An analysis of data from the Spitzer Space Telescope, Hubble Space Telescope, Chandra X-ray Observatory, and AKARI Infrared Astronomy Satellite is presented for the z = 0.036 merging galaxy system II ...Zw 096 (CGCG 448-020). Because II Zw 096 has an infrared luminosity of log(L IR/L ) = 11.94, it is classified as a Luminous Infrared Galaxy (LIRG), and was observed as part of the Great Observatories All-sky LIRG Survey (GOALS). The Spitzer data suggest that 80% of the total infrared luminosity comes from an extremely compact, red source not associated with the nuclei of the merging galaxies. The Spitzer mid-infrared spectra indicate no high-ionization lines from a buried active galactic nucleus in this source. The strong detection of the 3.3 Delta *mm and 6.2 Delta *mm polycyclic aromatic hydrocarbon emission features in the AKARI and Spitzer spectra also implies that the energy source of II Zw 096 is a starburst. Based on Spitzer infrared imaging and AKARI near-infrared spectroscopy, the star formation rate is estimated to be 120 M yr-1 and >45 M yr-1, respectively. Finally, the high-resolution B-, I-, and H-band images show many star clusters in the interacting system. The colors of these clusters suggest at least two populations--one with an age of 1-5 Myr and one with an age of 20-500 Myr, reddened by 0-2 mag of visual extinction. The masses of these clusters span a range between 106 and 108 M . This starburst source is reminiscent of the extranuclear starburst seen in NGC 4038/9 (the Antennae Galaxies) and Arp 299 but approximately an order of magnitude more luminous than the Antennae. The source is remarkable in that the off-nuclear infrared luminosity dominates the entire system.
We report the discovery of the optical afterglow of the γ-ray burst (GRB) 130702A, identified upon searching 71 deg{sup 2} surrounding the Fermi Gamma-ray Burst Monitor (GBM) localization. Discovered ...and characterized by the intermediate Palomar Transient Factory, iPTF13bxl is the first afterglow discovered solely based on a GBM localization. Real-time image subtraction, machine learning, human vetting, and rapid response multi-wavelength follow-up enabled us to quickly narrow a list of 27,004 optical transient candidates to a single afterglow-like source. Detection of a new, fading X-ray source by Swift and a radio counterpart by CARMA and the Very Large Array confirmed the association between iPTF13bxl and GRB 130702A. Spectroscopy with the Magellan and Palomar 200 inch telescopes showed the afterglow to be at a redshift of z = 0.145, placing GRB 130702A among the lowest redshift GRBs detected to date. The prompt γ-ray energy release and afterglow luminosity are intermediate between typical cosmological GRBs and nearby sub-luminous events such as GRB 980425 and GRB 060218. The bright afterglow and emerging supernova offer an opportunity for extensive panchromatic follow-up. Our discovery of iPTF13bxl demonstrates the first observational proof-of-principle for ∼10 Fermi-iPTF localizations annually. Furthermore, it represents an important step toward overcoming the challenges inherent in uncovering faint optical counterparts to comparably localized gravitational wave events in the Advanced LIGO and Virgo era.
We have mapped the key mid-IR diagnostics in eight major merger systems of the Toomre sequence (NGC 4676, NGC 7592, NGC 6621, NGC 2623, NGC 6240, NGC 520, NGC 3921, and NGC 7252) using the Spitzer ...Infrared Spectrograph. With these maps, we explore the variation of the ionized-gas, polycyclic aromatic hydrocarbon (PAH), and warm gas (H2) properties across the sequence and within the galaxies. While the global PAH interband strength and ionized gas flux ratios (Ne III/Ne II) are similar to those of normal star-forming galaxies, the distribution of the spatially resolved PAH and fine structure line flux ratios is significantly different from one system to the other. Rather than a constant H2/PAH flux ratio, we find that the relation between the H2 and PAH fluxes is characterized by a power law with a roughly constant exponent (0.61 ? 0.05) over all merger components and spatial scales. While following the same power law on local scales, three galaxies have a factor of 10 larger integrated (i.e., global) H2/PAH flux ratio than the rest of the sample, even larger than what it is in most nearby active galactic nuclei. These findings suggest a common dominant excitation mechanism for H2 emission over a large range of global H2/PAH flux ratios in major mergers. Early-merger systems show a different distribution between the cold (CO J = 1-0) and warm (H2) molecular gas components, which is likely due to the merger interaction. Strong evidence for buried star formation in the overlap region of the merging galaxies is found in two merger systems (NGC 6621 and NGC 7592) as seen in the PAH, Ne II, Ne III, and warm gas line emission, but with no apparent corresponding CO (J = 1-0) emission. The minimum of the 11.3/7.7 Delta *mm PAH interband strength ratio is typically located in the nuclei of galaxies, while the Ne III/Ne II ratio increases with distance from the nucleus. Our findings also demonstrate that the variations of the physical conditions within a merger are much larger than any systematic trends along the Toomre sequence.
