50 research outputs found
Jet-related Excitation of the [CII] Emission in the Active Galaxy NGC 4258 with SOFIA
We detect widespread [CII]157.7um emission from the inner 5 kpc of the active
galaxy NGC 4258 with the SOFIA integral field spectrometer FIFI-LS. The
emission is found associated with warm H2, distributed along and beyond the end
of southern jet, in a zone known to contain shock-excited optical filaments. It
is also associated with soft X-ray hot-spots, which are the counterparts of the
`anomalous radio arms' of NGC~4258, and a 1 kpc-long filament on the minor axis
of the galaxy which contains young star clusters. Palomar-CWI H-alpha integral
field spectroscopy shows that the filament exhibits non-circular motions within
NGC 4258. Many of the [CII] profiles are very broad, with the highest line
width, 455 km/s, observed at the position of the southern jet bow-shock.
Abnormally high ratios of L([CII])/L(FIR) and L([CII])/L(PAH7.7um) are found
along and beyond the southern jet and in the X-ray hotspots. These are the same
regions that exhibit unusually large intrinsic [CII] line widths. This suggests
that the [CII] traces warm molecular gas in shocks and turbulence associated
with the jet. We estimate that as much as 40% (3.8 x 10^39 erg/s) of the total
[CII] luminosity from the inner 5 kpc of NGC 4258 arises in shocks and
turbulence (< 1% bolometric luminosity from the active nucleus), the rest being
consistent with [CII] excitation associated with star formation. We propose
that the highly-inclined jet is colliding with, and being deflected around,
dense irregularities in a thick disk, leading to significant energy dissipation
over a wide area of the galaxy.Comment: Accepted for Publication in the Astrophysical Journal Oct 29 201
ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179
We present our high-resolution
(, 34 pc) observations of
the CO(6-5) line emission, which probes the warm and dense molecular gas, and
the 434 m dust continuum emission in the nuclear region of the starburst
galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The
CO(6-5) emission is spatially distributed in filamentary structures with many
dense cores and shows a velocity field that is characteristic of a
circum-nuclear rotating gas disk, with 90% of the rotation speed arising within
a radius of pc. At the scale of our spatial resolution, the
CO(6-5) and dust emission peaks do not always coincide, with their surface
brightness ratio varying by a factor of 10. This result suggests that
their excitation mechanisms are likely different, as further evidenced by the
Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and
Pa- equivalent width. Within the nuclear region (radius300 pc)
and with a resolution of 34 pc, the CO line flux (dust flux density)
detected in our ALMA observations is Jy km/s ( mJy), which
account for 22% (2.4%) of the total value measured by Herschel.Comment: Accepted for publication in Ap
Understanding the 8 micron vs. Pa-alpha relationship on sub-arcsecond scales in Luminous Infrared Galaxies
This work explores in detail the relation between the 8 micron and the
Pa-alpha emissions for 122 HII regions identified in a sample of 10 low-z LIRGs
with nearly constant metallicity (12 + log (O/H) ~ 8.8). We use Gemini/T-ReCS
high-spatial resolution (<~ 0.4" ~ 120 pc for the average distance of 60 Mpc of
our sample) mid-infrared imaging (at 8.7 micron or 10.3 micron) together with
HST/NICMOS continuum and Pa-alpha images. The LIRG HII regions extend the
L_8micron vs. L_Pa-alpha relation found for HII knots in the high-metallicity
SINGS galaxies by about two orders of magnitude to higher luminosities. Since
the metallicity of the LIRG sample is nearly constant, we can rule out this
effect as a cause for the scatter seen in the relationship. In turn, it is
attributed to two effects: age and PAH features. The L_8micron/L_Pa-alpha
ratio, which varies by a factor of ten for the LIRG HII regions, is reproduced
by a model with instantaneous star formation and ages ranging from ~ 4 to 7.5
Myr. The remaining dispersion around the model predictions for a given age is
probably due to differential contributions of the PAH features (the 8.6 micron,
in our case) to the 8 micron emission from galaxy to galaxy.Comment: 16 pages, 9 figures, accepted for publication in ApJ; paper with
full-resolution figures can be found at:
http://damir.iem.csic.es/extragalactic
ALMA Observation of NGC5135: The Circumnuclear CO(6-5) and Dust Continuum Emission at 45 Parsec Resolution[]
We present high-resolution (0.17\arcsec 0.14\arcsec) Atacama Large
Millimeter/submillimeter Array (ALMA) observations of the CO\,(6-5) line, and
435\um\ dust continuum emission within a 9\arcsec 9\arcsec\ area
centered on the nucleus of the galaxy NGC\,5135. NGC\,5135 is a well-studied
luminous infrared galaxy that also harbors a Compton-thick active galactic
nucleus (AGN). At the achieved resolution of 48 40\,pc, the CO\,(6-5)
and dust emissions are resolved into gas "clumps" along the symmetrical dust
lanes associated with the inner stellar bar. The clumps have radii between
45-180\,pc and CO\,(6-5) line widths of 60-88\,\kms. The CO\,(6-5)
to dust continuum flux ratios vary among the clumps and show an increasing
trend with the \FeII/Br- ratios, which we interpret as evidence for
supernova-driven shocked gas providing a significant contribution to the \co65\
emission. The central AGN is undetected in continuum, nor in CO\,(6-5) if its
line velocity width is no less than \,40\,\kms. We estimate that the AGN
contributes at most 1\% of the integrated CO\,(6-5) flux of 512
24Jy\kms\ within the ALMA field of view, which in turn accounts for
32\% of the CO\,(6-5) flux of the whole galaxy.Comment: 21 pages, 12 figures, Accepted for publication in Ap
The Spatial Extent of (U)LIRGs in the Mid-Infrared. II. Feature Emission
We present results from the second part of our analysis of the extended
mid-infrared (MIR) emission of the Great Observatories All-Sky LIRG Survey
(GOALS) sample based on 5-14 micron low-resolution spectra obtained with the
IRS on Spitzer. We calculate the fraction of extended emission as a function of
wavelength for all galaxies in the sample, FEE_lambda, and spatially separate
the MIR spectrum of galaxies into their nuclear and extended components.
We find that the [NeII] emission line is as compact as the hot dust MIR
continuum, while the polycyclic aromatic hydrocarbon (PAH) emission is more
extended. The 6.2 and 7.7 micron PAH emission is more compact than that of the
11.3 micron PAH, which is consistent with the formers being enhanced in a more
ionized medium. The presence of an AGN or a powerful nuclear starburst
increases the compactness of the hot dust MIR continuum, but has a negligible
effect on the spatial extent of the PAH emission on kpc-scales. Globally, the
spectra of the extended emission component are homogeneous for all galaxies in
GOALS. This suggests that the physical properties of star formation taking
place at distances farther than 1.5 kpc from the nuclei of (U)LIRGs are very
similar, resembling local star-forming galaxies with L_IR < 10^11 Lsun, as well
as star formation-dominated ULIRGs at z~2. In contrast, the MIR spectra of the
nuclear component of local (U)LIRGs are very diverse. This implies that the
observed variety of their integrated MIR properties arise, on average, only
from the processes that are taking place in their cores.Comment: 16 pages, 7 figures, accepted for publication in Ap