311 research outputs found
On the far-infrared metallicity diagnostics: applications to high-redshift galaxies
In an earlier paper we modeled the far-infrared emission from a star-forming
galaxy using the photoionisation code CLOUDY and presented metallicity
sensitive diagnostics based on far-infrared fine structure line ratios. Here,
we focus on the applicability of the [OIII]88/[NII]122 microns line ratio as a
gas phase metallicity indicator in high redshift submillimetre luminous
galaxies. The [OIII]88/[NII]122 microns ratio is strongly dependent on the
ionization parameter (which is related to the total number of ionizing photons)
as well as the gas electron density. We demonstrate how the ratio of 88/$122
continuum flux measurements can provide a reasonable estimate of the ionization
parameter while the availability of the [NII]205 microns line can constrain the
electron density. Using the [OIII]88/[NII]122 microns line ratios from a sample
of nearby normal and star-forming galaxies we measure their gas phase
metallicities and find that their mass metallicity relation is consistent with
the one derived using optical emission lines. Using new, previously
unpublished, Herschel spectroscopic observations of key far-infrared fine
structure lines of the z~3 galaxy HLSW-01 and additional published measurements
of far-infrared fine structure lines of high-z submillimetre luminous galaxies
we derive gas phase metallicities using their [OIII]88/[NII]122 microns line
ratio. We find that the metallicities of these z~3 submm luminous galaxies are
consistent with solar metallicities and that they appear to follow the
mass-metallicity relation expected for z~3 systems.Comment: 10 pages, 7 figures, MNRAS in pres
Smoking as a risk factor for autoimmune liver disease: what we can learn from primary biliary cirrhosis
Primary biliary cirrhosis (PBC) is a cholestatic liver disease characterised by the immune-mediated destruction of biliary epithelial cells in small intrahepatic bile ducts. The disease is characterised by circulating anti-mitochondrial antibodies (AMA) as well as disease specific anti-nuclear antibodies (ANA), cholestatic liver biochemistry, and characteristic histology. The disease primarily affects middle-aged females, and its incidence is apparently increasing worldwide. Epidemiological studies have indicated several risk factors for the development of PBC, with family history of PBC, recurrent urinary tract infection, and smoking being the most widely cited. Smoking has been implicated as a risk factor in several autoimmune diseases, including the liver, by complex mechanisms involving the endocrine and immunological systems to name a few. Studies of smoking in liver disease have also shown that smoking may progress the disease towards fibrosis and subsequent cirrhosis. This review will examine the literature surrounding smoking as a risk factor for PBC, as well as a potential factor in the progression of fibrosis in PBC patients
The CO-to-H2 conversion factor of molecular outflows. Rovibrational CO emission in NGC 3256-S resolved by JWST/NIRSpec
We analyze JWST/NIRSpec observations of the CO rovibrational v=1-0 band at
~4.67um around the dust-embedded southern active galactic nucleus (AGN) of
NGC3256 (d=40Mpc; L(IR)=10^11.6 Lsun). We classify the CO v=1-0 spectra into
three categories based on the behavior of P- and R-branches of the band: (a)
both branches in absorption toward the nucleus; (b) P-R asymmetry (P-branch in
emission and R-branch in absorption) along the disk of the galaxy; and (c) both
branches in emission in the outflow region above and below the disk. In this
paper, we focus on the outflow. The CO v=1-0 emission can be explained by the
vibrational excitation of CO in the molecular outflow by the bright mid-IR
~4.7um continuum from the AGN up to r~250pc. We model the ratios between the
P(J+2) and R(J) transitions of the band to derive the physical properties
(column density, kinetic temperature, and CO-to-H2 conversion factor, alpha_CO)
of the outflowing gas. We find that the 12CO v=1-0 emission is optically thick
for J<4, while the 13CO v=1-0 emission remains optically thin. From the
P(2)/R(0) ratio, we identify a temperature gradient in the outflow from >40K in
the central 100pc to <15K at 250pc sampling the cooling of the molecular gas in
the outflow. We used three methods to derive alpha_CO in eight 100pc (0.5")
apertures in the outflow by fitting the P(J+2)/R(J) ratios with non-LTE models.
We obtain low alpha_CO x 3.2e-4/[CO/H2] factors between 0.34 and 0.62 Msun (K
km/s/pc2)^-1. This implies that outflow rates and energetics might be
overestimated if a ULIRG-like alpha_CO, which is 1.3-2.4 times larger, is
assumed.
