117 research outputs found
CASSISjuice: open-source pipeline and offline complete atlas of Spitzer/IRS staring observations
Mid-infrared spectroscopy provides many important diagnostics on gas and dust
features in a wide variety of astrophysical objects. The Spitzer Infrared
Spectrograph observed more than 20000 targets with wavelengths as low as 5.2um
and as long as 38um, thereby complementing JWST/MIRI data for long wavelength
diagnostics and providing overall invaluable diagnostics together with JWST or
in view of future IR facilities. In order to maximize the science output of
Spitzer/IRS, the CASSIS atlas has provided reduced IRS spectra since 2011,
extracting and selecting the best spectrum from various methods.
We now present CASSISjuice, an offline version of the pipeline and atlas,
adding several hundred sources that had never cleared the pipeline in order to
make it complete for the first time. We updated the low- and high-resolution
pipelines in order to be able to process every IRS staring mode observation
(i.e., all observations but maps), and we also upgraded the high-resolution
pipeline to version 2. The new pipeline also associates the pointings within
"cluster" observations resulting in a single spectrum (possibly low- and
high-resolution) per position and therefore overall a single CASSISjuice ID per
targeted position.
The initial repositories are hosted at Zenodo, providing the open-source
pipeline code and the atlas itself with specific attention to producing the
smallest dataset possible. Version controlled repositories are also available
at GitLab, including Python notebooks to illustrate the offline manipulation of
the full atlas. The offline CASSISjuice atlas is meant to facilitate the
analysis of large samples and the identComment: arXiv-ony paper, please see suggested proper citations within pape
Chemical enrichment and physical conditions in I Zw 18
Abridged.
Low-metallicity star-forming dwarf galaxies are prime targets to understand
the chemical enrichment of the interstellar medium. The HI region provides
important constraints on the dispersal and mixing of heavy elements released by
successive star-formation episodes. Our primary objective is to study the
enrichment of the HI region and the interplay between star-formation history
and metallicity evolution.
We observed the most metal-poor star-forming galaxy in the Local Universe, I
Zw 18, with Hubble/COS. The abundances in the neutral gas are derived from
far-UV absorption-lines (HI, CII, CII*, NI, OI, ...) and are compared to the
abundances in the HII region. Models are constructed to calculate the
ionization structure and the thermal processes. We investigate the gas cooling
in the HI region through physical diagnostics drawn from the fine-structure
level of C+.
We find that HI region abundances are lower by a factor of ~2 as compared to
the HII region. There is no differential depletion on dust between the HI and
HII region. Using sulfur as a metallicity tracer, we calculate a metallicity of
1/46 solar (vs. 1/31 in the HII region). From the study of abundance ratios, we
propose that C, N, O, and Fe are mainly produced in massive stars. We argue
that the HI envelope may contain pockets of pristine gas with a metallicity
essentially null. Finally, we derive the physical conditions in the HI region
by investigating the CII* absorption line. The cooling rate derived from CII*
is consistent with collisions with H atoms in the diffuse neutral gas. We
calculate the star-formation rate from the CII* cooling rate assuming that
photoelectric effect on dust is the dominant gas heating mechanism. Our
determination is in good agreement with the values in the literature if we
assume a low dust-to-gas ratio (~2000 times lower than the Milky Way value).Comment: Accepted for publication in A&A. Fixed typos and reference
Infrared Classification and Luminosities For Dusty AGN and the Most Luminous Quasars
Mid-infrared spectroscopic measurements from the Infrared Spectrometer on
Spitzer (IRS) are given for 125 hard X-ray AGN (14-195 keV) from the Swift
Burst Alert Telescope sample and for 32 AGN with black hole masses from
reverberation mapping. The 9.7 um silicate feature in emission or absorption
defines an infrared AGN classification describing whether AGN are observed
through dust clouds, indicating that 55% of the BAT AGN are observed through
dust. The mid-infrared dust continuum luminosity is shown to be an excellent
indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray
luminosity, log vLv(7.8 um)/L(X) = -0.31 +- 0.35 and independent of
classification determined from silicate emission or absorption. Dust luminosity
scales closely with black hole mass, log vLv(7.8 um) = (37.2 +- 0.5) + 0.87 log
BHM for luminosity in erg per sec and BHM in solar masses. The 100 most
luminous type 1 quasars as measured in vLv(7.8 um) are found by comparing Sloan
Digital Sky Survey optically discovered quasars with photometry at 22 um from
the Wide-Field Infrared Survey Explorer, scaled to rest frame 7.8 um using an
empirical template determined from IRS spectra. The most luminous SDSS/WISE
quasars have the same maximum infrared luminosities for all 1.5 < z < 5,
reaching total infrared luminosity L(IR) = 10^14.4 solar luminosities.
