95 research outputs found
Teachers’ professional identity: validation of an assessment instrument for preservice teachers
This study aims to develop and validate an instrument to analyse future Secondary Education teachers' perceptions regarding the development of Teachers' Professional Identity (TPI). The data were collected from a sample of 733 participants who were students enrolled in the Master's Degree for Secondary Education teachers. The psychometric properties of the instrument were obtained by analysing content, and comprehension validity, construct validity and reliability. A first subsample was used for an Exploratory Factor Analysis, and a second one to verify the identified factor structure via Confirmatory Factor Analysis. The instrument is made up of 31 items in four scales namely the understanding of TPI, the development of TPI at various educational levels, the development of TPI in comparison with that of other professionals and the influencing factors. The results show that it has high levels of validity and reliability. Therefore, it provides TPI research field with an instrument to assess it during the initial teacher training period in consecutive training models where it seems to occur more identity crisis
Obscuration in AGNs: near-infrared luminosity relations and dust colors
We combine two approaches to isolate the AGN luminosity at near-infrared
wavelengths and relate the near-IR pure AGN luminosity to other tracers of the
AGN. Using integral-field spectroscopic data of an archival sample of 51 local
AGNs, we estimate the fraction of non-stellar light by comparing the nuclear
equivalent width of the stellar 2.3 micron CO absorption feature with the
intrinsic value for each galaxy. We compare this fraction to that derived from
a spectral decomposition of the integrated light in the central arc second and
find them to be consistent with each other. Using our estimates of the near-IR
AGN light, we find a strong correlation with presumably isotropic AGN tracers.
We show that a significant offset exists between type 1 and type 2 sources in
the sense that type 1 sources are 7 (10) times brighter in the near-IR at log
L_MIR = 42.5 (log L_X = 42.5). These offsets only becomes clear when treating
infrared type 1 sources as type 1 AGNs.
All AGNs have very red near-to-mid-IR dust colors. This, as well as the range
of observed near-IR temperatures, can be explained with a simple model with
only two free parameters: the obscuration to the hot dust and the ratio between
the warm and hot dust areas. We find obscurations of A_V (hot) = 5 - 15 mag for
infrared type 1 sources and A_V (hot) = 15 - 35 mag for type 2 sources. The
ratio of hot dust to warm dust areas of about 1000 is nicely consistent with
the ratio of radii of the respective regions as found by infrared
interferometry.Comment: 17 pages, 10 Figures, 3 Tables, accepted by A&
On the relation of optical obscuration and X-ray absorption in Seyfert galaxies
The optical classification of a Seyfert galaxy and whether it is considered
X-ray absorbed are often used interchangeably. But there are many borderline
cases and also numerous examples where the optical and X-ray classifications
appear to be in conflict. In this article we re-visit the relation between
optical obscuration and X-ray absorption in AGNs. We make use of our "dust
color" method (Burtscher et al. 2015) to derive the optical obscuration A_V and
consistently estimated X-ray absorbing columns using 0.3--150 keV spectral
energy distributions. We also take into account the variable nature of the
neutral gas column N_H and derive the Seyfert sub-classes of all our objects in
a consistent way.
We show in a sample of 25 local, hard-X-ray detected Seyfert galaxies (log
L_X / (erg/s) ~ 41.5 - 43.5) that there can actually be a good agreement
between optical and X-ray classification. If Seyfert types 1.8 and 1.9 are
considered unobscured, the threshold between X-ray unabsorbed and absorbed
should be chosen at a column N_H = 10^22.3 / cm^2 to be consistent with the
optical classification.
We find that N_H is related to A_V and that the N_H/A_V ratio is
approximately Galactic or higher in all sources, as indicated previously. But
in several objects we also see that deviations from the Galactic ratio are only
due to a variable X-ray column, showing that (1) deviations from the Galactic
N_H/A_V can simply be explained by dust-free neutral gas within the broad line
region in some sources, that (2) the dust properties in AGNs can be similar to
Galactic dust and that (3) the dust color method is a robust way to estimate
the optical extinction towards the sublimation radius in all but the most
obscured AGNs.Comment: 7 pages, 3 figures, accepted for publication by A&A; updated PDF to
include abstrac
Deriving a multivariate CO-to-H conversion function using the [CII]/CO(1-0) ratio and its application to molecular gas scaling relations
We present Herschel PACS observations of the [CII] 158 micron emission line
in a sample of 24 intermediate mass (9<logM/M<10) and low
metallicity (0.4< Z/Z<1.0) galaxies from the xCOLD GASS survey.
