228 research outputs found
A Multi-wavelength MOCASSIN Model of the Magellanic-type Galaxy NGC 4449
We use the photoionisation and dust radiative transfer code MOCASSIN to
create a model of the dwarf irregular galaxy NGC 4449. The best-matching model
reproduces the global optical emission line fluxes and the observed spectral
energy distribution (SED) spanning wavelengths from the UV to sub-mm, and
requires the bolometric luminosity of 6.25e9 Lsolar for the underlying stellar
component, M_d/M_g of 1/680 and M_d of 2.2e6 Msolar.Comment: 4 pages, 4 figures, submitted to Proceedings of the IAU Symposium
284: The Spectral Energy Distribution of Galaxies (SED2011
The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey
The dust in nearby galaxies absorbs a fraction of the
UV-optical-near-infrared radiation produced by stars. This energy is
consequently re-emitted in the infrared. We investigate the portion of the
stellar radiation absorbed by spiral galaxies from the HRS by modelling their
UV-to-submillimetre spectral energy distributions. Our models provide an
attenuated and intrinsic SED from which we find that on average 32 % of all
starlight is absorbed by dust. We define the UV heating fraction as the
percentage of dust luminosity that comes from absorbed UV photons and find that
this is 56 %, on average. This percentage varies with morphological type, with
later types having significantly higher UV heating fractions. We find a strong
correlation between the UV heating fraction and specific star formation rate
and provide a power-law fit. Our models allow us to revisit the IRX-AFUV
relations, and derive these quantities directly within a self-consistent
framework. We calibrate this relation for different bins of NUV-r colour and
provide simple relations to relate these parameters. We investigated the
robustness of our method and we conclude that the derived parameters are
reliable within the uncertainties which are inherent to the adopted SED model.
This calls for a deeper investigation on how well extinction and attenuation
can be determined through panchromatic SED modelling.Comment: 14 pages, 7 figures. Accepted for publication in Astronomy &
Astrophysic
Spin polarized electric currents in semiconductor heterostructures induced by microwave radiation
We report on microwave (mw) radiation induced electric currents in
(Cd,Mn)Te/(Cd,Mg)Te and InAs/(In,Ga)As quantum wells subjected to an external
in-plane magnetic field. The current generation is attributed to the
spin-dependent energy relaxation of electrons heated by mw radiation. The
relaxation produces equal and oppositely directed electron flows in the spin-up
and spin-down subbands yielding a pure spin current. The Zeeman splitting of
the subbands in the magnetic field leads to the conversion of the spin flow
into a spin-polarized electric current.Comment: 3 pages, 4 figure
The physical characteristics of the gas in the disk of Centaurus A using the Herschel Space Observatory
We search for variations in the disk of Centaurus A of the emission from
atomic fine structure lines using Herschel PACS and SPIRE spectroscopy. In
particular we observe the [C II](158 m), [N II](122 and 205 m), [O
I](63 and 145 m) and [O III](88 m) lines, which all play an important
role in cooling the gas in photo-ionized and photodissociation regions. We
determine that the ([C II]+[O I])/ line ratio, a proxy for the
heating efficiency of the gas, shows no significant radial trend across the
observed region, in contrast to observations of other nearby galaxies. We
determine that 10 - 20% of the observed [C II] emission originates in ionized
gas. Comparison between our observations and a PDR model shows that the
strength of the far-ultraviolet radiation field, , varies between
and and the hydrogen nucleus density varies between
and cm, with no significant radial trend in
either property. In the context of the emission line properties of the
grand-design spiral galaxy M51 and the elliptical galaxy NGC 4125, the gas in
Cen A appears more characteristic of that in typical disk galaxies rather than
elliptical galaxies.Comment: Accepted for publication in the Astrophysical Journal. 22 pages, 10
figures, 5 table
Linking dust emission to fundamental properties in galaxies: The low-metallicity picture
In this work, we aim at providing a consistent analysis of the dust
properties from metal-poor to metal-rich environments by linking them to
fundamental galactic parameters. We consider two samples of galaxies: the Dwarf
Galaxy Survey (DGS) and KINGFISH, totalling 109 galaxies, spanning almost 2 dex
in metallicity. We collect infrared (IR) to submillimetre (submm) data for both
samples and present the complete data set for the DGS sample. We model the
observed spectral energy distributions (SED) with a physically-motivated dust
model to access the dust properties. Using a different SED model (modified
blackbody), dust composition (amorphous carbon), or wavelength coverage at
submm wavelengths results in differences in the dust mass estimate of a factor
two to three, showing that this parameter is subject to non-negligible
systematic modelling uncertainties. For eight galaxies in our sample, we find a
rather small excess at 500 microns (< 1.5 sigma). We find that the dust SED of
low-metallicity galaxies is broader and peaks at shorter wavelengths compared
to more metal-rich systems, a sign of a clumpier medium in dwarf galaxies. The
PAH mass fraction and the dust temperature distribution are found to be driven
mostly by the specific star-formation rate, SSFR, with secondary effects from
metallicity. The correlations between metallicity and dust mass or total-IR
luminosity are direct consequences of the stellar mass-metallicity relation.
The dust-to-stellar mass ratios of metal-rich sources follow the well-studied
trend of decreasing ratio for decreasing SSFR. The relation is more complex for
highly star-forming low-metallicity galaxies and depends on the chemical
evolutionary stage of the source (i.e., gas-to-dust mass ratio). Dust growth
processes in the ISM play a key role in the dust mass build-up with respect to
the stellar content at high SSFR and low metallicity. (abridged)Comment: 44 pages (20 pages main body plus 5 Appendices), 11 figures, 9
tables, accepted for publication in A&
Insights into gas heating and cooling in the disc of NGC 891 from Herschel far-infrared spectroscopy
We present Herschel PACS and SPIRE spectroscopy of the most important
far-infrared cooling lines in the nearby edge-on spiral galaxy, NGC 891: [CII]
158 m, [NII] 122, 205 m, [OI] 63, 145 m, and [OIII] 88 m.
We find that the photoelectric heating efficiency of the gas, traced via the
([CII]+[OII]63)/ ratio, varies from a mean of
3.510 in the centre up to 810 at increasing
radial and vertical distances in the disc. A decrease in
([CII]+[OII]63)/ but constant
([CII]+[OI]63)/ with increasing FIR colour suggests that
polycyclic aromatic hydrocarbons (PAHs) may become important for gas heating in
the central regions. We compare the observed flux of the FIR cooling lines and
total IR emission with the predicted flux from a PDR model to determine the gas
density, surface temperature and the strength of the incident far-ultraviolet
(FUV) radiation field, . Resolving details on physical scales of ~0.6
kpc, a pixel-by-pixel analysis reveals that the majority of the PDRs in NGC
891's disc have hydrogen densities of 1 < log (/cm) < 3.5
experiencing an incident FUV radiation field with strengths of 1.7 < log
< 3. Although these values we derive for most of the disc are consistent with
the gas properties found in PDRs in the spiral arms and inter-arm regions of
M51, observed radial trends in and are shown to be sensitive to
varying optical thickness in the lines, demonstrating the importance of
accurately accounting for optical depth effects when interpreting observations
of high inclination systems. With an empirical relationship between the MIPS 24
m and [NII] 205 m emission, we estimate an enhancement of the FUV
radiation field strength in the far north-eastern side of the disc.Comment: Accepted for publication in A&A. 25 pages, including 17 figures and 3
tables, abstract abridged for arXi
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