We also report the first extragalactic detection of a broad
(sigma=590km/s=0.0091um) spectral feature at 4.645um associated with aliphatic
deuterium on polycyclic aromatic hydrocarbons (D_n-PAH).Comment: 17 pages, 12 figures. Submitted to A&
Warm-Dense Molecular Gas in the ISM of Starbursts, LIRGs and ULIRGs
The role of star formation in luminous and ultraluminous infrared galaxies is
a hotly debated issue: while it is clear that starbursts play a large role in
powering the IR luminosity in these galaxies, the relative importance of
possible enshrouded AGNs is unknown. It is therefore important to better
understand the role of star forming gas in contributing to the infrared
luminosity in IR-bright galaxies. The J=3 level of 12CO lies 33K above ground
and has a critical density of ~1.5 X 10^4 cm^-3. The 12CO(J=3-2) line serves as
an effective tracer for warm-dense molecular gas heated by active star
formation. Here we report on 12CO (J=3-2) observations of 17 starburst spirals,
LIRGs and ULIRGs which we obtained with the Heinrich Hertz Submillimeter
Telescope on Mt. Graham, Arizona.
Our main results are the following: 1. We find a nearly linear relation
between the infrared luminosity and warm-dense molecular gas such that the
infrared luminosity increases as the warm-dense molecular gas to the power
0.92; We interpret this to be roughly consistent with the recent results of Gao
& Solomon (2004a,b). 2. We find L_IR/M_H2 ratios ranging from ~10 to ~128
L_sun/M_sun using a standard CO-H2 conversion factor of 3 X 10^20 cm^-2 (K km
s^-1)^-1. If this conversion factor is ~an order of magnitude less, as
suggested in a recent statistical survey (Yao et al. 2003), then 2-3 of our
objects may have significant contributions to the L_IR by dust-enshrouded AGNs.Comment: 15 Pages, 2 figures, Accepted for Publication in Ap
A Spitzer Infrared Spectrograph Survey of Warm Molecular Hydrogen in Ultra-luminous Infrared Galaxies
We have conducted a survey of Ultra-luminous Infrared Galaxies (ULIRGs) with
the Infrared Spectrograph on the Spitzer Space Telescope, obtaining spectra
from 5.0-38.5um for 77 sources with 0.02<z <0.93. Observations of the pure
rotational H2 lines S(3) 9.67um, S(2) 12.28um, and S(1) 17.04um are used to
derive the temperature and mass of the warm molecular gas. We detect H2 in 77%
of the sample, and all ULIRGs with F(60um)>2Jy. The average warm molecular gas
mass is ~2x10^8solar-masses. High extinction, inferred from the 9.7um silicate
absorption depth, is not observed along the line of site to the molecular gas.
The derived H2 mass does not depend on F(25um)/F(60um), which has been used to
infer either starburst or AGN dominance. Similarly, the molecular mass does not
scale with the 25 or 60um luminosities. In general, the H2 emission is
consistent with an origin in photo-dissociation regions associated with star
formation. We detect the S(0) 28.22um emission line in a few ULIRGs. Including
this line in the model fits tends to lower the temperature by ~50-100K,
resulting in a significant increase in the gas mass. The presence of a cooler
component cannot be ruled out in the remainder of our sample, for which we do
not detect the S(0) line. The measured S(7) 5.51um line fluxes in six ULIRGs
implies ~3x10^6 solar-masses of hot (~1400K) H2. The warm gas mass is typically
less than 1% of the cold gas mass derived from CO observations.Comment: Accepted ApJ 01 September 2006, v648n1 issue. 14 pages 12 figures
IRAS 06361-6217 the f25/f60 ratio is 0.10 not 1.0
The Structure of IR Luminous Galaxies at 100 Microns
We have observed twenty two galaxies at 100 microns with the Kuiper Airborne
Observatory in order to determine the size of their FIR emitting regions. Most
of these galaxies are luminous far-infrared sources, with L_FIR > 10^11 L_sun.
