80 research outputs found
Properties of compact 250 μm emission and H II regions in M 33 (HERM33ES)
Aims. Within the framework of the HERM33ES key program, using the high resolution and sensitivity of the Herschel photometric
data, we study the compact emission in the Local Group spiral galaxy M33 to investigate the nature of the compact SPIRE emission
sources. We extracted a catalogue of sources at 250 μm in order to investigate the nature of this compact emission. Taking advantage
of the unprecedented Herschel resolution at these wavelengths, we also focus on a more precise study of some striking Hα shells in
the northern part of the galaxy.
Methods. We present a catalogue of 159 compact emission sources in M33 identified by SExtractor in the 250 μm SPIRE band that
is the one that provides the best spatial resolution. We also measured fluxes at 24 μm and Hα for those 159 extracted sources. The
morphological study of the shells also benefits from a multiwavelength approach including Hα, far-ultraviolet from GALEX, and
infrared from both Spitzer IRAC 8 μm and MIPS 24 μm in order to make comparisons.
Results. For the 159 compact sources selected at 250 μm, we find a very strong Pearson correlation coefficient with the MIPS 24 μm
emission (r_(24) = 0.94) and a rather strong correlation with the Hα emission, although with more scatter (r_(Hα) = 0.83). The morphological
study of the Hα shells shows a displacement between far-ultraviolet, Hα, and the SPIRE bands. The cool dust emission from
SPIRE clearly delineates the Hα shell structures.
Conclusions. The very strong link between the 250 μm compact emission and the 24 μm and Hα emissions, by recovering the star formation
rate from standard recipes for H II regions, allows us to provide star formation rate calibrations based on the 250 μm compact
emission alone. The different locations of the Hα and far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to
a dynamical age of a few Myr for the Hα shells and the associated cool dust
Properties of compact 250 \mu m emission and HII regions in M33 (HERM33ES)
Within the framework of the HERM33ES Key Project, using the high resolution
and sensitivity of the Herschel photometric data, we study the compact emission
in the Local Group spiral galaxy M33 to investigate the nature of the compact
SPIRE emission sources. We extracted a catalogue of sources at 250um in order
to investigate the nature of this compact emission. Taking advantage of the
unprecedented Herschel resolution at these wavelengths, we also focus on a more
precise study of some striking Halpha shells in the northern part of the
galaxy. We present a catalogue of 159 compact emission sources in M33
identified by SExtractor in the 250um SPIRE band that is the one that provides
the best spatial resolution. We also measured fluxes at 24um and Halpha for
those 159 extracted sources. The morphological study of the shells also
benefits from a multiwavelength approach including Halpha, far-UV from GALEX,
and infrared from both Spitzer IRAC 8um and MIPS 24um in order to make
comparisons. For the 159 compact sources selected at 250um, we find a very
strong Pearson correlation coefficient with the MIPS 24um emission (r24 = 0.94)
and a rather strong correlation with the Halpha emission, although with more
scatter (rHa = 0.83). The morphological study of the Halpha shells shows a
displacement between far-ultraviolet, Halpha, and the SPIRE bands. The cool
dust emission from SPIRE clearly delineates the Halpha shell structures. The
very strong link between the 250um compact emission and the 24um and Halpha
emissions, by recovering the star formation rate from standard recipes for HII
regions, allows us to provide star formation rate calibrations based on the
250um compact emission alone. The different locations of the Halpha and
far-ultraviolet emissions with respect to the SPIRE cool dust emission leads to
a dynamical age of a few Myr for the Halpha shells and the associated cool
dust.Comment: 4 pages, 3 figures, Accpeted for publication in the A&A Herschel
Special Issu
Cool gas and dust in M33: Results from the Herschel M33 extended survey (HERM33ES)
We present an analysis of the first space-based far-IR-submm observations of
M 33, which measure the emission from the cool dust and resolve the giant
molecular cloud complexes. With roughly half-solar abundances, M33 is a first
step towards young low-metallicity galaxies where the submm may be able to
provide an alternative to CO mapping to measure their H content. In this
Letter, we measure the dust emission cross-section using SPIRE and
recent CO and \HI\ observations; a variation in is present from a
near-solar neighborhood cross-section to about half-solar with the maximum
being south of the nucleus. Calculating the total H column density from the
measured dust temperature and cross-section, and then subtracting the \HI\
column, yields a morphology similar to that observed in CO. The H/\HI\ mass
ratio decreases from about unity to well below 10% and is about 15% averaged
over the optical disk. The single most important observation to reduce the
potentially large systematic errors is to complete the CO mapping of M 33.Comment: 5 pages, 5 figures Accepted for publication in Astronomy and
Astrophysic
Cool and warm dust emission from M33 (HerM33es)
We study the far-infrared emission from the nearby spiral galaxy M33 in order
to investigate the dust physical properties such as the temperature and the
luminosity density across the galaxy. Taking advantage of the unique wavelength
coverage (100, 160, 250, 350 and 500 micron) of the Herschel Space Observatory
and complementing our dataset with Spitzer-IRAC 5.8 and 8 micron and
Spitzer-MIPS 24 and 70 micron data, we construct temperature and luminosity
density maps by fitting two modified blackbodies of a fixed emissivity index of
1.5. We find that the 'cool' dust grains are heated at temperatures between 11
and 28 K with the lowest temperatures found in the outskirts of the galaxy and
the highest ones in the center and in the bright HII regions. The
infrared/submillimeter total luminosity (5 - 1000 micron) is estimated to be
1.9x10^9 Lsun. 59% of the total luminosity of the galaxy is produced by the
'cool' dust grains (~15 K) while the rest 41% is produced by 'warm' dust grains
(~55 K). The ratio of the cool-to-warm dust luminosity is close to unity
(within the computed uncertainties), throughout the galaxy, with the luminosity
of the cool dust being slightly enhanced in the center of the galaxy.
