1,036 research outputs found
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
1.65 micrometers (H-band) surface photometry of galaxies. III: observations of 558 galaxies with the TIRGO 1.5m telescope
We present near-infrared H-band (1.65 micron) surface photometry of 558
galaxies in the Coma Supercluster and in the Virgo cluster. This data set,
obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat
Infrared Telescope, is aimed at complementing, with observations of mostly
early-type objects, our NIR survey of spiral galaxies in these regions,
presented in previous papers of this series. Magnitudes at the optical radius,
total magnitudes, isophotal radii and light concentration indices are derived.
We confirm the existence of a positive correlation between the near-infrared
concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only
available in electronic form upon request to [email protected])Comment: 12 pages, 6 figures. Accepted for publication in A&A
Non-linear Dependence of L(B) on L(FIR) and M(H2) among Spiral Galaxies and Effects of Tidal Interaction
Through the study of a carefully selected sample of isolated spiral galaxies,
we have established that two important global physical quantities for tracing
star forming activities, L(FIR) and M(H2), have non-linear dependence on
another commonly cited global quantity L(B). Furthermore we show that simple
power law relations can effectively describe these non-linear relations for
spiral galaxies spanning four orders of magnitude in FIR and M(H2) and nearly
three orders of magnitude in L(B). While the existence of non-linear dependence
of M(H2) (assuming a constant CO-to-H2 conversion) and L(FIR) on optical
luminosity L(B) has been previously noted in the literature, an improper
normalization of simple scaling by L(B) has been commonly used in many previous
studies to claim enhanced molecular gas content and induced activities among
tidally interacting and other types of galaxies. We remove these non-linear
effects using the template relations derived from the isolated galaxy sample
and conclude that strongly interacting galaxies do not have enhanced molecular
gas content, contrary to previous claims. With these non-linear relations among
L(B), L(FIR) and M(H2) properly taken into account, we confirm again that the
FIR emission and the star formation efficiency L(FIR)/M(H2) are indeed enhanced
by tidal interactions. Virgo galaxies show the same level of M(H2) and L(FIR)
as isolated galaxies. We do not find any evidence for enhanced star forming
activity among barred galaxies.Comment: 19 pages and 5 figures, requires AAS style files, ApJ, accepte
The selective effect of environment on the atomic and molecular gas-to-dust ratio of nearby galaxies in the Herschel Reference Survey
We combine dust, atomic (HI) and molecular (H) hydrogen mass
measurements for 176 galaxies in the Herschel Reference Survey to investigate
the effect of environment on the gas-to-dust mass ()
ratio of nearby galaxies. We find that, at fixed stellar mass, the average
ratio varies by no more than a factor of 2
when moving from field to cluster galaxies, with Virgo galaxies being slightly
more dust rich (per unit of gas) than isolated systems. Remarkably, once the
molecular and atomic hydrogen phases are investigated separately, we find that
\hi-deficient galaxies have at the same time lower
ratio but higher ratio than \hi-normal systems. In
other words, they are poorer in atomic but richer in molecular hydrogen if
normalized to their dust content. By comparing our findings with the
predictions of theoretical models, we show that the opposite behavior observed
in the and ratios is
fully consistent with outside-in stripping of the interstellar medium (ISM),
and is simply a consequence of the different distribution of dust, \hi\ and
H across the disk. Our results demonstrate that the small environmental
variations in the total ratio, as well as in the
gas-phase metallicity, do not automatically imply that environmental mechanisms
are not able to affect the dust and metal content of the ISM in galaxies.Comment: 11 pages, 6 figures, 2 tables. Accepted for publication in MNRA
The Herschel Virgo Cluster Survey: II. Truncated dust disks in HI-deficient spirals
By combining Herschel-SPIRE observations obtained as part of the Herschel
Virgo Cluster Survey with 21 cm HI data from the literature, we investigate the
role of the cluster environment on the dust content of Virgo spiral galaxies.We
show for the first time that the extent of the dust disk is significantly
reduced in HI-deficient galaxies, following remarkably well the observed
'truncation' of the HI disk. The ratio of the submillimetre-to- optical
diameter correlates with the HI-deficiency, suggesting that the cluster
environment is able to strip dust as well as gas. These results provide
important insights not only into the evolution of cluster galaxies but also
into the metal enrichment of the intra-cluster medium.Comment: Letter accepted for publication in A&A (Herschel special issue
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
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
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 Ă
, 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
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