We describe a Herschel Space Observatory 194-671 m spectroscopic survey of a sample of 121 local luminous infrared galaxies and report the fluxes of the CO J to J-1 rotational transitions for , the N ...ii 205 m line, the C i lines at 609 and 370 m, as well as additional and usually fainter lines. The CO spectral line energy distributions (SLEDs) presented here are consistent with our earlier work, which was based on a smaller sample, that calls for two distinct molecular gas components in general: (i) a cold component, which emits CO lines primarily at J 4 and likely represents the same gas phase traced by CO (1−0), and (ii) a warm component, which dominates over the mid-J regime (4 < J 10) and is intimately related to current star formation. We present evidence that the CO line emission associated with an active galactic nucleus is significant only at J > 10. The flux ratios of the two C i lines imply modest excitation temperatures of 15-30 K; the C i 370 m line scales more linearly in flux with CO (4−3) than with CO (7−6). These findings suggest that the C i emission is predominantly associated with the gas component defined in (i) above. Our analysis of the stacked spectra in different far-infrared (FIR) color bins reveals an evolution of the SLED of the rotational transitions of vapor as a function of the FIR color in a direction consistent with infrared photon pumping.
TheSpitzerSurvey of Stellar Structure in Galaxies (
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) is an Exploration Science Legacy Program approved for theSpitzerpost–cryogenic mission. It is a volume-, magnitude-, and size-limited (
...d < 40 Mpc
d
<
40
Mpc
,|b| > 30°
|
b
|
>
30
°
,
m
Bcorr < 15.5
m
B
corr
<
15.5
, and
D
25 > 1′
D
25
>
1
′
) survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5 μm. Each galaxy is observed for 240 s and mapped to≥1.5 × D
25
≥
1.5
×
D
25
. The final mosaicked images have a typical 1σ rms noise level of 0.0072 and0.0093 MJy sr-1
0.0093
MJy
sr
-
1
at 3.6 and 4.5 μm, respectively. Our azimuthally averaged surface brightness profile typically traces isophotes atμ3.6μm(AB)(1σ) ∼ 27 mag arcsec-2
μ
3.6
μ
m
(
AB
)
(
1
σ
)
∼
27
mag
arcsec
-
2
, equivalent to a stellar mass surface density of∼1 M
⊙pc-2
∼
1
M
⊙
pc
-
2
.
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thus provides an unprecedented data set for the study of the distribution of mass and stellar structures in the local universe. This large, unbiased, and extremely deep sample of all Hubble types from dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also as a function of the local environment. The data from this survey will serve as a vital testbed for cosmological simulations predicting the stellar mass properties of present-day galaxies. This article introduces the survey and describes the sample selection, the significance of the 3.6 and 4.5 μm bands for this study, and the data collection and survey strategies. We describe the
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data analysis pipeline and present measurements for a first set of galaxies, observed in both the cryogenic and warm mission phases ofSpitzer. For every galaxy we tabulate the galaxy diameter, position angle, axial ratio, inclination atμ3.6μm(AB) = 25.5
μ
3.6
μ
m
(
AB
)
=
25.5
, and26.5 mag arcsec-2
26.5
mag
arcsec
-
2
(equivalent to≈μB(AB) = 27.2
≈
μ
B
(
AB
)
=
27.2
and28.2 mag arcsec-2
28.2
mag
arcsec
-
2
, respectively). These measurements will form the initial
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catalog of galaxy properties. We also measure the total magnitude and the azimuthally averaged radial profiles of ellipticity, position angle, surface brightness, and color. Finally, using the galaxy-fitting code GALFIT, we deconstruct each galaxy into its main constituent stellar components: the bulge/spheroid, disk, bar, and nuclear point source, where necessary. Together, these data products will provide a comprehensive and definitive catalog of stellar structures, mass, and properties of galaxies in the nearby universe and will enable a variety of scientific investigations, some of which are highlighted in this introductory
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survey paper.