Decomposing the emission of the dust into two components (one emitted by the
diffuse disk of the galaxy and one emitted by the spiral arms) we find that the
fraction of the emission in the disk in the mid-infrared (24 micron) is 21%,
while it gradually rises up to 57% in the submillimeter (500 micron). We find
that the bulk of the luminosity comes from the spiral arm network that produces
70% of the total luminosity of the galaxy with the rest coming from the diffuse
dust disk. The 'cool' dust inside the disk is heated at a narrow range of
temperatures between 18 and 15 K (going from the center to the outer parts of
the galaxy).Comment: 12 pages, 14 figures, accepted for publication in A&
PACS and SPIRE photometer maps of M33: First results of the Herschel M33 extended survey (HERM33ES)
Within the framework of the HERM33ES key project, we are studying the star
forming interstellar medium in the nearby, metal-poor spiral galaxy M33,
exploiting the high resolution and sensitivity of Herschel. We use PACS and
SPIRE maps at 100, 160, 250, 350, and 500 micron wavelength, to study the
variation of the spectral energy distributions (SEDs) with galacto-centric
distance. Detailed SED modeling is performed using azimuthally averaged fluxes
in elliptical rings of 2 kpc width, out to 8 kpc galacto-centric distance.
Simple isothermal and two-component grey body models, with fixed dust
emissivity index, are fitted to the SEDs between 24 and 500 micron using also
MIPS/Spitzer data, to derive first estimates of the dust physical conditions.
The far-infrared and submillimeter maps reveal the branched, knotted spiral
structure of M33. An underlying diffuse disk is seen in all SPIRE maps (250-500
micron). Two component fits to the SEDs agree better than isothermal models
with the observed, total and radially averaged flux densities. The two
component model, with beta fixed at 1.5, best fits the global and the radial
SEDs. The cold dust component clearly dominates; the relative mass of the warm
component is less than 0.3% for all the fits. The temperature of the warm
component is not well constrained and is found to be about 60K plus/minus 10K.
The temperature of the cold component drops significantly from about 24K in the
inner 2 kpc radius to 13K beyond 6 kpc radial distance, for the best fitting
model. The gas-to-dust ratio for beta=1.5, averaged over the galaxy, is higher
than the solar value by a factor of 1.5 and is roughly in agreement with the
subsolar metallicity of M33.Comment: 5 pages, 3 figures, accepted for publication in the A&A Herschel
Special Issu
The Herschel M33 extended survey (HerM33es): PACS spectroscopy of the star forming region BCLMP 302
Context: The emission line of [CII] at 158 micron is one of the strongest
cooling lines of the interstellar medium (ISM) in galaxies. Aims: Disentangling
the relative contributions of the different ISM phases to [CII] emission, is a
major topic of the HerM33es program, a Herschel key project to study the ISM in
the nearby spiral galaxy M33. Methods: Using PACS, we have mapped the emission
of [CII] 158 micron, [OI] 63 micron, and other FIR lines in a 2'x2' region of
the northern spiral arm of M33, centered on the HII region BCLMP302. At the
peak of H-alpha emission, we have observed in addition a velocity resolved
[CII] spectrum using HIFI. We use scatterplots to compare these data with PACS
160 micron continuum maps, and with maps of CO and HI data, at a common
resolution of 12 arcsec or 50 pc. Maps of H-alpha and 24 micron emission
observed with Spitzer are used to estimate the SFR. We have created maps of the
[CII] and [OI] 63 micron emission and detected [NII] 122 micron and NIII 57
micron at individual positions. Results: The [CII] line observed with HIFI is
significantly broader than that of CO, and slightly blue-shifted. In addition,
there is little spatial correlation between [CII] observed with PACS and CO
over the mapped region. There is even less spatial correlation between [CII]
and the atomic gas traced by HI. Detailed comparison of the observed
intensities towards the HII region with models of photo ionization and photon
dominated regions, confirms that a significant fraction, 20--30%, of the
observed [CII] emission stems from the ionized gas and not from the molecular
cloud. The gas heating efficiency, using the ratio between [CII] and the TIR as
a proxy, varies between 0.07 and 1.5%, with the largest variations found
outside the HII region.Comment: Accepted for publication in A&A. 12 pages, 12 figure
100 mum and 160 mum emission as resolved star-formation rate estimators in M33 (HERM33ES)
Over the past few years several studies have provided estimates of the SFR
(star-formation rate) or the total infrared luminosity from just one infrared
band. However these relations are generally derived for entire galaxies, which
are known to contain a large scale diffuse emission that is not necessarily
related to the latest star-formation episode. We provide new relations to
estimate the SFR from resolved star-forming regions at 100 mum and 160 mum. We
select individual star-forming regions in the nearby (840 kpc) galaxy M33. We
estimate the SFR combining the emission in Halpha and at 24 mum to calibrate
the emission at 100 mum and 160 mum as SFR estimators, as mapped with
PACS/Herschel. The data are obtained in the framework of the HERM33ES open time
key project. There is less emission in the HII regions at 160 mum than at 100
mum. Over a dynamic range of almost 2 dex in Sigma(SFR) we find that the 100
mum emission is a nearly linear estimator of the SFR, whereas that at 160 mum
is slightly superlinear. The behaviour of individual star-forming regions is
surprisingly similar to that of entire galaxies. At high Sigma(SFR), star
formation drives the dust temperature, whereas uncertainties and variations in
radiation-transfer and dust-heated processes dominate at low Sigma(SFR).
