572 research outputs found
Spitzer View of Lyman Break Galaxies
Using a combination of deep MID-IR observations obtained by IRAC, MIPS and
IRS on board Spitzer we investigate the MID-IR properties of Lyman Break
Galaxies (LBGs) at z~3, establish a better understanding of their nature and
attempt a complete characterisation of the population. With deep mid-infrared
and optical observations of ~1000 LBGs covered by IRAC/MIPS and from the ground
respectively, we extend the spectral energy distributions (SEDs) of the LBGs to
mid-infrared. Spitzer data reveal for the first time that the mid-infrared
properties of the population are inhomogeneous ranging from those with marginal
IRAC detections to those with bright rest-frame near-infrared colors and those
detected at 24mu MIPS band revealing the newly discovered population of the
Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity,
we examine the photometric properties of the population and we use stellar
population synthesis models to probe the stellar content of these galaxies. We
find that a fraction of LBGs have very red colors and large estimated stellar
masses M* > 5x10^10Mo. We discuss the link between these LBGs and
submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7mu
emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the
Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01.Comment: 4 pages, 2 figures, To appear in the proceedings of IAU Symposioum
245 : Formation and evolution of Galaxies Bulges (CUP
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
An infrared study of the double nucleus in NGC3256
We present new resolved near and mid-IR imaging and N-band spectroscopy of
the two nuclei in the merger system NGCA3256, the most IR luminous galaxy in
the nearby universe. The results from the SED fit to the data are consistent
with previous estimates of the amount of obscuration towards the nuclei and the
nuclear star formation rates. However, we also find substantial differences in
the infrared emission from the two nuclei which cannot be explained by
obscuration alone. We conclude that the northern nucleus requires an additional
component of warm dust in order to explain its properties. This suggests that
local starforming conditions can vary significantly within the environment of a
single system.Comment: Accepted for publication (MNRAS
Herschel-SPIRE-Fourier Transform Spectroscopy of the nearby spiral galaxy IC342
We present observations of the nearby spiral galaxy IC342 with the Herschel
Spectral and Photometric Imaging Receiver (SPIRE) Fourier Transform
Spectrometer. The spectral range afforded by SPIRE, 196-671 microns, allows us
to access a number of 12CO lines from J=4--3 to J=13--12 with the highest J
transitions observed for the first time. In addition we present measurements of
13CO, [CI] and [NII]. We use a radiative transfer code coupled with Bayesian
likelihood analysis to model and constrain the temperature, density and column
density of the gas. We find two 12CO components, one at 35 K and one at 400 K
with CO column densities of 6.3x10^{17} cm^{-2} and 0.4x10^{17} cm^{-2} and CO
gas masses of 1.26x10^{7} Msolar and 0.15x10^{7} Msolar, for the cold and warm
components, respectively. The inclusion of the high-J 12CO line observations,
indicate the existence of a much warmer gas component (~400 K) confirming
earlier findings from H_{2} rotational line analysis from ISO and Spitzer. The
mass of the warm gas is 10% of the cold gas, but it likely dominates the CO
luminosity. In addition, we detect strong emission from [NII] 205microns and
the {3}P_{1}->{3}P_{0} and {3}P_{2} ->{3}P_{1} [CI] lines at 370 and 608
microns, respectively. The measured 12CO line ratios can be explained by
Photon-dominated region (PDR) models although additional heating by e.g. cosmic
rays cannot be excluded. The measured [CI] line ratio together with the derived
[C] column density of 2.1x10^{17} cm^{-2} and the fact that [CI] is weaker than
CO emission in IC342 suggests that [CI] likely arises in a thin layer on the
outside of the CO emitting molecular clouds consistent with PDRs playing an
important role.Comment: 9 pages, 8 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
AEGIS: Infrared Spectral Energy Distributions of MIPS 70micron selected sources
We present 0.5 -160 micron Spectral Energy Distributions (SEDs) of galaxies,
detected at 70microns with the Multiband Imaging Photometer for Spitzer (MIPS),
using broadband imaging data from Spitzer and ground-based telescopes.
Spectroscopic redshifts, in the range 0.2<z<1.5, have been measured as part of
the Deep Extragalactic Evolutionary Probe2 (DEEP2) project. Based on the SEDs
we explore the nature and physical properties of the sources. Using the optical
spectra we derive Hbeta and [OII]-based Star Formation Rates (SFR) which are
10-100 times lower than SFR estimates based on IR and radio. The median offset
in SFR between optical and IR is reduced by a factor of ~3 when we apply a
typical extinction corrections. We investigate mid-to-far infrared correlations
for low redshift (>0.5) and high redshift (0.5<z<1.2) bins. Using this unique
``far-infrared'' selected sample we derive an empirical mid to far-infrared
relationship that can be used to estimate the infrared energy budget of
galaxies in the high-redshift universe. Our sample can be used as a template to
translate far-infrared luminosities into bolometric luminosities for high
redshift objects.Comment: 4 pages, 5 figures, accepted for publication in AEGIS ApJL Special
Issu
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
ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231
We have obtained a moderately long (100 kilosecond) ASCA observation of the
Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous
infrared galaxy (ULIRG) population. In the best-fitting model we do not see the
X-ray source directly; the spectrum consists of a scattered power-law component
and a reflection component, both of which have been absorbed by a column N_H
\approx 3 X 10^(22)/cm^2. About 3/4 of the observed hard X-rays arise from the
scattered component, reducing the equivalent width of the iron K alpha line.
The implied ratio of 1-10 keV X-ray luminosity to bolometric luminosity,
L_x/L_bol \sim 2%, is typical of Sy 1 galaxies and radio-quiet QSOs of
comparable bolometric luminosities, and indicates that the bolometric
luminosity is dominated by the AGN. Our estimate of the X-ray luminosity also
moves Mrk 231 in line with the correlations found for AGN with extremely strong
Fe II emission. A second source separated by about 2 arcminutes is also clearly
detected, and contributes about 25% of the total flux.Comment: 11 pages, 3 figures; to appear in ApJ Letter
Molecular line CO (2→1) observations of ultraluminous IRAS galaxies
CO (J=2→1) observations of six ultraluminous IRAS galaxies are presented. Four of these galaxies have no previous CO J=2→1 data and two have no previous CO detections at all. Based on these observations, molecular hydrogen masses are estimated and range from 5x109 to 1.8x1010 M⊙. The present data follow the well established correlation that exists between the infrared luminosity LIR and the molecular mass content. The high values of the LIR/MH2 suggest either an increased star formation efficiency and / or an additional source of luminosity such as an active nucleus. The ratio R=(J=2→1)/(J=1→0) between the J=2→1 and 1→0 line temperatures, is examined next using our J=2→1 intensities and other published CO J=1→0 data. For Arp 220, Mrk 231, Mrk 273 R lies in the range 0.7 to 1.1; for IRAS 05189 the CO intensity and the ratio R were both found to have extremely low values. The low values of R≤1 found for all galaxies, suggest that the line profiles are dominated by emission coming from optically thick thermalized CO. Finally the line profiles are examined and compared to published models concerning the distribution and kinematics of the gas. Assuming that the CO is distributed in a disk as in normal spiral galaxies, then this region is probably concentrated towards the center of the galaxies
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&
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