567 research outputs found
The silicate absorption profile in the ISM towards the heavily obscured nucleus of NGC 4418
The 9.7-micron silicate absorption profile in the interstellar medium
provides important information on the physical and chemical composition of
interstellar dust grains. Measurements in the Milky Way have shown that the
profile in the diffuse interstellar medium is very similar to the amorphous
silicate profiles found in circumstellar dust shells around late M stars, and
narrower than the silicate profile in denser star-forming regions. Here, we
investigate the silicate absorption profile towards the very heavily obscured
nucleus of NGC 4418, the galaxy with the deepest known silicate absorption
feature, and compare it to the profiles seen in the Milky Way. Comparison
between the 8-13 micron spectrum obtained with TReCS on Gemini and the larger
aperture spectrum obtained from the Spitzer archive indicates that the former
isolates the nuclear emission, while Spitzer detects low surface brightness
circumnuclear diffuse emission in addition. The silicate absorption profile
towards the nucleus is very similar to that in the diffuse ISM in the Milky Way
with no evidence of spectral structure from crystalline silicates or silicon
carbide grains.Comment: 7 Pages, 3 figures. MNRAS in pres
Professional Skills and Profiles in Journalism Demanded by Companies: Analysis of Offers at LinkedIn and Infojobs
The goal of this research is to analyze whether the profiles and professional skills in journalism demanded by companies in Spain correspond to those compiled in the Libro Blanco of the ANECA, or whether they have been modified over a decade later by the impact of the digital era and emergence of new employment needs. In the current setting of rapid and unpredictable changes, periodic analyses and research like this study are necessary. The methodology chosen was the analysis of the content of job offers directed to journalism graduates on the two most used job portals in Spain, Infojobs and LinkedIn, in September 2017. All the information in the offers was organized into two categories related to descriptive data about types of contracts and data over required skills. The results led to the conclusion that the professional skills currently demanded of journalism graduates differ qualitatively and quantitatively from the professional skills described by the ANECA in 2005. The skills most demanded by companies respond to the emergence of new professional profiles related to Web 2.0. However, it is also the case that companies do not seem to know precisely what skills a journalism graduate must have
Why Optically--Faint AGN Are Faint: The Spitzer Perspective
Optically--faint X-ray sources (those with f_X/f_R > 10) constitute about 20%
of X-ray sources in deep surveys, and are potentially highly obscured and/or at
high redshift. Their faint optical fluxes are generally beyond the reach of
spectroscopy. For a sample of 20 optically--faint sources in CDFS, we compile
0.4--24 um photometry, relying heavily on Spitzer. We estimate photometric
redshifts for 17 of these 20 sources. We find that these AGN are
optically--faint both because they lie at significantly higher redshifts
(median z ~ 1.6) than most X-ray--selected AGN, and because their spectra are
much redder than standard AGN. They have 2--8 keV X-ray luminosities in the
Seyfert range, unlike the QSO--luminosities of optically--faint AGN found in
shallow, wide--field surveys. Their contribution to the X-ray Seyfert
luminosity function is comparable to that of z>1 optically--bright AGN.Comment: Accepted for publication in the Astrophysical Journa
The Multitude of Unresolved Continuum Sources at 1.6 microns in Hubble Space Telescope images of Seyfert Galaxies
We examine 112 Seyfert galaxies observed by the Hubble Space Telescope (HST)
at 1.6 microns. We find that ~50% of the Seyfert 2.0 galaxies which are part of
the Revised Shapeley-Ames (RSA) Catalog or the CfA redshift sample contain
unresolved continuum sources at 1.6 microns. All but a couple of the Seyfert
1.0-1.9 galaxies display unresolved continuum sources. The unresolved sources
have fluxes of order a mJy, near-infrared luminosities of order 10^41 erg/s and
absolute magnitudes M_H ~-16. Comparison non-Seyfert galaxies from the RSA
Catalog display significantly fewer (~20%), somewhat lower luminosity nuclear
sources, which could be due to compact star clusters. We find that the
luminosities of the unresolved Seyfert 1.0-1.9 sources at 1.6 microns are
correlated with [OIII] 5007A and hard X-ray luminosities, implying that these
sources are non-stellar. Assuming a spectral energy distribution similar to
that of a Seyfert 2 galaxy, we estimate that a few percent of local spiral
galaxies contain black holes emitting as Seyferts at a moderate fraction, 10^-1
to 10^-4, of their Eddington luminosities. With increasing Seyfert type the
fraction of unresolved sources detected at 1.6 microns and the ratio of 1.6
microns to [OIII] fluxes tend to decrease. These trends are consistent with the
unification model for Seyfert 1 and 2 galaxies.Comment: accepted by Ap
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
Spitzer Power-law AGN Candidates in the Chandra Deep Field-North
We define a sample of 62 galaxies in the Chandra Deep Field-North whose
Spitzer IRAC SEDs exhibit the characteristic power-law emission expected of
