295 research outputs found
Extreme CO Isotopic Abundances in the ULIRG IRAS 13120-5453: An Extremely Young Starburst or Top-Heavy Initial Mass Function
We present ALMA CO (J=1-0, 3-2 and 6-5), CO (J=1-0) and
CO (J=1-0) observations of the local Ultra Luminous Infrared Galaxy,
IRAS 13120-5453 (dubbed "The Yo-yo"). The morphologies of the three isotopic
species differ, where CO shows a hole in emission towards the center. We
measure integrated brightness temperature line ratios of CO/CO
60 (exceeding 200) and CO/CO 1 in the central
region. Assuming optical thin emission, CO is more abundant than
CO in several regions. The abundances within the central 500 pc are
consistent with enrichment of the ISM via a young starburst (7Myr), a
top-heavy initial mass function or a combination of both.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Modeling the Infrared Emission from Cygnus A
The Spitzer Space Telescope provides a unique view of the Universe at
infrared wavelengths. Improved sensitivity and angular resolution over previous
missions enable detailed studies of astrophysical objects, both in imaging and
spectroscopic modes. Spitzer observations of active galactic nuclei can help
shed light on the physical conditions of the central regions of these active
glalaxies.
The nearby radio galaxy Cygnus A is one of the most luminous radio sources in
the local Universe. In addition to the high radio power, it is also very
luminous in the infrared. New Spitzer spectroscopy and photometry of Cygnus A
is combined with data from the literature at radio and sub-mm wavelengths. The
resulting complication is modeled with a combination of: a synchrotron emitting
jet, a burst of star formation, and emission from an AGN torus.
The infrared emission in Cyngus A shows contributions from all three
processes and the models are able to reproduce the observed emission over
almost 5 dex in frequency. The bolometric AGN luminosity is found to be ~10^45
erg s^-1, with a clumpy torus size of ~7 pc. Evidence is seen for a break in
the synchrotron spectrum in the mid-infrared. The relevant component of the
infrared emission suggests Cygnus A has a star formation rate of ~20 M_sun
yr^-1. Even in the absence of the AGN, it would still be a luminous infrared
source.Comment: MS thesis (Imaging Science). 94 pages. 35 figure
On the Interpretation of Far-infrared Spectral Energy Distributions. I: The 850 m Molecular Mass Estimator
We use a suite of cosmological zoom galaxy formation simulations and dust
radiative transfer calculations to explore the use of the monochromatic
luminosity (L) as a molecular gas mass (M) estimator in galaxies between for a broad range of masses.
For our fiducial simulations, where we assume the dust mass is linearly related
to the metal mass, we find that empirical L-M
calibrations accurately recover the molecular gas mass of our model galaxies,
and that the L-dependent calibration is preferred. We argue the
major driver of scatter in the L-M relation arises
from variations in the molecular gas to dust mass ratio, rather than variations
in the dust temperature, in agreement with the previous study of Liang et al.
Emulating a realistic measurement strategy with ALMA observing bands that are
dependent on the source redshift, we find that estimating S
from continuum emission at a different frequency contributes scatter
to the L-M relation. This additional scatter arises
from a combination of mismatches in assumed T and values, as
well as the fact that the SEDs are not single-temperature blackbodies.Finally
we explore the impact of a dust prescription in which the dust-to-metals ratio
varies with metallicity. Though the resulting mean dust temperatures are
higher, the dust mass is significantly decreased for low-metallicity
halos. As a result, the observationally calibrated L-M relation holds for massive galaxies, independent of the dust model, but
below L erg s (metallicities
) we expect galaxies may
deviate from literature observational calibrations by dex.Comment: 23 pages and 12 figures including appendices, published in the
Astrophysical Journal, abstract shortened due to arXiv restriction
Near infrared spectroscopy of the type IIn SN 2010jl: evidence for high velocity ejecta
The Type IIn supernova SN 2010jl was relatively nearby and luminous, allowing
detailed studies of the near-infrared (NIR) emission. We present 1 - 2.4 micron
spectroscopy over the age range of 36 - 565 days from the earliest detection of
the supernova. On day 36, the H lines show an unresolved narrow emission
component along with a symmetric broad component that can be modeled as the
result of electron scattering by a thermal distribution of electrons. Over the
next hundreds of days, the broad components of the H lines shift to the blue by
700 km/s, as is also observed in optical lines. The narrow lines do not show a
shift, indicating they originate in a different region. He I 1.0830 and 2.0587
micron lines both show an asymmetric broad emission component, with a shoulder
on the blue side that varies in prominence and velocity from -5500 km/s on day
108 to -4000 km/s on day 219. This component may be associated with the higher
velocity flow indicated by X-ray observations of the supernova. The absence of
the feature in the H lines suggests that this is from a He rich ejecta flow.
The He I 1.0830 micron feature has a narrow P Cygni line, with absorption
extending to ~100 km/s and strengthening over the first 200 days, and an
emission component which weakens with time. At day 403, the continuum emission
becomes dominated by a blackbody spectrum with a temperature of ~1900 K,
suggestive of dust emission.Comment: 17 pages, 18 figure
Recovering the Physical Properties of Molecular Gas in Galaxies from CO SLED Modeling
Modeling of the spectral line energy distribution (SLED) of the CO molecule
can reveal the physical conditions (temperature, density) of molecular gas in
Galactic clouds and other galaxies. Recently, the Herschel Space Observatory
and ALMA have offered, for the first time, a comprehensive view of the
rotational J = 4-3 through J = 13-12 lines, which arise from a complex, diverse
range of physical conditions that must be simplified to one, two, or three
components when modeled. Here we investigate the recoverability of physical
conditions from SLEDs produced by galaxy evolution simulations containing a
large dynamical range in physical properties. These simulated SLEDs were
generally fit well by one component of gas whose properties largely resemble or
slightly underestimate the luminosity-weighted properties of the simulations
when clumping due to non-thermal velocity dispersion is taken into account. If
only modeling the first three rotational lines, the median values of the
marginalized parameter distributions better represent the luminosity-weighted
properties of the simulations, but the uncertainties in the fitted parameters
are nearly an order of magnitude, compared to approximately 0.2 dex in the
"best-case" scenario of a fully sampled SLED through J = 10-9. This study
demonstrates that while common CO SLED modeling techniques cannot reveal the
underlying complexities of the molecular gas, they can distinguish bulk
luminosity-weighted properties that vary with star formation surface densities
and galaxy evolution, if a sufficient number of lines are detected and modeled.Comment: 13 pages, accepted by The Astrophysical Journa
WFPC2 LRF Imaging of Emission Line Nebulae in 3CR Radio Galaxies
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness
emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio
sources. We overlay the emission line images on high resolution VLA radio
images (eight of which are new reductions of archival data) in order to examine
the spatial relationship between the optical and radio emission. We confirm
that the radio and optical emission line structures are consistent with weak
alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS)
radio galaxies where both the radio source and the emission line nebulae are on
galactic scales and strong alignment is seen at all redshifts. There are weak
trends for the aligned emission line nebulae to be more luminous, and for the
emission line nebula size to increase with redshift and/or radio power. The
combination of these results suggests that there is a limited but real capacity
for the radio source to influence the properties of the emission line nebulae
at these low redshifts (z < 0.6). Our results are consistent with previous
suggestions that both mechanical and radiant energy are responsible for
generating alignment between the radio source and emission line gas.Comment: 80 pages, 54 figures. Accepted for publication in ApJ
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