Combining them with IRAM CO(1-0) measurements, we establish scaling relations
between integrated and molecular region [CII]/CO(1-0) luminosity ratios as a
function of integrated galaxy properties. A Bayesian analysis reveals that only
two parameters, metallicity and offset from the star formation main sequence,
MS, are needed to quantify variations in the luminosity ratio;
metallicity describes the total dust content available to shield CO from UV
radiation, while MS describes the strength of this radiation field. We
connect the [CII]/CO luminosity ratio to the CO-to-H conversion factor and
find a multivariate conversion function , which can be used up to
z~2.5. This function depends primarily on metallicity, with a second order
dependence on MS. We apply this to the full xCOLD GASS and PHIBSS1
surveys and investigate molecular gas scaling relations. We find a flattening
of the relation between gas mass fraction and stellar mass at
logM/M<10. While the molecular gas depletion time varies with
sSFR, it is mostly independent of mass, indicating that the low L/SFR
ratios long observed in low mass galaxies are entirely due to photodissociation
of CO, and not to an enhanced star formation efficiency.Comment: Submitted to MNRAS, this version after referee comments. 21 page
High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS
We report the detection of far-infrared (FIR) CO rotational emission from
nearby active galactic nuclei (AGN) and starburst galaxies, as well as several
merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using
Herschel-PACS, we have detected transitions in the J = 14 - 20 range
( 130 - 185 m, 1612 - 2300 GHz) with upper limits
on (and in two cases, detections of) CO line fluxes up to J = 30. The
PACS CO data obtained here provide the first well-sampled FIR extragalactic CO
SLEDs for this range, and will be an essential reference for future high
redshift studies. We find a large range in the overall SLED shape, even amongst
galaxies of similar type, demonstrating the uncertainties in relying solely on
high-J CO diagnostics to characterize the excitation source of a galaxy.
Combining our data with low-J line intensities taken from the literature, we
present a CO ratio-ratio diagram and discuss its potential diagnostic value in
distinguishing excitation sources and physical properties of the molecular gas.
The position of a galaxy on such a diagram is less a signature of its
excitation mechanism, than an indicator of the presence (or absence) of warm,
dense molecular gas. We then quantitatively analyze the CO emission from a
subset of the detected sources with Large Velocity Gradient (LVG) radiative
transfer models to fit the CO SLEDs. Using both single-component and
two-component LVG models to fit the kinetic temperature, velocity gradient,
number density and column density of the gas, we derive the molecular gas mass
and the corresponding CO-to-H conversion factor, , for each
respective source. For the ULIRGs we find values in the canonical
range 0.4 - 5 M/(K kmspc), while for the other objects,
varies between 0.2 and 14.} Finally, we compare our best-fit LVG model
..Comment: 39 pages, 3 figures; Accepted to Ap
A New Probe of Dense Gas at High Redshift: Detection of HCO+(5-4) Line Emission in APM 08279+5255
We report the detection of HCO+(5-4) emission from the Broad Absorption Line
(BAL) quasar APM08279+5255 at z=3.911 based on observations conducted at the
IRAM Plateau de Bure interferometer. This represents the first detection of
this molecular ion at such a high redshift. The inferred line luminosity,
uncorrected for lensing, is L'(HCO+)=(3.5+-0.6)x10^10 Kkms^-1pc^2. The HCO+
J=5-4 source position coincides within the errors with that reported from
previous HCN J=5-4 and high-J CO line observations of this quasar. The HCO+
line profile central velocity and width are consistent with those derived from
HCN. This result suggests that HCO+(5-4) emission comes roughly from the same
circumnuclear region probed by HCN. However, the HCN(5-4)/HCO+(5-4) intensity
ratio measured in APM08279+5255 is significantly larger than that predicted by
simple radiative transfer models, which assume collisional excitation and equal
molecular abundances. This could imply that the [HCN]/[HCO^+] abundance ratio
is particularly large in this source, or that the J=5 rotational levels are
predominantly excited by IR fluorescent radiation.Comment: Accepted for publication in ApJ Letters, May 2
Towards a resolved Kennicutt-Schmidt law at high redshift
Massive galaxies in the distant Universe form stars at much higher rates than
today. Although direct resolution of the star forming regions of these galaxies
is still a challenge, recent molecular gas observations at the IRAM Plateau de
Bure interferometer enable us to study the star formation efficiency on
subgalactic scales around redshift z = 1.2. We present a method for obtaining
the gas and star formation rate (SFR) surface densities of ensembles of clumps
composing galaxies at this redshift, even though the corresponding scales are
not resolved. This method is based on identifying these structures in
position-velocity diagrams corresponding to slices within the galaxies. We use
unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of
four massive star forming distant galaxies - EGS13003805, EGS13004291,
EGS12007881, and EGS13019128 in the AEGIS terminology - to determine the gas
and SFR surface densities of the identifiable ensembles of clumps that
constitute them. The integrated CO line luminosity is assumed to be directly
proportional to the total gas mass, and the SFR is deduced from the [OII] line.
