75 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
Cosmic Sands II: Challenges in Predicting and Measuring High-z Dust Temperatures
In the current era of high-z galaxy discovery with JWST and ALMA, our ability
to study the stellar populations and ISM conditions in a diverse range of
galaxies at Cosmic Dawn has rapidly improved. At the same time, the need to
understand the current limitations in modeling galaxy formation processes and
physical properties in order to interpret these observations is critical. Here,
we study the challenges in modeling galaxy dust temperatures, both in the
context of forward modeling galaxy spectral properties from a hydrodynamical
simulation and via backwards modeling galaxy physical properties from mock
observations of far-infrared dust emission. We find that, especially for the
most massive objects in our sample, neglecting to account for far-infrared dust
optical depth can significantly bias the dust properties derived from SED
modeling. Anisotropies in infrared emission, driven by the clumpy nature of
early star and structure formation, leads to an orientation angle bias in
quantities like infrared luminosities and apparent dust temperatures measured
from galaxy SEDs. We caution that conclusions inferred from both hydrodynamical
simulations and observations alike are susceptible to unique and nuanced
uncertainties that can limit the usefulness of current high-z dust
measurements.Comment: 17 pages, 12 figures. Submitted to ApJ. Comments welcome
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
Global Properties of Neutral Hydrogen in Compact Groups
Compact groups of galaxies provide a unique environment to study the
evolution of galaxies amid frequent gravitational encounters. These nearby
groups have conditions similar to those in the earlier universe when galaxies
were assembled and give us the opportunity to witness hierarchical formation in
progress. To understand how the compact group environment affects galaxy
evolution, we examine the gas and dust in these groups. We present new
single-dish GBT neutral hydrogen (HI) observations of 30 compact groups and
define a new way to quantify the group HI content as the HI-to-stellar mass
ratio of the group as a whole. We compare the HI content with mid-IR indicators
of star formation and optical [g-r] color to search for correlations between
group gas content and star formation activity of individual group members.
Quiescent galaxies tend to live in HI-poor groups, and galaxies with active
star formation are more commonly found in HI-rich groups. Intriguingly, we also
find "rogue" galaxies whose star formation does not correlate with group HI
content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG
1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is
discrepant with the HI. We speculate that this mismatch between mid-IR activity
and HI content is a consequence of strong interactions in this environment that
can strip HI from galaxies and abruptly affect star-formation. Ultimately,
characterizing how and on what timescales the gas is processed in compact
groups will help us understand the interstellar medium in complex, dense
environments similar to the earlier Universe.Comment: Accepted to A
The Importance of Hands-on Experience with Telescopes for Students
Proper interpretation and understanding of astronomical data requires good
knowledge of the data acquisition process. The increase in remote observing,
queue observing, and the availability of large archived data products risk
insulating astronomers from the telescope, potentially reducing their
familiarity with the observational techniques crucial in understanding the
data. Learning fundamental observing techniques can be done in at least three
ways: 1) College and university operated observing facilities, 2) Student
involvement in national facilities through competitive proposals, 3) Programs
at national facilities to increase upper-level undergraduate and graduate
student exposure to telescopes. We encourage both national organizations and
universities to include programs and funding aimed at supporting hands-on
experience with telescopes through the three methods mentioned.Comment: "State of the Profession" white paper for the 2010 Astronomy and
Astrophysics Decadal Surve
ALMA [NII] 205 micron Imaging Spectroscopy of the Interacting Galaxy System BRI 1202-0725 at Redshift 4.7
We present the results from Atacama Large Millimeter/submillimeter Array
(ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII])
and the underlying continuum of BRI 1202-0725, an interacting galaxy system at
4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two
Lyman- emitters (LAEs), all within 25 kpc of the QSO. We detect
the QSO and SMG in both [NII] and continuum. At the (or 6.6 kpc)
resolution, both QSO and SMG are resolved in [NII], with the de-convolved major
axes of 9 and 14 kpc, respectively. In contrast, their continuum
emissions are much more compact and unresolved even at an enhanced resolution
of . The ratio of the [NII] flux to the existing CO (76) flux is
used to constrain the dust temperature () for a more accurate
determination of the FIR luminosity . Our best estimated equals K for both galaxies (assuming an emissivity index
). The resulting ratios are
statistically consistent with that of local luminous infrared galaxies,
confirming that traces the star formation (SF) rate (SFR) in
these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of
5.1 yr ( 30%) assuming Chabrier
initial mass function, takes place within a diameter (at half maximum) of 1.3
(1.5) kpc, and shall consume the existing 5 of
molecular gas in 10 years.Comment: 4 pages, 1 table, 4 figures; accepted for publication in the ApJ
Letter
Complex Radio Spectral Energy Distributions in Luminous and Ultraluminous Infrared Galaxies
We use the Expanded Very Large Array to image radio continuum emission from
local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in 1 GHz
windows centered at 4.7, 7.2, 29, and 36 GHz. This allows us to probe the
integrated radio spectral energy distribution (SED) of the most energetic
galaxies in the local universe. The 4-8 GHz flux densities agree well with
previous measurements. They yield spectral indices \alpha \approx -0.67 (where
F_\nu \propto \nu^\alpha) with \pm 0.15 (1\sigma) scatter, typical of
nonthermal (synchrotron) emission from star-forming galaxies. The contrast of
our 4-8 GHz data with literature 1.5 and 8.4 GHz flux densities gives further
evidence for curvature of the radio SED of U/LIRGs. The SED appears flatter
near \sim 1 GHz than near \sim 6 GHz, suggesting significant optical depth
effects at the lower frequencies. The high frequency (28-37 GHz) flux densities
are low compared to extrapolations from the 4-8 GHz data. We confirm and extend
to higher frequency a previously observed deficit of high frequency radio
emission for luminous starburst galaxies.Comment: 7 pages, 3 figures, 1 table, accepted for publication in the EVLA
Special Issue of ApJ Letter
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