respective column densities and with N(H I) (3 and 4.5 \sigma
respectively). These findings favor the idea that C IV and O VI absorption
originate from different phases of a correlated structure and systems with
large velocity spread are probably associated with overdense regions. The
velocity offset between optical depth weighted redshifts of C IV and O VI
absorption is found to be in the range 0 < |\Delta v (O VI - CIV)| < 48 km/s
with a median value of 8 km/s. We compare the properties of O VI systems in our
sample with that of low redshift (z < 0.5) samples from the literature and find
that (i) the O VI components at low-z are systematically wider than at high-z
with an enhanced non-thermal contribution to their b-parameter, (ii) the slope
of the column density distribution functions for high and low-z are consistent,
(iii) range in gas temperature estimated from a subsample of well aligned
absorbers are similar at both high and low-z, and (iv) \Omega_{O VI} = (1.0 \pm
0.2) \times10^{-7} for N(O VI) > 10^{13.7} cm^{-2}, estimated in our high-z
sample, is very similar to low-z estimations.Comment: 21 pages, 16 figures, 9 tables, Accepted for publication in MNRA
A Study of Quasar Proximity in O VI Absorbers at z=2-3
(Abridged) With the goal of investigating the nature of OVI absorbers at high
redshifts, we study the effects of proximity to the background quasar. In a
sample of sixteen quasars at z(QSO) between 2.14 and 2.87 observed at 6.6 km/s
resolution with VLT/UVES, we detect 35 OVI absorption-line systems lying within
8000 km/s of z(QSO). The systems can be categorized into 9 strong and 26 weak
OVI absorbers. The strong absorbers are defined by the presence of either
broad, fully saturated OVI absorption or partial coverage of the continuum
source, and have log N(OVI)>~15.0; these systems are intrinsic to the AGN. The
weak (narrow) systems show no partial coverage or saturation, and are
characterized by log N(OVI)<14.5 and have a median total velocity width of only
42 km/s. The incidence dN/dz of weak OVI systems within 2000 km/s of the quasar
is 42+/-12. Between 2000 and 8000 km/s, dN/dz falls to 14+/-4, equal to the
incidence of intervening OVI absorbers. Whereas the accompanying H I and C IV
column densities are significantly lower (by a mean of ~1 dex) in the weak OVI
absorbers within 2000 km/s of z(QSO) than in those at larger velocities, the
OVI column densities display no dependence on proximity. Furthermore,
significant offsets between the HI and OVI centroids in ~50% of the weak
absorbers imply that (at least in these cases) the HI and OVI are not formed in
the same phase of gas. In summary, we find no firm evidence that quasar
radiation influences the OVI-bearing gas, suggesting the OVI is collisionally
ionized rather than photoionized, possibly in the multi-phase halos of
foreground galaxies. Non-equilibrium collisional ionization models are needed
to explain the low temperatures in the absorbing gas, which are implied by
narrow line widths (b<14 km/s) in over half of the observed OVI components.Comment: 27 pages, 10 figures all in color, accepted by MNRA
FUV and X-ray absorption in the Warm-Hot Intergalactic Medium
The Warm-Hot Intergalactic Medium (WHIM) arises from shock-heated gas
collapsing in large-scale filaments and probably harbours a substantial
fraction of the baryons in the local Universe. Absorption-line measurements in
the ultraviolet (UV) and in the X-ray band currently represent the best method
to study the WHIM at low redshifts. We here describe the physical properties of
the WHIM and the concepts behind WHIM absorption line measurements of H I and
high ions such as O VI, O VII, and O VIII in the far-ultraviolet and X-ray
band. We review results of recent WHIM absorption line studies carried out with
UV and X-ray satellites such as FUSE, HST, Chandra, and XMM-Newton and discuss
their implications for our knowledge of the WHIM.Comment: 26 pages, 9 figures, accepted for publication in Space Science
Reviews, special issue "Clusters of galaxies: beyond the thermal view",
Editor J.S. Kaastra, Chapter 3; work done by an international team at the
International Space Science Institute (ISSI), Bern, organised by J.S.
Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke