3,196 research outputs found
The spectral energy distribution of galaxies at z > 2.5: Implications from the Herschel/SPIRE color-color diagram
We use the Herschel SPIRE color-color diagram to study the spectral energy
distribution (SED) and the redshift estimation of high-z galaxies. We compiled
a sample of 57 galaxies with spectroscopically confirmed redshifts and SPIRE
detections in all three bands at , and compared their average SPIRE
colors with SED templates from local and high-z libraries. We find that local
SEDs are inconsistent with high-z observations. The local calibrations of the
parameters need to be adjusted to describe the average colors of high-z
galaxies. For high-z libraries, the templates with an evolution from z=0 to 3
can well describe the average colors of the observations at high redshift.
Using these templates, we defined color cuts to divide the SPIRE color-color
diagram into different regions with different mean redshifts. We tested this
method and two other color cut methods using a large sample of 783
Herschel-selected galaxies, and find that although these methods can separate
the sample into populations with different mean redshifts, the dispersion of
redshifts in each population is considerably large. Additional information is
needed for better sampling.Comment: 17 pages, 14 figures, accepted for publication in A&
The infrared emission of ultraviolet selected galaxies from z = 0 to z=1
We select galaxies in UV rest-frame at z=0, z~0.7 and z~1 together with a
sample of LBGs at z~1, the samples are built in order to sample the same range
of luminosity at any redshift. The evolution of the IR and UV luminosities with
z is analysed for individual galaxies as well as in terms of luminosity
functions. The L_IR/L_UV ratio is used to measure dust attenuation. This ratio
does not exhibit a strong evolution with z for the bulk of our sample galaxies
but some trends are found for galaxies with a strong dust attenuation and for
UV luminous sources: galaxies with L_IR/L_UV>10 are more frequent at z>0 than
at z=0 and the largest values of L_IR/L_UV are found for UV faint objects;
conversely the most luminous galaxies of our samples (L_UV> 2 10^{10} L_sun$),
detected at z=1, exhibit a lower dust attenuation than the fainter ones.
L_IR/L_UV increases with the K rest-frame luminosity of the galaxies at all the
redshifts considered and shows a residual anti-correlation with L_UV. The most
massive and UV luminous galaxies exhibit quite large specific star formation
rates. LBGs exhibit systematically lower dust attenuation than UV selected
galaxies of same luminosity but similar specific star formation rates. The
analysis of the UV+IR luminosity functions leads to the conclusion that up to z
= 1 most of the star formation activity of UV selected galaxies is emitted in
IR. Whereas we are able to retrieve all the star formation from our UV
selection at z=0.7, at z = 1 we miss a large fraction of galaxies more luminous
than ~ 10^{11} L_sun. The effect is found larger for Lyman Break Galaxies.Comment: 13 pages. accepted for publication (Astronomy and Astrophysics
The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569
We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster
The IRX-beta relation on sub-galactic scales in star-forming galaxies of the Herschel Reference Survey
UV and optical surveys are essential to gain insight into the processes
driving galaxy formation and evolution. The rest-frame UV emission is key to
measure the cosmic SFR. However, UV light is strongly reddened by dust. In
starburst galaxies, the UV colour and the attenuation are linked, allowing to
correct for dust extinction. Unfortunately, evidence has been accumulating that
the relation between UV colour and attenuation is different for normal
star-forming galaxies when compared to starburst galaxies. It is still not
understood why star-forming galaxies deviate from the UV colour-attenuation
relation of starburst galaxies. Previous work and models hint that the role of
the shape of the attenuation curve and the age of stellar populations have an
important role. In this paper we aim at understanding the fundamental reasons
to explain this deviation. We have used the CIGALE SED fitting code to model
the far UV to the far IR emission of a set of 7 reasonably face-on spiral
galaxies from the HRS. We have explored the influence of a wide range of
physical parameters to quantify their influence and impact on the accurate
determination of the attenuation from the UV colour, and why normal galaxies do
not follow the same relation as starburst galaxies. We have found that the
deviation can be best explained by intrinsic UV colour differences between
different regions in galaxies. Variations in the shape of the attenuation curve
can also play a secondary role. Standard age estimators of the stellar
populations prove to be poor predictors of the intrinsic UV colour. These
results are also retrieved on a sample of 58 galaxies when considering their
integrated fluxes. When correcting the emission of normal star-forming galaxies
for the attenuation, it is crucial to take into account possible variations in
the intrinsic UV colour as well as variations of the shape of the attenuation
curve.Comment: Accepted for publication in A&A, 18 pages, 14 figures. The paper with
high resolution figures can be downloaded at
http://www.oamp.fr/people/mboquien/HRS/boquien_IRX_beta.pd
UV Dust Attenuation in Star-forming Galaxies: II Calibrating the A(UV) vs. L_TIR/L_UV relation
We investigate the dependence of the total-infrared (TIR) to UV luminosity
ratio method for calculating the UV dust attenuation A(UV) from the age of the
underlying stellar populations by using a library of spectral energy
distributions for galaxies with different star formation histories. Our
analysis confirms that the TIR/UV vs. A(UV) relation varies significantly with
the age of the underlying stellar population: i.e. for the same TIR/UV ratio,
systems with low specific star formation rate (SSFR) suffer a lower UV
attenuation than starbursts. Using a sample of nearby field and cluster spiral
galaxies we show that the use of a standard (i.e. age independent) TIR/UV vs.
A(UV) relation leads to a systematic overestimate up to 2 magnitudes of the
amount of UV dust attenuation suffered by objects with low SSFR and in
particular HI-deficient star forming cluster galaxies. This result points out
that the age independent vs. relation cannot be used to study
the UV properties of large samples of galaxies including low star-forming
systems and passive spirals. Therefore we give some simple empirical relations
from which the UV attenuation can be estimated taking into account its
dependence on the age of the stellar populations, providing a less biased view
of UV properties of galaxies.Comment: 16 pages, 10 figures, 6 tables. Accepted for publication on MNRAS
main journal. High resolution version and tables also available at
http://www.astro.cf.ac.uk/pub/Luca.Cortese/UVattenuation.htm
AKARI/IRC Broadband Mid-infrared data as an indicator of Star Formation Rate
AKARI/Infrared Camera (IRC) Point Source Catalog provides a large amount of
flux data at {\it S9W} () and {\it L18W} ()
bands. With the goal of constructing Star-Formation Rate(SFR) calculations
using IRC data, we analyzed an IR selected
GALEX-SDSS-2MASS-AKARI(IRC/Far-Infrared Surveyor) sample of 153 nearby
galaxies. The far-infrared fluxes were obtained from AKARI diffuse maps to
correct the underestimation for extended sources raised by the point-spread
function photometry. SFRs of these galaxies were derived by the spectral energy
distribution fitting program CIGALE. In spite of complicated features contained
in these bands, both the {\it S9W} and {\it L18W} emission correlate with the
SFR of galaxies. The SFR calibrations using {\it S9W} and {\it L18W} are
presented for the first time. These calibrations agree well with previous works
based on Spitzer data within the scatters, and should be applicable to
dust-rich galaxies.Comment: PASJ, in pres
Towards understanding the relation between the gas and the attenuation in galaxies at kpc scales
[abridged]
Aims. The aim of the present paper is to provide new and more detailed
relations at the kpc scale between the gas surface density and the face-on
optical depth directly calibrated on galaxies, in order to compute the
attenuation not only for semi-analytic models but also observationally as new
and upcoming radio observatories are able to trace gas ever farther in the
Universe.
Methods. We have selected a sample of 4 nearby resolved galaxies and a sample
of 27 unresolved galaxies from the Herschel Reference Survey and the Very
Nearby Galaxies Survey, for which we have a large set of multi-wavelength data
from the FUV to the FIR including metallicity gradients for resolved galaxies,
along with radio HI and CO observations. For each pixel in resolved galaxies
and for each galaxy in the unresolved sample, we compute the face-on optical
depth from the attenuation determined with the CIGALE SED fitting code and an
assumed geometry. We determine the gas surface density from HI and CO
observations with a metallicity-dependent XCO factor.
Results. We provide new, simple to use, relations to determine the face-on
optical depth from the gas surface density, taking the metallicity into
account, which proves to be crucial for a proper estimate. The method used to
determine the gas surface density or the face-on optical depth has little
impact on the relations except for galaxies that have an inclination over 50d.
Finally, we provide detailed instructions on how to compute the attenuation
practically from the gas surface density taking into account possible
information on the metallicity.
Conclusions. Examination of the influence of these new relations on simulated
FUV and IR luminosity functions shows a clear impact compared to older oft-used
relations, which in turn could affect the conclusions drawn from studies based
on large scale cosmological simulations.Comment: 24 pages, 21 figures, accepted for publication in A&
Star formation and dust extinction properties of local galaxies from AKARI-GALEX All-Sky Surveys: First results from most secure multiband sample from FUV to FIR
The AKARI All-Sky Survey provided the first bright point source catalog
detected at 90um. Starting from this catalog, we selected galaxies by matching
AKARI sources with those in the IRAS PSCz. Next, we have measured total GALEX
FUV and NUV flux densities. Then, we have matched this sample with SDSS and
2MASS galaxies. By this procedure, we obtained the final sample which consists
of 607 galaxies. If we sort the sample with respect to 90um, their average SED
shows a coherent trend: the more luminous at 90um, the redder the global SED
becomes. The M_r--NUV-r color-magnitude relation of our sample does not show
bimodality, and the distribution is centered on the green valley between the
blue cloud and red sequence seen in optical surveys. We have established
formulae to convert FIR luminosity from AKARI bands to the total infrared (IR)
luminosity L_TIR. With these formulae, we calculated the star formation
directly visible with FUV and hidden by dust. The luminosity related to star
formation activity (L_SF) is dominated by L_TIR even if we take into account
the far-infrared (FIR) emission from dust heated by old stars. At high star
formation rate (SFR) (> 20 Msun yr^-1), the fraction of directly visible SFR,
SFR_FUV, decreases. We also estimated the FUV attenuation A_FUV from
FUV-to-total IR (TIR) luminosity ratio. We also examined the L_TIR/L_FUV-UV
slope (FUV- NUV) relation. The majority of the sample has L_TIR/L_FUV ratios 5
to 10 times lower than expected from the local starburst relation, while some
LIRGs and all the ULIRGs of this sample have higher L_TIR/L_FUV ratios. We
found that the attenuation indicator L_TIR/L_FUV is correlated to the stellar
mass of galaxies, M*, but there is no correlation with specific SFR (SSFR),
SFR/M*, and dust attenuation L_TIR/L_FUV. (abridged)Comment: 13 pages, 18 figures, accepted for publication in A&
Star Formation in Galaxies Along the Hubble Sequence
Observations of star formation rates (SFRs) in galaxies provide vital clues
to the physical nature of the Hubble sequence, and are key probes of the
evolutionary properties of galaxies. The focus of this review is on the broad
patterns in the star formation properties of galaxies along the Hubble
sequence, and their implications for understanding galaxy evolution and the
physical processes that drive the evolution. Star formation in the disks and
nuclear regions of galaxies are reviewed separately, then discussed within a
common interpretive framework. The diagnostic methods used to measure SFRs are
also reviewed, and a self-consistent set of SFR calibrations is presented as an
aid to workers in the field.Comment: 41 pages, with 9 figures. To appear in Volume 36 of the Annual Review
of Astronomy and Astrophysic
High mass star formation in normal late-type galaxies: observational constraints to the IMF
We use Halpha and FUV GALEX data for a large sample of nearby objects to
study the high mass star formation activity of normal late-type galaxies. The
data are corrected for dust attenuation using the most accurate techniques at
present available, namely the Balmer decrement and the total far-infrared to
FUV flux ratio. The sample shows a highly dispersed distribution in the Halpha
to FUV flux ratio indicating that two of the most commonly used star formation
tracers give star formation rates with uncertainties up to a factor of 2-3. The
high dispersion is due to the presence of AGN, where the UV and the Halpha
emission can be contaminated by nuclear activity, highly inclined galaxies, for
which the applied extinction corrections are probably inaccurate, or starburst
galaxies, where the stationarity in the star formation history required for
transforming Halpha and UV luminosities into star formation rates is not
satisfied. Excluding these objects we reach an uncertainty of ~50% on the SFR.
The Halpha to FUV flux ratio increases with their total stellar mass. If
limited to normal star forming galaxies, however, this relationship reduces to
a weak trend that might be totally removed using different extinction
correction recipes. In these objects the Halpha to FUV flux ratio seems also
barely related with the FUV-H colour, the H band effective surface brightness,
the total star formation activity and the gas fraction. The data are consistent
with a Kroupa and Salpeter initial mass function in the high mass stellar range
and imply, for a Salpeter IMF, that the variations of the slope cannot exceed
0.25, from g=2.35 for massive galaxies to g=2.60 in low luminosity systems. We
show however that these observed trends, if real, can be due to the different
micro history of star formation in massive galaxies with respect to dwarf.Comment: Accepted for publication on Ap
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