859 research outputs found
A Radio View of the Sky: the Cosmic History of Star-Forming and AGN Galaxies
We explore the cosmic evolution of radio detected star forming (SF) galaxies and active galactic nuclei (AGN), drawn from the VLA-COSMOS survey, out to z = 1.3. We present the 20 cm radio luminosity function for these populations, and find that SF galaxies evolve much more rapidly than low-power radio AGN. Our results imply that weak radio AGN (L_(1.4GHz) †5Ă10^(25) WHz^(â1)) occur in the most massive galaxies already at z ~ 1. They may significantly contribute to the heating of their surrounding medium and thus inhibit gas accretion onto their host galaxies, as recently suggested for the âradio modeâ AGN feedback in cosmological models
The Local Radio-IR Relation in M51
We observed M51 at three frequencies, 1.4 GHz (20 cm), 4.9 GHz (6 cm), and 8.4 GHz (3.6 cm), with the Very Large Array and the Effelsberg 100 m telescope to obtain the highest quality radio continuum images of a nearby spiral galaxy. These radio data were combined with deconvolved Spitzer IRAC 8 ÎŒm and MIPS 24 ÎŒm images to search for and investigate local changes in the radio-IR correlation. Utilizing wavelet decomposition, we compare the distribution of the radio and IR emission on spatial scales between 200 pc and 30 kpc. We show that the radio-IR correlation is not uniform across the galactic disk. It presents a complex behavior with local extrema corresponding to various galactic structures, such as complexes of H II regions, spiral arms, and interarm filaments, indicating that the contribution of the thermal and non-thermal radio emission is a strong function of environment. In particular, the relation of the 24 ÎŒm and 20 cm emission presents a linear relation within the spiral arms and globally over the galaxy, while it deviates from linearity in the interarm and outer regions as well in the inner region, with two different behaviors: it is sublinear in the interarm and outer region and overlinear in the central 3.5 kpc. Our analysis suggests that the changes in the radio/IR correlation reflect variations of interstellar medium properties between spiral arms and interarm region. The good correlation in the spiral arms implies that 24 ÎŒm and 20 cm are tracing recent star formation, while a change in the dust opacity, "Cirrus" contribution to the IR emission and/or the relation between the magnetic field strength and the gas density can explain the different relations found in the interarm, outer, and inner regions
A SINFONI view of Galaxy Centers: Morphology and Kinematics of five Nuclear Star Formation Rings
We present near-infrared (H- and K-band) integral-field observations of the
circumnuclear star formation rings in five nearby spiral galaxies. The data,
obtained at the Very Large Telescope with the SINFONI spectrograph, are used to
construct maps of various emission lines that reveal the individual star
forming regions ("hot spots") delineating the rings. We derive the
morphological parameters of the rings, and construct velocity fields of the
stars and the emission line gas. We propose a qualitative, but robust,
diagnostic for relative hot spot ages based on the intensity ratios of the
emission lines Brackett gamma, HeI, and [FeII]. Application of this diagnostic
to the data presented here provides tentative support for a scenario in which
star formation in the rings is triggered predominantly at two well-defined
regions close to, and downstream from, the intersection of dust lanes along the
bar with the inner Lindblad resonance.Comment: 45 pages incl. 4 tables and 12 (mostly color) figures. Accepted for
publication in AJ. A version with full resolution figures can be obtained at
ftp://ftp.rssd.esa.int/pub/tboeker/SINFONI/ms.pd
Interactions of the Galactic bar and spiral arm in NGC 3627
Aims: To gain insight into the expected gas dynamics at the interface of the Galactic bar and spiral arms in our own Milky Way galaxy, we examine as an extragalactic counterpart the evidence of multiple distinct velocity components in the cold dense molecular gas that populates a similar region at the end of the bar in the nearby galaxy NGC 3627.
Methods: We assembled a high-resolution view of molecular gas kinematics traced by CO(2-1) emission and extracted line-of-sight velocity profiles from regions of high and low gas velocity dispersion.
Results: The high velocity dispersions arise with often double-peaked or multiple line-profiles. We compare the centroids of the different velocity components to expectations based on orbital dynamics in the presence of bar and spiral potential perturbations. A model of the region as the interface of two gas-populated orbits families supporting the bar and the independently rotating spiral arms provides an overall good match to the data. An extent of the bar to the corotation radius of the galaxy is favored.
Conclusions: Using NGC 3627 as an extragalactic example, we expect situations like this to favor strong star formation events such as are observed in our own Milky Way since gas can pile up where the orbit families cross. The relative motions of the material following these orbits is most likely even more important for the build-up of high density in the region. The surface densities in NGC 3627 are also so high that shear at the bar end is unlikely to significantly weaken the star formation activity. We speculate that scenarios in which the bar and spiral rotate at two different pattern speeds may be the most favorable for intense star formation at such interfaces
Interactions of the Galactic bar and spiral arm in NGC 3627
Aims: To gain insight into the expected gas dynamics at the interface of the Galactic bar and spiral arms in our own Milky Way galaxy, we examine as an extragalactic counterpart the evidence of multiple distinct velocity components in the cold dense molecular gas that populates a similar region at the end of the bar in the nearby galaxy NGC 3627.
