1,637 research outputs found
The Herschel Comprehensive (U)LIRG Emission Survey (HERCULES): CO Ladders, Fine Structure Lines, and Neutral Gas Cooling
(Ultra) luminous infrared galaxies ((U)LIRGs) are objects characterized by their extreme infrared (8-1000 μm) luminosities (L_(LIRG) > 10^(11) L_☉ and L_(ULIRG) > 10^(12) L_☉). The Herschel Comprehensive ULIRG Emission Survey (PI: van der Werf) presents a representative flux-limited sample of 29 (U)LIRGs that spans the full luminosity range of these objects (10^(11) L_☉ ≤ L_(IR) ≤ 10^(13) L_☉). With the Herschel Space Observatory, we observe [C II] 157 μm, [O I] 63 μm, and [O I] 145 μm line emission with Photodetector Array Camera and Spectrometer, CO J = 4-3 through J = 13-12, [C I] 370 μm, and [C I] 609 μm with SPIRE, and low-J CO transitions with ground-based telescopes. The CO ladders of the sample are separated into three classes based on their excitation level. In 13 of the galaxies, the [O I] 63 μm emission line is self absorbed. Comparing the CO excitation to the InfraRed Astronomical Satellite 60/100 μm ratio and to far infrared luminosity, we find that the CO excitation is more correlated to the far infrared colors. We present cooling budgets for the galaxies and find fine-structure line flux deficits in the [C II], [Si II], [O I], and [C I] lines in the objects with the highest far IR fluxes, but do not observe this for CO 4 ≤ J_(upp) ≤ 13. In order to study the heating of the molecular gas, we present a combination of three diagnostic quantities to help determine the dominant heating source. Using the CO excitation, the CO J = 1-0 linewidth, and the active galactic nucleus (AGN) contribution, we conclude that galaxies with large CO linewidths always have high-excitation CO ladders, and often low AGN contributions, suggesting that mechanical heating is important
Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program II. Activity and radial velocity
Due to their low mass and luminosity, M dwarfs are ideal targets if one hopes
to find low-mass planets similar to Earth by using the radial velocity (RV)
method. However, stellar magnetic cycles could add noise or even mimic the RV
signal of a long-period companion. Following our previous work that studied the
correlation between activity cycles and long-term RV variations for K dwarfs we
now expand that research to the lower-end of the main sequence. Our objective
is to detect any correlations between long-term activity variations and the
observed RV of a sample of M dwarfs. We used a sample of 27 M-dwarfs with a
median observational timespan of 5.9 years. The cross-correlation function
(CCF) with its parameters RV, bisector inverse slope (BIS), full-width-at-half-
maximum (FWHM) and contrast have been computed from the HARPS spectrum. The
activity index have been derived using the Na I D doublet. These parameters
were compared with the activity level of the stars to search for correlations.
We detected RV variations up to ~5 m/s that we can attribute to activity cycle
effects. However, only 36% of the stars with long-term activity variability
appear to have their RV affected by magnetic cycles, on the typical timescale
of ~6 years. Therefore, we suggest a careful analysis of activity data when
searching for extrasolar planets using long-timespan RV data.Comment: 20 pages, 12 figures, 3 tables, accepted for publication in Astronomy
and Astophysic
Understanding the 8 micron vs. Pa-alpha relationship on sub-arcsecond scales in Luminous Infrared Galaxies
This work explores in detail the relation between the 8 micron and the
Pa-alpha emissions for 122 HII regions identified in a sample of 10 low-z LIRGs
with nearly constant metallicity (12 + log (O/H) ~ 8.8). We use Gemini/T-ReCS
high-spatial resolution (<~ 0.4" ~ 120 pc for the average distance of 60 Mpc of
our sample) mid-infrared imaging (at 8.7 micron or 10.3 micron) together with
HST/NICMOS continuum and Pa-alpha images. The LIRG HII regions extend the
L_8micron vs. L_Pa-alpha relation found for HII knots in the high-metallicity
SINGS galaxies by about two orders of magnitude to higher luminosities. Since
the metallicity of the LIRG sample is nearly constant, we can rule out this
effect as a cause for the scatter seen in the relationship. In turn, it is
attributed to two effects: age and PAH features. The L_8micron/L_Pa-alpha
ratio, which varies by a factor of ten for the LIRG HII regions, is reproduced
by a model with instantaneous star formation and ages ranging from ~ 4 to 7.5
Myr. The remaining dispersion around the model predictions for a given age is
probably due to differential contributions of the PAH features (the 8.6 micron,
in our case) to the 8 micron emission from galaxy to galaxy.Comment: 16 pages, 9 figures, accepted for publication in ApJ; paper with
full-resolution figures can be found at:
http://damir.iem.csic.es/extragalactic
Spitzer IRS Spectral Mapping of the Toomre Sequence: Spatial Variations of PAH, Gas, and Dust Properties in Nearby Major Mergers
We have mapped the key mid-IR diagnostics in eight major merger systems of
the Toomre Sequence (NGC4676, NGC7592, NGC6621, NGC2623, NGC6240, NGC520,
NGC3921, and NGC7252) using the Spitzer Infrared Spectrograph (IRS). With these
maps, we explore the variation of the ionized-gas, PAH, and warm-gas (H_2)
properties across the sequence and within the galaxies. While the global PAH
interband strength and ionized gas flux ratios ([Ne III]/[Ne II]) are similar
to those of normal star forming galaxies, the distribution of the spatially
resolved PAH and fine structure line flux ratios is significant different from
one system to the other. Rather than a constant H_2/PAH flux ratio, we find
that the relation between the H_2 and PAH fluxes is characterized by a power
law with a roughly constant exponent (0.61+/-0.05) over all merger components
and spatial scales. While following the same power law on local scales, three
galaxies have a factor of ten larger integrated (i.e. global) H_2/PAH flux
ratio than the rest of the sample, even larger than what it is in most nearby
AGNs. These findings suggest a common dominant excitation mechanism for H_2
emission over a large range of global H_2/PAH flux ratios in major mergers.