Comparing with Dust Obscured Galaxies from Spitzer and WISE surveys, we find no
evidence of hyperluminous obscured quasars whose maximum infrared luminosities
exceed the maximum infrared luminosities of optically discovered quasars.
Bolometric luminosities L(bol) estimated from rest frame optical or ultraviolet
luminosities are compared to L(IR).Comment: accepted for publication in The Astrophysical Journa
The Infrared Database of Extragalactic Observables from Spitzer I: the redshift catalog
This is the first of a series of papers on the Infrared Database of
Extragalactic Observables from Spitzer (IDEOS). In this work we describe the
identification of optical counterparts of the infrared sources detected in
Spitzer Infrared Spectrograph (IRS) observations, and the acquisition and
validation of redshifts. The IDEOS sample includes all the spectra from the
Cornell Atlas of Spitzer/IRS Sources (CASSIS) of galaxies beyond the Local
Group. Optical counterparts were identified from correlation of the extraction
coordinates with the NASA Extragalactic Database (NED). To confirm the optical
association and validate NED redshifts, we measure redshifts with unprecedented
accuracy on the IRS spectra ({\sigma}(dz/(1+z))=0.0011) by using an improved
version of the maximum combined pseudo-likelihood method (MCPL). We perform a
multi-stage verification of redshifts that considers alternate NED redshifts,
the MCPL redshift, and visual inspection of the IRS spectrum. The statistics is
as follows: the IDEOS sample contains 3361 galaxies at redshift 0<z<6.42 (mean:
0.48, median: 0.14). We confirm the default NED redshift for 2429 sources and
identify 124 with incorrect NED redshifts. We obtain IRS-based redshifts for
568 IDEOS sources without optical spectroscopic redshifts, including 228 with
no previous redshift measurements. We provide the entire IDEOS redshift catalog
in machine-readable formats. The catalog condenses our compilation and
verification effort, and includes our final evaluation on the most likely
redshift for each source, its origin, and reliability estimates.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in MNRAS. Full
redshift table in machine-readable format available at
http://ideos.astro.cornell.edu/redshifts.htm
Principal component analysis of the Spitzer IRS spectra of ultraluminous infrared galaxies
We present the first principal component analysis (PCA) applied to a sample
of 119 Spitzer Infrared Spectrograph (IRS) spectra of local ultraluminous
infrared galaxies (ULIRGs) at z<0.35. The purpose of this study is to
objectively and uniquely characterise the local ULIRG population using all
information contained in the observed spectra. We have derived the first three
principal components (PCs) from the covariance matrix of our dataset which
account for over 90% of the variance. The first PC is characterised by dust
temperatures and the geometry of the mix of source and dust. The second PC is a
pure star formation component. The third PC represents an anti-correlation
between star formation activity and a rising AGN. Using the first three PCs, we
are able to accurately reconstruct most of the spectra in our sample. Our work
shows that there are several factors that are important in characterising the
ULIRG population, dust temperature, geometry, star formation intensity, AGN
contribution, etc. We also make comparison between PCA and other diagnostics
such as ratio of the 6.2 microns PAH emission feature to the 9.7 micron
silicate absorption depth and other observables such as optical spectral type.Comment: 12 pages. MNRAS accepte
ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure Near the Closest Super-Star Cluster
We present ALMA observations of 30 Doradus -- the highest resolution view of
molecular gas in an extragalactic star formation region to date (~0.4pc x