Detailed modelling of both galaxies and individual star forming regions will be
needed to interpret similarities and differences between the two and assess the
fraction of diffuse emission in galaxies.Comment: 5 pages, 3 figures, accepted for publication in the A&A Herschel
special issu
Globules and pillars in Cygnus X: III. <i>Herschel</i> and upGREAT/SOFIA far-infrared spectroscopy of the globule IRAS 20319+3958 in Cygnus X
IRAS 20319+3958 in Cygnus X South is a rare example of a free-floating globule (mass ~240 M⊙, length ~1.5 pc) with an internal H II region created by the stellar feedback of embedded intermediate-mass stars, in particular, one Herbig Be star. In Schneider et al. 2012, (A&A, 542, L18) and Djupvik et al. 2017, (A&A, 599, A37), we proposed that the emission of the far-infrared (FIR) lines of [C II] at 158 μm and [O I] at 145 μm in the globule head are mostly due to an internal photodissociation region (PDR). Here, we present a Herschel/HIFI [C II] 158 μm map of the whole globule and a large set of other FIR lines (mid-to high-J CO lines observed with Herschel/PACS and SPIRE, the [O I] 63 μm line and the 12CO 16→15 line observed with upGREAT on SOFIA), covering the globule head and partly a position in the tail. The [C II] map revealed that the whole globule is probably rotating. Highly collimated, high-velocity [C II] emission is detected close to the Herbig Be star. We performed a PDR analysis using the KOSMA-τ PDR code for one position in the head and one in the tail. The observed FIR lines in the head can be reproduced with a two-component model: an extended, non-clumpy outer PDR shell and a clumpy, dense, and thin inner PDR layer, representing the interface between the H II region cavity and the external PDR. The modelled internal UV field of ~2500 G° is similar to what we obtained from the Herschel FIR fluxes, but lower than what we estimated from the census of the embedded stars. External illumination from the ~30 pc distant Cyg OB2 cluster, producing an UV field of ~150–600 G° as an upper limit, is responsible for most of the [C II] emission. For the tail, we modelled the emission with a non-clumpy component, exposed to a UV-field of around 140 G°
Dust and gas power-spectrum in M33 (HERM33ES)
Power spectra of de-projected images of late-type galaxies in gas and/or dust
emission are very useful diagnostics of the dynamics and stability of their
interstellar medium. Previous studies have shown that the power spectra can be
approximated as two power-laws, a shallow one at large scales (larger than 500
pc) and a steeper one at small scales, with the break between the two
corresponding to the line-of-sight thickness of the galaxy disk. We present a
thorough analysis of the power spectra of the dust and gas emission at several
wavelengths in the nearby galaxy M33. In particular, we use the recently
obtained images at five wavelengths by PACS and SPIRE onboard Herschel. The
large dynamical range (2-3 dex in scale) of most images allow us to determine
clearly the change in slopes from -1.5 to -4, with some variations with
wavelength. The break scale is increasing with wavelength, from 100 pc at 24
and 100micron to 350 pc at 500micron, suggesting that the cool dust lies in a
thicker disk than the warm dust, may be due to star formation more confined to
the plane. The slope at small scale tends to be steeper at longer wavelength,
meaning that the warmer dust is more concentrated in clumps. Numerical
simulations of an isolated late-type galaxy, rich in gas and with no bulge,
like M33, are carried out, in order to better interpret these observed results.
Varying the star formation and feedback parameters, it is possible to obtain a
range of power-spectra, with two power-law slopes and breaks, which nicely
bracket the data. The small-scale power-law is indeed reflecting the 3D
behaviour of the gas layer, steepening strongly while the feedback smoothes the
structures, by increasing the gas turbulence. M33 appears to correspond to a
fiducial model with an SFR of 0.7 Mo/yr, with 10% supernovae energy
coupled to the gas kinematics.Comment: 11 pages, 24 figures, accepted in Astronomy & Astrophysic
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