Early merger systems show a different distribution between the cold (CO J=1-0)
and warm (H_2) molecular gas component, which is likely due to the merger
interaction. Strong evidence for buried star formation in the overlap region of
the merging galaxies is found in two merger systems (NGC6621 and NGC7592) as
seen in the PAH, [Ne II], [Ne III], and warm gas line emission, but with no
apparent corresponding CO (J=1-0) emission. Our findings also demonstrate that
the variations of the physical conditions within a merger are much larger than
any systematic trends along the Toomre Sequence.Comment: 35 pages, accepted for publication in ApJ
Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS
We present the results of a {\it Hubble Space Telescope} ACS/HRC FUV, ACS/WFC
optical study into the cluster populations of a sample of 22 Luminous Infrared
Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated
broadband photometry we have derived ages and masses for a total of 484 star
clusters contained within these systems. This allows us to examine the
properties of star clusters found in the extreme environments of LIRGs relative
to lower luminosity star-forming galaxies in the local Universe. We find that
by adopting a Bruzual \& Charlot simple stellar population (SSP) model and
Salpeter initial mass function, the age distribution of clusters declines as
, consistent with the age distribution derived
for the Antennae Galaxies, and interpreted as evidence for rapid cluster
disruption occuring in the strong tidal fields of merging galaxies. The large
number of young clusters identified in the sample also
suggests that LIRGs are capable of producing more high-mass clusters than what
is observed to date in any lower luminosity star-forming galaxy in the local
Universe. The observed cluster mass distribution of is consistent with the canonical -2 power law used to describe the
underlying initial cluster mass function (ICMF) for a wide range of galactic
environments. We interpret this as evidence against mass-dependent cluster
disruption, which would flatten the observed CMF relative to the underlying
ICMF distribution.Comment: 63 pages, 58 Figures, 56 Tables, Accepted for publication in Ap
Local Luminous Infrared Galaxies. I. Spatially resolved observations with Spitzer/IRS
We present results from the Spitzer/IRS spectral mapping observations of 15
local luminous infrared galaxies (LIRGs). In this paper we investigate the
spatial variations of the mid-IR emission which includes: fine structure lines,
molecular hydrogen lines, polycyclic aromatic features (PAHs), continuum
emission and the 9.7um silicate feature. We also compare the nuclear and
integrated spectra. We find that the star formation takes place in extended
regions (several kpc) as probed by the PAH emission as well as the [NeII] and
[NeIII] emissions. The behavior of the integrated PAH emission and 9.7um
silicate feature is similar to that of local starburst galaxies. We also find
that the minima of the [NeIII]/[NeII] ratio tends to be located at the nuclei
and its value is lower than that of HII regions in our LIRGs and nearby
galaxies. It is likely that increased densities in the nuclei of LIRGs are
responsible for the smaller nuclear [NeIII]/[NeII] ratios. This includes the
possibility that some of the most massive stars in the nuclei are still
embedded in ultracompact HII regions. In a large fraction of our sample the
11.3um PAH emission appears more extended than the dust 5.5um continuum
emission. We find a dependency of the 11.3um PAH/7.7 um PAH and [NeII]/11.3um
PAH ratios with the age of the stellar populations. Smaller and larger ratios
respectively indicate recent star formation. The estimated warm (300 K < T <
1000 K) molecular hydrogen masses are of the order of 10^8 M_Sun, which are
similar to those found in ULIRGs, local starbursts and Seyfert galaxies.
