50,819 research outputs found
Searching for molecular outflows in Hyper-Luminous Infrared Galaxies
We present constraints on the molecular outflows in a sample of five
Hyper-Luminous Infrared Galaxies using Herschel observations of the OH doublet
at 119 {\mu}m. We have detected the OH doublet in three cases: one purely in
emission and two purely in absorption. The observed emission profile has a
significant blueshifted wing suggesting the possibility of tracing an outflow.
Out of the two absorption profiles, one seems to be consistent with the
systemic velocity while the other clearly indicates the presence of a molecular
outflow whose maximum velocity is about ~1500 km/s. Our analysis shows that
this system is in general agreement with previous results on Ultra-luminous
Infrared Galaxies and QSOs, whose outflow velocities do not seem to correlate
with stellar masses or starburst luminosities (star formation rates). Instead
the galaxy outflow likely arises from an embedded AGN.Comment: Accepted for publication in MNRAS. 13 pages, 11 figures, 4 table
The Luminous Starburst Ring in NGC 7771: Sequential Star Formation?
Only two of the twenty highly luminous starburst galaxies analyzed by Smith
et al. exhibit circumnuclear rings of star formation. These galaxies provide a
link between 10^11 L_sun systems and classical, less-luminous ringed systems.
We report the discovery of a near-infrared counterpart to the nuclear ring of
radio emission in NGC 7771. A displacement between the ~10 radio bright clumps
and the ~10 near-infrared bright clumps indicates the presence of multiple
generations of star formation. The estimated thermal emission from each radio
source is equivalent to that of ~35000 O6 stars. Each near-infrared bright knot
contains ~5000 red supergiants, on average. The stellar mass of each knot is
estimated to be ~10^7 M_sun. The implied time-averaged star formation rate is
\~40 M_sun per yr. Several similarities are found between the properties of
this system and other ringed and non-ringed starbursts. Morphological
differences between NGC 7771 and the starburst + Seyfert 1 galaxy NGC 7469
suggest that NGC 7771 may not be old enough to fuel an AGN, or may not be
capable of fueling an AGN. Alternatively, the differences may be unrelated to
the presence or absence of an AGN and may simply reflect the possibility that
star formation in rings is episodic.Comment: accepted for publication in The Astrophysical Journal (10 January
1999); 48 pages including 13 figures; AAS LaTe
Observational evidence for the presence of PAHs in distant Luminous Infrared Galaxies using ISO and Spitzer
We present ISOCAM 15 micron and MIPS 24 micron photometry of a sample of 16
distant Luminous Infrared Galaxies (LIRGs) characterized by a median luminosity
L(IR) 2x10^11 Lsol and redshift z = 0.7 (distributed from z = 0.1 to 1.2).
While some sources display 24/15 micron flux ratios also consistent with a
featureless continuum dominating their mid-infrared (MIR) spectral energy
distributions (SEDs), the presence of prominent emission features such as the
Polycyclic Aromatic Hydrocarbons is clearly required to explain the observed
colors for more than half of the sample. As a result, a general good agreement
is observed between the data and predictions from the local starburst-dominated
SEDs that have been used so far to constrain IR galaxy evolution. This is
consistent with the star-forming nature of LIRGs derived from previous works,
even though our approach cannot rule out the dominance of an AGN in some cases.
Our study also supports the possibility of tracing the total IR luminosity of
distant galaxies (up to z ~ 1) from their MIR emission.Comment: 4 pages, 3 figures, Astronomy & Astrophysics Letters (in press
Discovery of the Extremely Energetic Supernova 2008fz
We report on the discovery and initial observations of the energetic type IIn
supernova (SN), 2008fz. The optical energy emitted by SN 2008fz (based on the
light curve over a 88 day period), is possibly the most ever observed for a
supernova (1.4 x 10^51 erg). The event was more luminous than the type IIn SN
2006gy, but exhibited same smooth, slowly evolving light curve. As is
characteristic of type IIn SN, the early spectra of 2008fz initially exhibited
narrow Balmer lines which were replaced by a broader component at later times.
The spectra also show a blue continuum with no signs of Ca or Na absorption,
suggesting that there is little extinction due to intragalatic dust in the host
or circumstellar material. No host galaxy is identified in prior coadded images
reaching R ~ 22. From the supernova's redshift, z=0.133, we place an upper
limit on the host of M_R=-17. The presence of the SN within such a faint host
follows the majority of recently discovered highly luminous SN. A possible
reason for this occurrence is the very high star formation rate occurring in
low-mass galaxies in combination with the low metallicity environment, which
makes the production of very massive stars possible. We determine the peak
absolute magnitude of the event to be M_V = -22.3 from the initial photometry
and the redshift distance, placing it among the most luminous supernovae
discovered.Comment: Minor correction
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