luminous AGN. We study the multiwavelength properties of this sample, and
compare the AGN selected in this way to those selected via other Spitzer
color-color criteria. Only 55% of the power-law galaxies are detected in the
X-ray catalog at exposures of >0.5 Ms, although a search for faint emission
results in the detection of 85% of the power-law galaxies at the > 2.5 sigma
detection level. Most of the remaining galaxies are likely to host AGN that are
heavily obscured in the X-ray. Because the power-law selection requires the AGN
to be energetically dominant in the near- and mid-infrared, the power-law
galaxies comprise a significant fraction of the Spitzer-detected AGN population
at high luminosities and redshifts. The high 24 micron detection fraction also
points to a luminous population. The power-law galaxies comprise a subset of
color-selected AGN candidates. A comparison with various mid-infrared color
selection criteria demonstrates that while the color-selected samples contain a
larger fraction of the X-ray luminous AGN, there is evidence that these
selection techniques also suffer from a higher degree of contamination by
star-forming galaxies in the deepest exposures. Considering only those
power-law galaxies detected in the X-ray catalog, we derive an obscured
fraction of 68% (2:1). Including all of the power-law galaxies suggests an
obscured fraction of < 81% (4:1).Comment: Accepted for publication in the Astrophysical Journal, 27 pages, 20
figures, 5 tables, version with high-resolution figures and online-only
tables available at: http://frodo.as.arizona.edu/~jdonley/powerlaw
Stellar populations in local star-forming galaxies. I.-Data and modelling procedure
We present an analysis of the integrated properties of the stellar
populations in the Universidad Complutense de Madrid Survey of Halpha-selected
galaxies. In this paper, the first of a series, we describe in detail the
techniques developed to model star-forming galaxies using a mixture of stellar
populations, and taking into account the observational uncertainties. We assume
a recent burst of star formation superimposed on a more evolved population. The
effects of the nebular continuum, line emission and dust attenuation are taken
into account. We also test different model assumptions including the choice of
specific evolutionary synthesis model, initial mass function, star formation
scenario and the treatment of dust extinction. Quantitative tests are applied
to determine how well these models fit our multi-wavelength observations for
the UCM sample. Our observations span the optical and near infrared, including
both photometric and spectroscopic data. Our results indicate that extinction
plays a key role in this kind of studies, revealing that low- and
high-extinction objects may require very different extinction laws and must be
treated differently. We also demonstrate that the UCM Survey galaxies are best
described by a short burst of star formation occurring within a quiescent
galaxy, rather than by continuous star formation. A detailed discussion on the
inferred parameters, such as the age, burst strength, metallicity, star
formation rate, extinction and total stellar mass for individual objects, is
presented in paper II of this series.Comment: 18 pages, 8 PostScript figures, minor changes to match the published
versio
Luminosity and Stellar Mass Functions of Local Star-Forming Galaxies
We present the optical and near-infrared luminosity and mass functions of the
local star-forming galaxies in the Universidad Complutense de Madrid Survey. A
bivariate method which explicitly deals with the Halpha selection of the survey
is used when estimating these functions. Total stellar masses have been
calculated on a galaxy-by-galaxy basis taking into account differences in star
formation histories. The main difference between the luminosity distributions
of the UCM sample and the luminosity functions of the local galaxy population
is a lower normalization (phi^*), indicating a lower global volume density of
UCM galaxies. The typical near-infrared luminosity (L^*) of local star-forming
galaxies is fainter than that of normal galaxies. This is a direct consequence
of the lower stellar masses of our objects. However, at optical wavelengths (B
and r) the luminosity enhancement arising from the young stars leads to M^*
values that are similar to those of normal galaxies. The fraction of the total
optical and near infrared luminosity density in the local Universe associated
with star-forming galaxies is 10-20%. Fitting the total stellar mass function
using a Schechter parametrization we obtain alpha=-1.15+/-0.15,
log({M}^*)=10.82+/-0.17 Msun and log(phi^*)=-3.04+/-0.20 Mpc^{-3}. This gives
an integrated total stellar mass density of 10^{7.83+/-0.07} Msun Mpc^{-3} in
local star-forming galaxies (H_0=70 km s^{-1} Mpc^{-1}, Omega_M=0.3,
Lambda=0.7). The volume-averaged burst strength of the UCM galaxies is
b=0.04+/-0.01, defined as the ratio of the mass density of stars formed in
recent bursts (age<10 Myr) to the total stellar mass density in UCM galaxies.
Finally, we derive that, in the local Universe, (13+/-3)% of the total baryon
mass density in the form of stars is associated with star-forming galaxies.Comment: 12 pages, 2 PostScript figures, published in ApJL. Minor changes to
match the published versio
- âŠ