Finally we find that the [NeII] velocity fields for most of the LIRGs in our
sample are compatible with a rotating disk at ~kpc scales, and they are in a
good agreement with H-alpha velocity fields.Comment: Comments: 52 pages, accepted for publicacion in ApJ
The Spatial Extent of (U)LIRGs in the mid-Infrared I: The Continuum Emission
We present an analysis of the extended mid-infrared (MIR) emission of the
Great Observatories All-Sky LIRG Survey (GOALS) sample based on 5-15um low
resolution spectra obtained with the IRS on Spitzer. We calculate the fraction
of extended emission as a function of wavelength for the galaxies in the
sample, FEE_lambda. We can identify 3 general types of FEE_lambda: one where it
is constant, one where features due to emission lines and PAHs appear more
extended than the continuum, and a third which is characteristic of sources
with deep silicate absorption at 9.7um. More than 30% of the galaxies have a
median FEE_lambda larger than 0.5 implying that at least half of their MIR
emission is extended. Luminous Infrared Galaxies (LIRGs) display a wide range
of FEE in their warm dust continuum (0<=FEE_13.2um<=0.85). The large values of
FEE_13.2um that we find in many LIRGs suggest that their extended MIR continuum
emission originates in scales up to 10kpc. The mean size of the LIRG cores at
13.2um is 2.6kpc. However, once the LIR of the systems reaches the threshold of
~10^11.8Lsun, all sources become clearly more compact, with FEE_13.2um<=0.2,
and their cores are unresolved. Our estimated upper limit for the core size of
ULIRGs is less than 1.5kpc. The analysis indicates that the compactness of
systems with LIR>~10^11.25Lsun strongly increases in those classified as
mergers in their final stage of interaction. The FEE_13.2um is also related to
the contribution of an active galactic nucleus (AGN) to the MIR. Galaxies which
are more AGN-dominated are less extended, independently of their LIR. We
finally find that the extent of the MIR continuum emission is correlated with
the far-IR IRAS log(f_60um/f_100um) color. This enables us to place a lower
limit to the area in a galaxy from where the cold dust emission may originate,
a prediction which can be tested soon with the Herschel Space Telescope.Comment: 18 pages, 8 figures, accepted for publication in Ap
The SOPHIE search for northern extrasolar planets. II. A multi-planet system around HD9446
We report the discovery of a planetary system around HD9446, performed from
radial velocity measurements secured with the spectrograph SOPHIE at the 193-cm
telescope of the Haute-Provence Observatory during more than two years. At
least two planets orbit this G5V, active star: HD9446b has a minimum mass of
0.7 M_Jup and a slightly eccentric orbit with a period of 30 days, whereas
HD9446c has a minimum mass of 1.8 M_Jup and a circular orbit with a period of
193 days. As for most of the known multi-planet systems, the HD9446-system
presents a hierarchical disposition, with a massive outer planet and a lighter
inner planet.Comment: 7 pages, 6 figures, 3 tables, accepted for publication in A&
CASSIS: The Cornell Atlas of Spitzer/Infrared Spectrograph Sources. II. High-resolution observations
The Infrared Spectrograph (IRS) on board the Spitzer Space Telescope observed about 15,000 objects during the cryogenic mission lifetime. Observations provided low-resolution (R~60-127) spectra over ~5-38um and high-resolution (R~600) spectra over ~10-37um. The Cornell Atlas of Spitzer/IRS Sources (CASSIS) was created to provide publishable quality spectra to the community. Low-resolution spectra have been available in CASSIS since 2011, and we present here the addition of the high-resolution spectra. The high-resolution observations represent approximately one third of all staring observations performed with the IRS instrument. While low-resolution observations are adapted to faint objects and/or broad spectral features (e.g., dust continuum, molecular bands), high-resolution observations allow more accurate measurements of narrow features (e.g., ionic emission lines) as well as a better sampling of the spectral profile of various features. Given the narrow aperture of the two high-resolution modules, cosmic ray hits and spurious features usually plague the spectra. Our pipeline is designed to minimize these effects through various improvements. A super sampled point-spread function was created in order to enable the optimal extraction in addition to the full aperture extraction. The pipeline selects the best extraction method based on the spatial extent of the object. For unresolved sources, the optimal extraction provides a significant improvement in signal-to-noise ratio over a full aperture extraction. We have developed several techniques for optimal extraction, including a differential method that eliminates low-level rogue pixels (even when no dedicated background observation was performed). The updated CASSIS repository now includes all the spectra ever taken by the IRS, with the exception of mapping observations
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