0.6pc). The 30Dor-10 cloud north of R136 was mapped in 12CO 2-1, 13CO 2-1, C18O
2-1, 1.3mm continuum, the H30alpha recombination line, and two H2CO 3-2
transitions. Most 12CO emission is associated with small filaments and clumps
(<1pc, ~1000 Msun at the current resolution). Some clumps are associated with
protostars, including "pillars of creation" photoablated by intense radiation
from R136. Emission from molecular clouds is often analyzed by decomposition
into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar
trends in size, linewidth, and surface density to Milky Way clumps. The 30
Doradus clumps have somewhat larger linewidths for a given size than predicted
by Larson's scaling relation, consistent with pressure confinement. They extend
to higher surface density at a given size and linewidth compared to clouds
studied at 10pc resolution. These trends are also true of clumps in Galactic
infrared-dark clouds; higher resolution observations of both environments are
required. Consistency of clump masses calculated from dust continuum, CO, and
the virial theorem reveals that the CO abundance in 30 Doradus clumps is not
significantly different from the LMC mean, but the dust abundance may be
reduced by ~2. There are no strong trends in clump properties with distance
from R136; dense clumps are not strongly affected by the external radiation
field, but there is a modest trend towards lower dense clump filling fraction
deeper in the cloud.Comment: accepted to Ap
Dust in the Extremely Metal-Poor Blue Compact Dwarf Galaxy IZw18: The Spitzer Mid-Infrared View
IZw18, a blue compact dwarf (BCD) galaxy with the 2nd lowest metallicity
measured in a star-forming object, has been observed with all three instruments
on board the Spitzer Space Telescope. We present the deepest 5-36 micron
mid-infrared (mid-IR) spectrum of this galaxy as yet obtained, as well as 3.6
to 70 micron imaging results. As with SBS0335-052E, another BCD with similar
metallicity, IZw18 shows no detectable emission from polycyclic aromatic
hydrocarbons (PAHs). However, the continuum emission, from 15 to 70 micron, of
IZw18 has a much steeper slope, more characteristic of a typical starburst
galaxy of solar abundance. The neon abundance as measured from the infrared
fine-structure lines is ~1/23 Z_sun, and the sulfur abundance is ~ 1/35 Z_sun,
generally consistent with the nebular oxygen abundance of 1/30 Z_sun derived
from optical lines. This suggests that the extinction to the infrared emitting
regions of this galaxy is low, also in agreement with the optical Balmer line
ratios.Comment: Accepted by ApJ, 7 pages, 5 figure
Infrared view of the multiphase ISM in NGC 253 II. Modelling the ionised and neutral atomic gas
Context. Multi-wavelength studies of galaxies and galactic nuclei allow us to
build a relatively more complete picture of the interstellar medium (ISM),
especially in the dusty regions of starburst galaxies. An understanding of the
physical processes in nearby galaxies can assist in the study of more distant
sources at higher redshifts, which cannot be resolved. Aims. We aimed to use
observations presented in the first part of this series of papers to model the
physical conditions of the ISM in the nuclear region of NGC 253, in order to
obtain primary parameters such as gas densities and metallicities. From the
created model we further calculated secondary parameters such as gas masses of
the different phases, and estimated the fraction of [C II] 158 um from the
different phases, which allowed us to probe the nuclear star-formation rate.
Methods. To compare theory with our observations we used MULTIGRIS, a
probabilistic tool that determines probabilities for certain ISM parameters
from a grid of Cloudy models together with a set of spectroscopic lines.