This data constitutes the highest spatial resolution ever achieved on luminous
galaxies in the far infrared. Our data includes direct measurements of the
spatial structure of the sources, in which we look for departures from point
source profiles. Additionally, comparison of our small beam 100 micron fluxes
with the large beam IRAS fluxes shows how much flux falls beyond our detectors
but within the IRAS beam. Several sources with point- like cores show evidence
for such a net flux deficit. We clearly resolved six of these galaxies at 100
microns and have some evidence for extension in seven others. Those galaxies
which we have resolved can have little of their 100 micron flux directly
emitted by a point-like active galactic nucleus (AGN). Dust heated to ~40 K by
recent bursts of non-nuclear star formation provides the best explanation for
their extreme FIR luminosity. In a few cases, heating of an extended region by
a compact central source is also a plausible option. Assuming the FIR emission
we see is from dust, we also use the sizes we derive to find the dust
temperatures and optical depths at 100 microns which we translate into an
effective visual extinction through the galaxy. Our work shows that studies of
the far infrared structure of luminous infrared galaxies is clearly within the
capabilities of new generation far infrared instrumentation, such as SOFIA and
SIRTF.Comment: 8 tables, 23 figure
Epstein-Barr Virus as a Trigger of Autoimmune Liver Diseases
The pathogenesis of autoimmune diseases includes a combination of genetic factors and environmental exposures including infectious agents. Infectious triggers are commonly indicated as being involved in the induction of autoimmune disease, with Epstein-Barr virus (EBV) being implicated in several autoimmune disorders. EBV is appealing in the pathogenesis of autoimmune disease, due to its high prevalence worldwide, its persistency throughout life in the host's B lymphocytes, and its ability to alter the host's immune response and to inhibit apoptosis. However, the evidence in support of EBV in the pathogenesis varies among diseases. Autoimmune liver diseases (AiLDs), including autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC), and primary sclerosing cholangitis (PSC), have a potential causative link with EBV. The data surrounding EBV and AiLD are scarce. The lack of evidence surrounding EBV in AiLD may also be reflective of the rarity of these conditions. EBV infection has also been linked to other autoimmune conditions, which are often found to be concomitant with AiLD. This paper will critically examine the literature surrounding the link between EBV infection and AiLD development. The current evidence is far from being conclusive of the theory of a link between EBV and AiLD
The far-infrared/radio correlation and radio spectral index of galaxies in the SFR-M* plane up to z 2
[Abridged] We study the evolution of the radio spectral index and
far-infrared/radio correlation (FRC) across the star-formation rate-stellar
masse (i.e. SFR-M*) plane up to z 2. We start from a M*-selected sample of
galaxies with reliable SFR and redshift estimates. We then grid the SFR-M*
plane in several redshift ranges and measure the infrared luminosity, radio
luminosity, radio spectral index, and ultimately the FRC index (i.e. qFIR) of
each SFR-M*-z bin. The infrared luminosities of our SFR-M*-z bins are estimated
using their stacked far-infrared flux densities inferred from observations
obtained with Herschel. Their radio luminosities and radio spectral indices
(i.e. alpha, where Snu nu^-alpha) are estimated using their stacked 1.4GHz and
610MHz flux densities from the VLA and GMRT, respectively. Our far-infrared and
radio observations include the most widely studied blank extragalactic fields
-GOODS-N/S, ECDFS, and COSMOS- covering a sky area of 2deg^2. Using this
methodology, we constrain the radio spectral index and FRC index of
star-forming galaxies with M*>10^10Msun and 0<z<2.3. We find that
alpha^1.4GHz_610MHz does not evolve significantly with redshift or with the
distance of a galaxy with respect to the main sequence (MS) of the SFR-M* plane
(i.e. Delta_log(SSFR)_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). Instead,
star-forming galaxies have a radio spectral index consistent with a canonical
value of 0.8, which suggests that their radio spectra are dominated by
non-thermal optically thin synchrotron emission. We find that qFIR displays a
moderate but statistically significant redshift evolution as
qFIR(z)=(2.35+/-0.08)*(1+z)^(-0.12+/-0.04), consistent with some previous
literature. Finally, we find no significant correlation between qFIR and
Delta_log(SSFR)_MS, though a weak positive trend, as observed in one of our
redshift bins, cannot be firmly ruled out using our dataset.Comment: Accepted for publication in A&A; 18 pages, 10 figure
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A 15 µm selected sample of hHigh-z starbursts and AGNs
We report results from our Spitzer GO-1 program on IRS spectroscopy of a large sample of Luminous Infrared Galaxies and quasars selected from the European Large Area ISO Survey (ELAIS). The selected ELAIS sources have a wide multi-wavelength coverage, including ISOCAM, ISOPHOT, IRAC
and MIPS (from SWIRE), and optical photometry. Here we present the sample selection and results from the IRS spectroscopy
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