We identify the ensembles of clumps with the angular resolution available in
both CO and [OII] spectroscopy; i.e., 1-1.5". SFR and gas surface densities are
averaged in areas of this size, which is also the thickness of the DEEP2 slits
and of the extracted IRAM slices, and we derive a spatially resolved
Kennicutt-Schmidt (KS) relation on a scale of ~8 kpc. The data generally
indicates an average depletion time of 1.9 Gyr, but with significant variations
from point to point within the galaxies.Comment: 6 pages, 4 figures, 2 tables, accepted by Astronomy and Astrophysic
PHIBSS: molecular gas content and scaling relations in z~1-3 normal star forming galaxies
We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2
survey of the molecular gas properties in normal star forming galaxies (SFGs)
near the cosmic star formation peak. PHIBSS provides 52 CO detections in two
redshift slices at z~1.2 and 2.2, with log(M*(M_solar))>10.4 and
log(SFR(M_solar/yr))>1.5. Including a correction for the incomplete coverage of
the M*-SFR plane, we infer average gas fractions of ~0.33 at z~1.2 and ~0.47 at
z~2.2. Gas fractions drop with stellar mass, in agreement with cosmological
simulations including strong star formation feedback. Most of the z~1-3 SFGs
are rotationally supported turbulent disks. The sizes of CO and UV/optical
emission are comparable. The molecular gas - star formation relation for the
z=1-3 SFGs is near-linear, with a ~0.7 Gyrs gas depletion timescale; changes in
depletion time are only a secondary effect. Since this timescale is much less
than the Hubble time in all SFGs between z~0 and 2, fresh gas must be supplied
with a fairly high duty cycle over several billion years. At given z and M*,
gas fractions correlate strongly with the specific star formation rate. The
variation of specific star formation rate between z~0 and 3 is mainly
controlled by the fraction of baryonic mass that resides in cold gas.Comment: Submitted to the Astrophysical Journal; 14 figure
The applicability of FIR fine-structure lines as Star Formation Rate tracers over wide ranges of metallicities and galaxy types
We analyze the applicability of far-infrared fine-structure lines [CII] 158
micron, [OI] 63 micron and [OIII] 88 micron to reliably trace the star
formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the
Herschel Dwarf Galaxy Survey and compare with a broad sample of galaxies of
various types and metallicities in the literature. We study the trends and
scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24
micron) and far-infrared line emission, on spatially resolved and global galaxy
scales, in dwarf galaxies. We assemble far-infrared line measurements from the
literature and infer whether the far-infrared lines can probe the SFR (as
traced by the total-infrared luminosity) in a variety of galaxy populations. In
metal-poor dwarfs, the [OI] and [OIII] lines show the strongest correlation
with the SFR with an uncertainty on the SFR estimates better than a factor of
2, while the link between [CII] emission and the SFR is more dispersed
(uncertainty factor of 2.6). The increased scatter in the SFR-L([CII]) relation
towards low metal abundances, warm dust temperatures, large filling factors of
diffuse, highly ionized gas suggests that other cooling lines start to dominate
depending on the density and ionization state of the gas. For the literature
sample, we evaluate the correlations for a number of different galaxy
populations. The [CII] and [OI] lines are considered to be reliable SFR tracers
in starburst galaxies, recovering the star formation activity within an
uncertainty of factor 2. [Abridged]Comment: 35 pages, 13 figures, accepted for publication in A&A on May 7th 201
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