Results. We find that the hypothetical active galactic nucleus within NGC 253
has only a minor impact compared to the starburst on the heating of the ISM as
probed by the observed lines. We characterise the ISM and obtain parameters
such as a solar metallicity, a mean density of ~230cm-3 , an ionisation
parameter of log U = -3, and an age of the nuclear cluster of ~2 Myr.
Furthermore, we estimate the masses of the ionised (3.8 x 10^6 M_sol ), neutral
atomic (9.1 x 10^6 M_sol ), and molecular (2.0 x 10^8 M_sol ) gas phases as
well as the dust mass (1.8 x 10^6 M_sol ) in the nucleus of NGC 253.Comment: Accepted for publication in A&A; 15 pages, 10 Figures, 6 Table
Kinematic Structure of Molecular Gas around High-mass Star YSO, Papillon Nebula, in N159 East in the Large Magellanic Cloud
We present the ALMA Band 3 and Band 6 results of 12CO(2-1), 13$CO(2-1),
H30alpha recombination line, free-free emission around 98 GHz, and the dust
thermal emission around 230 GHz toward the N159 East Giant Molecular Cloud
(N159E) in the Large Magellanic Cloud (LMC). LMC is the nearest active
high-mass star forming face-on galaxy at a distance of 50 kpc and is the best
target for studing high-mass star formation. ALMA observations show that N159E
is the complex of filamentary clouds with the width and length of ~1 pc and 5
pc - 10 pc, respectively. The total molecular mass is 0.92 x 10^5 Msun from the
13CO(2-1) intensity. N159E harbors the well-known Papillon Nebula, a compact
high-excitation HII region. We found that a YSO associated with the Papillon
Nebula has the mass of 35 Msun and is located at the intersection of three
filamentary clouds. It indicates that the formation of the high-mass YSO was
induced by the collision of filamentary clouds. Fukui et al. 2015 reported a
similar kinematic structure toward a YSO in the N159 West region which is
another YSO that has the mass larger than 35 Msun in these two regions. This
suggests that the collision of filamentary clouds is a primary mechanism of
high-mass star formation. We found a small molecular hole around the YSO in
Papillon Nebula with sub-pc scale. It is filled by free-free and H30alpha
emission. Temperature of the molecular gas around the hole reaches ~ 80 K. It
indicates that this YSO has just started the distruction of parental molecular
cloud.Comment: 28 pages, 7 figures. Submitted to Ap
The dust properties and physical conditions of the interstellar medium in the LMC massive star forming complex N11
We combine Spitzer and Herschel data of the star-forming region N11 in the
Large Magellanic Cloud to produce detailed maps of the dust properties in the
complex and study their variations with the ISM conditions. We also compare
APEX/LABOCA 870um observations with our model predictions in order to decompose
the 870um emission into dust and non-dust (free-free emission and CO(3-2) line)
contributions. We find that in N11, the 870um can be fully accounted for by
these 3 components. The dust surface density map of N11 is combined with HI and
CO observations to study local variations in the gas-to-dust mass ratios. Our
analysis leads to values lower than those expected from the LMC low-metallicity
as well as to a decrease of the gas-to-dust mass ratio with the dust surface
density. We explore potential hypotheses that could explain the low observed
gas-to-dust mass ratios (variations in the XCO factor, presence of CO-dark gas
or of optically thick HI or variations in the dust abundance in the dense
regions). We finally decompose the local SEDs using a Principal Component
Analysis (i.e. with no a priori assumption on the dust composition in the
complex). Our results lead to a promising decomposition of the local SEDs in
various dust components (hot, warm, cold) coherent with that expected for the
region. Further analysis on a larger sample of galaxies will follow in order to
understand how unique this decomposition is or how it evolves from one
environment to another.Comment: 24 pages, 16 figures, accepted for publication in MNRA
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