Methods: We assembled a high-resolution view of molecular gas kinematics traced by CO(2-1) emission and extracted line-of-sight velocity profiles from regions of high and low gas velocity dispersion.
Results: The high velocity dispersions arise with often double-peaked or multiple line-profiles. We compare the centroids of the different velocity components to expectations based on orbital dynamics in the presence of bar and spiral potential perturbations. A model of the region as the interface of two gas-populated orbits families supporting the bar and the independently rotating spiral arms provides an overall good match to the data. An extent of the bar to the corotation radius of the galaxy is favored.
Conclusions: Using NGC 3627 as an extragalactic example, we expect situations like this to favor strong star formation events such as are observed in our own Milky Way since gas can pile up where the orbit families cross. The relative motions of the material following these orbits is most likely even more important for the build-up of high density in the region. The surface densities in NGC 3627 are also so high that shear at the bar end is unlikely to significantly weaken the star formation activity. We speculate that scenarios in which the bar and spiral rotate at two different pattern speeds may be the most favorable for intense star formation at such interfaces
A Study of Compact Radio Sources in Nearby Face-on Spiral Galaxies. II. Multiwavelength Analyses of Sources in M51
We report the analysis of deep radio observations of the interacting galaxy
system M51 from the Very Large Array, with the goal of understanding the nature
of the population of compact radio sources in nearby spiral galaxies. We detect
107 compact radio sources, 64% of which have optical counterparts in a deep
H Hubble Space Telescope image. Thirteen of the radio sources have
X-ray counterparts from a {\em Chandra} observation of M51. We find that six of
the associated H sources are young supernova remnants with resolved
shells. Most of the SNRs exhibit steep radio continuum spectral indices
onsistent with synchrotron emission. We detect emission from the Type Ic SN
1994I nearly a decade after explosion: the emission (Jy
beam at 20 cm, Jy beam at 6cm,
) is consistent with light curve models for Type Ib/Ic
supernovae. We detect X-ray emission from the supernova, however no optical
counterpart is present. We report on the analysis of the Seyfert 2 nucleus in
this galaxy, including the evidence for bipolar outflows from the central black
hole.Comment: 22 pages, 8 figures (5 color) in separate files, AASTeX. Full
resolution figures and preprint may be obtained by contacting
[email protected]. AJ accepte
Galaxy Evolution and Star Formation Efficiency in the Last Half of the Universe
We present the results of a CO(1-0) emission survey with the IRAM 30m of 30
galaxies at moderate redshift (z ~ 0.2-0.6) to explore galaxy evolution and in
particular the star formation efficiency, in the redshift range filling the gap
between local and very high-z objects. Our detection rate is about 50%. One of
the bright objects was mapped at high resolution with the IRAM interferometer,
and about 50% of the total emission found in the 27 arcsec (97 kpc) single dish
beam is recovered by the interferometer, suggesting the presence of extended
emission. The FIR-to-CO luminosity ratio is enhanced, following the increasing
trend observed between local and high-z ultra-luminous starbursts.Comment: 6 pages, 5 figures, To appear in the proceedings of "SF2A-2007:
Semaine de l'Astrophysique Francaise", (J. Bouvier, A. Chalabaev, and C.
Charbonnel eds
Characterizing spiral arm and interarm star formation
Interarm star formation contributes significantly to a galaxy's star
formation budget, and provides an opportunity to study stellar birthplaces
unperturbed by spiral arm dynamics. Using optical integral field spectroscopy
of the nearby galaxy NGC 628 with VLT/MUSE, we construct Halpha maps including
detailed corrections for dust extinction and stellar absorption to identify 391
HII regions at 35pc resolution over 12 kpc^2. Using tracers sensitive to the
underlying gravitational potential, we associate HII regions with either arm
(271) or interarm (120) environments. Using our full spectral coverage of each
region, we find that most HII region physical properties (luminosity, size,
metallicity, ionization parameter) are independent of environment. We calculate
the fraction of Halpha luminosity due to the diffuse ionized gas (DIG)
background contaminating each HII region, and find the DIG surface brightness
to be higher within HII regions compared to the surroundings, and slightly
higher within arm HII regions. Use of the temperature sensitive [SII]/Halpha
line ratio map instead of the Halpha surface brightness to identify HII region
boundaries does not change this result. Using the dust attenuation as a tracer
of the gas, we find depletion times consistent with previous work (2 x 10^9 yr)
with no differences between the arm and interarm, however this is very
sensitive to the DIG correction. Unlike molecular clouds, which can be
dynamically affected by the galactic environment, we see fairly consistent HII
region properties in both arm and interarm environments. This suggests either a
difference in arm star formation and feedback, or a decoupling of dense star
forming clumps from the more extended surrounding molecular gas.Comment: 10 pages, 4 figures, 1 table, accepted for publication in Ap
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